The velocity field of planetary gear pre forging directly reflects the metal flow law of the whole deformation process. As shown in the figure, the velocity field distribution under different reduction quantities of the scheme is shown. At the initial stage of deformation, only the upper outer surface of the planetary gear contacts with the tooth top of the tooth die. Under the action of the upper boss and the tooth top of the tooth die, the metal mainly flows downward, and the planetary gear is mainly deformed by rough pier. With the increase of the reduction, the height of the planetary gear becomes smaller, the radial dimension increases, the contact parts between the top of the gear die and the outer surface of the planetary gear continue to increase, and the flow direction of the metal also continues to shift to the transverse direction. When the reduction reaches a certain value, the tooth top of the gear die is in full contact with the planetary gear. As the reduction continues to increase, the back cone flash begins to appear, and the back cone flash continues to become thinner, the resistance of the flash groove to the metal continues to increase, and the metal flow begins to fill the tooth cavity.

According to the law of metal flow, the whole forming process can be divided into three stages: the first stage is from the beginning of deformation to the complete contact between the tooth top of the gear die and the outer surface of the planetary gear, and the metal is mainly rough forming; In the second stage, the tooth cavity is mainly filled with metal under the action of flash resistance; In the third stage, the tooth cavity is completely filled and horizontal flash is produced.