Wear characterization and wear mapping of a coated cutting tool : Development of cutting tool test fixture and wear testing

Abstract: Wear mechanisms of the cutting tools are well investigated worldwide. Usually researchers use the cutting process itself, turning by single point cutting, as their investigation method, which includes turning a metal cylinder with a pre-selected work-material and predetermined cutting conditions. Thereafter the tool worn surface is examined by scanning electron microscopy in order to characterize the tool wear mechanisms and tool failure. However, this may be the most appropriate way to investigate the wear mechanisms which occur during machining since it simulates the real operation. Metal cutting involves extreme conditions such as high temperature and high-pressure and the different condition results in different wear modes on the insert’s surface. The wear modes are overlapping and the transition boarder between them are not sharp making it difficult to obtain a detailed information of wear mechanisms. Because of these reasons many researchers try to refine the machining to a single condition e.g; high pressure, at the laboratory level in order to characterize the wear mechanisms and to get a more detailed information. In this thesis the wear tests of the cutting tool are performed by using a slider-on-flat-surface (SOFS) wear tester. SOFS involves a normal load, which applies to the sample and a tangential force that enables the sliding of the sample against a counterface. To enable conducting the wear tests in SOFS a newly design of tool holder was prepared. The wear tests were performed at different contact conditions and the stainless steel EN 1.4310 was used as the counterface material. After the tools were tested, the worn surface of the tool was examined by optical light microscopy and scanning electron microscopy in order to identify the wear rate and wear mechanisms. At low load the dominating wear mechanism was adhesive wear. The adhesive wear was induced by material pick-up during sliding i.e. material from the counterface was transferred to the insert’s surface. Further sliding results in delamination of the insert surface and removal of a part of the coatings material. At high load the dominating wear mechanism was a combination of severe adhesive wear and fracture of the coating material. The fracture of the coating material occurred because of overloading. Coating defects promote crack formation under high load and these cracks propagate through the coating during sliding movement and result in microchipping of the coating material. This procedure does not simulate the metal cutting but it still gives an understanding of the behavior of the coating material when it is exposed to a high mechanical stress.