Characteristics and Uses of Tool Surface Coating Technology
Choosing the right tool coating according to different applications is one of the most important factors in ensuring efficient processing. Proper selection of the coating can reduce the cost of each item or piece of each item, as this can reduce friction; reduce the heat up and down, reduce the cutting force; improve the feed rate and speed; improve the workpiece surface quality and reduce downtime. Choosing the right coating for a particular application can be complicated and laborious. Each coating that can be seen on the market has its advantages and disadvantages, and improper selection will shorten tool life and make the problem worse.
There are a number of tooling options available, including PVD coatings, CVD coatings, and composite coatings that are alternately coated with PVD and CVD. These coatings can be easily obtained from tool manufacturers or coating suppliers Floor. This article will introduce some of the common properties of the tool coating and some commonly used PVD, CVD coating options. When determining which coating is to be used most useful for cutting, each of the properties of the coating plays a very important role.
1. Characteristics of the coating
(1) hardness
The high surface hardness of the coating is one of the best ways to improve tool life. In general, the higher the hardness of the material or surface, the longer the life of the tool. Titanium nitride (TiCN) coatings have a 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 Hv3000 to 4000 (depending on the manufacturer). Surface hardness of up to Hv9000 CVD diamond coating on the application of the tool has been more mature, compared with the PVD coating tool, CVD diamond coating tool life increased by 10 to 20 times. The high hardness and cutting speed of the diamond coating can be improved by 2 to 3 times compared to the uncoated tool making it a good choice for cutting non-ferrous materials.
(2) wear resistance
Wear resistance refers to the ability of the coating to resist wear. Although the hardness of some of the workpiece material itself may not be too high, but in the production process to add the elements and the use of the process may cause the cutting edge of the tool crack or blunt.
(3) surface lubricity
High friction coefficient will increase the cutting heat, resulting in shorter coating life or even failure. While reducing the friction coefficient can greatly extend the tool life. Fine smooth or textured coated surfaces help to reduce the heat of cutting, because the smooth surface allows the chips to slip away from the rake face and reduce heat generation. Compared with the uncoated tool, the better surface finish of the coating tool can also be processed at a higher cutting speed, so as to further avoid the high temperature welding with the workpiece material.
(4) oxidation temperature
The oxidation temperature is the temperature at which the coating begins to decompose. The higher the oxidation temperature, the more favorable the cutting process under high temperature conditions. Although the hardness of the TiAlN coating may be lower than that of the TiCN coating, it is proved to be much more effective than the TiCN in high temperature processing. The reason why the TiAlN coating can maintain its hardness at high temperatures is that an alumina can be formed between the tool and the chip, and the alumina layer can transfer heat from the tool to the workpiece or chip. Compared with high-speed steel tools, carbide cutting tool cutting speed is usually higher, which makes TiAlN cemented carbide cutting tool preferred coating, carbide drill and end mill is usually used this PVDTiAlN coating.
(5) anti-cohesive
The anti-sticking properties of the coating prevent or reduce the chemical reaction of the tool with the material being processed to prevent the workpiece material from being deposited on the tool. In the processing of non-ferrous metals (such as aluminum, brass, etc.), the tool often produce BUE (BUE), resulting in tool chipping or workpiece size tolerance. Once the material is processed to adhere to the tool, the adhesion will continue to expand. For example, when the aluminum tapes are machined with the forming tap, the aluminum adhering to the taps on each hole is increased, and finally the tap diameter becomes too large, resulting in the workpiece size being discarded. Coatings with good resistance to cohesion can also play a very good role even in applications where the coolant is poor or has insufficient concentration.