Tool coating technology has developed rapidly and coated tools have been widely used. In 1969, Krupp and Sandvik of Sweden successfully developed the chemical vapor deposition (CVD) coating technology and introduced CVDTiC coated carbide insert products to the market. In the early 1970s, R. Runshan and A. Raghuran developed the physical vapor deposition (PVD) process and introduced PVDTiN high-speed steel cutting tools to the market in 1981. At that time, the CVD coating process temperature was about 1000°C, which was mainly used for the surface coating of carbide tools (blade); the PVD coating process temperature was below 500°C and 500°C, and was mainly used for the surface coating of high-speed steel tools. Later, CVD and PVD coating technologies continued to develop rapidly, with great progress in coating materials, coating equipment and processes, etc., and a multi-layered material coating technology was developed to make coated cutters (blade) The use of performance has been greatly improved. PVD coating technology was used in the past mainly for high-speed steel cutting tools. In recent years, with the rapid development of PVD coating technology, it has also been successfully used in cemented carbide tools (blade), occupying half of the field of carbide-coated tools (blade). . Nowadays, coated high-speed steel tools and coated carbide tools (blade) are widely used, accounting for more than 50% of the total use of all tools.
Advantages of coated cutters
Surface coating on a tough tool (blade) substrate, coating a thin layer (such as TiN, TiC, etc.) with high hardness, high wear resistance, high temperature resistant materials, making the tool (blade) comprehensive and good The overall performance. Uncoated high-speed steel hardness of only 62 ~ 68HRC (760 ~ 960HV), hard alloy hardness of only 89 ~ 93.5HRA (1300 ~ 1850HV); and the surface hardness after coating up to 2000 ~ 3000HV or more.
1 Because the surface coating material has high hardness and wear resistance, and high temperature resistance. Therefore, compared to uncoated tools (blade), coated tools allow higher cutting speeds, which improves cutting efficiency; or can increase tool life at the same cutting speed.
2 Because the coefficient of friction between the coating material and the material being processed is small, the cutting force of the coated tool (blade) is smaller than that of the uncoated tool (blade).
3 With a coated cutter (blade), the machined surface of the part is of good quality.
4 Because of the good overall performance of the coated cutter (blade), the coated carbide blade has better versatility. A coated carbide grade blade has a wider range of use.
Tool coating technology development and progress
The author visited the International Machine Tool Exhibition many times and collected a lot of information. He also listened to the technical reports of major tool companies and learned about the development and progress of surface coating technology for cutting tool products.
Advances in CVD Coating Technology
In the past, the surface coating of cemented carbide tools used high temperature chemical vapor deposition (HTCVD) process. In the atmospheric or negative pressure deposition system, the pure H2, CH4, N2, TiCl4, AlCl3, CO2 and other gases are uniformly mixed according to the composition of the sediment according to a certain ratio, and coated in turn to have a certain temperature (generally 1000 Carbide insert surface of ~1050°C), ie TiC, TiN, TiCN, Al2O3 or their composite coatings deposited on the surface of the insert. Until now, HTCVD is still the most used process. In addition to HTCVD, there is the Plasma Chemical Vapor Deposition (PCVD) process, which is another method of coating the surface of cemented carbide tools (blade). The coating process temperature is lower (700~800°C), so the bending strength of the blade is reduced. Because TiC and the matrix material have the closest linear expansion coefficients, TiC thin layers are usually coated on the surface of the substrate first, and TiN and Al2O3, such as TiC/TiN, TiC/Al2O3, TiC/TiCN/TiN, are coated on the outside.
Later, various combinations of multilayer coatings were developed. The author investigated and counted CVD-coated cemented carbide inserts from companies in Sweden, Germany, the United States, Japan, Korea, Israel, and China at numerous exhibitions. The coating materials had the following combinations: TiCN/Al2O3, TiCN/TiC /TiN, TiCN/TiC/Al2O3, TiCN/Al2O3/TiN, TiCN/TiC/Al2O3/TiN, TiCN/Al2O3/TiCN, TiN, TiC/TiCN/TiN, TiN/TiCN/TiN, etc. It can be seen that TiCN or TiN is mostly used as the bottom layer in recent years, because the substrate cemented carbide has been improved, for example, a gradient structure is used, and it is possible to use TiCN or TiN bottom. In addition, TiN coating should not be used alone, because the hardness of TiN is not much improved compared with cemented carbide, and TiN must be used in combination with TiC, TiCN, Al2O3, and so on.
Progress of PVD Coating Technology
In the early days, PVD coatings used "vacuum evaporation method", the film layer was often uneven, and the bond with the substrate was not solid enough. After the development of "vacuum magnetron sputtering method" and "vacuum plasma plating process", the effect was very good. Now the tool surface coating mainly uses the latter two methods.
