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Over the past several decades, significant gains in automobile fuel efficiency have been achieved through down-sizing, aerodynamic design and drive train improvements. As performance limits are approached in these areas, aluminum is being used to further reduce body weight by up to 40% compared to steel. In anticipation of the continued demand for more fuel efficient automobiles, aluminum sheet component unibody and extrusion and cast component space frame designs have been studied to address joining and structural performance. Joint geometries unique to specific body designs clearly illustrate the need for close linkage of the design and assembly functions. Joining and assembly methods that provide static and dynamic structural integrity, 15 to 20 year durability and that can be integrated into robust manufacturing systems are key to aluminum usage for auto body structure.

The advent of high speed computers permits the use of the finite element method to model complex sheet metal forming processes on a reasonable time scale. The design and development of sheet metal parts in the automotive industry and the need for improved sheet forming processes and reduced part development cost have led to the use of computer simulation in tool/die design of sheet metal pressings. An accurate constitutive description of plastic anisotropic yield loci and work hardening of material behavior in sheet forming is now a reality. The constitutive equation developed at Alcoa for describing anisotropic material behavior is consistent with polycrystalline plasticity, and it is expected to improve the computational accuracy of forming process for polycrystalline metals and alloys.

The need to substantially reduce the weight of automobiles to improve performance or meet CAFE requirements has led to an increased use of lightweight materials such as aluminum. To use aluminum efficiently in auto body structures, component and joint designs and joining methods are likely to differ from those traditionally used in steel bodies. With proper design, aluminum automotive frames can efficiently meet or exceed the performance requirements for stiffness, static strength, fatigue strength and crash performance. This paper presents some joint design concepts for aluminum frames and compares the performance of joining methods such as resistance spot welding (RSW), gas metal arc (GMA) welding, weld bonding, adhesive bonding, riveting and mechanical clinching for both unibody and spaceframe construction. Recommendations for preferred joining methods are also made based on the effect of design details on joint performance and assembly.

Determination of forming limit diagrams (FLDs) by experimental methods requires a significant amount of time and expertise in interpretation of data. Their construction can be especially difficult for aluminum alloys due to slightly negative or near zero strain rate sensitivity characteristics which create sharp strain gradients. For this reason a mathematical model which incorporates microstructural attributes, namely crystallographic texture, with a description of strain hardening behavior was developed by Barlat1 to predict the forming limit strains for a given material. Using Barlat, forming limit diagrams were predicted for various automotive body sheet alloys and verified against experimental data. Excellent correlation was found between the experimental and predicted diagrams. Prediction of limit strains requires approximately one-tenth of the time required for experimental diagrams and eliminates variations associated with experimental determination techniques.

Finite element modeling of sheet forming processes for complex automotive parts using an explicit dynamic code such as LS-DYNA3D is increasingly used for producibility analysis and die development. In modeling sheet metal forming processes, it is very common to represent material behavior by either Von Mises' or Hill's yield criterion using commercial finite element codes. However, these criteria do not provide an accurate representation of aluminum alloys. Recently, a new yield criterion proposed by Barlat has been incorporated into LS-DYNA3D to describe the anisotropic material behavior of aluminum alloys. This paper examines the influence of Von Mises', Hill's (1948) and Barlat's yield criteria on the FEM simulation results for the deep drawing of a square cup and cylindrical cup for aluminum alloys. The sensitivity of predicted results to yield criteria is examined for deformation behavior, strain localization and potential of wrinkling.

Classically, structural component fatigue design is based on testing and empirical models. First a series of average stress-life curves are generated from fatigue tests. Constant life diagrams are then developed accounting for mean stress effect, casting quality, surface finish, volume and other factors. Component design is then based on keeping the effective alternating stress below the diagram limit stress. While this procedure has worked well to design many components, it is based on extensive fatigue testing and empirical stress reduction factors. Thus, material and process improvements and computerization of the design process are difficult to incorporate into this test/empirical based design methodology. Fracture mechanics and damage tolerant design methodologies are used in aerospace for fatigue design. These methods predict well the fatigue life for surface scratches (rogue inspectable flaws) of about 0.25-1.27 mm in size.

