Abstract: This article focuses on the hot orbital forging process of aerospace cylindrical spur gear. It begins with an introduction to the significance of spur gear in various industries and the limitations of traditional machining methods. Then, it details the research on the hot orbital forging process, including the establishment of a finite element model, the analysis of forming laws, experimental verification, and the comparison of results. The article concludes with a summary of the key findings and the potential for future research in this area.
1. Introduction
1.1 Importance of Spur Gear in Aerospace Industry
Spur gear is fundamental components in mechanical transmissions, widely used in aerospace, automotive, and machinery fields. In the aerospace industry, they play a crucial role in ensuring the precise operation of various systems. For example, in aircraft engines and landing gear systems, spur gears are used to transmit power and control the movement of different parts. The performance and reliability of spur gear directly impact the overall performance and safety of aerospace equipment. High-quality spur gear is required to withstand extreme conditions such as high speeds, heavy loads, and harsh environments.
1.2 Traditional Machining vs. Plastic Forming of Spur Gear
Traditional machining methods for spur gear, such as cutting, have been well-established. However, they have several drawbacks. Cutting processes are often time-consuming and result in low material utilization rates. Moreover, the mechanical properties of spur gear teeth can be compromised as the fiber structure of the material is disrupted during machining. In contrast, plastic forming techniques, like precision forging, offer significant advantages. They can produce gears with a continuous fiber structure along the tooth surface, leading to improved mechanical properties and longer service lives. Additionally, plastic forming is more material-efficient and environmentally friendly.
1.3 Advantages of Hot Orbital Forging
Hot orbital forging is a promising plastic forming process. It requires significantly lower forming forces compared to traditional forging methods, typically only about 10% – 20% of the force required by conventional equipment. This reduction in force leads to less wear and tear on the equipment and lower energy consumption. During the hot orbital forging process, the impact vibration and noise are minimal, which is beneficial for the working environment and the lifespan of the equipment. The fine-grained microstructure formed during forging further enhances the mechanical properties of the spur gear, making them more suitable for high-performance applications in the aerospace industry.
2. Finite Element Model Establishment
2.1 Gear 3D Model Creation
The research focuses on a specific aerospace cylindrical spur gear. The geometric parameters of spur gear, as shown in Table 1, are crucial for accurately modeling the forging process.
| Parameters | Value |
|---|---|
| Number of teeth | 16 |
| Module/mm | 4.5 |
| Pressure angle/(°) | 20 |
| Addendum coefficient | 1 |
| Clearance coefficient | 0.25 |
| Addendum modification coefficient | 0.1917 |
| Tooth width/mm | 11 |
Using 3D CAD software, a detailed 3D model of the spur gear is constructed. This model serves as the basis for subsequent simulations and analyses.
2.2 Blank Design
Considering the structural characteristics of the cylindrical spur gear with protruding hubs at both ends, the blank is designed as a cylinder. The diameter of the blank is slightly smaller than that of spur gear hub. Based on the principle of equal volume, the shape and size of the blank are determined.
2.3 Orbital Die and Gear Cavity Design
The hot orbital forging process involves the coordinated movement of the orbital die and spur gear cavity. The orbital die rotates around the machine spindle while also rotating about its own axis, creating a complex motion pattern. The spur gear cavity moves upward at a constant feed rate. The angle between the orbital die’s axis and the machine spindle, known as the orbital angle, is a critical parameter that affects the metal flow and forming process. The 3D models of spur gear cavity and the orbital die are designed using CAD software.
2.4 Finite Element Model Setup
The.stl files of the orbital die, gear cavity, and blank are imported into the DEFORM – 3D preprocessor for positioning and assembly. To accurately capture the material flow in the tooth profile, the mesh of the blank’s tooth area is refined, with a mesh count of 100,000 and a refinement ratio of 0.01. In the simulation, the orbital die and gear cavity are modeled as rigid bodies, while the blank is considered a plastic body. The material of the blank is selected as 20CrMnTi, and a shear friction model with a friction coefficient of 0.25 is used for the interfaces between the die and the blank. Other simulation parameters, such as the feed rate of spur gear cavity, rotational speed of the orbital die, and temperatures of the blank and die, are set as shown in Table 2. The final finite element model.
3. Forming Law Analysis
3.1 Gear Forming Process
During the initial stage of hot orbital forging, the upper surface of the blank contacts the orbital die first, resulting in the formation of the protruding hubs. As the forging progresses, the hubs are fully formed, and the central part of the blank undergoes upsetting deformation, with the diameter increasing and the height decreasing. The shape of the blank resembles an inverted mushroom. In the middle stage, the upper part of the tooth profile begins to form due to the faster material flow in that region. Metal fills the tooth root first and then the tooth tip. In the final and finishing stages, the plastic deformation penetrates the entire tooth profile, and spur gear shape is fully formed, accompanied by the formation of petal – shaped flash. The changes in spur gear shape at different times. The filling process of a single tooth, clearly demonstrating the axial filling of the tooth profile and the faster filling speed at the upper end. The metal flow streamline in the axial and cross – sectional directions, indicating the compression and densification of the metal flow in the blank’s central region and the formation of dense streamlines in the tooth and flash areas.
