The 18CrNiMo7-6 spur gear of Zhengzhou Machinery Research Institute is taken as the research object. The spur gear is characterized by large modulus, large diameter, small tooth thickness and central hole. Its forming process is studied. The warm cold compound forming process has great advantages for the forming of parts with large deformation and high precision requirements, and is especially suitable for the precision forming of large modulus spur gears. In this paper, the warm cold composite forming process is adopted. Firstly, the forming effects under different process schemes are analyzed, the warm forging forming scheme is determined, and the structure and process parameters of the forming scheme are optimized. Secondly, the influence of different cold finishing quantities on the forming results is analyzed by numerical simulation method to determine the best finishing allowance. Finally, by adding the STL interface of Open Inventor file format, the virtual reality simulation of forging process is realized, and the interactive display ability of DEFORM-3D post-processing is improved. The main conclusions of the study are as follows:
(1) Three warm forging schemes of closed reverse extrusion, closed one-way upsetting extrusion and closed two-way upsetting extrusion are numerically simulated and analyzed by finite element method. The results show that the die wear is serious and the forming load is large in closed reverse extrusion. The closed one-way upsetting extrusion scheme has large forming load, large equivalent stress at the end tooth root and tooth shape, and large equivalent stress gradient of forgings. The two-way upsetting extrusion scheme of floating die has the advantages of uniform metal flow, relatively small forming load and abrasive wear, and improved stress condition of tooth root. It is the optimal forming scheme.
(2) The structure of the two-way upsetting extrusion scheme of the floating die is optimized, and a shunt groove is set at the tooth top of the end face (non important surface) of the spur gear. The numerical analysis results show that the forming load is reduced by about 30% after optimization, which can improve the stress condition of the die. The three important parameters of blank initial temperature, die preheating temperature and friction coefficient in the warm forging process are optimized. According to the optimization results, the best parameter combination is blank warm forging temperature 850 ℃, die preheating temperature 300 ℃ and friction coefficient 0.1.
(3) The cold forging process scheme is designed. According to Hooke’s law, the minimum single side cold finishing amount of the material is calculated to be 0.2mm. The influence of different finishing amounts on the forming results is analyzed by finite element method. The simulation results show that with the increase of finishing amount, the wear amount and forming load of tooth die increase, and the optimal finishing allowance is 0.2mm.
(4) By establishing a data bridge between finite element calculation software and virtual reality software, the finite element STL data can be imported into open inventor, the accurate plastic flow geometric model is established, the virtual reality simulation of spur gear precision forging process is realized on the platform of Open Inventor, and the expected effect is achieved.