Flexible roll forming of surface developable profiles from Dual Phase steel

Flexible Roll Forming (FRF) can roll-form variable cross-sectional profiles for Electric Vehicle (EV) production however, a major limitation exists due to flange wrinkling while forming high-strength steels. Flange wrinkling can be eliminated by reducing the required level of membrane deformation in the longitudinal direction. Although reducing the severity of the profile's transitions minimises the strains, the overall complexity of the parts is also lowered. Origami-based 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 study presents, for the first time, the analyses of forming a developable shape in a FRF operation. Firstly, analytical equations are applied to calculate the strains and forming stability of each pass which is followed by experimental FRF trials on two high-strength Dual Phase steels. Finally, Finite Element Analysis is used to investigate the forming behaviour of the two types of developable profiles. The experimental results show that the forming of one type of developable profile improves the shape, while the numerical analyses showed that an additional top-hat forming is required for the second profile type.