Closed-loop process control approaches and sensor evaluation for deep drawing tools with integrated piezoelectric actuators

Due to the design-driven increase in complexity of forming car body parts, it becomes more difficult to ensure a stable forming process. Piezoelectric actuators can influence the material flow of formed metal parts effectively. In this article the implementation of piezoelectric actuators in a large scale sheet metal forming tool of a car manufacturer is described. Additionally, it is shown that part quality can be assessed with the help of triangulation laser sensors, which are mounted on the blankholder. The resulting flange draw-in signals were used to reduce the occurrence of wrinkling or the rate of cracking. It was shown that two approaches of closed loop control algorithms, which were presented exemplary in this article, helped to improve the quality of the formed metal parts significantly. Subsequently it is shown that an iterative closed loop control needs more effort for preliminary studies to examine a proper interaction model while an in-line control algorithm can be implemented straight-forward if a well-chosen reference trajectory is taken.