This study explores the application of sand casting combined with 3D printing technology to manufacture a large-scale C95820 aluminum bronze double-suction impeller. The impeller features asymmetric dual-layer blades, uneven wall thickness (minimum 5 mm), and a diameter of 1,015 mm, presenting significant challenges for traditional casting methods. The research focuses on optimizing gating systems, defect mitigation, and leveraging additive manufacturing advantages for complex sand mold fabrication.
1. Process Design and Numerical Simulation
The bottom-gating system with four symmetrical runners demonstrated superior performance in minimizing oxide inclusions and air entrapment. The governing equation for fluid flow during mold filling can be expressed as:
$$ \frac{\partial \rho}{\partial t} + \nabla \cdot (\rho \mathbf{v}) = 0 $$
where \( \rho \) represents molten metal density and \( \mathbf{v} \) denotes flow velocity. Simulation parameters included:
| Parameter | Value |
|---|---|
| Pouring temperature | 1,150°C |
| Mold preheat temperature | 80°C |
| Interfacial heat transfer coefficient | 500 W/m²·K |
| Filling time | 120 s |
2. Solidification Analysis and Defect Control
The thermal history during solidification followed Fourier’s law of heat conduction:
$$ \frac{\partial T}{\partial t} = \alpha \nabla^2 T $$
where \( \alpha \) represents thermal diffusivity. Key findings from shrinkage porosity analysis showed:
| Defect Location | Volume Fraction (%) |
|---|---|
| Upper ring gate | 12.7 |
| Central riser | 18.3 |
| Blade root connections | <0.5 |
The optimized riser system included six elliptical top risers and four bottom blind risers, achieving directional solidification with 92% of defects concentrated in feeder systems.
3. Additive Manufacturing of Sand Molds
3D printing parameters for the sand casting molds:
| Parameter | Specification |
|---|---|
| Laser power | 900 W |
| Spot size | 1.1 mm |
| Scan speed | 2,900 mm/s |
| Layer thickness | 0.3 mm |
| Material | Resin-coated ceramsite |
Conformal venting channels reduced gas defects by 37% compared to traditional straight vents, with permeability calculated as:
$$ K = \frac{\phi^3}{180(1-\phi)^2} $$
where \( \phi \) represents sand porosity (typically 0.35-0.4 for 3D-printed molds).
4. Production Validation
The sand casting process achieved dimensional accuracy of CT10 grade, with post-casting inspection showing:
| Quality Metric | Result |
|---|---|
| Surface roughness (Ra) | 12.5-25 μm |
| Mechanical properties (UTS) | 655 MPa |
| Density | 7.45 g/cm³ |
| Lead time reduction | 68% vs traditional |
The successful integration of sand casting with 3D printing technology demonstrates significant advantages for complex hydraulic components, particularly in achieving net-shape casting of thin-walled (5-19 mm) aluminum bronze structures while maintaining metallurgical quality.