Extension of the forming limits in cold and warm forging by the FE based fracture analysis with the integrated damage model of effective stresses

In this article the simulations of different cold and warm forging processes, based on the application of the finite element software MSC.SuperForm 2002, are presented with special emphasis on the occurrence of fracture in the ductile material failure of the ferrous materials used. The model of effective stresses (MES) was modified and integrated into the FE simulations of various manufacturing processes in order to predict the particular damage evolution. The necessary material parameters are obtained from tensile and compression tests, using material of the same batch. The true stress–strain curves, at the moment of failure in the tensile tests, were obtained by an optical measurement of the parameters for the correction model after Bridgman. The damage criterion was applied to different cold and warm forging operations, during which a high susceptibility to cracking was observed in reality. Here the emphasis lies on the modelling of forging operations with predominantly complex three-dimensional material flow. The cold massive formed workpieces are a double cup with a hexagonal outer structure and hexagon socket screw. In both cases surface fissures can be observed in the production and a suitable approach for the reduction of material failure is the slight modification of critical geometries of the workpieces. The applicability of the MES on warm forging operations is demonstrated with the production of a journal bearing.