The cold precision forging of spur gear is developed on the basis of cold forging. There is no need to heat the blank during forming. The formed parts have the characteristics of high surface quality and good dimensional accuracy. However, due to the problems of poor metal plasticity, poor material fluidity, high deformation resistance, sharp increase of forming load, difficult filling of tooth die corners, serious die wear and low die service life at room temperature, the practical application and promotion of cold precision forging of spur gears are restricted to a certain extent.
Hu Chengliang and Liu Quankun of Hefei University of technology have made extensive and in-depth research on the cold precision forging of spur gears. They have carried out a large number of numerical simulation analysis and scientific research experiments on the metal flow law of spur gears in the process of cold precision forging, and put forward a design idea of combining the continuous forming design idea of infinite preform with the shunting principle, The influence of die shape on forming quality during closed forging of spur gear is studied, and the improvement measure of designing the end face shape of punch and die as waveform is put forward. The experiment shows that the filling effect of corner of spur gear can be improved. Aiming at the problems of excessive cold forging load and low die service life of spur gear, a two-step forming process based on rigid translation is proposed, and the deformation of two-step forming is allocated to reduce the forming load and improve the die service life.
In the last century, K. ohga and K. Kondo introduced the split flow principle into forging for the first time. Taking the spur gear as the research object, two split flow forming processes of hole split flow and shaft split flow were proposed. As shown in Figure 1, the basic principle of split flow forging of spur gear is shown. Wang Ke of Zhongbei university put forward four different shunting methods: hole shunting, shaft shunting, constraint hole shunting and constraint shaft shunting, and adopted MSC Spuerform numerically simulates four different shunting methods. The simulation results show that the shunting method can reduce the forming load, but can not ensure the full filling of the tooth profile. The proper restriction hole shunting and restriction shaft shunting design can improve the tooth profile filling, and the forming force will not surge.
In 1987, tuncer C [62], University of Birmingham, UK, first proposed the floating die, and the floating die process is shown in Figure 2. Because the characteristic of floating die forming is that the friction direction is consistent with the metal flow direction, the metal flow is easier to fill the die cavity. British scholar t.a.dean and Abdel raham and m.h.sadeghi of Khartoum University in Sudan have made a comprehensive and systematic research on the forming of spur gear by using the floating die process. Through the optimization design of preform shape and die structure, the variation laws of forming load, dimensional accuracy, tooth shape filling and jacking force in the forming process of spur gear are compared and analyzed, The tooth profile of forged spur gear obtained by experiment and the corresponding tooth profile of final forging die are compared and analyzed.
Cai. J and t.a.dean compared and analyzed the forging process of spur gear with fixed die structure and floating die structure. The limit load of forming spur gear with fixed die structure is 21% higher than that with floating die structure. With floating die process, the punch and die move downward together, which effectively reduces the friction resistance between die and metal blank surface, At the same time, the wear and load of punch are reduced. Tan Xianfeng of Nanchang University of Aeronautics and Astronautics, based on the problems of insufficient tooth filling and large forming load after cold precision forging of spur gear, the cold precision forging of spur gear was carried out with hollow blank and solid blank by means of numerical simulation and process experiment. The results show that, The use of floating die can reduce the precision forging load of straight cylindrical gear with solid blank and improve the filling effect, while the forming load of hollow blank is only 2.35%, and the filling effect of straight cylindrical gear has not been significantly improved. Yang Cheng of Xi’an Jiaotong University, based on the analysis of the filling resistance of cold precision forging of spur gear, puts forward a new precision forging device with adjustable movement of tooth die on the basis of floating die. The results of numerical simulation and process experiment show that by controlling the movement mode of die, the positive friction can be improved at the corners that are difficult to form, so as to promote tooth filling. The device of this method is complex, the control needs to be accurate, and it is difficult to popularize and apply in practice.
In view of the large forming load of cold precision forging and the low material utilization rate of single shunting load reduction method, many scholars began to integrate multiple processes. Choi. J C et al. Proposed a two-step forming process of “pre forging split hole split final forging forming”. This process has been successful in the precision forging of aluminum alloy gears, and can obtain Korean standard grade 5 spur cylindrical gears. Professors Wang Guangchun and Zhao Guoqun of Shandong University put forward a new forming process of spur gear “pre forging split flow area split final precision forging”, and carried out experiments with hollow blank and solid blank. The experimental results show that compared with closed upsetting extrusion, the forming load of hollow blank can be reduced by 40%, that of solid blank can be reduced by more than 50%, and the end face of forging is flat The tooth shape is fully filled. Professors Zhang Qingping and Zhao Guoqun proposed a two-step closed die forging inward shunting method to form a solid spur gear. The closed die forging extrudes the upper and lower end faces of the blank to form a spherical shunting cavity, but the tooth shape is not completely filled. The filled tooth shape of the final forging is shunted inward at the same time, and the excess metal shunts into the spherical shunting cavity. The shunting cavity is not fully filled, so the forming load is reduced. The first mock exam of two spring type cold closed upsetting process is proposed for the characteristics of Fang Quan water combined with floating die and diffusing forging technology at Henan University of Science and Technology. Firstly, the annular blank is pre forged and upsetted by the floating die with movable mandrel, and then the flow chamber of the movable mandrel is removed for split flow final forging. In the two-step forming process, there is no need to replace the die, which shortens the process flow and improves the processing efficiency. Wang gangchao [80] of Hefei University of technology, combined with the characteristics of active friction of floating die and load reduction by axial shunting process, analyzed and compared the forming quality and forming load of straight tooth cylindrical gear under only three process schemes: floating die process, floating die and axial shunting composite process and improved composite process, The spur gear with high forming quality can be obtained by using the improved process scheme, which is innovative.