Aluminium In Commercial Vehicles

Transcript

ALUMINIUM IN COMMERCIAL VEHICLES 1 EUROPEAN ALUMINIUM ASSOCIATION 2 A lum inium in C om m ercial Vehicles has been com piled by the European A lum inium A ssociation in answ er to the needs of m anufacturers and users of com m ercial vehicles and accessories. It is a com - pendium of basic inform ation on such aspects of alum inium as: •The reasons for using it •The m ain rolled, extruded and cast alloys available to m anufacturers; their properties, m echanical characteristics etc. •The design and calculation of structures, fatigue and collision behaviour •The joining of sem i-finished products: fabrication, w elding and other joining techniques •The corrosion resistance of alum inium alloys under service conditions •Surface treatm ent •C leaning and repair This guide w ill be of particular interest to design and process engineers, to repair and m aintenance m an- agers and m ore generally to anyone w ith an interest in the applications and developm ent of alum inium in road transport. G iven the obvious lim itations of a single volum e, it has not been possible to deal w ith all aspects in detail. W e have opted to present w hat w e regard as the m ost up-to-date concepts and have indicated the m ost relevant standards w hich the reader can refer to for further inform ation. The information in this publication is general in nature and is not intended for direct application to specific technical or scientific projects. The European Aluminium Association cannot be held liable for any damage, costs or expenses resulting from the use of the information in this publication. For additional information please contact your aluminium supplier to be able to discuss details directly with the relevant experts. FOREWORD 3 EUROPEAN ALUMINIUM ASSOCIATION I. FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 II. ALUMINIUM IN TRANSPORT . . . . . . . . . . . . . . . . 7 1. One century of aluminium in transport . . . . . . . . . . . . . . . . 8 2. Evolution of commercial vehicles . . . . . . . . . . . . . . . . . . . . 12 3. Aluminium applications and weight savings . . . . . . . . . . . 13 4. Today’s concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 III. WHY USING ALUMINIUM . . . . . . . . . . . . . . . . . . 15 1. Short pay-back . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2. Aluminium performance properties . . . . . . . . . . . . . . . . . . 18 3. Environmental and social Benefits . . . . . . . . . . . . . . . . . . . 22 4. On the road… . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 IV. FREQUENTLY ASKED QUESTIONS . . . . . . . . . . 29 1. Aluminium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2. Aluminium chassis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 3. Aluminium tippers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 4. Aluminium tankers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 V. ALUMINIUM ALLOYS FOR COMMERCIAL VEHICLES . . . . . . . . . . . . . . 39 1. Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2. International product designation . . . . . . . . . . . . . . . . . . . 41 3. Basic temper designations . . . . . . . . . . . . . . . . . . . . . . . . . 42 4. Subdivisions of H temper designations . . . . . . . . . . . . . . . 42 5. Subdivision of T temper designations . . . . . . . . . . . . . . . . 43 6. Typical alloys for commercial vehicles . . . . . . . . . . . . . . . . 44 7. Influence of temperature on mechanical properties . . . . 50 8. Influence of fabrication on the properties of the alloys . 52 9. List of standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 VI. DESIGN AND CALCULATION . . . . . . . . . . . . . . . 57 1. Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 2. Possibilities with aluminium . . . . . . . . . . . . . . . . . . . . . . . . 58 3. Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 4. Aluminium versus Steel . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 5. Limit state design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 6. Serviceability limit state . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 7. Ultimate limit state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 8. Fatigue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 9. Special design issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 C O N T E N T S 4 VII. FABRICATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 1. Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 2. Fabrication of products from plate . . . . . . . . . . . . . . . . . . 93 3. Fabrication of products from extrusions . . . . . . . . . . . . . . 98 4. Drilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 5. Tapping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 6. Deep Drawing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 7. Spinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 VIII. WELDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 1. Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 2. TIG welding (Tungsten Inert Gas) . . . . . . . . . . . . . . . . . . . 109 3. MIG welding (Metal Inert Gas) . . . . . . . . . . . . . . . . . . . . . 110 4. Plasma MIG welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 5. Laser welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 6. Laser MIG welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 7. Resistance welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 8. FSW - Friction Stir Welding . . . . . . . . . . . . . . . . . . . . . . . . 120 9. Surface preparation before welding . . . . . . . . . . . . . . . . 122 10. Quality control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 11. Design and prevention of deformation . . . . . . . . . . . . . . 126 IX. OTHER JOINING TECHNIQUES . . . . . . . . . . . . 129 1. Adhesive bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 2. Screwing and bold fastening . . . . . . . . . . . . . . . . . . . . . . 133 3. Riveting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 4. Snap-Lock & Clipping . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 X. DECORATION AND FINISHING . . . . . . . . . . . . 137 1. Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 2. Possibilities with aluminium . . . . . . . . . . . . . . . . . . . . . . . 138 3. Mechanical finishing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 4. Chemical decoration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 XI. CORROSION RESISTANCE . . . . . . . . . . . . . . . . . . . 145 1. Definition of corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 2. Corrosion of aluminium . . . . . . . . . . . . . . . . . . . . . . . . . . 146 XII. CLEANING OF ALUMINIUM COMMERCIAL VEHICLES . . . . . . . . . . . . . . . . . . . 153 1. Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 2. The nature of stains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 3. The choise of detergent . . . . . . . . . . . . . . . . . . . . . . . . . . 155 4. Application of the detergent . . . . . . . . . . . . . . . . . . . . . . 155 XIII. REPAIR OF ALUMINIUM COMMERCIAL VEHICLES . . . . . . . . . . . . . . . . . . . 157 1. Foreword . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 2. Execution of repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 3. Repair of aluminium chassis . . . . . . . . . . . . . . . . . . . . . . . . 159 4. MIG and TIG weld repairs . . . . . . . . . . . . . . . . . . . . . . . . . 160 Acknowledgments and photo credits . . . . . . . . . . . . . . . .162 5 EUROPEAN ALUMINIUM ASSOCIATION 6 1. ONE CENTURY OF ALUMINIUM IN TRANSPORT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2. EVOLUTION OF COMMERCIAL VEHICLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3. ALUMINIUM APPLICATIONS AND WEIGHT SAVINGS . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 4. TODAY’S CONCERNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 CHAPTER I I ALUMI NI UM I N TRANSPORT 7 EUROPEAN ALUMINIUM ASSOCIATION In 1903, the W right brothers m ade aviation history w hen they achieved the w orld’s first flight pow ered by a lightw eight engine m ade w ith alum inium com ponents. Today, alum inium is fundam ental to the aviation industry. It accounts for m ore than 60% of the structural w eight of the A irbus A 380, and up to 80% of short- and m id- range aircrafts. It w as in the 1920s that alu- m inium shipping applications started to expand due to new alloys becom ing available for m arine applications. 1. One century of al umi ni um i n transport Ai rbus A380 8 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER I I A LUM I N I UM I N TRA N SPORT 8 | 9 Today, 1000 high-speed passen- ger ships are in service, m ost of them have a structure and superstructure m ade of alu- m inium . C ruise ship superstruc- tures are com m only m ade of alum inium , w hile over half of all yachts are com pletely m ade out of alum inium . These ships take full advantage of alum inium ’s lightness and strength, as w ell as its corrosion- resistance, an indispensable prop- erty for m arine environm ents. Crui se shi p wi t h al umi ni um superst ruct ure Cat amaran UAI 50 (Babcock) 9 EUROPEAN ALUMINIUM ASSOCIATION In the 1980s, alum inium em erged as the m etal of choice to low er running costs and to im prove acceleration of m etros, tram w ays, intercity and high speed trains. In 1996, the TG V D uplex train w as introduced, transporting 40% m ore passen- gers w hile w eighing 12% less than the single deck version, all thanks to its alum inium struc- ture. Today, alum inium m etros and tram s operate in m any cities and alum inium trains are used all over the w orld. TGV Dupl ex (Al st om-SNCF) 10 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER I I A LUM I N I UM I N TRA N SPORT 10 | 11 The average volum e of alu- m inium used in passenger cars w as already 131kg in 2005. The sam e year, one car in every four produced in Europe had an alum inium bonnet and around one third of European cars w ere already equipped w ith alu- m inium bum per system s. Al umi ni um bonnet Al umi ni um bumper syst em prepared f or crash t est In 1899, a sm all sports car w ith an alum inium body w as unveiled at the Berlin international car exhibition. In 1948, Land Rover started using alum inium outer skin sheets. Today, besides w ell-know n alu- m inium -intensive cars like the A udi A 8, m any cars contain sig- nificant am ounts of alum inium . 11 EUROPEAN ALUMINIUM ASSOCIATION 1910 1930 1950 1976 TODAY H aving m ade its debut in Parisian buses in 1910, alum inium w as used for a variety of elem ents in com m ercial vehicles in the 1930s. The 1950s saw the first alu- m inium tankers, vans and tipping vehicles. Today, m ost tankers and silo sem i-trailers are m ade entirely of alum inium . It is also frequently used for vans, tipping or self-dis- charging bodies and a m ultitude of com ponents. C onsidering today’s European fleet, alum inium saves on average 800kg per artic- ulated vehicle. First aluminium parts in Parisian buses 2. Evol uti on of commerci al vehi cl es 12 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER I I A LUM I N I UM I N TRA N SPORT 12 | 13 The key concern of transport com panies is profitability. The rising diesel price and the investm ent in new engine tech- nologies increase costs, w hile it is hard to increase transport prices due to the high com peti- tion betw een operators. A ny investm ent m ust therefore have a very short payback tim e. C onsequently, vehicle m anufac- turers m ust constantly im prove their perform ance at m inim um costs. The choice of a m aterial w ill therefore depend on its price, its m echanical properties and its im pact on vehicle pro- duction costs. From a society point of view , energy efficiency, reduction of greenhouse gases and road safety are in the priority list of European authorities. C hapter III explains how alu- m inium helps to take up these challenges. 4. Today’s concerns 3. Aluminium applications and weight savings Some examples… G Components for tractors & rigid trucks - cabin & door: -200kg - chassis: -350kg - powertrain parts: -125kg - suspension parts: -110kg G Complete superstructures - rigid body: 90m2 = -800kg - tipping body: -800 to -2200kg - ADR fuel tank: 43000l = -1100kg - self-discharging body - silo G Components for superstructure - curtain rails: 2x13.5m = -100kg - front wall: -85kg - rear door: -85kg - side boards: 600mm = -240kg - stanchions: 10x600mm = -50kg - reefer floor G Safety parts - front bumpers : -15kg - rear bumpers : -15kg - side bumpers : -20kg - front and rear under-run protections G Trailers sub-structures - chassis: 13.5m = -700kg - chassis: 6m = -300kg - chassis+floor: 13,5m = -1100kg - legs: -35kg G Accessories - air pressure vessels: 6x60l = -54kg - diesel tank: 600l = -35kg - toolbox: -15kg - tail lift: -150kg - wheels: 14 rims = -300kg 13 EUROPEAN ALUMINIUM ASSOCIATION 14 1. SHORT PAY-BACK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1. 1. Increased payload + Higher residual value = Additional incomes . . . . . . . . . . . . . 16 1. 2. Fuel saving + long life + reduced maintenance = Cost savings . . . . . . . . . . . . . . . 16 1. 3. Make your own calculation on www.alutransport.org . . . . . . . . . . . . . . . . . . . . . 16 1. 4. Coping with road tolls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1. 5. Reduced risk of work accident . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2. ALUMINIUM PERFORMANCE PROPERTIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 2. 1. High strength-to-weight and high stiffness-to-weight ratios . . . . . . . . . . . . . . . . 18 2. 2. Durability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2. 3. Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 2. 4. Diversity & functionality of semi-finished products, castings and forgings . . . . . 20 2. 5. Easy to work with . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 3. ENVIRONMENTAL AND SOCIAL BENEFITS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3. 1. Aluminium reduces CO 2 emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3. 2. Aluminium as a complement to EURO IV & EURO V engines . . . . . . . . . . . . . . . . 22 3. 3. Aluminium improves road safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3. 4. Aluminium is easily and economically recycled . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 4. ON THE ROAD… . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 4. 1. Looking good forever . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 4. 2. Aluminium is easy to repair . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 CHAPTER I I I WHY USI NG ALUMI NI UM 15 EUROPEAN ALUMINIUM ASSOCIATION Aluminium reduces dead vehicle weight. When transporting high- density freight, which usually sat- urates the maximum gross vehi- cle weight, aluminium allows the loading of more goods. This translates into additional income and/or better competitiveness. Furthermore, used aluminium vehicles have a lot of success on the second, and even third hand market, where they are usually sold for a very good price. Finally, when they have reached the end of their long service life they still have a high scrap value. This is due to the fact that aluminium is easily recycled, without losing any of its quality and saving 95% of the primary energy input. Make your own payback calcula- tion on www.alutransport.org and have a look at the example beside. 1. Short pay-back 1.1. Increased payload + Higher residual value = Additional incomes A study conducted by the IFEU 1 in cooperation with the TU-Graz 2 concluded that 1 ton saved on the total weight of an articulated truck leads to a fuel saving of 0.6 litres /100 km. This saving occurs during trips made below the maximum gross vehicle weight, i.e. when trans- porting low-density goods, for partly loaded or empty trips. Aluminium’s well-known corro- sion resistance is an obvious advantage in road transport: It contributes to a long service life, especially in vehicles which work in conditions that can cause seri- ous corrosion problems. No painting or other surface protec- tion is required and it is easy to clean. Maintenance is therefore kept to a minimum. 1.2. Fuel saving + long life + reduced maintenance = Cost savings 1.3. Make your own calculation on www.alutransport.org 1. Institut für Energie und Umwelt Forschung, Heidelberg, Germany 2. Technical University of Graz, Austria 16 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER I I I WHY USI N G A LUM I N I UM 16 | 17 1.4. Copi ng wi t h road t ol l s A ccording to the “user pays” principle, an increasing num ber of countries are introducing road tolls that increase cost per kilo- m etre. O n the other hand, increasing payload w ith alu- m inium allow s spreading this extra cost over a bigger tonnage of goods. In countries w here road toll is lim ited to the heaviest vehicle category, “m ini-sem i-trailers”are built using a substantial am ount of alum inium allow ing the oper- ator to keep a good payload w hile not exceeding the w eight lim it w here a toll is applicable. 1.5. Reduced ri sk of work acci dent M obile parts that are m anipu- lated at each delivery, like drop- side w alls or rear doors, are lighter to m ove w hen m ade out of alum inium . This saves a lot of effort for the drivers. U sing extrusions w ith rounded edges or folded sheets w ith round corners for the floors of box vans reduces the risk of injuries. Mi ni -t rai l er (Tang Fahrzeugbau GmbH) Road t ol l st at i on 17 EUROPEAN ALUMINIUM ASSOCIATION A lum inium alloys used in com - m ercial vehicles have strength- to-w eight and stiffness-to- w eight ratios com parable w ith the m ost advanced m etals like high strength steel and titanium . These properties, am ong m any others, are taken into account w hen designing a vehicle. N o w eight saving can be obtained w ith alum inium if the design is sim ply copied from steel. D esigns optim ised for alum inium are based on specific sections (20 to 40% higher beam s), sm ooth transitions and clever joints, w hich norm ally give 40-60% w eight saving over com peting m etals, as explained below . To illustrate the upper and the low er lim its of alum inium light- w eighting, let’s analyze tw o extrem e equivalence philoso- phies “equal strength” and “equal stiffness”to traditional chassis beam . 2. Aluminium performance properties 2.1. Hi gh st rengt h-t o-wei ght and hi gh st i f f ness-t o-wei ght rat i os Comparison of weight-optimised designs made with 3 different metals and 2 design criteria EQUAL STRENGTH St andard Hi gh st rengt h Al umi ni um st eel st eel al l oy Strength 1 = 1 = 1 Stiffness 1 > 0.30 < 0.56 Weight 1 > 0.71 > 0.42 Section height 1 > 0.65 < 1.18 EQUAL STIFFNESS St andard Hi gh st rengt h Al umi ni um st eel st eel al l oy Strength 1 < 2.17 > 1.54 Stiffness 1 = 1 = 1 Weight 1 = 1 > 0.55 Section height 1 = 1 < 1.40 DEFINITION St andard Hi gh st rengt h Al umi ni um st eel st eel al l oy Yield strength (M Pa) 350 760 250 E-M odulus (M Pa) 210000 210000 70000 D ensity (kg/m 3 ) 7800 7800 2700 U nfair com parison! 18 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER I I I WHY USI N G A LUM I N I UM 18 | 19 A t equal strength: •The alum inium beam is the lightest, but has a low er stiffness than the standard steel beam . •The high-strength steel beam ranks second for lightness, but its stiffness is also the low est! •The alum inium solution is about 60% lighter than the stan- dard steel one (0.42 vs. 1) and still 40% lighter than the high strength steel one (0.42 vs. 0.71). A t equal stiffness: •The alum inium beam is the lightest, w ith 45% w eight saved (0.55 vs 1). •The high strength steel beam w eighs the sam e as the standard steel beam , because, based on the sam e parent m etal, both m aterials have identical elastic properties (E-m odulus). •C om pared to the standard steel beam , the alum inium one is about 50% stronger, and the high strength steel one about 120% . C om paring an alum inium beam designed for equal stiffness to a standard steel beam and a high strength m etal beam designed for equal strength to that standard steel beam , only show s sm all w eight saving for alum inium (0.55 vs. 0.71) but that compari- son is unfair, as the latter w ill have a m uch higher strength (1.54 vs. 1) and a m uch higher stiffness (1 vs. 0.30). Last but not least, w e should underline that further w eight optim isation is possible w ith alu- m inium because: •The above com parison is based on a standard beam design, the so-called “double T” •Finite elem ent m odelling allow s a m ore precise definition of m ost favorable section’s geom etry; •These sections, even if very com plex, can easily be produced w ith the alum inium extrusion process. •For parts w here strength is the leading criteria, high-strength alum inium alloys can also be used and provide further w eight savings 2.2. Durabi l i t y Som e operators still fear prob- lem s w ith alum inium trailer chas- sis in heavy duty applications, but they should know that the lifespan is not m aterial related if properly designed. Experienced m anufacturers opti- m ize their design for the m aterial they use and are able to produce alum inium chassis offering an equivalent or longer lifespan but at a m uch low er w eight than conventional m odels. It is also im portant to underline that alum inium vehicles often operate in transport segm ents w here the load factors are the highest (solid and liquid bulk, public w orks etc…). In other w ords, they are m uch m ore intensively used than conven- Unpai nt ed al umi ni um pat rol boat (Al l Ameri can Mari ne) 19 EUROPEAN ALUMINIUM ASSOCIATION tional ones, and this fact is taken into account in the design of alu- m inium vehicles. C orrectly used, alum inium alloys have been developed to offer optim um corrosion resistance in all environm ents. Just one exam - ple: the w idespread use of unpainted alum inium in m arine applications. 2.3. St abi l i t y A chieving IRTE 3 C lass A 4 tipping stability standard for an alu- m inium tipper chassis is no prob- lem . A lum inium , according to tests carried out in the sum m er of 2002 has no issues w ith flex- ing and easily provides the equiv- alent rigidity of steel. Indeed, a full-alum inium vehicle, significantly lighter than others, passed the IRTE C lass A test at 44 tonnes w ith its standard chassis, rem inding everyone that an appropriate design leads to both lightness and torsional stiffness. 3. Institute of Road Transport Engineers, U K. 4. “C lass A ”standard states that a trailer should be able to tilt sidew ays 7° w ithout falling w ith a fully loaded and raised body. Ti ppi ng st abi l i t y t est (STAS) 2.4. Di versi t y & f unct i onal i t y of semi -f i ni shed product s, cast i ngs and f orgi ngs Vehicle designers and m anufac- turers have a w ide range of alu- m inium alloy sem i-finished prod- ucts from w hich to choose: •Rolled sem is: sheets, tread plates (floor plates), pre-painted sheets •Extruded sem is: hollow or solid shapes, standard or custom ized •C astings and forgings 20 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER I I I WHY USI N G A LUM I N I UM 20 | 21 This diversity of sem i-finished products m akes it possible to: •D esign structural elem ents w ith special functions such as shapes w ith grooves for screw heads, hydraulic circuits, inertia shapes, snap-locks, w elding flanges etc. •Save on tim e and cost for assem bly and finishing. This can com pensate for the added raw m aterial cost of structures m ade from alum inium alloys com pared w ith equivalent steel structures. •Reduce stress due to w elding by placing castings at assem bly intersections or using special extrusions to divert w elding stresses into less stressed areas of a fabricated structure. •D esign com plex cast or forged shapes. 2.5. Easy t o work wi t h A lum inium alloys used in the m anufacture of com m ercial vehi- cles and their accessories are easy to process. They lend them - selves to a variety of shaping and joining techniques that w ill be review ed in chapters 7, 8 & 9. In a nutshell, alum inium can easily be •cut: saw ing, shearing, w ater jet, laser or plasm a cutting •m achined: m illing, drilling •bent •joined: w elding, adhesive bond- ing,bolting and riveting Furtherm ore, being light, alu- m inium is easy to handle in the w orkshop. Vari ous al umi ni um product s 21 EUROPEAN ALUMINIUM ASSOCIATION To achieve em ission reductions, it is not only im portant to develop low -em ission engines, but also to use them in the m ost rational w ay possible. Saving w eight w ith alum inium is a good w ay of achieving this objective as explained below . A lum inium contributes to the reduction of C O 2 em issions from road transport as follow s: •W hen carrying heavy goods, it increases the load capacity of vehicles and therefore im proves transport perform ance, allow ing m ore goods to be carried per trip. In this case, one ton saved on the dead w eight of an articu- lated truck saves 1,500 liters of diesel fuel over 100,000 km . •W hen carrying volum inous goods, it reduces the overall w eight, low ering fuel consum p- tion per kilom eter. In this case, one ton saved on the dead w eight of an articulated truck saves 600 liters of diesel fuel over 100,000 km . •W hen carrying passengers, it reduces the overall w eight and low ers fuel consum ption. O ne ton saved on an urban bus saves betw een 1,700-1,900 liters of diesel fuel per 100,000 km . Taking prim ary production, use stage and end-of-life recycling into account, life-cycle savings have been estim ated as follow s: •1kg of alum inium in today’s average articulated truck saves 28kg of C O 2 •1kg of alum inium in an urban bus typically saves 40-45kg of C O 2 3.2. Al umi ni um as a compl ement t o EURO IV & EURO V engi nes The European Environm ent D irectives for trucks date back to 1988, w hile the first standard lim iting em issions of nitrogen oxides (N O x) and particulates (PM ) from heavy-duty diesel engines w ere introduced at the beginning of the 1990’s. The EU RO IV and EU RO V stan- dards represent a dram atic reduc- tion of N O x and PM em issions. H ow ever, they also im pose new com bustion processes and exhaust after-treatm ent techni- ques representing an additional w eight-penalty up to 300kg. U sing m ore alum inium com po- nents allow s the m anufacturer to com pensate for this w eight penalty. The payload can there- fore be preserved and even increased. 3. Environmental and social Benefits 3.1. Al umi ni um reduces CO 2 emi ssi ons 22 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER I I I WHY USI N G A LUM I N I UM 22 | 23 In the context of its Road Safety A ction Program m e, the European C om m ission is looking into the introduction of crash energy absorption criteria for trucks. The alum inium industry has already developed several solutions for the autom otive and railw ay sec- tors and w ould be ready to take up this challenge for trucks. Regarding m etal deform ation that energy-absorbing elem ents undergo upon im pact, alu- m inium system s m ake it possible to absorb significantly m ore crash energy per unit of w eight than traditional system s. A s a rule of thum b, the light-w eight- ing potential exceeds 40% . For this reason, alum inium is very w ell suited for front, rear and side bum pers. A lum inium elem ents can also be used to im prove the energy absorbing potential of front and rear end under-run protection devices, and m ay also be used to build soft deform able truck noses. Last but not least, extra safety features alw ays m ean additional w eight, w hich can be balanced by replacing heavy m aterials by alum inium . 3.3. Al umi ni um i mproves road saf et y Truck wi t h crash-modul e 23 EUROPEAN ALUMINIUM ASSOCIATION U nlike traditional vehicles that are exported to end their life a long w ay from Europe, alu- m inium -intensive trailers gener- ally spend their entire life in our continent, w here they are even- tually dism antled 5 . D ue to the high value of alum inium scrap, the m otivation to sell to a scrap m erchant is very high and land- filling is avoided. Recycled alum inium does not loose any of its quality and saves 95% of the prim ary production energy input. The energy required to produce prim ary alu- m inium is not lost: it is “stored in the m etal”. 3.4. Al umi ni um i s easi l y and economi cal l y recycl ed 5. “The fate of alum inium from end-of- life com m ercial vehicles”, U niversité de Technologie de Troyes Al umi ni um t i pper on scrap yard (Gal l oo recycl i ng) 24 4. On the road… 4.1. Looki ng good f orever The m odern com m ercial vehicle cannot escape the pressures of industrial design. O perators w ant their vehicles to look good w ith clean, pleasing lines, som ething w hich alum inium alloy sem is are ideal for producing. For exam ple, using functional extrusions and plain or pre- painted alum inium sheet that is easy to shape, it is a straightfor- w ard m atter to produce vans w ith rounded body corners both inside and out. W ith tippers and self-discharging bodies, this m akes for a sm ooth unloading and easier cleaning. In addition, using double w all alu- m inium extruded boards allow s the preservation of a perfect exterior surface over the tim e. Im age conscious operators appre- ciate this type of construction very m uch. A lum inium is used to produce the lightest, the strongest and the m ost beautiful w heels. Last but not least, no corrosion w ill appear after im pact on alu- m inium parts, therefore preserv- ing the im age of the com pany. ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER I I I WHY USI N G A LUM I N I UM 24 | 25 8 years ol d al umi ni um t i ppi ng body re-used on a new t ruck 25 EUROPEAN ALUMINIUM ASSOCIATION 4.2. Al umi ni um i s easy t o repai r Few people know that Land Rovers have had alum inium clo- sure panels since 1948, and in the last 50 years, nobody has ever com plained about repair problem s. This illustrates the fact that repair is possible, but alu- m inium repair techniques are definitely different from those of steel. Leading chassis m anufac- turers have set up a European dealer netw ork w here an effi- cient repair service is offered. Doubl e wal l ext ruded boards f or t i ppers Forged al umi ni um wheel 26 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER I I I WHY USI N G A LUM I N I UM 26 | 27 Repai r of an al umi ni um t i pper (Benal u) 27 EUROPEAN ALUMINIUM ASSOCIATION 28 1. ALUMINIUM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 1. 1. What are the advantages of an aluminium vehicles? . . . . . . . . . . . . . . . . . . . . . . . 30 1. 2. Is there an additional cost for an aluminium vehicle? . . . . . . . . . . . . . . . . . . . . . . 30 1. 3. What are the main benefits for the environment? . . . . . . . . . . . . . . . . . . . . . . . . 30 1. 4. Is it necessary to paint an aluminium vehicle? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 1. 5. Is it possible to repair an aluminium vehicle? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 1. 6. Does aluminium burn ? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 2. ALUMINIUM CHASSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.1. How is an aluminium chassis designed and what are the weight savings achievable? . 32 2. 2. Are there different aluminium chassis designs? . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2. 3. Is the life of an aluminium chassis shorter than a steel chassis? . . . . . . . . . . . . . 34 2. 4. How does aluminium compete with high strength steel? . . . . . . . . . . . . . . . . . . . 34 3. ALUMINIUM TIPPERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 3. 1. Are there different aluminium tipping body designs? . . . . . . . . . . . . . . . . . . . . . . 35 3. 2. What about the wear resistance of aluminium tipping bodies . . . . . . . . . . . . . . . 35 3. 3. What type of chassis is needed for an aluminium tipper body? . . . . . . . . . . . . . . 36 3. 4. What about tipping stability? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 4. ALUMINIUM TANKERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 4. 1. How should a tank for the transport of dangerous goods (ADR) be designed? . 37 4. 2. Which alloys are suitable for ADR tanks? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 CHAPTER I V FREQUENTLY ASKED QUESTI ONS 29 EUROPEAN ALUMINIUM ASSOCIATION 1. Al umi ni um 1.1. What ar e t he advant ages of an al umi ni um vehi cl es? 1.2. I s t her e an addi t i onal cost f or an al umi ni um vehi cl e? Yes, alum inium vehicles are slightly m ore expensive than equivalent steel designs. If w e analyse the dif- ference in detail, w e can see that, w hen heavy goods are trans- ported, the additional investm ent is paid back after less than tw o years. M ake your ow n calculations on w w w .alutransport.org. 1.3. What ar e t he mai n benef i t s f or t he envi r onment ? A lum inium contributes to the reduction of C O 2 em issions from road transport as follow s: •W hen carrying heavy goods, it increases the load capacity of vehicles and therefore im proves transport perform ance, allow ing m ore goods to be carried per trip. In this case, one ton saved on the dead w eight of an artic- ulated truck saves 1,500 litres of diesel fuel over 100,000 km . •W hen carrying volum inous goods, it reduces the overall w eight, low ering fuel consum p- tion per kilom etre. In this case, one ton saved on the dead w eight of an articulated truck saves 600 litres of diesel fuel over 100,000 km . Taking prim ary production, use stage and end-of-life recycling into account, life-cycle savings have been estim ated 1 that 1kg of alum inium in today’s aver- age articulated truck saves 28kg of C O 2 . Truck fleet operators benefit from a better perform ance of their fleet. There is a significant payload increase w hich m akes the fleet m uch m ore profitable. A nother fact is cost savings that result from sm aller fleets w ith less staff, low er fuel bills and low er road toll costs. Trailer rental com panies can offer operators sem i-trailers w ith a bet- ter perform ance. D ue to the higher payload, the longer life and the higher residual value of the equipm ent these com panies can generate m ore profit by using state-of-the-art equipm ent. 1. CO 2 reduction potential of aluminium for articulated trucks, EA A (European A lum inium A ssociation), 2005 Al umi ni um bodi ed t ruck 30 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER I V FREQUEN TLY A SKED QUESTI ON S 30 | 31 N o, it is not. A lum inium w ith its natural «alum ina» layer has an excellent protection perform - ance. If an operator chooses to pay extra m oney (and w eight too!) for the paint finish, the m otivation to do so lies in hav- ing a fleet w ith a particular branding. 1.4. I s i t necessar y t o pai nt an al umi ni um vehi cl e? 1.5. I s i t possi bl e t o r epai r an al umi ni um vehi cl e? It is often said that alum inium vehicles cannot be repaired, how ever this is totally w rong. Few people know that Land Rover cars have had an alu- m inium body since the end of w orld w ar tw o, and in the last 50 years nobody has ever com - plained about repair problem s. This illustrates the fact that repair is possible as for any other m aterials, but alum inium repair techniques are definitely different from those of steel. Please refer to the C hapter XIV for detailed inform ation. Leading chassis m anufacturers have set up a European dealer netw ork w here an efficient repair service is offered. 1.6. Does al umi ni um bur n? N O , alum inium and its alloys are, under atm ospheric condi- tions, totally non-com bustible and do not contribute to the spread of fire. A lum inium alloys w ill how ever m elt at around 650°C , but w ith- out releasing harm ful gases. Repai r of an al umi ni um t i pper (St as) 31 EUROPEAN ALUMINIUM ASSOCIATION Leading European trailer m anu- facturers are using strength, stiffness and durability criteria. N o w eight saving can be obtained w ith alum inium if design is sim ply copied from steel. D esigns optim ised for alu- m inium are based on specific sections (20 to 40% higher beam s), sm ooth transitions and clever joints, w hich norm ally give 40-60% w eight saving over com peting m etals (see C hapter III), as explained below . 1) A good light-w eight trailer has to be as strong as a tradi- tional m odel. If this w ould be the sole criteria, the w eight sav- ing obtained w ith alum inium w ould be m axim ized (up to 60% ) and high strength steel solutions w ould provide about half the w eight saving achiev- able w ith alum inium (about 30% ). 2. Al umi ni um chassi s 2.1. How i s an al umi ni um chassi s desi gned and w hat ar e t he w ei ght savi ngs achi evabl e? Chassi s f or al umi ni um t i pper (Benal u) 32 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER I V FREQUEN TLY A SKED QUESTI ON S 32 | 33 2) A m inim um stiffness is gener- ally required. •If this stiffness has to be equal w ith standard steel m odels, w eight savings obtained w ith alum inium w ill be around 45% w ith a superior strength, but high strength steel cannot achieve any w eight saving. •If the m inim um stiffness required is low er than the one of standard steel m odels, w eight savings obtained w ith alum inium w ill be som ew here betw een 45% & 60% and w eight savings obtained w ith high strength steel som ew here betw een zero and half of w hat can be achieved w ith alum inium . 3) Vehicles durability m ust be insured. A s alum inium vehicles are m uch m ore intensively used than conventional ones, their resistance to fatigue m ust be higher. This result is obtained w ith a proper design. A m ong of a lot of others, higher sections, sm ooth transitions and clever joints are keys to success. 2.2. Ar e t her e di f f er ent al umi ni um chassi s desi gns? Each m anufacturer has its ow n design, w hich to a high degree depends on the w orking condi- tions the vehicle is m ade for and on the specific m anufacturing experiences of the chassis pro- ducer (e.g. som e prefer fully w elded constructions w hereas others prefer m ixed w elded and bolted constructions). It is also im portant to underline that alu- m inium vehicles are m uch m ore intensively used than conven- tional ones, and this fact is taken into account in the design of vehicles. A part from that, there are tw o dom inating design philosophies in the chas- sis w orld. In countries like Italy, w here equal stiffness w ith steel m odels seem s to be a m ust, deflection is the m ain criteria, and this gener- ally leads to longer lifetim e than conventional m odels, coupled w ith an attractive w eight saving. In other countries, equal lifetim e w ith steel m odels w ill be the m ain criteria. A good design w ill lead to, at least, an equivalent lifetim e, stiffness w ithin require- m ents (even though it m ay be slightly low er than steel m od- els), but the w eight saving w ill be m axim ized. In any case, they w ill usually be stronger than classic m odels, and the risk for starting yield failure from static overload w ill be low er for alum inium chassis. Chassi s f or al umi ni um t i pper (Leci ñena) 33 EUROPEAN ALUMINIUM ASSOCIATION The lifespan of a chassis is a design issue and not a m aterial issue. A lum inium chassis are m ostly used in transport segm ents w here the load factors are the highest (solid & liquid bulk tanks, tippers), nevertheless w ell designed vehicles can easily exceed 20 years of service life. 2.3. I s t he l i f e of an al umi ni um chassi s shor t er t han a st eel chassi s? 2.4. How does al umi ni um compet e w i t h hi gh st r engt h st eel ? W e should m ake a distinction betw een pure alum inium and alum inium alloys. Pure alum inium is never used in com m ercial vehicles. A w ide variety of alum inium alloys do exist, including high strength solutions. W hat is seldom com m unicated is that all alloys based on the sam e parent m etal have nearly the sam e elastic properties. This m eans that if som eone is looking for a lightw eight alter- native to a standard chassis w hile keeping the sam e stiff- ness, the only solution is to change the m aterial e.g. sw itch- ing from steel to alum inium (see C hapter III). Bol t ed al umi ni um chassi s f or t i pper (Menci ) 34 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER I V FREQUEN TLY A SKED QUESTI ON S 34 | 35 Yes, there are a lot of tipper variants and all of them can be built using dedicated alum inium sem i-products that offer high productivity for m anufacturers, as w ell as increased payload, low running costs and a great fleet im age to operators. For m ore details, please have a look at C hapter VI. 3. Al umi ni um ti ppers 3.1. Ar e t her e di f f er ent al umi ni um t i ppi ng body desi gns? 3.2. What about t he w ear r esi st ance of al umi ni um t i ppi ng bodi es The w ear condition can vary extrem ely from one load to another. Therefore it is not alw ays possible to link the actual hardness of an alloy to the w ear resistance. It w as found out that for a very large extent, the type of load is a decisive factor. The choice of m aterial for the construction of tipping trailers is now adays often a question of specific experiences, m aterial availability and m anufacturer’s specific production m ethods. Typical bottom plate m aterial is: •5083 H 32, H 321, H 34 •5086 H 24 •5383 H 34 •5454 H 22, H 24 •5456 H 34 or other, m ill-specific alloy types. Typical values for bottom plate thickness are listed below : •6 m m for light-duty opera- tions like agricultural products, coal or sand transport •8 m m for m edium -duty serv- ice like recycling products •10 m m for heavy-duty trans- port like gravel •U p to 12 m m in extrem e cases Please refer to C hapter VI for m ore details. 35 EUROPEAN ALUMINIUM ASSOCIATION Som e operators still fear prob- lem s w ith alum inium trailer chassis in heavy-duty applica- tions, but they should know that strength is not m aterial related. Indeed, strength, like stiffness and lifetim e, are only design criteria. Experienced m anufacturers are able to pro- duce alum inium chassis offering the sam e perform ance but at a m uch low er w eight than con- ventional steel m odels. 3.3. What t ype of chassi s i s needed f or an al umi ni um t i pper body? 3.4. What about t i ppi ng st abi l i t y? It is often said that achieving the IRTE 2 C lass A 3 tipping sta- bility standard for an alu- m inium tipper chassis w ould be difficult sim ply because "it flexes too m uch" or that, to provide the equivalent rigidity of a steel chassis "the lightness benefit w ould be practically elim inated", but tests run dur- ing sum m er 2002 confirm ed that both statem ents w ere totally w rong. Indeed, a full-alum inium vehicle, significantly lighter than others, passed the IRTE C lass A test at 44 tonnes w ith its standard chassis rem inding everybody that an appropriate design leads to both lightness and torsional stiffness. 2. British Institute of Road Transport Engineers (IRTE) 3. IRTE's "C lass A " stability standard for tipping on uneven ground states that a trailer should be able to tilt side- w ays 7° w ithout falling w ith a fully loaded and raised body. IRTE t i ppi ng st abi l i t y t est (STAS) 36 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER I V FREQUEN TLY A SKED QUESTI ON S 36 | 37 Tanks for the transport of dan- gerous goods have to be built according to the rules defined in the follow ing agreem ent and standards: •A D R: A greem ent for the transport of D angerous goods by Road 4 •EN 13094 “Tanks for the transport of dangerous goods - M etallic tanks w ith a w orking pressure not exceeding 0.5 bar - D esign and construction” •EN 14025 “Tanks for the transport of dangerous goods - M etallic pressure tanks - D esign and construction” M ore details are given in C hapter VI. 4. Al umi ni um tankers 4. See ADR, Annex A, Part 6, Chapter 6.8: http://w w w .unece.org/trans/danger/danger.htm 4.1. How shoul d a t ank f or t he t r anspor t of danger ous goods (ADR) be desi gned? 4.2. Whi ch al l oys ar e sui t abl e f or ADR t anks? Suitable alum inium alloys for that application are listed in standard EN 14286 “A lum inium and alum inium alloys - w eldable rolled products for tanks for the storage and transportation of dangerous goods”as w ell as in chapter V. A lum inium suppliers are listed in the “links”section of the w eb- site w w w .alutransport.org . Al umi ni um road t anker (Schrader) 37 EUROPEAN ALUMINIUM ASSOCIATION 38 1. FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2. INTERNATIONAL PRODUCT DESIGNATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 3. BASIC TEMPER DESIGNATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 4. SUBDIVISIONS OF H TEMPER DESIGNATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 5. SUBDIVISION OF T TEMPER DESIGNATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 6. TYPICAL ALLOYS FOR COMMERCIAL VEHICLES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 6. 1. Flat rolled products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 6. 2. Extruded products (forged products) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 6. 3. Castings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 6. 4. Selection guide for the different alloys (indicative) . . . . . . . . . . . . . . . . . . . . . . . 49 7. INFLUENCE OF TEMPERATURE ON MECHANICAL PROPERTIES . . . . . . . . . . . . . . . . . . . . 50 7. 1. Elevated temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 7. 2. Low and very low temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 8. INFLUENCE OF FABRICATION ON THE PROPERTIES OF THE ALLOYS . . . . . . . . . . . . . . . 52 8. 1. Work hardening of non-heat treatable alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 8. 2. Softening by annealing and recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 8. 3. Heat treatable alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 8. 4. Castings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 9. LIST OF STANDARDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 CHAPTER V ALUMINIUM ALLOYS FOR COMMERCIAL VEHICLES 39 EUROPEAN ALUMINIUM ASSOCIATION A lum inium in its pure form is a very soft m etal and hence not suited for structural applica- tions. Thanks to the addition of alloying elem ents such as cop- per, m anganese, m agnesium , zinc etc… and thanks to ade- quate production processes, the physical and m echanical proper- ties can be varied in a great range m aking it possible to have suitable alloys for literally all applications. A s the A lum inium Industry is a global industry there is the enor- m ous chance, that the product designation is uniform alm ost all over the w orld. C om pany spe- cific trade nam es are often com - plem ented by the standardized designation. A ll relevant standards are listed at the end of this chapter. 1. Foreword Al umi ni um rol l i ng mi l l 40 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER V A LUM I N I UM A LLOYS FOR COM M ERCI A L VEHI CLES 40 | 41 2. Internati onal product desi gnati on From these eight categories are three fam ilies so called “non heat treatable“, or “w ork hardening” alloys (1xxx, 3xxx, 5xxx) and four “heat treatable alloys”(2xxx, 4xxx, 6xxx, 7xxx). The 8xxx fam ily cannot be attributed to one or the other group. The alloy num ber can be pre- ceded by a letter X w hich indi- cates that it is an experim ental alloy, or follow ed by a letter A w hich says that this is a national variation of the basic alloy. The physical and m echanical properties of these alloys not only depend on their chem ical com po- sition but also to a great extent on the m anufacturing process in the alum inium plant and on the trans- form ation process of the sem i- finished to the finished product. These processes are characterized w ith the so called “tem per desig- nation”w hich attends the alloy num ber. W hen alloy num ber and tem per designation are indicated, the m etal is clearly identified and its properties defined. In order to identify the various alloys, 4-digit num bers have been standardized for w rought alloys (see EN 573-1) and 5-digit num bers for cast alloys. A list of all registered w rought alloys and their chem ical com posi- tion can be found in EN 573-3 for Europe and in the so-called “Teal sheets 1 ”at international level. A list of all registered cast alloys can be found in EN 1706. A selection of alloys for use in com m ercial vehicles w ill be pre- sented in section 6. The first digit of the alloy num ber indicates the dom inant alloying elem ent; the rem aining digits are just num bers for identification purposes (Table V.1). Just in the case of pure alum inium the last tw o digits of the 4-digit num ber indicate the percentage of purity above 99.0% . E.g. 1070 m eans alum inium w ith at least 99.70% of alum inium or, in other w ords less than 0.30% im purities. 1. The latest edition of the Teal Sheets is available for free dow nload from the EA A w ebsite http://w w w .eaa.net/en/about-alum inium /standards/international-registration/ CATEGORIES OF ALUMINIUM ALLOYS Dominant alloying element wrought alloy cast alloy N one (“pure alum inium ”) 1xxx C opper 2xxx 2xxx M anganese 3xxx Silicon 4xxx 4xxxx M agnesium 5xxx 5xxxx M agnesium and Silicon 6xxx Zinc and M agnesium (w ith or w ithout copper) 7xxx 7xxxx O ther elem ents (e.g. Iron or Lithium ) 8xxx TABLE V.1 41 EUROPEAN ALUMINIUM ASSOCIATION • F - as fabricated: this condi- tion designates products m ade by plastic deform ation w ithout any particular control of the rates of hardening or softening by defor- m ation or any heat treatm ent. • O - fully annealed: this con- dition is the m ost ductile and is obtained by the process of anneal- ing w ithout any subsequent w ork-hardening or by hot rolling at tem peratures above the recrystallisation tem perature. • H - strain-hardened and pos- sibly partially softened: this relates to strain-hardened prod- ucts w ith or w ithout subsequent holding at a tem perature high enough to induce partial soften- ing of the m etal. • T - heat treated: heat treat- m ent can com bine som e or all of the follow ing operations: solu- tion treatm ent, quenching, age hardening, artificial ageing and possible plastic deform ation. For m ore details, please refer to EN 515. 3. Basi c temper desi gnati ons 4. Subdi vi si ons of H temper desi gnati ons The first digit after H indicates the specific com bination of basic operations: • H1X: w ork-hardened only. These designations identify prod- ucts that are w ork-hardened to obtain the desired strength w ithout supplem entary heat treatm ent. • H2X: w ork-hardened and par- tially annealed. These designa- tions apply to products w hich are w ork-hardened m ore than the desired final am ount and then reduced in strength to the desired level by partial annealing. • H3X: w ork-hardened and sta- bilized. These designations apply to products w hich are w ork- hardened and w hose m echanical properties are stabilized either by a low tem perature heat treat- m ent or as a result of heat intro- duced during fabrication. For m ore details, please refer to EN 515. The second digit follow ing the letter H indicates the final degree of strain hardening, as identified by the m inim um value of the ulti- m ate tensile strength. • 8 has been assigned to the hard- est tem per norm ally produced. • Tem pers betw een O (annealed) and H X8 are designated by num erals 1 to 7. • HX4 designates tem pers w hose ultim ate tensile strength is approxim ately m idw ay betw een that of the O tem per and that of the H X8 tem pers. • HX2 designates tem pers w hose ultim ate tensile strength is approxim ately m idw ay betw een that of the O tem per and that of the H X4 tem pers. • HX6 designates tem pers w hose ultim ate tensile strength is approxim ately m idw ay betw een that of the H X4 tem pers and that of the H X8 tem pers • H X1, H X3, H X5, H X7 designate tem pers interm ediate betw een those defined above. N ote: These tem per designations are not included in EN 515. M echanical properties of these tem pers shall 42 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER V A LUM I N I UM A LLOYS FOR COM M ERCI A L VEHI CLES 42 | 43 be agreed betw een the m anufac- turer and the custom er. The third digit, w hen used, indi- cates a variation of a tw o-digit tem per. • HX11 applies to products that incur sufficient strain-hardening after the final annealing such that they fail to qualify as annealed but not so consistent an am ount of strain-hard- ening that they qualify as HX1. • H112 applies to products that m ay acquire som e strain-hardening from w orking at an elevated tem perature or from a lim ited am ount of cold w ork, and for w hich there are no upper m echanical property lim its. • H116 applies to products, m ade of those alloys of the 5XXX group in w hich the m agnesium content is 3% nom inal or m ore. Products are strain hardened at the last operation to specified tensile property lim its and m eet specified levels of corrosion resistance in accelerated type corrosion tests. C orrosion tests include inter-granular and exfoli- ation. This tem per is suitable for continuous service at tem pera- tures not higher than 65°C . The first digit follow ing the let- ter T is used to identify the spe- cific sequences of basic treat- m ents. N um erals 1 to 10 have been assigned as follow s: • T1: C ooled from an elevated tem perature shaping process and naturally aged to a substantially stable condition • T2: C ooled from an elevated tem perature shaping process, cold-w orked, and naturally aged to a substantially stable condition • T3: Solution heat-treated cold- w orked, and naturally aged to a substantially stable condition • T4: Solution heat-treated and naturally aged to a substantially stable condition • T5: C ooled from an elevated tem perature shaping process and then artificially aged • T6: Solution heat-treated and then artificially aged • T7: Solution heat-treated and over-aged/stabilized • T8: Solution heat-treated, cold w orked and then artificially aged • T9: Solution heat-treated, artifi- cially aged and then cold-w orked • T10: C ooled from an elevated tem perature shaping process, cold-w orked, and then artificially aged. For m ore details, please refer to EN 515. 5. Subdi vi si on of T temper desi gnati ons Ext rusi on press 43 EUROPEAN ALUMINIUM ASSOCIATION 6. Typi cal al l oys f or commerci al vehi cl es O ut of the vast variety of know n alloys as listed in EN 573-3 and in the Teal Sheets, just a few are of im portance for the m anufac- ture of com m ercial vehicles. Selection criteria are: • availability of sem i-finished products • m echanical properties • physical properties • suitability for fabrication • w eldability • corrosion resistance In the follow ing tables the m ost w idely used alloys for the appli- cation in com m ercial vehicles are presented. Al umi ni um coi l s 44 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER V A LUM I N I UM A LLOYS FOR COM M ERCI A L VEHI CLES 44 | 45 REFERENCE STANDARDS FOR MECHANICAL PROPERTIES OF WROUGHT ALLOYS – FLAT ROLLED PRODUCTS Alloy Standards 2 3003 EN 485-2 5005 EN 485-2 5059 EN 485-2 and EN 14286 5083 EN 485-2 and EN 14286 5086 EN 485-2 and EN 14286 5088 EN 485-2 and EN 14286 5182 EN 485-2 and EN 14286 5186 EN 14286 5383 EN 485-2 and EN 14286 5454 EN 485-2 and EN 14286 5754 EN 485-2 and EN 14286 6061 EN 485-2 6082 EN 485-2 TABLE V.2 6.1. Fl at r ol l ed pr oduct s In com m ercial vehicles, the m ost com m only used alloys are 3003, 5005, 5059, 5083, 5086, 5088, 5182, 5186, 5383, 5454, 5456, 5754, 6061 and 6082. The m echanical properties of these alloys can be found in the standards listed in Table V.2 and Table V.3 gives indications on engineering suitability. 2. See standards denom inations at the end of this chapter section 9. Al umi ni um rol l i ng sl abs 45 EUROPEAN ALUMINIUM ASSOCIATION ENGINEERING SUITABILITY FOR ROAD TRANSPORT APPLICATIONS – FLAT ROLLED PRODUCTS Alloy Temper Shaping Welding Anodizing Corrosion resistance 3003 H 14,H 24,H 16 B A A A 5005 H 14,H 24 B A A A 5059 O , H 111 B A A A 5083 O ,H 111 A A A A H 116,H 22,H 24, H 34 C A A A 5086 O ,H 111 A A A A H 116,H 22,H 24 C A A A 5088 O , H 111 A A A A 5182 O , H 111 A A A A 5186 O , H 111 A A A A 5383 H 22, H 32 B A A A 5454 O ,H 111 A A A A H 22,H 24 B A A A 5456 H 34 C A A A 5754 O ,H 111 A A A A H 22,H 24 B A A A 6061 T4 C A A A T6 D A A A 6082 T4 C A A A T6 D A A A A = very good; B = good; C = fair; D = poor, to be avoided TABLE V.3 46 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER V A LUM I N I UM A LLOYS FOR COM M ERCI A L VEHI CLES 46 | 47 6.2. Ext r uded pr oduct s (f or ged pr oduct s) In com m ercial vehicles, the m ost com m only used alloys are 6060, 6005A , 6008, 6106, 6082, 6061 and 7020. The m echanical properties of these alloys can be found in standard EN 755-2 and Table V.4 gives indications on their engi- neering suitability. ENGINEERING SUITABILITY – EXTRUDED & FORGED PRODUCTS Alloy Temper Welding Anodizing Corrosion resistance 6060 all A A A 6005A all A A A 6008 all A A A 6106 all A A A 6082 all A A A 6061 all A A A 7020 T6 A A C 7003 T6/T7 A A B 7108 T6/T7 A A B A = very good; B = good; C = fair; D = poor, to be avoided TABLE V.4 Al umi ni um ext rusi on bi l l et s 47 EUROPEAN ALUMINIUM ASSOCIATION 6.3. Cast i ngs In com m ercial vehicles, the m ost com m only used alloys are 21100, 42000, 42100, 43000, 44000. Their chem ical com position and m echanical properties can be found in standard EN 1706 and Table V.5 reflects their casting characteristics. CASTING CHARACTERISTICS Alloy Fluidity Resistance to Pressure Machinability Corrosion hot tearing tightness resistance 21100 C D D A D 42000 B A B B B/C 42100 B A B B B 43000 A A B B B 44000 A A A C B A = very good; B = good; C = fair; D = poor, to be avoided TABLE V.5 Semi -t rai l er chassi s beam made out of t wo ext ruded f l anges and a sheet as web Ext ruded rai l f or sl i di ng curt ai n 48 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER V A LUM I N I UM A LLOYS FOR COM M ERCI A L VEHI CLES 48 | 49 6.4. Sel ect i on gui de f or t he di f f er ent al l oys (i ndi cat i ve) Beside these w ell know n alloys it is possible to define, in coop- eration w ith the supplier of the sem is, tailor m ade products that offer best perform ance for the foreseen purpose. Al l oy, t emper 3003* , 5005* , 5052* 6005 T6, 6005A T6, 6063A T6 6060 T6, 6063 T6 * coat ed sheet s Van body Ti pper wi t h ri bbed si des Curt ai nsi der body Ti pper or sel f -di schargi ng body wi t h smoot h si des Al l oy, t emper 6005 T6, 6005A T6, 6005A T5 6005 T6 6060 T5/T6 6063 T6 6005AT6 5083 H111, 5754 H111 5083 H34/H32/H321 • 5086 H24 5383 H34 • 5454 H22/H24 5456 H34 i n case of sel f -di schargi ng f l oor Tank f or l i qui d bul k do not al l ow wei ght opt i mi zat i on of ADR t anks Chassi s beam: t wo prof i l es one pl at e Chassi s beam: one si ngl e prof i l e Al l oy, t emper 6005A T5/T6, 6082 T6 5083 H111/H34 5086 H111/H24 5456 H34 Si l o f or sol i d bul k Al l oy (O/H111 f or al l ) 5083, 5086, 5383, 5454, 5754 5182, 5186, 5059, 5088 OTHER APPLICATIONS Wheel s . . . . . . . . . . . . . . . . . . . . . . . . . . . 