3.2 Metal Flow Velocity Field
The deformation zone of the workpiece can be divided into an active deformation area and a passive deformation area. The active deformation area, where the tooth surface directly contacts the orbital die, experiences greater plastic deformation and faster metal flow. In the early stage of forging, the metal in the active deformation area mainly flows axially and radially to fill the die cavity. In the middle stage, after the hubs are filled, the metal in the blank’s central part fills spur gear cavity at different speeds, with the tooth root filling at a slower rate and the tooth tip at a faster rate. In the later stage, as the tooth profile is filled, the height decreases, the diameter increases, and flash is formed. In the finishing stage, some metal in the active deformation area still fills the tooth profile axially. The velocity field distribution at different times, with the maximum velocity located in the middle of the active deformation area and decreasing towards the sides.
3.3 Equivalent Stress Field
During the middle stage of forging, the tooth root, which is in direct contact with spur gear cavity, experiences higher stress, while the stress on the tooth tip is relatively low as the metal has not fully filled the cavity. In the later stage, as the lower tooth root is filled first, it experiences the maximum stress. As the plastic deformation propagates from bottom to top, the stress on the tooth root and tip increases, but decreases from bottom to top. In the finishing stage, the stress on the upper tooth tip decreases significantly after it is filled, while the lower tooth tip experiences higher stress. The equivalent stress distribution at different times.
3.4 Equivalent Strain Field
In the middle stage of forming, when the tooth profile begins to form, the equivalent strain is concentrated at the edges of the hubs, the center of the blank, and the tooth root, with the tooth root having a larger equivalent strain value. In the later stage, when the flash begins to form, the flash shows a small equivalent strain value, and the equivalent strain at the tooth root is larger and decreases from top to bottom. At the end of the feed motion, the equivalent strain on the tooth profile decreases from the tooth root to the tooth tip. In the finishing stage, the equivalent strain at the tooth root, center, and flash continues to increase, while that at the tooth tip remains almost unchanged. The equivalent strain distribution at different times.
3.5 Temperature Field
In the areas with less plastic deformation and in contact with the die, such as the upper and lower hubs, the temperature drops significantly due to heat conduction. In contrast, the tooth profile, which undergoes large plastic deformation, has a slower temperature drop. The temperature at the tooth tip is higher than that at the tooth root, and the temperature in the center of the blank remains almost unchanged. The temperature field distribution at different times.
3.6 Forming Load Variation
The axial forming load can be divided into four stages. In the initial stage, as the orbital die contacts the workpiece locally, the forming load increases slowly. In the middle stage, with the formation of the tooth profile, the axial load increases at a faster rate. In the later stage, due to the significant increase in the resistance to metal filling in the die cavity, the axial load reaches a maximum value of approximately 2500 kN. In the finishing stage, the axial load decreases rapidly with fluctuations. The radial load varies periodically, and in the finishing stage, when the lower die stops feeding and the orbital die only rotates, the radial load increases sharply and then decreases periodically. The radial load is much smaller than the axial load throughout the forging process. The variation curves of the axial and radial forming loads with time.
4. Experiment
Based on the results of the finite element simulation, the orbital forging dies and blanks are designed and manufactured. Hot orbital forging experiments are conducted on a T630 hot orbital forging machine using 20CrMnTi samples. The experimental results, indicate that the tooth profile of the forged gear is fully filled, and the shape of spur gear and the flash are consistent with the simulation results, verifying the accuracy of the finite element model.
5. Conclusion
5.1 Summary of Key Findings
In the hot orbital forging process of cylindrical spur gear, the blank deformation zone consists of an active deformation area and a passive deformation area. The tooth profile is gradually formed from the upper end to the lower end, and the blank takes on a mushroom – like shape. The equivalent strain and stress are maximum at the tooth root, and the temperature at the tooth root is lower than that at the tooth tip. The axial load increases gradually with plastic deformation, reaching a maximum value of about 2500 kN. The radial load varies periodically during the feed stage and is much smaller than the axial load. The experimental results of the hot orbital forging process are in good agreement with the finite element simulation results.
5.2 Significance and Potential for Future Research
The research on the hot orbital forging process of aerospace cylindrical spur gear provides valuable insights for the manufacturing of high – quality gears. The findings can be used to optimize the forging process, improve gear performance, and reduce production costs. Future research can focus on further optimizing the process parameters, exploring the effects of different materials and lubricants, and investigating the microstructure and mechanical properties of the forged gears in more detail. Additionally, the application of advanced simulation techniques and the development of intelligent manufacturing systems can enhance the efficiency and precision of the hot orbital forging process.
In conclusion, the hot orbital forging process shows great potential for the production of aerospace cylindrical spur gear, and continued research and development in this area will contribute to the advancement of the aerospace and mechanical engineering industries.