PCBN tools have extremely high hardness, good red hardness, oxidation resistance and fracture toughness, and are ideal tools for cutting ferrous metal materials. At present, PCBN cutting tools have been widely used in processing cast iron, hardened steel, high-speed steel, high-temperature alloy and other difficult-to-machine materials and precision machining fields, and have obtained significant technical and economic benefits.
How to process precision PCBN tools influenced by many factors including handling of raw materials,embryo body synthesis,grinding pcbn cutting edge,pcbn tools geometry parameters,inspection.Now let us know more detail .
1.Handling of Raw Materials
About the impurty handling:Because CBN powder contains WBN, HBN, pyrophyllite, graphite, magnesium, iron and other impurities; in addition, it and the binder powder contain adsorbed oxygen, water vapor, etc., which are not good for sintering. Therefore, it is necessary to purify the raw materials to ensure the performance of the synthetic polycrystalline cubic boron nitride.
Binder content :In terms of the selection and addition of binder materials, the total binder addition should be sufficient but not too much. The experimental results show that the wear resistance and flexural strength of polycrystalline cubic boron nitride are closely related to the mean free path (thickness of the binder phase layer). When the mean free path is 0.8-1.2 μm, the polycrystalline cubic boron nitride The boron wear ratio is the highest, and the amount of binder added is 10% to 15% (mass ratio).
Particle size ratio of CBN:In addition to the choice of binder, the determination of CBN particle size and particle size ratio is also very important. According to the requirements of processing accuracy and surface quality, the particle size of CBN used in the manufacture of cutting tools is roughly divided into: coarse particle size 20 ~ 30μm; medium particle size 3 ~ 10 microns; fine particle size 2 microns. Polycrystalline cubic boron nitride made of coarse grain size is difficult to make tools with high precision requirements, but its wear resistance and impact resistance are high, and polycrystalline cubic boron nitride made of fine grain size can meet precision requirements. machining and superfinishing requirements.
2.Embryo body synthesis/Brazing
The PCBN composite sheet is directly combined with the CBN layer and the cemented carbide substrate under high temperature and high pressure, and is made into various welded cutting tools or blades through cutting and welding processes.
3.Sharpneing of PCBN inserts
The produced PCBN tool body needs to be sharpened before it can be used for cutting, and the sharpened tool can obtain the correct geometry and surface roughness. Generally, it is divided into rough grinding, fine grinding and ultra-fine grinding process.
Coarse grinding adopts grains 180-240 resin bonded diamond grinding wheel, the feed rate is 0.01 mm/double stroke;
W10~W14 resin bonded grinding wheel is used for fine grinding, the feed rate is 0.005 mm/double stroke;
Ultra-fine grinding adopts diamond grinding wheels or grinding pastes of W5 to W3
special attention should be paid to the influence of the edge dressing of diamond grinding wheels on sharpening during grinding and sharpening. Although the PCBN tool swings back and forth on the entire end face of the grinding wheel during the sharpening process to make the surface of the grinding wheel wear out uniformly, in fact the surface of the grinding wheel is still prone to unevenness and must be repaired frequently.
4.Geometric parameters of PCBN tools
The service life of PCBN tool is closely related to its geometric parameters. Appropriate front and back angles can improve the impact resistance, chip removal ability and heat dissipation capacity of the tool. The size of the rake angle directly affects the stress on the cutting edge and the internal stress state of the insert. In order to avoid the excessive tensile stress caused by mechanical impact on the tool tip, a negative rake angle (-5°～-10°) is generally used. At the same time, in order to reduce the wear of the relief angle, the main and auxiliary relief angles are 6°, and the radius of the tool nose is 0.4 – 1.2mm rounded corners, and chamfered smooth grinding.
5.Inspection of PCBN cutting tools
In addition to testing physical properties such as hardness index, bending strength, and tensile strength, it is also necessary to use a high-power electron microscope to check the surface and edge treatment accuracy of PCBN tools. Then dimensional inspection, precision inspection, M value, and shape tolerance and roughness
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The silicon carbide substrate preparation process mainly includes raw material synthesis, silicon carbide crystal growth, ingot processing, ingot cutting, cutting piece grinding, grinding piece polishing, polishing piece cleaning, etc.Among them, the key and difficult points of preparation are mainly the crystal growth, cutting, grinding and polishing links, which are the key points and difficulties in the entire substrate production process, and become the bottleneck that limits the yield rate and production capacity of silicon carbide.
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