Shape Defects in The Flexible Roll Forming of Automotive Parts

Flexible roll forming allows variable cross sections of profiles to be made by using adaptive roll stands. The most common shape defects that occur during flexible roll forming are edge wave and longitudinal bow. These two defects are necessary to consider together for relatively thin-walled blanks because they usually occur simultaneously during flexible roll forming. To understand the occurrence of these defects, finite element (FE) simulations based on the rigid shell concept were carried out using three blanks with different shapes: trapezoid, concave, and convex. The FE analysis on the flexible roll forming process was performed first, and then the gap of rigid shell has been decreased for reducing the longitudinal bow in roll formed blank. The reduction of longitudinal bow in the web part usually causes edge wave in the flange part. The occurrence of shape defects is investigated based on the relationships among edge curvature, longitudinal stress at the edge, and longitudinal bow height. When longitudinal bow is reduced, the longitudinal stress at the edge of roll formed blank is changed from tensile to compressive in convex blank but in concave blank, tensile residual stress increases. Edge waves occur in the flanges of trapezoid and convex blanks as a result of decreased longitudinal bow. Lab-scale flexible roll forming experiments show multi-stand forming with a leveling roll is desirable to reduce both edge wave and longitudinal bow.