6061, 6082 Di esel f uel t anks . . . . . . . . . . . . . . . . . . . . . 5052, 5754 Tai l l i f t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6005A Fl oors . . . . . . . . . . . . . . . . . . . . . . . . 6082, 5086, 5754 Frami ng f or buses . . . . . . . . . . . . . . . . . . . .6060, 6005A Si des & roof s f or buses . . . . . . . . . . . . . . . . .3003, 5005 Crash modul es . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6008 Bumper beams, crash boxes & rol l over prot ect i ons . . . . . . . . . . . . . . . . . .7003, 7108 Suspensi on part s . . . . . . . . . . . . . . . . . . . . . . . . . .21100 St ruct ural component s-Hi nges-Support s . .42000, 42100 Compl ex shapes wi t h medi um st rengt h . . . . . . . .43000 Very compl ex shapes wi t hout st ruct ural f unct i on . . . . . . . . . . . . . . . . . .44000 49 EUROPEAN ALUMINIUM ASSOCIATION A lum inium alloys change their m echanical and corrosion resist- ance properties w hen subjected to tem peratures other than am bient tem perature. Tables V.6 & V.7 show the interrelationship betw een service tem perature and m echanical properties. In Figure V.1 this is show n for one alloy graphically. 7. Inf l uence of temperature on mechani cal properti es CHANGE IN MECHANICAL PROPERTIES OF 5086 O AFTER HOLDING AT TEMPERATURE FOR 10,000 HOURS Temperature Mechanical properties (*) C° R m (MPa) R p 0,2 (MPa) A% -196 390 140 34 -80 280 120 26 -28 270 120 24 +20 270 120 22 +100 270 120 26 +150 210 110 35 +200 155 105 45 TABLE V.6 CHANGE IN MECHANICAL PROPERTIES OF 6082 T6 AFTER HOLDING AT TEMPERATURE FOR 10,000 HOURS Temperature Mechanical properties (*) C° R m (MPa) R p 0,2 (MPa) A% -196 380 330 16 -80 330 295 13 -28 330 285 12 +20 320 285 12 +100 300 265 15 +150 240 220 18 +200 130 105 28 (*) M ean values. These properties are m easured at test tem perature. TABLE V.7 50 R m - R p 0 , 2 M Pa A % R m A % R p 0,2 -196 ° + 20 ° + 200 ° Tem perature °C 500 400 300 200 100 0 50 40 30 20 10 ®® ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER V A LUM I N I UM A LLOYS FOR COM M ERCI A L VEHI CLES 50 | 51 7.2. Low and ver y l ow t emper at ur es C ontrarily to m ost other engi- neering m etals, the m echanical properties im prove at low tem - peratures and especially the elongation, w hich m akes alu- m inium an ideal m etal for severe w inter conditions and even cryogenic applications (see Figure V.1) Further exam ples can be found in standard EN 12392 “A lum inium and alum inium alloys - W rought products - Special requirem ents for products intended for the pro- duction of pressure equipm ent”. CHANGE OF MECHANICAL CHARACTERITICS AS A FUNCTION OF TEMPERATURE FOR ALLOY 5086 O FIGURE V.1 7.1. El evat ed t emper at ur e The loss in strength at higher than am bient tem peratures is negligible for tem peratures up to 100°C (short tim e exposure) or 80°C (long tim e exposure). W hen subjected to even higher tem peratures, then the loss in m echanical properties is m oder- ate for non-heat treatable alloys in the O /H 111 tem per and for heat treatable alloys in the T1/T4 tem per. The loss in m echanical proper- ties at tem peratures above 100°C is very pronounced for non heat treatable alloys in the H 12, H 16 tem per as w ell as for heat treatable alloys in the T5/T6 tem per. 51 EUROPEAN ALUMINIUM ASSOCIATION 8.1. Wor k har deni ng of non- heat t r eat abl e al l oys H ardening is achieved by cold deform ation, know n as w ork hardening, that im proves the physical properties and the hard- ness of the m etal. It also reduces the m etal’s capacity for deform a- tion and its ductility (Figure V.2). The greater the deform ation or higher the w ork hardening rate, the m ore pronounced is the effect. It is also governed by the com position of the m aterial. The 5083 alloy, for exam ple, w hich contains betw een 4 and 4.9% of m agnesium , acquires a great hardness but its capacity for deform ation is less than that of the 5754 alloy w hich contains betw een 2.6 and 3.6% M g. W ork hardening is a general phe- nom enon that takes place w hat- ever the m ethod of deform ation used: rolling, deep draw ing, fold- ing, ham m ering, bending, press- ing, etc. This m eans that it w ill also occur during fabrication in the w orkshop. 8. Inf l uence of f abri cati on on the properti es of the al l oys M Pa A % R m A R p 0,2 Tem per 0 H 12 H 14 H 16 H 18 30 20 10 ® ® W ork hardening % 10 20 30 40 50 60 70 80 500 400 300 200 100 WORK HARDENING CURVE OF ALLOY 5083 FIGURE V.2 8.2. Sof t eni ng by anneal i ng and r ecover y It is possible to restore the ductil- ity of the w ork hardened m etal by heat treatm ent know n as “annealing” (partial or full annealing). In this process, w hich takes place at tem peratures betw een 150°C and 350°C , the hardness and m echanical charac- teristics of the m etal slow ly begin to decrease: this is the recovery phase [A -B] (Figure V.3). A t low er annealing tem peratures this leads to m edium -strength m aterial properties. They then fall aw ay m ore rapidly at high tem peratures above 280 °C during recrystal- lization [B-C ] and eventually attain a m inim um value that cor- responds to the m echanical char- acteristics of the fully annealed m etal [C -D ]. Restoration and annealing are accom panied by a change in the texture and size of the grains of m etal observed under a m icro- scope w ith X50 m agnification. The texture can change from a fibrous structure to a fully recrys- tallized structure (Figure V.3). The grain can grow in size during recrystallization and annealing. This grow th is revealed during subsequent w orking, e.g. fold- ing, by the rough “orange peel” effect on the surface of the m etal. G rain grow th above around 100 m icrons reduces the deform ation capacity of w ork hardening alum inium alloys. The follow ing conditions are essential if a fine-grained annealed structure is to be achieved: • The m etal m ust have under- gone a sufficient rate of defor- m ation corresponding to a rela- T - t Ta 52 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER V A LUM I N I UM A LLOYS FOR COM M ERCI A L VEHI CLES 52 | 53 H a r d n e s s Recovery Recrystallization A nnealing Tim e A C B D O HARDNESS CURVE DURING ANNEALING FIGURE V.3 M icrographic view s tive reduction in section of at least 15% . This is “critical w ork hardening”. If this condition is not m et, then heat treatm ent m ust be restricted to restoration w ithout recrystallization, • A rapid tem perature gradient of 20 to 60°C per hour, • Tem peratures over 350 to 380°C m ust be avoided, • H olding tim es m ust be lim ited to 2 hours m axim um . For 5000 series alloys, annealing is usually perform ed betw een 320°C and 380°C for 30 to 120 m inutes. Note: Non-heat treatable alloys in the annealed temper (O, H111) can only be brought to higher strength by work hardening. 8.3. Heat t r eat abl e al l oys If som e plastic deform ation m ust be done on products of heat treatable alloys, it should be car- ried out in the T4 tem per; first the allow able degree of deform ation is bigger than for the T6 tem per and second there is alm ost no effect of w ork hardening. If for the final product e.g. a bent extrusion in a 6XXX alloy T6 tem - per is needed, age hardening can be carried out. Table V.8 gives an indication how to proceed, using typically a hot air furnace. 6000 SERIES ARTIFICIAL AGEING Alloy Initial temper Artificial ageing Final Temper* 6060 T1 - T4 6 h at185°C T5 - T6 or 8 h at175°C 6005 T1 - T4 8 h at175°C T5 - T6 6106 T1 - T4 8 h at175°C T5 - T6 6061 T4 8 h at175°C T6 6082 T1 - T4 16 h at165°C or 10 h at170°C T5 - T6 or 8 h at175°C * T5, for an initial tem per of T1, T6 for an initial tem per of T4. TABLE V.8 (typical) 53 EUROPEAN ALUMINIUM ASSOCIATION 8.4. Cast i ngs C asting is the shortest path from m olten m etal to the fin- ished product. It is recom - m ended for geom etrically-com - plex parts. It is advantageous to involve the foundry from the conceptual phase into the design process. The expert of the foundry, know ing the plants equipm ent, the process of m ak- ing the m ould, the flow of m etal into the m ould, the cooling and shrinking of the cast piece etc. can be of great help during the design phase. W hen the design of a casting is optim ized in view of its production it is in m ost cases possible for the foundry to guarantee m uch better m echan- ical properties than those listed in standard EN 1706, especially w ith respect to elongation. The Table V.5 (see section 6.3) m erits som e explanation. The alloy 21100 needs very careful design of the pieces w ith respect to the casting process and, in addition to that, the m etal treatm ent in the foundry, especially the degassing of the m olten m etal, m ust be carried out very carefully in order to m inim ize m icro-porosity. The index B or C in the colum n “M achinability”has been put because of the w earing of the cutting tools due to the high sil- icon content of the alloys. The corrosion resistance of cast pieces w ith the as-cast surface is better than for m achined sur- faces of the sam e piece due to the m uch thicker oxide layer. Desi gn of cast i ng par t s G enerally speaking it is essential to be aw are of production pos- sibilities and lim itations from the initial developm ent stage of a new com ponent, not just in term s of the choice of alloy and casting technique but also in term s of design. There are a num ber of basic rules w hich designers should follow : • Sections should be kept uni- form and thickness transitions should be sm ooth, avoiding a build-up of m etal at intersections so as to reduce the risk of shrink- age porosity during cooling, • For the sam e reason, isolated bosses should be avoided and w alls m ust be correctly sized to assist running, • There should be a fillet at every inside corner to avoid cracking during the casting operation (this is particularly im portant for 21100 alloys), • The filling design should be som ew hat asym m etrical to ensure controlled solidification and uniform feed, • The num ber of intersections and undercuts should be kept to a m inim um as they com plicate tooling and the casting opera- tion and hence increase the cost. This applies equally to deburring operations, • The choice of dim ensional tolerances m ust allow for the casting technique and any sub- sequent heat treatm ent defor- m ation can occur during solu- tion treatm ent and quenching. Fl ywheel house cast i ng f or t ruck engi ne (Brabant Al ucast ) 54 ALUMINIUM IN COMMERCIAL VEHICLES CHA PTER V A LUM I N I UM A LLOYS FOR COM M ERCI A L VEHI CLES 54 | 55 9. Li st of standards • EN 485 Aluminium and aluminium alloys – Sheet, strip and plate Part 1: Technical conditions for inspection and delivery Part 2: M echanical properties Part 3: Tolerances on dim ensions for hot rolled products Part 4: Tolerances on dim ensions for cold rolled products • EN 515 Aluminium and aluminium alloys – Wrought products – Temper designations • EN 573 Aluminium and aluminium alloys – Chemical composition and form of wrought products Part 1: N um erical designation system Part 2: C hem ical based designation system Part 3: C hem ical com position Part 4: Form s of products • EN 755 Aluminium and aluminium alloys – Extruded rod/bar, tube and profiles Part 1: Technical conditions for inspection and delivery Part 2: M echanical properties Part 3: Round bars, tolerances on dim ensions and form Part 4: Square bars, tolerances on dim ensions and form • EN 1706 Aluminium and aluminium alloys – Castings – Chemical composition and mechanical properties • EN 12392 Aluminium and aluminium alloys – Wrought products – Special requirements for products intended for the production of pressure equipment • EN 14286 Aluminium and aluminium alloys – Weldable rolled products for the storage and transport of dangerous goods Registration record series Teal Sheets: International alloy designations and chemical composition limits for wrought aluminium and wrought aluminium alloys available for free dow nload from the EA A w eb- site: http://w w w .eaa.net/en/about-alum inium /standards/international-registration/ 55 EUROPEAN ALUMINIUM ASSOCIATION EUROPEAN ALUMINIUM ASSOCIATION 56 1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 2. POSSIBILITIES WITH ALUMINIUM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 3. SYMBOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 4. ALUMINIUM VERSUS STEEL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 5. LIMIT STATE DESIGN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 5. 1. Philosophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 5. 2. What is the ultimate limit state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 5. 3. What is the serviceability limit state . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 6. SERVICEABILITY LIMIT STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 7. ULTIMATE LIMIT STATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 7. 1. Cross section classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 7. 2. Load bearing resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 7. 3. Welded connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 7. 4. Bolted connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 8. FATIGUE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76 8. 1. Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 8. 2. Practice: comparison between good and bad chassis solutions . . . . . . . . . . . . . . 82 9. SPECIAL DESIGN ISSUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 9. 1. Tanks for the transport of dangerous goods - ADR . . . . . . . . . . . . . . . . . . . . . . . . 86 9. 2. Tippers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 10. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 CHAPTER VI DESI GN AND CALCULATI ON 57 EUROPEAN ALUMINIUM ASSOCIATION 1. Introducti on The new European design code for alum inium structures is used as a basis for this chapter. The nam e of this standard is: EN 1999 Eurocode 9: D esign of alum inium structure Part 1-1 G eneral structural rules Part 1-2 Structural fire design Part 1-3 Structures susceptible to fatigue Part 1-4 C old-form ed structural sheeting Part 1-5 Shell structures Part 1-1 is used for all static design and Part 1-3 for all fatigue design show n in this chapter. A new European standard for the execution of structural alum ini- um is under developm ent and is soon ready for publication. It is recom m ended to use relevant parts of this standard for execu- tion of alum inium com ponents for use in com m ercial vehicles. The nam e of this standard is: EN 1090-3: Execution of steel structures and alum inium struc- tures –Part 3: Technical require- m ents for alum inium structures 2. Possi bi l i ti es wi th al umi ni um The advantages of designing w ith alum inium are: •H igh strength-to-w eight ratio •Possibilities to create your ow n cross-sections w ith the extrusion technique •G ood corrosion resistance •Long vehicle life •Easy to w ork w ith •Easy to repair Especially for product design, the use of tailor-m ade profiles is a great advantage for alum inium com pared w ith other m etals. In profile design the m aterial can be placed w here the effect of the m aterial is optim al regarding resistance. D etails can be m ade in such a w ay that it w ill ease the fabrication and assem bling of the com ponents. 3. Symbol s Frequently used sym bols are defined in this section: f o characteristic value of 0.2 % proof strength f u characteristic value of ulti- m ate tensile strength f ub characteristic ultim ate tensile strength of bolt E m odulus of elasticity d bolt diam eter d o hole diam eter t w all thickness A cross section area W section m odulus γ M partial safety factor for resist- ance (see the definitions in sec- tion 5.2), in EN 1999-1-1: Subscript Ed is used for factored load effects. It m ay be on axial force (N Ed ), bending m om ent (M Ed ), shear force (V Ed ), torsion (T Ed ) and forces in connection w ith bolted connections (F v,Ed for shear force and F t,Ed for tension force). 58 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 58 | 59 Both steel and alum inium are m etals w ith relatively high strength. Both m aterials are incom bustible and w ill not con- tribute to a fire. For structural purposes the m ain differences are: Elasticity: The m odulus of elas- ticity (E-m odulus) of alum inium is 1/3 of that of steel. This m eans that an alum inium beam w ith the sam e cross-section and the sam e loads as a steel beam w ill have a deflection 3 tim es that of the steel beam . Weight: The density of alum ini- um is 1/3 of that of steel. This m eans that a steel beam w ill w eigh 3 tim es m ore than an alu- m inium beam w ith the sam e cross-section. Welding: W hen w elding a hard- ened alum inium alloy som e of the hardening effects w ill be lost. The strength in the heat affected zone (H A Z) w ill be reduced. This reduction depends on the alloy, tem per, type of product and w elding procedure. O rdinary steel has no strength reduction after w elding. Thermal elongation: The coef- ficient of therm al elongation of alum inium is tw ice that of steel. This m eans that an alum inium m em ber w ill get tw ice the ther- m al elongation as a sim ilar steel m em ber w ith the sam e tem pera- ture difference. Since the elastic m odulus of alum inium is 1/3 of steel, the stresses in an alum inium m em ber w ith fixation are 2/3 of that in a sim ilar steel m em ber. M ost of the structural alum inium alloys have relatively high “strength-to-E m odulus” ratio. This effect is especially clear w hen the alum inium alloy is strain-hardened or heat-treated. Structural alum inium alloys have roughly tw ice the “strength-to-E m odulus”ratio than standard steel. H ow ever, w hen com pared w ith high strength steels, structural alum inium alloys have about the sam e “strength-to-E m odulus” ratio. It should also be noted that the elastic m odulus of an alloy m ainly depends on its parent m etal. In other w ords, all alu- m inium alloys have very sim ilar E- m odulus, but this is also valid for steel alloys. C onsequently, the so called “high strength steels” don’t have better elastic proper- ties than m ild steel. Steel designers often use the strength of the m aterial as gov- erning criteria w hen designing a steel structure and check after- w ards w hether the deflection is w ithin the requirem ent. W hen designing an alum inium structure, it w ill often be the deflection criterion that w ill be governing. For that reason, the design procedure w ill start w ith the deflection criterion and it w ill be checked afterw ards if the stress or the resistance of the structure is w ithin the lim its. The deflection of m em bers under bending load depends on the m odulus of elasticity (E) and on the m om ent of inertia (I) togeth- er w ith the load and the span. W ith the sam e span and load, it w ill be the product E x I that w ill determ ine the deflection. To get the sam e deflection of steel and alum inium beam s in bending, the m om ent of inertia of the alum inium beam m ust be three tim es that of steel. If the increase in the m om ent of inertia is to be done only by increasing the thickness of the w eb and flanges, the alum inium beam w ill have the sam e w eight as the steel beam . 4. Al umi ni um versus Steel 59 EUROPEAN ALUMINIUM ASSOCIATION To save w eight, the alum inium beam s in bending have to be higher. A n exam ple w ill illustrate this: A n alum inium beam shall have the sam e deflection as an IPE 240 steel beam . The m om ent of inertia and the m ass of the IPE 240-beam are I = 38.9 · 10 6 m m 4 . m ass = 30.7 kg/m . The alum inium beam m ust have a m om ent of inertia of I =116.7 · 10 6 m m 4 to get the sam e deflection. If the height of the alum inium alloy beam shall be 240 m m , this w ill be satisfied by an I-beam of I 240 x 240 x 12 x 18.3 w hich has a m om ent of inertia and the m ass of I = 116.6 · 10 6 m m 4 m ass = 30.3 kg/m If the height of the alum inium alloy beam can be 300 m m , the deflection criteria w ill be satisfied by an I 300 x 200 x 6 x 12.9 w hich has a m om ent of inertia of I = 116.7 · 10 6 m m 4 and a m ass =18.4 kg/m w hich is a w eight saving of 40% . A n I 330 x 200 x 6 x 10 w ill have a m om ent of inertia of I = 117.3 · 10 6 m m 4 and a m ass = 15.8 kg/m w hich give a w eight saving of 49% . These three different alum inium beam s w ill give the sam e deflection as an IPE 240 steel beam . It w ill be the shape and stability of the beam that w ill determ ine the w eight of the beam . Table VI.1 show s the beam s and the w eight savings. ® ® ® ® ® ® t h ® ® w b Steel Aluminium Aluminium Aluminium M om ent in inertia in m m 4 38.9 10 6 116.6 10 6 116.7 10 6 117.3 10 6 E x I (N /m m 2 ) 8.17 10 12 8.16 10 12 8.17 10 12 8.21 10 12 h (m m ) 240 240 300 330 b(m m ) 120 240 200 200 w (m m ) 6.2 12 6 6 t (m m ) 9.8 18.3 12.9 10 U nit w eight (kg/m ) 30.7 30.3 18.4 15.8 W eight in % of the steel beam 100 % 99 % 60 % 51 % TABLE VI.1 60 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 60 | 61 The stress in an alum inium struc- ture designed according to deflection criteria is very often low . In the follow ing exam ple a steel beam , IPE 240 is com pared w ith an alum inium beam I 330 x 200 x 6 x 10 (both beam s are show n in the table VI.1). The deflection criterion is 1/250 of span (24 m m ), the span is 6000 m m and the load is 11.6 kN /m . In the Figure VI.1. the stress-strain curves for steel S355 and alu- m inium EN A W -6082 T6 is show n. The stress and strain for both the steel and alum inium beam is also show n. W ith the sam e deflection, the sam e load and the sam e span, the steel beam has a bending stress of 161 M Pa w hile the alum inium beam has a bending stress of 73 M Pa. This is the m axim um stress w hen the deflection is 24 m m for both beam s. EN AW-6082 T6 S355 0,1 0,2 0,3 0,4 0,5 0,6 0,7 ® 300 200 100 STRESS COMPARISON BETWEEN ALUMINIUM AND STEEL BEAMS FIGURE VI.1 0 , 1 0 5 0 , 0 7 7 161 73 σ ( M p a ) ® ε (% ) A dditional com parison of w eight-optim ized beam s are also given in C hapter III, section 2.1 61 EUROPEAN ALUMINIUM ASSOCIATION 5.1. Phi l osophy Lim it state design and partial safety factor m ethod are the m ethods that the new design standards are based on. In Europe the EN 19xx standards are the basis for this m ethod for all structural m aterials in civil engineering. For alum inium the actual standards are: EN 1990 Eurocode –Basis for structural design EN 1991 Eurocode 1 –A ctions on structures. A ll parts EN 1999 Eurocode 9 –D esign of alum inium structures 5. Li mi t state desi gn EN 1990 gives the partial safety factor on loads and rules for com bination of loads to give the different action effects. EN 1991 gives the characteristic loads for structures and buildings such as self w eight, live loads, w ind loads, snow loads, traffic loads etc. EN 1999 gives the design rules for alum inium structures. The ultimate limit state is the condition w here the safety of the structure is calculated. A struc- ture shall not collapse and design in accordance w ith the ultim ate lim it state shall avoid structural failure. The partial safety factor for the resistance (γ M ) shall take care of the scattering of the strength properties and the geom etry of the cross section. For connec- tions the partial safety factor shall in addition take care of uncertainties in the w elds and in the bolts and bolt configuration. The partial safety factor for the load effects (γ F ) shall take care of the scattering of the determ ina- tion of the loads and the proba- bility in the com bination of dif- ferent loads. The partial safety factor is different for the differ- ent types of loads, their certainty and how they are com bined. D ead loads (i.e. self w eight of structure) have a low partial safe- ty factor w hile the live load (i.e. all forces that are variable during operation, e.g. w eight of goods, road vibrations etc…) has a high- er partial safety factor. 5.2. What i s t he ul t i mat e l i mi t st at e 62 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 62 | 63 The condition to be fulfilled is: R k ≥ γ F . E k γ M w here: R k is the characteristic value of the resistance; it m ay be axial tension or com pression, bending m om ent, shear or a com bined resistance. E k is the characteristic value of the load effects; it m ay be axial tension or com pression, bending m om ent, shear or a com bined load effect on a cross section or a connection. γ M is the partial safety factor for the resistance, also often called m aterial factor. γ F is the partial safety factor for the load effects, also often called load factor. This relation is show n in the Figure VI.2. Typical values for the partial safe- ty factor for the resistance are 1.10 (g M1 ) for m em bers and 1.25 (γ M2 and γ Mw ) for bolt and rivet connections and w elded connec- tions. These are the m aterial fac- tors for building and civil engi- neering and m ay also be used in all structural design because the m aterial, the geom etrical dim en- sions and the fabrication of con- nections are alm ost sim ilar in all alum inium structures. ® FIGURE VI.2 F r e q u e n c y ® The serviceability lim it state is the condition w here the service- ability criteria have to be satis- fied. The m ost used serviceability criteria are: •D eflection lim its in all directions •D ynam ic effects like vibrations In serviceability lim it states both the partial safety factor for the resistance (g M ) and the partial safety factor for the load effects (γ F ) are 1.0. Typical values for the load effect factors in buildings and civil engi- neering are 1.2 for dead loads and 1.5 for live loads. For design of com ponents for com m ercial vehicles the follow ing load fac- tors m ay be used: D ead load: 1.1 Live load: 1.5 E k R k E k . γ F < R k γ M 5.3. What i s t he ser vi ceabi l i t y l i mi t st at e 63 EUROPEAN ALUMINIUM ASSOCIATION A ll calculations in serviceability lim it state are elastic calculations. Elastic deform ations are calculat- ed and com pared w ith the lim its for deflections. The sizes of vibra- tions have to be calculated in the sam e m anner. If the vibration has a high num ber of cycles, the m em bers and the connection details have to be checked for fatigue. N orm ally the calculations of elas- tic deflections are based on the m om ent of inertia for the gross cross-section of the m em ber. For m em bers in cross-section class 4 (see section 7.2.4 in EN 1999-1-1) it is necessary to reduce the m om ent of inertia, if the stresses of the com pression part of the cross section are higher than the stresses w hen local buckling occurs. M om ent of inertia for calculation of deflections for cross section class 4 m em bers: I ser = I gr - σ gr (I gr - I eff ) f o W here: σ gr is m axim um com pressive stress in serviceability lim it state in the cross section, based on the gross cross-section properties (positive in the form ula) I gr is the m om ent of inertia for the gross cross-section I eff is the m om ent of inertia of the effective cross-section in ultim ate lim it state, w ith allow ance for local buckling 7.1. Cr oss sect i on cl asses C ross-sections are classified in 4 classes. In Table VI.2 the differ- ent classes identify how the cross-section behaves during com pression and bending. This is directly linked to the resistance (load bearing capacity) of the cross-section. Thin parts of a cross-section m ay buckle at low stresses, and this w ill reduce the resistance of the cross-section. This is taken care of w ith the rules for cross-section classification. 