The chrome hardened bar is a connecting part that supports the work of the piston. Most of them are used in the cylinder and cylinder movement executing parts, and are a moving part with frequent movement and high technical requirements. Taking a hydraulic cylinder as an example, it consists of a cylinder, a piston rod (cylinder rod), a piston, and an end cover. The quality of its processing directly affects the life and reliability of the entire product. The piston rod has high processing requirements, and its surface roughness requirement is Ra 0.4 to 0.8 um, which requires strict requirements on coaxiality and wear resistance. The basic feature of the cylinder rod is the slender shaft machining, which is difficult to process and has always plagued the processing personnel.