Ohga K and Konda K first proposed to apply the shunting process to the precision forging technology of spur gears in, so as to reduce the forming load through material shunting and facilitate the filling of tooth profile. The split flow method is developed, and the inward split flow method is proposed to form spur gears. The split flow method is especially suitable for the near net shape of spur gears, so it has developed rapidly and attracted the in-depth study of many scholars. The forming principle of split flow forging is shown in the figure.
Wang gangchao of Hefei University of technology, combined with the floating die technology, put forward the tooth top shunting, tooth cavity shunting and upper tooth end shunting technology. It is found that the tooth top shunting technology can not only effectively improve the filling condition of gears, but also greatly reduce the forming load. Cheng Yu of Xi’an Jiaotong University analyzed the influence of the shape of the shunting hole on the forming of spur gears, and found that selecting the appropriate size of the shunting hole can reduce the forming load, but the effect is general. Teng Hongchun et al. Put forward the one-time forming process scheme of forward extrusion and constrained split flow cold extrusion, which can well improve the filling performance of gears. Shi Wenchao of Hefei University of technology found that the second process can effectively reduce the working load by comparing and analyzing the two processes of only using floating four die and using floating concave die to split up and down the tooth end. Kou Shuqing et al. Put forward the two-step forming process of split flow final forging of pre forging constraint hole in closed die forging. It is found that this process can not only significantly improve the corner filling capacity, but also greatly reduce the working load. Zhang Qingping of Shandong University proposed to form spur gear by pre forging, split flow and final forging. Compared with the traditional closed upsetting and extrusion process, the tooth shape is full and the forming load is greatly reduced. Feng chongqian of Yanshan University used the hot precision forging process of floating die and hollow shunting method to upset and extrude spur gear. It was found that the hollow shunting method not only reduced the forming load, but also prolonged the service life of the die.