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status quo
Since the advent of the first generation of CVD vapor-deposited TiC cemented carbide inserts in the late 1960s, coating technology has greatly contributed to the development of cemented carbide tools. In the early 1980s, PVD vapor deposition of TiN was successfully applied to high speed steel tools, which was hailed as a revolution in the performance of high speed steel tools. Since then, the coating technology has achieved rapid development, the coating process is becoming more and more mature, and the application range of coating tools is more and more extensive.
The proportion of coated tools used in Western industrialized countries to indexable inserts has increased from 26% in 1978 to 90% in 2005. About 80% of the tools used in new CNC machine tools are coated tools. Sweden's Sandvik Coromant and Kennametal's coated inserts have a ratio of more than 85%, and the proportion of carbide coated blades used on CNC machines in the US is 80%. Coatings for Swedish and German turning. The tools are all above 70%. Japan and Russia coating technology development and application are also in the forefront of the world. China's coated knives started late, but the progress is fast, and the coating outlets are spread all over the country. Many cities have their own coating centers, which undertake external processing business. The factories and mines are not to be outdone. Several large tool factories in China have coating machines. More than 10, but most of them are used in low-end products such as twist drills. Coating companies in industrialized countries such as Germany have set up camps in China and engaged in the processing of coated tools. Due to lack of resources and efficient machining, as well as advances in CNC technology and the increase in difficult materials, coated tools are moving forward at an alarming rate.
New developments in coating technology
Throughout the development process of CVD and PVD technologies, several common laws can be found. When the first generation of coated products enters the market, the first thing to solve is the localization of coating equipment to meet market needs; the second is to develop a new generation of coating components to improve the processing efficiency of the tool; the third is to develop Multi-layer coating and control technology make the surface of the coated tool have comprehensive mechanical properties of various materials, and implement personalized service for different processing objects such as cutting and drawing. The new development of coating technology is mainly reflected in the following three aspects:
(1) Diffusion of film materials The most widely used coating materials are TiC, TiN, TiCN and Al2O3. Today's most widely used TiAlN ternary coatings in cemented carbide coated tools, and can adjust the composition ratio of Al elements to obtain different film properties. The coating material evolved from the original TiC and TiN monolayers to the current composite coating. The emergence of composite coatings and related technologies allows the coating to improve the bonding strength with the substrate and the composite properties of a variety of materials. The multi-component composite thin materials such as TiN/NbN and TiN/CNx developed in recent years have greatly improved the life of coating tools. The diversification of the coating process combination brings about multi-component composite coatings such as TiAlN, TiAlCN and CrSiN, which enables the tool to obtain excellent comprehensive properties such as high wear resistance, low friction, good thermal stability and oxidation resistance. (2) Soft coating
High hardness is the main goal pursued in the development of early coating technology, but not all materials are suitable for hard coating. For example, high-strength aluminum alloys, titanium alloys and some valuable materials are not suitable for processing with hard-coated tools, while soft coatings better solve the difficult processing problems of the above materials. Soft coatings mainly include MoS2, WS2, TaS2 and the like.
(3) Nano-coating Recently, American scholars have developed nano-coated tools. These coated tools can be used in different combinations of various coating materials to meet different functional and performance requirements. The material has excellent anti-friction and anti-wear properties and self-lubricating properties, suitable for high-speed dry cutting, especially suitable for use on CNC machine tools. It is a representative nano-mixed film composed of AlTiN grains and amorphous Si3N4 nano-components, the hardness of which can reach 45GPa, and the stability and oxidation resistance of the film can reach 1000 °C.
PVD and CVD will coexist for a long time. As early as more than 20 years ago, PVD coatings have been put into industrial production. People have been exploring the problem of using PVD instead of CVD. After many twists and turns, ideas and practices have become a bubble.
Although PVD has the advantage that CVD is difficult to compare, it can also carry out a variety of hard coatings other than Al2O3, but the facts show that CVD cars and milling tools are better than PVD. In the future, the two coatings will coexist and complement each other in the cutting tool coating for a long time, and occupy their own share in the coating product due to their respective advantages. The two technologies can also be combined with each other to complement each other, as is the case with the currently applied PCVD coating technology.
Application of coated tools
Coating technology is currently widely used in various sectors such as machinery, electronics, optics, aerospace, chemical, textile and food industries. High-tech means not only can deposit various metals and alloys, but also deposit a variety of compounds, not only on the metal substrate, but also on non-metals such as ceramics, diamonds, glass and even plastics. It is no exaggeration to say that Coating technology has penetrated into all areas of the national economy, and its role and effectiveness are obvious to all. Whether it is at the domestic or foreign machine tool expo, people will see a wide variety of coating tools with different methods, and application examples are numerous.
Several issues to be noted in the coating:
(1) Ideal tool material The tool material used for coating must be an ideal good material and should not stay at a qualified level. As the saying goes, good steel should be used on the blade. At present, the market for tool materials is not standardized, and there is a mixture of fake and fake. In the selection of materials, materials should be intensified inspection, put a good level of each level, or do not give up before.
(2) Hardness inspection If the hardness of the tool is not suitable for coating, the coating technology is no better. For example, high-speed steel tools below 65HRC, 501 steel end mills with hardness greater than 68HRC, and so-called low-alloy high-speed steel drills, the coating effect is not necessarily good. By appropriate heat treatment, the hardness of the tool can be controlled within the customer's satisfaction, and the ideal coating will be added. JB/T8365-96 "Titanium nitride coated tool technical specification", requires high-speed steel tool coating hardness ≥ 2000HV, but many coating products on the market currently do not reach this value, often low-hardness decorative plating, or The thickness of the coating is not up to standard.
(3) The demagnetization treatment should be performed before the demagnetization coating, because the magnetic properties will affect the coating effect.
Current status and prospects of tool coating technology
Coating the tool is a major change in the machining industry. It is a layer of refractory compound coated on the substrate with high toughness of the tool, so that the performance of the tool is obtained. Greatly improved. Coated tools can improve processing efficiency, processing accuracy, extend life and reduce costs, and are therefore of widespread concern worldwide.