1. introduction
The surface coating technology of cutting tools is a material surface modification technology developed in response to market demand in recent decades. The use of coating technology can effectively increase the service life of the cutting tool, so that the tool can obtain excellent overall mechanical performance, thereby greatly improving the machining efficiency. Therefore, the coating technology and materials, and cutting process technology are called three key technologies in the field of cutting tool manufacturing. In order to meet the requirements of high-efficiency, high-precision, and high-reliability in modern machine processing, the development of coating technology and its application in tool manufacturing have become increasingly important in manufacturing countries all over the world. After many years of development, China's tool coating technology is currently in a critical period. That is, the original technology can no longer meet the increasing requirements of cutting processing, and the coating facilities of major domestic tool manufacturers have also reached a period of time when they must be replaced. Therefore, we fully understand the current status and development trend of the tool coating technology at home and abroad, aim at the advanced level of international coating technology, and have a plan, step by step development of tool coating technology (especially PVD technology), which is to improve the manufacturing level of cutting tools in China. Significance.
2. Foreign Tool Coating Technology Status and Development Trend
The tool coating technology can be generally divided into chemical vapor deposition (CVD) technology and physical vapor deposition (PVD) technology, which are respectively reviewed as follows.
2.1 Development of foreign CVD technology
Since the 1960s, CVD technology has been widely used in the surface treatment of carbide indexable cutting tools. Due to the relatively easy preparation of the metal source for vapor deposition of CVD process, deposition of TiN, TiC, TiCN, TiBN, TiB2, Al2O3, single-layer and multi-layer composite coatings can be achieved, and the strength of the coating and substrate bonding is higher. Thickness of 7 ~ 9μm, so to the middle and late eighties, the United States has 85% of carbide tools used surface coating treatment, of which CVD coating accounted for 99%; to the mid-nineties, CVD coating Cemented carbide inserts still account for over 80% of coated carbide cutting tools.
Although the CVD coating has good wear resistance, the CVD process also has its inherent defects: First, the processing temperature is high, which can easily cause the bending strength of the tool material to decrease; second, the internal tensile stress of the film is easy to cause the tool to use. Micro-cracking occurs; third, exhaust gas and waste liquid discharged from the CVD process cause significant environmental pollution, which contradicts the concept of green manufacturing that is strongly advocated at present. Therefore, since the mid-1990s, the development and application of high-temperature CVD technology have been subject to certain Constraints.
In the late 1980s, the low-temperature chemical vapor deposition (PCVD) technology developed by Krupp.Widia reached a practical level, and its process temperature has been reduced to 450-650°C, effectively inhibiting the generation of η phase, and can be used for thread cutting tools and milling cutters. , Die coating TiN, TiCN, TiC, but so far, PCVD process in the field of tool coating is not widely used. In the mid-1990s, the emergence of new technologies for medium-temperature chemical vapor deposition (MT-CVD) revolutionized CVD technology. MT-CVD technology is a new process in which CCN-containing organic compound acetonitrile (CH3CN) is used as the main reaction gas, and TiCl4, H2, and N2 are decomposed and chemically reacted to generate TiCN at 700-900°C. The dense fibrous crystalline form of the coating can be obtained by MT-CVD technology, and the coating thickness can reach 8 to 10 μm. This coating structure has extremely high abrasion resistance, thermal shock resistance and toughness, and can be deposited on the surface of the insert by high-temperature chemical vapor deposition (HT-CVD) process. Al2O3, TiN, etc. High temperature oxidation resistance, and being processed Materials with low affinity and good self-lubricating properties. MT-CVD coated inserts are suitable for use in high speed, high temperature, high load, dry cutting conditions and can have a life expectancy that is approximately double that of conventional coated inserts. At present, CVD (including MT-CVD) technology is mainly used for the surface coating of carbide turning tools. Coated tools are suitable for high-speed roughing and semi-finishing of medium and heavy cutting. CVD technology can also realize α-Al2O3 coating, which is currently difficult to achieve PVD technology, so in the dry cutting process, CVD coating technology still occupies an extremely important position.
2.2 Development of Foreign PVD Technology
PVD technology appeared in the late 1970s. Because its processing temperature can be controlled below 500°C, it can be used as the final treatment process for the coating of high-speed steel tools. Due to the adoption of PVD technology, the cutting performance of high-speed steel tools can be greatly improved, so this technology has been rapidly promoted since the 1980s. By the end of the 1980s, the PVD coating ratio of high-speed steel complex cutters in industrial developed countries has exceeded 60%. .
