What are the methods and characteristics of ultra precision grinding and polishing
Grinding is a commonly used semi finishing and finishing method. The grinding wheel is a cutting tool for grinding. Grinding is a comprehensive result of three functions of sliding, scratching and cutting on the workpiece surface by a large number of randomly distributed abrasive particles on the wheel surface. The basic characteristics of grinding are as follows:
1. High grinding speed leads to high grinding temperature. In general cylindrical grinding, v=35m/s, and high-speed grinding v ＞ 50m/s. 80%~90% of the cutting heat generated by grinding is transferred to the workpiece (10%~15% is transferred to the grinding wheel, and 1%~10% is taken away by the grinding debris). In addition, the thermal conductivity of the grinding wheel is very poor, which is easy to cause surface burns and microcracks on the workpiece. Therefore, a large amount of cutting fluid should be used to reduce the grinding temperature.
2. It can obtain high machining accuracy and small surface roughness value, and the machining accuracy can reach IT6-IT4, and the surface roughness value can reach Ra0.8-0.02 μ m。 Grinding can not only finish machining, but also rough grinding, rough grinding and heavy load grinding.
3. The large back grinding force is caused by the large negative rake angle of the abrasive grain and the large blunt radius rn of the cutting edge, which results in the larger back grinding force than the tangential grinding force, resulting in the larger contact width between the grinding wheel and the workpiece. It will cause elastic deformation of workpiece, fixture and machine tool and affect the machining accuracy. Therefore, when machining workpieces with poor rigidity (such as grinding slender shafts), corresponding measures should be taken to prevent the machining accuracy from being affected by workpiece deformation.
4. The grinding wheel has a self sharpening effect in the grinding process. The grinding grains are broken to produce sharp new edges and corners, and a new layer of sharp grinding grains is exposed due to the falling off of the grinding grains, which can partially restore the cutting ability of the grinding wheel. This phenomenon is called the self sharpening effect of the grinding wheel, which is conducive to grinding.
5. Be able to process high hardness materials. In addition to processing common structural materials such as cast iron, carbon steel, alloy steel, etc., grinding can also process high hardness materials that are difficult to cut with common tools, such as quenched steel, hard alloy, ceramics, glass, etc. But it is not suitable for finishing nonferrous metal workpieces with large plasticity.
2023-01-07
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