Effect of Preforming Shape on Formability of Two-step Cylindrical Stretch Forming

Abstract

The formability of steel sheets must be improved to form complex car parts. Multistep forming is one way of improving this formability. However, for stretch forming, the relationship between preforming shape and formability in the main forming or how to design the preforming shape has not yet been reported. In this study, we showed that the forming height limit in the main forming was determined by the central cross-sectional line length of the shape after preforming in the case of forming a circular truncated cone shape in two steps as indicated in a previous report. Moreover, we also investigated the preformed shape other than the truncated cone shape studied, and the optimization of the preformed shape to improve the formability by FEM analysis and verified it in a pressing trial.