Stress-based springback reduction of a channel shaped auto-body part with high-strength steel using response surface methodology

In this paper, an optimum design is carried out with finite element analysis to determine process parameters which reduce the amount of springback and improve shape accuracy of a deep drawn product with the channel shape. Without springback simulation usually performed with an implicit solving scheme, the study uses the amount of stress deviation through the sheet thickness direction in the deep drawn product as an indicator of springback. The simulation incorporates the explicit elasto-plastic finite element method for calculation of the final shape and the stress deviation of the final product. The optimization method adopts the response surface methodology in order to seek the optimum condition of process parameters such as the blank holding force and the draw-bead force. The present optimization scheme is applied to the design of the variable blank holding force in the U-draw bending process and the application is further extended to the design of draw-bead force in a front side member formed with advanced high-strength steel (AHSS) sheets made of DP600. Results demonstrate that the optimum design of process parameters decreases the stress deviation throughout the thickness of the sheet and reduces the amount of springback of the channel shaped part. The present analysis provides a guideline in the tool design stage for controlling the evolution of springback based on the finite element simulation of complicated parts.