The successful application of PVD technology in the field of high-speed steel cutting tools has attracted the attention of manufacturing industries all over the world. While competing to develop high-performance, high-reliability coating equipment, it also expands its application fields, especially in cemented carbide, The application of ceramic tools has been further studied. The research results show that compared with the CVD process, the PVD processing temperature is low, and the bending strength of the tool material has no effect at 600 °C (see Table 1 for test results); the internal stress state of the film is compressive stress and is more suitable for The coating of hard and complex carbide tools; PVD process has no adverse impact on the environment, in line with the development direction of modern green manufacturing. With the advent of the era of high-speed cutting, the decline in the proportion of high-speed steel cutting tools, the application of cemented carbide tools and ceramic cutting tool applications has become an inevitable trend. Therefore, industrialized countries have been working on carbide cutting tools since the early 1990s. The research of PVD coating technology has achieved breakthrough progress since the mid-nineties. PVD coating technology has been widely used in cemented carbide end mills, drills, step drills, oil hole drills, reamers, taps, and indexable positions. Coatings for milling inserts, special tools, welding tools, etc.
Table 1 Effect of PVD Coating on Bending Strength of Cemented Carbide Materials at Different Temperatures
Carbide grades - average bending strength (MPa) - uncoated - coating (300 °C) - coating (600 °C) - coating (700 °C)
M20-2109-2266-2129-2059
M30-2285-2469-2370-1894
PVD technology has not only improved the bonding strength between the film and tool matrix materials, but also the coating composition has evolved from the first generation of TiN to multiple composite coatings such as TiC, TiCN, ZrN, CrN, MoS2, TiAlN, TiAlCN, TiN-AlN, and CNx. Floor. The emergence of nanoscale coatings such as ZX coatings (ie, TiN-AlN coatings) has led to new breakthroughs in the performance of PVD-coated tools. The new coating has high bonding strength with the substrate, the coating film hardness is close to CBN, the oxidation resistance is good, the peeling resistance is strong, and the surface roughness of the tool can be significantly improved, and the shape and precision of the cutting edge of the precision tool can be controlled effectively. The quality of the process is comparable to uncoated tools.
After decades of research and development, various tool coating processes have been widely used in carbide and HSS cutting tools. The main development stages and application areas of the coating process are shown in Table 2.
Table 2 Development Period and Application Field of Major Coating Processes
Time - Coating Composition - Coating Methods - Main Applications
1968-TiC, TiN-CVD-Carbide Tool, Mold Coating
1973-TiCN, TiC+Al2O3-CVD-Carbide Tool, Die Coating
1979 - TiN-PVD - HSS Tool Coating
1981-TiC+Al2O3+TiN, Al-ON-CVD-Carbide Tool Coating
1982-TiCN-MT-CVD-Carbide Tool Coating
1984-TiCN-PVD-Carbide, High Speed ​​Steel Milling Cutter, Drill Bit Tool Coating
1986 -Diamond, CBN-CVD, PVD-Carbide Tool Coating
1989-TiAlN-PVD-Carbide milling cutter coating (for steel, cast iron processing)
1990-TiN, TiCN, TiC-PCVD-Moulds, Thread Cutters, Milling Cutters, etc.
1991-TiAlN+CrC-PVD-Car, Milled Titanium Alloy
1993-TiN+TiCN(CVD)+TiN(PVD)-CVD+PVD-Carbide Milling Tools
1993-CrN-PVD-Titanium alloy, copper alloy processing
1994 - MoS2-PVD - High Speed ​​Steel Complex Tool Coating
1995-TiN-AlN-PVD-Carbide Milling Insert Coating
1996 - Thick Film Fibrous TiCN-MT-CVD-Carbide Turned Tool Coatings (for rough and semi-finishing)
1996 - CNx-CVD, PVD-HSS Tool Coating
2000-TiAlCN-PVD-Carbide Blade Coating
The current development of coating technology in the world has the following tendency: As single coating materials are difficult to meet the requirements for improving the comprehensive mechanical performance of tools, coating components will tend to be diversified and compounded; coating components are to meet different cutting processing requirements. Will be more complex and more targeted; in the composite coating, the thickness of each single component coating will become thinner and thinner, and will gradually become nanometer; the coating process temperature will become lower and lower, and the tool coating process In a more rational direction, it is expected that PVD and MT-CVD processes will become mainstream technologies.
