Research On The Key Technology Of Cold Forging Forming For Spur Gear

Gears are widely used an an important part in power transmission device in car. With thehigh-speed development of automotive industry, the quantity demand and manufacturing of gear areimproved. For the cold precision gear forging has a lot of advantages when compared toconventional gear shaping, such as better mechanical properties, higher productivity, lower energyconsumption and less environmental pollution etc. Cold precision forging has become an alternativemethod to conventional method in gears manufacturing. This paper studied the gear forging processsystematically surrounded by some key issues.Blank of20CrMnTi produces deformation and phase transition, treated combininghigh-pressure torsion(HPT) with cycle heating and cooling(CHC). The results of simulation andexperiment show that this scheme can refine the grain size. First, aimed at the least grain size, themethod of combination of effectively.grey relational analyzing with numeric simulation is used tooptimize the process of HPT, by taken the five key parameters (height-diameter ratio of blank,temperature, descent velocity of punch, torsional velocity of lower die, friction factor,etc)as designedvariables. Between720℃and840℃, the blank is treated with CHC, and then the best scheme ofgrain refined is found. Finally, the HPT and cycle heating and cooling are combined to refine thegrain. The result shows the method can obtain effect grain refinement.Combined the floating-die technology, the research of closed-forging for spur gear with flatface is carried for analyze the forming mechanism and process parameters'influence rule of fomingload. At the basis, the experiment of closed forging is carried out with the blank treated by CHC. Theforming load decreased greatly compared with the blank with conventional annealing. Based on theresults of numerical simulation and physical experiments, the mould for forming20CrMnTi steelgear is designed and made.According to the radial deformation of the metal flow mode(RD mode), the new formingprocess is given for forging spur gear with flat face and big modulus, and it is verified by the resultsof numerical simulation and physical experiment. Compared with the conventional flow mode, thedeformation force in RD mode is reduced. The metal forming rule of RD mode is found bynumerical simulation. The effect on the deform force has been studied by these important factor,such as number of teeth, modulus, height of gear, friction coefficient, root radius, width and depth oftooth, shape and depth of overflow groove, etc.Through physical experiments, the conclusion furtherconfirmed that the process can improve forming quality and reduce deformation force, and the gearpart can be ejected out easily. On accout of the spur gear with boss, a forming technology combined closed-forgingperforming with local loading finish-forming is presented based on the principle of local loading.Through numerical simulation analysis, it is found that the forming method is fit for the gear withgreat height-diameter ratio, which can reduce the forming force greatly and ensure the formingquality. However, for the gear with smaller height-diameter ratio, the forming quality has noguarantee, which the large pitting appears in the bottom of the forging. The reason leads to thephenomenon that material flow speed is quick towards the center hole of punch. On accout of thespur gear with smaller height-diameter ratio, a forming technology combined local loading withdivided-flow on gear side is given. Results of simulation show that the forming process is feasible.Finally, the finish-forming optimization is completed on the basis of the orthogonal test.