In the early years, PVD coatings were used only for high-speed steel tools, and the coating material was almost exclusively TiN. Later, the coating process was improved, a variety of coating materials and multilayer coatings were developed, and a large number of applications were also made on carbide cutting tools. The coating effect has greatly improved over the past. TiN coating materials are still in use, and emerging coating materials are TiAlN and AlTiN, which are superior to TiN.
Europe has the highest level of PVD coating technology and is ahead of other countries and regions. Well-known manufacturers include Oerlkon Balzers, Germany's PVT Plasma Vacuum Technology, and Denmark's Unimerco. Their PVD coating equipment and technology are advanced, there are many varieties of coating materials, and coated cutters and other products have good performance.
Some well-known high-speed steel and carbide tool plants in foreign countries have coated cutters (blade) products, but the coating equipment and processes have been purchased from or cooperated with professional companies of coating technology rather than self-developed. It is reported that Sweden's Sandvik and Israel's Iska's PVD coating equipment was purchased from Oerlikon Balzers. China should also do this. This is a good and fast path. For example, China Harbin No. 1 Tool Factory cooperated with German PVT company to set up a Kazakhstan-based Powit Coating Co., Ltd. joint venture company. Oerlikon Balzers has 77 coating centers around the world, a center in Suzhou, Tianjin and Hanjiang, China, and tool manufacturers in China's neighboring cities and regions. The coating products are mostly coated at the above centers. The coating facilities of Zhuzhou Cemented Carbide Plant in Hunan and Changcheng Cemented Carbide Plant in Zigong, Sichuan were imported from abroad.
Application of New CVD Coating Technology in Superhard Material Coatings
Using "hot filament CVD method", "plasma jet CVD method", "flame combustion method" and other processes can deposit diamond thin film (10μm) on the surface of hard alloy or high-speed steel cutter. The mechanical and physical properties of the CVD diamond film lie between the natural diamond and the hot pressed polycrystalline PCD diamond, and can effectively process non-ferrous metals.
If the deposition time is increased, a thick film with a thickness of more than 0.5 mm can be deposited on the substrate or the substrate (usually a silicon wafer). The thick film is peeled from the substrate and cut into small pieces of a certain shape, and the small pieces are then brazed on a substrate blade (generally a carbide cutting tool). CVD thick-film diamond tools have a wider range of applications than thin-film-coated tools. At CIMT2007, many domestic and international tool companies have CVD thin film diamond coated tool products, but only a few manufacturers have thick film products. Beijing Dongfang Tiandi Superhard Material Tools Co., Ltd. can produce diamond thick film cutting tools and has many years of experience. Thick film tools have a wide range of applications and can process a variety of non-ferrous metals, non-metallic hard materials and particle reinforced composite materials.
Application of New PVD Coating Technology in Coating of Superhard Materials
The physics department of Wuhan University uses DC reactive magnetron sputtering to deposit a carbon nitride (CxNy) superhard coating film on the surface of the tool. The thickness is only a few microns and the hardness can reach 40~50GPa. CxNy coated cutters can cut black and non-ferrous metals.
Experimental data
The author has conducted long-term research on the cutting performance of coated high-speed steel and carbide tools (blade) and conducted many scientific experiments. Here are some of the experimental data as follows:
1 In the same cutting conditions, the service life of coated cutter blades is 3 to 5 times longer than uncoated cutters (blade). Under the same cutting conditions, the cutting speed of the coated tool is 20-30% higher than the uncoated tool at the same tool life.
2 Under the same cutting conditions, the cutting force of the coated cutter (blade) is less than that of the uncoated one. Compared with uncoated ones, the authors use coated TiC cemented carbide inserts to reduce the main cutting force Fc by 3%~4%, and the Fc of TiN or TiC/TiN coated inserts can be reduced by about 6%. The decrease of Ff and depth of cut force Fp is particularly significant. Al2O3 coated inserts and cutting forces are similar to TiN coated inserts.
3 I have used CVD coated diamond thick film tools, processed silicon aluminum alloy, a variety of hard aluminum, lead brass, oxygen free copper, titanium iodide and fiber reinforced and particle reinforced composite materials, etc., have achieved better results . However, the tool used for ultra-precision cutting is not as effective as a natural diamond tool.
4 I have used CxNy coated high-speed steel drills to drill holes in high-strength steels. Compared with uncoated drills, the service life of coated drills is 7 to 9 times longer. Applying CxNy to other HSS tools also has a significant effect. Once again, CxNy was coated on cemented carbide inserts for turning steel. The effect was not satisfactory. Its service life was no more than that of ordinary TiC-coated carbide inserts.
There is still a big gap between China's tool coating technology and industrial developed countries, and the number of coated tools is still very far away, accounting for only about 20% of all tools. Among them, CNC machine tools and machining centers use a lot more, and on ordinary non-CNC machine tools, they are pitifully low because of factors such as understanding problems and prices. We should strive to improve the level of tool coating technology and application technology, and promote the use of coated tools to promote the improvement of cutting and machining.