6. Servi ceabi l i ty l i mi t state 7. Ul ti mate l i mi t state 64 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 64 | 65 Class 1 Class 2 Class 3 Class 4 Cross-sections that can form a plastic hinge w ith the rotation capacity required for plastic analy- sis w ithout reduction of the resistance. C ross-section that can develop their plastic m om ent resistance, but have lim ited rotation capacity. C ross-section w here the calculated stress in the extrem e fibre of the alu- m inium m em ber can reach its proof strength. Cross-section that w ill get local buckling before attainm ent of proof stress in one or m ore parts of the cross-section. The resistance m ay be calculated on the basis of plastic behaviour tak- ing the m aterial harden- ing effect into account. Rules are given in EN 1999-1-1. A nnex F. The resistance m ay be calculated on the basis of perfectly plastic behaviour for the m ate- rial using the conven- tional elastic lim it as the lim it value. Rules are given in EN 1999-1-1. A nnex F. The resistance is calculated on the basis of elastic design. The resistance is calculat- ed on basis of an effec- tive cross-section. Rules for calculating the effec- tive cross-section are given in EN 1999-1-1, 6.1.5 EN 1999-1-1, 6.1.4 gives rules how to classify any cross-section. A β value (i.e. w idth to thickness ratio) is calculated as: β = η . b t w here: b = the w idth of a cross-section part t = the corresponding thickness η = a value depending on the stress situation and if the part is an outstand or an internal cross- section part Lim its are given for the β value for the different classes and for w elded or unw elded parts and for outstand or internal parts. M ost alum inium structures in com m ercial vehicles w ill be opti- m ised regarding w eight. C ross section classes 1 and 2 w ill there- fore seldom be used. Elastic design in cross section class 3 and 4 w ill be the norm al situation. TABLE VI.2 7.2. Load beari ng resi st ance The load bearing resistance shall alw ays be higher than the fac- tored load effects. EN 1999-1-1 gives rules for cal- culating the load bearing resist- ances for different kinds of m em - bers exposed by different load effects. In the Table VI.3, som e of these rules are listed, and refer- ences are given: 65 EUROPEAN ALUMINIUM ASSOCIATION Situations Ref. EN 1999-1-1 Resistance Tension 6.2.3 The sm aller of: N o,Rd = A g . f o , N u,Rd = 0,9 . A net . f u or N u,Rd = A eff . f u γ M1 γ M 2 γ M 2 N o,Rd is the design resistance to general yielding. N u,Rd is the design resistance to axial force of the net cross-section at holes for fasteners or the effective cross-section at w elds. A g is the gross cross-section. A net is the net area of cross-section. A eff is the effective area of cross-section taking the H A Z effects into account. C om pression (w ith no buckling) 6.2.4 The sm aller of: N u,Rd = A net . f u , N c,Rd = A eff . f o γ M2 γ M1 N u,Rd is the design resistance to axial force of the net cross-section at holes for fasteners. N c,Rd is the design resistance to axial force at each cross-section. A net is the net section area w ith deduction for holes and if required the effects of H A Z softening at the cross section w ith holes. A eff is the effective section area based on the reduced thickness allow ing for the effect of local buckling. Bending m om ent 6.2.5 6.2.5.2 6.2.5.1 Bending m om ent resistance in a net section: M u,Rd = W net . f u γ M2 Bending m om ent resistance in each cross section: M c,Rd = α . W el . f o γ M1 W net is the elastic m odulus of the net section allow ing for holes and H A Z softening. W el is the elastic m odulus of the gross section. α is the shape factor given in table 6.4 in EN 1999-1-1, 6.2.5. Shear 6.2.6 6.7.4 6.7.5 6.7.6 The design value for shear resistance for non-slender sections: V Rd = A V . f o √3 .γ M1 A v is the shear area. For slender w ebs and stiffened w ebs the rules for capacity of plate girder w ebs have to be used (plate buckling). TABLE VI.3 66 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 66 | 67 Situations Ref. EN 1999-1-1 Resistance Torsion 6.2.7 6.2.7.2 6.2.7.3 The design St. Venants torsion m om ent resistance w ithout w arping: T Rd = W T,pl . f o √3 .γ M1 W T,pl is the plastic torsion m odulus For torsion w ith w arping the capacity is the sum of tw o internal effects. For com bined shear force and torsional m om ent the capacity is given by a reduced shear capacity. Bending and shear 6.2.8 The shear force w ill reduce the m om ent resistance. If the shear force is less than half of the shear force resistance, the effect of the m om ent resistance is so sm all that it can be neglected. Bending and axial force 6.2.9 6.2.9.1 6.2.9.2 6.2.9.3 Form ulae are given for the com bined effect of an axial tension and bending m om ents about one or tw o axis for: •open cross-sections •hollow sections and solid cross-sections •m em bers containing localized w elds Bending, shear and axial force 6.2.10 The shear force w ill reduce the com bined axial tension and m om ent resistance. If the shear force is less than half of the shear force resistance, the effect of the com bined axial tension and m om ent resistance is so sm all that it can be neglected. W eb bearing 6.2.11 This is for design of w ebs subjected to localized forces caused by concentrated loads or reactions applied to a beam . C om pression (buckling resistance) 6.3 M em bers subject to axial com pression m ay fail in one of the three w ays listed below : •flexural •torsional or flexural torsional •local squashing The design buckling resistance of a com pression m em ber is: N b,Rd = κ . χ . A eff . f o γ M1 κ is a factor to allow for effect of the H A Z at w elds χ is the reduction factor for the relevant buckling m ode A eff is the effective area of the cross section. (For cross section class 1, 2 and 3 this is the gross cross-section, for cross section class 4 it is reduced for local buckling effects) 67 EUROPEAN ALUMINIUM ASSOCIATION Situations Ref. EN 1999-1-1 Resistance M em bers in bending and axial com pression 6.3.3 6.3.3.1 6.3.3.2 6.3.3.3 6.3.3.4 6.3.3.5 M em bers subject to bending and axial com pression m ay fail in one of the tw o w ays listed below : •flexural buckling •lateral-torsional buckling C om bination form ulas are given for m em bers w ith axial com pression in com bination w ith bending about one or tw o axis and fail for flexural buckling. These form ulas are given for: •open double sym m etric cross-section •solid cross-section •hollow cross-section and tube •open m ono-sym m etrical cross-section C om bination form ula for open cross-section sym m etrical about m ajor axis, centrally sym m etric or double sym m etric cross-section is given for lateral- torsional buckling. Form ulas are also given for calculation of the follow ing effects: •m em bers containing localized w elds •m em bers containing localized reduction of cross-section •unequal end m om ents and/or transverse loads Plate girders 6.7 6.7.2 & 6.7.3 6.7.4 & 6.8 6.7.6 6.7.5 6.7.7 6.1.5 6.3.2 A plate girder is a deep beam w ith a tension flange, a com pression flange and a w eb plate. The w eb is usually slender and m ay be reinforced by transverse or/and longitudinal stiffeners. W ebs buckle in shear at relatively low applied loads, but considerably am ount of post-buckled strength can be m obilized due to tension field action. Plate girders are som etim es designed w ith transverse w eb reinforcem ent in form of corrugations or closely-spaced transverse stiffeners (extrusions). Plate girders can be subjected to com binations of m om ent, shear and axial loading, and to local loading on the flanges. Because of their slender proportions they m ay be subjected to lateral torsional buckling, unless properly supported along the length. Failure (buckling) m odes m ay be: •w eb buckling by com pressive stresses •shear buckling •interaction betw een shear force and bending m om ent •buckling of w eb because of local loads on flanges •flange-induced w eb buckling •torsional buckling of flange (local buckling) •lateral torsional buckling 68 7.3. Wel ded connect i ons 7.3.1. General The rules given in EN 1999-1-1, clause 8.6, apply to structures w elded by M IG or TIG and w ith w eld quality in accordance w ith EN 1090-3. C ertified w elders are highly recom m ended. Recom m ended w elding consum - ables can be found in: •C hapter VIII, section 3.8 •EN 1999-1-1, section 3.3.4 •EN 1011-4 W hen w elding hardened alu- m inium alloys, part of the hard- ening effect w ill be destroyed. In a w elded connection it can be three different strengths: •the one of the parent (not heat affected) m aterial (f o ) •the one in the heat affected zone (f o,HAZ ) •the one of the w eld m etal (f w ) N orm ally it w ill be necessary to check the stresses in the H A Z and in the w elds. The strength in H A Z is depend- ent on the alloy, the tem per, the type of product and the w elding procedure. Values are given in Table 3.2 in EN 1999-1-1. The strength in the w eld (w eld m etal) is dependent on the filler m etal (w elding consum ables) and the alloys being w elded. Values are given in Table 8.8 in EN 1999-1-1. Single sided butt w elds w ith no backing is practically im possible to w eld in alum inium . If single sided butt w elds cannot be avoided, the effective seam thickness can be taken as: •the depth of the joint prepara- tion for J and U type •the depth of the joint preparation m inus 3 m m or 25% , w hichever is the less for V or bevel type In addition to the single sided butt w eld, a fillet w eld m ay be used to com pensate for the low penetration of the butt w eld. W hen designing a w elded connec- tion som e few practical precautions should be taken into account. •Provide good access to the w elding groove. The “w elding head”of the equipm ent used for w elding alum inium is rather large, so there m ust be enough space around the w eld. •G ood access is also needed for checking the w eld. A ll w elds shall be 100 % visually exam ined in addition to som e non-destruc- tive testing (N D T). •Full penetration single sided butt w elds are im possible to w eld w ithout any backing. If possible, position the w elds in areas w here the stresses are low . 7.3.2. Butt weld H eavy loaded m em bers should be w elded w ith full penetration butt w elds. The effective thickness of a full penetration butt w eld should be taken as the thickness of the thinnest connecting m em - ber. The effective length should be taken as the total length if run-on and run-off plates are used. If not, the total length should be reduced by tw ice the effective thickness. (Figure VI.3) ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 68 | 69 ® ® ® ®b t F,σ F,σ ® ® ® ®b t F,τ F,τ Butt w eld subject to norm al stresses Butt w eld subject to shear stresses FIGURE VI.3 69 EUROPEAN ALUMINIUM ASSOCIATION D esign form ulas for butt w elds: N orm al stress, tension or com - pression, perpendicular to w eld axis: σ ⊥ ≤ f w γM w Shear stress: τ ≤ 0,6 . f w γM w C om bined norm al and shear stress: √σ 2 ⊥ + 3 . τ 2 ≤ f w γM w 7.3.3. Fillet weld A fillet w eld is defined w ith the throat thickness “a”given in m m . The Figure VI.4 show s how to m easure the throat thickness. The effective length should be taken as the total length of the w eld if: •the length of the w eld is at least 8 tim es the throat thickness •the length of the w eld does not exceed 100 tim es the throat thickness w ith a non-uniform stress distribution •the stress distribution along the length of the w eld is constant FIGURE VI.4 ® ® ® ® ® ® t 1 ® ® t 2 g 1 ® ® a a ® ® a pen EXAMPLE OF UNIFORM STRESS DISTRIBUTION FIGURE VI.5 EXAMPLE OF NON UNIFORM STRESS DISTRIBUTION FIGURE VI.6 τ τ τ τ 70 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 70 | 71 The forces acting on a fillet w eld shall be resolved into stress com - ponents w ith respect to the throat section (see Figure VI.7). These com ponents are: σ ⊥ : norm al stress perpendicular to the throat section σ  : norm al stress parallel to the w eld axis τ ⊥ : shear stress acting on the throat section perpendicular to the w eld axis τ  : shear stress acting on the throat section parallel to the w eld axis D esign form ula for fillet w eld: √σ 2 ⊥ + 3 . (τ 2 ⊥ + τ 2 II ) ≤ f w γM w ® ® ® ®® FIGURE VI.7 σ ⊥ ® σ II F,σ a ® ® τ II τ τ ⊥ 71 EUROPEAN ALUMINIUM ASSOCIATION 7.3.4. Heat affected zone The stress in the heat affected zone has to be checked. The stress is calculated for the sm all- est failure plane for both butt w elds and fillet w elds. The sketches below (ref. BS 8118) indicate the failure plane for som e w elds (Figures VI.8, VI.9, VI.10, VI.11): W : w eld m etal, check of w eld F: heat affected zone, check of fusion boundary T: heat affected zone, check of cross section BUTT WELD FIGURE VI.8 ® ® ® ® ® ® t F W F P v P a P v P a T BUTT WELD FIGURE VI.10 T FILLET WELD FIGURE VI.11 ® ® P v P a ® ® P v P a ® ® W F T t F ® ® t FILLET WELD FIGURE VI.9 ® ® t ® ® P v P a T T T F W ® ® t ® ® P v P a T T T F W W F F F 72 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 72 | 73 7.4. Bol t ed connect i ons The rules for bolted connections are given in EN 1999-1-1, clause 8.5. M inim um , regular and m axim um spacing, end and edge distances for bolts are given in the Table VI.4. Minimum Regular Maximum e 1 = 1.2 . d 0 e 2 = 1.2 . d 0 p 1 = 2.2 . d 0 p 2 = 2.2 . d 0 e 1 = 2.0 . d 0 e 2 = 1.5 . d 0 p 1 = 2.5 . d 0 p 2 = 3.0 . d 0 e 1 = 4 . t + 40mm e 2 = 4 . t + 40mm p 1 ≤ { 14 . t 200mm p 2 ≤ { 14 . t 200mm p 1 = 2.2 . d 0 p 2 = 2.4 . d 0 p 1 = 2.5 . d 0 p 2 = 3.0 . d 0 p 1 ≤ { 14 . t 200mm p 2 ≤ { 14 . t 200mm p 1 = 2.2 . d 0 p 1 = 2.5 . d 0 O uter lines: p 1 ≤ { 14 . t 200mm Inner lines: p 1 ≤ { 28 . t 400mm The m axim um clearance for fit- ted bolts is 0.3 m m and for non- fitted bolts 1.0 m m . Failure m odes for bolted connec- tions m ay be: •block tearing, failure in shear in a row of bolts along the shear face of a bolt group and tension failure along the tension face of the bolt group •shear failure in the bolt •bearing failure of the bolt hole •tension failure of the bolt •punching shear around the bolt head or nut •com bined shear and tension failure o)outer line i)inner line d 0 is the diam eter of the hole and t = thickness of the plate TABLE VI.4 73 EUROPEAN ALUMINIUM ASSOCIATION Failure mode Formula Parameters Shear resistance per shear plane F v,Rd = α v . f ub . A γ M2 α v = 0.6 for steel bolts, 4.6, 5.6 and 8.8 α v = 0.5 for steel bolts, 4.8, 5.8, 6.8 and 10.9 α v = 0.5 for stainless steel and alum inium bolts A is the cross-section of the bolt at the shear plane Bearing resistance F b,Rd = k 1 . α b . f u . d . t γ M2 k 1 = smallest of 2.8 e 2 - 1.7 d 0 { 2.5 for edge bolts k 1 = smallest of 1.4 p 2 - 1.7 d 0 { 2.5 for inner bolts α b = smallest of α d f ub f u { 1.0 α d = e 1 for end bolts 3 . d 0 α d = p 1 − 1 for inner bolts 3 . d 0 4 Tension resistance F t,Rd = k 2 . f ub . A s γ M2 k 2 = 0.9 for steel bolts k 2 = 0.5 for alum inium bolts k 2 = 0.63 for countersunk steel bolts A s is the tensile stress area of the bolt Punching shear resistance B p,Rd = 0,6 . π . d m . t p . f u γ M2 d m is the m ean of across points and across flats of a bolt head or the nut or the outer diam eter of the w asher t p is the thickness of the plate under the bolt head or the nut C om bined shear and tension F v,Ed + F t,Ed ≤ 1.0 F v,Rd 1.4 . F t,Ed F v,Ed is the load effect of shear F t,Ed is the load effect of tension TABLE VI.5 74 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 74 | 75 C onnection details that carry ten- sile forces, and w here the tensile forces don’t go directly through the bolts, additional forces in the bolts have to be accounted for. These forces are called prying forces (Q ) and they can be con- siderable large. See the figure VI.12. FIGURE VI.12 N = F N + Q N = F N + Q Q Q 2 F N Truck bodi es f or beverage t ransport 75 EUROPEAN ALUMINIUM ASSOCIATION 8.1. Theor y Structures w ith repeating loads m ay be susceptible to fatigue w hen the num ber of load cycles is high, even w hen the loads give low stresses in the structure. Fatigue failure starts w ith devel- opm ent of a crack at a point w ith stress concentrations. W ith con- tinuous repeating loads the crack w ill grow , this w ill be show n as one striation in the failure sur- face for each load cycles. The dis- tance betw een the striations is depending on the stress range and that is giving the grow ing speed. The stress range is defined as the algebraic differ- ence betw een the stress peak and the stress valley in a stress cycle. A t low stress ranges the crack grow s slow ly and w ith high stress range it grow s fast. (Figure VI.5) 8. Fati gue Trai l er f at i gue t est i ng i n l aborat ory (Benal u) 76 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 76 | 77 Rules for fatigue design are given in EN 1999-1-3. The rules are based on quality levels given in EN 1999-1-3 and EN 1090-3. •The fatigue strength depends on: •type of detail (design) •stress range •num ber of cycles •stress ratio •quality of m anufacturing FIGURE VI.13 ® ® ® ® ® ® ® ® ® ® ® ® σ σ m ax σ m σ m in 3 1 2 T 0 σ 3 σ 3 ∆ σ 1. Stress peak 2. Stress valley 3. Stress cycle ∆σ Stress range σ 3 Stress am plitude The pict ure is showing t he st riat ions in a fat igue failure surface of an aluminium t ube. 77 EUROPEAN ALUMINIUM ASSOCIATION The properties of the parent m aterial have very little influence on the fatigue strength in practi- cal structures and com ponents. For connections the properties of the parent m aterial have no influence at all. For a plate or extrusion w ith no m anufacturing or only holes and notches the standard deviate betw een EN AW 7020 and all other structural alloys. The fatigue strength is given as SN curves for the different details. A ll detail categories given in EN 1999-1-3 have their ow n SN curve. A typical SN curve is show n on the Figure VI.14. 1). N um ber of cycles (10 8 ) at w hich the cut-off lim it is defined 2). For low cycles fatigue, this part of the curve m ay not be cor- rect, other calculation m ethods are recom m ended (A nnex F of EN 1999-1-3). It shall be checked that the m axim um design stress range don’t result in a tensile stress exceeding the design stress in ultim ate lim it state. FIGURE VI.14 10 4 10 5 10 6 10 7 10 8 10 9 N 2) a c d m 2 1 b 1 m 1 N L 1) ® ® ® 2 . 10 e N C 5 . 10 e N D ∆σ ∆σ C ∆σ D ∆σ L a. Fatigue strength curve b. Reference fatigue strength c. C onstant am plitude fatigue lim it d. C ut-off lim it S 78 5.1 63-4,3 C ontinuous autom atic w elding B C 5.2 56-4,3 C C 5.3 45-4,3 A ny backing bars to be continuous C D 5.4 45-4,3 B C 5.5 40-4,3 C D ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 78 | 79 The stress ratio, R, is the m ini- m um stress divided by the m axi- m um stress in a constant am pli- tude stress history or a cycle derived from a variable am pli- tude stress history. Favourable stress ratio w ill enhance the fatigue strength for som e cases com pared w ith the values given in the standard. For initiation sites in base m aterial aw ay from connections, there w ill be an increase in the fatigue strength for R < +0.5. For initiation site at w elded or m echanical fastened connections in sim ple structural elem ents, w here the residual stresses has been established, taking into account any preac- tion or lack of fit, there w ill be an increase in the fatigue strength for R < -0.25. For other cases there w ill be no change from the values in the standard. Som e typical details categories are show n in the Table VI.6. The first row in the table gives the detail type num ber, the second row gives the detail category, the third gives a sketch of the detail and also show ing the initiation site and the direction of the stress, the fourth gives the w eld type, the fifth gives the stress param eter, the sixth gives stress concentrations already allow ed for, the seven gives the w elding characteristics, the eight gives the quality level for the internal im perfections and the ninth gives the quality level for the surface and geom etrical im perfections. The requirem ents for the quality levels are found in EN ISO 10042 and additional requirem ents are given in EN 1090-3. TABLE VI.6 N o m i n a l s t r e s s a t i n i t i a t i o n s i t e Full penetration butt w eld W eld caps ground flush Full penetration butt w eld C ontinuous fillet w eld A t w eld discontinuity A t w eld discontinuity A t w eld discontinuity ∆σ ® ® ® ® ® ® ∆σ ∆σ ® ® ∆σ ® ® ® ® ∆σ ® ® ∆σ ® ® ® ® 79 EUROPEAN ALUMINIUM ASSOCIATION D etail types 5.4 and 5.5 are an exam ple w here the sam e detail has different fatigue strength depending on the quality of the w eld. The SN curves that correspond to these detail categories are show n on Figure VI.15. The num erical values for the sam e curves are show n in the Table VI.7 : INFLUENCE OF WELD QUALITY ON FATIGUE STRENGTH FIGURE VI.15 500 400 300 200 150 100 50 40 30 20 15 10 5 ∆σ N /m m 2 N C N O N L 10 4 10 3 10 6 10 7 10 8 10 9 63-4,3 56-4,3 45-4,3 40-4,3 36-4,3 28-4,3 S N 80 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 80 | 81 SLOPE Cycles N m 1 m 2 1E+05 1E-06 2E+06 5E+06 1E+07 1E+08 1E+09 4,3 6,3 126,4 74,0 63,0 50,9 45,6 31,6 31,6 4,3 6,3 112,4 65,8 56,0 45,3 40,5 28,1 28,1 4,3 6,3 90,3 52,9 45,0 36,4 32,6 22,6 22,6 4,3 6,3 80,3 47,0 40,0 32,3 29,0 20,1 20,1 4,3 6,3 72,3 42,3 36,0 29,1 26,1 18,1 18,1 4,3 6,3 56,2 32,9 28,0 22,6 20,3 14,1 14,1 TABLE VI.7 Fat i gue f i el d t est (Benal u) 81 EUROPEAN ALUMINIUM ASSOCIATION The follow ing sections show s good and bad design solutions for alum inium trailer chassis. They all refer to the load case described in Figure VI.16. 8.2. Pr act i ce: compar i son bet w een good and bad chassi s sol ut i ons ® ® ® ® ® ® ® ® ® ® ® ® 7300 3000 2150 1000 1250 7 3 0 0 115 N cm BOUNDARY CONDITIONS AND BEAM GEOMETRY AS A BASIS FOR THE FINITE ELEMENT ANALYSIS FIGURE VI.16 ® ® ® ®®® ® ® ® ® ® ® ® ® ® 1 6 5 1900 941 R1000 7300 6 0 100 4 0 0 R1000 1 Load case with 0,5x115 N/cm is used (dashed rectangle). Cross section of the beam is a simple symmetrical H-section with a flange-width of 150 mm, flange-thickness of 12 mm and web-thickness 8 mm. (1: To achieve the gooseneck, a part of the web has been cut off and re-joined by welding at a distance of 60 mm from the lower flange.) 82 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 82 | 83 8.2.1. Gooseneck The G ooseneck area of the chas- sis beam w ill be the m ost stressed part and has to be very carefully treated to avoid prob- lem s. G enerally good precautions w ill be: •It is of utm ost im portance to avoid all w elding or heat treat- m ent on, or near, the flanges. •N o w elded or bolted attach- m ents to, or near, the flanges in this area. •N o joining of the beam s and/or reinforcem ent of the beam s in this area. •N o sudden variation of m aterial thickness or properties in this area. It is obviously m andatory to fol- low the fabrication or shop draw ings, design m anuals, w eld- ing procedures, Q A -m anuals and the designer’s guidance through- out the w hole fabrication process. Figures VI.17, VI.18 and 6.19 pres- ent a few lifespan exam ples depending on the geom etry of the G ooseneck (i.e. curvature radius). O ne can see the increase in stress level is approxim ately 70% and the increased deflection (δ) approxim ately 23% . The consequence w ill be a rela- tive lifespan decrease of 50 % PLAIN CHASSIS BEAM, R = 1000 mm (σ max = 43 MPa, δ = 5.3 mm) FIGURE VI.17 PLAIN CHASSIS BEAM, R = 450 mm (σ max = 73 MPa, δ = 6.9 mm) FIGURE VI.18 σ max = 43 M Pa σ max = 73 M Pa ® ® PLAIN CHASSIS BEAM, R = 300 mm (σ max = 85 MPa, δ= 7.5 mm) FIGURE VI.19 σ max = 85 M Pa ® 83 EUROPEAN ALUMINIUM ASSOCIATION from the norm al radius of 450 m m to 350 m m . A s illustrated, an increased radius of 1000 m m w ill offer very low stresses and dem onstrates sim ply the im por- tance of sm ooth transitions. 8.2.2. Perforation The fixture of the supporting legs to the chassis beam w ill norm ally be located at the highest stressed area of the chassis beam , i.e. in the gooseneck area. H ence a per- foration of the bottom flange by boltholes m ust be avoided as w ell as any w elding on or near the flange. Figures VI.20 and VI.21 show the consequence of perforating the flange com pared to the w eb in this area. The reduced relative lifespan w ill be as m uch as >80% due to the effect of stress concentration in the perforated area of the flange. For the situation w ith the perfo- ration through the w eb, the lifes- pan w ill not be reduced. Both exam ples show the im portance of a location aw ay from the m ost stressed area of the beam . If a perforation through the flange is inevitable, the location should be as close as possible to the edge of the flange (as far from the w eb as possible). N ote that HOLE IN CHASSIS BEAM FLANGE, (ø = 20 mm): σ max = 102 MPa FIGURE VI.20 σ max = 102 M Pa ® σ = 73 M Pa ® HOLE IN CHASSIS BEAM FLANGE, (ø = 20 mm): σ max = 73 MPa (on flange) FIGURE VI.21 σ = 35 M Pa ® σ max = 73 M Pa ® 84 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 84 | 85 required m inim um distance from the edge should be according to actual standards, norm ally 1,5ø – 2,0ø depending on direction of load, etc. A lso note that local bending capacity of flange m ust be checked according to actual location. 8.2.3 Welding A fixture by w elding in the w eb area of the beam is a m uch-used alternative to bolting, and w ill be fully acceptable as long as w eld- ing is avoided in or near the flange (i.e. in the m ost stressed area of the beam ). Figures VI.22 and VI.23 illustrate the conse- quence of w elding on the flange and on the w eb. The lifespan reduction w ill be as m uch as >90% in the case of the fixture by w elding on flange, due to the effect of stress concentra- tion in the w elded area of the flange and the decreased m ateri- al properties due to heating. The fixture by w elding in the w eb area w ill be of no effect to lifes- pan. In both cases a geom etrical- ly perfect w eld is assum ed. In real life, im perfections are com m on and therefore good w orkm an- ship and after treatm ent of w elds m ust be considered. FIXTURE BY WELDING ON FLANGE: σ max = 97 MPa FIGURE VI.22 σ max = 97 M Pa ® σ = 73 M Pa ® FIXTURE BY WELDING ON WEB: σ max = 73 MPa (on flange) FIGURE VI.23 σ max = 73 M Pa ® σ = 25 M Pa ® 85 EUROPEAN ALUMINIUM ASSOCIATION 9. Speci al desi gn i ssues 9.1. Tank s f or t he t r anspor t of danger ous goods - ADR Tanks for the transport of dan- gerous goods have to be built according to the rules defined in the follow ing agreem ent and standards: •ADR: Agreem ent for the trans- port of Dangerous goods by Road 1 •EN 13094 “Tanks for the transport of dangerous goods - M etallic tanks w ith a w orking pressure not exceeding 0.5 bar - D esign and construction” •EN 14025 “Tanks for the transport of dangerous goods - M etallic pressure tanks - D esign and construction” In particular, tank shell thickness (e) is determ ined by the follow - ing equivalence form ula, w here e 0 is the m inim um shell thickness for m ild steel and R m and A , the tensile strength and elongation of the m etal chosen. e = e 0 × 464 3 √ (R m × A ) 2 Furtherm ore, absolute m inim um shell thicknesses are fixed depending on the type of tank, the shell dim ension and the m aterial used. For tanks protected against dam age: •For shells w ith circular cross-section ≤ 1.80 m : e 0 = 3 m m e cannot be low er than 4,00 m m for alum inium alloys 2 •For shells w ith circular cross-section > 1.80 m e 0 = 4 m m e cannot be low er than 5,00 m m for alum inium alloys •For other tanks: e 0 = 5 m m for shells w ith circular cross-section ≤ 1.80 m e 0 = 6 m m for shells w ith circular cross-section > 1.80 m 1. See A D R - A nnex A –Part 6 –C hapter 6.8: http://w w w .unece.org/trans/danger/danger.htm 2. W hatever the result of the equivalence form ula is. Al umi ni um road t ankers (Schrader) 86 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 86 | 87 Suitable alum inium alloys for that application are listed in standard EN 14286 “A lum inium and alu- m inium alloys - w eldable rolled products for tanks for the stor- age and transportation of dan- gerous goods”. See also C hapter V, section 6.4 in this m anual. For tanks protected against dam - age, several alloys listed in EN 14286 allow m anufacturing tank shells w ith e = 5.3 m m (corre- sponding to R m x A = 6600) and even e = 5.0 m m (for those w ith R m x A ≥ 7152). 9.2. Ti pper s 9.2.1. Construction Tipper body trailers (or “dum p bodies”) are constructed in tw o different versions: •C om bination of plates and extrusions (m ore frequently used version) •Extrusion intensive construc- tion, w here all sides of the trailer are m ade of clam ped and / or w elded extrusion profiles A nother version w hich cam e up in the last few years is a m aterial –m ix version w ith a steel bottom plate and alum inium side- w alls (bolted to the steel plate). Tw o m ain tipper types can be dif- ferentiated: •Rectangular trailer •H alf –pipe trailer Independent from the type of tip- per, all extrusion cross –sections and the thickness of the plates are calculated w ith respect to: Al umi ni um t i pper bodi es (St as) 87 EUROPEAN ALUMINIUM ASSOCIATION W ear is not only taken into account for the calculation of the actual plate or extrusion thick- ness, especially of the bottom plate, but also for the type of alu- m inium to be chosen. 9.2.2.1. Defintion of Wear The m echanism of w ear is quite com plex. W ear generally occurs w hen one surface (usually harder than the other) cuts off m aterial from the second. The area of con- tact betw een the tw o surfaces is thereby very sm all and concen- trated on surface asperities. The shear forces are transferred through these points and so the local forces can be very high. A brasives can act like in a grind- ing process w here the abrasive is fixed relative to one surface or in a lapping process, w here the abrasive tum bles, producing a series of indentations. •A ctual load (com pression / tension) •Bending forces (static and dur- ing tipping operation) •O ther forces like shear stress, deflection, buckling In addition, the type of products to be transported has to be taken into consideration during design of the tipper. This is due to the fact, that the load can be just concentrated locally and on a very sm all area or it can be divid- ed quite uniform across the w hole bottom of the tipper body. 9.2.2. Wear W ear (or abrasion- resistance) is the m ost discussed issue w hen it com es to the construction of an alum inium tipper. A lot of uncer- tainties about the abrasion – resistance of the alum inium as w ell as the totally different type of loads m akes it nearly im possi- ble to find a perfect solution for each transport problem . 