Grinding characteristics of PCD and PCD tool sharpening technology (2)
October 15, 2018
(1) Large grinding force Diamond is the hardest material among minerals. The wear amount of friction with various metal and non-metal materials is only 1/50~1/800 of cemented carbide; the hardness of PCD ( HV) is 80-120KN/mm2, second only to single crystal diamond, much higher than hard alloy. When grinding PCD with diamond grinding wheel, the initial cutting strength is very high, about 10 times higher than that of cemented carbide (0.4MPa); the specific grinding energy can reach 1.2×104～1.4×105J/mm3; therefore, the grinding force is much higher. For grinding cemented carbide.
(2) The grinding ratio is very small. Because the hardness and wear resistance of PCD are very high (relative wear resistance is 16 to 199 times that of cemented carbide), the grinding ratio is only 0.005 to 0.033 when grinding PCD. 1/1000~1/100000 of cemented carbide; 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 long and the processing efficiency is low. In addition, when the hardness, content, and particle size of PCD are different, the grinding time is also very different.
(3) The influence of particle size is very large. The PCD materials are mainly divided into three types according to the particle size: coarse grain size (20～50μm), medium grain size (about 10μm) and fine grain size (~5μm), grinding force and grinding. It is several times to several tens of times different. The coarse-grained PCD has the highest grinding ratio and the most difficult grinding. After grinding, the cutting edge is the most severe and the worst quality, but the wear resistance is the strongest. The fine-grained PCD grinding ratio is relatively low, and the grinding is easy. The quality of the cutting edge is best after grinding.
4 PCD cutting tool sharpening requirements for tooling
Based on the above-mentioned grinding characteristics of PCD, the requirements for sharpening equipment when grinding PCD with diamond grinding wheel are much higher than that of general tool grinding machines. There are:
(1) The machine tool has good process system rigidity. Due to the high hardness of the PCD material, the grinding machine must have high resistance to deformation, especially the spindle system and the tool clamping system. When the PCD cutting tool is sharpened, the grinding force is generally 100-500N. Therefore, the machine tool has a large shaft diameter and a high axial rigidity and strength of the bearing.
(2) The machine tool has a short stroke swinging mechanism with adjustable stroke and adjustable speed. The PCD grinding ratio is extremely low. The grinding mechanism of PCD is mainly caused by the continuous impact of the diamond grinding wheel on the PCD material, resulting in micro-crushing, wear, shedding and solution. The result of mixing mechanical action with oxidation and graphitization thermochemistry. Therefore, the use of a short-range swing mechanism is beneficial to improve the grinding efficiency and improve the cutting edge quality. Generally, the swing distance is 0 to 50 mm, and the swing speed is 20 to 60 beats/min.
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