Influence of bending angle function on local thinning defects of roll-formed sheets based on segmental boundary combination optimization

In the sheet forming process, the final bending angle is mostly determined based on experience rather than based on a reliable theoretical framework. Furthermore, the local bent areas tend to decrease in thickness. Thus, it is difficult to control the quality of the final products. In this study, we developed an optimized bending angle function by combining segment boundaries to improve the final sheet forming quality and reduce the local thinning defects. The finite element submodel method was used to establish a high-definition thickness-sensitive numerical model for the bottom bending area of the hat-shaped part. This method accurately simulated the thickness variation law of the bending area of roll forming and analyzed the optimization function of the bending angle of the segment boundary as well as the process parameters for local thinning. Finally, roll-bending experiments were conducted to analyze the bending angle distribution conditions and the change law with respect to the process parameters of the cap-shaped parts in case of local thinning defects to verify the accuracy of the finite element simulation process. The results showed that the local thinning defect in the bending area of the hat-shaped part was smaller during roll bending, and the forming quality obtained was better than that obtained using other previously reported methods. The experimental data were consistent with the simulation data, verifying the accuracy of our proposed approach. Moreover, the thickness of the thinning defect was influenced by the process parameters; the plate bending radius and yield strength increased, and thickness thinning gradually decreased. Furthermore, the local thinning defects increased with the increasing plate thickness.