9.2.2.2. Factors i nfl uenci ng the wear The w ear condition can vary extrem ely from one load to another. Therefore it is not alw ays possible to link the actual hardness of a w ork-hardened alloy to the w ear resistance 3 . It w as found out that for a very large extent, the type of load is a decisive factor. Soft goods like potatoes, fruits, sugar beets or other agricultural products are m uch less abrasive than m ineral goods. In case of m ineral goods like stones, pow - ders, cem ent, chalk etc. the size, form (sharpness) and hardness of the m aterial is by far the m ost critical factor regarding abrasion (in laboratory tests even the change of a type of sand increased the w ear by 35% ). 3. Abrasive wear of aluminium alloys rubbed against sand, K. Elleuch, S. M ezlini, N . G uerm azi, Ph. Kapsa, W ear 261 (2006) 1316–1321 Product i on of al umi ni um t i pper bodi es (Schmi t z) 88 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I DESI GN A N D CA LCU LATI ON 88 | 89 Even the w ear debris acts there- by as an additional source for abrasion. A lso the num ber of tipping opera- tions is to be considered. The m ore often the trailer is tilted, the m ore often abrasion occurs. The num - ber of cycles has a linear function w hen set into relation to the m ass lost of the alum inium plate. Very often, tippers are used by the transport com panies for other products than they are originally m ade for and so a reli- able calculation of the lifetim e of an alum inium bottom plate can- not be determ ined. 9.2.3. Material selection The choice of m aterial for the bottom plate of tipping trailers is now adays often a question of specific experience, m aterial availabilty and m anufacturer´s specific production m ethods. Typical bottom plate m aterial is: •5083 H 32, H 321, H 34 •5086 H 24 •5383 H 34 •5454 H 22, H 24 •5456 H 34 or other, m ill-specific alloy types. 10. Ref erences •EN 1999-1-1 Eurocode 9 Design of aluminium structures, Part 1-1 General structural rules. •EN 1999-1-3 Eurocode 9 Design of aluminium structures, Part 1-3Structures susceptible to fatigue. •EN 1090-3 Execution of steel structures and aluminium struc- tures, Part 3 Technical require- ments for aluminium structures •EN-ISO 10042 Arc-welded joints in aluminium and its weldable alloys – Guidance on quality lev- els for imperfections. •BS 8118 Structural use of alu- minium, Part 1 Code of practice for design. •A D R: A greem ent for the trans- port of D angerous goods by Road. •EN 13094 Tanks for the trans- port of dangerous goods - Metallic tanks with a working pressure not exceeding 0.5 bar - Design and construction. •EN 14025 Tanks for the trans- port of dangerous goods - Metallic pressure tanks - Design and construction. •EN 14286 Aluminium and alu- minium alloys - weldable rolled products for tanks for the stor- age and transportation of dan- gerous goods. Ful l al umi ni um t i pper (Menci ) 89 EUROPEAN ALUMINIUM ASSOCIATION 90 1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 1. 1. 5000 series alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 1. 2. 6000 series alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 1. 3. 7000 series alloys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 2. FABRICATION OF PRODUCTS FROM PLATE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 2. 1. Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 2. 2. Marking out . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 2. 3. Cutting to shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 2. 4. Edge rolling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 2. 5. Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 2. 6. Non-machinable faces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97 3. FABRICATION OF PRODUCTS FROM EXTRUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 3. 1. Storage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 3. 2. Cutting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 3. 3. Bending . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 4. DRILLING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 4. 1. Twist drill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 4. 2. Straight flute drill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 4. 3. Gun drill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102 4. 4. Half-round or three quarter round drill . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 5. TAPPING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 5. 1. Chip removal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 5. 2. Upsetting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 5. 3. Threaded inserts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 6. DEEP DRAWING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 7. SPINNING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 7. 1. Advantages of spinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 7. 2. Diameter of spinning blanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 CHAPTER VI I FABRI CATI ON 91 EUROPEAN ALUMINIUM ASSOCIATION The form ing operations used in the com m ercial vehicle industry are m any and various. The m an- ufacturer w ill cut, fold, roll and bend sem i-finished sheets and extrusions to produce a vehicle or an accessory. These operations, som e of w hich such as cutting and drilling can now be program m ed and auto- m ated, are carried out according to rules w hich w e have sum m a- rized in this chapter. In certain cases and in som e countries they are also standardized, and the relevant standards are referred to w here they exist. In any case, it is very im portant to use equipm ents dedicated to alu- m inium . M ost alum inium alloys used in com m ercial vehicles belong to the fam ily of alum inium -m agne- sium alloys (5000 series) for rolled products or to the alum inium -sili- con-m agnesium fam ily (6000 series) for extruded products. 1.1. 5000 ser i es al l oys In soft conditions, 5000 series alloys have excellent form ing properties as suggested by the difference betw een proof stress and ultim ate tensile strength and by the level of elongation 1 . A s m etals are hardened by m echanical cold w orking, it m ay be necessary to im prove ductility so as to continue form ing by m achine or by hand. This is done by annealing 2 , a process that is easy to accom plish either in a furnace or w ith a w elding torch, using tallow as a tem perature indicator w hich turns a light brow n colour at 340 °C . H eat indicator crayons or even a stick pyrom eter m ay also be used. If necessary, inter-stage anneal- ing can be repeated betw een shaping operations, how ever there is one golden rule: only anneal the m etal if it becom es difficult to w ork, in other w ords w hen the w ork-hardening rate is greater than or at least equal to the so-called critical w ork- hardening rate. 1.2. 6000 ser i es al l oys These are used m ainly as extruded sections. The m ain alloy elem ents are m agnesium and silicon. These are heat treatable alloys supplied in the T6 or T5 condi- tion and, less com m only, in the T4 or T1 condition 3 . G enerally speaking the shaping properties of this fam ily of alloys in the fully heat-treated condi- tion are lim ited. N evertheless shaping should be perform ed cold as heating w ill considerably reduce m echanical properties (approx. 40 % ). M ore com plex shaping of the extrusions m ay be done in the T1 or T4 condition, before ageing to full hardness in T5 or T6. In this case it is beneficial to do the form ing w ithin a short tim e w in- dow of a few days after the solu- tion heat-treatm ent to T1 or T4, 1. Introducti on 1. Please refer to EN 485-2. 2. For 5000 alloys w ith M g content above 3% , this m ust be done very care- fully to prevent sensitization to inter- granular corrosion. See also C hapter XI, section 2.2.6. 3. Please refer to C hapter V section 5, for an explanation of these tem pers. 92 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I FA BRI CATI ON 92 | 93 i.e. before that the m aterial gets hardened by cold-ageing. If very extensive shaping is to be done, it is possible to do this in a tim e-span of a few m inutes after the treatm ent to T1 or T4. 1.3. 7000 ser i es al l oys These extrusions are used in som e high-strength applications w ithin transportation, autom o- tive and sports equipm ent. The m ain alloy elem ents are zinc and m agnesium . The extrusions are used in the T5, T6 or a T7 over-aged condition. The shaping m ay take place in the T1 or T4 condition, before the m aterial is artificially aged. M ore com plex form ing is done in the T4 condition, shortly after the solution heat treatm ent, before ageing to T6 or T7. Before using 7000 alloys, prior consultation w ith the supplier is strongly recom m ended. The general m ethods of alum inium alloy fabrication and the m achines used are not very different from those used for steel. Alum inium alloys are easy to fabricate. H ow ever, their relative softness m ust be taken into account and it is essential to use special tools to avoid dam aging alum inium surfaces. Risks of contam ination from traces of ferrous and cuprous m etals m ust also be avoided as these can cause local- ized corrosion. It is essential to w ork in an environm ent w here such risks are m inim ized. 2.1. St or age A lum inium sheets are classified by fam ily of alloy and stored upright w hen m ore than 0.8 m m thick (Figure VII.1). Thin sheets (less than 0.8 m m ) should be stored flat. A lum inium sheets should never be placed directly on the ground, even if concreted, and should be kept aw ay from splash w ater, condensation and hostile envi- ronm ents. They are best stored under cover in a ventilated area and separat- ed by tim ber blocks to prevent condensation stains. 2. Fabri cati on of products f rom pl ate STO RA G E FIGURE VII.1 93 EUROPEAN ALUMINIUM ASSOCIATION 2.2. M ar k i ng out Scribing tools should not be used, since any tracing m arks w hich m ight be left on the fin- ished com ponent can becom e crack starters under high loads. This precaution is not necessary w here the scribe indicates a cut- ting line. A s a general rule it is advisable to trace using a hard pencil (e.g. 5H ) w hich is easier to see and easy to erase in case of error. 2.3. Cut t i ng t o shape Plate or crocodile shears can be used to m ake straight cuts. The rating of the shear should be m ore or less the sam e as for cut- ting non-alloyed steel w ith low carbon content and the sam e thickness. Saw ing is a com m on cutting process w hich is very econom ical for alum inium alloys. 2.3.1. Band saw The m ost com m on type of saw is the band saw . This can be a sim - ple tim ber band saw but w ith a blade of specially designed pro- file to break and dislodge the alum inium chips from betw een the saw teeth. This is achieved by the alterna- tion or pitch of the teeth and by the clearance angle defined Figure VII.2. 2.3.2. Circular saw As w ith the band saw , the saw pitch varies w ith the thickness or section to be saw n but the process of cutting, w hich is a function of the m achine characteristics, m akes it sim ilar to m illing (Figure VII.3). W ith the band saw and circular saw , the cutting speeds for 3000, 5000 and 6000 series alloys are as follow s: •H SS blade: 600 m /m in to 1000 m /m in. •C arbide blade: 800 m /m in to 1500 m /m in. The portable m illing saw is a tool that can be used to straight cut products up to 20 m m thick and w ith good rates of advance. It m ay be preferable to use a jig- saw for thicknesses of 6 m m or less. The jigsaw is highly m anoeuvrable and can be used to cut com plex curves. BA N D SAW FIGURE VII.2 ® ® ® ® ® ® ® ® ® 2,5 to 8 m m 1,8 t 55° t 3° to 0° THE CHARACTERISTICS O F A BAND SAW FO R ALUM INIUM ARE AS FO LLO W S: •E (thickness) = D iam eter of flyw heel 1000 •W idth = 10 to 30 m m •Tooth pitch = 2.5 to 8 m m ; tw o teeth m ust alw ays be in action •Lubricant = tallow or soluble oil. SAW - M ILLIN G O R C IRC U LA R FIGURE VII.3 ® ® ® ® ® ® ® ® 25° h p d ®® ® ® ® ® ® ® ® ® ® ® t – 3 t – 3 t t 60° 60° d: draw of 8° over 1 m m of w idth 94 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I FA BRI CATI ON 94 | 95 2.3.3. Fluid jet M etals, including alum inium alloys, can be cut using w ater jets bearing abrasive particles (PA SER process) at high pressures (3000 bars and over). G ranules of garnet, corundum or other very hard m inerals are used. The advantage of this process is that it does not affect the m etal- lurgical condition of the product and is very versatile. Its perform ance is also excellent, and in alum inium , thicknesses betw een 1 and 100 m m can be cut at rates of 3500 m m /m in dow n to 30 m m /m in for the larg- er thickness. Wat er j et cut t i ng (SAG) 95 EUROPEAN ALUMINIUM ASSOCIATION 2.3.4. Plasma There are tw o plasm a cutting techniques (Figure VII.4): •traditional plasm a, w ith a draft of som e 6°, •w ater VO RTEX plasm a, w ith a very sm all cutting draft, of the order of 2°. C om pared to traditional plasm a, w ater VO RTEX plasm as facilitate greatly increased cutting speeds and reduce nuisance factors such as sm oke, noise, ozone discharge. The process requires substantial am ounts of pow er how ever. The plasm a is form ed in a special torch, and an inert gas (usually argon or nitrogen) m oving at great speed is dissociated under the effect of an electric arc to attain the plasm a state. O w ing to its high cutting speed (several m etres per m inute), its quality and precision of cut and suitability for autom ation, a plas- m a cutting m achine can be a highly profitable investm ent, even for short production runs. 2.3.5. Laser cutting This process is m ainly used in the autom otive industry. M ore inform ation can be found in the A lum inium A utom otive M anual (w w w .eaa.net/aam ). Note: The width of the heat affected zone is less than 1 mm whatever the alloy and for all thicknesses. However cracking is sometimes observed in the short transverse dimension (Figure VII.5) that can attain a depth of some 2 mm. Whatever the thickness of the product, machining off 2 mm of material will restore the metal's original qualities. This is obviously unnecessary if the cut pieces are intended for use as welding blanks. PLA SM A TEC H N IQ U ES FIGURE VII.4 ® ® + + - ® ® C ooling w ater ® Electrode ® Plasm agen gas Plasm agen gas Electrode ® ® W ater cone Plasm a colum n Vortex w ater inlet ® Plasm a in vortex Plasm a in free air - FIBRE O RIEN TATIO N FIGURE VII.5 ® ® ® ® ® ® D ire c t io n o f ro llin g Transverse direction L o n g it u d in a l d ir e c t io n s h o r t t r a n s v e r s e d i r e c t i o n ® C opper ® 96 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I FA BRI CATI ON 96 | 97 2.4. Edge r ol l i ng This shaping technique requires no special equipm ent for alu- m inium . The rollers m ust of course be clean and have sm ooth surfaces. 2.5. Bendi ng For m ultiple folds, holes should be used to m ark the crossover points of the fold lines to avoid causing cracks w hen the folds are m ade. A lum inium does not require any special bending tools, and con- ventional table bending m achines or presses are perfectly adequate provided the w orking parts of the tooling are free from unacceptable irregularities. The bending radii to be observed as a function of the thickness are given in standard EN 485-2. 2.6. Non-machi nabl e f aces A s w ith bending, one w orth- w hile precaution is to rem ove all score m arks from the edges caused by cutting so as to pre- vent the form ation of cracks at points of deep deform ation. Shaping is carried out on the 5754, 5086 and 5083 grades (and on other alloys in the sam e fam ily) in the annealed or H 111 condition. In som e cases shaping m ay call for inter-stage anneal- ing 1 , and this can be done as described before using an annealing torch and tallow as tem perature indicator. Inter-stage annealing can be carried out several tim es in the course of the shaping opera- tion; how ever care should be taken to avoid annealing a m etal that is only slightly w ork- hardened to prevent the risk of grain enlargem ent. Pl asma cut t i ng (Benal u) 1. For 5000 alloys w ith M g content above 3% , this m ust be done very care- fully to prevent sensitization to inter- granular corrosion. See also C hapter XI, section 2.2.6. 97 EUROPEAN ALUMINIUM ASSOCIATION Extrusions are usually individually protected in packing cases to prevent problem s such as fret- ting in transit. 3.1. St or age Extrusions are best left in their original packing cases until required. A s w ith alum inium sheets, they should never be set dow n directly on the ground, even if concreted, and should be kept aw ay from splash w ater, condensation and hostile envi- ronm ents to prevent possible corrosion during storage. 3.2. Cut t i ng The processes of saw ing described above are also suitable for cutting alum inium extrusions . 3.3. Bendi ng The bending of extrusions on an industrial scale m ay be carried out w ith different m ethods and m eans. 3. Fabri cati on of products f rom extrusi ons 3-poi nt press bendi ng (Benal u) 98 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I FA BRI CATI ON 98 | 99 3.3.1. Bending by 3-point press-bending This m ay be done w hen the bend radius is sm all com pared to the height of the extrusion section, and w hen the accuracy (spring- back) of the bend as w ell as the optics are not so im portant. It is typically perform ed in a sim ple tool in a (m ostly) hydraulic press. 3.3.2. Bending by 3-point press-bending with rotating dies This process is typically using a tool in a press or a bending m achine. The rollers m ay be kinder to the extrusion w ork piece than by the m ethod in 3.2.1 due to less abrasive sliding action betw een tools and w ork piece. 3.3.3. Bending by compression bending A sliding tool forces the extrusion to follow a circular die. The extrusion is not m oving length- w ise relative to the die. 99 EUROPEAN ALUMINIUM ASSOCIATION 3.3.4. Bending by compression roll-forming It is identical w ith 3.3.3, but w ith a rotating w heel instead of the sliding tool. Very severe reform ing m ay be m ade. It is usually per- form ed in roll-form ing m achines w ith purpose-built tools. 3.3.5. Bending by rotary draw bending It is m ostly perform ed in stan- dard tube-bending m achines. 3.3.6. Stretch-bending over a fixed tool (“swing arm stretch-bending”) The ends of the profile are gripped to stretch-bend the profile against a fixed last w hich has the form of the finished product. In m any cases this form m ay be a bending sw eep built-up by com pounded radii. N early all of the cross section of the extrusion w ill be subjected to tensile stress above the yield stress lim it, and this applies to the full length of the w ork piece. This m eans that the spring-back effect on global shape w ill be little, con- stant and predictable. W hen a closed extrusion is form ed in this w ay, the outer w all m ay be sub- jected to sagging. This m ay be countered by using a basic extru- sion w ith an outer w all w hich is barrel-shaped outw ard or by inserting a suitable elastic m aterial (e.g. rubber). The operation m ay be perform ed by a dedicated tool in a press or in a stretch-bending m achine. Bendi ng over rot at i ng t ool s 100 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I FA BRI CATI ON 100 | 101 3.3.7. Stretch bending by rotating dies (rotary stretch bending) By this m ethod the extrusion is gripped at its ends and bent over one ore tw o (norm ally tw o) rotating dies having a contour corresponding to the final prod- uct shape. The stretching com es as a result of the rotation and m ay effectively be controlled by the location of the rotary axes. A s opposed to the situation in conventional stretch bending m ethod (3.3.6), the bending starts at the end and propagates tow ards the centre of the extru- sion. The prim ary bending m om ent is generated by the rotating dies, and is typically con- stant along the w orkpiece. The process is characterized by very low transversal (shear) forces and thus also low contact forces betw een extrusion and dies. Rotary stretch bending can be im plem ented in a dedicated press tool or in a stand-alone bending m achine. 3.3.8. Three-dimensional stretch-bending O ver fixed or rotating dies (lasts), the extrusion si gripped at its ends, and stretched into a three- dim ensional shape (“out of the plane”). This m ay be done w ith tools w here the m ovem ents are defined m echanically, or in pro- gram m able tools or m achines. 3.3.9. Manipulation of the cross section This is usually perform ed by indenting or pressing in a dedi- cated tool in a press. 3.3.10. Mechanical calibration of parts of the extrusion This is usually perform ed by com - pression-stretching or expansion- stretching in a dedicated tool in a press. 3.3.11. Achievable bending radius The achievable radii for bent extrusions are highly dependent on the geom etry of the profiles and are difficult to predict. Therefore it is advisable to carry out tests on specim en. Table VII.1 gives guidance for bending of hollow circular tubes. If sm aller radii are needed, filling of the tubes w ith sand before bending is helpful. D: Outside diameter t: Thickness BENDING HOLLOW TUBES (D ≤ 90mm) BENDING RADIUS AS A FUNCTION OF RATIO D/t Alloy Temper Ratio D/t 5 10 15 20 25 30 5754 H 111 1 to 1.5 D 2.5 to 3 D 3.5 to 4 D 4.5 to 5 D 6 to 7 D 8 to 9 D 6060 O 1 to 1.5 D 2.5 to 3 D 3.5 to 4 D 4.5 to 5 D 5 to 6 D 7 to 9 D T5 2 to 2.5 D 3 to 4 D 4 to 5 D 6 to 7 D 8 to 10 D 12 to 15 D TABLE VII.1 101 EUROPEAN ALUMINIUM ASSOCIATION D rilling alum inium alloys is a sim - ple operation but calls for careful sharpening and polishing of the drills given the relative softness of the alum inium alloys used in the m anufacture of com m ercial vehicles. If inadequate sharpen- ing causes the drill to bend or buckle, it w ill tear the m etal around the part of the hole that is already drilled. The follow ing types of drill can be used for drilling alum inium alloys 3 : •the standard tw ist drill - the m ost com m on type, •the straight flute drill, •the gun drill, •the half-round or three quarter round drill. 4.1. Tw i st dr i l l To have a substantial sharpening gradient, the helix angle m ust be 40° w hile the point angle varies from 120° to 140° according to the shape of the neck, w ith a clearance angle of 8°. The other characteristics of the tw ist drill are as follow s: •cutting speed 30 to 80 m /m in depending on rating and the desired quality - for very accurate holes the ideal speed is 30 m /m in, •penetration rate determ ined by the drill diam eter: 0.05 m m /rev for a 2 m m diam eter drill, to 0.3 m m /rev for a 30 m m diam eter drill, •soluble oil cooling, •point height : this m ust exceed the thickness of the drilled m aterial. 4.2. St r ai ght f l ut e dr i l l This drill facilitates rapid chip rem oval and is m ore efficient for alum inium alloys of m edium hardness than the tw ist drill. The four cylindrical w itnesses also prevent "triangulation" of the hole and provide drill guidance. 4.3. Gun dr i l l This type of drill is excellent for large diam eter holes of 20 m m and over, also for drilling stacked sheets. The drilling conditions are the sam e as for the standard tw ist drill. 4.4. Hal f - r ound or t hr ee quar t er r ound dr i l l These drills are used m ainly in boring operations. The accuracy of the bore diam eter achieved w ith these tools is of the order of 0.02 m m : •cutting speeds are betw een 10 and 15 m /m in, •rate of advance is 0.05 m m /rev, •cooling is w ith cutting oil. 4. Dri l l i ng 3. Steel tw ist drills can be used for sm all runs w ith m ainly m anual tools. 102 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I FA BRI CATI ON 102 | 103 Threads in alum inium m ay be m ade, w hen other joining tech- niques are not applicable 4 . If threads are m ade in alum ini- um , care should be taken to ensure that the thread length is sufficient for the purpose. The thread length m ay be betw een 1 and 2 tim es the m ajor diam eter of the threads, and m ust depend on the application, the alloy as w ell as the tem per of the m ateri- al. For exam ple, the necessary thread length of a high strength 6000 alloy in T6 m ay be 1.2 tim es the m ajor thread diam eter. C onversely a softer alloy dem ands a longer thread length. There are tw o m ethods of tapping: •by chip rem oval, •by upsetting. 5. Tappi ng DIAMETER OF PILOT HOLES FOR THREAD TAPPING ∅ nominal 4 5 6 8 10 12 14 16 18 20 Pitch 0.70 0.80 1 1.25 1.50 1.75 2 2 2.5 2.5 D iam eter 3.2 4.2 4.9 6.6 8.3 10 11.7 13.7 15 17 TABLE VII.2 4. In a connection, w here continuous joining m ethods such as w elding or bonding are used, no additional fasten- ers should be applied. Threaded holes in alum inium should only be used w here no other possibility exists and the yield strength of the m etal exceeds 200 N /m m 2. The bearing length of the bolt should be 1,5 x diam eter of the bolt. If the bolts m ust be used for repeated loosening and tightening, inserts should be applied e.g. H elicoils. 5.1. Chi p r emoval O nly taps w ith straight threads should be used to avoid seizing the m etal at the flanks. Table VII.2 gives diam eters for pilot holes for tapping alum inium alloys in the 5000 and 6000 series. Pilot holes for these alloys in the annealed condition m ust be som e 3-5% bigger than in Table VII.3 and for castings w ith 12 and m ore % silicon content som e 2% sm aller. The cutting speed varies from 10 to 50 m /m in depending on the m achine and m ethod of clam p- ing the tap, w hether floating or in a chuck. C ooling is done w ith cutting oil. 103 EUROPEAN ALUMINIUM ASSOCIATION 5.2. Upset t i ng The thread is achieved by plastic deform ation of the m etal using a tap w ith- a rounded polygon sec- tion that has no cutting w edge. The diam eter of the pilot hole w ill depend on the desired thread depth, and m ust be drilled accurately. U psetting speeds can attain 50 m /m in, cooling is done w ith cutting oil. Tapping by upsetting offers a num ber of advantages w ith alu- m inium alloys: •the tap has a long life, •it increases the hardness of the thread, its tearing resistance and fatigue strength, •no chips. 5.3. Thr eaded i nser t s It is usual to use threaded inserts –available in diam eters M 2 to M 68 (Figure VII.9) – w hen screw ed alum inium alloy assem - blies are required to be frequent- ly dism antled. The inserts are in the form of a spring m ade from rolled w ire or are a diam ond sec- tion m ade of stainless steel. C aptive threads can also be used. These have one or tw o flights that grip the flanks of the screw thread and counteract the loos- ening effects of dynam ic stress- es, vibrations or therm al shock. Boring is done using a standard tw ist drill, but tapping m ust be done w ith a special tap. A ll chips and cutting fluid m ust be rem oved from the bore before the insert is fitted. Threaded inserts are fitted w ith pneum atic hand tools w hich hold them by a driver at the top end of the thread. This can then be broken off after fitting. Threaded inserts can also be used to repair a tap in alum inium that is w orn or has been rejected during m anufacture. D eep draw ing is m ainly used in the autom otive sector. For m ore inform ation on that technique, please refer to the A lum inium A utom otive M anual: http://w w w .eaa.net/aam / H ELI-C O IL IN SERTED TH REA D FIGURE VII.9 ® ® N otch D river 6. Deep drawi ng 104 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I FA BRI CATI ON 104 | 105 Spinning is a form ing technique used in the com m ercial vehicle industry to m ake som e com po- nents such as tank-ends. 7.1. Advant ages of spi nni ng The tools used in spinning are very sim ple, being basically the internal shape of the required form . H ow ever production tim es can be up to 20 longer than for deep draw ing. C alculations com bining the cost of tooling and production costs show that spinning is com petitive for short runs. 7. Spi nni ng D IA M ETER O F SPIN N IN G BLA N KS FIGURE VII.10 ® ® ® ® ® ® ® ® ® ® D D d H h ∅ blank = D × Π 2 ∅ blank = h + D 4 3 ∅ blank = H + d 7.2. Di amet er of spi nni ng bl ank s Three form ulae are used to quickly determ ine the diam eter of blanks for the m ost com m on shapes (Figure VII.10). In spin- ning, the diam eter of the blank is less critical for the success of a part than it is in deep draw ing, and it is only the cost of the m aterial that dictates shape opti- m ization. A sim plified calculation is adequate for prototypes. Spi nni ng of an al umi ni um t ank-end (Köni g) 105 EUROPEAN ALUMINIUM ASSOCIATION EUROPEAN ALUMINIUM ASSOCIATION EUROPEAN ALUMINIUM ASSOCIATION 106 CHAPTER VI I I WELDI NG 1. FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 2. TIG WELDING (TUNGSTEN INERT GAS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 2. 