Methods to obtain net shape in aluminum sheet forming using active binder force control

The objective of the present investigation is to: (1) understand and analyze the effects of restraining force on the springback phenomena when stamping aluminum sheet; and (2) develop a strategy to control the binder force during the forming operation in order to reduce springback and simultaneously avoid tearing failure. Based on finite element analyses of the process, we were able to determine a binder force history which leads to a significant reduction in the amount of springback incurred by the formed part without reaching critical stretching conditions. The corresponding history of draw-in vs. punch displacement was recorded and identified as the desired draw-in history to be followed in later closed-loop simulations. In order to ensure that identical bending moment distributions were obtained in the fully loaded stage regardless of possible variations in process parameters such as initial binder force setting and friction conditions, a closed-loop control algorithm was developed whereby the binder force is altered during the process to robustly provide a repeatable stretching history. This control method ensured that the desired draw-in history was followed, thereby the same amount of reduced springback on the final product was successfully obtained, thus compensating for variations in process conditions.