3 Status and Development Trend of Tool Coating Technology in China
3.1 Development of CVD Technology in China
China began to study CVD coating technology in the early 1970s. Due to its strong specificity, there are not many domestic research institutes. In the mid-1980s, the development of CVD tool coating technology in China reached a practical level, and the level of process technology was comparable to the international level at that time, but it was slow to develop in the following decade (similar to the situation in foreign countries); in the 1990s At the end of the year, China began to research and develop MT-CVD technology. The research and development of MT-CVD process and equipment is expected to be basically completed in 2001. According to research objectives, process technology and equipment will reach the current international advanced level; China's PCVD technology research began In the early 1990s, PCVD process technology was mainly used for mold coating, and its application in the field of cutting tools is still very limited. Overall, the overall development level of domestic CVD technology is not far behind the international level. Until the successful development of MT-CVD technology, the overall level of tool CVD coatings in China will be able to keep pace with the international advanced level.
3.2 Development of PVD Technology in China
The research and development of PVD coating technology in China started from the early 1980s to the middle of the 1980s, and successfully developed the small hollow cathode ion coating machine and developed the TiN coating process technology for high-speed steel tools. During this period, due to the promising market for cutting tool coating, a total of seven large-scale tooling plants have imported large-scale PVD coating equipment from abroad (all of which are mainly high-speed steel TiN coating processes). The introduction of technology and equipment has mobilized the development of domestic PVD technology. Many research institutes and large vacuum equipment factories have started the development of large-scale ion coating machines, and developed a variety of PVD coating equipment in the early 1990s. However, most of the equipment performance indicators are not high enough to guarantee the quality of tool coating. At the same time, the expected market efficiency has not been achieved. Therefore, most companies have not conducted further in-depth research on PVD tool coating technology, resulting in nearly ten years of domestic PVD tool coating. The development of technology has stagnated. Although the domestically developed cemented carbide TiN-TiCN-TiN multi-component composite coating process technology was successfully developed in the late 1990s and reached a practical level, the CNx coating technology has a major breakthrough in R&D, but compared with the international development level, China's tool PVD Coating technology still lags behind by about 10 years. At present, the foreign tool PVD coating technology has been developed to the fourth generation, while the domestic is still at the second generation level, and is still mainly monolayer TiN coating.
4 Problems and Countermeasures in the Development of Tool PVD Coating Technology in China
4.1 Problem Analysis
Compared with foreign countries, the research and development of tool PVD coating technology in China is not too late. In the early development stage, a large number of internationally advanced coating equipments were introduced at the time. In the late 1980s, domestic coating equipment was also obtained. Rapid development, but the technology is widely used in high-speed steel cutting tools in the mid-1990s. So far, although domestic research on cemented carbide tools for TiCN coatings has achieved breakthroughs, the coating products in the domestic market are still dominated by TiN coatings. Analysis of the reasons can be summarized as the following:
(1) Impact of early introduction of centralized introduction on the subsequent development of domestic PVD technology
In the mid-1980s, the introduction of foreign PVD technology and equipment brought about a high starting point for the development of this technology in China, but also solved the problem of high-speed steel tool coating. However, the manufacturers that introduced the equipment are all domestic tool production backbones. Enterprises (whose cutting tool products have a high domestic market share), the introduction of these advanced coating equipment has met the production requirements of these companies for a long time, so the demand for domestic PVD technology and equipment is not so strong. To a certain extent, it has affected the application and development of domestic PVD equipment in the field of tool manufacturing. On the other hand, the PVD technology in the mid-1980s is still in the early stages of development. With the continuous development of this technology, new technologies emerge after the 1990s. The technologies introduced by these enterprises in the early days need to be updated. However, the expensive prices make it difficult for companies to introduce new technologies and new equipment again. As a result, domestic companies have missed the best time to develop PVD technologies.
(2) insufficient attention is paid to the research and development of new processes
Although the most advanced PVD technology was introduced at the time in the 1980s, PVD technology was still at the initial stage of development. Domestic space and development speed for its subsequent development could not be fully estimated; in addition, physical coating technology was to collect electronic physics, materials, and vacuum. The new technology of control technology has high requirements for personnel allocation in terms of research, production, and application. Most of the companies that introduce PVD technology emphasize production, and have insufficient allocation of developers and funds to promote further autonomy of process technology. Development, new processes, new technologies still need to be re-introduced, and re-introduction costs are very expensive (such as Balzers's equipment upgrade from TiN coating process to TiCN coating process, only the hardware modification fee will need 300,000 US dollars), so the impact The research and development of new coating technologies and equipment in the country.
