Design of precision finishing method for cold extruded sun gear with internal-external tooth shapes

The dimensional accuracy of cold extruded sun gear is poor since the material flow is considerably complex in the forming process. A novel precision finishing method was proposed in this study to improve the dimension accuracy of cold extruded sun gear, and a new finite element (FE) prediction strategy was developed to obtain an in-depth understanding of the deviation distribution laws of the finished sun gear. Then, the forming laws of internal-external gears such as material flow, tooth deformation, forming load, and tooth accuracy were analyzed using FE simulation and verified experiment. The investigation results show that the single deviations in profile and helix both first diminished remarkably, and then rose gradually, while the single M value deviation decreased remarkably with increasing the tooth width. The simulation results of teeth deviations are well agreed with the experimental ones, which verifies the reliability of the FE prediction strategy. Moreover, the profile accuracy of external gear can be improved from ninth to seventh class, lead accuracy can be enhanced from tenth to eighth class, and total M value deviation of internal spline is reduced to 72.3 μm, which proves the feasibility and effectiveness of the precision finishing method.