On Edge Waves Occurring in Forming a Circular Channel Section with Side Flanges by Cold Roll Forming

Abstract

The mechanism of the occurrence of edge waves occurring in forming a strip into a circular channel section with side flanges by a single stand roll forming has been experimentally investigated from the relations between the forming conditions and the membrane strains and stresses produced during passage through the rolls. It was found that the product after roll forming was contracted longitudinally at the center of the circular channel section, and elongated at the shoulder portion, and had both conditions (contraction, elongation) at the edge portion according to the forming conditions. It was also found that the transverse distribution zone of both the positive longitudinal residual membrane strain and stress in the flange ranged from the shoulder portion to beyond the middle point of the flange in the absence of edge waves. In this experiment, when the maximum value of the longitudinal compressive membrane strain at the center of the circular channel section was over 0.4%, without fail, edge waves occurred for the thickness of the strip over 0.8 mm. Finally, it was confirmed that the elastic-plastic buckling occurred at the edge portion of the strip through the rolls according to the magnitude of the thickness and the width of the strip. On the basis of the experimental results mentioned above and the theory of the buckling of the plates, the critical condition on the occurrence of edge waves in the forming of the circular channel section with side flanges was obtained.