To enhance automobile weight reduction and to improve collision safety, the use of high-strength steel for press-formed parts has been expanding. However, dimensional accuracy defects occur because the use of a press-formed sheet metal induces springback behavior. In this paper, we propose a new forming method as a solution to this problem, here referred to as tension control (TC) forming. TC forming uses a technique that entails adding tension to a material after bending, it is effective for reducing springback. To implement this technique, the early stage of forming has some clearance between the die and the blankholder, then, the clearance is closed during the midst of forming, and then tension is added to the material during the latter half of the forming process. Experiments were carried out to investigate the effects of what on practical parts of high-strength steel. As a result, the proposed method is found effective for reducing springback in four types of high-strength steel. Furthermore, the effects of clearance and strokes with tension are clarified by elasto-plastic FEM, taking into account the Bauschinger effect.
