Trends in PVD Tool Coating Technology

The tool is one of the most active elements of the cutting system. With the development of technology, the feed rate and cutting speed of coated tools have been increased, while their service life has also been extended. PVD is a standard term for surface treatment, which is a physical process of transferring molecules or atoms onto the surface of a substrate to give it special properties such as high strength, wear resistance and heat dissipation.

Coated tools have the following characteristics:

(1) The surface coating material has strong wear resistance, high hardness, high temperature resistance and other characteristics.

(2) Coated tools have good overall performance, which also makes the versatility of coated tools has been further improved, so that it can have a wider range of applications.

(3) With the rapid development of science and technology, coating technology has also been developed, the oxidation resistance and high temperature resistance of coated tools will become more prominent, to complete high-speed cutting processing and improve the efficiency of cutting.

Specific applications of PVD coating technology in tool production

Twenty years ago all coating tools used in the machining industry were predominantly "all-purpose tools", i.e. they could be used in many different applications. This has now changed, as the demands on tool performance have increased and tools are often selected for specific machining situations. The current development of tool materials will revolve around fast, hard and dry tools. Therefore, in the process of coating tools, multi-layer superhard coatings can be used to optimise thermal protection and thus extend tool life.

In the field of drilling and milling, PVD-coated tools are more adaptable than CVD-coated tools. The main reason for this is that the CVD coated milling cutters are not worn out by the coating, but by the fact that the inserts are severely damaged during use, making them unusable. This problem is solved by the use of sputter coating technology in the PVD coating process. Large-scale industrial production under precisely controlled conditions requires that the surface and coating thickness of each batch of tool material should be controlled to within ∼1um, even when the system is operating under high load during the specific production process and the density of the microstructure is high. In addition, the coating thickness distribution does not vary along the cutting tool, so that the cutting tool is always sharp for the specific application and meets the requirements.

Modern tools are often used in high-speed cutting applications and to meet this demand, TiAlN coated cutting tools produced by applying the PVD method are widely used and are being rapidly promoted. The PVD method implants Al atoms within the various interstices of the Ti N crystals, ultimately forming a gap-free, complete crystal assembly. Currently, the latest TiAlN coatings are able to make the aluminium content exceed 50%, which gives TiAlN coatings new characteristics. Analysis shows that when the aluminium content exceeds 50%, a dense layer of Al2O3 will appear at the top of the coating, and when it is subjected to A12O3 wear, the Al present in the TiAlN will oxidise again to form a new A12O3 layer, so that the TiAlN coating can protect the tool even when it is working at high temperatures and speeds.