Abstract
The optimization of the high and low-speed switching point in the die casting process of transmission main housing is crucial to ensure the quality and mechanical properties of the cast component. This study investigates the filling behavior of the 9AT transmission main housing during die casting by employing simulation and experimental validation. The results reveal that the optimal switching point is located at 560 mm, with a low-speed of 0.2 m/s and a high-speed of 3.5 m/s, leading to a smooth filling process and minimal porosity. This optimized process was adopted for trial production, resulting in dense castings with satisfactory mechanical properties.
Introduction
The transmission system is a vital component in automotive engines, significantly impacting driving comfort and fuel efficiency. The introduction of advanced multi-speed transmissions, such as the 9-speed automatic transmission (9AT), offers enhanced performance and efficiency compared to traditional 6-speed transmissions. However, the complexity of the 9AT transmission’s structure poses challenges during the die casting process, particularly in terms of ensuring a defect-free casting with high mechanical properties.
Die casting is a widely used manufacturing process for producing intricate metal parts with excellent dimensional accuracy and surface finish. However, the process is highly sensitive to various parameters, including the high and low-speed switching point during the injection stage. This study focuses on optimizing this critical parameter to minimize defects and maximize casting quality.
Materials and Methods
Transmission Main Housing Design
The 9AT transmission main housing (Figure 1) is designed to accommodate four groups of planetary gears and six shift mechanisms. Its complex structure, with varying wall thicknesses and numerous reinforcing ribs, poses challenges during the filling process. The average wall thickness is approximately 6 mm, with the thinnest section measuring 4 mm and the thickest section reaching 30 mm.
40%
AI作图中
Figure 1: 3D model of the 9AT transmission main housing, showing its intricate design and varying wall thicknesses.
Material Selection
ADC12 aluminum alloy was selected for the die casting process due to its favorable mechanical properties, high fluidity, and good casting performance. Table 1 presents the chemical composition of ADC12 alloy.
Table 1: Chemical Composition of ADC12 Alloy
| Element | Range (%) |
|---|---|
| Si | 9.6 – 12.0 |
| Cu | 1.5 – 3.5 |
| Ni | ≤ 0.55 |
| Fe | ≤ 1.3 |
| Zn | ≤ 1.0 |
| Mg | ≤ 0.3 |
| Mn | ≤ 0.5 |
| Pb | ≤ 0.2 |
| Sn | ≤ 0.2 |
| Ti | ≤ 0.3 |
| Cr | ≤ 0.05 |
| Al | Balance |
Die Casting Machine and Process Parameters
A Bühler CATAT305 die casting machine with a locking force of 30,500 kN was selected for the production of the transmission main housing. The initial metal temperature was set at 680°C, and the mold temperature was maintained at 200°C. The total mass of the casting was approximately 12.6 kg, with a total projection area of 265,327 mm².
Table 2: Preliminary Die Casting Process Parameters
| Parameter | Value |
|---|---|
| Metal Initial Temperature | 680°C |
| Mold Initial Temperature | 200°C |
| Total Mass | 12.6 kg |
| Total Projection Area | 265,327 mm² |
| Injection Pressure | 80 MPa |
| Safety Factor | 1.2 |
| Low-Speed Injection Rate | 0.2 m/s |
| High-Speed Injection Rate | 3.5 m/s |
Simulation Setup
Flow-3D software was employed to simulate the filling process of the transmission main housing. Three simulation schemes were designed, with the high and low-speed switching points set at 480 mm, 520 mm, and 560 mm, respectively. These switching points were chosen based on the metal’s flow path within the mold cavity.
Results and Discussion
Filling Process Simulation
The simulation results for the three schemes are presented. The simulation results indicate that Scheme 3, with a switching point at 560 mm, exhibits the smoothest filling process and the lowest probability of entrapped gas. In Scheme 1, the metal front forms a jet flow, leading to significant turbulence and entrapped gas. Scheme 2 improves upon Scheme 1 but still exhibits some turbulence in the shallower cavity regions. In contrast, Scheme 3 achieves a laminar flow pattern, minimizing turbulence and gas entrapment.
Porosity Analysis
The porosity analysis confirms the findings from the filling simulations. The porosity probability is highest in Scheme 1, particularly in the shallow cavity regions, where gas entrapment is more likely. As the switching point is moved further into the cavity (Schemes 2 and 3), the porosity probability decreases, with Scheme 3 exhibiting the lowest porosity levels.
