The cold extrusion precision plastic forming technology of spur gear has the advantages of saving materials, improving production efficiency, ensuring the surface quality and dimensional accuracy of parts, and obtaining good comprehensive mechanical properties. It is a development trend of spur gear forming in the future. Only when the cold extrusion precision plastic forming technology of spur gears is successfully applied to mass industrial production, can it give full play to its great economic benefits and potential. Taking the spur cylindrical gear (sun gear) in the wheel reducer of a truck as the research object, a reasonable and feasible process scheme for cold extrusion forming spur cylindrical gear (sun gear) is formulated. The structural parameters of continuous cold extrusion concave die cavity and combined concave die are optimized. The optimization results are applied to the trial production of continuous cold extrusion, The products that fully meet the requirements of quality and accuracy are obtained. The relevant work completed and important conclusions obtained in this paper are as follows:
① The structure of spur cylindrical gear (sun gear) is analyzed. The outer teeth are spur cylindrical teeth and the inner teeth are involute spline teeth. The gear precision of the external teeth is required to be high. After the external teeth are extruded, the gear precision must be improved through finishing in order to meet the assembly and use requirements. Therefore, the spur cylindrical gear (sun gear) must complete three important processes: external tooth forming, external tooth finishing and internal tooth forming.
② According to the structural characteristics of spur gear (sun gear), three efficient cold extrusion forming process schemes are formulated, and the finite element models of the three forming process schemes are established respectively. Through the numerical simulation results, the forming quality and the basic plastic deformation characteristics such as velocity field, stress field and strain field in the cold extrusion process of spur gear (sun gear) are analyzed in detail. The simulation results show that the continuous extrusion forming process of external teeth in the form of “part pressing part” is feasible. The three process schemes are comprehensively evaluated and analyzed from the three aspects of material utilization, production efficiency and process feasibility. Finally, the third scheme is determined, that is, continuous extrusion forming external teeth, finishing external teeth and broaching forming internal teeth.
③ The important structural process parameters of continuous cold extrusion cavity, die entry angle and splitting thickness, are simulated and analyzed by single factor respectively, and the die entry and exit angle is obtained α= When the splitting thickness B = 1mm at 55 °, the maximum forming load of the external teeth of the straight tooth cylindrical gear formed by continuous cold extrusion is relatively small, and better forming quality is obtained.
④ An optimization strategy combining experimental design, numerical simulation analysis, Kriging approximate model and genetic algorithm is adopted, and the optimization strategy is applied to the design of external tooth combined die of continuous cold extrusion spur gear. The equivalent inner diameter D1, radial diameter ratio N2, N3, N4 and radial interference coefficient of the external tooth cavity of spur cylindrical gear with combined die core are constructed λ 2、 λ 3 and other structural parameters are used as the input variables of the optimal design, and the maximum equivalent stress value of the concave model cavity is the Kriging approximate model of the response value. The optimal combination of structural parameters is obtained by global optimization of the model combined with genetic algorithm: D1 = 88.35mm, N2 = 1.7872, N3 = 3.0329, N4 = 4.0001, λ 2=0.0025， λ 3=0.0021。 According to the optimized structural parameters, the finite element model is established for CAE analysis and verification. The maximum equivalent stress of the combined die core is far less than the allowable stress of the material, and the circumferential tensile stress will not be generated on the inner wall of the die core cavity. It is proved that the accuracy and rationality of the optimization results show that the optimization strategy is feasible in the optimization design of the combined die with complex cavity.
⑤ The continuous cold extrusion production of spur gear (sun gear) is trial produced by using the optimized die and process scheme. The contour of the external tooth parts formed by continuous cold extrusion is quite consistent with the simulation results, and the tooth breakage and cracking of the combined die do not occur in the forming process, which verifies the accuracy of the simulation analysis and the feasibility of the optimization strategy. For the external gear parts formed by continuous cold extrusion, shaving after machining can significantly improve the gear accuracy, and broaching the internal gear after normalizing, so as to obtain products that fully meet the requirements of quality and accuracy.