Types, properties and characteristics of diamond tool materials and tool applications
Diamond is an allotrope of carbon, and it is the hardest material found in nature. Diamond tools have high hardness, high wear resistance and high thermal conductivity, and are widely used in the processing of non-ferrous metals and non-metallic materials. Especially in the high-speed cutting of aluminum and silicon-aluminum alloys, diamond tools are the main types of cutting tools that are difficult to replace. Diamond tools that can achieve high efficiency, high stability, and long-life machining are indispensable and important tools in modern CNC machining.
⑴ Types of diamond tools
① Natural diamond tool: Natural diamond has been used as a cutting tool for hundreds of years. The natural single crystal diamond tool has been finely ground, and the cutting edge can be ground extremely sharp. The cutting edge radius can reach 0.002μm, which can realize ultra-thin cutting and can It is a recognized, ideal and irreplaceable ultra-precision machining tool for processing extremely high workpiece precision and extremely low surface roughness.
② PCD diamond tool: Natural diamond is expensive, and polycrystalline diamond (PCD) is widely used in cutting. Since the early 1970s, polycrystalline diamond (Polycrystauine diamond, PCD for short) was developed After success, natural diamond tools have been replaced by artificial polycrystalline diamond in many occasions. PCD raw materials are rich in sources, and its price is only a few tenths to one tenth of natural diamonds.
PCD tools cannot grind extremely sharp edges, and the surface quality of the processed workpieces is not as good as that of natural diamond. It is not convenient to manufacture PCD inserts with chip breakers in the industry. Therefore, PCD can only be used for fine cutting of non-ferrous metals and non-metals, and it is difficult to achieve ultra-precision mirror cutting. ③ CVD diamond tools: From the late 1970s to the early 1980s, CVD diamond technology appeared in Japan. CVD diamond refers to the synthesis of diamond film on heterogeneous substrates (such as cemented carbide, ceramics, etc.) by chemical vapor deposition (CVD). CVD diamond has exactly the same structure and characteristics as natural diamond.
The performance of CVD diamond is very close to that of natural diamond, and it has the advantages of natural single crystal diamond and polycrystalline diamond (PCD), and overcomes their shortcomings to a certain extent.
⑵ Performance characteristics of diamond tools
① Extremely high hardness and wear resistance: Natural diamond is the hardest substance found in nature. Diamond has extremely high wear resistance. When processing high-hardness materials, the life of diamond tools is 10 to 100 times that of cemented carbide tools, or even hundreds of times.
② It has a very low coefficient of friction: the coefficient of friction between diamond and some non-ferrous metals is lower than that of other cutting tools, the coefficient of friction is low, the deformation during processing is small, and the cutting force can be reduced.
③ The cutting edge is very sharp: the cutting edge of diamond tools can be sharpened, and the natural single crystal diamond tool can be as high as 0.002-0.008μm, which can be used for ultra-thin cutting and ultra-precision machining.
④ Has high thermal conductivity: diamond has high thermal conductivity and thermal diffusivity, cutting heat is easily dissipated, and the temperature of the cutting part of the tool is low.
⑤ Low thermal expansion coefficient: The thermal expansion coefficient of diamond is several times smaller than that of cemented carbide, and the change in tool size caused by cutting heat is very small, which is especially important for precision and ultra-precision machining that requires high dimensional accuracy.
⑶ Application of diamond tools
Diamond tools are mostly used for fine cutting and boring of non-ferrous metals and non-metallic materials at high speed. It is suitable for processing various wear-resistant non-metals, such as FRP powder metallurgy blanks, ceramic materials, etc.; various wear-resistant non-ferrous metals, such as various silicon-aluminum alloys; various non-ferrous metal finishing processing.
The disadvantage of diamond tools is that they have poor thermal stability. When the cutting temperature exceeds 700°C to 800°C, it will completely lose its hardness; in addition, it is not suitable for cutting ferrous metals, because diamond (carbon) is easy to bond with iron at high temperatures. The atomic action converts the carbon atoms into a graphite structure, and the tool is easily damaged.