PCD is sintered by specially treated diamond and a small amount of binder under high temperature and high pressure. The disordered arrangement of diamond grains gives PCD uniform, extremely high hardness, and wear resistance.
PCD can be used for cutting tools, grinding wheel dressing, geological drilling, measuring tool probes, wire drawing tools, sandblasting tools, etc. However, the high hardness and high wear resistance of PCD also bring great difficulties to its processing.
Scholars at home and abroad have carried out a lot of research and experiments on the processing problems caused by the high hardness and high wear resistance of PCD materials, including electrical discharge machining, ultrasonic machining, electrochemical machining, laser machining, etc., and have achieved certain results. However, the comprehensive analysis found that these processing technologies are currently most suitable for the rough processing of PCD materials.
In order to obtain good PCD cutting edge quality, the most ideal processing method is still grinding with a diamond grinding wheel.
The grinding process of PCD is mainly the result of a mixture of mechanical and thermochemical aspects.
The mechanical action is the micro-breaking, wear, shedding, or cleavage of the diamond formed by the continuous impact of the diamond grinding wheel abrasive particles on the PCD material; the thermochemical action is that the high temperature formed by the diamond grinding wheel grinding PCD causes the diamond to oxidize or graphitize.
As a result of the mixed action of the two, the PCD material is removed. Its grinding processing characteristics are mainly:
(1) Great grinding force
Diamond is the substance with the highest hardness among the known minerals, and the wear amount of friction with various metals and non-metallic materials is only 1/50~1/800 of that of cemented carbide; the hardness (HV) of PCD is 80~120KN/mm2, second only to single-crystal diamond, much higher than cemented carbide. When grinding PCD with a diamond grinding wheel, the initial cutting strength is very high, which is about 10 times that of cemented carbide (0.4MPa); the specific grinding can reach 1.2×104～1.4×105J/mm3; much higher than that of cemented carbide.
(2) The grinding ratio is very small
Due to the high hardness and wear resistance of PCD (the relative wear resistance is 16 to 199 times that of cemented carbide), the grinding ratio of PCD is only 0.005 to 0.033. It is about 1/1000～1/100000 of cemented carbide; the grinding efficiency is only 0.4～4.8mm3/min. Therefore, in order to ensure the cutting edge quality and removal amount of the cutting tool, the grinding time is very long and the processing efficiency is very low. In addition, when the hardness, content and particle size of PCD are different, the grinding time is also very different.
(3) The particle size has a great influence
PCD materials used in cutting tools are mainly divided into three categories according to particle size: coarse particle size (20-50μm), medium particle size (about 10μm) and fine particle size (~5μm). The grinding force and grinding ratio differ from several times to dozens of times. Coarse-grained PCD has the highest grinding ratio and is the most difficult to grind. After grinding, the cutting edge has the most serious serration and the worst quality, but the wear resistance is the strongest; The cutting edge quality is the best after grinding.
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