The PCD cutting tool is sintered at high temperature and high pressure by the polycrystalline diamond tip and the cemented carbide substrate. It can not only take advantage of diamond's high hardness, high thermal conductivity, low friction coefficient, low thermal expansion coefficient, low affinity with metals and non-metals, high elastic modulus, no cleavage surface, isotropy, etc., but also take into account the high strength of cemented carbide.
Polycrystalline diamond (PCD) is a polycrystal formed by mixing micron-sized diamond powder with a small amount of metal powder (such as Co) and sintering at high temperature (1400°C) and high pressure (6000MPa).
Compared with other tool materials, PCD has the performance characteristics of high hardness and wear resistance, high thermal conductivity, low coefficient of thermal expansion, low coefficient of friction, fast cutting heat dissipation, low cutting temperature, small thermal deformation, and can reduce the machined surface roughness. However, PCD is not suitable for processing ferrous metals and their alloys because of its strong affinity with iron group elements.
The PCD composite sheet that has been commercially supplied is prepared by sintering a 0.5-0.7mm thick PCD layer on a cemented carbide substrate. Therefore, it has both the high hardness and wear resistance of PCD and the good strength and toughness of cemented carbide.
PCD tools show excellent cutting performance in high-speed cutting of non-ferrous metals and their alloys and non-metallic materials, and have been widely used in automotive, aviation, aerospace, building materials and other industrial fields. However, the high hardness and high wear resistance of PCD make it difficult to sharpen the tool, which is mainly reflected in the small removal rate of the material, the large loss of the grinding wheel, the low sharpening efficiency, and the serrated edge.
Commonly used PCD cutting tool sharpening processes include diamond grinding wheel mechanical grinding, electric discharge grinding, electrolytic grinding, etc. Among them, diamond grinding wheel mechanical grinding is the most mature in technology and is currently the most widely used. Although this method has low sharpening efficiency and high processing cost, it can obtain good cutting edge quality and complete, smooth front and rear rake surfaces.
The characteristics of PCD materials determine the requirements for PCD cutting tool grinding machines: they cannot be equivalent to ordinary tool grinding machines, that is, they must meet the following conditions:
1) The grinding wheel spindle and the machine tool as a whole are required to have high rigidity and stability to maintain the constant pressure of the grinding wheel on the PCD material during sharpening.
2) The grinding wheel frame can swing laterally to ensure that the end face of the grinding wheel wears evenly, and the swing frequency and amplitude of the grinding wheel frame can be adjusted.
3) Equipped with optical projection device and high-precision rotary table.
4) Special diamond grinding wheel is used.
In a word, PCD tools show advantages that are incomparable with other tools in the field of cutting processing such as non-metallic materials, non-ferrous metals and their alloy materials, and metal matrix composite materials due to their good processing quality and economical processing.
With the deepening of the theoretical research of PCD cutting tools and the further promotion of application technology, the status of PCD cutting tools in the field of superhard cutting tools will become increasingly important, and its application scope will be further expanded.
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