Characteristics and uses of tool "armored" surface coating technology
The tool is “armoredâ€, ie the tool coating. As we all know, the tool surface coating technology is a high-quality surface modification technology developed in response to market demand. Because this technology can make the cutting tool obtain excellent comprehensive mechanical properties, it can not only effectively improve the tool life, but also Significantly improve the machining efficiency, so this technology has been related to materials, processing technology and called the 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 pay great attention to the development of coating technology. Choosing the right tool coating for different applications is one of the most important factors in ensuring efficient machining. Proper selection of coatings can reduce the cost per project or piece, as this reduces friction; reduces heat and cold shrinkage, reduces cutting forces; increases feed rate and speed; improves workpiece surface quality and reduces downtime. Choosing the right coating for a particular application can be a complex and laborious task. Every coating that can be seen on the market has its advantages and disadvantages, and improper selection can shorten tool life and make the problem worse. A wide variety of tool coatings are available, including PVD coatings, CVD coatings, and composite coatings with alternating PVD and CVD coatings, which are readily available from tool manufacturers or coating suppliers. Floor. This article will introduce some of the common properties of tool coatings as well as some common PVD and CVD coating options. Each of the properties of the coating plays an important role in determining which coating is most beneficial for cutting. 1. Characteristics of the coating (1) Hardness The high surface hardness brought by the coating is one of the best ways to improve the life of the tool. In general, the higher the hardness of the material or surface, the longer the life of the tool. Titanium Nitride (TiCN) coatings have higher hardness than Titanium Nitride (TiN) coatings. Due to the increased carbon content, the hardness of the TiCN coating is increased by 33%, and the hardness varies from about Hv 3000 to 4000 (depending on the manufacturer). The use of CVD diamond coatings with surface hardness up to Hv9000 is relatively mature on tools, and the lifetime of CVD diamond coated tools is 10 to 20 times higher than that of PVD coated tools. The high hardness and cutting speed of diamond coatings can be 2 to 3 times better than uncoated tools, making it a good choice for non-ferrous materials. (2) Abrasion resistance Abrasion resistance refers to the ability of a coating to resist abrasion. Although the hardness of some workpiece materials may not be too high, the elements added during the production process and the processes used may cause the cutting edges of the tool to crack or blunt. (3) Surface lubricity High friction coefficient increases the heat of cutting, resulting in shortened or even lost coating life. Lowering the coefficient of friction can greatly extend tool life. A smooth, smooth or textured coating surface helps reduce heat of cut because the smooth surface allows the chips to slide away from the rake face quickly and reduce heat generation. Compared to uncoated tools, coated tools with better surface lubricity can be machined at higher cutting speeds to further avoid high temperature welding with workpiece materials. (4) Oxidation temperature The oxidation temperature refers to the temperature at which the coating begins to decompose. The higher the oxidation temperature value, the more advantageous the cutting process under high temperature conditions. Although the TiAlN coating may have a lower room temperature hardness than the TiCN coating, it has proven to be much more effective than TiCN in high temperature processing. The reason why the TiAlN coating retains its hardness at high temperatures is the formation of a layer of alumina between the tool and the chip, which transfers heat from the tool to the workpiece or chip. Carbide tools typically have higher cutting speeds than high-speed steel tools, making TiAlN the preferred coating for carbide tools. Carbide drills and end mills typically use this PVDTiAlN coating. (5) Anti-adhesion The anti-adhesion of the coating prevents or reduces the chemical reaction between the tool and the material being processed, and prevents the workpiece material from depositing on the tool. When machining non-ferrous metals (such as aluminum, brass, etc.), built-in chips (BUE) often occur on the tool, causing tool chipping or workpiece size. Once the material being processed begins to adhere to the tool, the adhesion will continue to expand. For example, when an aluminum workpiece is machined by a forming tap, the aluminum adhered to the tap increases after each hole is machined, and finally the diameter of the tap becomes too large, causing the workpiece size to be out of service. Coatings with good anti-blocking properties work well even in applications where the performance of the coolant is poor or the concentration is insufficient. 2. Commonly used coatings (1) Titanium nitride coating (TiN) TiN is a general-purpose PVD coating that improves tool hardness and has a high oxidation temperature. This coating is used for high speed steel cutting tools or forming tools for very good machining results. (2) Titanium Nitride Coating (TiCN) The carbon added to the TiCN coating improves tool hardness and provides better surface lubricity, making it an ideal coating for high speed steel tools. (3) Nitrogen aluminum titanium or nitrogen titanium aluminum coating (TiAlN/AlTiN) The aluminum oxide layer formed in the TiAlN/AlTiN coating can effectively improve the high temperature processing life of the tool. This coating is available for cemented carbide tools primarily used for dry or semi-dry machining. Depending on the ratio of aluminum to titanium contained in the coating, the AlTiN coating provides a higher surface hardness than the TiAlN coating, making it a viable coating option for high speed machining. (4) Chromium nitride coating (CrN) The good adhesion resistance of the CrN coating makes it the preferred coating in the processing of built-up edge defects. With this almost invisible coating, the processing properties of HSS tools or carbide tools and forming tools will be greatly improved. (5) Diamond coating (Diamond) CVD diamond coating can provide the best performance for non-ferrous metal processing tools. It is ideal for processing graphite, metal matrix composite (MMC), high silicon aluminum alloy and many other high abrasive materials. Coating (Note: Pure diamond coated tools cannot be used to machine steel because a large amount of cutting heat is generated when machining steel and chemical reactions occur, causing damage to the adhesion between the coating and the tool). The coatings used for hard milling, tapping and drilling are different and have their specific application. In addition, multi-layer coatings can be used, which also embed other coatings between the surface layer and the tool base to further increase tool life. 3. Successful application of coatings A cost-effective application of a coating may depend on many factors, but for each particular processing application, there is usually only one or several possible coating options. The correct choice of coating and its properties may mean a difference between a significant increase in processability and little improvement. Cutting depth, cutting speed and coolant can all have an effect on the application of the tool coating. Since there are many variables in the processing of a workpiece material, one of the best ways to determine which coating to use is through trial cutting. Coating suppliers are continually developing new coatings to further improve the coating's high temperature, friction and wear resistance. It is always a good thing to work with the coating (tool) manufacturer to verify that the latest and best tool coatings are used in the process.
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