Abstract
The surface quality of spur gears directly influences their transmission accuracy during gear transmission, which in turn significantly affects their fatigue life. 20CrMnTi steel, commonly used for spur gears, exhibits high impact load capacity and good wear resistance. The hobbing process and subsequent shot peening process of spur gears alter their surface quality. Therefore, studying the surface quality of spur gears is of great importance. This paper combines experimental and finite element simulation methods to investigate the hobbing process and shot peening process.
1. Introduction
In mechanical transmission systems, spur gear play a crucial role. The surface quality of spur gear impacts their transmission precision, which further affects their fatigue life and operational reliability. Research on the manufacturing processes of spur gear, particularly the hobbing process and subsequent surface treatments such as shot peening, is essential for improving gear performance.
2. Literature Review
Previous studies have investigated various aspects of spur gear manufacturing. Gao Niping found that the surface quality of gears processed by hobbing could be improved by enhancing the quality of the hob’s rake face or increasing the radius of the top edge. Wu et al. established a cost model for gear hobbing based on power curves and the impact of cutting parameters on hob lifespan to reduce costs and enhance productivity.
Researchers have also explored the use of different lubricants and cutting techniques. Khalilpourazary et al. discovered that dispersing alumina nanoparticle lubricants in cutting oil during gear hobbing reduced hob wear and gear surface roughness. Chaubey et al. compared the surface finish, microstructure, and microhardness of helical gears processed by hobbing, milling, and electrical discharge machining (EDM), finding that EDM-processed gears had higher microhardness and superior microstructure but poorer surface finish.
Finite element simulation has been employed to analyze gear cutting processes. Dong et al. modeled the complex motion relationship between the hob and gear blank, simulating the entire hobbing process in finite element software to predict cutting forces, temperatures, torques, stress distributions, and hob wear.
3. Research Objectives and Methodology
The primary objectives of this study are to investigate the influence of various cutting parameters on the cutting power, surface roughness, and microhardness of spur gear during the hobbing process and to establish a foundation for optimizing process parameters and enhancing the effectiveness of subsequent shot peening.
3.1 Experimental Setup
3.1.1 Hobbing Process and Material
The experimental material was 20CrMnTi steel, chosen for its high strength, toughness, and fatigue resistance. The hobbing process was conducted on an HI-008 hobbing machine, with specific cutting parameters as shown in Table 1.
Table 1: Hobbing Processing Parameters
| Hob Speed (r/min) | Feed Rate (mm/r) |
|---|---|
| 165 | 0.47 |
| 165 | 0.83 |
| 165 | 1.2 |
| 204 | 1.2 |
| 275 | 1.2 |
3.1.2 Measurement Methods
Cutting power was measured using a multimeter and clamp-on ammeter. Surface roughness was measured with a profilometer, and surface morphology was observed using an ultra-depth microscope. Microhardness was measured using a microhardness tester.
3.2 Finite Element Simulation
The motion relationship between the hob and gear blank was analyzed, and simplified models of the hob and gear blank were created in CREO. Finite element simulations were conducted in DEFORM, analyzing chip formation, cutting forces, and equivalent stresses under various cutting parameters.
4. Experimental Results and Analysis
4.1 Influence of Cutting Parameters on Cutting Power
The cutting power increased with higher hob speeds due to increased friction and material removal rates. Similarly, an increase in feed rate led to an increase in cutting power as the area of material removed increased.
4.2 Influence of Cutting Parameters on Surface Roughness
Table 2 summarizes the surface roughness measurements for different cutting parameters.
Table 2: Surface Roughness Measurements
| Hob Speed (r/min) | Feed Rate (mm/r) | Surface Roughness (μm) |
|---|---|---|
| 165 | 0.47 | 0.654 |
| 165 | 0.83 | 0.721 |
| 165 | 1.2 | 0.832 |
| 204 | 1.2 | 0.789 |
| 275 | 1.2 | 0.589 |
Increasing the feed rate decreased the density of cutting marks, leading to increased surface roughness. Conversely, higher hob speeds reduced surface roughness, with the lowest roughness value of 0.589 μm observed at 275 r/min.
4.3 Influence of Cutting Parameters on Microhardness
Increasing the feed rate slightly increased the surface hardness of the gears, likely due to increased plastic deformation and work hardening. Within a certain range of hob speeds, increasing the speed also increased surface hardness, but excessively high speeds caused a decrease in hardness.
5. Finite Element Simulation Results
The finite element simulations revealed that during the hobbing process, the top edge of the hob initially contacts the gear blank, followed by the side cutting edges, forming the final chip morphology. Increasing the feed rate increased the cutting forces and equivalent stresses due to the larger area of material removal. The simulations also showed that higher hob speeds reduced cutting time and generated lower surface roughness, aligning with the experimental findings.
6. Shot Peening Experiment
Based on the hobbing experiments and simulations, the optimal hobbing parameters for the shot peening experiment were determined: a hob speed of 275 r/min and a feed rate of 0.47 mm/r. Shot peening was conducted using cast steel shots with a diameter of 0.4 mm, and pressures of 0.2 MPa and 0.3 MPa were applied.
7. Conclusion
This study investigated the influence of cutting parameters on the cutting power, surface roughness, and microhardness of spur gear during the hobbing process using experimental and finite element simulation methods. The results showed that increasing the hob speed reduced cutting time and surface roughness while increasing feed rate increased cutting power and surface roughness. Optimal hobbing parameters were identified for subsequent shot peening, aiming to improve the surface integrity and fatigue life of spur gear.