Effectiveness of ultrasonic vibration on press forming

In press forming, it is most important to prevent wrinkling and cracking. A small clearance between the upper and lower dies is effective for preventing wrinkle generation. However, the small clearance increases sliding resistance between sheet material and dies and causes cracking of sheet material. On the other hand, large deformation of sheet material requires multi-step press working which involves incremental small deformations in order to avoid wrinkling and cracking. But this method requires a number of dies so that it increases cost and development time. In press forming, lubricant to reduce sliding resistance of sheet material is used for preventing wrinkling and cracks. However, the use of lubricant such as chlorofluorocarbon and trichloroethane has been restricted due to environmental concerns. The development of new press working techniques that do not use lubricant is thus desired. Since wrinkling and cracking are mainly caused by friction between sheet material and dies, forming techniques which can decrease the friction without lubricant are needed.