Abstract: The traditional inverse analysis method (TIAM) of sheet metal stamping gives bad estimation of stress distribution mainly due to the loss of history of deformation. Elements near the die entrance radius are subjected to bending and unbending during forming operation. Moreover, stress accumulation can usually be found in die entrance zone. A fast and reliable searching scheme is used to find elements passing by die entrance radius during the deformation process. The followed procedure has been used to modify stress distributions. An efficient stress-strain relation for multi-step loading is introduced to update stress distributions. This constitutive equations can avoid the complexity of incremental finite element method (FEM) based stress/strain updating algorithms, while can consider the effects of die entrance radius on deformation history. Deep drawing of the U-bending test proposed in Numisheet’93 demonstrates that these constitutive equations can significantly enhance the prediction of stress distribution by comparison with incremental FEM based software ABAQUS/Standard.

Key words: Die entrance radius, Inverse analysis method, Sheet metal stamping, Stress improvement