Effects of Shape of Formed Parts and Forming Method on Stretch Flangeability in Flange-up Forming for Joint Flange

Abstract

Numerical analyses of press-forming were carried out to analyze the mutual effects of forming methods and the shape of formed parts, such as width W and wall angle θ_w on flange-up formability for a joint flange within the edge of the formed part, when the bending curvature of the blank sheet around the base of the flange, 1/R_m, was focused on. It was clarified that a decrease in 1/R_m in the early forming stage affects the suppression of the thickness decrease in the flange edge, leading to wrinkling around the flange base, unless the excessive material volume is reduced before the press stroke reaches the bottom. Then, the effects of the newly developed pad, the shape of which corresponds to the punch shoulder part, on the formability, which can control the bending behavior, were investigated by both numerical analyses and experiments of press-forming. The results showed that the newly developed pad improves the formability and enables flange-up forming even for ultra high strength steel with sheet shape optimization.