One, cutting tool coating
By chemical or physical methods on the cutter surface formed some film, causes the cutting tool to obtain excellent cutting performance, to meet the requirements of high speed machining; since the early 1970s hard coated tool since the advent, chemical vapor deposition (CVD) technique and regulating qi by physical vapour deposition (PVD) technology have been developed, in order to improve the performance of the tool to create a new chapter in the history of. Compared with uncoated cutting tools, the coating has obvious advantages: it can improve the cutting tool life effectively, improve the cutting efficiency, improve the machining accuracy and improve the surface quality of the workpiece.
Two, the characteristics of cutting tool coating:
1, the use of coating technology can not reduce the strength of the cutting tool conditions, greatly improve the surface hardness of the tool, the current can reach the hardness is close to 100GPa;
2 with the rapid development of coating technology, the chemical stability and high temperature oxidation resistance of the thin film are more outstanding, which makes it possible to make high speed machining.
3 lubricating film has good solid lubrication performance, can effectively improve the processing quality, but also suitable for dry cutting;
4 coating technology as the final step in the manufacturing process, has little effect on the accuracy of the tool, and can be used to repeat the coating process.

Three, commonly used coating
1, titanium nitride coating: titanium nitride (TiN) is a general-purpose PVD coating, can improve the hardness of the tool and has a high oxidation temperature. The coating is used for high speed steel cutting tools or forming tools to obtain very good results.
2, chromium nitride coating: CrN coating has good anti bonding properties, which make it easy to produce the product of the processing of the chip becomes the first choice coating. After coating this virtually invisible coating, the machining performance of high speed steel or hard alloy tools and forming tools will be greatly improved.
3. Diamond coated CVD diamond coating can deliver optimal performance for non ferrous metal material processing tool, machining of the graphite and metal matrix composite (MMC), high silicon aluminum alloy and many other high abrasion materials ideal coating (Note: pure diamond coated tools cannot for pieces of steel processing, because processing steel parts will produce a large number of cutting heat, and cause a chemical reaction, the destruction of the adhesion between the coating and the tool layer).
4, the addition of carbon elements in the coating of titanium carbide (TiCN) can improve the hardness of the cutting tool and obtain better surface lubrication, which is an ideal coating for high speed steel cutting tools.
5, the alumina layer formed in the TiAlN /:TiAlN coating (AlTiN / AlTiN) can effectively improve the high temperature working life of the tool. The coating is mainly used for dry or semi dry cutting of hard alloy tool. According to the different proportion of coating in the aluminum and titanium, AlTiN coating can provide higher than TiAlN coating surface hardness, therefore it is high speed machining field and a feasible coating of choice.
Four: coating technology and knowledge of cutting tool coating
1, the titanium carbide (TiCN) coating has higher hardness than that of titanium nitride (TiN) coating. With the increase of carbon content, the hardness of TiCN coating increased by 33%, and the change of its hardness was about Hv3000 - 4000 (depending on the manufacturer).
2, CVD diamond coating: the surface hardness of up to CVD Hv9000 diamond coating on the cutting tool has been more mature, compared with the PVD coated tools, CVD diamond coated tool life increased by 10 - 20 times. The high hardness of diamond coated cutting tool makes the cutting speed can be increased by 2 - 3 times than that of the uncoated tool, which makes the temperature of CVD diamond oxidation temperature is the temperature value of the coating. The higher the oxidation temperature, the better the cutting process in the high temperature condition. Although the normal temperature of TiAlN coating may be lower than that of TiCN coating, it is proved that it is much more effective than TiCN in high temperature processing. TiAlN coating in high temperature can still maintain the hardness of the reason is that the tool and chip between the formation of NC micro signal cncdar a layer of alumina, alumina layer can heat from the cutting tool to the workpiece or chip. Compared with high-speed steel cutting tools, carbide cutting tools are usually higher, which makes the TiAlN become the preferred coating of cemented carbide tools, carbide drill and end mill are usually used in this kind of PVDTiAlN coated carbide coated tools become a good choice for non-ferrous metals and non-metallic materials cutting.
3, the hard film on the surface of the cutter of the material have requirements are as follows: high hardness, good wear resistance; (2) and chemical properties of stability, no chemical reaction with the workpiece material; the heat resistant to oxidation, low friction coefficient, and the matrix firmly attached. Single coating material is difficult to meet the technical requirements of the above. The development of coating material, which has been developed from the initial single TiN coating, TiC coating, has experienced the development of TiC A12O3 composite coating, TiN, TiAlN, and TiCN, TiN, NbN / CN, TiN /, etc..
