1. Brief introduction of boron nitride superhard materials
Cubic boron nitride (CBN) is a superhard material synthesized by hexagonal boron nitride and catalyst under high temperature and pressure. The hardness of this kind of superhard material is second only to that of diamond. The thermal stability of cubic boron nitride is much higher than that of diamond, which has greater chemical stability to iron-based metal elements. Therefore, cubic boron nitride abrasives are widely used in the field of cutting and grinding of iron-based metal products, and their properties are excellent.
2. Application of Boron Nitride Polycrystals in Metal Cutting
Cubic boron nitride polycrystalline (PCBN) tool is a kind of superhard material product which is made of many fine grain (0.1-100 micron) CBN. In addition to its high hardness and wear resistance, it also has high toughness, chemical inertia, red hardness and other characteristics, and can be grinded with diamond grinding wheel. It has excellent cutting performance in all aspects of cutting, and can achieve stable cutting at high temperature. It is especially suitable for processing various hardened and difficult-to-machine materials such as quenched steel, tool steel and chilled cast iron and so on. The cutters has the advantages of sharp cutting, good shape retention, high wear resistance, small wear per unit, fewer revisions, and is favorable for automatic processing. It is suitable for all cutting processes from roughing to finishing.
PCBN has most of the properties that CBN has, and overcomes the shortcomings of directional cleavage of CBN single crystal plane.
PCBN has many performance advantages:
1. High hardness. The hardness of PCBN tool is only next to that of diamond tool, which is much higher than that of cemented carbide and ceramic tool. Therefore, hardened steel, cast iron and cemented carbide with hardness of HRC60 or above can be machined.
2. High wear resistance. The wear resistance of PCBN cutters is much higher than that of cemented carbide and ceramics. The service life of PCBN tool is usually 3-5 times than that of ceramics cutters and 5-15 times than that of cemented carbide cutters.
3. High chemical inertia. PCBN is not easy to react with iron group elements and their alloys at the temperature of 1200 ~ 1300℃, which overcomes the chemical affinity between polycrystalline diamond tools and iron. PCBN has high oxidation resistance and has much less bonding and diffusion effect on various materials than cemented carbide.
4. High thermal stability. The heat resistance of PCBN can reach 1400 C, which is much higher than that of diamond cutters (700 ~ 800 ℃). It has been proved that the cutting temperature above 1100℃ can maintain high cutting performance, which is suitable for dry cutting.
5. High thermal conductivity. Among all kinds of cutting materials, the thermal conductivity of PCBN is 79.54W/(m.k), second only to diamond, which is much better than that of cemented carbide. With the increase of temperature, the thermal conductivity of PCBN will be improved.
6. Low friction coefficient. Compared with other cutting materials, PCBN has lower friction coefficient. The friction coefficient between PCBN and different materials is approximately 0.1-0.3, while that of cemented carbide is 0.4-0.6. With the increase of cutting speed and the decrease of the friction coefficient, the cutting force reduces and the phenomenon of chip sticking reduces.
Henan E-Grind Abrasives Co., Ltd., as cubic boron nitride manufacturers
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