Effects of circular holes on the web warping of perforated blanks in flexible roll forming

To meet the demands of highly functional parts, high-precision manufacturing technology that can provide sound semifinal perforated components having variable cross sections is frequently required. When a relatively short blank is formed into a variable section by a flexible roll forming process, web warping such as longitudinal bows and crossbows can be generated in the formed products. In this study, the characteristic features of web warping occurring in the flexible roll forming of perforated blanks were investigated both numerically and experimentally. In order to investigate the cause of web warping, the stress and strain variations during flexible roll forming are examined in terms of the shapes of blank and hole orientations of perforated blanks. The results show that longitudinal bows and crossbows are primarily caused by the nonuniformity of longitudinal and transverse strains between the flange and the web. In addition, the degree of web warping is sensitive to the shapes of the blanks and the hole orientations. From the process analysis, a guideline for the perforation of holes in convex, concave and trapezoid blanks is proposed to reduce web warping.