Numerical investigation of draw bending and deep drawing taking into account cross hardening

Sheet metal forming is one of the most important manufacturing processes. Computer simulation has become the tool for modeling such processes and also for predicting the springback in the final part. The talk will deal with two different metal forming processes, namely draw bending and deep drawing of a cup. In the draw bending case a metal strip is clamped into a testing device in such a way that it is bent over a roller. The strip is then moved along so that it undergoes bending and back bending while passing the roller. Subsequently the strip is released resulting in springback. Due to the geometry of a strip springback is significant in this process. Since during the draw bending process the state of stress is not the same in the middle of the strip and at the outer edge, high residual stresses remain in the workpiece. Though taken into account in the finite element model, contact is here of minor importance. Contact and also cross-hardening plays a more significant role in the second process. During the deep drawing a compression takes place in circumferential direction and in radial direction the ma- terial undergoes bending and unbending. Therefore orthogonal loading path changes occur. Some metals exhibit an increase of the yield stress after orthogonal strain path changes, i.e. so-called cross hardening. This is also the case for the air hardening steel LH 800 which is the material for both processes. To take the cross hardening into account one needs a material which goes beyond stan- dard isotropic and kinematic hardening. Such a model has been implemented via the user-material interface of LS-Dyna and ABAQUS. A comparison with standard hardening models as well as a com- parison of the results for the two different FE-codes will be given in the talk. Both processes were investigated also experimentally which facilitates a comparison of simulation results and test results. The parameter identification was done with LS-Opt and is subject of the contribution "Identification of an advanced hardening model for single phase steels" given by Muhammad Noman which will be presented at this conference as well.