(3) The lack of unity, rationality and cooperation in the development of domestic equipment
In the late 1980s, some domestic vacuum equipment manufacturers and research institutes were overly optimistic about the PVD tool coating market. They have increased the development of various types of PVD coating equipment. However, due to lack of in-depth understanding of the cutting process and tool coating process. The cooperation with the tool factory is not enough. Therefore, most of the coating equipment developed cannot meet the requirements of the tool coating process. In particular, the coating technology of precision high-speed steel tools still cannot reach the level of mass production. Since most of these devices can only be used for the coating of twist drills, the coating costs for twist drills are extremely low, and the profit for the corresponding coating equipment is also very low. Therefore, after the 1990s, most vacuum equipment manufacturers have developed. Direction to other industries (such as decorative coatings, etc.).
(4) The lack of after-sales service restricts the promotion and application of domestic coating equipment
To date, most coating equipment manufacturers in China have not been able to provide a complete tool coating process technology (including pretreatment process, coating process, post-coating process, detection technology, coating tool application technology, etc.). Incompleteness brings many technical problems to the user's production; in addition, due to the inability of equipment manufacturers to provide long-term technical services, domestic coating equipment is difficult to guarantee long-term stability and normal use, thereby greatly limiting the promotion of PVD coating equipment. application.
(5) Instable coating quality restricts the application of coating technology
The high cost of the imported equipment led to the high coating price, the coating cost could even exceed 50% of the tool price; due to the different introduction channels, different equipment selection basis, resulting in a large difference in equipment process level, affecting the coating tool The use of effects; due to the quality of the domestic coating tool is not stable, the coating tool inspection standards are not complete, so in the application area caused a high coating price, coating quality is unstable and the coated tool performance is not obvious after the improvement of the bad impression. Seriously affected the application and rapid development of tool coating technology.
(6) The low level of domestic machining restricts the rapid development of coating technology
In the 1980s, the application of CNC machine tools in China was still very limited, and the machining was still at a relatively low level. The application of high-speed steel tools accounted for more than 80% of all cutting tools. The carbide cutting tools were still based on welding tools. The indexing insert is mainly used for turning tools (usually CVD coating is more commonly used), and the overall hard alloy end mills, drills, reamers and other applications are less applied, so the requirements for the coating of PVD carbide tools are not very urgent. This, to a certain extent, also affected the further development of coating technology.
4.2 Countermeasures and Suggestions
With the development of industries such as automotive, aerospace, aerospace and heavy machinery in China, and the rapid spread of CNC machine tools, China's machining technology is moving in the direction of high-speed machining and green manufacturing. High-speed hobbing, high-speed milling and dry cutting processes Application imposes higher requirements on tool coating technology. Taking high-speed gear hobbing as an example, the advanced technology requires the use of a hob MoS2 soft coating technology. Compared with TiN coatings, the service life can be more than doubled. In high-speed milling, carbide milling tools use TiAlN, TiAlCN, or TiNAlN coatings. A single TiN coating is not suitable for such machining. The demand of the market forces the country to accelerate the research and development of new PVD technologies.
The author believes that in order for China's new PVD coating technology to develop rapidly and orderly, efforts should be made to do the following:
(1) Strengthen project planning and management
The tool industry management department should strengthen the planning and management of the PVD coating project, define the short-, medium-, and long-term development goals of the new PVD coating technology in China, establish a policy of continuous and planned development, and pass “government, production, and learningâ€. The organic combination of research, research and business has enabled the project to have both policy support and capital protection. China has also had successful experience in this respect: In the mid-1980s, in order to base itself on self-development on the basis of introduction and improve the overall level of coating technology in the tool industry, the Machine Tool Division of the former Ministry of Machinery Industry has organized industry-wide efforts to introduce equipment. The hot-cathode arc magnetron plasma coating machine developed for technical research has been successfully applied in the tool industry, and this has led to the popularization and application of domestic TiN coating tools.
(2) Establish a unified research, development and service system
Establish a unified research, development and service system, systematically introduce international advanced technologies, strengthen the digestion and absorption of imported technologies and collaborative research work in accordance with the development trend of coating technology and domestic and foreign market demands, and gradually enhance self-development capabilities. The patented technology ultimately fulfills the purpose of satisfying the domestic market demand and participating in the international market competition.
(3) Establish the industry standard for tool coating technology
Establish industry inspection standards for coating equipment and coating tools, strictly control the quality of coated tools, and ensure that large-scale application of coating technology is promoted.
