Influence of 1st Step Shape on the Formability of Circular Truncated Cone Stretch Forming in Two-Step Forming

Abstract

The formability of steel sheets must be improved to form complicated car parts. Multistep forming is one way of improving the formability. The shape after preforming could influence the formability in the main step of multistep forming. However, no relationship has been reported between the shape after preforming and the final shape in the case of stretch forming. In this study, circular truncated cones were formed by two-step forming consisting of preforming and main forming, with combinations of various shapes after preforming and final shapes in order to investigate the effect of the shape after preforming on the forming limit in final forming. The results show that the forming limit height in main forming is affected by the preforming shape. In addition, the forming limit height in main forming is determined by the central cross sectional line length of the shape after preforming.