Abstract
Recently, hydroforming technologies have been applied to complex-shaped auto mobile parts, so that the number of hydroforming parts after bending has increased. In this study, deformation behavior of a tube during hydroforming after bending is investigated. First, a tube is bent by 45 degrees by rotary draw bending. The bent tube is then introduced into a hydroforming die and expanded to a rectangular cross section at a 50% expanding ratio. We use several types of loading paths of internal pressure and axial feeding. Results show that, in the case of a high-initial pressure path, bursting occurs on the intermediate side of the tube during axial feeding. When the internal pressure is decreased to prevent bursting, bursting still occurs on the compression side in the case of high pressure during axial feeding. On the other hand, in the case of low internal pressure during axial feeding, wrinkles form after a maximum pressure increase. Finally, a sample that features no bursting or wrinkles is successfully obtained. It is found that the gap between the bent tube and the hydroforming die on the compression side should be small to prevent bursting or wrinkles from occurring, so that the bending radius before hydroforming should be large.