The surface coating technology of cutting tools is a material surface modification technology developed in response to market demand in recent decades. The use of coating technology can effectively increase the service life of the cutting tool, so that the tool can obtain excellent overall mechanical performance, thereby greatly improving the machining efficiency. Therefore, the coating technology and materials, and cutting process technology are called three key technologies in the field of cutting tool manufacturing. In order to meet the requirements of high-efficiency, high-precision, and high-reliability in modern machine processing, the development of coating technology and its application in tool manufacturing have become increasingly important in manufacturing countries all over the world. After many years of development, China's tool coating technology is currently in a critical period. That is, the original technology can no longer meet the increasing requirements of cutting processing, and the coating facilities of major domestic tool manufacturers have also reached a period of time when they must be replaced. Therefore, we fully understand the current status and development trend of the tool coating technology at home and abroad, aim at the advanced level of international coating technology, and have a plan, step by step development of tool coating technology (especially PVD technology), which is to improve the manufacturing level of cutting tools in China. Significance.
2. Foreign Tool Coating Technology Status and Development Trend
The tool coating technology can be generally divided into chemical vapor deposition (CVD) technology and physical vapor deposition (PVD) technology, which are respectively reviewed as follows.
2.1 Development of foreign CVD technology
Since the 1960s, CVD technology has been widely used in the surface treatment of carbide indexable cutting tools. Due to the relatively easy preparation of the metal source for vapor deposition of CVD process, deposition of TiN, TiC, TiCN, TiBN, TiB2, Al2O3, single-layer and multi-layer composite coatings can be achieved, and the strength of the coating and substrate bonding is higher. Thickness of 7 ~ 9μm, so to the middle and late eighties, the United States has 85% of carbide tools used surface coating treatment, of which CVD coating accounted for 99%; to the mid-nineties, CVD coating Cemented carbide inserts still account for over 80% of coated carbide cutting tools.
Although the CVD coating has good wear resistance, the CVD process also has its inherent defects: First, the processing temperature is high, which can easily cause the bending strength of the tool material to decrease; second, the internal tensile stress of the film is easy to cause the tool to use. Micro-cracking occurs; third, exhaust gas and waste liquid discharged from the CVD process cause significant environmental pollution, which contradicts the concept of green manufacturing that is strongly advocated at present. Therefore, since the mid-1990s, the development and application of high-temperature CVD technology have been subject to certain Constraints.
In the late 1980s, the low-temperature chemical vapor deposition (PCVD) technology developed by Krupp.Widia reached a practical level, and its process temperature has been reduced to 450-650°C, effectively inhibiting the generation of η phase, and can be used for thread cutting tools and milling cutters. , Die coating TiN, TiCN, TiC, but so far, PCVD process in the field of tool coating is not widely used. In the mid-1990s, the emergence of new technologies for medium-temperature chemical vapor deposition (MT-CVD) revolutionized CVD technology. MT-CVD technology is a new process in which CCN-containing organic compound acetonitrile (CH3CN) is used as the main reaction gas, and TiCl4, H2, and N2 are decomposed and chemically reacted to generate TiCN at 700-900°C. The dense fibrous crystalline form of the coating can be obtained by MT-CVD technology, and the coating thickness can reach 8 to 10 μm. This coating structure has extremely high abrasion resistance, thermal shock resistance and toughness, and can be deposited on the surface of the insert by high-temperature chemical vapor deposition (HT-CVD) process. Al2O3, TiN, etc. High temperature oxidation resistance, and being processed Materials with low affinity and good self-lubricating properties. MT-CVD coated inserts are suitable for use in high speed, high temperature, high load, dry cutting conditions and can have a life expectancy that is approximately double that of conventional coated inserts. At present, CVD (including MT-CVD) technology is mainly used for the surface coating of carbide turning tools. Coated tools are suitable for high-speed roughing and semi-finishing of medium and heavy cutting. CVD technology can also realize α-Al2O3 coating, which is currently difficult to achieve PVD technology, so in the dry cutting process, CVD coating technology still occupies an extremely important position.
2.2 Development of Foreign PVD Technology
PVD technology appeared in the late 1970s. Because its processing temperature can be controlled below 500°C, it can be used as the final treatment process for the coating of high-speed steel tools. Due to the adoption of PVD technology, the cutting performance of high-speed steel tools can be greatly improved, so this technology has been rapidly promoted since the 1980s. By the end of the 1980s, the PVD coating ratio of high-speed steel complex cutters in industrial developed countries has exceeded 60%. .
