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First, the development of superhard tool materials
Superhard tool material refers to natural diamond and synthetic diamond and CBN (cubic boron nitride) with similar hardness and performance. Since natural diamonds are relatively expensive, artificial polycrystalline diamond (PCD), polycrystalline cubic boron nitride (PCBN), and composites thereof are mostly used in production.
As early as the 1950s, the United States used synthetic diamond micropowder and CBN micropowder to form large-sized polycrystalline blocks as tool materials under the action of high temperature, high pressure, catalyst and binder. Since then, South Africa's DEBEEM, the former Soviet Union and Japan have also been successfully developed. In the early 1970s, diamond or CBN and cemented carbide composite sheets were introduced. They were sintered or pressed on a cemented carbide substrate with a layer of 0.5 MM to 1 MM PCD or PCBN to solve the superhard tool material. The problems of low bending strength, difficulty in setting welding, etc., make the application of superhard tools into the practical stage.
The research and application of superhard tool materials in China began in the 1970s, and in 1970, the first grinding wheel factory of the first superhard materials and products in China was built in Guiyang, from 1970 to 1990. In the middle of the year, the annual output of superhard materials increased from only 460,000 carats to 35 million carats. Around the 1990s, many superhard material production professional factories introduced complete sets of superhard material synthesis equipment and technology from abroad, which enabled the production to be rapidly improved. By 1997, the annual output of synthetic diamond in China had reached 500 million carats. With an annual output of 8 million carats, CBN ranks first in the world in the production of superhard materials.
Diamond has extremely high hardness and wear resistance, and its microhardness is up to 10000 HV, making it the hardest material in tool materials. At the same time, its friction coefficient is small, it has no affinity with non-ferrous metals, the chips are easy to flow out, the thermal conductivity is high, it is not easy to produce built-up edge when cutting, the surface quality is good, and it can effectively process non-ferrous metal materials and non-metal materials, such as Non-ferrous metals such as copper and aluminum and their alloys, ceramics, sintered cemented carbides, various fiber and particle reinforced composites, plastics, rubber, graphite, glass and various wear-resistant woods (especially solid wood and plywood) Such as composite materials).
The disadvantage of diamond is poor toughness and low thermal stability. It is easy to carbonize at 700 to 800 ° C, so it is not suitable for processing steel materials. Since iron atoms are easily reacted with carbon atoms at high temperatures, they are converted into a graphite structure. In addition, when it is used to cut a nickel-based alloy, it also wears out quickly.
Second, the main varieties and applications of superhard tools
At present, the main types of superhard tool materials that have been applied or are being tested in the world are as follows.
1. Natural and synthetic large single crystal diamond
Single crystal diamonds are available in both natural diamond (ND) and synthetic diamond. Single crystal diamond used to make cutting tools must be large particles (mass greater than 0.1G, minimum diameter not less than 3MM). ND is the hardest material among minerals currently known. Its microhardness is up to 10000HV, its wear resistance is good, its cutting edge is very sharp, its blade roughness is small, its friction coefficient is low, its anti-adhesiveness is good, its thermal conductivity High, it is not easy to stick to the knife and produce built-up edge when cutting, and the surface quality is good. The hardness, anti-wear and corrosion resistance and chemical stability of natural diamond ensure the long life of the tool, ensure long-term normal cutting, and reduce the influence of tool wear on the machined parts; its higher thermal conductivity Reduces cutting temperature and thermal deformation of parts. The excellent properties of natural large single crystal diamonds meet most of the requirements for precision and ultra-precision cutting tool materials. Although they are expensive, they are still recognized as ideal precision and ultra-precision cutting tool materials. Can be widely used in processing nuclear reactors and Other high-tech fields of various mirrors, missiles and rockets in the ground gyro, computer hard disk substrate, accelerator electron gun ultra-precision processing and traditional watch parts, jewelry, pen, colored Precision machining of metal decorative parts. In addition, it can also be used to make medical tools. The disadvantage of ND is that it is chemically reacted when it comes into contact with iron elements. It is carbonized (ie, graphitized) at 700-800 ° C, and is generally not suitable for processing steel materials.
