The forging process of gear blank can be divided into upsetting stage, full step transition stage and extrusion flash stage. The upsetting stage starts from the contact between the blank and the surface of the upper die cavity to the contact between the blank metal and the side wall of the die cavity, that is, free upsetting.
The filling step transition stage starts from the contact between the drum side of the blank and the side wall of the die until the whole side surface fits with the die wall and the step transition is completely filled. At this stage, the blank is slowly squeezed into the die cavity and gradually enters different three-dimensional compressive stress states.
The flow of the deformed metal is blocked by the side wall of the mold cavity. The deformation speed of the blank in the height direction is always uneven. The flow in the middle is fast, the flow at the upper and lower ends is slow, and the speed at the upper end is faster than that at the lower end. With the continuous increase of the contact area and the continuous decline of the metal temperature in contact with the mold, the difference in speed becomes more and more obvious, as shown in the figure. In order to improve the uneven flow, improve the filling quality at the transition of hub, spoke and rim steps, and reduce the forming force, the principle of shunting and decompression is proposed.