Current situation and Prospect of the hottest tool

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Status and Prospect of tool coating technology

since the advent of the first generation tic Chemical Technology vapor deposition (CVD) coated cemented carbide blade in the late 1960s, coating technology has played a great role in promoting the development of cemented carbide tools. In the early 1980s, the emergence of tin physical vapor deposition (PVD) coated high-speed steel tools was known as a revolutionary change in the performance of high-speed steel tools. For decades, coating technology has been widely used in the process of improving the performance of cutting tools. This paper introduces the progress of coating technology from the following three aspects and looks forward to the development trend after 2000: (1) the application of tool coating technology; (2) New development of coating technology; (3) CVD and PVD are complementary in tool coating

1 application of tool coating technology

at present, most machining enterprises have realized or are realizing that the application of tool coating technology is an effective way to improve cutting efficiency and reduce machining costs. With the improvement of coating technology and equipment, the coating cost has decreased by 1//3 compared with the initial stage. Therefore, the application of coating technology will increase the variety of tools, and the proportion of coated tools in the total number of tools will also continue to expand

from the proportion of coated tools (coated carbide and coated high-speed steel tools) in all used tools, the size of this proportion varies with the size of the factory. For large-scale and well managed factories abroad, the monthly cost of tool coating is more than 50000 US dollars, and the coated tools account for 85% of all the tools they use (or sell); The monthly coating cost of tools consumed by smaller factories is less than $50000, and coated tools account for 55% of all their tools. At present, only a few large cemented carbide plants in China have CVD coating equipment, and the coating blade accounts for a small proportion. In terms of PVD coated high-speed steel tools, it is mainly used in the coating treatment of fried dough twist drills and gear tools in China. It is estimated that the coated fried dough twist drills have accounted for about 50% of the total amount of fully ground fried dough twist drills. Taking Jiangsu Danyang Feida and Tiangong two large tool groups as examples, the annual coating cost of fried dough twist drill is more than 5million yuan, and about 20 sets of PVD equipment are used for fried dough twist drill coating. The major gear cutter factories in China have PVD equipment to provide coating services for their products. In addition, the gear manufacturers themselves have coated cutters in adjacent coating factories, and the proportion of coated cutters in gear cutters has been greater than 60%. In recent years, the concept of recoating gear tools after grinding to improve cutting efficiency has been gradually recognized by the gear processing industry. Therefore, the coating amount of gear tools will be further increased in the future

with the popularization and application of coating technology, the work of establishing coating centers (or coating factories) in industrial concentrated areas has been greatly developed. There are hundreds of coating centers in operation in industrial developed countries, and each coating center has several PVD and CVD equipment. For example, Balzers and multi arc, two famous tool coating equipment manufacturing companies (producing PVD equipment), have established many coating centers around the world. The income of the two companies in the coating center is more generous than that of their sales of coating equipment. At present, although there are many coating factories in China, such as six coating factories in Danyang, Jiangsu Province alone, the technical level and scale can not meet the requirements of coated high-quality tools. Therefore, it is urgent to establish a coating center with development ability and high-tech level in China, and its coating business should also be expanded from cutting tools to molds, mechanical parts and high-end jewelry

2 new development of coating technology

looking at the development process of CVD and PVD technology, we can find several common laws. When the first generation of CVD tic coated cemented carbide blades and PVD tin coated tools enter the market, the first problem to be solved is to design and manufacture stable and reliable technical equipment for batch coated tools, and gradually improve it to meet the market demand; Secondly, develop a new generation of coating components to further improve the cutting efficiency of coated tools; The third stage is to develop multi-layer coating and control technology, so that the tool surface has the comprehensive physical and mechanical properties of a variety of coating materials, so as to meet the needs of processing different metals

when people began to study new coatings, they all focused on the transition group elements carbon and nitride, because they have high hardness. Table 1 lists some physical and mechanical properties of wear-resistant compounds. It is not difficult to prepare these coatings by CVD and PVD technology. The key is whether the coating quality can play its own properties and the anti-wear role in the cutting process

Table 1 Physical and mechanical properties of several materials

material melting point

(° C) density

(g/cm) hardness

(HV) modulus of elasticity

(kn/mm) linear expansion coefficient

(/k) high temperature resistance

oxidation performance tic30674 0 general tin29505 4 general tib232254 8 general zrn29827 2 better crn16506 General Al2O3, 320473 4 good cemented carbide 1700

~1800 4.5~5.6 poor high speed steel 15007.8900 12 very poor

the study of tool wear mechanism shows that in high-speed cutting, the temperature of the tip can reach up to 900 ° C. at this time, the wear of the tool is not only mechanical friction wear (the main form of wear behind the tool), but also bonding wear, diffusion wear and oxidation wear (the main form of tool edge wear and crescent wear). Therefore, The cutting process can be regarded as a physical and chemical change process of a micro region

titanium carbide is a high hardness wear-resistant compound, which has good friction and wear resistance; The hardness of titanium nitride is slightly low, but it has high chemical stability, and can greatly reduce the friction coefficient between the tool and the workpiece. Considering the coating processability, both of them are ideal coating materials, but no matter titanium carbide or titanium nitride, a single coating is difficult to meet the comprehensive requirements of high-speed cutting for tool coating

