Synthetic diamonds replace natural diamond tools Currently, single crystal diamonds, PCD (or PCD/CC), and CVD diamonds have been successfully used as turning tools, boring tools, drills, reamers, cutters, forming tools, and cutting tools. Part of the production material.
The variety of diamond materials must be selected according to the nature of the material being processed and the processing requirements. In addition to meeting the technical requirements, the requirements for economic and environmental performance should also be met.
PCD and PCD/CC materials PCD and PCD/CC are the most commonly used diamond materials in production. They are not only suitable for general mechanical processing but also widely used in automobiles, motorcycles, high-speed trains, petroleum, chemicals, construction, and wood processing. Aerospace and other industrial sectors. In the field of automobiles and motorcycles, PCD and PCD/CC are suitable for machining wear-resistant parts such as skirts, pin holes, cylinder blocks, transmissions, and carburetors of engine aluminum alloy pistons. Most of these parts are aluminum matrix composites with high silicon content (Si>12%). The hard particles with high hardness (such as the hardness of SiC is as high as 3000 to 3500 HV) are distributed in the aluminum alloy matrix and are like grinding wheels. The abrasive particles in the blade will scratch and impact the cutting edge of the tool, so that the cutting edge wears quickly. The higher the hardness of the hard particles, the larger the size of the particles, and the greater the number of particles, the faster the tool wears. Therefore, it is difficult to process with a conventional hard alloy cutting tool, and the tool life is very low or it cannot be used at all. Diamond is the hardest material known in the world, and its practical use proves that it is the best tool material for processing aluminum matrix composites.
With PCD diamond processing of aluminum matrix composites, the cutting speed up to 800 ~ 1000m/min, tool life can be several times or even several times higher than that of cemented carbide, surface roughness value up to Ra0.025 ~ 0.012μm. Figure 2 shows an example of an aluminum-based composite screw pump housing that uses a PCD tool to drill 20% SiC crucibles.
When PCD (or PCD/CC) cutters are used to process carbon fiber and glass fiber reinforced plastic (FRP), the cuttings are powdered, the cutting temperature is low, and the cutting length is 10 times that of a K type carbide cutting tool, but the wear is not hard. 1/3 of the alloy tool.
PCD (or PCD/CC) cutters are also suitable for the processing of pre-fired hard alloys and wear-resistant non-metallic materials such as ceramics, rubber, graphite, glass and various wear-resistant woods.
The performance of a PCD tool depends primarily on its application and the process involved, but choosing the appropriate grade and particle size can also affect it. Different types of PCD inserts have different cutting performance due to their different composition.
At present, PCD inserts do not have the same international classification as cemented carbide. Each manufacturer has its own variety and grade, and it must be selected according to the manufacturer's sample when it is used.
DeBeers PCD inserts are available in 002, 010, and 025, and the average grain size is 2 μm (fine grain), 10 μm (medium grain), and 25 μm (coarse grain). The larger the grain size, the better the grinding property, the higher the tool life, but the rougher cutting edge and the poor quality of the cutting edge make it difficult to make high-precision tools. The middle grain is generally used as the general grade of machining; the fine-grained tool is The radius of the blunt edge of the cutting edge is small and it is easy to machine a good surface quality. Therefore, the crystal grains of polycrystals are continuously refined, and there are fine crystals having a size of 1 μm or less and 0.5 μm or less. It is necessary to select crystal grains of different sizes according to different process requirements such as coarse and fine processing.
Single crystal diamond tool materials, single crystal diamond and PCD (or PCD / CC) and PCD (or PCD / CC) and CVD diamond can complement each other well, there are also some cross-application areas.
The surface of the workpiece cut by the single crystal diamond is continuous, and the surface of the workpiece cut by the PCD exhibits a micrometer-level discontinuous state. Therefore, the PCD is only suitable for the common mechanical processing field. For some polishing processes with special requirements, When preparing Al2O3 mirrors, only the use of natural single crystal diamond can achieve the required surface roughness and dimensional tolerances.
Natural diamond is less commonly seen in large-size diamonds, but it has now become possible to synthesize large-size diamonds. When it is used to process highly wear-resistant laminated wood, its performance is superior to that of PCD diamond and does not cause premature passivation of the cutting edge. When processing aluminum matrix composites, either PCD or TFD (CVD thick film) can be used. Figure 3 shows the tool wear curve when machining 40% SiCυ A356MMC with both PCD and TFD diamonds. The cutting conditions used in the test of Fig. 3 were: cutting speed 400m/min, feed rate 0.05mm/r, back-feed amount (cutting depth) 0.5mm, and addition of cutting fluid. It can be known from the experiment that processing 40% of SiC crucible aluminum matrix composites, the use of thick-film diamond TFD best effect, PCD025 second, PCD002 tool life is the lowest.
Due to the complementarity of various types of diamonds on the adaptation surface, the machining range of diamond cutters has been expanded. Artificial synthetic diamonds have replaced natural diamonds, and CVD diamonds have replaced PCD diamonds. Cutting machining has thus entered a new era of high efficiency and economical processing. The degree of substitution depends on both technical and economic factors. In particular, the degree of difficulty in forming, sharpening and welding of inserts will directly affect diamond tools. The price and performance.
Usually PCD cutters are suitable for rough machining and require higher fracture toughness in the production of the knife, CVD thick film and single crystal diamond tools are mostly used for high-speed finishing and semi-finishing.
