Based on the design of process flow, the main purpose of closed hot die forging step is to realize the change of internal structure of helical gear billet from as cast to as forged through metal plastic flow, refine grains and improve local possible casting defects. Compared with open die forging, closed die forging has higher material utilization rate, but it has more strict requirements on the flow of forging materials. For the shape and tooth profile design of helical gear closed hot die forging preform, we need to consider not only the effect of helical gear blank hot forging, but also the influence of helical gear casting tooth profile on casting process. Based on the above factors, it is proposed to use the preform with approximate trapezoidal tooth profile in the closed hot die forging step.
If the helical gear adopts the approximate trapezoidal tooth shape with full tooth height, the workpiece will have too much impact on the hot die forging die during die forging, which will affect the service life of the die; Moreover, if the tooth groove of the casting is too deep in the casting process, it will also have an adverse impact on the filling cavity of liquid metal and the solidification process of the casting.
In closed die forging, by setting a shunting space on the die or blank, the material can always have room for free flow in the forming process of the workpiece, which can significantly improve the flow filling performance of metal materials, reduce the die bore pressure and forming load, and effectively reduce the wear of the die in the processing process; Moreover, it can reduce the requirements for the specific accuracy of blanking. This method is called shunting method. Some studies have shown that the application of shunting technology to helical gear forming can not only effectively solve the problem of insufficient filling at the corner lines of tooth profile, but also greatly reduce the internal pressure and forming load of die bore.