Springback Prediction and Control in Multi-Stage Sheet Metal Forming

Several forming operations are required to form a complex part, which is known as the multi-stage forming process. Inherently, the final geometry of the stamped part is affected by springbacks from every forming operation. First, the theory on springback after unloading in bending and the technologies of numerical simulation are investigated. The latter includes the numerical solution procedure of springback in multi-stage forming, the time steps of numerical calculation, and the transmission of blank information from the previous stage to the next. Then a sample automotive structural piece, the upper inner panel, has been simulated and validated. Entire forming procedure is simulated with an explicit-implicit coupled FEA program, which is based on the simulation of “loading-unloading of springback-reloading”. Finally, by means of forming process modification, effects of various diefaces including the drawbeads and stiffening beads are investigated to enhance the final part shape. The validation of simulation procedure and the forming process modification method are presented through the comparison of the simulation results with experimental results.