Abstract
The shot peening strengthening process has been widely used to improve the fatigue life of spiral bevel gear by inducing residual compressive stress on their surface and subsurface. However, inappropriate process parameters often lead to an increase in surface roughness, which can adversely affect the gear’s contact performance. This study aims to accurately predict and control the microscopic surface morphology and roughness of spiral bevel gear after shot peening. A simulation method coupling discrete element method (DEM) and finite element method (FEM) is proposed. The prediction error of the simulation model is within 20%, demonstrating its accuracy. Based on this model, the relationship between different shot peening parameters and the post-shot peening microscopic morphology of the tooth surface is investigated. The results reveal that the surface roughness initially increases and then decreases with longer shot peening times, and that both shot velocity and diameter significantly affect roughness, with the latter having a more prominent impact.
Introduction
Spiral bevel gear is crucial components in high-end aerospace equipment, particularly in power transmission systems. These gears often operate under high-speed and heavy-load conditions, making them prone to fatigue wear, thereby necessitating strict requirements for surface integrity. Shot peening, a commonly used surface enhancement technique, can improve the fatigue life of gears by inducing residual compressive stress on their surfaces. However, improper shot peening parameters can increase surface roughness, reducing friction and wear resistance, and potentially leading to microcracks, thereby compromising fatigue performance.
Previous studies on shot peening surface roughness primarily relied on random distribution finite element models, focusing on planar or cylindrical surfaces. However, spiral bevel gear possess complex curved tooth surfaces, where the narrow gaps between teeth increase the likelihood of collisions between shot peening. Consequently, this study proposes a simulation method that integrates DEM and FEM to accurately predict the microscopic morphology and roughness of spiral bevel gear post-shot peening.
Experimental Setup
Sample Preparation
The sample used in this study was a spiral bevel gear made from AISI 9310 high-strength alloy steel, with a chemical composition outlined in Table 1. The tooth surface underwent carburizing and quenching, resulting in a surface hardness of 62 HRC.
Table 1: Chemical Composition of AISI 9310 Steel (%)
| Element | Content |
|---|---|
| C | 0.12 |
| Si | 0.25 |
| Mn | 0.55 |
| P | 0.003 |
| S | 0.002 |
| Cr | 1.25 |
| Ni | 3.34 |
Shot Peening Process
The shot peening process was conducted using a compressed air shot peening machine, employing S110 cast steel shot with a nominal diameter of 0.3 mm and a hardness range of 55-62 HRC. The shot peening intensity was set at 0.196 A, with a shot flow rate of 9 kg/min and an air pressure of 4.5 bar. The nozzle was moved at a speed of 150 mm/min, maintained perpendicular to the tooth root at a distance of 180 mm. During shot peening, spiral bevel gear rotated at 10 r/min on a workbench.
Surface Roughness Measurement
After shot peening, the spiral bevel gear was sectioned, and the tooth surfaces were cleaned using an ultrasonic bath. The microscopic morphology was measured using a Wyko NT9100 white light interferometer at three rectangular regions near the large, middle, and small ends of spiral bevel gear. Each measurement area was 0.5 mm x 0.5 mm, with a 20x objective lens.
Simulation Model Development
Coupling DEM and FEM
Given the complex curved tooth surfaces of spiral bevel gear, collisions between shot peening丸 are highly probable. Therefore, a simulation model integrating DEM and FEM was developed to accurately predict post-shot peening surface morphology. Figure 1 illustrates the simulation workflow, starting with DEM to capture collision dynamics and ending with FEM to calculate surface roughness.
Figure 1: Workflow of the Coupled DEM-FEM Simulation Model
Discrete Element Model (DEM)
The DEM model was established using commercial software EDEM to simulate the motion of shot peening丸 from the nozzle outlet to the tooth surface. The geometric model, shown in Figure 2, includes a meshed tooth surface extracted from Hypermesh. The initial shot velocity was calculated using Equation 1:
v=16.35P1.53qm+P+29.5P0.598d+P+4.83P
where v is the initial velocity (m/s), d is the shot diameter (mm), qm is the shot flow rate (kg/min), and P is the nozzle pressure (bar).
Figure 2: DEM Geometric Model of the Shot Peening Process
Collision data, including impact velocity and position, were extracted from EDEM and transformed from the machine tool coordinate system to spiral bevel gear coordinate system for input into the FEM model.
Finite Element Model (FEM)
The FEM model was created in Abaqus/CAE to calculate post-shot peening surface roughness. The target plate, representing the tooth surface, was modeled with refined mesh elements (C3D8R) in the impact region. Figure 3 shows the geometric configuration of the target plate and shot model.
Material properties, such as elastic modulus, Poisson’s ratio, and density, were assigned to both the shot and target plate. The Johnson-Cook model was used to describe the material behavior of the target plate under varying strain rates and temperatures.
Results and Discussion
Simulation vs. Experimental Results
The simulation model was validated by comparing predicted and measured surface roughness (S_a) values. As shown in Table 2, the predicted and measured roughness values agree within 20%, confirming the model’s accuracy.
Table 2: Comparison of Experimental and Simulated S_a Values
| Region | Experimental S_a (μm) | Simulated S_a (μm) | Error (%) |
|---|---|---|---|
| a | 0.938 | 1.091 | 16.2 |
| b | 0.817 | 0.927 | 13.5 |
| c | 0.741 | 0.883 | 19.2 |
Effect of Shot Peening Time
The effect of shot peening time on surface roughness (S_a) was investigated. As shown in Figure 5, S_a initially increases and then slightly decreases with increasing shot peening time. Full coverage was achieved at 50 seconds under the specified process parameters.
Figure 5: Effect of Shot Peening Time on S_a
Effect of Shot Velocity
The influence of shot velocity on S_a was studied by varying the initial velocity from 30 to 50 m/s. S_a increases with higher shot velocities, indicating rougher surfaces.
Effect of Shot Diameter
The effect of shot diameter on S_a was also examined. As demonstrated, larger shot diameters significantly increase S_a, primarily due to increased kinetic energy and plastic deformation.
Conclusion
This study presents a coupled DEM-FEM simulation model for predicting the microscopic surface morphology of spiral bevel gear post-shot peening. The model’s accuracy, validated against experimental results, demonstrates prediction errors within 20%. The study reveals that surface roughness (S_a) initially increases and then slightly decreases with longer shot peening times, achieving full coverage at 50 seconds. Both shot velocity and diameter significantly affect S_a, with the latter having a more pronounced effect. This research provides a robust tool for optimizing shot peening processes to enhance the surface quality and fatigue life of spiral bevel gear.