Synthetic diamond replaces natural diamond making tools Currently, single crystal diamond, PCD (or PCD/CC), and CVD diamond are successfully used as cutting tools, boring tools, drill bits, reamers, milling cutters, forming knives, and cutting tools. Part of the materials produced.
The variety of diamond materials must be selected according to the nature of the materials being processed and the processing requirements. In addition to meeting the technical requirements, the requirements of 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 the general machining field, but also widely used in the automotive, motorcycle, high-speed train, petroleum, chemical, construction, wood processing and aerospace industries. In the field of automobiles and motorcycles, PCD and PCD/CC are suitable for processing wear parts such as skirts, pin holes, cylinder blocks, gearboxes and carburetor of engine aluminum alloy pistons. Most of these components are aluminum-based composites with high niobium content (Si>12%), and the hard particles with high hardness (such as SiC hardness of 3000~3500HV) are distributed in the aluminum alloy matrix, just like the grinding wheel. The abrasive grains in the same way will scratch and impact the cutting edge of the tool, and the cutting edge will wear 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 machine with conventional carbide tools, and the tool life is very low or not 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-based composites.
Using PCD diamond to process aluminum-based composite materials, the cutting speed can reach 800~1000m/min, the tool life can be several times or even several times higher than that of cemented carbide, and the surface roughness value can reach Ra0.025~0.012μm. Figure 2 shows an application example of an aluminum-based composite spiral pump casing drilled with a PCD cutter for 20% SiCυ.
When processing carbon fiber and glass fiber reinforced plastic (FRP) with PCD (or PCD/CC) tools, the chips are powdered, the cutting temperature is low, and the cutting length is 10 times that of the K-type cemented carbide tool, but the wear is not hard. 1/3 of the alloy tool.
PCD (or PCD/CC) tools are also suitable for processing pre-fired carbides 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 the choice of the appropriate grade and particle size will also affect it. Different kinds of PCD inserts have great differences in cutting performance due to their different composition components, so be careful when selecting them.
At present, PCD blades are not classified internationally like cemented carbide. Each production plant has its own variety and grade. When using it, it must be selected according to the manufacturer's sample.
DeBeers produces PCD inserts of 002, 010 and 025, with average grain sizes of 2 μm (fine grain), 10 μm (medium grain) and 25 μm (coarse grain). The larger the grain size, the better the wearability, the higher the tool life, but the rougher cutting edge and the poor cutting edge quality, making it difficult to make high-precision tools; the medium grain is generally used as a general grade for machining; The edge of the cutting edge has a small radius and is easy to process a good surface quality. Therefore, the crystal grains of the polycrystal are continuously refined, and there are fine crystals of 1 μm or even 0.5 μm or less, and crystal grains of different sizes are required according to different process requirements such as roughing and finishing.
Single crystal diamond tool material
Single crystal diamond and PCD (or PCD/CC) and PCD (or PCD/CC) and CVD diamond can complement each other well, and there are some cross-cutting applications.
The surface of the workpiece cut by the single crystal diamond is continuous, and the surface of the workpiece cut by PCD exhibits a discontinuous state of the order of micrometers. Therefore, the PCD is only suitable for the general machining field. For some polishing processes with special requirements, For the preparation of Al2O3 mirrors, only the use of natural single crystal diamonds can achieve the required surface roughness and dimensional tolerances.
Large-size diamonds are rare in natural diamonds, but synthetic large-size diamonds are now possible. When it is used to process highly wear-resistant layered wood, its performance is superior to that of PCD diamond, which does not cause premature passivation of the cutting edge. When processing aluminum-based composite materials, either PCD or TFD (CVD thick film) can be used. Figure 3 shows the tool wear curve when machining 40% SiCÏ…A356MMC material with both PCD and TFD diamond. The cutting conditions used in the test in Figure 3 are: cutting speed 400m/min, feed rate 0.05mm/r, backing knife amount (cutting depth) 0.5mm, adding cutting fluid. It can be seen from the experiment that the processing of 40% SiCÏ… aluminum-based composite material has the best effect with thick-film diamond TFD, followed by PCD025, and PCD002 has the lowest service life.
Due to the complementarity of various types of diamonds on the adapting surface, the processing range of diamond tools has been expanded. The synthetic diamond replaces natural diamond, and the trend of CVD diamond replacing PCD diamond is becoming more and more obvious. As a result, the cutting process has entered a new era of efficient and economical processing. The degree of substitution depends on both technical and economic factors. In particular, the difficulty of forming, sharpening and welding the blades will directly affect the diamond tools. The price and performance.
Usually PCD tools are suitable for roughing and require high fracture toughness in the production of CVD thick film and single crystal diamond tools for high speed finishing and semi-finishing.
Http://news.chinawj.com.cn Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn
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