2. Polycrystalline diamond and polycrystalline diamond composite blades
PCD is also called diamond sintered body, which is a polycrystalline material obtained by polycrystallizing many diamond single crystal powders by a metal bond agent such as cobalt under high temperature and high pressure. Although its hardness is slightly lower than that of natural single crystal diamond, it is a polymerization of randomly oriented diamond grains, which is isotropic and has no cleavage surface. Therefore, it does not have a large difference in strength, hardness and wear resistance on different crystal faces like large single crystal diamond, and is brittle due to the presence of a cleavage surface. When cutting, the cutting edge is not very sensitive to accidental damage, and has strong anti-wear ability. It can keep sharp cutting edges for a long time. It can use high cutting speed and large backing knife during processing. It is 10 to 50 times higher than WC-based cemented carbide tools, and the source of PCD raw materials is rich. Its price is only one-tenth to one-tenth of ND. PCD tools have extremely high hardness and long life, and low friction. Coefficients, sharp edges, excellent thermal conductivity and low coefficient of expansion have become a high-performance alternative to traditional WC-based carbide tools. Polycrystalline diamond compact (PDC) tool materials were developed on the basis of PCD research. Cemented carbide as a matrix material for PCD has both good toughness and hardness, as well as solderability and compatibility with PCD. Therefore, it has both the hardness and wear resistance of diamond, and the advantages of toughness and weldability of cemented carbide.
3, CVD diamond
CVD diamond is prepared at low pressure, which is different from large single crystal diamond, while PCD and PDC are synthesized under high temperature and high pressure. There are three types of CVD diamonds: the first is a CVD diamond coating deposited on a suitable substrate (including a diamond-like DLC coating); the second is an unsupported CVD diamond thick film with a thickness of 1 MM; the third is A CVD diamond single crystal film or a quasi-single crystal film epitaxially grown on a diamond seed. Since CVD diamond is pure diamond that does not contain any metal catalyst, its thermal stability is close to that of natural diamond. Like high-temperature and high-pressure synthetic polycrystalline diamond, CVD polycrystalline diamond grains are also disorderly arranged, without brittle cleavage planes and isotropic. Compared with PCD and PDC tools, CVD coated tools have the advantages of complex tool shape, low cost and multiple blades. However, there is also a defect that the bonding strength between the diamond coating and the substrate is low and the delamination of the CVD diamond coated edge is easy to be peeled off.
So far, the application market of CVD diamond is still not big; the main advantage of CVD diamond thick film compared with PDC is that its thermal stability is good, the disadvantage is that the cohesive strength between the grains is low, the internal stress is large, the relative brittleness is large and not Electrical conductivity. In particular, the lack of electrical conductivity hinders its application in electrical discharge (EDM) cutting and polishing processes. This technology has been widely used in the diamond tool processing industry, especially in the production and finishing of woodworking tools.
4, polycrystalline cubic boron nitride
At present, polycrystalline cubic boron nitride (PCBN) tools on the market can be divided into three types according to composition and manufacturing methods: integral polycrystalline cubic boron nitride cutter, polycrystalline cubic boron nitride composite sheet and electroplated cubic boron nitride cutter. It has high hardness and wear resistance, high heat resistance, good chemical stability and thermal conductivity, and low friction coefficient. PCBN has similar structure and properties to PCD and PDC cutter materials, but Wear resistance is worse than PCD and PDC. However, PCBN has good chemical resistance and exhibits good thermal stability at a high temperature of 1200 °C. At present, 50% of PCBN tools are used in the automotive industry, including for machining engine casings, brake discs, drive shafts, cylinder bores, engine inlet and outlet valve seats, etc. In addition, about 20% are used for heavy equipment (such as rolls). Processing. In recent years, with the rapid development of computer 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 is also becoming more and more popular. At the same time, many advanced cutting concepts have been introduced, such as High-speed cutting, hard machining, car grinding, dry cutting, etc. PCBN tool materials have become an indispensable tool material in modern cutting.
Its role is to fasten the outer part of the exposed cap, to prevent moisture or other corrosive substances
This prevents moisture or other corrosive substances from entering the inside, thus playing the role of rust prevention, thus improving its own and the use of the connection time.
Abstract The development and application of superhard tool materials. First, the development of superhard tool materials Superhard tool material refers to natural diamond and synthetic diamond and CBN (cubic boron nitride) with similar hardness and performance. Due to the natural diamond price ratio...