Indirect Strain Control in Aluminum Stamp Formed Pans

Abstract

A stamp forming die whose flexible blank holder (BH) was designed using finite element (FE) analysis was built. The tooling also included active draw beads, local wrinkling sensors, and local force transducers. Wrinkling was controlled using a proportional–integral–derivative (PID) feedback loop and blank holder force (BHF). Local forces in the tooling were also controlled using blank holder forces in a PID feedback loop. A third closed-loop control system that could be used to control local punch forces (LPF) near draw beads featured an advanced PID controller with a Smith Predictor and Kalman Filter. A Bang–bang controller was also incorporated into that control system in order to prevent control saturation. Fuzzy logic was used to transition from one controller to the other. Once closed-loop control was implemented, tests were performed in order to evaluate the strains in the pans for various forming conditions. These results were compared to open-loop tests and it was found that the strains' paths for closed-loop control tests resulted in convergence and were further from the forming limit than strains from open-loop control tests. Furthermore, it was seen that the strains in critical regions had more uniform strain fields once closed-loop control of local punch forces was implemented. Hence, it was concluded that controlling local punch forces resulted in the indirect control of strains in critical regions.