The development trend of modern cutting tool coati

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The development trend of modern cutting tool coating technology

the development of manufacturing industry cannot be separated from cutting tools. Modern cutting tools have become one of the key factors to improve the technical level of manufacturing industry. The requirements of cutting processing are increasing day by day. High speed, high precision, high efficiency, intelligence and environmental protection have become the pursuit goals of cutting processing; The energy level of the processed material continues to improve; High strength and ultra-high strength materials, high toughness, difficult to cut and other materials are emerging in endlessly; Under the new situation, special requirements for machining are put forward, such as hard machining with machining hardness above 50HRC, micro lubrication and dry cutting without lubrication are constantly emerging. In short, the personalized characteristics of machining are becoming increasingly apparent

in the face of these changes, if it is required to adapt to these requirements in the design and manufacturing process of tools or the overall performance of tool materials, it is technically difficult. Especially for tool materials, it is not only extremely uneconomical in the use of resources, but also requires materials to meet the increasingly complex comprehensive cutting performance, which is usually difficult to achieve

looking at a large number of examples of tool cutting failure, it can be seen that most of the failures are often inseparable from the surface properties composed of the physical, chemical, mechanical and other states of the material surface, that is, modern cutting has higher and higher requirements for the surface properties of tool materials, which effectively promotes the research of surface engineering technologies such as vapor deposition technology. The experimental results show that the comprehensive cutting performance of the cutting tool surface can be given by the method of material surface modification technology. As one of the tool material surface modification technologies, chemical vapor deposition (CVD) and physical vapor deposition (PVD) technology have achieved very ideal results in the application of modern cutting tools

at present, among the cemented carbide tools that are the mainstream of cutting tools, coated cemented carbide tools have accounted for more than 80%. Among them, PVD technology, due to its low process temperature, will not affect the performance of tool substrate, and the variety of process schemes, makes its application more and more widely. Coating technology has become one of the three core technologies of modern cutting tools

in recent years, the continuous improvement of cutting requirements and the energy level of processed materials, as well as the reduction of environmental pollution caused by cutting, have effectively promoted the development of modern cutting tool coating technology. The multi-component composite coatings such as TiAIN, tiaicn, CrSiN and multi-layer coating in the multi-component alloying of film materials and the diversification of coating process combination make the tools obtain good comprehensive properties such as high wear resistance, low friction, good thermal stability and strong oxidation resistance, which greatly improves the performance of modern cutting tools; The microstructure of nano components and nano thin film coating makes the cutting of difficult to machine materials get a new solution; Diamond coating and diamond-like carbon coating (DLC) have achieved good results in processing graphite parts, fiber reinforced non-metallic materials and non-ferrous alloy materials. In order to adapt to the development of coating technology, the coating process equipment has also achieved integration, modularization and intelligence, making the coating technology increasingly personalized

diversification of film materials

at present, the development trend of modern cutting tool coating technology is the diversification of film materials. Multi element alloying of film materials is still the main research direction at present, that is, using the characteristics that binary nitrides and carbides of transition metals can often be mutually soluble, alloy elements are added to Ti-N films to form composite nitride coatings

for example, TiAIN ternary coating, which is currently the most widely used in cemented carbide coated tools, can obtain different film properties by adjusting the composition ratio of AI elements. For example, by adding carbon to Ti-N, through the solid solution and precipitation of carbon atoms, Ti (C, n) ternary coatings can be formed. Compared with the single coating of Ti-N, these multicomponent coatings have good comprehensive properties, improved oxidation resistance temperature and wear resistance, and low friction coefficient. Adding AI and C elements to Ti-N at the same time can form the Quaternary film of tiaicn (see Figure 1). The film has good thermal stability, high wear resistance and low friction, and has been widely used in coated end mills in the field of hard machining. For example, it is used for the forming and processing of hardened modules, which not only improves the processing efficiency and obtains a good machined surface, but also solves the deformation problem caused by forming first and then heat treatment, and improves the manufacturing accuracy of the mold

Figure 1. The Quaternary film layer of tiaicn

theoretically, all kinds of elements can become the elements of membrane materials, but the actual application still has certain limitations. In addition to the above membrane materials, at present, CrN, TiB2, CrSiN, ZrN, Al2O3, wc/c, MoS2 and NbN are commercially applied

diversification of process combination

another trend of coating is the diversification of process combination. At present, a single coating can not adapt to the increasingly complex working conditions and service conditions in modern machining. Therefore, a variety of process combinations of coatings came into being, first of all, from single-layer coating to multi-layer coating. Multilayer film is a film structure with periodic changes in composition or structure formed by deposition of one metal or alloy on another metal or alloy. Every two adjacent layers form a cycle (see Figure 2). The composition, thickness and number of cycles of each layer of metal and alloy can be selected according to needs. In addition, CVD is looking forward to chemical enterprises to achieve breakthroughs in these technologies and the process combination of PVD, The combined process of pre nitriding (ion nitriding) and PVD has been commercially applied. At the same time, gradient coating and nano film composite technology have also been widely used

