Study On Precision Forging Process And Mould Design Of Spur Bevel Gear

Using precision forging process to produce gears, the material and power are saved, the cost is reduced and the efficiency is enhanced. At the same time, the abilities of anti-wear, anti-erode, anti-bending and anti-fatigue of the precision forging gear are improved. Therefore, the technology on precision forging gear becomes the development tendency of gear manufacturing industry. The technology of precision forging spur bevel gear is first used because of its structure characteristics. At present, the precision forging process of spur bevel gear is already well developed. According to the modulus and the material of the spur bevel gear, the suitable precision forging process can be chosen.Using hot-forging-warm-sizing process to form big module spur bevel gear is widely applied. In general, this process is well developed, but problems of unsuccessful corner filling, excessive forming load and early failure of tooth die always take place due to the large deformation of gear teeth. In the hot-forging-warm-sizing process, multi-factors affecting the accuracy of gear teeth exist, and then it's difficult to design teeth profile and hard to keep teeth profile accuracy. Hence, in this paper, the hot-forging-warm-sizing process of planetary gear and axle shaft gear is researched, and the final forging part, pre-forging part and the billet are designed. During designing the pre-forging part, the shape of gear teeth is modified as vary clearance taper tooth. Compared with the duplex taper tooth, the depth of gear teeth is increased.The design of tooth shape is very important in the precision forging process of spur bevel gear. In this paper, the parametric equations of involute tooth profile are established. Once the basic parameters of spur bevel gear are determined, using curve commands of UG the involute tooth profile of spur bevel gear can be draw out according to the parametric equations established. The tooth profile relationship of forging part, mould and electrode is studied, and the mathematical relationship of the basic tooth parameters of forging part, mould and electrode is deduced. Thus the tooth profiles in precision forging process of spur bevel gear can be designed easily and exactly. At last, the new model of tooth form design of nonlinear expansion hot forging part is put forward, and the tooth profile equations of nonlinear expansion hot forging part are presented. During pre-forging planetary gear, the height-to-diameter of the billet is important for improving the filling of gear teeth and increasing the life-time of the teeth die. Using Deform-3D software, a three-dimensional FEM numerical simulation of pre-forming planetary gear is preformed, and three design schemes with different height-to-diameter of the billet are researched. And then the effective strain distributions, effective strain rate distributions, effective stress distributions, velocity distributions and the load-stroke curves are investigated. A feasible scheme is attained by analyzing numerical simulation results of these schemes. During final forging spur bevel gear, the shape of pre-forging part is one major factor which affects the filling of gear teeth and forming load. Using Deform-3D software, a three-dimensional FEM numerical simulation of final forging planetary gear and axle shaft gear is preformed. The simulation results show that the shape of pre-forging part designed in this paper has improved the sequence of teeth filling. The metal first fills the tooth crests, then fills the tooth profiles, and fills the tooth roots at last. According to the simulation results, it is ascertained that the tooth profile is well filled, and forging part with full gear teeth can be obtained under lower forming load.According to the process design and the simulation results, the pre-forging die structure and the final forging die structure for precision forging spur bevel gears are designed. The steering of dies is right and the forging part can take off mould smoothly. The main points of the design and the manufacture of tooth die are elaborated. The method to increase the life-time of tooth die and the selection of the die material is discussed.