Principle and theoretical analysis of continuous roll forming for three-dimensional surface parts

Continuous roll forming （CRF） is a novel forming process for three-dimensional surface parts, in which a pair of bendable forming rolls is used as sheet metal forming tool. By controlling the gap between the upper and lower forming rolls, sheet met- al is non-uniformly extended in the longitudinal direction while it is bent in the transverse direction during the rolling process. As a result, longitudinal bending is gained and a doubly curved surface is formed. With the rotations of the forming rolls, the sheet metal is deformed consecutively, and a three-dimensional surface part is shaped continuously. In this paper, the mecha- nism of the three-dimensional surface formation in CRF is set forth. Through theoretical analysis of the CRF process, the gov- erning equations for the bending deformation in rolling process are presented. Based on the simplification on the deformation and material model, the formulation to calculate the longitudinal bending deformation is derived, and the methods to design the compression ratio and the roll gap are given, the effects of compression ratio of rolling and the width of blank sheet on the longitudinal bending curvature are analyzed. The forming experiments on typical surface parts and measured results show that forming results with good precision can be obtained by CRF process.