With the in-depth research on the forming process of spur gears and the continuous development of market demand, the modern manufacturing industry has continuously improved the product quality requirements of spur gears, and the precision forming of spur gears has always been a research hotspot. The compound forming process scheme of straight tooth cylindrical gear through continuous “cold extrusion + cold shaping” is proposed. How to optimize the cold extrusion die design, improve the cold extrusion forming quality of straight tooth cylindrical gear, reduce the forming load and improve the service life of the die is one of the key points of the compound forming process scheme. Most of the previous studies started with the cold extrusion formability of spur gears or single factor and single objective analysis of the forming process, but less used the multi-objective optimization method to balance and optimize the forming quality and forming load of cold extrusion gears. Aiming at the problems of large end machining allowance, large tooth tip collapse angle and large forming load in the cold extrusion process of spur gear, this chapter first analyzes the influence law of main process parameters on the forming quality of spur gear, determines the reasonable factors and corresponding levels of each process parameter, and then puts forward the combination of numerical simulation and experimental design, Taking the response surface method as the optimization method, the three target values of end face machining allowance, tooth tip collapse angle and forming load are balanced and optimized, and the best combination of process parameters is obtained to guide the actual production.
Aiming at the problems of large end machining allowance, large tooth tip collapse angle and large forming load in the cold extrusion process of spur gear, firstly, the influence law of main process parameters on the forming quality of spur gear is analyzed, and the reasonable factors of each process parameter and their corresponding level are determined. Secondly, the combination of numerical simulation and experimental design is proposed, Taking the response surface method as the optimization method, the three target values of end face machining allowance, tooth tip collapse angle and forming load are balanced and optimized, and the best combination of process parameters is obtained to guide the actual production. The main conclusions are as follows:
① The size of the injection angle will affect the inner and outer metal flow velocity. When the injection angle is small, the inner and outer metal flow is more uniform; When the die angle is large, the flow velocity of the inner metal is obviously faster than that of the outer metal. The inner and outer metal flows unevenly, and the faster inner metal has a radial pulling effect on the slower outer metal. Therefore, the amount of tooth top collapse angle and end face convexity increase with the increase of die angle. However, the forming load decreases with the increase of die angle.
② With the increase of splitting angle thickness, the resistance of metal axial flow becomes stronger, the flow speed of outer metal becomes slower, and the axial flow speed difference of inner and outer metal becomes larger. Therefore, the amount of tooth top collapse angle and end face convexity increase with the increase of splitting angle thickness, and the forming load increases with the increase of splitting angle thickness.
③ The length of sizing band is one of the key parameters to ensure the cold extrusion quality and forming accuracy of spur gears. If the sizing belt is too short, the plastic deformation occurs outside the constraint area of the die, resulting in the reduction of the forming quality and accuracy of spur gears. If the sizing belt is too long, it will cause the surface strain of the extrusion and the defects of die sticking.
④ Based on the response surface method (RSM), three target response tooth tip collapse angles are established respectively δ， According to the second-order response models of design variables X1 (tooth tip fillet), X2 (die entry angle), X3 (splitting angle thickness) and X4 (sizing belt length), the fitting degrees of the regression models obtained are 98.36%, 99.01% and 99.06% respectively. The prediction accuracy is good and can better describe the response of the three objective functions to the design variables.
⑤ The experimental parameters are further optimized by MATLAB software, and the optimal process parameters of cold extrusion forming of large modulus spur gear are obtained: X1 is 1.6mm, X2 is 40 ℃, X3 is 2mm and X4 is 15mm.
⑥ Error analysis and production practice show that the optimal combination of process parameters can effectively reduce the collapse angle of tooth top δ、 The end face convexity h and forming load f provide a certain guiding role for the cold extrusion production of similar large modulus spur gears.