Numerical Study on Effect of Bilinear Pressure Path on Corner Filling in Hydroforming of Tube in Box-Shape Die

Die corner filling is very important in tube hydroforming process. Definition of the internal pressure path is a key factor in improving the corner filling.  However, the factors that cause improvement of corner filling are still unclear. In this paper, effect of bilinear pressure path on corner filling in hydroforming of tube in box-shape die is studied using both finite element simulation and experiment. For this pressure path, pressure increases to an initial pressure and then it increases to a final pressure (calibration pressure) linearly. It is shown that, an initial pressure lower than yield pressure of the tube is caused a small wrinkle which is eliminated into the corner of die and thus the corner filling is improved, whereas for other pressure paths with higher initial pressures a round bulging occurred in former stages of deformation, and thus the corner filling of die is deteriorated.