With the rapid development of urban rail transit systems, the demand for high-performance ductile iron castings for traction motor housings has significantly increased. This article presents a comprehensive study on the foundry technology development of a QT500-7 grade ductile iron casting with complex geometry, highlighting key process parameters and simulation-assisted optimization methods.
1. Technical Requirements and Challenges
The motor housing features a thin-walled barrel structure (760 mm × 500 mm × 580 mm) with varying wall thickness from 10 mm to 90 mm. Key challenges include:
- X-ray inspection requirements: Grade 2 for critical areas, Grade 3 for non-critical zones
- Multiple isolated hot spots at intersections of ribs, mounting brackets, and safety lugs
- Shrinkage porosity prevention in thick sections
2. Process Design Methodology
The casting process was developed using MAGMA simulation software to predict solidification patterns and optimize feeding system design.
2.1 Pouring System Calculation
The gating system was designed using empirical formulas:
Pouring time calculation:
$$ t = K \sqrt{G} $$
Where:
t = pouring time (s)
K = empirical coefficient (1.85)
G = total metal weight (180 kg)
Choke area determination:
$$ S_{choke} = \frac{G}{0.31\mu t \sqrt{H}} $$
Where:
μ = flow coefficient (0.48)
H = effective metal head (35 cm)
| Parameter | Value |
|---|---|
| Calculated pouring time | 25 s |
| Metal rise speed | 1.92 cm/s |
| Choke area (adjusted) | 12 cm² |
2.2 Feeding System Optimization
The feeding system was designed based on modulus calculations:
$$ M = \frac{V}{A} $$
Where:
M = modulus (cm)
V = volume (cm³)
A = cooling surface area (cm²)
| Location | Original Modulus | After Riser Addition |
|---|---|---|
| Upper bracket | 1.6 cm | 1.9 cm |
| Junction box | 1.4 cm | 1.7 cm |
3. Process Validation and Improvement
Initial trials revealed shrinkage porosity in the junction box area. Improvement measures included:
- Adding chill plates (50 mm × 80 mm × 10 mm)
- Modifying riser size (1.3× modulus amplification factor)
- Adjusting chemical composition
| Element | C | Si | Mn | Cu | Mg |
|---|---|---|---|---|---|
| Content | 3.64 | 2.83 | 0.38 | 0.40 | 0.045 |
| Property | Requirement | Result |
|---|---|---|
| Tensile Strength | ≥500 MPa | 570 MPa |
| Yield Strength | ≥320 MPa | 423 MPa |
| Elongation | ≥7% | 15.5% |
4. Critical Process Parameters for Ductile Iron Casting
Key factors in successful production of ductile iron castings include:
- Modulus-based riser design
- Controlled cooling rate through chills
- Proper Mg treatment (0.04-0.06% residual)
- Post-inoculation practice
The final process achieved 98% soundness in X-ray inspection, demonstrating that simulation-assisted process design significantly reduces development time for complex ductile iron castings. This methodology provides valuable guidance for similar thin-walled ductile iron casting projects in heavy machinery and transportation applications.