Analysis of shape defects during flexible roll forming of steel/aluminum double-layered blanks

Flexible roll forming is an advanced sheet-metal-forming process that allows the production of parts with variable cross-sections. Double-layered blanks can have enhanced properties such as a high stiffness-to-weight ratio and high corrosion resistivity when combined with suitable materials. However, in the flexible-roll-forming process of double-layered blanks, additional shape defects and interface delamination can occur owing to their inhomogeneous mechanical properties compared with those of single-layered blanks. In this study, investigations on shape defects generated during the flexible-roll-forming process of steel/aluminum double-layered blanks were performed. Shape defects such as web-warping, wrinkling, and delamination at the interface were investigated on three different blanks with trapezoidal, convex, and concave shapes. The results show that the process-induced longitudinal strains significantly affect the occurrence of shape defects. Moreover, the longitudinal strains strongly depend on the blank shapes, their stacking order, and mechanical properties of the constituent layers.