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1. tool materials should have basic properties

The choice of tool material has a great influence on tool life, machining efficiency, machining quality and machining cost. Cutting tool to withstand high pressure, high temperature, friction, impact and vibration and other effects. Therefore, the tool material should have the following basic properties:

(1) Hardness and wear resistance. The hardness of the tool material must be higher than the hardness of the workpiece material, which is generally required to be above 60HRC. The higher the hardness of the tool material, the better the wear resistance.

(2) strength and toughness. The tool material should have high strength and toughness, so as to withstand the cutting force, impact and vibration, to prevent the tool brittle fracture and chipping.

(3) Heat resistance. The tool material has good heat resistance, can withstand high cutting temperature, and has good oxidation resistance.

(4) Process performance and economy. Tool materials should have good forging performance, heat treatment performance, welding performance; grinding performance, etc., and to pursue a high performance-to-price ratio.

Types, properties, characteristics and applications of 2. tool materials

1. Diamond tool material

Diamond is an alloisomer of carbon, which is one of the harder materials found in nature. Diamond tools have high hardness, high wear resistance and high thermal conductivity, and are widely used in the processing of non-ferrous and non-metallic materials. Especially in aluminum and silicon aluminum alloy high-speed cutting, diamond tool is difficult to replace the main cutting tool varieties. Diamond cutting tools, which can achieve high stability and long life, are indispensable and important tools in modern CNC machining.

(1) Types of diamond tools

Natural diamond tools: natural diamond as a cutting tool for hundreds of years of history, natural single crystal diamond tools after fine grinding, cutting edge can be extremely sharp, cutting edge radius of up to 0.002μm, can achieve ultra-thin cutting, can be processed out of high precision and very low surface roughness, is recognized, ideal and can not be replaced by ultra-precision machining tools.

② PCD diamond tools: natural diamond is expensive, diamond is widely used in cutting or polycrystalline diamond (PCD), since the early 1970 s, the use of high temperature and high pressure synthesis technology to prepare polycrystalline diamond (Polycrystauine diamond, referred to as PCD blade developed successfully, in many cases natural diamond tools have been replaced by artificial polycrystalline diamond. PCD is rich in raw materials, and its price is only one tenth to one tenth of that of natural diamond. PCD tool can not be extremely sharp cutting edge, the surface quality of the workpiece is not as good as natural diamond, now the industry can not easily manufacture with chip breaker PCD blade. Therefore, PCD can only be used for fine cutting of non-ferrous metals and non-metals, and it is difficult to achieve ultra-precision mirror cutting.

③ CVD diamond tools: Since the late 1970 s to early 1980 s, CVD diamond technology has emerged in Japan. CVD diamond refers to the synthesis of diamond films on heterogeneous substrates (such as cemented carbide, ceramics, etc.) by chemical vapor deposition (CVD). CVD diamond has exactly the same structure and characteristics as natural diamond. The performance of CVD diamond is very close to that of natural diamond, which has the advantages of natural single crystal diamond and polycrystalline diamond (PCD), and overcomes their shortcomings to a certain extent.

The performance characteristics of diamond tools

Extremely high hardness and wear resistance: Natural diamond is a harder substance that has been found in nature. Diamond has a very high wear resistance, processing high hardness materials, the life of the diamond tool for the carbide tool lO ~ 100 times, even up to several hundred times.

② has a very low coefficient of friction: the coefficient of friction between diamond and some non-ferrous metals is lower than that of other tools, the coefficient of friction is low, the deformation during processing is small, and the cutting force can be reduced.

The cutting edge is very sharp: the cutting edge of the diamond tool can be very sharp, and the natural single crystal diamond tool can be as high as 0.002 ~ 0.008μm, which can be used for ultra-thin cutting and ultra-precision machining.

4 has a high thermal conductivity: diamond thermal conductivity and thermal diffusion rate is high, the cutting heat is easy to dissipate, the tool cutting part of the low temperature.

⑤ has a low thermal expansion coefficient: the thermal expansion coefficient of diamond is several times smaller than that of cemented carbide, and the change of tool size caused by cutting heat is very small, which is particularly important for precision and ultra-precision machining with high dimensional accuracy requirements.

Application of diamond tools

Diamond tools are mostly used for fine cutting and boring of non-ferrous metals and non-metallic materials at high speed. Suitable for processing a variety of wear-resistant non-metal, such as glass fiber reinforced plastic powder metallurgy blank, ceramic materials, etc.; a variety of wear-resistant non-ferrous metals, such as a variety of silicon aluminum alloy; a variety of non-ferrous metal finishing.

The disadvantage of diamond tools is poor thermal stability, cutting temperature of more than 700 ℃ ~ 800 ℃, will completely lose its hardness; in addition, it is not suitable for cutting ferrous metals, because the diamond (carbon) at high temperature easily with iron atoms, the carbon atoms into graphite structure, the tool is easily damaged.

2. Cubic boron nitride tool material

The second superhard material, cubic boron nitride (CBN), synthesized by a method similar to the diamond manufacturing method, is second only to diamond in hardness and thermal conductivity, has excellent thermal stability, and does not oxidize when heated to 10000C in the atmosphere. CBN has extremely stable chemical properties for ferrous metals and can be widely used in the processing of steel products.

⑴ Types of cubic boron nitride cutting tools

Cubic boron nitride (CBN) is a substance that does not exist in nature. It can be divided into single crystal and polycrystalline, namely CBN single crystal and polycrystalline cubic boron nitride (Polycrystalline cubic bornnitride, referred to as PCBN). CBN is one of the alloisomers of boron nitride (BN) and is structurally similar to diamond.