1. Manual TIG welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 2. 2. Automatic TIG welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 2. 3. TIG welding with AC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 2. 4. TIG welding with DC, reverse polarity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 2. 5. Edge preparation for TIG welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 2. 6. Choice of filler wire or rod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 2. 7. Selection of welding process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 3. MIG WELDING (METAL INERT GAS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 3. 1. Manual MIG welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112 3. 2. Automatic MIG welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 3. 3. Smooth current MIG Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 3. 4. Pulsed current MIG welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 3. 5. Wire pulsation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 3. 6. CMT – Cold Metal Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 3. 7. Edge preparation for MIG welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 3. 8. Choice of filler wire or rod . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 3. 9. Selection of welding process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 4. PLASMA MIG WELDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 5. LASER WELDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118 6. LASER MIG WELDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 119 7. RESISTANCE WELDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 8. FSW - FRICTION STIR WELDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 9. SURFACE PREPARATION BEFORE WELDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 10. QUALITY CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 10. 1. Approval procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 10. 2. Inspecting welded joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 10. 3. Weld defects & approval criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 11. DESIGN AND PREVENTION OF DEFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 11. 1. Causes of deformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 11. 2. Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126 107 EUROPEAN ALUMINIUM ASSOCIATION 1. Foreword W elding is the m ost com m on m ethod of joining used in the m anufacture of com m ercial vehi- cles and their bodies e.g. tanks, tippers, dum pers, chassis etc. The different physical, chem ical and m echanical properties of alum inium com pared w ith those of steel lead to the specific behaviour of alum inium during w elding. In an atm osphere con- taining oxygen, a w ell anchored oxide layer builds up on alum ini- um . This layer has a m elting point of som e 2000°C against the m elting interval of 630-660°C for the m etal underneath. For quality w elds this layer m ust be rem oved or at least broken up. D espite the fact that the m elting interval of alum inium is by far low er than that of steel, the high therm al conductivity and the high m elting energy m ake that, for arc w elding, alum inium requires about the sam e am ount of energy as steel. The therm al elongation of alu- m inium is tw ice that of steel and the loss in volum e of the w eld pool during solidification is im portant, causing distortion of the joint, if no rem edial m easures are taken. O ne m ethod of m ini- m izing distortion is to select a process w ith sm all energy input. TIG and M IG arc w elding are the tw o processes m ost com m only used in the com m ercial vehicle industry. The technical progress m ade by other techniques such as plasm a, laser, resistance or friction stir w elding and the ever grow ing diversity of sem i-fin- ished products w ill encourage the application of such w elding m ethods w hich have up to now been little used in the com m er- cial vehicle industry. Wel der (STAS) 108 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I I WELDI N G 108 | 109 In this process, an electric arc is struck betw een a refractory elec- trode m ade of tungsten and the w orkpiece, w hile a shroud of inert gas, usually argon, shields the electrode and protects the m olten pool against oxidation. This process uses a high-frequen- cy stabilized A C pow er source. The oxide film is rem oved during the negative phase, w hile the positive phase ensures penetra- tion and cooling of the electrode. TIG w elding is suitable for m etal thicknesses betw een 1 and 6 m m . There is a TIG version w here heli- um is used as the shielding gas. This helps achieving a high tem - perature in the arc but requires direct current w ith straight polarity. The effect of oxide film rem oval is w eaker but the w elding pow er is higher and products 10 to 12 m m thick can be w elded w ith a single pass. H ow ever this process is strictly for autom atic w elding only ow ing to the difficulty of keeping the arc at a constant controlled height w ithin 0.5 m m . 2. TIG wel di ng (Tungsten Inert Gas) PRIN C IPLE O F TIG W ELD IN G FIGURE VIII.1 ® C ontact (for current) Filler M etal A rc ® ® ® ® ® Shielding G as Shielding G as N ozzle Tungsten Electrode W elding Pow er Source W eld Seam ® W ork Piece ® 109 EUROPEAN ALUMINIUM ASSOCIATION 2.1. M anual TI G w el di ng For m anual TIG w elding, the filler m aterial is a hand-held rod fed into the w eld pool. The m anual process is used m ainly for sm all w elds, circular w elds and rela- tively thin com ponents. M A N U A L A N D M EC H A N ISED TIG W ELD IN G FIGURE VIII. 2 M anual TIG W elding Fully M echanised TIG W elding 2.2. Aut omat i c TI G w el di ng H ere, the w elding torch is auto- m atically guided and, if filler is used, it is fed autom atically from a reel. A utom atic TIG w elding is an attractive proposition for w elding large production runs, especially w hen there is no access to the back of the w eld. The fabrication of com pressed air reservoirs is a good exam ple of the use of autom atic TIG w eld- ing. These reservoirs consist of a sheet rolled and w elded to form the straight cylindrical centre sec- tion to w hich tw o deep-draw n ends are w elded. If the ends are butt joined to the centre w ithout any backing to prevent the prob- lem s associated w ith m oisture retention, autom atic TIG w elding can be used to m ake an easy connection. It is also possible to support the w eld pool by supply- ing the argon from inside the reservoir. TIG w el di ng of an ai r pressure vessel (SAG) 110 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I I WELDI N G 110 | 111 2.3. TI G w el di ng w i t h AC It is especially w ell suited for butt and corner w elds on pieces in the thickness range 1-6 m m . Full penetration w elds can be m ade w ithout backing bar. Tack w elds m ust not be rem oved before exe- cuting the seam w eld. C hanges in w eld direction are easy to fol- low w ith the torch and do not require any dressing. The process can also be used to sm ooth the surface of a M IG w eld. The w elding speed is low er than for M IG w eld and, for w ork pieces thicker than 6 m m , pre- heating is required. The slow w elding speed is also responsible for a w ider heat affected zone and greater distortion of the assem blies. For fillet w elds extrem e care is needed to achieve full penetra- tion w ithout lack of fusion at the root. In the tank and silo production, double side TIG w elding of butt w elds in vertical upw ards posi- tion leads to excellent quality, provided the tw o operators con- trol the process w ell. 2.4. TI G w el di ng w i t h DC, r ever se pol ar i t y In this process the arc length is below 1 m m , ideally 0.5 m m , w hich m eans that it is m ainly used for m achine w elding. For m anual operation only short lengths can be executed in prac- tice. O ne such application is stitch w elding of assem blies before the seam w elding. The sm all cross section of these stitches is such that they are com pletely m olten up w hile lay- ing the first pass of M IG w eld over it and don’t need to be reduced in cross section by m echanical m eans. The oxide film rem oval is w eaker w ith this process so it is neces- sary to reduce the oxide layer by m echanical m eans before w eld- ing. 2.5. Edge pr epar at i on f or TI G w el di ng In EN ISO 9692-3 this inform ation is given com prehensively, so that w e just indicate a few exam ples for typical joints in vehicle m anu- facturing (Table VIII.1, p. 115). To avoid sharp notches, especial- ly at the root of the w eld, all edges m ust be carefully de- burred before w elding. Instead of grinding discs, m illing tools should be used, because residues of the disc on the surface can cause porosity in the w eld. 2.6. Choi ce of f i l l er w i r e or r od See section 3.8 2.7. Sel ect i on of Wel di ng pr ocess See section 3.9 111 EUROPEAN ALUMINIUM ASSOCIATION W ith M IG w elding the alum ini- um alloy w ire is both the elec- trode and the filler m aterial. It uncoils autom atically from a reel to the w elding tool (gun or torch) as it is used up. The w elding energy is supplied by a D C pow er source (sm oothed current). C onnection is m ade w ith reverse polarity (i.e. m inus to the w ork- piece) to ensure rem oval of the oxide film and the fusion of the w ire electrode at the sam e tim e. Several M IG processes do exist... PRIN C IPLE O F M IG W ELD IN G FIGURE VIII.4 W ire Transport Rolls ® W elding Pow er Source ® W orkpiece ® A rc ® ® ® ® W ire Electrode C ontact N ozzle (for C urrent) Shielding G as N ozzle ® W eld Seam 3.1. M anual M I G w el di ng In its m anual version, M IG is cer- tainly the m ost com m on w eld- ing process used in the com m er- cial vehicle industry, producing high quality w elds at an attrac- tive quality/cost ratio. A s the filler w ire, that is the con- sum able electrode, is alw ays autom atically fed from a reel, the m anual M IG w elding is also know n as "sem i-autom atic M IG w elding". M anual M IG w elding is used for all w elds of a com plex nature w here the dim ensions and thick- ness of the products are com pat- ible w ith the M IG process and w hen autom ation is not consid- ered to be profitable. If w e consider the exam ple of a tank consisting in sheets rolled and w elded to form cylindrical sections, w e can see that the lon- gitudinal w eld can be m ade by autom atic M IG w hile the circular w elds w hich join the sections to one another are usually m ade m anually on a turntable in tw o opposing passes. The choice betw een m anual or autom atic M IG w ill depend largely on accessibility. 3. MIG wel di ng (Metal Inert Gas) 112 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I I WELDI N G 112 | 113 3.2. Aut omat i c M I G w el di ng H ere, the w elding torch is auto- m atically guided. This is norm ally used for very long straight w elds w here an autom atic system is profitable. A good exam ple is fabrication of chassis side m em bers consisting of tw o “T”sections w elded to either edge of a central plate w hich form s the w eb of the built-up beam . The tw o w elds w ould norm ally be m ade auto- m atically and at the sam e tim e to avoid problem s of deform ation. A utom atic w elding is also pre- ferred w here an attractive appearance is desirable, e.g. for stiffening channel w elded to the side panels of vehicle bodies. H ere the appearance and size of the w eld bead can be repeated to achieve the im pression of con- sistency. Finally, autom atic w elding - both TIG and M IG - provides a repeat- able w elding quality provided of course that the w elding param e- ters are fully defined to begin w ith. 3.3. Smoot h cur r ent M I G Wel di ng This fast and econom ical process allow s depositing a great quanti- ty of filler m etal per unit of tim e. The energy input is such that butt w elds can only be produced w ith the use of a backing bar, either integrated into the shape of the extrusion or as tem porary rem ovable feature in stainless steel, copper or even alum inium . D ue to the relatively high w eld- ing speed, the heat affected zone 1 is narrow er than w ith TIG w elding and thus the distortion of the assem blies is less. Thin gauge m aterial below 3 m m is difficult to w eld w ith this process because of the high energy of the arc. If no other equipm ent is available, then a thin gauge filler w ire m ay be used w ith reduced energy input, but then the w ire feed can cause instability of the process even if a push-pull equipm ent is used. If the preassem bly of structures is carried out w ith stitches in the M IG process, these short runs m ust have a sim ilar cross section as the first w eld pass and be som e 100 m m long to be sound. Before production w elding, these stitches m ust be reduced in cross section by m echanical m eans (no disc grinders), so that they can be m olten up w ith the w eld pass and do not leave im perfections near the root. 1. The extent of the heat affected zone and the strength in the heat affected zone are given in EN 1999-1-1. Wel di ng of si de panel s f or t i ppers (Menci ) 113 EUROPEAN ALUMINIUM ASSOCIATION 3.4. Pul sed cur r ent M I G w el di ng A n im provem ent of the M IG process has been achieved by superim posing a pulsed current over the m ain current, the object being to m aintain a low average current level w ithout sacrificing arc stability. The filler m etal is transferred to the w eld pool every tim e the cur- rent is high (i.e. one drop of m etal per pulse). The "cold tim es" w hen the current is low ensure that arc stability is m aintained. There are three operating m odes: •synergetic mode: only the rate of uncoiling has to be regu- lated. The voltage and frequency are regulated by electronic logic circuits; •manual mode: all the w eld- ing param eters are adjustable; •programme mode: each param eter can be stored for use according to production requirem ents. The pulsed M IG process is lim ited to thin products of 2 < t ≤ 5 m m and to vertical fillet w elds. This process m akes it possible to w eld thin gauge m aterial w ith standard filler w ire. A s the w eld pool can be better controlled, butt w elds up to 5 m m thickness can be executed w ithout backing bar. Furtherm ore it is very helpful for w elding in the vertical and the over head position. The opti- m al m achine setting is m ore dem anding than for standard M IG because there are m uch m ore param eters to be defined. The w idth of the heat affected zone is analogue to the one for standard M IG as is also the am ount of distortion of the w ork pieces. For w elding over stitches see rem ark under 3.3 above. 3.5. Wi r e pul sat i on For gauges betw een 1 and 3 m m , a com plem entary option “the w ire pulsation”could be added to the previously described “current pulsation”in order to im prove the arc stability. This “w ire pulsation” induces a double pulsation to cur- rent signal and consequently to the heat input. For T-joint of dis- sim ilar gauges, the heat input dis- tribution is difficult to m aintain constant w ith classical pulsed cur- rent. This double pulsation of cur- rent insures the concentration of heat input at the exact location of the joint. 3.6. CM T – Col d M et al Tr ansf er For M IG w elding gauges low er than 1 m m , the C M T process (C old M etal Transfer) could be used. W hen detecting a short- circuit, this process retracts the w ire so as to help detach the droplet. The therm al input is im m ediatly reduced and the short-circuit current is kept sm all. Wel di ng of a t ruck door 114 Process Welding Weld Thickness Preparation Remarks position bead TIG A ll positions O ne side only 0.8 < t <1.5 A slight peak form ed by the edges lim its deform ation TIG H orizontal O ne side only 0.8 < t < 5 C ham fered card, stainless steel support, clam ped w eld TIG A ll positions O ne side only 1.5 < t < 5 Tack-w elded free edges back-w eld possible Tack-w elded free edges. TIG A ll positions O ne side only 4 < t < 6 A ngle sam e principle but w ith offset bevel M IG A ll positions O ne side only 2.5 < t < 6 Back-w eld necessary after w ith back-w eld gouging to base of first pass M IG A ll positions O ne side only 2.5 < t < 6 Stainless steel support M IG A ll positions O ne side only 2.5 < t < 6 M IG H orizontal O ne side only 6 < t < 25 Back-w eld necessary after and overhead* w ith back-w eld gouging to base of first pass. C learance: 1.5 m m m ax. M IG H orizontal O ne side only 4 < t < 25 Ribbed stainless and vertical* steel support ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I I WELDI N G 114 | 115 3.7. Edge pr epar at i on f or M I G w el di ng Just the m ost frequent exam ples are given in the Table VIII.1 For m ore details please consult EN ISO 9692-3. * X-shaped bevels are preferred for com ponents 6 m m > t > 25 m m to restrict deform ation due to w elding. TABLE VIII.1 ED G E PREPA RATIO N 80° 2 m m 1 m m 1 m m 1 m m 1 m m 2 m m e e 80° 80° 115 EUROPEAN ALUMINIUM ASSOCIATION C H O IC E O F FILLER M ETA LS A S A FU N C TIO N O F TH E A LLO Y C O M BIN ATIO N TABLE VIII.2 (a) 5000 series alloys w ith m ore than 3.5% M g are sensitive to intergranular corrosion w hen exposed to tem peratures over 65°C and w hen used in certain aggressive environm ents (see section 2.2.6 in C hapter XI). (b) 5000 series alloys w ith less than 3% M g and 3000 series alloys that contain m agnesium m ay be sensitive to hot cracking. (c) The m echanical perform ance of the w eld depends on the internal soundness of the castings. G assed m aterials and injection m ouldings are considered to be non-w eldable. (d) The percentage of silicon in the filler w ire m ust be as near as possible to that in the casting. (e) The w elding of alum inium -silicon castings (40000 series) to 5000 series alloys should be avoided w here possible as M g2Si inter- m etallics form in the w eldm ent and w eaken the joint. Each com bination has three possible choices - indicated w here the lines intersect - depending on the selected criterion: O ptim um m echanical properties: top line –O ptim um resistance to corrosion: m iddle line –O ptim um w eld- ability: bottom line The filler m etal indicated is: 4 : series 4xxx ¡ 4043A , 4045, 4047A – 5 : series 5xxx ¡ 5356, 5183, 5556A Alloy A W rought 5 5000 Series 5 (a) M g < 3% 4 - 5 (b) W rought 5 5 5000 Series 5 5 M g > 3% (a) 5 5 W rought 5 - 4 5 - 4 5 - 4 6000 Series 5 5 5 4 4 4 W rought 5 - 4 5 - 4 5 - 4 5 - 4 7000 Series 5 5 5 w ithout copper 4 4 4 C ast 4 (e) 5 - 4 (e) 4 4 4 (d) Si > 7% 4 5 4 4 (c) 4 4 4 4 W rought W rought W rought W rought C ast Alloy B 5000 Series 5000 Series 6000 Series 7000 Series Si > 7% M g < 3% M g > 3% w ithout copper (c) 116 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I I WELDI N G 116 | 117 M ost of the alloys listed in C hapter V are w eldable and also com binations of these alloys are possible. W elding consum ables are not available in exactly the sam e chem ical com position as the base m etal to be joined. There are w ires and rods in the 4XXX and 5XXX series, nam ely 4043A , 4045, 4047A , 5183, 5356 and 5556A in the m arket (see also ISO 18273). In the Table VIII.2 , w ith the recom m endation of the best suited w eld consum - able, w e distinguish betw een dif- ferent requirem ents for the w eld: optim al strength, good corrosion resistance and w eldability. A choice m ust be m ade according to the relative im portance of these three requirem ents. The w eld consum ables should be stored in their sealed package and once a package is open, it should be kept in a dry atm os- phere, because hum idity on the surface of the w ire or rod causes porosity in the w eld. If open reels of filler w ire are exposed to am bient clim atic conditions for a longer period (m onths), it is rec- om m ended to dry them in a w arm ing box at approx. 80 ° C for one night before use. SELEC TIO N O F W ELD IN G PRO C ESS TABLE VIII.3 Process TIG M IG A tm osphere Inert Inert Electrode Refractory C onsum able C urrent A .C . D .C . Sm ooth Pulsed Pulsed Pulsed Special effect W ire pulsation C old M etal Transfer Suitability Thickness range (m m ) 0.8 ≤ t ≤ 5 0.2 ≤ t ≤ 10 3 ≤ t 2 ≤ t 1 ≤ t ≤ 5 t ≤ 1 M anual yes no yes yes difficult no A utom atic yes yes yes yes yes yes Industrial robot no no yes yes yes yes 3.9. Sel ect i on of w el di ng pr ocess 3.8. Choi ce of f i l l er w i re or rod 117 EUROPEAN ALUMINIUM ASSOCIATION This process com bines the high m elting capacity of the M IG process w ith the nearly ideal shape of the plasm a arc and its very good gas shield for the w elding pool. The result is an extrem ely good quality of w elds, especially the absence of porosi- ty. The plasm a arc is m aintained betw een the plasm a ring nozzle of the torch and the w ork piece, the M IG arc is in the centre of the plasm a arc. Both arcs have the sam e polarity w here the high kinetic energy of the plasm a arc destroys the oxide layer on the w ork piece. M echanical rem oval of the oxide layer can be dis- pensed w ith. The process is w ell suited for applications w ith high require- m ents for tightness and surface aspect. It is possible to carry out butt w elds of up to 10 m m thick- ness in one pass w ith the edge preparation in V. The w elding speed is higher than for M IG w elding. 4. Pl asma MIG wel di ng 5. Laser wel di ng Laser w elding of alum inium alloys is developing rapidly paral- lel w ith the developm ent of ever grow ing pow er of laser sources. There are on one side C O 2 lasers of up to 20 KW and m ore and N d:YA G lasers of 6 KW and m ore. W ith the C O 2 laser, the ori- entation of the beam is lim ited, w hereas w ith the N d:YA G laser optical fibres allow to bring the laser beam directly to the w eld zone. This gives high flexibility especially for robot w elding. The high reflectivity of alum inium m akes it necessary to install the laser equipm ent in a separate room , w here during operation of the equipm ent, nobody w ithout adequate eye protection has access. The sensor w hich em its the signals necessary for the m otion control of the laser beam m ust be very effective for not being disturbed by reflections. The process is m ainly used for thin gauge m aterials (1 –4 m m ) and the pieces to be joined m ust fit perfectly as is the case e.g. in the production of tailored blanks for the car industry. The achievable w elding speeds are up to 12m /m in w ith thick- ness of around 1m m and still 1-3 m /m in w ith thicknesses betw een 1.5 and 3 m m . C om pared w ith standard arc w elding, laser w elding allow s the production of com ponents w ith reduced geom etrical distortions and residual stresses, as w ell as narrow er heat affected zone, a direct consequence of the high w ork speed and thus the low heat input. The laser w elding process is preferably used w ith filler w ire for alum inium alloys. 118 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I I WELDI N G 118 | 119 6. Laser MIG wel di ng The com bination of a standard arc w elding process w ith the laser w elding process allow s to benefit from the advantages of both processes, w hich are good process stability, high w elding speed and enhanced bridging capacity. The laser beam runs ahead of the M IG arc but both focus on the sam e point of the m etal surface. The shielding gas is provided by the M IG torch. Preferably a m ix- ture of helium (70% ) and argon (30% ) is used. This process is ideal for continuous autom atic w elds up to 10 m m thickness in one pass, w here the require- m ents for fit up of the pieces to be joined is less stringent than for pure laser w elds. The sam e safety m easures as for laser w elding m ust be applied. Laser w el di ng 119 EUROPEAN ALUMINIUM ASSOCIATION This technique is very com m on in the autom otive industry and not so w idespread in the C om m ercial Vehicles industry. For this reason, w e do not give details here. Interested readers should refer to the Alum inium Autom otive M anual: w w w .eaa.net/aam 7. Resi stance wel di ng This is an innovative process w hich had been developed by TW I Ltd (The W elding Institute) and is protected by patents in Europe, U SA and A ustralia. A nyone using the process needs a license from TW I. The process operates in the solid phase of the m etal below the m elting point of the alloy. A tool in the form of a finger w ith a shoulder is rotated and m oved into the m etal w ith a defined rotational speed along the con- tact line betw een the tw o parts to be joined. The friction of the tool in the m etal supplies the needed energy to heat the local zone to the desired tem perature. Through the rotation and the translation of the tool the m ate- rial in the w eld zone is plastically deform ed to create the w eld. The process can be used for butt w elds, overlap w elds, T –sec- tions and corner w elds. For each of these joint geom etries specific tool designs are necessary. The process can be used in all posi- tions i.e. horizontal, vertical, overhead and orbital. The process can be used for w elds up to 50 m m thickness from one side and up to 100 m m from tw o sides. A dvantages are: •H igh productivity, i.e. low cost potential •Low distortion, even in long w elds •Excellent m echanical proper- ties as proven by fatigue, tensile and bend tests •N o fum e •N o porosity •N o spatter •Low shrinkage •C an operate in all positions •Energy efficient •N o consum able tool ( one tool typically can be used for up to 1000 m of w eld length in 6000 series alloys) •N o filler w ire •N o gas shielding •N o w elder certification •Som e tolerance to im perfect w eld preparations –thin oxide layers can be accepted •N o grinding, brushing or pick- ling required in m ass production 8. FSW - Fri cti on Sti r Wel di ng Fri ct i on St i r Wel di ng 120 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I I WELDI N G 120 | 121 The lim itations of the FSW process are continuously reduced by inten- sive research and developm ent. H ow ever, the m ain lim itations of the FSW process are at present: The relatively high investm ent requires a high degree of repeatability in order to m aterial- ize the cost saving potential W ork pieces m ust be rigidly clam ped Backing bar required (except w here self-reacting tool or direct- ly opposed tools are used Keyhole at the end of each w eld C annot m ake joints w hich require m etal deposition (e.g. fil- let w elds) U p to now the dim ensionally biggest equipm ent can cope w ith w ork pieces up to 20 m long. Fri ct i on st i r w el ded t ai l l i f t prof i l es 121 EUROPEAN ALUMINIUM ASSOCIATION 9. Surf ace preparati on bef ore wel di ng For quality w elds it is recom - m ended to m achine the edges (see section 3.7) of sheet to be w elded after w ater jet, plasm a or laser cutting to rem ove this rough surface w ith a thick oxide layer and also w ith m icro cracks in order to avoid w eld defects such as cracks and oxide inclu- sions. The sam e should be done for plate w ith thickness over 10 m m that has been sheared. There is a great risk of cracks in the short transverse direction, w here a rem oval of 2 m m via m illing or routing is adequate. The m etal to be w elded m ust be dry and w ithout contam ination of any grease or other products that evaporate under the action of the arc. To achieve this clean surface, the pieces to be w elded should be brought into the w ork- shop tw o days before produc- tion. This w ill allow condensation that m ight occur w hen the tem - perature in the storage area is low er than in the w orkshop to dry off. Im m ediately before w elding, the edges to be joined and their sur- roundings m ust be properly degreased using a solvent such as acetone or industry alcohol. A void trichlorethylen, w hich transform s under the effect of the arc into the poisonous gas phosgene. W hen the solvent on the surface has evaporated, a further cleaning w ith a stainless steel w ire brush (hand-operated or rotary) is recom m ended. O utdoor w elding is not advis- able. If it cannot be avoided, the w elding environm ent m ust be screened off. Wel di ng of t i pper body (SCHMITZ) 122 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I I WELDI N G 122 | 123 10. Qual i ty control Q uality control enables m anufac- turers to judge the quality of the products they fabricate and m ore specifically to grade the quality of a w elded joint against an acceptable level of defined defects. The level of acceptable defects is determ ined by: •the types and directions of load (static and dynam ic), •the levels and variations in stress, •possible hazards to personnel, •the technical and financial im pact of the failure of the w eld- ed structure, •the possibility of routine oper- ational inspection and control. 