The Key Technology On Precision Forming Process By Hot Forging And Cold Ironing Of Cylindrical Spur Gears

Cylindrical spur gear is a kind of typical gear component, usually being manufactured by cutting process. Gears manufactured by precision forming take the advantages of high materials utilizing, production efficiency, product quality and so on. Furthermore, the metal streamlines on the gear tooth will not be cut off and distribute along the tooth profile, so that the strength and life of the gears increase. Thus the cylindrical spur gear manufactured by plastic forming process has broad application prospects.The process of precision plastic forming is widely applied in cylindrical and bevel gears with small module and diameter. It is difficult to manufacture the spur gears with small module and diameter by precision forming method due to the high forming load and die stress. Hot forging process has the disadvantages of low forming accuracy and surface finish, which leads to little industry application. A process combining hot forging and cold ironing for the cylindrical spur gears with large dimension above was put forward. The process can not only reduce the forming load and die stress, but also form gears with high accuracy, providing a viable method for manufacturing spur gears with large module and dimension.The prediction model of forming load of hot forging of gears was built by combining theoretical analysis and FE simulation. The effects of gear dimension and material stress states on the forming load were analyzed. The formula was further deduced to calculate the dimension range of forged gears for the presses with different nominal pressure, which was of instructive significance for the presses selecting.The involute accuracy controlling method was presented for hot precision forging of gears. A theoretical model was presented for involute profile deflection of workpiece and tooth die in hot precision forging and cold ironing of gears. The theoretical model and FE simulation both calculated the effects of thermal die expansion, elastic die expansion, thermal workpiece contraction, and elastic workpiece recovery to tooth deflection. The results show that the thermal workpiece contraction is the major effect factor to tooth deflection. An equation set of modified involute of die tooth was proposed based on the deflection model. The involute accuracy of forged gears achieved the1Oth class. The nonuniformity of die deflection along the tooth width was analyzed by combining the theoretical calculation and FE simulation, so that the deflection distribution along the tooth width was obtained. The measured results of forged gears showed good consistency with the FE simulation.The method of involute and lead accuracy controlling was presented for hot precision forging of gears. A theoretical model was presented for involute profile deflection of workpiece and tooth die in cold ironing gears. The theoretical model and FE simulation both calculated the effects of elastic die expansion and elastic workpiece recovery to tooth deflection. The involute of die tooth was modified based on the deflection model. The involute accuracy of ironed gears achieved the8th class. The elastic deflection regulation of the toothed die in cold ironing process was analyzed. The crown shape of workpiece tooth was obtained by FE simulation. The three zones of the ironing die were designed so that the crown of the workpiece was reduced. The measured results of ironed gears esured the validity of the analysis and FE simulation. The lead error of the ironed gears achieved8th class, effectively improving the accuracy of the formed gears.The modified lead of die tooth was proposed in cold ironing tool to reduce the crown shape of workpiece tooth. The measured results of ironed gears showed good consistency with the FE simulation.The metal flow law and die stress et al. in precision forming process is studied in this research. The effects of tool structure and relief-cavity on material flow, forming load, and die stress in hot precision forging of gears were analyzed by using FEM. The effects of several process parameters on material flow, forming load, and workpiece stress in cold ironing of gears were also analyzed by using FEM. The optimal process of hot forging and cold ironing was decided. The hot forging and cold ironing trials ensured the vality of FE simulation.The microstructure evolution in precision forming of gears was observed. The microstructure evolution during hot forging, annealing, cold ironing, and hardening was analyzed in turn. The microstructure of the gears manufactured by conventional cutting process and precision forming process were compared, revealing the microcosmic mechanism of the precision formed gears.The results of the study were applied in a planetary gear, forming gears with fine surface finish, high accuracy and fine microstructure, with material utilization increased. The paper provides theoretical and experimental foundation and great reference value for the research of the precision forming of cylindrical spur gears. And it also provides an important guidance for the industrial application of gear manufacturing by precision forming process.