Fig. 2 Tian's multilayers

in the study of multilayers, the toughness of multilayers is improved by using the interface effect and interlayer coupling effect of multilayers, as well as the toughening mechanisms such as crack tip passivation, crack branching and interface cracking along the interface, so as to obtain many characteristics different from monolayers. In a variety of process combinations, as long as through reasonable process design, the film structure with good comprehensive performance can be obtained in recent years

nanostructure of microstructure

nanostructure of microstructure is also the hot spot of coating research at present. In the study, it was found that some superhard nanocomposite film systems showed superior mechanical properties, such as the tin CrN/AlN nanocomposite layer shown in Figure 3, and its maximum hardness could reach 45gpa under the optimal composite film cycle

Figure 3 tin CrN nano film

a representative is the nano hybrid film composed of AITiN grains and amorphous Si3N4 nano components, whose hardness can also reach 45gpa, and the stability and oxidation resistance of the film can reach 1000 ℃. It can be seen that adding a small amount of Si to tin film can refine tin grains, even to the nanometer level, and improve its hardness to 40~50gpa. Therefore, in the new round of coating research, the nanostructured film containing Si may become the representative of the new generation of coatings

the film of nano components (grains) is another microstructure of the coating film (see Figure 4), also known as nanocrystalline film, such as a newly developed TiAIN nanocrystalline film coating, which has high heat resistance, has excellent processing effect in the processing of steel, titanium and titanium alloys, heat-resistant alloys and other materials, and can also work hardened die steel, Its main feature is that there are 15 coatings. In the experiment, the prepared nanocomposite catalyst is coated on the upper layer of cordierite honeycomb ceramic carrier, and the thickness of the film is 0.08 ~ 0.13MM nanocrystalline film. However, in the study of nano multilayers, there is still a lot of work to be done on the growth mode, interface structure, microhardness with modulation period and the strengthening and toughening mechanism of multilayers

Figure 4 nanocrystalline mixed film

diamond coating

another bright spot in coating technology is diamond coating. Diamond film has excellent mechanical, thermal, electrical and optical properties, and its hardness reaches 100GPa. Diamond coating is one of the new tool coating technologies that have been successfully studied in recent years. It is mainly used to process non-metallic workpiece such as graphite parts and fiber reinforcement, as well as micro tool coating. CC dia diamond coating developed by German cemecon company is a pure crystal diamond coating, which especially meets the performance requirements of graphite processing (see Figure 6)

figure 5A nanocrystalline multilayer film figure 5B nanocrystalline multilayer model figure

figure 6A crystal structure diamond coating figure 6B nanostructure diamond coating

in the currently known materials, this crystal structure has the highest hardness and wear resistance, and usually one tool can complete the manufacture of large and complex components, Because it fully reflects the organic combination of matrix material and tool geometry of graphite under specific application conditions. However, the diamond coating with SP3 as the main structural component has problems such as high internal stress, poor thermal stability and the catalytic effect between SP3 and ferrous metal, which will affect its adhesion. Therefore, in the diamond coating, the transition layer between the substrate and the diamond film is the key. A preparation method is reported in the literature: first, a layer of nano tin is deposited on the steel surface by laser evaporation, Then the diamond nanoparticles are deposited on the tin coating by CVD method, and then coated with a layer of tin. The diamond nanoparticles are embedded in two layers of tin film to form a nanocomposite coating. This coating structure not only has good hardness, heat resistance and impact resistance, but also has strong adhesion to the steel substrate

diamond coating not only shows good performance in processing graphite parts, but also shows excellent performance in the processing of high silicon aluminum alloy and laminated titanium alloy composites. It avoids the tendency that the elements in the composite material lead to the rapid wear of the blade and the adhesion and transfer of other elements to the blade. Due to the shortcomings of poor thermal stability of diamond film and certain limitations in use, diamond-like carbon coating (also known as graphite-like coating) with SP2 structure has also begun commercial application in recent years (see Figure 7). The hardness of DLC can reach 20 ~ 40gpa, but there is no problem of catalytic effect with ferrous metals. It has low friction coefficient and good moisture resistance. It can be used to process steel materials

Figure 7 DLC coating

the friction coefficient of diamond coating or DLC coating is only 1/6 ~ 1/12 of that of steel. It has self-lubricating function in cutting, which can effectively reduce or eliminate the pollution caused by cutting fluid in cutting, realize micro lubrication and dry cutting, improve the technical level of cutting, greatly increase the ratio of effective machining in the whole cutting, promote efficient machining, and reduce the processing cost, At the same time, it can also form a composite film with comprehensive performance and life less than 1/5 of the average life of industrial products with wear-resistant film. At present, the coating has been applied in the cutting field

development of coating equipment

in order to adapt to the rapid development of coating technology, the development of coating equipment has also changed rapidly in recent years. The highly integrated, modular structure and intelligent operation of the whole machine not only realize the modernization of equipment, but also meet the needs of timely technical upgrading. The process is becoming increasingly personalized, flexible adjustment, and has high stability and reliability, It can realize the lean production and clean (green) production of coating, thus greatly improving the technical performance of cutting tools, increasing the added value of cutting tools, making cutting tools become products with high-tech content, providing a good material foundation for China's NC machining technology and automatic production, truly realizing the mutual drive and common development of coating technology and modern cutting tools, and boosting the development of China's manufacturing industry


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