The quality requirements of precision parts processing are relatively high, so it is impossible to use one process to meet its requirements, but to gradually achieve the required processing quality with several processes. In order to ensure the quality of processing and the rational use of equipment and manpower, the processing of parts is usually divided into four stages: rough processing, semi-finishing, finishing and finishing according to the nature of the process. 1. In the rough machining stage, the task is to remove most of the excess metal on the blank, so that the blank can solve the finished part in terms of shape and size. Therefore, the main purpose is to improve productivity. 2. In the semi-finishing stage, the task is to make the main surface reach a certain accuracy and leave a certain machining allowance to prepare for the processing of precision parts on the main surface (such as fine turning and fine grinding). And it can complete some secondary surface processing, such as reaming, tapping, milling keyway, etc. 3. In the finishing stage, its task is to ensure that the main surfaces meet the specified dimensional accuracy and surface roughness requirements. The main goal is to fully guarantee the processing quality 4. In the finishing stage, the precision and surface roughness of the parts are very high. The surface (above IT6 and surface roughness below Ra0.2um) needs to be finished. The main purpose is to improve the processing of precision parts. Accuracy, reduce the surface roughness value. One side is not used to improve position accuracy.