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    Types of Cutting Tool Coatings: How to Select the Ideal Coating for Cutting Tools

    Tool coating is one of the issues that can improve tool life. According to different cutting methods or environments, it can be divided into many different components. Technology can be divided into chemical and physical types. Is the coating you are using currently correct? This article will introduce the coating technology and types so that you can better understand and choose the most suitable method.

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    Carbide tools coating method

    During the past half-century, in order to improve tool performance and tool surface coating technology has become mainstream. Like the armor of a tool, the coating has the characteristics of strong protection, acid resistance, oxidation resistance, and wear resistance, which can improve the surface hardness and thermal stability coefficient of the tool, also reduce the friction coefficient to increase the cutting speed, thereby increasing the machining efficiency and tool life. Tool coating technology can be divided into two categories: CVD (chemical) and PVD (physical)

    Chemical vapor deposition

    CVD uses chemical technology to produce solid materials with high purity and good performance. It is widely used in the surface treatment of hard alloys which can be turned into tools. For example, the semiconductor industry will use this technology to grow thin films. For CVD, the reaction source is introduced into the reaction chamber in the form of gas, and the chemical reaction is carried out through oxidation, reduction, and substrate reaction, the products will deposit on the surface of the substrate by internal diffusion finally. Different products may also be produced during the reaction, but most of them will be carried away with the airflow and will not remain in the reaction chamber.

    CVD technology is mainly used for hard and metal turning tool coatings. It is suitable for high-speed machining of medium and heavy cutting. In comparison, CVD equipment is simpler, the process is mature, has many types of deposits, a high rate and is easy to control, moreover there is a high degree of permeability and uniformity. It can obtain multi-layer coatings of different structures with uniform thickness, and the most important thing is that the process cost is low, which is suitable for mass production.

    Physical vapor deposition

    PVD is an industrial manufacturing industry. It mainly deposits thin films by physical reactions, that is, vacuum coating (evaporation deposition) which is mostly used for the surface treatment of cutting tools and various molds, as well as the fabrication of semiconductor devices. The difference between PVD and CVD is that the adsorption and desorption of PVD are physical, while CVD is chemical, and PVD has a wide range of applications. PVD can be used for most material films, but the uniformity of film thickness will be a problem.

    PVD technology is mainly suitable for integrated solid carbide tools and high-speed steel tools and is widely used in the coating of carbide drills, milling cutters, taps, and welding tools. The coating temperature of PVD is lower than the tempering temperature of high-speed steel tools, so it will not hurt the hardness and dimensional accuracy. No heat treatment is required after coating, also the thickness of the coating is only a few microns to maintain the original accuracy. The whole process is clean and pollution-free.

    Type of coating

    Only relying on a single coating cannot meet the requirements of improving various mechanical properties, therefore, the components of the coating are gradually diversified and compounded. According to different cutting machining requirements, the coating can be divided into more complex, and composite coating, also the thickness of each component coating is getting thinner and thinner, and even tends to be nanosized. Here are some common coatings for your reference:

    The advantages of coating

    By comparison, the coated tool has a higher surface hardness, good wear resistance, stable chemical properties, heat resistance, oxidation resistance, etc., and the life of the tool is 3 to 5 times longer than that of the uncoated tool during the cutting process, moreover, it can improve cutting speed and accuracy, and even reduce costs. After the knife with better toughness is coated, the knife can have a better comprehensive performance.

    In terms of hardness, the original high-speed steel of 760 to 960HV and the carbide of 1300HV to 1850HV can be increased to more than 2000 to 3000HV, therefore, the coating is very important for the tools.


    Conclusion

    Tool life has always been a topic of great concern in many manufacturing industries. Whether it is discussed during the cutting process or monitored through other ways, it is expected to find problems as soon as possible and minimize costs, and coating is one of the factors that will affect the tool’s life. Using different coating tools for different cutting methods and workpiece materials will help optimize the entire process and the benefits.

    Main image photo by Read01

    References Wikipedia / KKNEWS

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