Effects of cutting edge residual stresses on the wear behavior of PVD-coated cutting tools

Cutting tools have successfully been coated with thin hard layers in order to improve their wear and thermal properties for longer tool life. Apart from composition and layer structure (single, combined, multi layer), the process related residual stresses have the most important effects on resulting tool properties. An in-process variation of the coating conditions enables a specific adjustment of residual stress depth distributions in coating and coating-substrate-compound, resp., for an improved tool behaviour. Particular attention is paid to the highly curved surface directly in the cutting edge, as here frequently wear initiation takes place. In this tool range process related different deposition conditions prevail than on flat surfaces. An experimental determination of residual stresses directly in the cutting edge is not possible with the so far applied methods. Raman spectroscopy offers the potential, in a combination with X-ray diffractometric methods, to be applied for the necessary locally resolved measurements. The first part of this project deals with the preparation of the Raman method for residual stress measurement at common (Ti,Al)N coatings. In the second part targetedly relations between cutting edge residual stresses and wear behavior of the tools will be analyzed. The goal of this project will be reached, when the causes of wear initiation have been understood and recommendations for a design of cutting edge residual stresses can be given.