2019 Volume 60 Issue 705 Pages 283-288
In the draw forming of ultrahigh-strength steel sheets into the L or T shape seen at the end of automobile parts, the top face easily wrinkles and the vertical wall easily breaks. For satisfactory forming, good elongation characteristics of the material are necessary. For this reason, it is difficult to form small-elongation ultrahigh-strength steel sheets into the L or T shape by draw forming. In this study, fundamental research has been carried out on the forming of an ultrahigh-strength steel sheet into the T model shape by finite element method (FEM) analyses and press experiments. The draw forming and the new bending method utilizing high-load pads “free bend sheet forming” were compared and the states and mechanisms of forming failure generation were analyzed. In free bend sheet forming, it was confirmed that an ultrahigh-strength steel sheet with a tensile strength of up to 1470 MPa can be formed into the T model shape by suppressing the generation of cracks and wrinkles.
