PCD is made by sintering specially treated diamond with a small amount of binder at high temperature and ultra-high pressure. The unordered arrangement of diamond grains gives PCD uniform, high hardness and wear resistance.PCD can be used for cutting tools, grinding wheel dressing, geological drilling, measuring tool probe, wire drawing tool, sandblasting tool, etc. However, the high hardness and high wear resistance of PCD also bring great difficulties to its processing.
Scholars at home and abroad have conducted a lot of research and tests on the processing problems, including EDM, ultrasonic machining, electrochemical machining, laser machining, etc., and achieved certain results. However, the final research data show that these processing technologies are most suitable for the roughing of PCD materials. In order to obtain high-quality PCD cutting edges and improve the efficiency of grinding, the best machining method is still grinding or grinding with diamond wheels.
The main process of PCD grinding is mechanical and thermochemical mixing. Mechanical action refers to the result of the fine crushing, abrasion, peeling or cracking of the diamond formed by the continuous impact of the diamond grinding wheel abrasive on the PCD material during the production process. Thermochemistry refers to the process of oxidizing or graphitizing PCD at high temperatures by a diamond wheel. The combination of the two results in the removal of the PCD material. Its grinding processing characteristics are mainly as follows:
(1) Great grinding force
Diamond is the hardest substance in the known minerals, and the wear amount of friction with various metallic and non-metallic materials is only 1/50 ~ 1/800 of that of cemented carbide. The hardness (HV) of PCD is 80 ~ 120KN/mm2, which is second only to single-crystal diamond and much higher than cemented carbide.
When PCD is ground with a diamond wheel, the initial cutting strength is very high, about 10 times that of cemented carbide (0.4mpa). Specific grinding capacity: 1.2 × 104 ~ 1.4 × 105J / mm3; Therefore, the grinding force is much higher than that of cemented carbide grinding.
(2) The grinding ratio is very small
Due to the high hardness and wear resistance of PCD (the relative wear resistance is 16 ~ 199 times that of cemented carbide). Therefore, in order to ensure the cutting tool edge quality and removal, grinding time is very long, processing efficiency is very low. In addition, when the hardness, content and particle size of PCD are different, the grinding time is also different.
(3) Particle size has a great influence
PCD materials used in cutting tools are mainly divided into three types according to the particle size: coarse particle size (20 ~ 50 cm), medium particle size (about 10 cm) and fine particle size (~ 5 cm). The difference in grinding force and grinding ratio is several times to dozens of times. Coarse grain PCD has the highest grinding ratio, the most difficult grinding, the most serrated edge after grinding, the worst quality, but the strongest wear resistance. Fine-grained PCD has the lowest grinding ratio, the easiest grinding and the best edge quality after grinding.
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