PREDICTION OF SPRING-BACK AND SIDE-WALL CURL IN 2-D DRAW BENDING

Accurate prediction of spring-back is essential for the design of tool s used in automotive sheet-stamping operations. The 2-D draw bending o peration presents a complex form of spring-back occurring in sheet-met al forming since the sheet undergoes stretching, bending and unbending deformations. These three sets of deformation can create complex stre ss-strain states in the sheet which result in the formation of side-wa ll curls after the sheet is allowed to unload. Accurate prediction of the side-wall curl requires using finite-element shell models which ca n account for curvature and stress variation through the thickness cau sed by bending and unbending of sheet. Since such models are generally computationally intense, an alternative and efficient method of predi cting side-wall curls is desirable. This paper describes a novel and r obust method for predicting spring-back and side-wall curls in 2-D dra w bending operations, using moment-curvature relationships derived for sheets undergoing plane-strain stretching, bending and unbending defo rmations. This model makes use of the membrane finite-element solution to calculate spring-back. The accuracy of the model is verified by co mparison with finite element (ABAQUS) and experimental results.