ACCOMMODATION OF SPRINGBACK ERROR IN CHANNEL-FORMING USING ACTIVE BINDER FORCE CONTROL - NUMERICAL SIMULATIONS AND EXPERIMENTS

Springback in a forming process is due to the elastic deformation of t he part during unloading. This manufacturing defect can be accounted f or through proper tooling design or through proper design and control of the magnitude and history of restraining force. Using finite elemen t analysis of the process: (1) the effects of restraining force on the springback phenomena when stamping channels from aluminum sheet are i nvestigated; (2) a strategy to control the binder force during the for ming operation in order to reduce springback and simultaneously avoid tearing failure is described; and (3) a binder force control strategy which provides robustness in the presence of process parameter uncerta inty is implemented. The process history and controller design using f inite element analyses is then experimentally verified : excellent agr eement between simulation and experiments is obtained. A binder force history, which leads to a significant reduction in the amount of sprin gback incurred by the formed part without reaching critical stretching conditions, was proposed. Although an optimal forming history was fou nd, in order to ensure that part shape error remained minimized even i n the event of variations in processing parameters such as friction, a closed-loop control algorithm was developed whereby the binder force is altered during the process in order to provide a robust, repeatable stretching history. Experiments were performed using a double-action servo-controlled process and were found to produce the desired results demonstrating both the accuracy of the numerical simulation and the s uccess of the proposed active-binding force control method to obtain n et shape.