Draw bead simulator tests were performed on various tool materials using aluminum alloys 2008-T4 and 6111-T4. The tool materials included hardened cast steel J435/0050A, D2 alloy, cast steel with ion nitride and PVD chromium nitride surface treatments, and cast steel with standard chromium and Wearalloy™ chromium coatings. Friction and galling behavior were monitored over an extended period of testing which allowed differentiation of the tool materials and alloys. Wearalloy™ and CrN tool coatings consistently demonstrated improved ability to prevent material transfer for both aluminum alloys, in spite of friction coefficients which were higher than the uncoated and ion nitrided tools. The ion nitrided surface exhibited the lowest friction coefficients of the surface treatments tested, but showed appreciably more wear. For a given lubricant and dilution ratio, alloy 2008-T4 exhibited an increased tendency for material transfer compared to alloy 6111-T4 for all tool materials tested.

IN WELDBONDING, a joint is produced by (a) spotwelding through an uncured adhesive bondline or (b) flowing adhesive by capillary action into the bond area after spotwelding. Weldbonding can offer higher joint strength, reduced joint weight, improved fatigue life and, in some aircraft-oriented investigations, showed reduced manufacturing costs(1,2). Although weldbonding has had repeated use in the Russian aircraft industry(3,4), it has not been widely employed in American manufacturing to date. The most intensive efforts to develop the process have resulted from contracts sponsored by the U. S. Air Force(4). The only aluminum alloys used in these investigations were the high strength aircraft alloys and the emphasis was to develop the highest strength weldbond joints with economics a secondary consideration. These studies usually included the use of special surface treatments on the aluminum, special adhesives, and carefully controlled curing conditions.

Repair of aluminum heat exchangers is relatively easy when the appropriate techniques are used. Three flux and three fluxless repair procedures are discussed in detail. Two tables list the recommended in-plant and field repair techniques for various heat-exchangers based on application and method of manufacture. Easy field repair of Freon-type soldered heat-exchangers using an intermediate temperature solder and noncorrosive flux is described.

ALUMINUM engines promise a gain in the power/weight ratio and possibilities of production economies. Aluminum has already proved its value for some parts; only the adaptation of design for high production methods delays full realization of the metal's potentials. This paper describes the problems encountered in adapting the V-type engine to fabrication methods using aluminum alloy parts. Applications of aluminum in crankcase and cylinder block, cylinder liners and heads, intake manifold, pistons, and bearings are also discussed.

This paper explains the reflectance characteristics of anodized aluminum and describes the finishing treatments which produce the desired low glow appearance required by The Proposed Federal Motor Vehicles Safety Standards. Certain of these low gloss producing treatments are easily incorporated into existing finishing lines and in many cases are more economical to apply than the present bright specular finish. The materials and processes used to satisfy this proposed standard are discussed fully.

This paper describes work conducted to understand the process mechanisms which cause electrode deterioration and inconsistent weld quality when welding aluminum auto body sheet. Surface objectives were found to be different at the outer and inner surfaces of the sheet. Various surface treatments were investigated and compared to arrive at an optimum treatment. Best overall results were obtained with a conversion coated inner surface and an arc-cleaned outer surface applied immediately before welding. Results were verified with an extended life test which produced more than 7,000 welds without a dud.

Two new aluminum alloys, 6009 and 6010, for auto body sheet are described and technical data are presented. The 6XXX-series alloys are ideal for body sheet in several respects, providing excellent corrosion resistance, improved spot weldability, and freedom from Luder's lines, together with favorable response to aging in many paint bake cycles. The result is a combination of excellent formability in the T4 temper and, after aging, higher strength than achievable in any other aluminum alloy system having other characteristics desired in body sheet. The latter translates to excellent dent resistance, superior even to that of steel. Furthermore, scrap loop problems are eliminated; compatible alloys 6009 and 6010 may be used together to obtain optimum strength and formability without any penalties in scrap utilization. Forming, aging, finishing, and joining data for these alloys are presented.

The use of polished aluminum fuselage skins has been a standard on U.S. commercial jet transport aircraft for decades. Increasingly stringent environmental regulations for paint stripping combined with fuel and maintenance savings allows consideration of flying polished non-painted aircraft. Boeing, McDonnell Douglas and Embraer currently manufacture commercial aircraft with polished alclad aluminum fuselages. Commercial airlines such as American Airlines, USAir, Eastern, Northwest and ASA fly non-painted fleets. These customers require the aircraft to be delivered with a polished appearance incorporating minimum fleet graphics. The manufacturing of polished aircraft requires unique production and handling procedures to fabricate all exterior panels with identical color match and reflectivity.