1. Introduction
In the realm of modern manufacturing, titanium alloy components play a crucial and irreplaceable role in numerous industries. Among them, the titanium alloy brush box, a key part of generators, demands high – performance casting technology due to its specific structural features and working environment requirements. This paper delves deep into the research of the casting technology for titanium alloy brush box castings, aiming to provide a comprehensive and in – depth understanding of the entire process, from problem identification to solution implementation.
1.1 Significance of Titanium Alloy Brush Box in Generators
The brush box serves as an essential component within generators. Operating under harsh conditions, it must possess excellent corrosion resistance. Additionally, its lightweight nature is crucial for reducing the overall weight of the generator, improving energy efficiency. High – precision dimensions are necessary to ensure seamless integration with other parts, and superior mechanical properties guarantee its long – term stable operation. As such, the quality of the titanium alloy brush box directly impacts the performance and reliability of the entire generator system.
1.2 Research Objectives
The primary objective of this research is to develop a highly efficient and reliable casting process for titanium alloy brush boxes. This involves identifying and resolving the technical challenges associated with the casting process, improving the casting quality, increasing production efficiency, and reducing production costs. By achieving these goals, we aim to offer valuable guidance for the casting of similar titanium – based components.
2. Product Structure Characteristics and Casting Process Difficulties
2.1 Product Structure Characteristics and Technical Requirements
The titanium alloy brush box under study has specific dimensions of 238mm×33mm×70mm and weighs approximately 0.74kg. With a basic wall thickness of 3.5mm and a minimum wall thickness of 1mm, it exhibits a slender shape. The complex structure features small gaps between the partitions, as illustrated in Figure 1 (Insert Figure 1: 3D view of the brush box here).
| Technical Requirement | Specification |
|---|---|
| Casting Dimension Accuracy | CT6 – CT7 level in accordance with GB/T6414 |
| Material | TC4 alloy |
| Tensile Strength | ≥890MPa |
| Yield Strength | ≥820MPa |
| Elongation After Fracture | ≥5% |
| Section Shrinkage | ≥10% |
| Delivery Condition | Finished through precision machining |
2.2 Analysis of Casting Process Difficulties
- Filling Difficulty: The thin – walled structure of the brush box, especially the 1mm minimum wall thickness, poses a significant challenge during gravity casting. The molten metal may struggle to fully fill the mold cavity, resulting in unfilled areas and casting defects.
- Deformation Risk: The slender shape of the part makes it prone to deformation during the casting process. Thermal stress and uneven cooling can cause the cast brush box to deviate from its intended dimensions.
- Shell – Making and Core – Related Issues: The small 1.5mm gap between the partitions makes shell – making a difficult task. The long and thin cores required have low strength, increasing the risk of deformation and fracture. Moreover, the cores are surrounded by molten metal, which may lead to the “run – fire” phenomenon, where the molten metal leaks through the core, and subsequent cleaning is arduous. If not properly addressed, these issues can block the partition gaps and render the casting useless.
3. Casting Process Design Schemes
3.1 Scheme One
In this approach, the brush box is directly connected to the sprue in a vertical upward orientation. Risers and vents are only installed at the upper end of the brush box. To prevent deformation, reinforcing ribs are added at the weak parts of the casting, as shown in Figure 2 (Insert Figure 2: Schematic of Scheme One here).
- Advantages: This scheme offers a short molten metal flow path, enabling smooth entry of the metal into the mold shell. It exhibits strong filling capacity, resulting in a good surface finish of the casting. The high filling efficiency also contributes to a relatively high yield rate, which can reach up to 45%.
- Disadvantages: However, the area where the casting is connected to the sprue has a slow solidification rate. This makes it susceptible to shrinkage porosity and shrinkage cavities, leading to less dense internal structures.
3.2 Scheme Two
To enhance the filling capacity, the top – gating method is adopted in this scheme (refer to Figure 3: Schematic of Scheme Two here).
- Advantages: The gating system is simple and compact, facilitating the molding process and saving metal materials. The molten metal can easily fill the mold cavity, and the temperature distribution, with higher temperatures at the top and lower temperatures at the bottom, promotes a bottom – up solidification sequence. This is beneficial for the riser to perform its feeding function, effectively preventing casting defects such as misruns and cold shuts, especially in thin – walled castings.
- Disadvantages: Despite its advantages, this scheme has a relatively low yield rate of only 35%. This is mainly due to issues such as the complex flow of molten metal and potential gas entrapment during the filling process.
