Keywords: ductile damage, manufacturing processes, finite element method.

Cold forming processes are still widely used in the metal industry to produce parts at high production rates with high mechanical strengths and close repetitive tolerances. On the other hand, cold deformation requires very ductile materials in order to produce parts without significant damage. During the multi-stage cold forming processes, materials are submitted to non-monotonic multiaxial loadings and sometimes, even reverse loadings. For such a complex strain path, the prediction of damage evolution becomes really intricate. The aim of this paper is to highlight the specific points to be addressed in order to predict the damage computation for cold forging processes.

A modified Lemaitre damage formulation is coupled with the material behaviour to address a ductile damage study for cold forming processes. This model is used to predict crack initiation on a screw formed with a two-stage cold forming process. Numerical simulations are performed using the Forge2009R finite element software. Material parameters are identified using inverse analysis. Comparisons with experiments show the ability of the model to predict failure depending on the geometry of the initial billet.

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