Research On Cutting Performance Of PCBN Tool When Cutting PM Valve Seat

With the promotion and application of low lead and unleaded gasoline, powder metallurgy (PM) valve seat, rely on its excellent physical properties such as self-lubricating, be widely used in the auto field. However, ordinary tools wear quickly when machining this kind of parts, due to the high hardness, porosity of PM materials and many microscopic hard particles in it. Polycrystalline Cubic Boron Nitride (PCBN) can be used to cut PM valve seat because of the high hardness, wear resistance, better surface quality of workpiece.Different material of PM valve seat were processed by three kinds of PCBN tools, in order to know which kind of PCBN tool was suitable for cutting the appointed Powder Metallurgy material. In addition, cutting tool life of different PM material was calculated to analyze the processing performance. It turned out BN100PCBN (made in Japan) was the better tool for cutting PM valve seat, with the longer cutting path and less tool wear.Moreover, the failure modes of cutting tools were observed by Scanning Electron Microscope (SEM) and tool wear mechanism could be studied by energy spectrum analysis. The result shows that, breakage failure was the main reason for the tool failure, including surface spalling and tipping; adhesive, dispersion and oxidation wear were the main reason for tool wear mechanism, mechanical wear exists in the whole cutting process.Cutting force and surface roughness of PM valve seat with BN100PCBN tool, were studied by changing the orthogonal experiment parameters, which contains corner radius, cutting speed, feeding rate and cutting depth. On the same cutting condition, there wear no significant difference of the cutting force and surface roughness between these three kinds of PCBN tools, and the trend were almost same. The factor which effect cutting force most is cutting depth, then feeding rate and cutting speed. Corner radius has little influence on cutting force, however radial force increase significantly with corner radius increase, and axial force in contrast.The surface roughness first reduce then increase with the increase of corner radius, it would get the lowest value when r=0.3mm. Melting copper PM valve seat (V571and V581) is more easily affected by cutting parameters than unmalting copper PM valve seat (V531), but each roughness value changed little. At last, cutting force empirical equation is established to forecast cutting force value, and the significance test show that it can be used prosperity for the application of forecasting model.