Abstract
Aluminum alloy cabins are a type of revolving barrel wall casting characterized by uneven wall thickness and hot spots distributed in the upper, middle, and lower sections. As a fully processed product, the cabin must be defect-free upon processing and meet strict requirements in appearance, size, and performance. This paper discusses the low pressure casting process of aluminum alloy cabins, examining various aspects such as product design, pouring system, metal mold structure, and process parameters. The results indicate that an optimized pouring system integrated with a metal mold and sand core ensures complete feeding of hot spots and stable casting with minimal defects. Additionally, suitable metal mold designs and parameters facilitate continuous production and minimize raw material consumption.
1. Introduction
Aluminum alloys are widely used in various industries due to their low density, high strength, excellent electrical and thermal conductivity, and corrosion resistance. Aluminum alloy cabins, as large-scale castings, play a crucial role in aerospace applications, where they serve as housing for control systems and electronic components. The complex structure and uneven wall thickness of these cabins pose significant challenges during casting, often leading to defects such as porosity, shrinkage, and cold shuts.
Low pressure casting, with its moderate equipment investment and capability for metal mold combined with sand core production, offers a stable and efficient solution for aluminum alloy cabins. This paper delves into the low pressure casting process of aluminum alloy cabins, providing insights into the product design, pouring system, metal mold design, and process optimization.
2. Product and Casting Requirements
2.1 Product Specification
The aluminum alloy cabin under study is made of ZL114A material and has an outer diameter of 336.08 mm and a height of 455 mm. The cabin exhibits uneven wall thickness, ranging from 2 mm to 37 mm, with thicker sections located in the upper, middle, and lower parts.
2.2 Quality Requirements
The aluminum alloy cabin must meet stringent quality requirements as a fully processed product:
- Appearance: The cabin surface must be smooth and free from defects.
- Internal Quality: After 100% X-ray inspection, the cabin must be free from porosity, cracks, shrinkage, and inclusions.
- Dimensional Accuracy: Linear and geometric tolerances must comply with relevant standards (GB/T1804-m and GB/T1184-H).
- Performance: The cabin must possess adequate mechanical properties for its intended application.
3. Low Pressure Casting Process Design
3.1 Casting System Design
The low pressure casting process involves the use of a metal mold combined with a sand core to achieve stable filling and complete feeding of hot spots. The pouring system is designed as follows:
- Gate Design: A stepped in-gate system is employed, feeding from the upper, middle, and lower sections. The gates are embedded within the sand core, utilizing its insulating properties to maintain metal temperature during filling.
- Simulation Analysis: Using ProCAST software, the filling and solidification processes are simulated to optimize gate placement and ensure sequential solidification.
3.2 Metal Mold Design
The metal mold is designed with an upper and lower split structure to facilitate mold opening and part ejection. Key design considerations include:
- Ejection Mechanism: Symmetrically placed ejector pins ensure smooth part ejection from the mold.
- Draft Angles: Appropriate draft angles are applied to the mold cavity to prevent part sticking during ejection (Table 1).
Table 1: Draft angles for the metal mold
| Mold Section | Draft Angle (°) | Depth (mm) |
|---|---|---|
| Upper Cavity | 0.5 | 61.37 |
| Lower Cavity | 5.0 | 56.84 |
3.3 Process Parameters
The process parameters are optimized through simulation and experimentation to ensure stable filling and minimal defects. The optimized parameters are listed in Table 2.
Table 2: Optimized process parameters for low pressure casting
| Parameter | Value |
|---|---|
| Metal Temperature (°C) | 700 |
| Mold Temperature (°C) | 320 |
| Filling Pressure (MPa) | 0.036 |
| Filling Rate (MPa/s) | 0.0008 |
| Holding Pressure (MPa) | 0.060 |
| Holding Time (s) | 360 |
| Cooling Time (s) | 240 |
4. Defect Analysis and Solutions
4.1 Defect Analysis
Despite optimization efforts, initial production runs identified two primary defects: local shrinkage and black patches on the inner wall.
- Local Shrinkage: Shrinkage was observed in the middle section due to inadequate feeding.
- Black Patches: The inner wall exhibited black patches after machining, indicating oversize dimensions in certain areas.
4.2 Solutions
- Improving Feeding: The linear gate in the middle section was replaced with a cross-shaped gate to enhance feeding and eliminate shrinkage.
- Adjusting Mold-Core Clearance: The metal mold cavity dimensions were reduced by 1 mm to account for thermal expansion, ensuring a proper fit with the sand core during closing and preventing cracking.
5. Production Verification and Results
Following the implemented solutions, production runs were conducted to verify the effectiveness of the modified process. Key findings include:
- Defect Reduction: The modified pouring system and metal mold design significantly reduced shrinkage and black patches, leading to an overall improvement in part quality.
- Process Stability: Continuous production runs demonstrated the reliability and efficiency of the optimized low pressure casting process.
- Dimensional Accuracy: Post-processing inspections confirmed dimensional accuracy within specified tolerances.
Table 3: Defect reduction results
| Defect Type | Before Modification | After Modification |
|---|---|---|
| Local Shrinkage | Present | Eliminated |
| Black Patches | Present | Significantly Reduced |
| Dimensional Tolerances | Non-compliant in some areas | Fully compliant |
6. Conclusion
The low pressure casting process for aluminum alloy cabins has been successfully optimized through detailed design modifications and process parameter tuning. Key findings and conclusions are:
- Effective Feeding: The cross-shaped gate design effectively addressed local shrinkage issues in the cabin’s thick sections.
- Improved Dimensional Accuracy: Adjustments to the metal mold cavity dimensions prevented sand core cracking and ensured dimensional accuracy.
- Stable Production: The optimized process parameters and mold design facilitated stable and continuous production with minimal defects.
Future work may focus on further enhancing process automation and implementing inline quality control measures to further improve efficiency and part quality.