The successful application of PVD technology in the field of high-speed steel cutting tools has attracted the attention of manufacturing industries all over the world. While competing to develop high-performance, high-reliability coating equipment, it also expands its application fields, especially in cemented carbide, The application of ceramic tools has been further studied. The research results show that compared with the CVD process, the PVD processing temperature is low, and the bending strength of the tool material has no effect at 600 °C (see Table 1 for test results); the internal stress state of the film is compressive stress and is more suitable for The coating of hard and complex carbide tools; PVD process has no adverse impact on the environment, in line with the development direction of modern green manufacturing. With the advent of the era of high-speed cutting, the decline in the proportion of high-speed steel cutting tools, the application of cemented carbide tools and ceramic cutting tool applications has become an inevitable trend. Therefore, industrialized countries have been working on carbide cutting tools since the early 1990s. The research of PVD coating technology has achieved breakthrough progress since the mid-nineties. PVD coating technology has been widely used in cemented carbide end mills, drills, step drills, oil hole drills, reamers, taps, and indexable positions. Coatings for milling inserts, special tools, welding tools, etc.
Table 1 Effect of PVD Coating on Bending Strength of Cemented Carbide Materials at Different Temperatures
Carbide grades - average bending strength (MPa) - uncoated - coating (300 °C) - coating (600 °C) - coating (700 °C)
M20-2109-2266-2129-2059
M30-2285-2469-2370-1894
PVD technology has not only improved the bonding strength between the film and tool matrix materials, but also the coating composition has evolved from the first generation of TiN to multiple composite coatings such as TiC, TiCN, ZrN, CrN, MoS2, TiAlN, TiAlCN, TiN-AlN, and CNx. Floor. The emergence of nanoscale coatings such as ZX coatings (ie, TiN-AlN coatings) has led to new breakthroughs in the performance of PVD-coated tools. The new coating has high bonding strength with the substrate, the coating film hardness is close to CBN, the oxidation resistance is good, the peeling resistance is strong, and the surface roughness of the tool can be significantly improved, and the shape and precision of the cutting edge of the precision tool can be controlled effectively. The quality of the process is comparable to uncoated tools.
After decades of research and development, various tool coating processes have been widely used in carbide and HSS cutting tools. The main development stages and application areas of the coating process are shown in Table 2.
Table 2 Development Period and Application Field of Major Coating Processes
Time - Coating Composition - Coating Methods - Main Applications
1968-TiC, TiN-CVD-Carbide Tool, Mold Coating
1973-TiCN, TiC+Al2O3-CVD-Carbide Tool, Die Coating
1979 - TiN-PVD - HSS Tool Coating
1981-TiC+Al2O3+TiN, Al-ON-CVD-Carbide Tool Coating
1982-TiCN-MT-CVD-Carbide Tool Coating
1984-TiCN-PVD-Carbide, High Speed ​​Steel Milling Cutter, Drill Bit Tool Coating
1986 -Diamond, CBN-CVD, PVD-Carbide Tool Coating
1989-TiAlN-PVD-Carbide milling cutter coating (for steel, cast iron processing)
1990-TiN, TiCN, TiC-PCVD-Moulds, Thread Cutters, Milling Cutters, etc.
1991-TiAlN+CrC-PVD-Car, Milled Titanium Alloy
1993-TiN+TiCN(CVD)+TiN(PVD)-CVD+PVD-Carbide Milling Tools
1993-CrN-PVD-Titanium alloy, copper alloy processing
1994 - MoS2-PVD - High Speed ​​Steel Complex Tool Coating
1995-TiN-AlN-PVD-Carbide Milling Insert Coating
1996 - Thick Film Fibrous TiCN-MT-CVD-Carbide Turned Tool Coatings (for rough and semi-finishing)
1996 - CNx-CVD, PVD-HSS Tool Coating
2000-TiAlCN-PVD-Carbide Blade Coating
The current development of coating technology in the world has the following tendency: As single coating materials are difficult to meet the requirements for improving the comprehensive mechanical performance of tools, coating components will tend to be diversified and compounded; coating components are to meet different cutting processing requirements. Will be more complex and more targeted; in the composite coating, the thickness of each single component coating will become thinner and thinner, and will gradually become nanometer; the coating process temperature will become lower and lower, and the tool coating process In a more rational direction, it is expected that PVD and MT-CVD processes will become mainstream technologies.
