Analysis on the Cause of Twisting Defects Occurred in Sheet Panel Formed Through Local Embossing and Edge Bending

Recently, significantly thinner sheet steels are tested and applied in digital display equipment than previous ones, therefore many cases of shape defects such as twisting, oil canning and curvatures in stamped panels are reported from stamping factories. In order to study the cause of twisting defects of stamped panel, simulative tests by 800×500 and 240×180 size blank and numerical simulation were done and analyzed the effects of forming conditions and material characteristics on twisting defects. It was found that the residual stress in stamped panel is the source of twisting and it increases as the difference between residual stress in panel center (positive stress component due to emboss forming) and marginal regions (negative stress value) increases. Both the residual stress difference in blank and twisting deformation increased in dense emboss formed cases than sparse embossing cases. Twisting deformation was increased if thinner blank, more curved blank and higher yield stress sheet applied cases.