Wear and breakage of TiAlN- and TiSiN-coated carbide tools during high-speed milling of hardened steel

In the high-speed machining of hardened steel for the die and mould industry, determining how to reduce the wear of coated carbide tools and improve their machining efficiency and quality has been an important subject. This study investigated the high-speed machining of hardened steel (SKD11/HRC 62, S136/HRC 51) using two types of PVD-coated carbide tools (TiAlN and TiSiN) to determine the mechanism of cutting tool wear and breakage and the effects of tool angle, tool diameter, tool extended length, cutting force and cutting-induced vibration on the tools. The results indicated that the dominant wear patterns of coated carbide tools included flank wear, rack face wear, breakage and micro-chipping. The modes of breakage of the coated carbide tools used for the high-speed milling of hardened steel were coating peeling, chipping and tip breakage. The lives of the cutting tools coated with TiSiN were longer than those of the tools coated with TiAlN due to reduced abrasive wear. The tool extended length during machining caused chips to transform from spiral chips into c-shaped chips and produce sawtooth chips as the length increased. The selection of the optimal tool extended length can deliver the minimum cutting force, a small degree of tool wear and the best machining quality. The characteristics of the cutting force can distinctly reflect abnormal conditions as the cutting tool wears. A tool with a small rake angle, suitable clearance angle and large helix angle will not only reduce the cutting force but also ensure a smooth cutting process and generate less cutting tool wear.