Current status and development trend of the hottes

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The status quo and development trend of tool coating technology

1 introduction

as we all know, tool surface coating technology is a high-quality surface modification technology developed in response to market demand. Because this technology can enable cutting tools to obtain excellent comprehensive mechanical properties, it can not only effectively improve tool service life, but also greatly improve machining efficiency. Therefore, this technology has been combined with materials Machining process is called three key technologies of cutting tool manufacturing. In order to meet the requirements of high efficiency, high precision and high reliability of modern machining, countries all over the world attach great importance to the development of coating technology. At present, the development of tool coating technology in China is at a very critical moment, especially the PVD coating technology. On the one hand, the original technology can not meet the changing requirements of machining; On the other hand, the coating equipment of major tool factories in China has reached a period when it must be upgraded. Therefore, the planned and step-by-step development of PVD technology can not only promote the technical level of cutting tool products in China, but also obtain huge economic and social benefits

2 current situation and development trend of international tool coating technology

tool coating technology can still be divided into two categories, namely CVD (chemical vapor deposition of safety device of electronic tensile testing machine) and PVD (physical vapor deposition)

2.1 development of international CVD technology

cvd technology has been widely used in cemented carbide indexable tools since it appeared in the 1960s. In the CVD process, the metal source required for vapor deposition is relatively easy to prepare, and tin, tic, TiCN, tibn, TiB2, Al2O3 and other single-layer and multi-layer composite coatings can be realized. The coating has high bonding strength with the substrate, and the film thickness can reach 7 ~ 9 μ m. Comparatively speaking, CVD coating has better wear resistance. In the middle and late 1980s, 85% of cemented carbide tools in the United States were coated, of which the CVD coating accounted for 99%; In the mid-1990s, CVD coated carbide blades still accounted for more than 80% of coated carbide tools. However, CVD process also has its inherent defects. First, the high processing temperature is easy to cause the decrease of bending strength of tool materials; The second is that the film is in the state of tensile stress, which is easy to cause microcracks in use; Third, the exhaust gas and waste liquid discharged by CVD process will cause industrial pollution, have a great impact on the environment, and conflict with the green industry advocated at present. Therefore, the development of high-temperature CVD technology has been restricted to a certain extent since the mid-1990s

in the late 1980s, the PCVD (low temperature chemical vapor deposition) technology developed by Krupp widia reached the practical level, and its process treatment temperature has been reduced to 450 ℃ ~ 650 ℃, effectively inhibiting η Phase can be coated with tin, TiCN, tic, etc. for thread cutters, milling cutters, molds, etc., but so far PCVD process is not widely used in the field of tool coating

what really caused the mutation of CVD technology was the emergence of a new mt-cvd (medium temperature chemical vapor deposition) technology in the mid-1990s. The new mt-cvd is a new method that uses acetonitrile (CH3CN) containing c/n as the main reaction gas and TiCl4, H2, N2 to produce decomposition and chemical reaction at 700 ~ 900 ℃ to produce TiCN. It can obtain a dense fibrous crystalline coating with a coating thickness of 8 ~ 10 μ m。 This coating structure has extremely high wear resistance, thermal shock resistance and toughness, and can deposit Al2O3, tin and other materials with good high-temperature oxidation resistance, low affinity with processed materials and good self-lubricating performance on the surface through ht-cvd (high temperature chemical vapor deposition) process technology. The mt-cvd coated blade is suitable for high-speed, high-temperature, heavy load and dry cutting conditions. Its service life can be about twice as long as that of the ordinary coated blade

from the current development, CVD process (including mt-cvd) is mainly used for the surface coating of cemented carbide turning tools. The coated tools are suitable for high-speed rough machining and semi finishing of medium and heavy cutting, especially α- Al2O3 coating is difficult to realize by PVD technology at present, so CVD coating technology still plays an extremely important role in dry cutting

Figure 1 profile of new mt-cvd coating

2.2 development of PVD technology in the world

pvd technology appeared in the late 1970s. Because its process treatment temperature can be controlled below 500 ℃, it can be used as the final treatment process for the coating of high-speed steel tools. PVD technology can greatly improve the cutting performance of high-speed steel tools, so this technology has been rapidly popularized and applied in the 1980s. At the end of 1980s, the proportion of PVD coating on complex high-speed steel cutting tools in industrial developed countries has exceeded 60%

The successful application of PVD technology in the field of high-speed steel cutting tools has attracted great attention all over the world. While competing to develop high-performance and high reliability coating equipment, people have also conducted more in-depth research on the expansion of its application field, especially in the field of cemented carbide and ceramic cutting tools. Compared with CVD process, PVD process has lower treatment temperature, and has no effect on the bending strength of tool material below 600 ℃ (see Table 1 test results); The inner part of the film is compressive stress, which is more suitable for the coating of cemented carbide precision and complex tools; The PVD process has no adverse impact on the environment, which is in line with the current development direction of green industry; In addition, with the arrival of the era of high-speed machining, the application proportion of high-speed steel tools has decreased, and the application proportion of cemented carbide and ceramic tools has increased. Therefore, industrial developed countries have been committed to the research of PVD coating technology for cemented carbide tools since the early 1990s. In the mid-1990s, the PVD coating technology for cemented carbide tools has made a breakthrough, and is widely used in cemented carbide end mills, drill bits Coating treatment for step drill, oil hole drill, reamer, tap, indexable milling insert, special-shaped cutter, welding cutter, etc

