Minimizing wrinkling formation of GPa-grade steels in multi-stage crash forming process

This paper newly proposes a strategy for constructing the multi-stage forming procedures to minimize the wrinkling formation with GPa-grade steels in the crash forming. Although the optimum design variables were adopted in the conventional crash forming, it is not possible to control the wrinkling formation in severe cases. In the multi-stage crash forming, the safe forming window against the wrinkling formation for the pre-stage forming has been constructed with numerical simulations representing the effects of design variables such as die radius, die angle, step height variations, and flange lengths. It does not only substantially reduce the area fraction of the wrinkling formation, but also recommend the other optimum design variables by interpreting the safe forming window. Experimental validations were carried out by applying the design variables suggested by the safe forming window for the multi-stage forming, which is compared with the conventional crash forming with TRIP1180 steel sheet.