titanium carbonitride (TiCN) is a nitrogen atom in a single tic lattice? (N) For the composite compound formed by occupying the position of the original carbon atom (c) in the lattice, there are two ideal modes for the proportion of carbon and nitrogen atoms in ticxny, namely tic0.5n0.5 and tic0.3n0.7. Because TiCN has the comprehensive properties of tic and tin, its hardness (especially high temperature hardness) is higher than tic and tin, so it is an ideal tool coating material

no material can compare with alumina (Al2O3) in terms of anti-oxidation and anti diffusion wear properties. However, because the physical and chemical properties of alumina and matrix materials are too different, a single alumina coating can not be made into an ideal coated tool. With the emergence of multi-layer coating and related technologies, the coating can not only improve the bonding strength with matrix materials, but also have the comprehensive properties of a variety of materials

so far, the CVD coating of cemented carbide blades can be roughly divided into four series: tic/tin, tic/ticn/tin, tic/al2o3 and tic/al2o3/tin. The first two categories are applicable to ordinary semi precision and finish machining, and the latter two categories are applicable to high-speed and heavy load cutting

whether the coating components can exert their due performance on the coated tool depends largely on the technical level of the coating process, because the bonding strength between the coating and the substrate, the coating and interface structure, preferred orientation, the thickness of each single layer and the total thickness are important factors that determine the performance of the coated tool, and these factors are directly related to the coating process. In addition to the blade material and geometric parameters, the differences in cutting performance of the tools with the same coating series prepared by various manufacturers are mainly caused by different coating processes and control technologies. Therefore, there are still many problems to be solved in improving CVD process and control technology

the above principles for selecting coating materials are also applicable to PVD coating. Because the PVD technology of Al2O3 (phase a) coating has not been completely broken through, the coating series containing Al2O3 cannot be coated in large quantities by PVD process, and the other two composite coating series have been applied in PVD coating in recent years. Technically, it is easy to prepare multilayer coatings composed of hundreds of layers (each layer is 50~1000nm thick) in the PVD process. When the thickness of single layer is 20~50nm, the wear resistance of this coating is the best. At present, tin/ticn, tic/ticn/tin, tin/zrn and other multilayer coatings have been applied to cemented carbide tools and parts through the PVD process, which does not mean that testing can not be done. It can be applied to the coating of high-speed steel tools, and its service life is more than twice that of a single tin PVD coating. Among them, ZrN coating is expected to generate a total revenue of $1.181 billion from Paek 3D printing by 2026, and cutting tools are particularly suitable for processing materials such as stainless steel

tialn is the only PVD coating containing aluminum. During the cutting process, aluminum oxidizes to form Al2O3, which plays the role of oxidation resistance and diffusion wear resistance. However, its oxidation resistance is slightly worse than that of a single Al2O3 coating, because Al2O3 formed in TiAlN is generated and worn away during the cutting process. But in high-speed cutting, its effect is better than TiCN coating without aluminum. Figures 1 and 2 show the approximate proportion of various coating components in CVD and PVD coated tools

tialn/al2o3 multilayer PVD coating has been successfully studied in the laboratory. At present, 400 layers (with a total thickness of 5 m) of multilayer coated cemented carbide tools can be prepared. The coating hardness of this tool is 4000hv, and its cutting performance is better than that of tic/al2o3/tin coated tools. It can be expected that further research on PVD process technology and expansion of the application of multiple multi-layer coatings on different cutting tools will achieve greater technical and economic benefits. The automatic calculation of other experimental machines shows that the coherent data of hard materials such as TiB2, HFN, TiNb, etc. can be used as coating materials, but because their physical and mechanical properties have no obvious advantages over the previous coating series, they are rarely used in actual production. In addition, CrN PVD coating is especially suitable for coating treatment of various molds because of its outstanding toughness and wear resistance

diamond coating is a new tool coating material successfully studied in recent years. This coated tool is especially suitable for processing non ferrous metals and fiber materials. Diamond coated cemented carbide blades and integral cemented carbide multi edge tools have achieved great success in processing printed circuit boards and silicon aluminum alloys. The tool life is dozens of times longer than that of uncoated cemented carbide tools. There are many technologies for preparing diamond coating, such as CVD, PVD and PCVD. No matter what technology, as long as the diamond film can be uniformly coated on each geometric surface of the tool, with sufficient bonding strength, stable process control and meeting the requirements of mass production, it can achieve good benefits in the industrial application of diamond coated tools. The method of welding the diamond thick film prepared by CVD on the edge of cemented carbide blade cannot replace the application of diamond coating technology in cutting tools. At present, there are 94 specifications of diamond coated carbide end mills, more than 100 sizes of diamond coated carbide fried dough twist drills, more than 180 specifications of diamond coated indexable blades, and various coated forming tools. In short, the varieties, specifications and application scope of diamond coated cemented carbide tools will be further expanded in the future

3 mutual supplement of CVD and PVD technology in tool coating

since tin PCD coated high-speed steel tools were put into industrial application in the early 1980s, people have been exploring whether PVD can be used to replace CVD process to coat cemented carbide blades. Due to the low temperature of the PVD process, the strength of the cemented carbide blade itself will not be reduced, and the blade edge can be ground very sharp, thus reducing the power consumption of the machine tool

although PVD has incomparable advantages over CVD

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