Improving the properties of exterior body panels in automobiles using variable blank holder force

Constant blank holder forces (BHFs) are currently more frequent compared to variable BHFs in sheet-metal forming processes. Exterior body panels used in the automotive industry are examples of sheet-metal products. These panels often feature curves in one or more directions. The work reported here has shown that major improvements in the critical properties of a double-curved panel can be achieved using a variable BHF. In the panels investigated here, springback was significantly reduced and dent resistance increased. These improvements were achieved using a strong initial BHF followed by a sharp decrease in force nearing the end of the punch stroke. Moreover, the robustness of the process was also greatly increased using variable rather than constant BHF.