3 Status and Development Trend of Tool Coating Technology in China
3.1 Development of CVD Technology in China
China began to study CVD coating technology in the early 1970s. Due to its strong specificity, there are not many domestic research institutes. In the mid-1980s, the development of CVD tool coating technology in China reached a practical level, and the level of process technology was comparable to the international level at that time, but it was slow to develop in the following decade (similar to the situation in foreign countries); in the 1990s At the end of the year, China began to research and develop MT-CVD technology. The research and development of MT-CVD process and equipment is expected to be basically completed in 2001. According to research objectives, process technology and equipment will reach the current international advanced level; China's PCVD technology research began In the early 1990s, PCVD process technology was mainly used for mold coating, and its application in the field of cutting tools is still very limited. Overall, the overall development level of domestic CVD technology is not far behind the international level. Until the successful development of MT-CVD technology, the overall level of tool CVD coatings in China will be able to keep pace with the international advanced level.
3.2 Development of PVD Technology in China
The research and development of PVD coating technology in China started from the early 1980s to the middle of the 1980s, and successfully developed the small hollow cathode ion coating machine and developed the TiN coating process technology for high-speed steel tools. During this period, due to the promising market for cutting tool coating, a total of seven large-scale tooling plants have imported large-scale PVD coating equipment from abroad (all of which are mainly high-speed steel TiN coating processes). The introduction of technology and equipment has mobilized the development of domestic PVD technology. Many research institutes and large vacuum equipment factories have started the development of large-scale ion coating machines, and developed a variety of PVD coating equipment in the early 1990s. However, most of the equipment performance indicators are not high enough to guarantee the quality of tool coating. At the same time, the expected market efficiency has not been achieved. Therefore, most companies have not conducted further in-depth research on PVD tool coating technology, resulting in nearly ten years of domestic PVD tool coating. The development of technology has stagnated. Although the domestically developed cemented carbide TiN-TiCN-TiN multi-component composite coating process technology was successfully developed in the late 1990s and reached a practical level, the CNx coating technology has a major breakthrough in R&D, but compared with the international development level, China's tool PVD Coating technology still lags behind by about 10 years. At present, the foreign tool PVD coating technology has been developed to the fourth generation, while the domestic is still at the second generation level, and is still mainly monolayer TiN coating.
4 Problems and Countermeasures in the Development of Tool PVD Coating Technology in China
4.1 Problem Analysis
Compared with foreign countries, the research and development of tool PVD coating technology in China is not too late. In the early development stage, a large number of internationally advanced coating equipments were introduced at the time. In the late 1980s, domestic coating equipment was also obtained. Rapid development, but the technology is widely used in high-speed steel cutting tools in the mid-1990s. So far, although domestic research on cemented carbide tools for TiCN coatings has achieved breakthroughs, the coating products in the domestic market are still dominated by TiN coatings. Analysis of the reasons can be summarized as the following:
(1) Impact of early introduction of centralized introduction on the subsequent development of domestic PVD technology
In the mid-1980s, the introduction of foreign PVD technology and equipment brought about a high starting point for the development of this technology in China, but also solved the problem of high-speed steel tool coating. However, the manufacturers that introduced the equipment are all domestic tool production backbones. Enterprises (whose cutting tool products have a high domestic market share), the introduction of these advanced coating equipment has met the production requirements of these companies for a long time, so the demand for domestic PVD technology and equipment is not so strong. To a certain extent, it has affected the application and development of domestic PVD equipment in the field of tool manufacturing. On the other hand, the PVD technology in the mid-1980s is still in the early stages of development. With the continuous development of this technology, new technologies emerge after the 1990s. The technologies introduced by these enterprises in the early days need to be updated. However, the expensive prices make it difficult for companies to introduce new technologies and new equipment again. As a result, domestic companies have missed the best time to develop PVD technologies.
(2) insufficient attention is paid to the research and development of new processes
Although the most advanced PVD technology was introduced at the time in the 1980s, PVD technology was still at the initial stage of development. Domestic space and development speed for its subsequent development could not be fully estimated; in addition, physical coating technology was to collect electronic physics, materials, and vacuum. The new technology of control technology has high requirements for personnel allocation in terms of research, production, and application. Most of the companies that introduce PVD technology emphasize production, and have insufficient allocation of developers and funds to promote further autonomy of process technology. Development, new processes, new technologies still need to be re-introduced, and re-introduction costs are very expensive (such as Balzers's equipment upgrade from TiN coating process to TiCN coating process, only the hardware modification fee will need 300,000 US dollars), so the impact The research and development of new coating technologies and equipment in the country.
