Diamond tool materials are divided into single crystal diamonds (both natural and artificial, natural single crystal diamonds are expensive, partially replaced by synthetic single crystal diamonds), synthetic polycrystalline diamonds (PCD) and synthetic polycrystalline diamonds and hard alloy composite blades. (PCD/CC) and CVD diamond.
Single crystal diamond
Single crystal diamond used as a cutting tool must be large particles (mass greater than 0.1g, minimum diameter not less than 3mm), mainly used for precision and ultra-precision machining applications with high surface roughness, geometric accuracy and dimensional accuracy. field.
Natural single crystal diamond is the most wear resistant material in diamond. Its own fine texture, after fine grinding, the radius of the cutting edge of the cutting edge can be as small as 0.008 ~ 0.005μm. However, the natural single crystal diamond is brittle, its crystal anisotropy, crystal hardness of different crystal planes or the same crystal plane in different directions, and the appropriate direction must be selected for sharpening and use. Due to the harsh conditions of use and the limited resources of natural single crystal diamond, the price is very expensive, so PCD, PCD/CC and CVD diamond tools are mostly used in production. Natural single crystal diamond is mainly used in the ultra-precision machining of some non-ferrous metals or in the production of gold jewelry.
Synthetic single crystal diamond has good consistency in size, shape and performance. At present, due to the maturity of high temperature and high pressure technology, it is possible to prepare synthetic single crystal diamond of a certain size, especially when processing highly wear-resistant layered wood. The performance is better than PCD diamond and does not cause premature passivation of the cutting edge.
Synthetic polycrystalline diamond (PCD) and synthetic polycrystalline diamond and carbide composite inserts (PCD/CC)
PCD is a polycrystalline material obtained by crystallizing many diamond single crystal powders at a high temperature (about 1800 ° C) and a high pressure (5 to 6 MPa) using a metal bond such as cobalt. The hardness is slightly lower than that of single crystal diamond, but it is The polymerization of randomly oriented diamond grains is isotropic and can be sharply oriented when used as a cutting tool. It is not necessary to use the best cleavage surface as the rake face like natural diamond. When cutting, the cutting edge is very insensitive to accidental damage, and has strong anti-wear ability. It can keep sharp cutting edges for a long time. It can use high cutting speed and large back-feeding amount during processing (eat deep). The service life is generally 10~500 times higher than that of WC-based cemented carbide tools, and because of the conductivity of the metal bond in PCD, PCD is easy to cut and form, and the source of raw materials is rich, and its price is only one-tenth of that of natural diamond. To a fraction of a dozen, it has become a high-performance alternative to traditional WC-based carbide tools.
In order to improve the toughness and weldability of the PCD insert, a diamond composite blade (PCD/CC) is formed by sintering or pressing a layer of 0.5 to 1 mm thick PCD on the surface of the cemented carbide. PCD/CC can be used to make tools by welding or machine clamp. Due to its good weldability, easy regrind and low cost, it is widely used. It should be pointed out that the sharpness and surface quality of PCD and PCD/CC cutters are not as good as single crystal diamond, and the workability is poor, the grinding ratio is small, and it is difficult to form according to the geometry of the cutter head. Conveniently manufacture products with complex geometries such as chipbreaker indexable inserts and end mills.
CVD diamond
CVD diamond is a high abrasion resistant pure diamond material that does not contain a binder and is prepared at low pressure (<0.1 MPa). CVD diamonds are mainly available in CVD thin film coating (CD) and CVD thick film (TFD).
The CD is formed by depositing a film-like diamond consisting of polycrystals on a cemented carbide substrate (usually a K-type alloy) by a CVD (Chemical Vapor Deposition) process with a thickness of about 10 to 30 μm.
Because the base is easy to make complex shapes, it is suitable for tools with complex geometry, such as taps, drills, end mills and indexable inserts with chipbreakers. CD tools for CD tools in the international tool market, such as CD1810 from Sweden's Sandvik and KCD25 from Kennametal, USA, are mainly used for high-speed precision machining of non-ferrous metals and non-metallic materials, and tool life is longer than uncoated carbide tools. Increase nearly ten times or even dozens of times. However, CD tools are not suitable for processing metal-based composite materials, because the hard particles in the composite material will wear a layer of coating on the surface of the tool in a short time, so although the price of CD tools is lower than that of similar PCD tools, However, due to the small adhesion between the diamond film and the matrix material, its wide application is limited.
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