2009 Volume 49 Issue 11 Pages 1736-1743
In our series of studies, the outflow characteristics of a pressure medium used for a sheet hydroforming process have been investigated. The variation of hydraulic pressure during a square-cup sheet hydroforming process was examined, focusing on correlation with sheet deformation. In the initial stage, the outflow of the pressure medium remained stable because a greater extent of pre-bulging arose around the die shoulder just after the process commenced. When the pre-bulging ceased, the pressure medium was sealed in the chamber. Thus, the hydraulic pressure began to increase rapidly within the chamber, and fell in the flange area. The punch stroke at which the hydraulic pressure in the chamber began to rise was highly dependent on the blank holding force because the height of pre-bulging was determined by this force. When the sheet conformed completely to the die shoulder, the pressure medium was also sealed at the shoulder. Therefore, the hydraulic pressure on the die shoulder as well as in the flange area started to fall. The correlation between the critical punch stroke for fracture and the hydraulic pressure in the flange area was also examined.