(3) The lack of unity, rationality and cooperation in the development of domestic equipment
In the late 1980s, some domestic vacuum equipment manufacturers and research institutes were overly optimistic about the PVD tool coating market. They have increased the development of various types of PVD coating equipment. However, due to lack of in-depth understanding of the cutting process and tool coating process. The cooperation with the tool factory is not enough. Therefore, most of the coating equipment developed cannot meet the requirements of the tool coating process. In particular, the coating technology of precision high-speed steel tools still cannot reach the level of mass production. Since most of these devices can only be used for the coating of twist drills, the coating costs for twist drills are extremely low, and the profit for the corresponding coating equipment is also very low. Therefore, after the 1990s, most vacuum equipment manufacturers have developed. Direction to other industries (such as decorative coatings, etc.).
(4) The lack of after-sales service restricts the promotion and application of domestic coating equipment
To date, most coating equipment manufacturers in China have not been able to provide a complete tool coating process technology (including pretreatment process, coating process, post-coating process, detection technology, coating tool application technology, etc.). Incompleteness brings many technical problems to the user's production; in addition, due to the inability of equipment manufacturers to provide long-term technical services, domestic coating equipment is difficult to guarantee long-term stability and normal use, thereby greatly limiting the promotion of PVD coating equipment. application.
(5) Instable coating quality restricts the application of coating technology
The high cost of the imported equipment led to the high coating price, the coating cost could even exceed 50% of the tool price; due to the different introduction channels, different equipment selection basis, resulting in a large difference in equipment process level, affecting the coating tool The use of effects; due to the quality of the domestic coating tool is not stable, the coating tool inspection standards are not complete, so in the application area caused a high coating price, coating quality is unstable and the coated tool performance is not obvious after the improvement of the bad impression. Seriously affected the application and rapid development of tool coating technology.
(6) The low level of domestic machining restricts the rapid development of coating technology
In the 1980s, the application of CNC machine tools in China was still very limited, and the machining was still at a relatively low level. The application of high-speed steel tools accounted for more than 80% of all cutting tools. The carbide cutting tools were still based on welding tools. The indexing insert is mainly used for turning tools (usually CVD coating is more commonly used), and the overall hard alloy end mills, drills, reamers and other applications are less applied, so the requirements for the coating of PVD carbide tools are not very urgent. This, to a certain extent, also affected the further development of coating technology.
4.2 Countermeasures and Suggestions
With the development of industries such as automotive, aerospace, aerospace and heavy machinery in China, and the rapid spread of CNC machine tools, China's machining technology is moving in the direction of high-speed machining and green manufacturing. High-speed hobbing, high-speed milling and dry cutting processes Application imposes higher requirements on tool coating technology. Taking high-speed gear hobbing as an example, the advanced technology requires the use of a hob MoS2 soft coating technology. Compared with TiN coatings, the service life can be more than doubled. In high-speed milling, carbide milling tools use TiAlN, TiAlCN, or TiNAlN coatings. A single TiN coating is not suitable for such machining. The demand of the market forces the country to accelerate the research and development of new PVD technologies.
The author believes that in order for China's new PVD coating technology to develop rapidly and orderly, efforts should be made to do the following:
(1) Strengthen project planning and management
The tool industry management department should strengthen the planning and management of the PVD coating project, define the short-, medium-, and long-term development goals of the new PVD coating technology in China, establish a policy of continuous and planned development, and pass “government, production, and learningâ€. The organic combination of research, research and business has enabled the project to have both policy support and capital protection. China has also had successful experience in this respect: In the mid-1980s, in order to base itself on self-development on the basis of introduction and improve the overall level of coating technology in the tool industry, the Machine Tool Division of the former Ministry of Machinery Industry has organized industry-wide efforts to introduce equipment. The hot-cathode arc magnetron plasma coating machine developed for technical research has been successfully applied in the tool industry, and this has led to the popularization and application of domestic TiN coating tools.
(2) Establish a unified research, development and service system
Establish a unified research, development and service system, systematically introduce international advanced technologies, strengthen the digestion and absorption of imported technologies and collaborative research work in accordance with the development trend of coating technology and domestic and foreign market demands, and gradually enhance self-development capabilities. The patented technology ultimately fulfills the purpose of satisfying the domestic market demand and participating in the international market competition.
(3) Establish the industry standard for tool coating technology
Establish industry inspection standards for coating equipment and coating tools, strictly control the quality of coated tools, and ensure that large-scale application of coating technology is promoted.
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