10.1. Approval procedures The procedures are either con- tractual betw een client and sup- plier or self-regulated by the fab- ricator. W elders m ust be certified and qualified in accordance w ith EN ISO 9606-2. W elding proce- dure specification m ust be in accordance w ith EN ISO 15609- 1, EN ISO 15612, EN ISO 15613 and EN ISO 15614-2. Test specim ens m ust be subm it- ted for tensile or bending tests. Bending tests are im portant because they: •detect bonding that is hard to identify in non-destructive testing, •help achieve a good balance of param eters w ith a view to pre- venting these defects. The type of inspection carried out on w elded joints w ill natural- ly depend on the w ork rate of the w eldm ents. In the fabrication shop it is possi- ble to perform the follow ing non-destructive tests (N D T) in addition to visual inspection: •dye penetration tests are valu- able for detecting leaks and em ergent cracks, •w eld shape tests (geom etrical shape), •radiography, used to detect internal defects (porosity, cracks, inclusions) in butt joints, •ultrasonic tests It m ay also be prudent to per- form som e destructive tests on reference specim ens. A n inspection plan m ust be m ade containing: •extent of inspection before w elding •extent of inspection and N D T •N D T m ethods to be used •acceptance criteria (quality level) in accordance w ith EN ISO 10042 10.2. I nspect i ng w el ded j oi nt s 123 EUROPEAN ALUMINIUM ASSOCIATION W eld defects and quality levels are given in EN ISO 10042. G uidance for choice of quality level is given in EN 1090-3. A n international nom enclature of defects has been established and is given in EN ISO 6520-1 w hich lists 6 groups of im perfections: •G roup 100: C racks •G roup 200: C avities and w orm holes •G roup 300: Solid inclusions •G roup 400: Lack of fusion and penetration •G roup 500: D efects of shape •G roup 600: Sundry defects LISTS SO M E C O M M O N W ELD D EFEC TS A N D TH EIR C A U SES TABLE VIII.4 N° Type of D efect Likely C ause Photos of Im perfections 101 C racks Base alloy unsuitable Poor choice of filler m etal Incorrect w elding sequence Excessive clam ping Sudden cooling 104 C rater cracks Pass finished w ith sudden arc cutoff 2012 Irregular w orm holes W ork inadequately degreased W ork and/or filler w ire dirty or w et Insufficient protection by inert gas (low gas flow or leak in the system ) Pass begun on cold com ponent H igh arc voltage W eld cooled too quickly 2014 A ligned w orm holes Incom plete penetration (double pass) Tem perature gradient betw een backing and w ork too abrupt Excessive gap betw een edges of the joint 300 Solid inclusions D irty m etal (oxides, brush hairs) 303 O xide inclusions Poor gas shielding M etal stored in poor conditions C astings Defect 104 Defect 2012 Defect 101 10.3. Wel d def ect s & appr oval cr i t er i a 124 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I I WELDI N G 124 | 125 N° Type of D efect Likely C ause Photos of Im perfections 3041 Tungsten inclusions Electrode diam eter too sm all (TIG ) Poor handling by w elder Excessive current density Poor quality of tungsten electrode 402 Incom plete penetration Inadequate cleaning (presence of oxide) Incorrect bevel preparation on thick w ork (too tight, excessive shoulder) G ap betw een w orkpieces too sm all (or incon-sistent) Low current, especially at the start of the seam W elding speed too fast H igh arc voltage 4011 Lack of fusion H igh arc voltage on edges Low current, especially at the start of the seam W ork cold (difference in thickness betw een m aterials to be w elded) 502 Excessive thickness Poor pow er control (poor U /I m atch) W elding speed too slow Poor edge preparation on thick w ork Insufficient starting current 507 M isalignm ent W ork positioned incorrectly Incorrect w elding sequence 508 A ngle defect Excessive w elding pow er Incorrect w elding sequence 509 C ollapse W ire speed too fast Torch speed too slow Poor torch guidance 602 Splatter (or beads) Incorrect arc control Problem in electrical contact to ground Defect 402 Defect 502 Defect 507 Defect 402 Defect 300 125 EUROPEAN ALUMINIUM ASSOCIATION 11.1. Causes of def or mat i on In m achine w elded structures, deform ation can be caused by: 11.1.1. The direction of the welds It is a w ell know n fact that a bead contracts m ost at the end of the w eld, w hich is w hy the greatest deform ation occurs in the end zones. So far as possible therefore it is essential to orient the w eld tow ards the outside of the w ork- piece so as to release as m uch stress as possible. O therw ise, w ith the w eld facing the m iddle of the com ponent, the contraction stresses are “trapped”and defor- m ation w ill be greater as a result. The end of the w eld m ust be fin- ished to prevent any danger of cracking on the end crater. 11.1.2. The effect of punching This is norm ally due to design error. If w e take the exam ple of a bulkhead inside a tank, it is essential that the bulkhead, w hich is either deep-draw n or spun, has a dow n flanging rest- ing flat against the body of the tank and by w hich the bulkhead is w elded to it. This approach should prevent the problem of punching due to the w eld con- tracting and should m inim ise deform ation (Figure VIII.4). Sim ilarly, w here the body of a tank has to be stiffened, it is essential to place a support plate betw een the stiffener and the skin of the tank to prevent defor- m ation by the effect of punching due to w eld contraction (Figure VIII.5). In the absence of a sup- port plate the tank w ould deform under the effect of sub- sequent dynam ic stresses. 11.2. Sol ut i ons There are a num ber of solutions to the above problem s: 11.2.1. Use of extrusions It is w orthw hile using extrusions in the fabrication of chassis as this can help to: •position assem blies in less stressed areas, •m ake w elds that elim inate deform ation. 11. Desi gn and preventi on of def ormati on U PSTA N D W ELD IN G FIGURE VIII.4 ® U pstand 126 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I I WELDI N G 126 | 127 C hassis side m em bers for instance are usually fabricated from tw o extrusions form ing the tw o flanges of the m em ber and a sheet for the w eb. The assem bly show n in Figure VIII.6 can be autom atically M IG w elded w ith tw o w elding torch- es operating sim ultaneously. Both m ethods of butt joining are possible, i.e. w ith the side m em - ber positioned vertically or hori- zontally. The choice of position w ill be dictated chiefly by the design of the w elding bench. W hen the side m em ber is hori- zontal a support w ill be needed to counteract angular deflection. 11.2.2. End stops These m ust be positioned so as to allow free elongation of the assem blies during w elding. "C om pressing" a w eld, i.e. pre- venting its elongation, greatly exaggerates contraction and hence subsequent deform ation. 11.2.3. Predeforming Som e w eld deform ations can be offset by predeform ing the areas to be w elded in such a w ay that the assem bled com ponents "com e right" after w elding. If the m etal is only predeform ed in the elastic zone by clam ping, the results can be very erratic, and it is therefore advisable to predeform by bending the m etal in the plastic zone. In this w ay, the results w ill be predictable and repeatable. W ELD IN G W ITH SU PPO RT PLATE FIGURE VIII.5 FA BRIC ATIN G A C H A SSIS M EM BER FIGURE VIII.6 H orizontal (flat) Vertical (flat) ® ® ® ® 127 EUROPEAN ALUMINIUM ASSOCIATION EUROPEAN ALUMINIUM ASSOCIATION 128 CHAPTER I X OTHER JOI NI NG TECHNI QUES 1. ADHESIVE BONDING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 1. 1. Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 1. 2. Advantages and disadvantages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 1. 3. Types of adhesives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 1. 4. Application of adhesives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 1. 5. Creep and ageing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 2. SCREWING AND BOLT FASTENING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 3. RIVETING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 4. SNAP-LOCK & CLIPPING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 129 EUROPEAN ALUMINIUM ASSOCIATION 1.1. Def i ni t i on A dhesive bonding is defined as a process of joining parts using a non-m etallic substance (adhe- sive) w hich undergoes a physical or chem ical hardening and by thus leading to a joining of the parts through surface forces (adhesion) and internal forces (cohesion). A dhesion can be physical attrac- tion betw een the adhesive and the m etal surface, real chem ical bonding betw een the adhesive m olecules and the m etal atom s or m echanical interlocking betw een the adhesive and the surface roughness of the m etal. C ohesion is the inner strength of the adhesive itself as a result of physical and/or chem ical forces betw een the com ponents of the adhesive. 1. Adhesi ve bondi ng Physi cal at t ract i on f orces bet w een adhesi ve and met al surf ace Chemi cal bondi ng bet w een adhesi ve mol ecul es and met al at oms Mechani cal i nt erl ocki ng bet w een adhesi ve and surf ace roughness of t he part s t o be j oi ned Physi cal and/or chemi cal i nt eract i on bet w een t he adhesi ve mol ecul es PRINCIPLE OF ADHESIVE BONDING FIGURE IX.1 ADHESION COHESION Source: Talat lectures 130 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER I X OTHER JOI N I N G TECHN I QU ES 130 | 131 1.2. ADVANTAGES AND DI SADVANTAGES Advantages 1. Load distributed uniformly at right angle to loading direction 2. Microstructure unaffected 3. Distortion-free joining 4. Different materials can be joined 5. Very thin parts can be joined 6. Weight saving 7. Heat-sensitive materials can be joined 8. Metals with different electrochemical potentials can be joined (insulating effect of adhesive) 9. High strength joining in combination with other methods (screwing, welding…) 10. High fatigue strength and good vibration damping Disadvantages 1. Influence of time on process properties 2. Pre-treatment of joined surfaces necessary 3. Limited form stability 4. Process parameters must be held in narrow ranges 5. Change of the properties in time (ageing of the adhesive) 6. Complicated control of process 7. Low peeling strength 8. Low adhesive layer strength requires large joining areas 9. Limited repair possibilities 10. Difficult strength calculation Source: Talat lectures 1.3. Types of adhesi ves Adhesives can be divided into 3 sub- groups depending on their form ing reaction and polym er structure: •Polym erisation: A n exotherm ic process in w hich m onom ers link together to form m acrom olecules (polym ers). Therm oplastics like m ethylacrylates, polyvinyl chlo- rides, polyvinyl acetates and rub- ber polym ers belong to this group •Polycondensation: W ater is pro- duced as a result of the chem ical reaction. Therm oplastics like polyam ides and polysulfones as w ell as durom ers like phenol form aldehyde resins, urea resins, m elam ine resins and polym ides, are all produced by polycondensation. •Polyaddition: D uring this process the hydrogen atom s are rearranged. Very com m on adhe- sives for m etal bonding like epoxy resins and polyurethanes are produced by polyaddition. C om bination of adhesive bonding and m echanical joining (e.g. rivet- ing or bolting) can elim inate som e of the above-listed disadvantages. 131 EUROPEAN ALUMINIUM ASSOCIATION 1.4. Appl i cat i on of adhesi ves A s adhesive bonding is w orking by surface forces, prerequisites for a w ell functioning adhesive joint are a) the choice of an appropriate adhesive for the m aterials to be com bined b) the existence of a suitable m aterial surface A suitable surface m eans, that the surface area m ust be large enough to transfer the applied forces and that it is capable to ensure a proper bonding. This can be achieved through a suitable pre-treatm ent. A ny residues of dirt like m oisture, oils, dust etc. m ust be rem oved prior to application of the adhe- sive. This can be done by chem - ical m eans w ith the use of detergents, degreasers or etch- ing agents or m echanically by grinding. In any case the surface m ust be absolutely clean before gluing. It m ight be favourable to use a prim er for better w etting of the m etal surface by the adhesive as w ell. The joint construction should be related to the adhesion process and its requirem ents for large bonding areas. Peeling and cleaving forces on adhesive joints m ust be avoided and bending forces should be reduced to a m inim um . The adhesive can be applied m anually (e.g. w ith the use of cartridges) or for larger areas w ith autom ated m achines. The bonding should take place in a dry and w ell ventilated and dust-free w orkshop. The w ork m ust be done in strict com pliance w ith the m anufactur- er´s rules. The production param - eterssuch as resin/hardenerratio, duration and pressure com ponent fit up during adhesive curing,curing tem perature, etc. m ust be con- trolled properly. 1.5. Cr eep and agei ng The durability of adhesive joints depends on factors such as prop- er pre-treatm ent, chem ical com - position of the adhesive and service conditions like stresses, tem perature, hum idity and expo- sure to ultraviolet radiation (poly- m ers are sensitive to this kind of radiation and tend to lose their m echanical properties). The ageing of bonded joints can be caused by creep under stress (creep can be defined as tim e- dependent increase in the length of visco-elastic sub- stances subject to a constant tensile load). A dhesive joints should therefore be inspected regularly to pre- vent dam ages and to enable repair prior to a possible failure. Prot ot ype f l oor sect i on made of bonded sheet s and ext ruded st i f f eners Patented by A lcan 132 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER I X OTHER JOI N I N G TECHN I QU ES 132 | 133 Bolting creates a joint w hich can be opened and closed as m any tim es as necessary. It is besides w elding the m ost conventional m ethod for joining m etals. In contradiction to w elding, differ- ent m etals can be joined. In com m ercial vehicles this is m ost likely the connection betw een steel and alum inium (e.g. the connection betw een chassis and tank or tipper body). Special precautions should be taken to avoid galvanic corrosion, please refer to C hapter XI. The choice of the fastening geom etry w ill depend on the result of the calculation of the applied stresses. In the com bina- tion of steel screw s w ith alum ini- um plates, the risk of galvanic corrosion m ust be considered: insulating gaskets should be placed around the contact area betw een both m etals. 2. Screwi ng and bol t f asteni ng Riveting is today a w idespread joining m ethod in different sec- tors of industry, including com - m ercial vehicle construction. A s it is a very safe and easy-to- apply technique, riveting has becom e a very com m on m ethod for joining assem blies e.g. in the construction of the bodies of refrigerated trailers. M achine riveting has a lot of advantages: •H igh-speed: M achine riveting allow s fast operations w ith the use of pneum atic or hydraulic tools •Ease of control: the clam ping force is alw ays guaranteed by the system as it is less than the force needed to snap the rivet •O ptical appearance: M achine riveting can be com bined w ith a plastic capping of the rivet •It does not require skilled operators •M ixed joints are possible: dif- ferent m etals, plastics, sandw ich or honeycom b panels Rivets can be divided into 2 m ain subcategories: self pierc- ing rivets and conventional riv- ets w hich require holes that m ust be drilled prior to riveting. C onventional can be sorted into tw o fam ilies: •Lockbolts w hich visually look like they create the sam e type of connection as a conventional bolt, but unlike conventional nuts and bolts; they w ill not w ork loose, even during extrem e vibration. They can only be used w hen both sides of the joint are accessible. Lockbolts consist of a pin w hich is inserted in the hole and a collar w hich is placed on the pin from the opposite end. The tool is placed over the fastener pintail and activated, the pin head pulls against the m aterial, the tool anvil then push’s the collar against the joint, at this stage the initial clam p is generated. The tool then sw ages the collar into the pin. The pintail then breaks and the installation is com plete (Figure IX.2). 3. Ri veti ng 133 EUROPEAN ALUMINIUM ASSOCIATION Lockbolt strength characteristics Clamp force or pre-load: dur- ing the installation process, as the tool engages and pulls on the pintail, the joint is pulled together before the conical shaped cavity of the nose assem bly is forced dow n the collar, progressively locking (sw aging) it into the grooves of the harder pin. The pin and sw aged collar together form the installed fastener. The squeezing action reduces the diam eter of the collar, increasing its length, w hich in turn stretches the pin, generat- ing a clam p force over the joint. Shear strength of lockbolts varies according to the m ateri- al strength and m inim al diam - eter of the fastener. By increas- ing the diam eter or the grade of m aterial, the shear strength of the fastener can be increased. The tensile strength of lock- bolts is dependent on the shear resistance of the collar m aterial and the num ber of grooves it fills. •Blind rivets, w hich are used w hen only one side is accessible. Blind rivets are characterised by breaking off of the rivet stem after fastening the connection by LOCKBOLTS FIGURE IX.2 BLIND RIVET FIGURE IX.3 SELF-PIERCING RIVET FIGURE IX.4 deform ation of the rivet (there- fore they are often called “breakstem rivets”). (Figure IX.3) •Self piercing rivets do not require previous drilling. The rivet part of the bolt is pierced through the m etal sheet. The further closing m otion of the tool, together w ith the specially shaped counter die causes the rivet head to be form ed in such a w ay that the pierced sheet is covered over in the joining region. (Figure IX-4). 134 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER I X OTHER JOI N I N G TECHN I QU ES 134 | 135 The Snap-Lock is a design w hich uses serrated com ponents m ak- ing assem bly easy and quick. The snap-lock design allow s sid- ing to be notched and locked into place w ithout face nailing. Stresses are distributed over the entire length of the profile and not m erely concentrated on the m echanical fixing point (rigidity). 4. Snap-l ock & cl i ppi ng CLIPPING PRINCIPLE FIGURE IX.5 Reef er f l oor assembl ed by bondi ng (Schmi t z) 135 EUROPEAN ALUMINIUM ASSOCIATION 136 CHAPTER X DECORATI ON AND FI NI SHI NG 1. FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 2. POSSIBILITIES WITH ALUMINIUM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 3. MECHANICAL FINISHING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 3. 1. Brushing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 3. 2. Polishing /Buffing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139 4. CHEMICAL DECORATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 4. 1. Anodizing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 4. 2. Painting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 137 EUROPEAN ALUMINIUM ASSOCIATION There are several m ethods for decoration and finishing of an alum inium surface. A lthough all of the m ethods used for other m aterials are applicable, special attention has to be paid to alu- m inium ´s characteristic proper- ties. In each case, especially the softness of the surface and the existence of the oxide layer have to be considered. There are 2 m ain m ethods of decoration and finishing: •M echanical finishing - Brushing - Polishing (or “buffing”) •C hem ical Finishing - A nodising - Painting Today, painting is the m ost com - m on w ay to decorate trucks and trailers. A lthough alum inium can be used w ithout any surface protection and keeps its natural beauty throughout a w hole trailer life, it is m ost likely to use different sur- face treatm ent m ethods to opti- m ise the attractiveness and opti- cal appearance of a trailer, to pro- tect it from severe atm ospheric conditions and to give space for com pany logos or advertise- m ents. 1. Foreword 2. Possi bi l i ti es wi th al umi ni um Al umi ni um t anker (Trai l or) 138 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER X DECORATI ON A N D FI N I SHI N G 138 | 139 3.1. Br ushi ng Brushing is a rather seldom ly used m ethod for the decoration of trucks and trailers. It can m ostly be seen on tankers for the transport of fluid goods. Like polishing, brushing is based on abrasion effects betw een the brush surface and the alum ini- um surface. D ue to the brush being the harder part, alum ini- um is rem oved from the surface by an abrasive effect. Brushing is done w ith rotary brushing tools or m achines. N orm ally no additional brushing com pounds or chem icals w ill be used. Like for every surface treatm ent of alum inium , the part to be brushed has to be cleaned and degreased properly before applying the brushing process. The cleaning is done to rem ove any dust, dirt, oil, em ulsion or other residues from the rolling process prior to brush- ing and to prevent particles from being squeezed into the surface during brushing. To secure a uni- form surface appearance, it is of great advantage to use an auto- m atic process w ith several brushes in one single station, w hich are sim ultaneously controlled. 3.2. Pol i shi ng / Buf f i ng Polishing or buffing is a quite com m on m ethod in the N orth A m erican m arket to provide a decorative surface finish. 3 m ain m ethods can be applied: •U se of m irror-finished alum ini- um sheets and plates fabricated in the rolling m ill •Polishing / buffing of m ill finish sheets to the desired surface appearance •M anual polishing The use of m irror-finished plates or the use of already buffed or polished sheets has the advan- tage, that the w ork on site is reduced to the m anual polishing of w eld seam s or places w hich have been dam aged during fab- rication. G reat care m ust be taken w hen handling or w orking w ith these sheets, as every little trace of a m echanical defect caused by fabrication m ust be m anually polished. M irror finished plates are fabri- cated in the rolling m ill by the use of a special rolling routine w ith w ork rolls w hich have near- ly no surface roughness. This m akes it a very dem anding process and great care m ust be taken to secure a reliable and constant quality of the sheets. Buffing or polishing of large plates is done on autom atic lines, w here the surface is polished w ith rotary polishers across the w hole w idth of the sheet at the sam e tim e. The rotary polishers have special pads on their sur- face, w hich polish the alum inium surface under the help of polish- ing com pounds. The polishing com pounds w orks as a slight abrasive and rem oves the top layer of the alum inium surface in the range of the surface rough- ness produced by the rolling m ill. A s the result of polishing is very m uch depending on the type of alloy and tem per, the surface hardness, the type of polishing paste and the m achine setting (like rotational speed, pressure and type of pad), this is a m ethod of “trial and error”to find the right setting per specification. 3. Mechani cal f i ni shi ng 139 EUROPEAN ALUMINIUM ASSOCIATION In any case, before polishing, the alum inium plates should be degreased and cleaned to rem ove any kind of dust and dirt to prevent abrasive particles from being ground into the alum inium surface. The sam e rules apply for m anual polishing. This process is difficult to apply and a large and exten- sive experience is necessary to reach a satisfactory and repro- ducible result. A fter rem oval of surface dirt or oil, the m anual process starts w ith a rotary pol- isher and the use of quick- cut- ting abrasive paste. The pad should be a w ool com pounding type. Speed of the polisher m ust be lim ited to prevent burning of the surface. The polisher should be m oved back and forth, up and dow n to ensure a uniform abra- sion of the surface. A s the pad w ill suddenly turn black (caused by the polishing residue), great care m ust be taken to regularly clean or change the pad. A fter the rough first polish, the type of paste should be changed to one w ith low er abrasion. Before applying the final polishing step, it is useful to clean the surface again to rem ove the black residue, w hich m ight be trapped into the surface. The final result of m anual polishing should be a m irror-like, uniform , sw irl-m ark, black speck- and bright sparkle- free surface. To keep the m irror-like surface throughout a long period, it m akes sense to apply a clear coat system , as exposure to norm al atm osphere w ould lead to a bleaching of the polished surface. Al umi ni um t i pper (Benal u) Al umi ni um t ank (LAG) 140 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER X DECORATI ON A N D FI N I SHI N G 140 | 141 4.1. Anodi zi ng Anodizing is an electrochem ical pro- cess to reinforce the natural oxide film on the alum inium surface. A nodising is done in a sulphuric solution at a certain electric cur- rent. The natural oxide film is thereby new ly built and the process can be controlled to reach 4. Chemi cal decorati on STRU C TU RE O F TH E A N O D ISED LAYER FIGURE X.1 ® ® N otch Sealed cells A lum inium Pore C ell w all Barrier layer (base of the cell) ® ® ® ® ® certain thicknesses of the oxide layer (in the range of 1000 tim es of the natural oxide film ). A nodising not only produces m ost frequently a silver- m att sur- face, but at the sam e tim e enables increasing hardness, cor- rosion resistance and resistance to abrasion. The process is applied discontinuously on com ponents like castings, extrusions and plates or continuously on coils. The structure of the anodic film is determ ined by the process param eters (type of bath, applied current etc.) and consists of hexagonal cells. The center of the cells includes a m icro-pore w ith a diam eter of m icrom eters. These pores have to be sealed to close them and to guarantee an excel- lent corrosion resistance. This is done in boiling w ater under the use of sealants. (Figure X.1) 4.2. Pai nt i ng 4.2.1. Introduction Painting is the m ost usual w ay of decoration for com m ercial vehi- cles. D ue to the natural oxide film on the alum inium surface, it is of vital im portance for a w ell adherent and durable organic coating to apply an efficient sur- face preparation. It is therefore not sufficient to clean the bare alum inium surface and to degrease it prior to paint application. It is essential to rem ove also the natural oxide layer, because it disturbs adhe- sion of the paint system . This can be done in 2 w ays: Chemical pre-treatment by etching (after degreasing or by a combine degreasing/etching process) D egreasing of alum inium sur- faces can be done w ith fluid degreasing solvents, supplied e.g. by paint producers. The objective of cleaning and degreasing are: • to rem ove any kind of fatty or oily residues, or traces of dirt and dust from the surface • to prevent electrostatic charging. 141 EUROPEAN ALUMINIUM ASSOCIATION To apply a degreasing solvent properly, it is necessary to w ipe the surface w ith a fresh m ois- tened cloth and then clean it w ith a new , fresh and dry cloth. A lum inium has am photeric prop- erties, w hich m eans that it can be dissolved either in an acidic or alkaline environm ent. Etching of com m ercial vehicles is norm ally done by applying the etching agent by spraying. A lkaline etch- ing agents are based on caustic soda, silicates, phosphates, car- bonates and sodium hydroxide. The concentration of sodium hydroxide and the tem perature of the etching agent have a large influence on the speed and rate of the etching process. Etching can also be done on the base of acidic solutions w ith phosphoric acid or nitric acid. Etching leaves a rough and very m oisture-sensi- tive surface behind. It is therefore essential to rinse carefully w ith fresh w ater after etching (about 20 m inutes). Mechanical treatment sby grinding or blasting G rinding is to be done on a clean and degreased surface to prevent oil being trapped into the alum ini- um , w hich could lead to adhesion problem s of the paint. The grain- ing of the grinding disk should have a grain size of 120-180. Blasting allow s a m ore uniform treatm ent of the vehicle and reaches areas w hich cannot be reached by a m anual grinding m achine. It is essential to use iron-free blasting abrasives like non-recycled corundum , as iron can lead to corrosion problem s 1 . The rate of abrasion during blast- ing is very low and w ell below 0.1 m m and therefore in the sam e range as etching. A fter grinding (w hich is also used to flatten the w elding seam s and to plane out scratches) or blast- ing it is necessary to rem ove traces of the abrasives by com - pressed air and then to clean the surface again. 1. The incrustation of iron particles on the alum inium surface is a source of gal- vanic corrosion that w ill lead, in the presence of m oisture, to superficial m icro-pitting. Cl eani ng bef ore pai nt i ng (LAG) 142 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER X DECORATI ON A N D FI N I SHI N G 142 | 143 4.2.2. Application of the primer The prim er should be applied directly after the pre-treatm ent of the surface to prevent the rebuild- ing of the oxide film or to prevent any dust being attracted by the vehicle during longer periods of w aiting tim e. Prim ers (or “w ash prim ers”) are used as adhesive agents to m aintain the necessary bonding forces betw een the sub- strate (alum inium surface) and the paint system . They are also w ork- ing as corrosion inhibitors, as they prevent w ater vapour diffusion through the paint system from getting in contact w ith the alu- m inium surface. Prim ers m ade of epoxy- resins are a w ell suited m aterial for pre-treating alum ini- um , but need a thoroughly treat- ed bare m etal surface. The prim er is norm ally applied by spray gun and the thickness of the w ash prim er or reaction prim er layer is about 10 µm . 