Wrinkling compensation by Flexible Roll Forming a developable profile

Abstract Flexible Roll Forming (FRF) can form complex shapes with variable cross-sections along the length from high-strength steel. Widespread application of the FRF process in automotive manufacturing is however limited due to wrinkling defects that occur in the flange. Flange wrinkling can be eliminated by reducing the required level of membrane deformation and compressive stresses that develop in the longitudinal direction. This is conventionally achieved by reducing the severity of the transition regions but also limits the overall complexity of the parts that can be formed. Developable profiles can be created from curved creased folding without membrane stretching or compression. In FRF, such types of profiles can be formed by combining a variation in width and depth over the length of the part. This reduces the required longitudinal deformation while at the same time providing shape complexity. This study presents, for the first time, the analyses of forming a developable shape in a FRF operation. For this, first analytical equations are applied to calculate the deformation and forming stability of a developable component and of a reference variable depth component without a developable shape. This is followed by experimental FRF trials and shape deviation analysis for both forming conditions. Finally, Finite Element Analysis is used to investigate the forming behaviour of the two types of developable profiles. The results indicate that the forming of a surface developable can reduce wrinkling issues in the FRF process. However, the intermediate forming stages are non-developable, and this can lead to longitudinal compression and wrinkling issues that, if too severe, remain in the flange when the final developable shape is formed.