On Longitudinal Curvature and Transition of Strain of Sheet Steel in Forming a Groove with Wide Flanges by Cold Roll Forming

Abstract

Roll forming of sheet steel into a trapezoidal groove with wide flanges has hitherto been carried out by a progressive development of bends (turn-up treatment). Since the allowable pass height per stand is small for this process, many roll stands must be provided to prevent edge waves and flawing. In order to rectify this defect, an experimental investigation of a method of transforming a circular arc groove into a trapezoidal groove has been carried out under several conditions. It is found that the value of longitudinal curvature is proportional to 2.1 power of the thickness of sheet steel and also to several powers of the pass height. It increases with the increase in the width of the specimen, ranging from the length measured along the roll profile to twice this length, and has a constant value for a width of specimen over twice the length measured along the roll profile. It was also found that the curvature depends strongly on the inlet angle. Other factors such as the ratio of roll diameters, the ratio of surface velocities, and so on, affect the curvature but little. Finally, it has been confirmed through experiments in tandem roll forming that the value of the surface strain varies complexly and remarkably with the position, but that the value of the membrane strain is small and within the elastic limit. Therefore, it is considered that forming a groove by this method is approximately a pure bending process.