Development of foreign cutting tool coating technology

Abstract: The surface coating technology of cutting tools is a material surface modification technology developed in recent decades in response to market demand. The coating technology can effectively improve the service life of the cutting tool, and the tool can obtain excellent comprehensive mechanical properties, thereby greatly improving the machining efficiency.

The surface coating technology of cutting tools is a material surface modification technology developed in recent decades in response to market demand. The coating technology can effectively improve the service life of the cutting tool, and the tool can obtain excellent comprehensive mechanical properties, thereby greatly improving the machining efficiency. Therefore, coating technology together with materials and cutting processes is called the three key technologies in the field of cutting tool manufacturing. In order to meet the requirements of modern machining for high efficiency, high precision and high reliability, the manufacturing industry in the world has paid more and more attention to the development of coating technology and its application in tool manufacturing.

Tool coating technology can be divided into chemical vapor deposition (CVD) technology and physical vapor deposition (PVD) technology, which are reviewed as follows.

1. foreign CVD technical development <br> <br> since the 1960's, CVD technique is widely used in turning carbide surface treatment position of the tool. Since the preparation of the metal source required for vapor deposition in the CVD process is relatively easy, deposition of single-layer and multi-layer multi-layer composite coatings such as TiN, TiC, TiCN, TiBN, TiB2, Al2O3, etc. can be realized, and the bonding strength between the coating and the substrate is high, and the film is high. Thickness can reach 7 ~ 9μm, so by the middle and late 1980s, 85% of cemented carbide tools in the United States used surface coating treatment, of which CVD coating accounted for 99%; by the mid-1990s, CVD coating Carbide inserts still account for more than 80% of coated carbide tools.

Although the CVD coating has good wear resistance, the CVD process has its own defects: First, the processing temperature is high, which tends to cause the bending strength of the tool material to decrease; secondly, the inside of the film is in a tensile stress state, which is easy to cause the tool to be used. Microcracks are generated when the CVD process emits exhaust gas and waste liquid, which is in conflict with the current green manufacturing concept. Therefore, since the mid-1990s, the development and application of high temperature CVD technology has been limited. Restricted.

At the end of the 1980s, the low temperature chemical vapor deposition (PCVD) technology developed by Krupp.Widia reached a practical level. The processing temperature has been reduced to 450-650 ° C, which effectively suppresses the generation of η phase. It can be used for thread cutters and milling cutters. The molds are coated with TiN, TiCN, TiC, etc., but so far, the PCVD process has not been widely used in the field of tool coating. In the mid-1990s, the emergence of new technologies for medium temperature chemical vapor deposition (MT-CVD) revolutionized CVD technology. MT-CVD technology is a new process for the decomposition and chemical reaction of TiCL4, H2 and N2 at 700-900 °C to form TiCN with C/N organic acetonitrile (CH3CN) as the main reaction gas. The coating of dense fibrous crystalline form can be obtained by MT-CVD technology, and the coating thickness can reach 8-10 μm. The coating structure has high wear resistance, thermal shock resistance and toughness, and can be deposited on the surface of the blade by high temperature chemical vapor deposition (HT-CVD) process, such as Al2O3, TiN, etc. A material with low material affinity and good self-lubricating properties.

The MT-CVD coated inserts are suitable for use in high speed, high temperature, high load, dry cutting conditions and have a life expectancy that is approximately double that of conventional coated inserts. At present, CVD (including MT-CVD) technology is mainly used for the surface coating of cemented carbide turning tools, and the coating tool is suitable for high speed roughing and semi-finishing of medium and heavy cutting. CVD technology can also achieve α-Al2O3 coating, which is currently difficult to achieve PVD technology, so CVD coating technology still plays an important role in dry machining.

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