Mechanical mechanism of continuous roll forming for three-dimensional surface parts and the calculation of bending deformation

Continuous roll forming(CRF) is a new forming method for sheet metal, the three-dimensional surface part can be formed by using two bended forming rolls. The mechanical analysis on the deformation process from sheet blank to the curved surface in CRF is carried out, the deformation and material models are simplified, according to the equilibrium of internal force in the formed surface, the basic equations for governing bending deformation in longitudinal direction(rolling direction of forming rolls) are set forth, the formulations for calculating the radius of bending curvature in longitudinal direction based on the rolling strain are presented, and the method to design the gap between the upper and lower rolls is given. Analysis results show that, when the initial rolling strain is linearly distributed in the height direction, there are no residual stresses in the final formed surface, in addition, the bending curvature in longitudinal direction is determined by the maximum height difference and the compression ratio difference in the cross-section. Through the analyses on the process of CRF, the condition to realize the continuous roll forming for curved surface is achieved and the effects of the compression ratio difference and the geometrical parameters of the curved surface on the bending deformation in longitudinal direction are obtained. Experimental examples of CRF verify the effectiveness and practicability of the proposed theory and formulations. © 2013 Journal of Mechanical Engineering.