Metal cutting or grinding wheel will form heat on the surface of metal. Because of heat and metal deformation, surface structure of workpiece will be destroyed and deteriorated layer of workpiece surface will be formed. It is necessary to remove the deteriorated layer and obtain accurate workpiece accuracy, and to adopt ultra-precision processing. It is mainly made of fine-grained and low-hardness oil stones, which ultimately achieve a very small roughness and high accuracy, and a relatively high productivity. The cutting process of ultra-precision machining is different from that of mirror grinding. The workpiece is continuously cut until a certain surface roughness is obtained. It is meaningless to prolong the processing time excessively to damage the surface quality of the workpiece. Ultra-precision machining mainly has three kinds of processing state, cutting state, semi-cutting state and interface polishing. 1. Cutting state. The main reason is that the contact surface is relatively small, the unit pressure is relatively large, there will be numerous cutting lines on the surface of the workpiece, no glossy network, can be observed Falling Abrasive particles. 2. Semi-cutting state, with the removal of the workpiece's surface wave crest, the workpiece's surface will become flat and the number of cutting Abrasives will increase. The main feature is that the surface of the workpiece will become shallow and glossy, and the traces of abrasive peeling can still be seen. 3. Mirror polishing state. With the continuous processing, the cutting thickness will become thinner, until the final oxidation to black iron oxide, the surface will become very smooth, the main features are that the surface of the workpiece can not see grinding lines, there is a comprehensive gloss, abrasive particles and cutting shedding can not be seen. The grinding effect on the workpiece's machined surface will gradually change into polishing effect, and its processing process is continuous and automatic conversion. Ultra-precision machining of workpiece is mainly to obtain relatively small roughness.