During machining, cutting tools will be subjected to several aspects of damage, such as cutting heat, high pressure, wear and heat oscillation. The temperature of the cutting edge will exceed 1000 ℃. This extreme heat will destroy the binding force of the various components of the tool material, and may also lead to a harmful chemical reaction between the tool and the processed material. Wear is what always happens during cutting: The contact surface between the tool and the processed material will support pressure greater than 140bar (2000PSI). The rapid heating and cooling of the cutting tools are very common situation in the processing: During cutting, the blade is heated; when the blade is removed from the cutting surface, the blade is cooled. This mechanical oscillation often occurs on the surface of a discontinuous process. Mechanical oscillations sometimes play the role of lathe work, depending on the operation and processing of the workpiece.
1. AlTiN coating
In order to solve these problems in the cutting process, many cutting tools have deposited AlTiN coating on PVD coating equipment by arc deposition technology. AlTiN coatings are mainly used in dry high speed machining and have many advantages, such as high hardness (Hv>30GPa), good wear resistance and high temperature oxidation resistance (850 ℃) and low thermal conductivity.
2. Aluminum oxide (Al2O3) coating
Some applications require special coatings, such as aluminum oxide coatings. Aluminum oxide coatings on cemented carbide inserts have the advantage of resistance to crater wear and thermal cracking. The alumina coatings are usually deposited by CVD (Chemical Vapor Deposition) methods. But there are some disadvantages, because it is deposited at high temperature (1000 ℃), and the brittleness of cemented carbide will affect the application of blade in metal cutting, especially in milling. The alumina PVD coating offers many advantages because of its lower deposition temperature range (typically between 350 ℃ and 600 ℃). In particular, its high temperature stability, chemical stability and low thermal conductivity are superior to other coatings. In the milling of stainless steel or the cutting of difficult-to-cut materials, PVD alumina coatings show better performance compared with conventional PVD coatings. By analyzing the interface microstructure of the AlTiN coating and the alumina coating, it is known that the aluminum oxide coating and the face-centered cubic lattice AlTiN bond very well. The structure analysis shows that the alumina coating is the amorphous chromium structure in y phase, and the grain size is about 5~10 nm.
3. Mixed coating equipment
PVD ion plating coating equipment using mixed coating technology: cathodic arc evaporation technology and magnetron sputtering technology are mixed in a process. The hybrid technology combines the advantages of PVD hard coatings with excellent wear resistance, low friction coefficient and low chemical activity. The arc coating, as a binding layer, provides the necessary abrasion resistance to the whole coating, and the alumina coating has temperature and chemical stability.
In addition, the alumina coating can also be used as a separate coating in some special cases. The alumina coating is deposited by a unique design of the sputtering cathode combined with the optimum design system for the process gas. The closed circuit magnetic field formed by the electromagnetic induction coil forms plasma with a high ionization rate near the workpiece, thereby realizing the required coating performance.
The tool coating deposited by arc technology, such as AlTiN coating, can further improve the application performance of the tool. The next step in the development of tool coating technology should be based on the hybrid technology of arc technology and sputtering technology. It is the combination of these two technologies to form a foundation for new breakthroughs in tool application performance.