Abstract
This article discusses the process development and optimization of steel castings for bearing liners, focusing on the challenges faced in casting thin-walled structures with intricate geometries. Through a comprehensive analysis of casting difficulties and the integration of advanced technologies such as CAE (Computer-Aided Engineering) 3D simulation and sand 3D printing, a refined casting process is proposed to ensure high-quality products. The key aspects of pouring position selection, riser and chill design, gating system optimization, and the application of sand 3D printing technology are thoroughly examined. The results demonstrate a significant improvement in casting quality, productivity, and cost-effectiveness.
1. Introduction
Bearing liners play a crucial role in reducing wear, supporting rotating components, damping vibrations, and dissipating heat. The casting process for bearing liners, particularly those with complex geometries and thin-walled features, poses numerous challenges. This article delves into the development and optimization of a casting process for a specific bearing liner made from ZG15Cr12 steel, focusing on enhancing casting quality and reducing defects.
2. Product Description and Technical Requirements
The bearing liner under study is designed to support and reduce friction in a rotating system. Its dimensions are φ240 mm in diameter and 165 mm in height, with a maximum wall thickness of 32 mm and a minimum of only 4 mm. The product features five circular ribs for enhanced heat dissipation, each with a thickness of 4 mm and a height of 14 mm .
Table 1: Chemical Composition of ZG15Cr12 Steel (wt.%)
| Element | C | Si | Mn | Cr | P | S |
|---|---|---|---|---|---|---|
| Range | ≤0.15 | ≤0.60 | ≤0.80 | 11.5-13.5 | ≤0.035 | ≤0.025 |
Table 2: Mechanical Properties of ZG15Cr12 Steel After Quenching and Tempering
| Property | Value | Unit |
|---|---|---|
| Ultimate Tensile Strength (R<sub>m</sub>) | ≥590 | MPa |
| Yield Strength (R<sub>eL</sub>) | ≥390 | MPa |
| Elongation (A) | ≥25 | % |
| Impact Toughness (Z) | ≥55 | J |
The bearing liner must be free from defects such as shrinkage porosity, shrinkage cavities, cracks, and cold shuts. Post-processing includes a 15-minute hydrostatic pressure test without any leaks or seepage.
3. Casting Challenges
The thin walls and intricate ribbed structure of the bearing liner present several challenges during the casting process:
- Thin Rib Formation: The thin ribs (4 mm thick) are difficult to form due to poor steel fluidity, increasing the risk of cold shuts.
- Temperature Control: Maintaining the required pouring temperature is challenging due to the small casting weight relative to the capacity of the melting furnace.
- Defect Minimization: Avoiding defects such as shrinkage porosity, shrinkage cavities, and cracks is essential to ensure product quality.
4. Casting Process Design and Optimization
To address these challenges, a comprehensive casting process design incorporating CAE 3D simulation and sand 3D printing technology was undertaken.
4.1 Pouring Position Selection
The pouring position was strategically chosen to ensure optimal filling and minimize defects . A bottom-pouring approach was adopted for the following reasons:
- Stable Filling: The bottom-pouring system promotes a smooth and steady filling of the mold cavity, reducing turbulence and gas entrapment.
- Efficient Feeding: The position facilitates the placement of a top feeder, ensuring effective feeding and minimizing shrinkage defects.
- Efficient Production: A multi-cavity mold increases the pouring weight per mold, improving the control of pouring temperature.
4.2 Riser and Chill Design
The riser and chill design were critical to ensure proper feeding and cooling, respectively. A single top riser was used, sized based on the casting modulus and feeding requirements . Chills were strategically placed to accelerate local cooling and refine the microstructure.
Table 3: Riser and Chill Design Parameters
| Component | Material | Dimensions (mm) | Purpose |
|---|---|---|---|
| Riser | ZG15Cr12 | Diameter: 100, Height: 150 | To provide adequate feeding and prevent shrinkage defects |
| Chills | Cast iron | Various sizes | To accelerate local cooling and refine the microstructure |
4.3 Gating System Design
A bottom-pour open gating system was designed, with cross-sectional area ratios of 1:2:5 for the sprue, runner, and ingate, respectively . This system ensures a smooth and laminar flow of molten metal, minimizing turbulence and gas entrapment.
Table 4: Gating System Design Parameters
| Component | Cross-Sectional Area Ratio | Purpose |
|---|---|---|
| Sprue | 1 | To channel metal into the mold |
| Runner | 2 | To distribute metal evenly |
| Ingate | 5 | To feed metal into the mold cavity |
4.4 CAE 3D Simulation
CAE 3D simulation was employed to predict and mitigate potential casting defects. Simulation results were used to fine-tune the riser, chill, and gating system designs .
Table 5: Simulation Parameters
| Parameter | Value | Unit |
|---|---|---|
| Material | ZG15Cr12 | – |
| Pouring Temperature | 1595 ± 5 | °C |
| Molten Metal Weight | 14 | kg |
| Solidification Time | Simulated | – |
- Porosity Simulation: Identified potential areas of shrinkage porosity and verified the effectiveness of the riser design in mitigating these defects.
- Hot Spot Analysis: Assessed the location and intensity of hot spots to ensure controlled cooling and minimize cracking.
4.5 Sand 3D Printing Technology
Sand 3D printing technology was employed to manufacture the casting mold, offering several advantages over traditional sand molding methods:
- Design Flexibility: Enables the production of complex mold geometries without the need for cores or split molds.
- Improved Accuracy: Provides higher dimensional accuracy and surface finish.
- Reduced Lead Time: Accelerates the mold-making process, shortening the time-to-market.
5. Melting and Pouring
The steel was melted in an induction furnace and degassed with argon to remove impurities. The pouring temperature was maintained at 1595 ± 5 °C to ensure proper fluidity and feeding.
6. Production Verification
The optimized casting process was verified through production trials. The final castings exhibited excellent surface finish, uniform wall thickness, and no visible defects. Hydrostatic testing confirmed the absence of leaks or seepage.
7. Conclusion
Through a comprehensive process development and optimization effort, a high-quality casting process for ZG15Cr12 bearing liners was successfully established. The integration of CAE 3D simulation and sand 3D printing technology significantly improved casting quality, reduced development time, and minimized production costs. The optimized process resulted in defect-free castings with excellent mechanical properties, meeting or exceeding customer specifications. This work demonstrates the value of advanced technologies in addressing complex casting challenges and enhancing manufacturing efficiency.