Die design method for sheet springback

A new method for designing general sheet forming dies to produce a desired final part shape, taking springback into account, has been developed. The method is general in that it is not limited to operations having particular symmetry, die shapes, or magnitude of springback shape change. It is based on iteratively comparing a target part shape with a Finite Element-simulated part shape following forming and springback. The displacement vectors at each node are used to adjust the trial die design until the target part shape is achieved, hence the term “displacement adjustment method” (DA) has been applied. DA has been compared with the “springforward” method of Karafillis and Boyce (K&B), which is based on computing the constraint forces to maintain equilibrium following forming. DA was found to converge in cases when K&B does not, and in cases when both methods converge, DA is many times faster. In general, i.e. nonsymmetric parts, K&B can return inaccurate results whereas DA does not. The suitability and application of the two methods is discussed, along with the origins of the differences.