FORMING OF TAILOR-WELDED BLANKS

Beginning in 1992, tailor-welded blanks (TWBs) were used in the United States automotive industry to consolidate parts, reduce tolerances, s ave weight, and increase stiffness. This business is expanding rapidly ; more than $500 million of annual TWB sales are expected by 1997. Wel ds in steel are generally stronger than the base material, such that w eld failure by preferential localization is not a critical issue. Howe ver, the forming characteristics of TWBs must be understood in order t o design and produce high-quality parts with reasonable production and tooling costs. Three formability issues were addressed in this study: the intrinsic ductility and relative formability of three weld types (CO2 and Nd:YAG laser welds and mash-seam welds with and without mecha nical postweld processing); the value and correspondence of mechanical tests to each other and to press performance; and the prediction of t he forming behavior using the finite element method (FEM). Two failure modes for TWBs were identified. While the local ductility of welds ca n differ greatly, little difference in press formability was measured among the weld types. More important than weld ductility are the chang ed deformation patterns which depend on the differential strength but depend little on local weld properties. Finite element method (FEM) si mulations of dome tests and scale fender-forming operations show good agreement with measurements, as long as boundary conditions are known accurately. The importance of weld-line displacement is discussed and several simulations are compared with experiments.