Experimental and numerical investigation on the delamination behaviour of PVD-coated tools in turning of austenitic steel

A fundamental wear cause in turning of austenitic steel with coated tools is the delamination of the coating around the cutting edge and the adjacent contact area. This is due to the strong adhesive effect between material and tool. The coating’s adhesion is influenced by several terms, e.g. coating process, substrate pre-treatment, coating system, substrate as well as by micro and macro geometry of the tool. This research work is focused on two fundamental aspects: the influence of the macro geometry on the delamination behaviour of the PVD-coating, and the possibility to use FEM simulation of chip formation as a useful tool for the interpretation of the coating’s failure. Several orthogonal cutting tests were performed under dry conditions, varying the rake angle between −15° and + 15°. Simultaneously, a FEM-model for the simulation of the thermal and mechanical loads of the tool was developed. The numerical model was verified by comparing simulation and experiments in terms of cutting forces and chip underside temperature. Experimental and numerical results show that high contact stress in the area of the rake face favours the partial removal of the coating by the sliding chip. According to this, large positive rake angles reduce the tendency towards coating delamination.