Mitigating springback defects in variable-curvature elliptical panels through multi-pass roll forming optimised by the UOSDM method

Abstract

The bending angle is a critical parameter in the roll-forming process. An appropriate bending angle distribution can enhance the forming quality of sheets and minimize defects. However, research on the bending angles and mechanisms of variable curvature surface plates remains in the preliminary stages of exploration. Therefore, this study focuses on long plates with variable-curvature elliptical surfaces, and a generalized bending angle assignment formula (IEBAF) for curved plates is derived based on the standing edge end projections. Subsequently, a bending angle distribution method (the universal optimised springback defect method, UOSDM) is proposed to address springback defects in variable-curvature elliptical plates. The mechanisms of forming plasticity and its influence on the quality of the formed sheets are investigated through finite element simulations and experimental verifications employing various bending angle formation methods. The results indicate that during the multi-pass roll forming process of variable-curvature elliptical panels using the UOSDM method, the reductions in stress and strain before and after unloading are 6 MPa and 0.02, respectively. This method exhibits minimal data error and achieves optimal forming effects. The experimental and simulated springback angles of the panels fabricated using the UOSDM roll bending method are 1.42° and 1.34°, respectively. Compared to other methods, the springback value is minimized, resulting in the best final forming effect of the panels. The simulation closely matches experimental data, validating the model's accuracy and the proposed method's effectiveness. This research offers significant theoretical foundations and technical support for the precise forming of variable-curvature surface components.