Forging is divided into manual forging and machine forging, and machine forging is divided into free forging and press forging. We commonly used cold heading, cold forging, hot forging are all press forging, need to use the mold Cold forging is a metal working process. At room temperature, the metal billet is subjected to pressure by a mold to produce plastic deformation of the metal, thereby obtaining parts of the desired shape and size. Cold heading is mainly used for processing bolts, nuts and other standard parts, is the use of mold at room temperature to make metal wire or bar block rough, such as upsetting one end of the wire into a bolt head, high production efficiency and stable product quality. Hot forging is carried out at high temperature (steel is generally 800-1250 ℃), and the billet is heated above the recrystallization temperature, and the plasticity increases and the deformation resistance decreases. Recrystallization can eliminate work hardening and is suitable for large and complex parts. Cold forging is also carried out at room temperature, through pressure to produce plastic deformation of the metal, the process will appear work hardening. It is suitable for the production of parts with relatively simple shape, high precision and large batch. Compared with hot forging, the dimensional accuracy of parts after cold forging is higher, because there is no effect of thermal expansion and contraction. The surface quality is also better and a higher finish can be achieved.