Force-based closed-loop control of stamp forming processes have in the past been investigated in order to improve the formability of sheet metal when forming automotive body panels. Previous researchers have controlled local forces and wrinkling using active draw beads and variable blank holder forces. However, it has been recognized that strain-based control in critical locations may be more effective. This study is an initial examination of strain-based control. In order to simplify the problem of strain control, cup forming was utilized and a quasi-automatic proportional control system was utilized. Both finite element analysis and experimental results were examined. It was demonstrated that control at the punch nose resulted in better strain control than at the die shoulder. For this study, two approaches were considered for control. For the first approach, if the effective strains were within +/−0.005 of the target strain, the process was said to be in control while the second approach used a factor of 10% deviation from the target strain to be in control. It was shown that the second method resulted in improved control. However, a third approach, which was a synthesis of the first two approaches resulted in very close agreement between the target strains and the strains from the controlled simulations.

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