Study On The Forming Mechanism And Application Of Hollow Divided Flow Forging Technology

There are many kinds of gears, which are extensively used in automobile, aircrafts, ships, machine tools and so on, especially in the transmission system of various kinds of vehicles. There are nearly 40 gears in a car, and half of which can be produced by precision die forging process. At present, the large industrialization production of bevel gears has been achieved by precision die forging process, as well as automobile starter gears and synchronizer blocking rings. Hence, a remarkable benefit in social, economic aspects were made on saving energy. And environmental protection, the quantity and performance of the products were improved. But reports are few, about the studies on joint gears, reverse gears and spur gears with big modulus which have complicated structure and great difficulty of being formed. German ThyssenKrupp Automotive Company and Japan Nichidai Company developed precision forging forming processes on joint gears and reverse gears. And those processes have been applied to production. Duo to technical security, there is no pubulic papers. The process of forming spur gears with big modulus has not been reported yet. Domestic research and application on joint gears and spur gears with big modulus have just started internally. In this paper, it is targeted as realizing the precision die forging of those gears. Classical plastic forming theory, finite element simulation and corresponding experiments were used to study the forming mechanism and application of hollow divided flow forging technology. The main research contents and results of this paper are as follows:Hollow divided flow forging technology was studied and some research results were achieved. When the flat spur gear is obtained from the solid cylinder blank through conventional closed die forging technology, most of the metal of the blank flows along the axial and the radial flow is very little. The equivalent strain is low; however the equivalent stress is high during the forming process. As a result, the forming force increases rapidly and the teeth of the gear are not formed competely. Nevertheless, by adopting hollow divided flow forging technology in the forming process of the flat spur gear, the matal flows along the axial combined with the radial. The equivalent strain increases and the equivalent stress decreases. Meanwhile, the teeth of the gear are formed well.The main factors that influence the forming force and the interrelation of these factors were analyzed. An optimal model of target function was developed for obtaining the minimal forming force. The calculation formula for the forming force of the hollow divided flow forging technology was derived, as well as the calculation formula for the radius of the ring blank used in hollow divided flow forging technology. The optimization design was implemented.Conventional closed die forging technology of joint gear was analysed by means of traditional plasticity theory and thermodynamic couple numerical simulation in rigid-viscoplastic finite element method, through which the forming rules were obtained. Because the metal of the blank flows too long and the tangential stress of die is too high, the fracture of die and forging defects appear. According to the key technical problems, the hollow divided flow forging technology of joint gear was developed, the same as the optimum design of the shape of pre-forging. The structure of the three-stage die was designed. As well, corresponding experiments were carried out. The results show that the forging is qualified, and the hollow divided flow forging technology of joint gear is feasible.Problems such as low material utilization and large forming force exist in the forming process of the spur gear with big modulus, when using the thick wall seamless tube through extrusion with core shaft. To solve the above-mentioned problems, hot closed extrusion shceme and cold extrusion finishing hollow divided flow forging technology were proposed. The die structure design was completed. Based on coupled thermo-mechanical simulation in rigid-viscoplastic finite element method and elastoplastic finite element method, the forming processes were simulated by the software Deform-3D. Then, corresponding experiments were conducted and the results perfectly matched the simulation results.Based on the theoretical research results, a hollow divided flow forging technology production line was put into production in cooperative enterprise. The production line includes blanking, heating,16000KN three-stage hot die forging press, heat treatment furnace and 6300KN precision forging hydraulic press. Batch process of two crosspiece joint gear precision forging was done and larger economic benefit was achieved. The hollow divided flow forging technology and the die of spur gears with big modulus provide a scientific basis for forming the precision forging of the driving axle planetary gear in relevant enterprises.