PCBN is based on cemented carbide, and a layer of cubic boron nitride (CBN) single crystal fine powder (0.5~1.6mm thick) is placed on top of it, and the binder is subjected to high temperature (1400~ 2600°C) and high pressure (7~9Gpa) to press the polycrystalline tool material.
Due to the small particle size of single crystal CBN, and the existence of "cleavage planes" that are easy to split, single crystal CBN cannot be directly used to manufacture cutting tools. Therefore, most of the cutting tools used in the industry are PCBN.
1. Characteristics of PCBN
CBN has high hardness and excellent wear resistance
CBN is artificially synthesized, its hardness is second only to that of diamond, and the grain hardness can reach HV8000~ HV9000, which is much higher than that of ceramics and cemented carbide. The hardness of the PCBN composite sheet (usually HV3000 ~ HV5000) mainly depends on the content of CBN, generally the content of CBN is between 40% and 95%. The hardness of PCBN increases with the increase of CBN content. The relationship between wear resistance and CBN content is not a monotonic relationship, and there are different optimal values under different processing conditions. When machining heavy steel molds, when the CBN content is about 55%, the tool is the most wear-resistant.
CBN has high thermal stability
The heat-resistant temperature of cubic boron nitride is as high as 1400 ~ 1500 ℃, which is almost double that of diamond (700-800 ℃). Cubic boron nitride is transformed from cubic crystal to hexagonal crystal and begins to soften when it is above 1370 ° C. It can be used to make tools for high-speed cutting of superalloys, and its cutting speed is 3-5 times higher than that of cemented carbide tools.
Cubic boron nitride has strong chemical stability
Cubic boron nitride is a very chemically inert substance. In neutral reducing gas medium, it is stable to acid and alkali. It only reacts with carbon at 2000 °C, and does not react with iron group materials at 1200~1300 °C. react. The bonding and diffusion effects of cubic boron nitride and various materials are much smaller than those of cemented carbide, and can be used to cut steel materials that diamond cannot cut.
Cubic boron nitride has excellent thermal conductivity
The thermal conductivity of cubic boron nitride is 79.54w/m.k, second only to diamond (146.5w/m.k). And with the increase of temperature, the thermal conductivity of cubic boron nitride gradually increases, which is beneficial to the temperature control of the cutting area and the reduction of the diffusion wear of the tool.
Cubic boron nitride has a lower coefficient of friction
The friction coefficient between PCBN and different materials is 0.1~0.3. The lower friction coefficient reduces the cutting force, reduces the cutting temperature, and is not easy to generate chips, which is beneficial to improve the surface quality of the processed material.
The cubic boron nitride tool can be regrind
The polycrystalline cutting edge of the PCBN tool adopts advanced inlay technology, and the inlay is firm. The synthetic diamond resin grinding wheel with a grain size of 180-240 can be used for sharpening on a common tool grinder, which is convenient for users and reduces tool costs.
2. Classification of polycrystalline cubic boron nitride tools
Polycrystalline cubic boron nitride (PCBN) cutting tools can be divided into integral polycrystalline cubic boron nitride sintered body (referred to as PCBN sintered body) and polycrystalline cubic boron nitride composite sheet (referred to as PCBN composite blade) and Electroplated cubic boron nitride cutting tools are most widely used with PCBN composite inserts.
3.Application of polycrystalline cubic boron nitride cutting tools
PCBN is composed of numerous small and disorderly arranged CBN single crystals, with no cleavage planes and no macroscopic directionality, which will greatly reduce the effect of splitting, and will continuously expose fresh crystals as the cutting tool wears. . PCBN has similar structure and properties to PCD and PCD tool materials, but its wear resistance is worse than that of PCD and PDC. Since PCBN has good chemical corrosion resistance and shows good thermal stability at a high temperature of 1200 ° C, the relatively high temperature of the tool tip will not have any adverse effect on it, on the contrary, it can also be used in cutting hard When used in high-quality iron alloys, it can accelerate cutting.
With the continuous development of cutting technology, cubic boron nitride tools are widely used in the processing of high-hardness and difficult-to-machine materials.
1) The cubic boron nitride tool can be turned instead of grinding, and hard turning of high hardness and difficult-to-machine materials
Because cubic boron nitride tools have high hardness and wear resistance, red hardness. Therefore, the overall polycrystalline cubic boron nitride tool can be used for hard turning of hard-to-machine materials with high hardness.
(2) Suitable for high-speed and ultra-high-speed cutting
PCBN tools are most suitable for high-speed cutting of cast iron, hardened steel and other materials. From the relationship between the tool flank wear and the cutting distance when the PCBN tool cuts cast iron and hardened steel, it can be seen that when the cutting speed exceeds a certain limit, the higher the cutting speed, the smaller the PCBN tool flank wear speed, that is, high speed. The life of the tool under cutting is rather high, which is especially suitable for modern high-speed cutting.
(3) Dry cutting
The cubic boron nitride tool uses dry cutting to reduce environmental pollution. The use of coated or ceramic tools requires wet cutting, and iron filings are not easy to clean. The use of cubic boron nitride cutting tools can not only cut high-hardness cast iron with a large margin, without adding cutting fluid, it can not only ensure the hygiene of the site, but also recycle the iron scraps.
(4) Suitable for automatic processing and difficult-to-machine material processing
PCBN tools have high hardness and wear resistance, and can process high-precision parts for a long time at high cutting speeds, greatly reducing the number of tool changes and the time spent on tool wear compensation downtime. Therefore, PCBN tools are very suitable for CNC machine tools and processing equipment with a high degree of automation, and can fully utilize the high efficiency of the equipment.
4.the life of polycrystalline cubic boron nitride tool
The life of PCBN tools is 3-5 times that of ceramic tools and 5-15 times that of carbide tools. High wear resistance and long life greatly improve the machining accuracy of the workpiece, reduce the number of tool changes and sharpening, and improve work efficiency.
In recent years, with the rapid development of CNC (computer numerical control) processing technology and the widespread use of CNC machine tools, the application of PCBN tools that can achieve high efficiency, high stability and long life processing has become increasingly popular. Machining concepts, such as high-speed cutting, hard machining, turning grinding, dry cutting, etc. PCBN tool material has become an indispensable and important tool material in modern machining.