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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.

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.

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.

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.

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.

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.