Suppression of Springback for Longitudinally Curved Part by Imparting In-plane Compression Stress in Press Forming

Abstract

Dimensional accuracy defects caused by springback behavior are one of the serious problems in press forming for automobile parts using ultrahigh-strength steel sheets. In particular, in hat-shaped parts curved in the longitudinal direction, camber back, which is a kind of springback behavior, occurs. In this study, in order to suppress camber back, a new press-forming method that can impart in-plane compression stress was investigated using parts with a simple hatshaped section and a W-shaped section simulating automotive parts. As a result, it was found that the amount of camber back decreases on applying compression stress in the longitudinal direction, because the bending moment caused by the difference between stress in the punch bottom area and that in the flange area was reduced. It was also clarified that the sensitivity of the amount of camber back to tensile strength was lowered when this forming method was used. Furthermore, a forming method in which buckling in both ends under a high compression condition can be prevented was developed.