Diamond, as an ultra-hard tool material, has been used in cutting processing for hundreds of years. In the history of tool development, from the late 19th century to the mid-20th century, tool materials were mainly represented by high-speed steel; in 1927, Germany first developed cemented carbide tool materials, which were widely used; in the 1950s, Sweden and the United States respectively synthesized artificial diamonds, marking the beginning of an era of cutting tools represented by ultra-hard materials. In the 1970s, poly-crystalline diamond was synthesized using high-pressure synthesis technology, solving the problem of the scarcity and high cost of natural diamonds, and expanding the application range of poly-crystalline diamond tools to several fields such as aerospace, automotive, electronics, and stone.
Diamond tools have high hardness, high compressive strength, good thermal conductivity, and good wear resistance, which can achieve very high machining accuracy and efficiency in high-speed cutting. These characteristics of diamond tools are determined by the state of diamond crystals. In diamond crystals, the four valence electrons of carbon atoms bond in a tetrahedral structure, with each carbon atom forming covalent bonds with four adjacent atoms, forming a diamond structure. This structure has very strong bonding strength and directionality, giving diamond extremely high hardness. Although poly-crystalline diamond is a sintered body of fine-grained diamonds with different orientations and contains a binder, its hardness and wear resistance are still lower than those of single-crystal diamond. However, because the poly-crystalline diamond sintered body is isotropic, it is not easy to crack along a single cleavage plane.
Major performance indicators of poly-crystalline diamond tool materials:
The hardness of poly-crystalline diamond can reach 8000HV, which is 80 to 120 times that of cemented carbide;
The thermal conductivity of poly-crystalline diamond is 700W/mK, which is 1.5 to 9 times that of cemented carbide, and even higher than that of PCBN and copper, therefore the heat transfer of poly-crystalline diamond tools is rapid;
The friction coefficient of poly-crystalline diamond is generally only 0.1 to 0.3 (the friction coefficient of cemented carbide is 0.4 to 1), thus poly-crystalline diamond tools can significantly reduce cutting force;
The thermal expansion coefficient of poly-crystalline diamond is only 0.9×10 -6 to 1.18×10 -6, which is only about 1/5 of that of cemented carbide, thus poly-crystalline diamond tools have small thermal deformation and high machining accuracy;
Polycrystalline diamond tools have very low affinity with non-ferrous metals and non-metallic materials, making it difficult for chips to adhere to the cutting edge and form built-up edges during machining.
Industrialized countries have started research on poly-crystalline diamond tools relatively early, and their applications are already quite mature. Since the first artificial diamond was synthesized in Sweden in 1953, a large number of research results on the cutting performance of poly-crystalline diamond tools have been achieved, and the application scope and usage of poly-crystalline diamond tools have rapidly expanded. The application range of poly-crystalline diamond tools has expanded from initial turning operations to drilling and milling. Surveys on ultra-hard tools conducted by a Japanese organization have shown that the main considerations for choosing poly-crystalline diamond tools are based on the advantages of surface accuracy, dimensional accuracy, and tool life after machining with poly-crystalline diamond tools.
With the development of tool technology in China, the market for poly-crystalline diamond tools is also continuously expanding. Currently, China First Automobile Group has more than one hundred usage points for poly-crystalline diamond turning tools, and many artificial board enterprises also use poly-crystalline diamond tools for wood processing. The application of poly-crystalline diamond tools has also further promoted research on their design and manufacturing technology.
Analysis of the application of poly-crystalline diamond tools in recent years shows that poly-crystalline diamond tools are mainly used in the following two areas:
Processing of difficult-to-machine non-ferrous metals: When processing difficult-to-machine non-ferrous metals with ordinary tools, defects such as rapid tool wear and low processing efficiency often occur, while poly-crystalline diamond tools can exhibit good processing performance. For example, poly-crystalline diamond tools can effectively process the new engine piston material, hypereutectic silicon aluminum alloy (the machining mechanism of this material has already been studied).
Processing of difficult-to-machine non-metallic materials: Polycrystalline diamond tools are very suitable for processing difficult-to-machine non-metallic materials such as stone, hard carbon, carbon fiber-reinforced plastics (CFRP), and artificial boards.
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