1. Introduction
Investment casting is a precision casting process that has been widely used in the manufacturing of various components with complex geometries and high dimensional accuracy requirements. In the production of mining flatbed wheel castings, ensuring the quality of the castings is of utmost importance due to the critical role these wheels play in the mining industry. This article focuses on the optimization of the investment casting process for wheel castings of mining flatbed trucks, aiming to improve the casting quality and production efficiency.
1.1 Background
Mining flatbed wheels are essential components in the mining industry, and their quality directly affects the performance and safety of mining vehicles. The traditional investment casting process for these wheels often encounters challenges such as shrinkage porosity and shrinkage holes, which can lead to reduced mechanical properties and even casting rejection. Therefore, it is necessary to optimize the casting process to overcome these issues.
1.2 Objectives
The main objectives of this study are as follows:
- Analyze the existing investment casting process for mining flatbed wheel castings and identify the factors contributing to the formation of defects.
- Optimize the casting process by improving the process parameters and the design of the gating system.
- Validate the optimized process through numerical simulation and production trials to ensure the reduction of shrinkage porosity and the improvement of casting quality.
2. Casting Process Analysis
2.1 Casting Structure and Material
The wheel casting is a rotary disk-shaped component with a complex structure. It has a flange on one end, a hub, a rim, and several spokes. The material used for the casting is ZG35CrMnSi, which exhibits high strength, impact resistance, and wear resistance. The chemical composition of ZG35CrMnSi is shown in Table 1.
| Element | C | Si | Mn | P | S | Cr | Ni | Cu | Mo | V |
|---|---|---|---|---|---|---|---|---|---|---|
| Composition (%) | 0.4 | 0.75 | 1.2 | 0.03 | 0.03 | 0.8 | 0.3 | 0.25 | 0.15 | 0.05 |
2.2 Initial Casting Process
The initial investment casting process includes the selection of the pouring position and the design of the gating system. The pouring position is chosen to achieve sequential solidification and minimize the formation of shrinkage defects. A side-gating system is selected due to its advantages in metal fluidity and casting soundness. The gating system consists of a pouring cup, a sprue, a runner, and an ingate. The dimensions of the gating system are determined based on the casting volume and the desired filling time.
2.3 Numerical Simulation of the Initial Process
To evaluate the initial casting process, numerical simulation is conducted using casting simulation software. The simulation results show the filling and solidification behavior of the casting. During the filling process, the molten metal flows smoothly without significant turbulence or air entrainment. However, the solidification analysis reveals the presence of shrinkage porosity at the bottom of the wheel rim and in the areas near the spokes. The shrinkage porosity is mainly caused by the improper design of the gating system and the lack of effective feeding during solidification.
3. Process Optimization
3.1 Improvement of the Gating System
To address the shrinkage porosity issue, the gating system is redesigned. Two additional ingates are added at the bottom of the wheel casting to enhance the feeding ability and promote more uniform solidification.
3.2 Optimization of Process Parameters
The casting process parameters, including pouring temperature, pouring speed, and shell preheating temperature, are optimized through orthogonal experiments. The factors and levels for the orthogonal experiments are shown in Table 2.
| Level | Pouring Temperature (°C) | Pouring Speed (mm/s) | Shell Preheating Temperature (°C) |
|---|---|---|---|
| 1 | 1530 | 270 | 750 |
| 2 | 1555 | 280 | 900 |
| 3 | 1580 | 290 | 1000 |
Nine experimental runs are conducted according to the orthogonal array, and the shrinkage porosity of each casting is measured. The experimental results are analyzed using analysis of variance (ANOVA) to determine the significant factors and their optimal levels.
4. Results and Discussion
4.1 Effect of Gating System Improvement
The numerical simulation of the improved gating system shows a significant reduction in shrinkage porosity. The new design allows for better feeding of the molten metal during solidification, resulting in a more compact casting structure. The shrinkage porosity rate is reduced from the initial value of 13.13% to 8.65%, indicating the effectiveness of the gating system improvement.
4.2 Effect of Process Parameter Optimization
The results of the orthogonal experiments and ANOVA analysis indicate that the shell preheating temperature and the pouring temperature have a significant impact on the shrinkage porosity of the casting. The optimal combination of process parameters is determined as follows: pouring temperature of 1530 °C, pouring speed of 290 mm/s, and shell preheating temperature of 1000 °C. Under these conditions, the shrinkage porosity is further reduced to a minimum value.
4.3 Comparison of Different Casting Processes
To illustrate the improvement achieved through the optimization process, a comparison is made between the initial casting process and the optimized process. The shrinkage porosity distribution and the overall quality of the castings are evaluated. The results show that the optimized process significantly reduces the shrinkage porosity and improves the mechanical properties of the wheel castings.
5. Production Validation
To confirm the practical applicability of the optimized casting process, production trials are carried out. A batch of wheel castings is produced using the optimized process parameters and gating system design. The castings are inspected for dimensional accuracy, surface quality, and internal defects. The inspection results show that the castings meet the quality requirements, and the production efficiency is also improved compared to the initial process.
6. Conclusion
In this study, the investment casting process for wheel castings of mining flatbed trucks is optimized through a combination of gating system improvement and process parameter optimization. The following conclusions can be drawn:
- The addition of two ingates at the bottom of the wheel casting effectively reduces the shrinkage porosity by improving the feeding ability during solidification.
- The optimization of process parameters, especially the shell preheating temperature and the pouring temperature, further minimizes the shrinkage porosity and improves the casting quality.
- The production validation confirms the effectiveness and practicality of the optimized casting process, which can be applied in actual production to improve the quality and production efficiency of mining flatbed wheel castings.
Future work can focus on further optimizing the casting process by considering other factors such as mold materials and coating thickness. Additionally, the application of advanced sensing and control technologies in the casting process can enhance the process stability and product quality.