Press Forming Process of Closed-profile Automotive Parts Without Flange

Abstract

Automobiles are required weight reduction and improvement of collision safety. Additionally, rigidity of vehicle bodies is important performance that affects driving stability. Collision safety and rigidity of vehicles are strongly affected by strength and rigidity of the structural components. Accordingly, they are made of high strength steel / ultra-high strength steel and have closed cross section shapes (closed-profiles). Conventional closed-profile components are currently assembled by spot welding of two press-formed parts. Flanges of press-formed parts are required for spot welding and inhibit weight reduction. In the present situation, a new forming method was developed for closed-profile parts without flanges. The developed method was constituted three forming processes by using conventional mechanical press machines. In the 1st process, a steel sheet was partially stretched for adjustment of the cross section length and formed folds at ridgeline positions of the final shape. In the 2nd process, the formed sheet in 1st process was bent by press forming. In the 3rd process, the formed sheet in 2nd process was closed to hexagonal cross section shape by side tools which were driven transversely by cams. And finally it was added compression in plain by the punch. Trial product by the developed forming method satisfied the target performances (bending and torsion rigidity and collision strength). Weight reduction ratio was 39% by optimization of the cress section shape and removing flanges.