As a typical brittle material, cutting problems of isotropic pyrolysis graphite are very prominent, and the surface quality is difficult to control. The cutting parameters such as cutting speed, cutting depth, feed rate and the influence of tool front angle on machined surface roughness are analyzed by using PCD tool. The research and analysis of the experimental results show that the feed rate has the greatest influence on the surface roughness, while the cutting speed and back engagement of the cutting edge have little effect on the surface roughness. Increasing the negative front angle of the tool is beneficial to improve the machined surface quality of isotropic pyrolysis graphite.

Based on the analysis of nano printing test results of isotropic pyrolysis graphite and the study of strain gradient theory of crystal structure and head shape, the critical cutting thickness of isotropic pyrolysis graphite material is calculated. The critical cutting thickness is about 335.63~134.15 nm. In this range, the brittle-plastic transition occurs in isotropic pyrolysis graphite material. And plastic removal more frequently occurs. According to the brittle plastic transformation mechanism in ultra-precision cutting of brittle materials, the ultra-precision turning model of isotropic pyrolysis graphite is established. The accuracy of the established ultra-precision cutting model are verified by ultra-precision turning test results.

In order to solve the problem of too fast cutting-tool wear in isotropic pyrolysis graphite cutting process, the cutting experiment was carried out by using polycrystalline diamond (PCD) tool. The wear form, wear law of PCD tool in cutting process, and the effect of tool wear on surface machining quality were studied. The experimental results show that the wear of PCD tool mainly occurs on the rear surface of the tool. And the wear forms are abrasive wear and oxidation wear. The wear area can be divided into two kinds of morphology: parallel grooves and serious wear. In the initial wear stage, the length of the wear band increases sharply. And it gets into the normal wear stage after cutting 1200m. In the cutting process, graphite chips and tool edge collapse also appear in wear area. At the beginning of cutting, with the increase of cutting distance, the machined surface roughness increases sharply. And the maximum surface roughness reaches 1.7 μm when the cutting distance is 600m.

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