This paper presents an optimized lost foam casting (LFC) process for manufacturing medium-large Siemens motor shell castings with complex geometries. Through systematic parameter adjustments and material innovations, we achieved significant improvements in dimensional accuracy and production efficiency compared to traditional furan resin sand processes.
1. Mold Design Considerations
For motor shells measuring 1,240 × 800 × 700 mm with 5mm-thick cooling fins, we developed differential shrinkage coefficients:
$$
\begin{cases}
\text{Radial shrinkage: } 1.35\% \\
\text{Axial shrinkage: } 1.15\%
\end{cases}
$$
The shrinkage compensation formula for critical dimensions:
$$ D_{mold} = D_{casting} \times (1 + \alpha) $$
Where α represents the shrinkage coefficient (0.0135 radial/0.0115 axial).
2. Gating System Design
The stepped gating system configuration achieves progressive filling:
| Layer | Number of Gates | Cross-section Ratio |
|---|---|---|
| Top | 8 | 1:2.5:1 (Sprue:Runner:Gate) |
| Middle | 6 | 1:2.5:1 |
| Bottom | 6 | 1:2.5:1 |
The total gate area calculation follows:
$$ A_{total} = 1.25A_{sprue} + 2.5A_{runner} + A_{gate} $$
3. Critical Process Parameters
Key parameters for successful lost foam casting:
| Parameter | Value Range |
|---|---|
| Pouring Temperature | 1,490-1,500°C |
| Vacuum Level | -0.065 to -0.07 MPa |
| EPS Density | 25-26 g/L |
| Drying Time | 48 hours |
4. Coating Formulation
The coating composition significantly affects casting quality:
$$ \text{Coating Performance Index} = \frac{\text{High Temp Strength} \times \text{Peelability}}{\text{Cracking Tendency}} $$
| Component | Percentage | Function |
|---|---|---|
| Zircon Flour | 45% | Refractoriness |
| Bentonite | 8% | Green Strength |
| Fe₂O₃ | 2% | Peelability Enhancement |
5. Metallurgical Control
Chemical composition requirements for ASTM48A30C:
| Element | Range (%) |
|---|---|
| C | 3.15-3.25 |
| Si | 1.6-1.8 |
| Mn | 0.7-0.9 |
The carbon equivalent (CE) calculation:
$$ CE = C + \frac{Si}{3} + \frac{P}{3} $$
Maintained at 3.8-4.0 for optimal fluidity and shrinkage control.
6. Economic Analysis
Cost comparison between lost foam casting and resin sand processes:
| Cost Factor | LFC | Resin Sand |
|---|---|---|
| Pattern Material | $33/ton | $0 |
| Binder System | $30/ton | $140/ton |
| Labor Cost | $200/ton | $400/ton |
Total savings through lost foam casting:
$$ \text{Savings} = (140 + 400) – (33 + 30 + 200) = \$277/\text{ton} $$
7. Quality Validation
The optimized lost foam casting process demonstrates:
- Surface roughness improvement: Ra 12.5 → Ra 6.3 μm
- Dimensional accuracy: ±0.5mm for critical features
- Production yield increase: 89% → 97%
Mechanical properties achieved:
$$ \sigma_b \geq 240\text{MPa}, \quad \text{HB} = 190 \pm 10 $$
This comprehensive approach to lost foam casting process optimization provides a reliable solution for producing high-quality motor shells while significantly reducing manufacturing costs compared to conventional methods.