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. Generally, processing above or below normal temperature will cause chemical or phase changes of the workpiece, which is called hot processing. Cold working can be divided into cutting and pressure machining according to the difference of machining methods. Hot working commonly includes heat treatment, forging, casting and welding.