The upsetting extrusion process principle of spur gear is shown in Fig. 1, which means that the tooth punch moves downward, and the metal blank flows along the radial direction after plastic deformation due to upsetting in the concave mold cavity, gradually filling the concave mold tooth cavity. The upsetting extrusion process can be roughly divided into two stages. The first stage is the free upsetting deformation stage of the blank under the action of the punch. The upper and lower end faces of the blank contact with the punch and concave die to produce friction resistance and hinder the radial flow of the blank, but the metal flow in the core and middle of the blank is not limited, and the shape gradually changes from a cylinder to a single drum.
The second stage is the filling stage of the tooth cavity. With the increase of the deformation degree of the metal blank, the drum part of the blank begins to contact the tooth root, resulting in the reduction of the free surface of the blank forming and the increase of the deformation resistance. The load gradually increases with the continuation of the deformation. At the end of the deformation, a completely closed space is formed between the blank and the die, and the forming load increases sharply. The forming load increases sharply at the end of deformation, which has little significance for the filling of spur gears. Most of the tooth tops of the upper and lower surfaces of the parts have collapse angles.