at present, the PVD technology not only improves the bonding strength between the film and the tool matrix material, but also develops the coating composition from the first generation tin to multiple composite coatings such as tic, TiCN, ZrN, CrN, MoS2, TiAlN, tialcn, tin AlN, CNx, etc. due to the emergence of nano coatings (see Figure 2, 3zx coatings, i.e. tin AlN coatings), the quality of PVD coated tools has made a new breakthrough. This film coating not only has high bonding strength The hardness is close to CBN and the oxidation resistance is good. It can effectively control the shape and accuracy of the precision tool edge. In high-precision machining, its machining accuracy is no less than that of uncoated tools

average bending strength of cemented carbide brand (MPA) uncoated coating (300 ℃) coating (600 ℃) coating (700 ℃) m202109226621292059 m302285246923701894 Table 1 Effect of PVD coating on bending strength of cemented carbide materials at different temperatures ⑴

from the development of coating technology at present, it is difficult to be accepted by the market because a single coating material can not meet the requirements for comprehensive mechanical properties of cutting tools, The diversification of coating composition has become an inevitable trend; In order to meet different machining requirements, the coating composition will be more complex and targeted; The composition of each single layer will become thinner and thinner, and gradually tend to be nano; The coating temperature will be lower and lower; The tool coating process will develop in a more reasonable direction. It is expected that PVD and mt-cvd processes will become the mainstream

Figure 2 ZX coating characteristics Figure 3 ZX coating structure

serial number time coating composition coating method main application fields 1 1968 tic, tin CVD cemented carbide tools, mold coating 2 1973 TiCN, tic+al2o3 CVD cemented carbide tools, mold coating 3 1979 tin PVD high speed steel tool coating 4 1981 tic+al2o3+tin, al-o-n CVD cemented carbide tool coating 5 1982 TiCN mt-cvd cemented carbide tool coating 6 1984 TiCN PVD cemented carbide High speed steel milling cutter and drill bit coating 7 Diamond, CBN CVD and PVD cemented carbide cutter coating in 1986 8 TiAlN PVD cemented carbide milling cutter coating in 1989 was used for steel and cast iron processing 9 tin, TiCN and tic PCVD were used for molds, thread cutters and milling cutters in 1990 10 tialn+crc PVD turning and milling titanium alloys in 1991 11 tin+ticn (CVD) +tin (PVD) cvd+pvd cemented carbide milling cutters in 1993 12 CrN PVD was used for titanium alloys Copper alloy processing 13 in 1994, MoS2 PVD was used for high-speed steel complex tool coating 1. The added additives can be repeatedly reprocessed without seriously damaging their original functions. 4 in 1995, tin- AlN PVD cemented carbide milling blade coating 15 in 1996, thick film fibrous TiCN mt-cvd cemented carbide turning tool coating, rough and semi finish machining 16 in 1996, CNx CVD PVD has been used for high-speed steel tool coating 17 tialcn PVD cemented carbide blade coating in 2000 Table 2 main coating process development period and application field

3.1 development of CVD technology in China

the research on CVD coating technology in China originated in the early 1970s. Due to the strong specificity of this technology, there are not many domestic units engaged in its research. In the mid-1980s, the domestic CVD tool coating technology reached practicality, and its process technology was equivalent to the international level; In the following ten years, the development was similar to that of the international community and was relatively slow; At the end of the 1990s, the research on mt-cvd began in China. It is expected that the research on the process and equipment will be completed in 2001. At that time, the equipment and process technology will reach the current international advanced level. The research of PCVD technology in China began in the early 1990s. This technology is mainly used in mold coating, and is not widely used in the field of cutting tools. Generally speaking, the domestic CVD technology is not much different from the international level. If the mt-cvd technology is successfully developed, the overall technology will keep pace with the international advanced level

3.2 the development of PVD technology in China

the research and development of PVD coating technology in China began in the early 1980s. In the mid 1980s, the small and medium-sized hollow cathode ion coating machine and tin coating technology for high-speed steel cutting tools were successfully developed. At the same time, due to the promising market prospect of tool coating, seven large-scale tool factories in China have introduced large-scale PVD coating equipment, all of which are based on high-speed steel tin coating process. The introduction of imported technology and equipment has mobilized the development upsurge of domestic PVD technology. Major domestic vacuum equipment plants and many scientific research institutions have launched the research and development of large-scale ion plating machines, and developed a variety of PVD equipment in the early 1990s. However, due to the poor performance indicators of most equipment, the tool coating process can not be guaranteed, and the expected market benefits have not been realized, most units have abandoned the further research work of PVD tool coating technology, resulting in the situation that the domestic tool PVD coating technology has been in a stagnant state in the past decade. Although at the end of the 1990s, China successfully developed the cemented carbide tin TiCN tin multi-component composite coating technology and reached the practical level (see Table 3), and CNx coating technology also made major breakthroughs (see Table 4), compared with the international level, China's tool PVD coating technology is about 10 years behind. At present, the PVD technology of cutting tools abroad has developed to the fourth generation, while it is still at the level of the second generation in China, and it is still dominated by single-layer tin coating

tool No. tool coating spindle speed (r/min) cutting speed (m/min) feed rate (mm/r) machining quantity (pieces) test stop reason 1 TiCN 1400880.214 480 workpiece slag dropping 2 TiCN 1400880.214 170 workpiece slag dropping 3 TiCN 1400880.214 315 workpiece slag dropping 4 uncoated 1400880.214 70 workpiece slag dropping remarks engine block of machined parts, machined material tl-009, hardness hb195+40, dry cutting table 3 overall hard joint

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