4, in the process of coating tool manufacturing, the coating is chosen, in which the coating is the most directly related to the coating's hardness, wear resistance, high temperature oxidation resistance, lubrication and anti bonding properties. Oxidation temperature is the temperature of the coating, the higher the oxidation temperature, the better the cutting process in the high temperature condition. Although the normal temperature of TiAlN coating may be lower than that of TiCN coating, it is proved that it is much more effective than TiCN in high temperature processing. TiAlN coating can still maintain its hardness at high temperature because of the formation of a layer of alumina between the cutting tool and chip, the alumina layer can heat from the tool to the workpiece or chip. Compared with high-speed steel cutting tools, the cutting speed of cemented carbide tools is usually higher, which makes the TiAlN become the first choice of cemented carbide tools, carbide drill and end milling cutter is usually used in this PVDTiAlN coating.
5, from the point of view of application technology: in addition to the cutting temperature, cutting depth, cutting speed and cooling liquid are likely to have an impact on the application of tool coating.
Five, commonly used coating material progress and super hard coating technology
The most mature and most widely used technology of hard coating materials is TiN. At present, the use of TiN coated high speed steel cutting tool has accounted for 70% of the high speed steel cutting tools, and some of the non - heavy wear of the 50% - 90%. Because of the high technical requirements of modern metal cutting tools, the TiN coating is increasingly unable to adapt. The oxidation resistance of the TiN coating is poor, and when the temperature reaches 500, the film is obviously oxidized, and it can not meet the need of the. TiC has higher microhardness, so the wear resistance of the material is better. At the same time, it has a strong adhesion to the substrate, and the TiC is used as the substrate in the coating.
The development of TiCN and TiAlN, also made the performance of the coated tool on a level. TiCN can reduce the internal stress of the coating, improve the toughness of the coating, increase the thickness of the coating, prevent the spread of the crack, and reduce the cutting edge of the cutting tool. TiCN is set as the main wear layer of the coating tool, which can significantly improve the life of the tool. TiAlN good chemical stability, oxidation wear, processing of high alloy steel, stainless steel, titanium alloy, nickel alloy, tin coated tool than increased life expectancy 3 - 4 times. In the TiAlN coating, if there is a high Al concentration, the coating surface can generate a very thin non product A12O3, a layer of hard material inert protective film, which can be used for high speed machining. Nitrogen doped titanium carbide TiCNO has a very high microhardness and chemical stability, which can produce the equivalent of TiC ten A12O3 composite coating.
In the above hard thin film materials, the micro hardness of HV can exceed 3 kinds of 50GPa: diamond film, cubic boron nitride CBN, carbon nitride.
The temperature requirement of a number of deposited diamond films is 900, 600, and so the technology is often used to deposit diamond films on the surface of cemented carbide tools. Commercialization of diamond carbide tools is a major achievement in recent years.
CBN in the field of hardness and thermal conductivity is second only to diamond, the thermal stability is excellent, in the atmosphere of heating up to 1000 C and no oxidation. CBN has a very stable chemical properties for the iron family metal, and it can be widely used in the processing and grinding of steel products. CBN coating not only has excellent wear resistance, but also can in the very high cutting speed cutting heat resistant steel, titanium alloy, quenched steel, cutting high hardness of chilled cast iron rolls, doped carbon quenched materials and the tool wear very serious Si - Al alloy and other. The method of synthesizing CBN thin film by low pressure gas is mainly PVD and CVD. CVD including chemical transport PCVD, hot filament assisted heating PCVD, ECR, CVD; PVD is reactive ion beam plating, reactive steam plating, laser evaporation and ion beam assisted deposition method. CBN synthesis technology, in the basic research and application technology are still a lot of work to do, including the reaction mechanism and film forming process, plasma diagnostics and mass spectrometry analysis, the determination of the optimum process conditions, the development of high-efficiency equipment, etc..
The carbon nitride may have the hardness to reach or exceed the diamond. The success of the synthesis of carbon nitride is a very good example of molecular engineering. As a super hard material of carbon nitride, it is expected that there are many other valuable physical and chemical properties, and the research of carbon tetrachloride has become a hot topic in the world.
(Note: CVD: chemical coating; PVD: physical coating)