# A Study on the Effect of Gear Hobbing Process Parameters on the Residual Stress of the Tooth Root
## 1 Introduction  
The gear is a crucial component in transmitting motion and power, and its performance directly impacts the service life, reliability, and overall performance of major equipment [1]. The manufacturing process for a high-performance gear formation is mainly divided into two main steps: semi-finishing gear machining and finishing gear grinding [2]. Hobbing, as the initial processing step from a blank tooth to a gear, plays a vital role in determining the quality and performance of the gear. Residual stress is a critical factor affecting gear performance. Residual tensile stress will promote crack initiation and reduce the bending fatigue strength of the tooth root, while residual compressive stress can enhance the bending fatigue strength of the tooth root by slowing down crack propagation [3]. Therefore, if the residual compressive stress could be either preset at the tooth root or reduced by improving the process parameters of hobbing, it would significantly contribute to increasing the bending fatigue life of the gear. In recent years, there have been numerous studies conducted on the residual stress of the gear grinding process in gear finishing technology. [PERSON] et al. [4] studied the distribution pattern of residual stress in the helical bevel gears of heavy vehicles under different grinding parameters and calculated the residual stress of helical bevel gear grinding based on the mechanothermal coupling finite element simulation method. The findings revealed that the convex surface of the gear, parallel to the grinding direction, exhibited the lowestresidual compressive stress, and tensile stress occurred on the tooth surface, while compressive stress was observed on the subsurface during the grinding process. [PERSON] et al. [5] proposed a calculation model for residual stress in spiral level gears based on generative grinding and discovered that different grinding parameters at each point on the spiral level gear, under the same grinding conditions (grinding speed, generative speed, grinding depth), affected the distribution of residual stress on the tooth surface. [PERSON] et al. [6] adopted the thermo-elastoplastic coupling structural analysis method, considering the tangential grinding force and grinding parameters, to calculate the residual stress distribution caused by the movement of the heat source, and their results indicated that residual stress would be generated along the profile when the grinding temperature exceeded 300 \({}^{\circ}\)C. [PERSON] et al. [7] established a model for the tooth surface of face gear grinding based on the machine tool structure and the meshing mechanism with a large radius disc wheel. The findings revealed that the residual stress in face gear grinding is influenced by the grinding contact width, grinding contact length, and the number of dynamic effective grinding edges. [PERSON] et al. [8] proposed a method, based on motion analysis of form grinding and a thermodynamic coupling finite element simulation calculation, to calculate the residual stress on the tooth surface of spur gear form grinding and analyzed the correlation law between the grinding parameters and the residual stress. The results indicated that the grinding wheel feed depth increasing resulted in a decrease in residual tensile stress on the tooth surface during form grinding. [PERSON] et al. [9] established a grinding model considering the position of abrasive particles and analyzed the distribution of residual stress during grinding, finding that both feed speed and cutting depth had an impact on the profile and axial residual stress. It can be seen from the above that different grinding process parameters have different effects on the residual stress of the gear, and the process parameters are an effective method for controlling residual stress. The existing research results also show that appropriate residual stress can be obtained by selecting appropriate process parameters, so as to improve the fatigue life of parts [10].