Development of a novel forming method to restrain wall curvature for stamping products using general purpose ultra-high tensile strength steel sheets

Abstract

In recent years, automobile manufacturing requires both weight reduction for environmental measures and high strength for safety. For this reason, the use of ultra-high tensile strength steel sheets for frame components is increasing. For the application of ultra-high tensile strength steel sheets, it is necessary to pay attention to measures to ensure dimensional accuracy for press forming. Among them, wall curvature countermeasures are very important technologies. In this study, a novel forming method without generating wall curvature was developed using a simple hat model, and then a prototype mold was produced and confirmed. This novel forming method is a combination of the advantages for draw forming and cam bending forming. To form a shape so as not to fracture or wrinkle in a process similar to drawing, and to prevent wall curvature of a vertical wall part of a hat section in a process similar to cam bending. The forming motion consists of downward descent and multi-step sliding while holding the specimen in one forming process. In the FEM analysis before the production of the prototype mold, the conventional forming method and the novel forming method were evaluated from the viewpoint of the wall curvature, and the novel forming method gave the best results with the minimum wall curvature. The evaluation of the formed panel using the prototype mold also gave the same results as the FEM analysis. This paper shows that the developed forming method hardly generates the wall curvature even when the ultra-high tensile steel sheet is used.