PCBN (polycrystalline cubic boron nitride) is in high temperature and high pressure will be fine CBN material by bonding phase (TiC, TiN, Al, Ti, etc.) sintered together of polycrystalline material, is currently the use of synthetic hardness second only to diamond tool material, it and diamond collectively referred to as superhard tool material. PCBN is mainly used to make knives or other tools.

PCBN cutting tools can be divided into integral PCBN blades and PCBN composite blades sintered with cemented carbide.

PCBN composite blade is a layer of 0.5~1.0mm thick PCBN sintered on cemented carbide with good strength and toughness. Its performance has good toughness and high hardness and wear resistance. It solves the problems of low bending strength and welding difficulties of CBN blade.

⑵ The 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 that of other high hardness materials. The outstanding advantage of CBN is that the thermal stability is much higher than that of diamond, which can reach more than 1200 ℃ (diamond is 700~800 ℃). Another outstanding advantage is that it is chemically inert and does not react with iron at 1200~1300 ℃. The main performance characteristics of cubic boron nitride are as follows.

① High hardness and wear resistance: CBN crystal structure is similar to diamond, with similar hardness and strength to diamond. PCBN is especially suitable for processing high hardness materials that can only be ground before, and can obtain better surface quality of the workpiece.

It has high thermal stability: the heat resistance of CBN can reach 1400~1500 ℃, which is almost l times higher than that of diamond (700~800 ℃). PCBN tool can be used than carbide cutting tool 3~5 times higher speed high-temperature alloy and hardened steel.

3 excellent chemical stability: with iron materials to 1200-1300 ℃ also does not have a chemical effect, not as sharp as diamond wear, then it can still maintain the hardness of cemented carbide; PCBN tool is suitable for cutting hardened steel parts and chilled cast iron, can be widely used in high-speed cutting of cast iron.

4 has good thermal conductivity: although the thermal conductivity of CBN can not catch up with diamond, but in all kinds of tool materials, the thermal conductivity of PCBN is second only to diamond, which is much higher than that of high speed steel and cemented carbide.

⑤ has a lower coefficient of friction: low coefficient of friction can lead to the cutting force is reduced, the cutting temperature is reduced, and the quality of the machined surface is improved.

⑶ Cubic Boron Nitride Tool Application

Cubic boron nitride is suitable for finishing all kinds of hardened steel, hard cast iron, high temperature alloy, hard alloy, surface spraying materials and other difficult cutting materials. The machining accuracy can reach IT5 (hole is IT6), and the surface roughness value can be as small as Ra1.25 ~ 0.20 μm.

Cubic boron nitride tool material toughness and bending strength is poor. Therefore, the cubic boron nitride turning tool should not be used for low speed, impact load roughing; at the same time not suitable for cutting plastic materials (such as aluminum alloy, copper alloy, nickel-based alloy, plastic steel, etc.), because the cutting of these metals will produce serious chip, and the processing surface deterioration.

3. Ceramic tool material

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 play a very important role in CNC machining, and ceramic cutting tools have become one of the main cutting tools for high-speed cutting and difficult-to-machine material processing. Ceramic tools are widely used in high-speed cutting, dry cutting, hard cutting and machining of difficult-to-machine materials. Ceramic cutting tools can process high-hard materials that traditional cutting tools cannot process at all, realizing "turning instead of grinding". The better cutting speed of ceramic cutting tools can be 2 ~ lO times higher than that of cemented carbide cutting tools, thus greatly improving the cutting production efficiency. The main raw materials used in ceramic cutting tool materials are rich elements in the earth's crust, the popularization and application of ceramic cutting tools is of great significance to improve productivity, reduce processing costs and save strategic precious metals, and will greatly promote the progress of cutting technology.

(1) Types of ceramic tool materials

Ceramic tool material types can generally be divided into alumina based ceramics, silicon nitride based ceramics, composite silicon nitride alumina based ceramics three categories. Among them, alumina-based and silicon nitride-based ceramic tool materials are widely used. The performance of silicon nitride based ceramics is superior to that of alumina based ceramics.

The performance and characteristics of ceramic cutting tools

① High hardness, good wear resistance: Although the hardness of ceramic tools is not as high as PCD and PCBN, it is much higher than carbide and high-speed steel tools, reaching 93-95HRA. Ceramic tools can process high-hard materials that are difficult to process with traditional tools, and are suitable for high-speed cutting and hard cutting.

High temperature resistance, good heat resistance: ceramic tools can still be cut at high temperatures above 1200 ℃. Ceramic tools have good high temperature mechanical properties, A12O3 ceramic tool oxidation resistance is particularly good, the cutting edge even in the red hot state, can be used continuously. Therefore, the ceramic tool can realize dry cutting, so that cutting fluid can be omitted.

The chemical stability is good: the ceramic tool is not easy to bond with the metal, and corrosion resistance, good chemical stability, can reduce the adhesive wear of the tool.

Low friction coefficient: ceramic tools and metal affinity is small, low friction coefficient, can reduce the cutting force and cutting temperature.

⑶ Ceramic knife has application

Ceramic is one of the tool materials mainly used for high-speed finishing and semi-finishing. Ceramic 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, hardened steel, etc.), can also be used to cut copper alloy, graphite, engineering plastics and composite materials.

The performance of ceramic tool material has the problems of low bending strength and poor impact toughness, which is not suitable for cutting at low speed and impact load.