Pre-bulging effect during sheet hydroforming process of aluminum alloy box with unequal height and flat bottom

Pre-bulging effect on the sheet hydroforming process of irregular box with unequal height and flat bottom was investigated by means of numerical simulation and experiment. The influences of pre-bulging height and pre-bulging pressure on the forming were discussed respectively. The pressure loading path was optimized. The results show that pre-bulging has important influences on the forming results. Too high pre-bulging height causes the crack and obvious crease at the punch nose near the lowest corner. Too low pre-bulging height causes fracture at the punch nose of the highest corner. Pre-bulging pressure has a smaller effect on the fracture at the punch nose of the highest corner when the pre-bulging height is reasonable. But over high pre-bulging pressure causes crack and obvious crease at the punch nose near the lowest corner. Failure can be avoided by using reasonable pre-bulging height and pre-bulging pressure.