| 摘要 |
When hydroforming a steel pipe (6), a tubular deformation assisting member (10) made of an incompressible material softer than the steel pipe (6) is fitted on the outer peripheral surface of the steel pipe (6). The deformation assisting member (10) is attached at least to an area corresponding to a projection (1b) provided at the inner surface of the die assembly (5), the projection being earliest brought into contact with the outer peripheral surface of the steel pipe (6) during hydroforming. When hydroforming the steel pipe (6), the material of the deformation assisting member (10) plastically flows near corner portions (X1, Y1) at which the deformation assisting member (10) is brought into contact with the projection (1b). This plastic flow accelerates circumferential uniform extension of the steel pipe (6). <IMAGE> |
