The Research On Polycrystalline Cubic Boron Nitride Tools Hard Cutting The Powder Metallurgy Valve Seats

The Powder Metallurgy valve seats, which has excellent mechanical properties of high-temperature wear resistance, corrosion resistance and high temperature stability, plays an important part of the Engine Valve. Ordinary tools machining this kind of parts wear quickly, because the high hardness, porosity, contains many microscopic hard particles. And the valve seats requires high dimensional accuracy and surface roughness, so it brings a lot of difficulties in machining.One of the methods solving the Problem is to use new material cutting tools. Polycrystalline Cubic Boron Nitride (PCBN) tools has a strong advantage in hard cutting Powder Metallurgy valve seats, because of its high hardness, wear resistance, and high surface roughness of the machined work piece. This thesis, firstly, observed the valve seat on metallographic structure and scanning electron microscopy (SEM). And laid the foundation for the reasonable chosen of PCBN tool parameters.According to the cutting test of PCBN tools hard cutting Powder Metallurgy valve seats, the thesis studied the impact of cutting parameters on the cutting process, like cutting force, temperature of cutting zone and chip morphology. And then the experience equation of cutting force and temperature of cutting zone with cutting parameters is established. The results of the test show that:With the increase in cutting speed, the main cutting force Fz will be reduced in a given range (89～113m/min) and this result is effected by the powder metallurgy emerge softening phenomenon. It is the main characteristics of PCBN cutting powder metallurgy materials that radial force Fy has been greater than the main cutting force Fz. It mainly due to the PCBN tools the depth of cutting, nose radius and tool chamfering. With the increase of cutting speed, the temperature of cutting zone rises, the formation of saw-tooth chip intensifying, and last became unit chips.According to the production test in a company, the tools life of PCBN turning Powder Metallurgy valve seat’s bores and rounding is obtained. The wear morphology and failure modes of the PCBN tools have been analyzed. The main kinds of wear are rake wear, micro-chipping, flank wear, flaking and breakage, and the main form of failure is chipping.