Microstructure and Mechanical Properties
Based on the simulation results, Scheme 3 was selected for trial production. Microstructural analysis (Figure 6) reveals a fine-grained microstructure, primarily consisting of α-Al dendrites and α-Al + Si eutectic phases. The mechanical properties (Table 3) of the castings meet the specified requirements, with tensile strengths exceeding 190 MPa and elongation percentages exceeding 1%.
Table 3: Mechanical Properties of the Transmission Main Housing (Scheme 3)
| Sample Location | Tensile Strength (MPa) | Elongation (%) |
|---|---|---|
| Near Gate | 272.0 | 3.4 |
| End of Casting | 230.6 | 2.7 |
Conclusion
This study demonstrates the significance of optimizing the high and low-speed switching point in the die casting process of the 9AT transmission main housing. By employing simulation and experimental validation, the optimal switching point at 560 mm was identified, leading to a smooth filling process and minimal porosity. The resulting castings exhibit fine-grained microstructures and satisfactory mechanical properties, confirming the effectiveness of the optimized process parameters.
The findings of this study can be applied to other complex die casting applications, guiding the selection of process parameters to minimize defects and enhance casting quality. Further research can explore the impact of other process variables, such as metal temperature and mold design, on the overall casting performance.
Acknowledgments
The authors would like to acknowledge the support from the following funding agencies: the New Energy Vehicle Low-Cost Aluminum Alloy and Forming Key Technology Development and Industrialization Application Project (JZ2022AFKJ0032), the Fundamental Research Funds for the Central Universities (JZ2021HGTB0100), and the Hefei Science and Technology Major Project (2022-SED-0029).
References
- G. Anlin, “Automatic Transmission (I) – An Overview of Automatic Transmissions,” Automotive Technology, vol. 5, no. 1, pp. 1-3, 2001.
- Z. Chaofeng, G. Xuxun, and W. Bin, “Development and Prospects of Automotive Transmission Technology,” Automotive Research and Development, vol. 5, pp. 15-18, 2005.
- X. Xiaoxiao, “Dynamic Modeling and Control Strategy Research on the Shifting Process of Motor-Transmission Coupling System,” Ph.D. dissertation, Tsinghua University, Beijing, China, 2014.
- J. Xuejian, F. Zhumu, Z. Wenchun, et al., “Research and Prospects of Automatic Transmission Shifting Schedules,” Journal of Agricultural Machinery, vol. 3, pp. 139-141, 2003.
- H. Honghu, “ZF’s Revolutionary Transmission Design Concept: From 8AT to 9AT,” Automobile and Parts, vol. 45, no. 1, pp. 30-31, 2011.
- X. Xiaomeng, H. Honglin, and Y. Xinqiang, “Effect of Gating System on the Quality of Die-Cast Clutch Housing,” Special Casting & Nonferrous Alloys, vol. 12, pp. 1282-1284, 2016.
- B. Bo, “Process Optimization, Microstructure, and Defect Control of Aluminum Alloy Die Castings for Automobile Applications,” Ph.D. dissertation, Southeast University, Nanjing, China, 2017.
- H. Weihong, S. Haizhang, H. Zhiyuan, et al., “Application of High-Vacuum Die Casting Technology in Automotive Transmission Cases,” Special Casting & Nonferrous Alloys, vol. 38, no. 5, pp. 514-516, 2018.
- Y. Zhang, L. Liandeng, P. Pengpeng, et al., “Simulation of RSF Semi-Solid Die Casting Process for Thin-Walled Aluminum Alloy Filter Heat Sink Housing,” Special Casting & Nonferrous Alloys, vol. 36, no. 2, pp. 165-168, 2016.
- Y. Xiaoxiang and S. Xiaoping, “Design and Optimization of Die Casting Process for Aluminum Alloy Transmission Case,” Foundry, vol. 70, no. 3, pp. 311-315, 2021.
- L. Qiliang, S. Senquan, and Y. Liang, “Lightweight Design of a Heavy-Duty Commercial Vehicle Transmission Case,” Journal of Mechanical Transmission, vol. 44, no. 4, pp. 26-31, 2020.
- I. Alan, B. Tau, et al., “The Evolution of Technology for Materials Processing Over the Last 50 Years: The Automotive Example,” Journal of the Minerals, Metals & Materials Society, vol. 59, no. 2, pp. 48-57, 2007.