4. Simulation Scheme Design
To assess the rationality of the above – mentioned gating system designs, numerical simulation of the brush box casting process is carried out using the ProCAST software. The three – dimensional model diagrams of the two gating schemes are imported into the PreCAST software for pre – processing. The following parameters are set uniformly for both schemes:
| Parameter | Value |
|---|---|
| Brush Box Material | Titanium alloy |
| Mold Shell Material | Mullite |
| Contact Surface Type | COINC |
| Interface Heat Exchange Coefficient | |
| Pouring Temperature | 1800℃ |
| Pouring Speed | 6kg/s |
| Cooling Method | Air – cooling |
| Initial Temperature of Mold Shell | 25℃ |
| Casting Method | Gravity casting (Radiation is ignored) |
5. ProCAST Simulation Results and Analysis
5.1 Results and Analysis of Scheme One
By analyzing the temperature field changes during the solidification process of the casting in Scheme One using the PreCAST software, we obtain the results as shown in Figure 4 (Insert Figure 4: Temperature field changes during the solidification process of Scheme One here).
- Advantages: At the beginning of solidification, the casting solidifies relatively quickly, and the temperature difference within the casting is small. This indicates that it is less likely to generate stress, deformation, and hot cracks. Additionally, the vents located at the top of the casting are conducive to gas discharge.
- Disadvantages: However, the areas connected to the sprue have a slow solidification rate. As shown in Figure 5 (Insert Figure 5: Casting simulation results of Scheme One here), shrinkage porosity or shrinkage cavities are likely to occur in these areas, and the internal structure of the brush box itself may also have shrinkage – related defects.
5.2 Results and Analysis of Scheme Two
The temperature field changes during the solidification process of the casting in Scheme Two are presented in Figure 6 (Insert Figure 6: Temperature field changes during the solidification process of Scheme Two here).
- Advantages: The casting solidifies gradually from bottom to top, with a solidification time of 12.9s. The cross – runner can effectively feed the casting, resulting in a good feeding effect and a dense, shrink – free casting structure. The molten metal is mainly concentrated in the sprue and cross – runner, and the long solidification time of the cross – runner (822s) allows it to continuously feed the connected casting, reducing the occurrence of shrinkage porosity and shrinkage cavities. The vents at the top of the casting also facilitate gas discharge. As shown in Figure 7 (Insert Figure 7: Casting simulation results of Scheme Two here), most of the defects are located in the gating system, and only a few defects are present in the brush box body, indicating a reasonable gating system design.
- Improvement Measures: To further optimize Scheme Two, risers are added to the areas prone to defects, and insulating cotton is placed on the sprue and cross – runner to enhance the sequential solidification characteristics. The improved gating system is shown in Figure 8 (Insert Figure 8: Improved gating system of Scheme Two here), and the corresponding simulation results are presented in Figure 9 (Insert Figure 9: Simulation results of the improved gating system of Scheme Two here). After the improvement, the solidification process becomes more uniform, and the number of defects is significantly reduced.
6. Experimental Verification
In accordance with the production process of titanium and titanium alloy precision casting, a 3D model is first printed using a 3D printer. After mold repair, the brush box casting is produced through a series of processes such as gating system assembly, slurry coating, drying, pre – heating, roasting, and pouring, following Scheme Two.
The inspection results show that the product dimensions meet the requirements of CT7 level in GB/T6414 – 2017, and the product quality complies with the standards of GJB2896A – 2017. The 3D printed model is shown in Figure 10 (Insert Figure 10: 3D printed brush box model here), the as – cast and simply – processed brush box is shown in Figure 11 (Insert Figure 11: Simply – processed brush box casting after pouring here), and the fully – processed casting is shown in Figure 12 (Insert Figure 12: Processed brush box casting here).
7. Conclusion
- Scheme Design and Simulation – Based Optimization: Based on the structural characteristics of the brush box casting, two process schemes were designed. Through numerical simulation of the two schemes, the changes in the temperature field during the solidification process and the distribution of defects were analyzed. Scheme Two was selected for further process optimization due to its relatively better comprehensive performance.
- Achievement of Sequential Solidification and Defect Elimination: By improving the cooling conditions of the sprue and cross – runner in Scheme Two, sequential solidification of the casting was achieved. This effectively eliminated shrinkage porosity and shrinkage cavity defects, meeting the design requirements of the casting. The research findings provide valuable references for the process design and optimization of similar thin – walled and high – precision box – shaped castings.
8. Future Research Directions
- Material – Process Interaction: Further research could focus on the interaction between the titanium alloy material and the casting process. For example, exploring the influence of different alloy compositions on the casting performance, such as fluidity, solidification behavior, and defect formation.
- Advanced Casting Technologies: Investigating the application of advanced casting technologies, such as vacuum casting or semi – solid casting, to further improve the quality of titanium alloy brush box castings. These technologies may offer better control over the casting process and potentially reduce defects more effectively.
- Automation and Intelligentization: With the development of industry 4.0, introducing automation and intelligentization into the casting process of titanium alloy brush boxes can improve production efficiency, reduce human errors, and enhance the consistency of product quality. This could involve the use of robotic systems for mold handling, automated pouring, and real – time process monitoring and control.
In conclusion, the research on the casting technology of titanium alloy brush box castings is a continuous and evolving field. Through continuous exploration and innovation, we can expect to achieve higher – quality castings, lower production costs, and more efficient manufacturing processes in the future.
