Stretch bending defect control of L-section SUS301L stainless-steel components with variable contour curvatures

The stretch bending of L-section variable-curvature SUS301L stainless-steel roof bending beams for metro vehicles was numerically simulated. The causes of defects such as wrinkling, section distortion, and poor contour accuracy were analysed, and the corresponding control methods were proposed. The simulation results demonstrated that wrinkling in the small-arc segment could be eliminated by setting the die clearance and adjusting the elongation reasonably. Owing to the sidewall shrinkage of the profile in the process of stretch bending, the die groove depth was correspondingly reduced. Each section of the profile was effectively supported by the bottom of the die groove, and the section distortion could be controlled. Springback was the main reason for the poor contour accuracy, which could be compensated by modifying the die surface based on the springback value. Using the above defect control methods, forming experiments were performed on a new type of stretch bending die with variable die clearance and groove depth developed in this work. Finally, high-quality components were obtained, which verified the efficacy of the defect control methods.