Precision mirror grinding technology of the hottes

2022-08-03
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Precision mirror grinding technology of steel bonded carbide

1 problems of steel bonded carbide in grinding

steel bonded carbide is prepared by powder metallurgy with tool steel or alloy steel as bonding phase and refractory metal carbides (mainly WC and TIC) as hard phase. Its microstructure is characterized by fine hard phase grains dispersed in the steel matrix. The hard phase in the alloy mainly endows the material with high hardness and wear resistance, and the bonding phase endows the material with the properties of steel. Therefore, the steel bonded cemented carbide has the comprehensive properties of steel and cemented carbide, which makes it widely used in various fields. However, its own processing and manufacturing is very difficult, especially precision processing, because the hardness difference between hard phase and bonding phase is large, the steel base is easy to be removed, while hard points are not easy to be removed, and its grains are easy to peel off from the alloy surface, thus forming pores with the same size as hard phase grains on the surface. At the same time, the toughness of the steel base is large. Under certain grinding temperature, contact pressure and relative speed, the grinding debris fills the air between the abrasive particles and the calculated cross arm travel error should not exceed 1% of the hole, so that the grinding wheel sharply blocks the workpiece surface and burns. Therefore, it is difficult to obtain low surface roughness by traditional machining methods, and the multi-stage grinding efficiency is low and the cost is high

steel bonded cemented carbide is grinded with metal bonded ultra-fine grain diamond wheel with electrolytic continuous dressing (ELID). The surface roughness can develop large-size high load bearing, low hardness isolation bearing, high damping isolation bearing and sliding bearing with low friction coefficient up to about 10 nm, and the efficiency is high. In this experiment, the ELID mirror grinding technology is used to precisely machine the steel bonded carbide, and it is easy to obtain a low roughness mirror

2 basic principle of ELID grinding technology

electrolytic dressing mirror grinding is a new ultra precision machining technology developed in Japan in the early 1990s. It uses cast iron or iron fiber bonded diamond or CBN grinding wheels, and uses the anodic dissolution phenomenon in the electrolysis process to carry out electrolytic dressing grinding on the grinding wheels. The electrolytic power supply uses DC pulse power supply, and the electrolyte uses aqueous solution of weak electrolyte. The cast iron grinding wheel is an anode. During electrolysis, the iron element on the surface of the grinding wheel becomes Fe2O3 oxide film, so that the diamond or CBN abrasive that cannot be electrolyzed protrudes from the surface of the grinding wheel. The blunt abrasive falls off in time with the electrolysis, so that the grinding wheel is always in a sharp state. At the same time, the generated oxide film also plays a role in restraining the continuation of the electrolysis process, so that the wear of the grinding wheel will not be too fast. When the abrasive grains on the surface of the grinding wheel are worn, the oxide film is scraped and removed by the surface of the workpiece. The electrolysis process continues, and the surface of the grinding wheel continues to be trimmed. This is a cycle process, which can not only avoid the excessive loss of the grinding wheel, but also automatically maintain the grinding state of the grinding wheel surface [1 ~ 3], as shown in the figure below

3 application of ELID grinding technology to steel bonded carbide

3.1 test conditions

see Table 1, table 2

Table 1 test equipment

3.2 grinding effect and analysis

mirror grinding of steel bonded carbide under the above conditions, the workpiece surface roughness ra=0.003 μ m~0.011 μ m。 If finer grinding wheels are used, many listed companies are expanding their own production capacity to digest orders (above W1), Ra value will be significantly reduced and better surface roughness will be achieved

by analyzing the grinding effect, we found that the surface roughness of the workpiece is closely related not only to the particle size and type of the grinding wheel abrasive used, but also to the ratio of the grinding fluid. The chemical properties of the grinding fluid with different composition and content are very different, and the machined surface roughness is different. Using hdmy-110 and hdmy-200 grinding fluids, we have processed the test pieces of optical glass, sapphire, quenched steel, cemented carbide, cermet, PCBN, monocrystalline silicon and other materials that reach the mirror surface. However, for steel bonded carbide, the mirror surface that can reach 13 can not be machined. Instead, the special grinding fluid hdmy-201, diamond and CBN mixed abrasive iron-based grinding wheel are used to grind the steel bonded carbide that can reach the mirror surface under the same other conditions. This is mainly because the composition and content of grinding fluid have a great impact on the electrolytic speed, film-forming speed, film-forming thickness, film hardness, and the surface structure and properties of the machined workpiece. According to the different materials to be processed, the composition and proportion of grinding fluid, and the type and proportion of iron-based grinding wheel abrasive are reasonably adjusted

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