Springback in plane strain stretch/draw sheet forming

Abstract Accurate prediction of springback is essential for the design of tools used in automotive sheet stamping operations. The plane strain stretch/draw operation presents a complex form of springback occurring in sheet metal forming since the sheet undergoes stretching, bending and unbending deformations. The two-dimensional draw bending is an example of such an operation in which the complex stress-strain states in the sheet cause the formation of side wall curls after the sheet is allowed to unload. Accurate prediction of the side wall curl requires using finite element shell models which can account for curvature and through-thickness stresses caused by bending and unbending of the sheet. Since such models are generally slow and expensive to use, an alternative and efficient method of predicting side wall curls will be desirable. This paper describes a novel and robust method for predicting springback in general and side wall curls in the two-dimensional draw bending operation as a special case, using moment-curvature relationships derived for sheets undergoing plane strain stretching, bending and unbending deformations. This model modifies a membrane finite element solution to calculate through-thickness strains and stresses and springback. Accuracy of this model's predictions are verified by comparisons with finite element (ABAQUS) and experimental results.