Precision machining is a process of changing the overall dimension or performance of the workpiece with machining machinery. According to the temperature state of the workpiece to be processed, it is divided into cold processing and hot processing. Generally, it is processed at normal temperature without causing chemical or phase changes of the workpiece, which is called cold processing. The process of using datum in the processing and assembly of precision machined parts is called datum process. The benchmarking process is divided into different, according to the use of assembly datum, measurement datum and position datum. Machining process flow is the step of workpiece or part manufacturing and processing. The process of directly changing the shape, size and surface quality of blank by machining is called machining process flow. For example, the processing process of an ordinary part is rough machining - finish machining - assembly - Inspection - packaging, which is a general process.