Investigation of crack formation on the Galvalume coating of roll formed roof panels

Roll forming of pre-coated and pre-painted sheet metal is a common industrial practice. Cracking of metal coating and/or paint at the sharp edges need to be considered and eliminated during the roll design phase of a new product. The sheet deformation in the lateral (transverse) direction during roll forming is a combination of pure bending and stretching in a step-by-step gradual deformation. Closed form equations of simple bending cannot model this type of deformation. Moreover, due to the free edges, approximations for draw bending cannot be used either, and thus the use of finite element analysis is necessary. In this paper, an investigation on roll forming of pre-coated and pre-painted roof panels have been conducted to eliminate the reported crack formation on the coating and paint. Finite element method was used to test various roll designs, and optimal roll geometry was proposed.