Since both CBN crystals and diamond crystals are of the zinc blende type, and the lattice constants are similar, and the chemical bond types are the same, CBN has a hardness and compressive strength close to that of diamond, and because it is composed of N and B atoms, it has a ratio. Diamond is more thermally stable and chemically inert. PCBN is used in various fields of cutting with its superior cutting performance, especially in the cutting of high hardness materials and difficult materials. The main properties of PCBN tool materials are as follows:
(1) It has high hardness and wear resistance. The microhardness of CBN single crystal is HV 8000-9000, which is the second highest hardness material known at present. The hardness of PCBN composite sheet is generally HV3000-5000. Therefore, it has higher wear resistance than hard alloys and ceramics when processing high-hardness materials, and can reduce dimensional deviation or dimensional dispersion in processing of large parts, especially suitable for equipment with high degree of automation, and can reduce tool change. Adjust the knife assist time to make full use of its performance.
(2) It has high thermal stability and high temperature hardness. The heat resistance of CBN can reach 1400-1500 °C, and the hardness at 800 °C is the normal temperature hardness of Al2O3/TiC ceramic. Therefore, when the cutting temperature is high, the material to be processed will be softened, and the hardness difference between the tool and the tool will increase. It is beneficial to the cutting process and has little effect on the tool life.
(3) It has high chemical stability. CBN has high oxidation resistance and does not produce oxidation at 1000 °C. It does not react with iron-based materials at 1200-1300 °C, but it will hydrolyze with water at 1000 °C, resulting in a large amount of CBN is worn out, so care must be taken to select the type of cutting fluid when wet cutting with PCBN tools. Under normal circumstances, the wet cutting does not significantly improve the life of the PCBN tool, so the dry cutting method is often used when using the PCBN tool.
(4) Has good thermal conductivity. The thermal conductivity of CBN material is lower than that of diamond but much higher than that of hard alloy. With the increase of cutting temperature, the thermal conductivity of PCBN tool increases continuously, so the heat at the tip of the tool can be quickly transmitted, which is beneficial to the machining accuracy of the workpiece. Improvement.
(5) has a lower coefficient of friction. The coefficient of friction between CBN and different materials is between 0.1 and 0.3, which is much lower than the friction coefficient of cemented carbide (0.4 to 0.6), and slightly decreases with the increase of friction speed and positive pressure. Therefore, the low friction coefficient and excellent anti-adhesive ability make it difficult for CBN tools to form a retention layer or built-up edge when cutting, which is beneficial to the improvement of the surface quality.