4.2.3. Final coating The application of the final coating system can be done in different w ays, but is anyhow not specific for alum inium . In any case, it is of vital im portance to use paint system s w ith coordinated properties. The technical rules of the paint suppliers have to be strictly obeyed. The final coating system can be sep- arated into 2- or 3-layer system s w ith or w ithout the use of fillers and basecoats. Fillers are needed to flat- ten unevenness and/or to increase thickness of the coating system . For preparation of the surface, the prim er layer has to be ground w ith a sm ooth grinding disk (roughness 300-400). Fillers have also to be ground before application of the topcoat system . The paint is norm ally applied w ith spray guns. Drying tim es and tem - peratures have to be controlled. It m ight be necessary to apply an interm ediate fine grinding of the single paint layers. A typical painting procedure of a silo tank trailer could be 2 : •Etching / degreasing inside and outside by spraying w ith an inhibit- ed etching agent based on phos- phoric acid •Rinsing w ith fresh w ater for about 20 m inutes •Final assem bly of the vehicle •G rinding of the tank surface w ith a m anual grinding m achine to rem ove sm all surface dam ages •Cleaning and degreasing w ith degreasers or silicone rem overs •Application of the w ash prim er onto the outer tank surface. Layer thickness 8-10 µm . •Drying of the tank at room tem - perature (20°C) or at elevated tem - peratures up to 80°C •Rem oval of unevenness w ith a filler; grinding of the filler layer •Rem oval of dirt and dust by w iping w ith a m oisturized cloth •A pplication of the 1st paint layer (basecoat or w et-in-w et filler) in 2 steps w ith a com bined layer thickness of 60-70 µm . Special attention should be paid to the area of stone chipping. •A pplication of the topcoat (clear-coat) in the desired colour after m ax. 2 hrs. Final coating thickness 50 –60 µm . •D rying of the top layer Extrusion profile system s used e.g. in tipping trailers can be painted in 2 w ays: either the trailer can be painted as a w hole or the profiles can be painted individually and then being assem bled. The gener- al rules for decoration m entioned above are also valid for these types of constructions. In any case it is essential for a suf- ficient and long lasting paint dec- oration to apply a w ell conduct- ed preparation of the surface as m entioned before. Problem s w ith the paint decoration often are not related to the paint or the alum inium itself, but m ore w ith an insufficient pre-treatm ent. 2. Koew ius, G ross, Angehrn Aluminium- Konstruktionen des Nutzfahrzeugbaus, A lum inium Verlag, D üsseldorf, 1990. 143 EUROPEAN ALUMINIUM ASSOCIATION 144 1. DEFINITION OF CORROSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 2. CORROSION OF ALUMINIUM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 2. 1. The natural oxide layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 2. 2. Types of aluminium corrosion in commercial vehicles . . . . . . . . . . . . . . . . . . . . 147 2. 3. Further references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151 CHAPTER XI CORROSI ON RESI STANCE 145 EUROPEAN ALUMINIUM ASSOCIATION 1. Def i ni ti on of corrosi on C orrosion is a electrochem ical interaction betw een a m etal and its environm ent w hich results in changes in the properties of the m etal and w hich m ay often lead to im pairm ent of the function of the m etal, the environm ent, or the technical system of w hich these form a part (definition as per EN ISO 8044). C orrosion can occur locally (“pit- ting”), or it can extend across a w ide area to produce general deterioration. 2. Corrosi on of al umi ni um 2.1. The nat ur al oxi de l ayer A clean alum inium surface is very reactive and w ill react sponta- neously w ith air or w ater to form alum inium oxide. This oxide builds a natural protective layer on each alum inium surface w ith a thickness of around 1 –10 nm . The oxide layer is chem ically very stable, has a good adhesion to the m etal surface, repairs itself and protects the alum inium from further corrosion. (Figure XI.1) The oxide layer can be destroyed in strong acidic or alkaline envi- ronm ents or w here aggressive ions are present. A ggressive ions can destroy the layer locally and lead to local corrosion attack (“pitting”). A typical case for this reaction is the contact betw een alum inium and chloride ions, w hich are present in seaw ater or road salts. Som e alloying elem ents m ight increase the corrosion resistance of the oxide layer, w hile others can w eaken it. Vehicle m anufacturers or fleet operators should contact the alu- m inium supplier in any case of critical w orking conditions like elevated tem peratures or aggres- sive loads. Aluminium substrate Natural oxide layer (Al 2 O 3 ) FIGURE XI.1 146 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER X I CORROSI ON 146 | 147 A lthough highly resistant to cor- rosion through its natural oxide film , the follow ing types of corro- sion can occur in com m ercial vehicle construction or operation: •G alvanic corrosion •C revice corrosion •Pitting corrosion •Filiform corrosion 2.2.1. Galvanic corrosion G alvanic or bim etallic corrosion can occur w hen tw o different m etals (or electroconductive non-m etallic m aterials) com e into direct or indirect contact w ith each other in the presence of an electrolyte. The reason for this type of corrosion is the dif- ference in the electrochem ical potential of the tw o m etals. A lum inium is a very electronega- tive m etal and therefore special attention has to be paid w hen alum inium is used in com bina- tion w ith other m etals under the presence of an electrolyte (such as w ater). In an electrochem ical reaction, the alum inium is w ork- ing as an anode and is dissolving, w hile the other m etal retains its integrity. In this case, the alum inium ions react w ith the oxygen of the w ater to alum ina (A l 2 O 3 ), w hich builds a w hite layer on the alu- m inium surface. 2.2. Types of al umi ni um cor r osi on i n commer ci al vehi cl es 147 EUROPEAN ALUMINIUM ASSOCIATION There are 3 m ain prerequisites for galvanic corrosion: •2 different m etals w ith differ- ent electrochem ical potential •presence of an electrolyte •direct or indirect contact betw een the 2 m etals The electrolyte enables the flow of electrons betw een the 2 m et- als. This can happen if the m etals are w etted by the electrolyte (e.g. w ater containing salt) or em erged in the electrolyte. In com m ercial vehicles, this type of corrosion can occur w here steel and alum inium parts are bolted, riveted or screw ed together and w here rainw ater or road splash w ater can com e in contact w ith the m etal parts. (Figure XI.2) To avoid direct contact betw een the 2 m etals and to prevent entrapm ent of w ater, it is neces- sary to w ork w ith insulating m aterial (such as neoprene or other elastom ers) betw een the m etals and to use sealing com - pounds to close constructive gaps. (Figure XI.3) PRINCIPLE OF A GALVANIC CELL BUILT WITH ALUMINIUM AS ANODE FIGURE XI.2 Electron Flow Electrolyte Cathode (e.g. copper) Anode (Aluminium) 2Al 2Al 3+ + 6e - 6H + + 6e - 3H 2 ® ® ® A lum inium G asket (PVC , elastom er) O ther m etal (Steel…) Bolt ® ® ® Sleeve and insulating w ashers PREVEN TIO N O F G A LVA N IC C O RRO SIO N FIGURE XI.3 e - 148 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER X I CORROSI ON 148 | 149 2.2.2. Crevice corrosion C revice corrosion occurs in sm all constructive recesses. In a crevice there w ill be the possibility for accum ulation of m oisture because of capillary forces and deposits of aggressive m edia. Therefore, especially in the road w ater splash zone, constructive gaps should alw ays be closed as far as possible, as the penetrat- ing w ater m ight contain aggres- sive ions (e.g. from road salts). The corrosion rate of crevice cor- rosion is norm ally very low due to the corrosion product –alum ina –being very stable and building a sealing of the crevice. (Figure XI.4) 2.2.3. Pitting corrosion Pitting corrosion is the m ost com - m on corrosion form seen on alu- m inium , characterised by the developm ent of sm all local pits in the surface. The diam eter and the depth of the pits varies and depends on different param eters related to the alum inium itself (type of alloy, rate of cold w orking, heat treatm ents) or to its environ- m ent (presence of aggressive ions). Pitting corrosion occurs on sites w here the natural oxide film is dam aged or im perfect due to diverse reasons like m anufactur- ® ® ® Sealing of access to crevice Possible crevice Sealing of the crevice itself Tight fastening of bolts and rivets necessary CREVICES AND HOW TO PREVENT THEM FIGURE XI.4 ing related circum stances (areas w hich have been ground, w eld discontinuities etc.). The pits are form ed w ith a rapid increase in depth after initiation follow ed by a slow er grow th. This is due to the corrosion product - alum ina – that is not soluble in w ater and therefore adheres to the surface of the m etal inside the pits. The alum ina then obstructs the direct contact betw een the alum inium surface and the corrosive m edi- um and by this slow s dow n the corrosion speed. (Figure XI.5) This slow dow n in the rate of pit- ting corrosion explains the fact that alum inium equipm ent can be used for decades in certain envi- ronm ents (country air, sea air, sea w ater) w ithout any protection. In other w ords, pitting corrosion is quite norm al and does not im pact the durability of vehicles. PITTING CORROSION FIGURE XI.5 ® A l u m i n a A l u m i n a ® ® ® ® ® C I - C I - C I - C orrosion A ttack 149 EUROPEAN ALUMINIUM ASSOCIATION 2.2.4. Constructive measures to prevent corrosion Som e general rules shall be applied to prevent corrosion (in m ost cases to prevent any kind of w ater trap or areas w here con- densation can occur): •C onstructive gaps should be avoided or, if not possible, should be sealed. (Figure XI.6) •W ater traps should be avoid- ed. A ssem blies should be con- structed w ith the open side dow nw ards. (Figure XI.7) •W eld discontinuities shall, also w ith regard to other issues like stress, fatigue etc., be strictly avoided. (Figure XI.8) •M aterials having different elec- trochem ical potential have to be separated from each other by coatings or insulating m aterials. 2.2.5. Filiform corrosion Filiform corrosion (also know n as under-film corrosion) occurs under paint or enam el layers. It depends m ostly on environm en- tal conditions and the quality of the surface treatm ent prior to painting. The corrosion filam ents U nsuitable solutions Better solutions Run of Run of FIGURE XI.7 ® W atertight seal FIGURE XI.6 W eld discontinuities FIGURE XI.8 ® ® have a w orm -like appearance and are readily visible. Filiform corrosion does not attack the m etal surface, but affects the surface appearance. The m ode of corrosion is quite sim ilar to pitting w ith the front of the attack being supported by m oisture w hich penetrates the surface layer and leads to oxygen concentrated areas and by thus acting as an anode. Filiform corro- sion is m ainly an aesthetic effect, but could lead in certain construc- tion parts to delam inating of the surface layer system . To prevent this type of corrosion it is of vital im portance to follow the instructions of the paint supplier, especially w ith regard to a proper surface treatm ent under the use of a suitable prim er system . 150 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER X I CORROSI ON 150 | 151 2.2.6. 5000 series alloys and elevated temperatures W hen held for long periods at elevated tem peratures (betw een 65°C and 200°C ), alum inium - m agnesium alloys containing m ore than 3% of m agnesium undergo m etallurgical changes that can lead to intergranular corrosion if the tw o conditions below are both satisfied: •Precipitation of a continuous bead of A l 8 M g 5 interm etallic com pounds occurs along the grain boundaries (sensitization). These A l 8 M g 5 precipitations are anodic to the bulk m aterial. •Presence of an aggressive m edium , e.g. a saline solution on the bare surface of the m aterial. This phenom enon has been studied m any tim es w ith a view to gauging the influence of the follow ing param eters for sensitization: •The m agnesium content and the production process largely deter- m ine the kinetics of sensitization of 5000 series m aterial. Proper routes to m inim ize susceptibility are w ell established at suppliers. •M anufacturing processes like form ing and therm al joining (w elding) m ight reduce resistance of final product to sensitization. •The therm al load (i.e. tem per- ature m ultiplied by tim e of expo- sure) is m ore im portant than the tem perature alone. For exam ple, if 65°C is often given as a lim it in catalogues or m anuals, it takes tw o years to sensitize a 5086 alloy at that tem perature, w hile at 100°C , several m onths are necessary. The fastest sensitiza- tions are generally observed betw een 130°C and 200°C . But even if a m aterial is sensi- tized, corrosion w ill only happen in aggressive environm ents, i.e. w hen a corrosive electrolyte gets in contact w ith the m etal surface. Experience has confirm ed this. There are road tankers for heavy fuel oil, w hich have seen 20 years and m ore of service, running 8 to 10 hours a day, w hich is at least 50,000 hours of cum ulative operation at 65-70°C . A s a general guideline, the use of alloys w ith a m axim um of 3% of m agnesium is strongly recom - m ended w here exposure for long periods to tem peratures in excess of about 75°C occurs. W hen the use of 5000 alloys w ith higher M g content is desired, consulta- tion w ith the m aterial producer is recom m ended and their applica- bility m ust be evaluated in detail, taking into account the therm al exposure of the part during its total lifetim e. 2.2.7. Other forms of corrosion O ther form s of corrosion do exist, but the alloys and tem pers m ost currently used in com m ercial vehicles are not prone to these types of corrosion. 2.3. Fur t her r ef er ences •Corrosion of aluminium, C . Vargel, ed. Elsevier •w w w .corrosion-alum inium .com 151 EUROPEAN ALUMINIUM ASSOCIATION EUROPEAN ALUMINIUM ASSOCIATION 152 1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 2. THE NATURE OF STAINS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154 3. THE CHOICE OF DETERGENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 4. APPLICATION OF THE DETERGENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 CHAPTER XI I CLEANING OF ALUMINIUM COMMERCIAL VEHICLES 153 EUROPEAN ALUMINIUM ASSOCIATION Regular cleaning of a com m ercial vehicle is a prerequisite to ensure a long lifetim e. A ny kind of dirt is rem oved, the optical attractive- ness is kept and critical parts like w heels, axles, brakes and hydraulic system s can be better optically controlled. C orrosion is prevented and dam ages due to m echanical friction betw een m oving parts can be avoided. In case of tank trailers, there are often strict legal regulations con- cerning the transport of food- stuff or there are other regula- tions for strict cleaning w hen dif- ferent chem icals are transported w hich m ight interfere w ith the goods transported before. In som e cases, alum inium cannot be used as a construction m ateri- al due to the cleaning instruc- tions, w hich specify the use of strong aciduous or alkaline chem icals In general, cleaning of an alu- m inium vehicle is not different from cleaning any other vehicle. It can be done on autom atic w ashing lines as w ell as m anual- ly w ith the use of high pressure spray guns, brushes and cloths. 1. Introducti on Commerci al vehi cl e cl eani ng st at i on (Int erservi ce Arras) 154 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER X I I CLEA N I N G OF A LU M I N I U M COM M ERCI A L V EHI CLES 154 | 155 Stains on com m ercial vehicles m ay have the follow ing origins: •Road caused: dirt, salts, m ud, w ater splash, tyre w ear •Fuel caused: diesel exhaust, soot •Load caused: cem ent, asphalt, chalk, residues of agricultural products etc. •Environm entally caused: effects of air pollution, dust A ll these elem ents, in connection w ith hum idity, can lead to local corrosion and fading or destruc- tion of the paint layer. In this respect, residues of previ- ously transported goods prior to a new load m ight also be seen as contam ination and require inten- sive cleaning. 2. The nature of stai ns The detergent used for cleaning an alum inium vehicle m ust be com - patible w ith alum inium , m eans it m ust not be too aggressive. In general, a detergent has to: •H ave a strong effect on all kinds of dirt The cleaning of a vehicle should not take place in direct sunlight. Each detergent should be tested on a raw alum inium surface prior to first use. The detergent can be used either in autom atic w ashing lines or can be applied m anually w ith the use of high pressure spray guns, brushes, cloths etc. Its m ain cleaning effects are: •C hem ical Som e elem ents of the detergent dissolve the dirt or m ineral salts w ithout attacking the surface 3. The choi ce of detergent •A llow an efficient rem oval of aggressive dirt •C reate a bright visual appear- ance of the surface •Build up a protective film on top of the paint •Be in com pliance w ith specific regulations •Be biologically degradable •Be harm less to the user D etergents are a com plex m ix- ture of up to 20 ingredients to enable diverse functions at the sam e tim e: degreasing, slight etching, w ashing, conserving etc. 4. Application of the detergent •Physical Stains are rem oved by decreasing the surface tension. Therefore deter- gents contain w etting elem ents •M echanical Stains are rem oved by spraying w ith pressurised detergent or by abrasion w hen using brushes •Tem perature H igher tem peratures, or even w ater steam , increase the clean- ing effect by increasing the speed of the chem ical reaction betw een the detergent and the stain. Spraying should be done from bottom to top of the vehicle to prevent streaking. The residence tim e should be sufficient to dis- solve the stains. The detergent should not dry on the vehicle sur- face and w ashing should be fol- low ed by intensive rinsing w ith de-ionized w ater. 155 EUROPEAN ALUMINIUM ASSOCIATION EUROPEAN ALUMINIUM ASSOCIATION EUROPEAN ALUMINIUM ASSOCIATION 156 1. FOREWORD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158 2. EXECUTION OF REPAIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 3. REPAIR OF ALUMINIUM CHASSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 4. MIG AND TIG WELD REPAIRS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 4. 1. Choice of alloy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 4. 2. Preparations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 4. 3. Welding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161 CHAPTER XI I I REPAIR OF ALUMINIUM COMMERCIAL VEHICLES 157 EUROPEAN ALUMINIUM ASSOCIATION 1. Foreword Repair of com m ercial vehicles should be done w ith the sam e care as new construction. In general, all rules, m aterials and m ethods used for new construc- tion should also be applied for repair causes. Repair is a case-to-case decision, w hether sm all dam aged parts can be repaired w ithout dis- assem bling the structure or w hether dam aged com ponents (plates, extrusions) m ust be cut out and replaced com pletely. In any case, dam ages should never just be “over-w elded”. This m ethod does not reflect a reasonable w ay of repair. A ny parts, w hich have been cut out due to dam ages, m ust alw ays be replaced w ith the sam e type of alloy as originally used. This has to be applied to ensure a safe and constant stress deviation across the vehicle and to prevent a w eakening of the construction. It has to be taken into consider- ation, that especially tankers or silo trailers are regarded as pres- surized vessels under the European Pressure Vessel Regulation 97/23/EU . This requires additional testing m ethods for repairs and supervi- sion by certified supervision bodies (like TÜ V). Repair should therefore be car- ried out by the m anufacturer of the original vehicle or in certi- fied repair w orkshops: qualified w elders, w orking m ethods according to state-of-the-art technologies, suitable w ork organisation, etc. are necessary. Insi de vi ew of a repai red al umi ni um t ank (Fel dbi nder) 158 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER X I I I REPA I R OF A LU M I N I U M COM M ERCI A L V EHI CLES 158 | 159 A sophisticated repair of an alu- m inium com m ercial vehicle should be done according to the follow ing procedures: •Identification of the dam age - H ow m uch m etal has been destructed? - A ny further dam ages w hich could not be seen during first inspection? •C ut out of dam aged com po- nents •Identification of originally used m aterial specification •O rder of replacem ent m aterial according to detected specification •O rder of suitable w elding filler w ire (according to norm s or specific regulations) •Pre-cut of replacem ent part under consideration of the ther- m al shrinking during w elding •Pre-form replacem ent m ateri- al if necessary •Rem oval of original coating in the repair zone •Fixing of the replacem ent part to the vehicle; if necessary addi- tional form ing to the vehicle contour to prevent too m uch stress during w elding •Joining of the replacem ent part to the vehicle structure by suitable w elding m ethods. •Visual control of the w eld quality •If necessary or m andatory (pressure vessels), then non- destructive testing (ultrasonic, x- ray) of the w eld seam •G rinding or flattening of the w eld seam •Repair of the coating •Final control; it m ight be required to let all steps of repair be checked by a supervisory organisation. 2. Executi on of repai r 3. Repai r of al umi ni um chassi s The case of alum inium chassis deserves a particular attention, as a non-professional repair m ay lead to a deterioration of both the static capacity and fatigue strength. To avoid this kind of problem s, please read C hapter VI, section 8, dedicated to fatigue. Beginning w ith fatigue theory, that chapter also illustrates how good practices for perforating and w elding can secure long lifespan to vehicle. Out si de vi ew of a repai red al umi ni um t ank (Fel dbi nder) 159 EUROPEAN ALUMINIUM ASSOCIATION A road vehicle can sustain dam - age and w ill need to be repaired. Repairing a com m ercial vehicle m ade from alum inium alloys is no m ore difficult than repairing a steel vehicle, but should be done according to a strict procedure in a properly equipped w orkshop by skilled operatives under the supervision of an official body and/or classification society if the vehicle's duty calls for this. N o repair w ork should com - m ence w ithout-know ing the type of freight (liquid, pow der etc.) w hich the vehicle has been used to carry and before taking the appropriate safety precau- tions: cleaning, degassing, w ith explosim eter checks, dust rem oval etc. as necessary. 4.1. Choi ce of al l oy The alloy of the sem i-finished products used for the repair w ork m ust be the sam e as (or com patible w ith) the original alloys as indicated in the m anu- facturer's m anual. 4.2. Pr epar at i ons This is the m ost im portant phase as it w ill determ ine the quality and strength of the repair: •for cutting out, preference should be given to the plasm a torch or a carbide cutting w heel rather than a high speed steel (H SS) w heel or abrasive w heels that m ight introduce inclusions into the w eld seam , •very carefully grind the area to be w elded to rem ove all traces of paint and various residues, •carefully degrease w ith suit- able agent 4. MIG and TIG wel d repai rs Wel di ng of si l o body (Fel dbi nder) 160 ALUMINIUM IN COMMERCIAL VEHICULES CHA PTER V I I I WELDI N G 160 | 161 4.3. Wel di ng The rules for repairing are basi- cally as described in C hapter VII for form ing and as described in this chapter for w elding. W hen carrying out repairs it is essential to: •hold the com ponents, e.g. tank, chassis etc., securely in their relative positions. C lam ps should be adjusted to allow expansion how ever, as too m uch restriction could aggravate the adverse effects of contraction. It is also useful to m ark areas of the structure likely to suffer m axi- m um stress, referring to the m anufacturer's design calcula- tions if these are available, •support built-up parts to con- trol clearances, •pay particular attention to the w eld direction. The purpose of this is to lim it deform ation and m inim ize the risk of hot cracking. Volum e contraction in the w eld bead is approxim ately 6 % betw een the fluid state and the solid state at am bient tem pera- ture. It is this phenom enon w hich causes the risk of cracking, •change the path of w elds in order to avoid going back over an original w eld (Figure VIII.7), •perform any necessary tests, e.g. radiography, dye penetration etc., •chose the right w elding process (TIG or M IG ). TIG w eld- ing is preferable for m inor repairs w here access from behind is not possible as it is easier to use and allow s better penetration control than M IG w elding. C om pact TIG w elding m achines w eighing less than 20 kg are now available on the m arket capable of delivering a w elding current of around 160 A . These m achines are easy to carry and are ideal for sm all, localized repairs. For m inor repairs such as a breach in the skin of a tank, the patch m ust be perfectly m atched to the shape of the breach but should be slightly enlarged by ham m ering to com pensate for contraction follow ing w elding. W ithout this precaution the residual stress m ight w ell cause system atic cracking. This phe- nom enon is m ore pronounced the sm aller the patch. W ELD REPA IR FIGURE VIII.4 ® N ew w eld 161 ACKNOWLEDGEM ENTS Mai n wri ters: Jürg Zehnder, Rei nhard Pri tzl aff , Stei nar Lundberg, Bernard Gi l mont. Project team: Asmund Brol i , Roal d Pedersen, Benoî t Lancrenon, Mi chel e Tri bol di , Di etri ch Wi eser, Ral f Bal duck, Kl aus Vi eregge. Sponsori ng compani es: Al can Engi neered Products, Al coa Europe, Al eri s Europe, AMAG, El val , Hydro Al umi ni um, Metra, Novel i s, Sapa The project team i s parti cul arl y gratef ul to Al can Engi neered Products f or havi ng authori zed to use some texts, tabl es and f i gures comi ng f rom the f ol l owi ng publ i cati ons: • Al umi ni um i n Commerci al Vehi cl es, Pechi ney-Rhenal u • Al umi ni um and the Sea, Al can Aerospace, Transportati on and Industry PHOTO AND TABLE CREDI TS Document produced by European A lum inium A ssociation A ISBL A venue de Broqueville, 12 BE - 1150 Brussels - Belgium Telephone: +32 2 775 63 40 Fax: +32 2 775 63 43 w w w .alum inium .org U nder the D irection of Bernard G ilm ont D esigned: M arc H ernu, Plage C oordination: Pierre Jouhaud, PLJ édition-com m unication 1 Benalu Benalu 4 M enci EAA library 6, 8 Airbus Airbus 9 Hydro Alum inium Hydro Alum inium 9 Babcock Babcock 10 Alstom , SNCF Alstom , SNCF 11 M ercedes 11 Hydro Alum inium Hydro Alum inium 12 Alum inium -Verlag Alum inium -Verlag 12 Alusuisse Alcan Engineered Products 12 Trailor Trailor 16 Benalu Benalu 17 Tang Fahrzeugbau G m bH Tang Fahrzeugbau G m bH 19 All Am erican M arine All Am erican M arine 20, 36 Stas Stas, IRTE 21 Alcan, Alcoa, Brabant Alucast Alcan, Alcoa, Bernard G ilm ont 23 Alcan Engineered Products Alcan Engineered Products 24 G alloo Recycling Bernard G ilm ont 25 ATM , PVC Transports Patrick Van Crom brugghe 26 M enci Bernard G ilm ont 26 Alcoa W heel Products Europe Alcoa W heel Products Europe 27 Benalu Benalu 28 Pezzaioli Pezzaioli 30 Alcoa Europe Alcoa Europe 31 Stas Stas 32 Benalu Benalu 33 Leciñena Leciñena 34 M enci M enci 37 Schrader Schrader 40, 43 Alcan Engineered Products Alcan Engineered Products 44, 45, 47 Various alum inium plants EAA library 48 M enci Bernard G ilm ont 48 Alcoa Europe Alcoa Europe 54 Brabant Alucast Bernard G ilm ont 75 Alcoa Europe Alcoa Europe 76, 81 Benalu Benalu 82 Alum inium -Verlag Alum inium -Verlag 86 Schrader Schrader 87 Stas Stas 88 Schm itz Schm itz 89 M enci M enci 90, 105 König Ursula Berndsen 95 SAG Alutech SAG Alutech 97, 98, 99 Benalu Bernard G ilm ont 100 Sapa Sapa 108 Stas Stas 110 SAG Alutech SAG Alutech 112 M enci Bernard G ilm ont 114 Sachsenring Ursula Berndsen 119 Alcan Engineered Products Alcan Engineered Products 120 Sapa Sapa 121 Hydro Alum inium Hydro Alum inium 122 Schm itz Schm itz 128, 132 Alcan Engineered Products Bernard G ilm ont 135 Alcan Engineered Products Alcan Rhenalu Issoire 138 Trailor Trailor 140 LAG LAG 140 Benalu Benalu 142 LAG LAG 152, 155 Interservice, Arras Christian Vargel 156, 158, 159, 162 Feldbinder Feldbinder Page Company or brand Photographer or source Page Company or brand Photographer or source 162