① Because the surface coating material has high hardness, wear resistance and high temperature resistance. Therefore, compared with uncoated tools (blades), coated tools allow higher cutting speed, thus improving cutting efficiency; Or that tool life can be improve at the same cutting speed.
② Because the friction coefficient between the coated material and the processed material is small, the cutting force of the coated tool (blade) is smaller than that of the uncoated tool (blade).
(3) The coated cutter (blade) is used for machining, and the machined surface quality of the parts is better.
(4) Due to the comprehensive performance of coated tools (blades) and the versatility of coated cemented carbide blades, a coated cemented carbide brand blade has a wide range of applications. In the past, high temperature chemical vapor deposition (HTCVD) was used for the surface coating of cemented carbide tools. In the normal pressure or negative pressure deposition system, pure H2, CH4, N2, TiCl4, AlCl3, CO2 and other gases are evenly mixed according to the composition of the deposit, and then coated on the surface of cemented carbide blade at a certain temperature (generally 1000~ 1050℃), that is, TiC, TiN, TiCN and Al2O3 are deposited on the blade surface. Up to now, HTCVD is still the most widely used process. In addition to HTCVD, there is also plasma chemical vapor deposition (PCVD), which is another method to coat the surface of cemented carbide tools (blades). Because the coating temperature is low (700~800℃), the bending strength of the blade is reduced. Because the linear expansion coefficient of TiC is the closest to the matrix material, a thin layer of TiC is usually coated on the surface of the matrix first, and then TiN and Al2O3 are coated, such as TiC/TiN/TiN.
Later, various combinations of multilayer coatings were developed. The author investigated and counted the products of CVD coated cemented carbide blades in Sweden, Germany, USA, Japan, South Korea, Israel and China. Coating materials have the following combinations: TiCN/Al2O3, TiCN/TiC/TiN, TiCN/TiC/Al2O3, TiCN/Al2O3/TiN, TiCN /TiC/Al2O3/TiN. It can be seen that in recent years, TiCN or t in is often used as the bottom layer. Because the matrix cemented carbide has been improved, such as gradient structure, it is possible to use TiCN or TiN as the bottom layer. In addition, TiN coaTiNg is not suitable to be used alone, because compared with cemented carbide, the hardness of TiN is not greatly improved, and tin must be used in combination with TiC, TiCN, Al2O3 and so on. Early PVD coatings were all made by vacuum evaporation, and the film layer was often uneven and the combination with the substrate was not strong enough. Later, vacuum magnetron sputtering and vacuum ion plating were developed, and the results were good. At present, the latter two methods are mainly used for tool surface coating.
In the early days, PVD coating was only used for high-speed steel tools, and tin was almost the only coating material. Later, the coating process was improved, and a variety of coating materials and multilayer coatings were developed, which were also widely used in cemented carbide tools. The coating effect has made great progress than before. TiN coating materials are still in use, and newly emerging coating materials are TiAlN and AlTiN, which have better application effect than TiN.
Europe has the highest level of PVD coating technology, ahead of other countries and regions. Well-known manufacturers include CemeCon Coating Technology Co., Ltd. in Germany, OerlkonBalzers in Kanbar, PVT plasma vacuum technology in Germany and Unimerco in Denmark. Their PVD coating equipment and technology are advanced, coating materials are various, and coating tools and other products have good performance.
Some well-known foreign high-speed steel and cemented carbide tool factories have coated tools (blades), but coating equipment and technology are mostly purchased or cooperated from coating technology professional companies, rather than developed by themselves. It is reported that the PVD coating equipment of sandvik Company in Sweden and iscar Company in Israel are all purchased from Orientam Balchas Company. China should do the same, which is a good and fast road. For example, China Harbin No.1 Tool Factory cooperated with Germany PVT Company to establish Harbin Gongyi Puweite Coatings Co., Ltd. Olkin Cambal Chas Company has 77 coating centers all over the world, one center in Sujinhan, China, and tool manufacturers in neighboring cities and regions of China, where most of their coating products are coated. The coating equipment of Zhuzhou Cemented Carbide Factory in Hunan and Zigong Great Wall Cemented Carbide Factory in Sichuan are imported from abroad. Diamond films (10μm) can be deposited on the surface of cemented carbide or high speed steel tools by hot filament chemical vapor deposition, plasma jet chemical vapor deposition and flame combustion. The mechanical and physical properties of CVD diamond film are between natural diamond and hot-pressed polycrystalline PCD diamond, which can effectively process non-ferrous metals.
If the deposition time is increased, a thick film with a thickness greater than 0.5 mm can be deposited on the substrate or substrate (usually silicon wafer). Stripping the thick film from the substrate, cutting it into small pieces with a certain shape, and then brazing the small pieces on the substrate blade (usually cemented carbide tool) for later use. The application range of CVD thick film diamond tools is larger than that of thin film coated tools. In CIMT2007, many tool companies at home and abroad have CVD thin film diamond coated tool products, but only a few manufacturers have thick film products. Beijing Dongfang Tiandi superhard material tool company can produce diamond thick film tool products and has many years of experience. Thick film cutter has a wide range of applications, and can process all kinds of non-ferrous metals, non-metallic hard materials and particle reinforced composite materials. The Department of Physics of Wuhan University deposited a carbon nitride (CxNy) superhard coating film on the tool surface by DC reactive magnetron sputtering, with a thickness of only a few microns and a hardness of 40~50GPa. CxNy coated cutter can cut ferrous and nonferrous metals.
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The cutting performance of coated high speed steel and cemented carbide tools (blades) has been studied for a long time, and many scientific experiments have been carried out. Some experimental data are as follows:
① Under the same cutting conditions, the service life of coated tool blades is 3~5 times that of uncoated tools (blades). Under the same cutting conditions and the same tool life, the cutting speed of coated tools is 20~30% higher than that of uncoated tools.
② Under the same cutting conditions, the cutting force of coated cutter (blade) is smaller than that of uncoated cutter. Compared with uncoated blades, the main cutting force Fc can be reduced by 3%~4%, and the Fc of TiN or TiC/TiN coated blades can be reduced by about 6%, especially the feed force Ff and cutting depth force Fp. The reduction effect of Al2O3 coated blade and cutting force is close to that of TiN coated blade.
③ The author used CVD coated diamond thick film cutter to process silicon-aluminum alloy, all kinds of hard aluminum, lead brass, oxygen-free copper, titanium iodide and fiber reinforced and particle reinforced composites, and achieved good results. But the effect of ultra-precision tools is not as good as that of natural diamond tools.
④ The author used CxNy coated high-speed steel bit to drill holes in high-strength steel. Compared with uncoated bit, the service life of coated bit is increased by 7~9 times. Coating CxNy on other high-speed steel tools also has remarkable effect. In addition, coating CxNy on cemented carbide blades to turn steel is not ideal, and its service life is not longer than that of ordinary TiC coated cemented carbide blades.
Compared with developed countries, there is still a big gap between China's tool coating technology and the number of coated tools, and coated tools only account for about 20% of all tools. Among them, CNC machine tools and machining centers are widely used, but they are rarely used on ordinary non-CNC machine tools because of understanding problems and prices. Efforts should be made to improve the level of tool coating technology and application technology, vigorously promote the application of coated tools, and promote the improvement of cutting and mechanical manufacturing level.