###### Abstract
analyzed, in detail, the influence of process parameters such as the billett temperature, deformation speed and friction coefficient on the precision forging of spiral bevel gears and finally provided a relevant basis for the precision forming and die design of spiral bevel gears [11]. [PERSON] et al. analyzed the defects, such as low die life and insufficient filling, of forgings in the closed forging process of spiral bevel gear and proposed to modify the die structure to eliminate the forging defects [12]. [PERSON] et al. proposed a new type of \"outer-closed-inner-open\" type die, which adopts the step-by-step forming process with expanded corner preforming and then final forming, significantly reducing the forming load so as to precisely forge the driven curved bevel gear with a full tooth shape and clear contour [13]. Based on the elastic-plastic finite element theory, [PERSON] et al. used DEFORM-3D software to carry out a finite element simulation to simulate the parameter changes in the tooth blank in the process of forging and forming, investigated the important influence of the structure of the forging die on the internal metal flow of the spiral bevel gear forging, and put forward an optimization method for the spiral bevel gear-forging die structure [14]. The above research was mainly carried out on the basis of hot forging, although the forming load is small and the equipment investment is low, but the forged spiral bevel gears are seriously oxidized, with low precision and poor comprehensive mechanical properties. For this reason, the technologists and scholars concerned have proposed the use of a warm-forging-forming process. Warm forming is a plastic deformation in which the metal is heated to an appropriate temperature range below the recrystallization temperature. During warm-forging deformation, the work hardening is reduced by different degrees, so the forging deformation force is lower than that of cold forging but higher than that of hot forging. The accuracy, surface roughness, surface oxidation, decardurization and mechanical properties of forgings are better than those of hot forgings and similar to those of cold forgings. It has the advantagesof both hot and cold deformation and avoids their respective drawbacks. [PERSON] et al. analyzed the development trend of precision-forging technology and proposed the process advantages and development prospects of warm forging [15]. [PERSON] et al. summarized the application of warm-forging technology in the automotive industry and its latest development trend through the practical application of warm forging of several common automotive parts [16]. [PERSON] et al. evaluated the mechanical properties and microstructure of 27 MnSiV56 steel after warm forging at temperatures ranging from 1033 K to 1123 K. Compared with hot forging, the mechanical strength value is increased by about 50 MPa, and the impact toughness is almost doubled [17]. [PERSON] et al. compared the microstructural changes in metallic materials under hot forging and warm forging and found that warm forging can obtain a higher surface quality of parts [18]. [PERSON] et al. carried out a numerical simulation on the warm-forging process of cylindrical spur gear; analyzed the influence of forging speed, die preheating temperature and other process parameters on the forming process; and obtained better process parameters, which played a guiding role in the actual production [19]. [PERSON] et al. used FEM to analyze the maximum forging load and strain distribution of internal helical gear forgings under different isothermal forging process parameters of the module, number of teeth and die temperature, and they determined the power demand of internal helical gear warm forging [20]. In view of the complex shape of the gear with shaft, [PERSON] et al.