Analytical model for prediction of sidewall curl during stretch-bend sheet metal forming

Curl is the curvature that results from non-uniform through-thickness strain present in sheet stampings that involve material flow over a die radius. In order to understand and control curl for tight fit-up tolerances, an analytical model that can provide a reliable measure for the amount of curl would be very helpful. In this study, a model is developed based on the moment–curvature relationship during stretch-bend sheet forming operations. The analytical model includes the variables of applied tension, yield strength, elastic modulus, bending radius, and sheet thickness. These are the primary factors affecting curl during sheet stamping operations. For the verification of analytical model, sidewall curl is experimentally measured after deformation of a strip using a bending-under-tension test system. The results show a good relationship between the theoretically predicted value and the experimentally obtained one, especially in the regions of high curl.