Tool coating is an important key to improving tool life and can be divided into many different types according to different cutting methods or environments. Choosing the right tool coating for your needs, can help extend tool life and optimize production process.
What is Tool Coating?
Tool coating is a method that can improve the wear resistance of the tool. The coated tool is obtained by coating a thin layer of refractory metal or non-metallic compound with good wear resistance on the surface of cemented carbide or high-speed steel (HSS) substrate with good strength and toughness by a vapor deposition method.
Carbide tool coating method:
To improve tool performance, tool surface coating technology is one of the factors to improve. The coating provides the tool with strong protection, acid resistance, oxidation resistance, and wear resistance. The coating can improve the surface hardness and thermal stability coefficient of the tool, and reduce the friction coefficient to increase the cutting speed, thereby increasing the processing efficiency and tool life.
- Chemical vapor deposition (CVD):
CVD is a chemical technology that utilizes the production of solid-state materials with high purity and good performance. It is widely used in cemented carbide and can be converted into the surface treatment of cutting tools. In CVD technology, the reaction source is introduced into the reaction chamber in the form of gas, and the chemical reaction is carried out through the reaction of oxidation and reduction with the substrate, and then the product is deposited on the surface of the substrate by internal diffusion. In the reaction process, different by-products may also be produced, but most of them will be carried away with the gas flow and will not remain in the reaction chamber.
CVD technology is mainly used for hard and gold turning tool coatings. It is suitable for high-speed machining of medium and heavy cutting. In comparison, CVD equipment is simple, the process is mature, there are many types of deposits, the rate is high and easy to control, and there is a high degree of penetration. It can obtain multi-layer coatings of different structures with uniform thickness. And its production process cost is low, and it is more suitable for mass production.
- Physical vapor deposition (PVD):
PVD is physical vapor deposition, which mainly deposits thin films by physical reactions, that is, vacuum coating (evaporation). The PVD process is mostly used for the surface treatment of cutting tools and various molds, as well as the production 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 almost most material films, but the uniformity of film thickness will need to be overcome. production constraints.
PVD technology is mainly suitable for solid carbide tools and high-speed tool steel tools and is widely used in the treatment of coatings such as carbide drills, milling cutters, taps, and welding tools. The coating temperature of PVD is lower than the tempering temperature of high-speed tool steel, so it will not hurt the hardness and dimensional accuracy. After coating, there is no need for heat treatment, and the thickness of the coating is only a few microns, which can maintain the accuracy of the original workpiece, and the manufacturing process is also cleaner, pollution-free, and pollution-free.
What Types of Tool Coatings are there?
Relying on a single coating alone cannot meet the requirements of improving various mechanical properties, so the components of the coating are gradually diversified and compounded. According to different cutting processing requirements, the coating can be divided into more complex, and in the composite coating, the thickness of each component coating is getting thinner and thinner, and even tends to be nanosized.
The following are some common coatings:
- Titanium nitride coating (TiN):
TiN is a general-purpose PVD coating that increases tool hardness and has a higher oxidation temperature. A good machining results can be obtained for high-speed steel cutting tools or forming tools.
- Chromium Nitride Coating (CrN):
The good adhesion resistance of CrN coating makes it easy to produce a built-up edge, and it is also widely used. The application of this almost invisible coating will improve the machining performance of high-speed steel or carbide cutting tools and forming tools.
- Diamond coating (Diamond):
CVD diamond coatings provide optimum performance for non-ferrous metal machining tools and are suitable coatings for machining graphite, metal matrix composites (MMC), high silicon aluminum alloys, and many other highly abrasive materials.
- Titanium Nitride Carbide Coating (TiCN):
The carbon element added in the TiCN coating can improve the hardness of the tool and obtain better surface lubricity, which is suitable for high-speed steel tools.
