Numerical Simulation On Composite Forming Process Of Forging And Casting For Automobile Rear Axle Spiral Bevel Gear

With the rapid expansion of automobile production and sales, the appeal for the quantity, capacity and cost control of spiral bevel gears, the important transmission part in rear axle main reducer of automobile, is becoming higher. Generally, spiral bevel gears are formed by forging and machining. Forging has needless steps and high expenditure. With minor manufacturing productivity and heavy material breakage,machining may weaken the strength and working life of gears by cutting off the metal fiber structures. Therefore, it is imperative to improve the long-established formation technology. This paper raises a new approach to form spiral bevel gears which is the combined process of forging and casting. The numerical simulation studies of the composite process not only optimize the tooth profile and relevant parameters but also verify the superiority of the composite forming process. The simulation results show that combined forming process has a potential practical value for forcefully promoting the quality of spiral bevel gears, material utilization and the production efficiency.Main research contents and relevant conclusions of this paper are as follows:1.Gear shape and size of the cold precision forging preform is an influential factor affecting the spiral bevel gear cold precision forging process. Non-uniform diffusion tooth profile plan and uniform diffusion tooth profile plan are raised. The numerical simulation reports of cold precision forging by DEFORM-3D software show the load-stroke curve, distribution of stress-strain and metal flow conditions of different plans. After comparing the simulation results of above plans, it is obvious that the forming quality of non-uniform diffusion tooth profile plan is better when the amount of cold precision forging is 0.6mm. In this way, the optimal tooth profile of spiral bevel gear cold forging preform is determined.2.Tooth profile and preform taper of the closed hot die forging preform deeplyaffect the closed hot die forging process of spiral bevel gears. The tooth profile design is required to ensure eliminating the casting defects and reaching the demands of the closed hot die forging process. The approximate trapezoidal tooth profile plan is presented based on divided flow theory. This plan keeps a divided flow space on the tooth top of closed hot die forming preform so as to improve the rational flow of metal and the ability of filling mold cavity. Reducing the taper of closed hot die forming preform can ensure the forming priority of small tooth end. That is beneficial to improve the metal flow status to make each part of the gear tooth forming at the same time. The simulation results reveal that the forming quality is best when the taper of preform is 3° smaller than that of the hot die and tooth height reaches to5.8mm. In this way, the optimal tooth profile and taper of spiral bevel gear closed hot die forging preform is determined.3.After comparing various casting processes according to the quality requirement of the hot die forging, coated sand casting process is chosen to form forging preform precisely and the type of casting material is given. Gating and rising combined casting plan and center-top casting plan are designed. The size of the riser and gating system is calculated. Anycasting software is adopted to analyze the filling and solidification process of the cast part. The simulation results show that center top casting plan is more suitable for the precision casting of spiral bevel gear forging preform.4.The effects of casting temperature and casting speed on the forming quality of spiral bevel gear are studied in this paper. The casting defects conditions with different casting temperature and casting speed reveal that shrinkage defects of the cast parts are less when the casting temperature is higher in a certain range. Besides,casting speed affects the distribution of residual air in the upper surface of gear castings. In this way, it is confirmed that the optimum casting temperature is 1640℃and the optimum casting speed is 0.8m/s.