Closed-loop control of the sheet metal stamping process with active drawbeads, a flexible blankholder and variable active blank holder forces

Sheet metal stamp forming is subject to failure due to tearing and wrinkling. These failures are more likely to occur when forming with thinner steels or aluminum. The implementation of closed-loop control to prevent these failures while forming shallow oval pans is the focus of the research presented here. Extensive testing using open and closed-loop control resulted in a methodology that improves the performance of a die system by reducing part failure due to tearing or wrinkling. Open-loop tests were performed in order to study the die operational envelope, examining punch force, local punch forces, and wrinkling for a wide variety of conditions. By introducing closed-loop control of wrinkling and local punch forces using active drawbeads and active blankholder pressure, wrinkling was entirely eliminated and tearing was reduced or eliminated within most of the available punch stroke for the die system developed for various lubrication conditions. Strains were measured for open and closed-loop tests. FEA simulations of open-loop tests were performed and compared to test data. Closed-loop control tests were found to indirectly control strains near the active drawbeads.