Cubic boron nitride (CBN) is a substance that does not exist in nature. It can be divided into single crystal and polycrystalline, that is, CBN single crystal and polycrystalline cubic boron nitride (Polycrystalline cubic bornnitride, referred to as PCBN). CBN is one of the isomers of boron nitride (BN), and its structure is similar to that of diamond.
PCBN (polycrystalline cubic boron nitride) is a polycrystalline material that sinters fine CBN materials through a bonding phase (TiC, TiN, Al, Ti, etc.) under high temperature and high pressure. Diamond tool material, it and diamond collectively referred to as superhard tool material. PCBN is mainly used to make knives or other tools.
PCBN tools can be divided into integral PCBN inserts and PCBN composite inserts sintered with cemented carbide. PCBN composite inserts are made by sintering a layer of PCBN with a thickness of 0.5 to 1.0mm on a cemented carbide with good strength and toughness. Its performance has both good toughness and high hardness and wear resistance. The problems of low bending strength and welding difficulties of CBN inserts are solved.
⑵ Main properties and characteristics of cubic boron nitride Although the hardness of cubic boron nitride is slightly lower than that of diamond, it is much higher than other high hardness materials. The outstanding advantage of CBN is that its thermal stability is much higher than that of diamond, which can reach above 1200°C (700-800°C for diamond). reaction. The main performance characteristics of cubic boron nitride are as follows.
① High hardness and wear resistance: The crystal structure of CBN is similar to that of diamond, and has similar hardness and strength to diamond. PCBN is especially suitable for processing high-hardness materials that could only be ground before, and can obtain better surface quality of workpieces.
② High thermal stability: The heat resistance of CBN can reach 1400-1500°C, which is almost 1 times higher than that of diamond (700-800°C). PCBN tools can cut high-temperature alloys and hardened steels at a speed 3 to 5 times higher than that of cemented carbide tools.
③Excellent chemical stability: It does not have a chemical effect with iron-based materials at 1200-1300°C, and it will not wear out as sharply as diamond. At this time, it can still maintain the hardness of cemented carbide; PCBN tools are suitable for cutting hardened steel Parts and chilled cast iron, can be widely used in high-speed cutting of cast iron.
④ Good thermal conductivity: Although the thermal conductivity of CBN is not as good as that of diamond, the thermal conductivity of PCBN is second only to diamond among various tool materials, and is much higher than that of high-speed steel and cemented carbide.
⑤ Low coefficient of friction: A low coefficient of friction can reduce the cutting force during cutting, reduce the cutting temperature, and improve the quality of the machined surface.
⑶ Application of Cubic Boron Nitride Cutting Tools Cubic boron nitride is suitable for finishing various difficult-to-cut materials such as hardened steel, hard cast iron, high-temperature alloy, hard alloy, and surface spraying materials. The machining accuracy can reach IT5 (the hole is IT6), and the surface roughness can be as small as Ra1.25~0.20μm.
Cubic boron nitride tool material has poor toughness and bending strength. Therefore, cubic boron nitride turning tools are not suitable for rough machining with low speed and high impact load; Severe built-up edge will occur in the case of metal, which will deteriorate the machined surface.
Types, properties and characteristics of ceramic tool materials and tool applications
Ceramic cutting tools have the characteristics of high hardness, good wear resistance, excellent heat resistance and chemical stability, and are not easy to bond with metal. Ceramic cutting tools occupy a very important position in CNC machining. Ceramic cutting tools have become one of the main cutting tools for high-speed cutting and difficult-to-machine materials processing. Ceramic cutting tools are widely used in high-speed cutting, dry cutting, hard cutting and cutting of difficult-to-machine materials. Ceramic knives can efficiently process high-hard materials that traditional knives cannot process at all, and realize "replacing grinding with a car"; the optimal cutting speed of ceramic knives can be 2 to 10 times higher than that of cemented carbide knives, thus greatly improving the production efficiency of cutting processing The main raw material used in ceramic tool materials is the most abundant element in the earth's crust. Therefore, the popularization and application of ceramic tools is of great significance to improve productivity, reduce processing costs, and save strategic precious metals, and will also greatly promote the development of cutting technology. progress. ⑴ Types of ceramic tool materials
The types of ceramic tool materials can generally be divided into three categories: alumina-based ceramics, silicon nitride-based ceramics, and composite silicon nitride-alumina-based ceramics. Among them, alumina-based and silicon nitride-based ceramic tool materials are the most widely used. The performance of silicon nitride-based ceramics is superior to that of alumina-based ceramics
⑵ Performance and characteristics of ceramic cutting tools
The performance characteristics of ceramic cutting tools are as follows.
① High hardness and good wear resistance: Although the hardness of ceramic tools is not as high as that of PCD and PCBN, it is much higher than that of cemented carbide and high-speed steel tools, reaching 93-95HRA. Ceramic tools can process high-hardness materials that are difficult to process with traditional tools, and are suitable for high-speed cutting and hard cutting.
② High temperature resistance and good heat resistance: Ceramic tools can still cut at high temperatures above 1200 °C. Ceramic knives have good high-temperature mechanical properties, and the oxidation resistance of A12O3 ceramic knives is particularly good. Even if the cutting edge is in a red-hot state, it can be used continuously. Therefore, ceramic tools can achieve dry cutting, which can save cutting fluid.
③ Good chemical stability: ceramic cutting tools are not easy to bond with metal, and are corrosion-resistant and chemically stable, which can reduce the bonding wear of cutting tools. ④ Low coefficient of friction: The affinity between ceramic tools and metal is small, and the coefficient of friction is low, which can reduce cutting force and cutting temperature.
⑶ ceramic knives have applications
Ceramics are one of the tool materials mainly used for high-speed finishing and semi-finishing. Ceramic cutting tools are suitable for cutting all kinds of cast iron (gray cast iron, ductile iron, malleable cast iron, chilled cast iron, high alloy wear-resistant cast iron) and steel (carbon structural steel, alloy structural steel, high strength steel, high manganese steel, quenched steel etc.), can also be used to cut copper alloys, graphite, engineering plastics and composite materials.
There are problems of low bending strength and poor impact toughness in the performance of ceramic tool materials, which are not suitable for cutting under low speed and impact load.
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