Characterization of the longitudinal bow during flexible roll forming of steel sheets

Flexible roll forming is an advanced sheet metal forming process that allows for the production of variable cross-section profiles. Longitudinal bow is one of the major shape defects found in roll-formed products. To characterize the degree of longitudinal bow during flexible roll forming, experiments were conducted on three different blank shapes: trapezoid, convex and concave. Symmetric U-sections with variable cross-sections were roll formed using the three sheet materials with different strengths from each blank shape. The effects of process variables on the longitudinal strain and longitudinal bow were analyzed both experimentally and by using finite element simulations based on ABAQUS-Implicit 6.14. The results show that the transversal nonuniformity of the longitudinal strain is one of the fundamental causes of longitudinal bow in roll-formed products. The bow height as a function of blank shape increases in the order of concave, trapezoid, and convex. The bow characteristics on the basis of blank shapes and material parameters provides a better understanding of the non-uniform longitudinal strain and bow height during flexible roll forming with high reliability. Furthermore, to reduce the longitudinal bowing, leveling roll is introduced. The effect of leveling roll on longitudinal bowing was investigated experimentally. The results show that longitudinal bowing was reduced with the use of three blank shapes when leveling roll was applied to a flexible roll forming process.