- Nitrogen Aluminum Titanium or Nitrogen Titanium Aluminum Coating (TiAlN/AlTiN):
The alumina layer formed in the TiAlN/AlTiN coating can effectively improve the high-temperature machining life of the tool. Mainly used in dry or semi-dry machining, suitable for coating carbide tools. Depending on the ratio of aluminum and titanium contained in the coating, AlTiN coating can provide higher surface hardness than TiAlN coating, which is suitable for high-speed machining.
- Coating equipment:
Coatings for hard milling, tapping, and drilling are different and each is suitable for its specific application. In addition, multi-layer coatings can be used, which embed other coatings between the surface layer and the tool base, thereby increasing the service life of the tool.
What are the Advantages of the Tool Coating Process?
The coated tool has a higher surface hardness, good wear resistance, stable chemical properties, heat resistance, oxidation resistance, etc., during the cutting process, the life of the tool is 3 to 5 times longer than that of the uncoated tool, and the cutting speed and precision, and even lower costs. After the knife with better toughness is coated, the knife can have a more comprehensive and good comprehensive performance. After coating, it also helps to improve the hardness of the tool, so the coating process is important for the tool.
Characteristics of Coated Tools:
The high surface hardness brought about by the coating is one way to increase tool life. The harder the material or surface, the longer the tool life. Titanium carbide nitride (TiCN) coatings have higher hardness than titanium nitride (TiN) coatings. Due to the increase of carbon content, the hardness of TiCN coating increases by 33%, and its hardness varies from about Hv3000 to 4000. It is also often used in the coating of CVD diamond tools, which can increase the life of CVD diamond-coated tools by about 10 to 20 times. The high hardness and cutting speed of diamond coating can be 2 to 3 times higher than that of uncoated tools, which is a suitable choice for cutting non-ferrous materials.
- Oxidation temperature:
Oxidation temperature refers to the temperature at which the coating begins to decompose. The higher the oxidation temperature value, the more favorable it is for machining under high-temperature conditions. The reason why the TiAlN coating can maintain its hardness at high temperature is that a layer of aluminum oxide can be formed between the tool and the chip, and the aluminum oxide layer can transfer heat from the tool to the workpiece or chip. Carbide tools generally have higher cutting speeds than HSS tools, and carbide drills and end mills are usually coated with PVDTiAlN.
- Wear resistance:
Abrasion resistance refers to the ability of a coating to resist abrasion. While some workpiece materials may not be too hard on their own, the elements added during production and the processes used can cause tool cutting edges to chip or become dull.
- Surface lubricity:
A high coefficient of friction increases cutting heat, which can lead to reduced coating life or even failure. And reducing the coefficient of friction can extend tool life. A finely smooth or regular-textured coating surface helps reduce the heat of cutting, as the smooth surface reduces heat generation by allowing chips to slide quickly off the rake face. Coated tools with better surface lubricity can also be machined at higher cutting speeds than uncoated tools, further avoiding high-temperature fusion welding with the workpiece material.
The anti-stick properties of the coating prevent or mitigate chemical reactions between the tool and the material being machined, preventing workpiece material from depositing on the tool. When machining non-ferrous metals (such as aluminum, brass, etc.), BUE often occurs on the tool, resulting in tool chipping or workpiece size out of tolerance. Once the material being machined begins to adhere to the tool, the adhesion will continue to expand. Coatings with good anti-blocking properties work well even in applications with poor coolant properties or insufficient concentrations.
Application of Tool Coating:
The application of a good coating depends on many factors, so it is a matter of trial and error to choose the right coating for different specific processing applications. The correct choice of coating and its properties will be critical in enhancing or improving processability. Depth of cut, cutting speed, and coolant can all have an impact on how well the tool coating is applied. Since there are many variables in the machining of workpiece material, one of the best ways to determine which coating to use is through trial cuts. Coating suppliers are constantly developing new coatings to further improve the high temperature, friction, and wear resistance of coatings.
The service life of the tool will be monitored from the cutting process, or other indicators and the cost will be minimized. The coating of the tool is one of the key factors affecting the life of the tool. According to different cutting methods and workpiece materials, choosing different but suitable tool coatings will help to optimize the entire process and optimize the production efficiency.