Investigation of factors which cause breakage during the hydroforming of an automotive part

Tube hydroforming is receiving an increasing amount of attention, due to the increased interest in the preservation of the global environment and demand for impact-damage resistance for automobile body-structures. Knowledge of the process is, however, still insufficient to produce high-quality products in an efficient way. In the research reported in this paper, an automotive part formed with multistage processes was analyzed with an elastoplastic finite element method (FEM) code which was developed with a static explicit method. The computed distributions of the thickness strain were compared with the experimental results. Good agreement was obtained, which confirmed the validity of the code. Further analysis revealed that the weld line of a tube is crucial for tube hydroforming simulation, especially for the strain distribution. Subsequently, factors which cause the breakage on the inside of the bent portion of the product were investigated, which referred to both deformation processes and strain paths. This investigation clarified factors which cause the breakage of the product.