This study investigates the precision investment casting process optimization of a 42CrMo4 steel fixed disk component for automotive air-conditioning compressors. Through numerical simulation and orthogonal experimental design, we establish optimal process parameters to minimize shrinkage defects while maintaining production efficiency.
1. Component Structure and Process Requirements
The fixed disk exhibits complex geometry with maximum dimensions of 126mm × 75mm × 72mm and average wall thickness of 7mm. Critical quality requirements include:
- Zero tolerance for cracks or slag inclusions
- Surface roughness ≤ Ra 6.3μm
- Dimensional accuracy within CT6-7
2. Gating System Design
The sprue-runner-gate system was designed using UGNX10.0, with key parameters calculated as:
$$v = \frac{0.22 \sqrt{h}}{\delta \cdot \ln\left(\frac{T}{380}\right)}$$
Where:
v = Pouring velocity (cm/s)
h = Casting height (cm)
δ = Wall thickness (cm)
T = Pouring temperature (°C)
| C | Si | Mn | Cr | Mo | P | S |
|---|---|---|---|---|---|---|
| 0.38-0.45 | 0.17-0.37 | 0.50-0.80 | 0.90-1.20 | 0.15-0.25 | ≤0.035 | ≤0.035 |
3. Numerical Simulation Parameters
The ProCAST simulation considered critical precision investment casting factors:
- Shell thickness: 6mm (6-layer quartz sand/silica sol)
- Heat transfer coefficient: 500 W/(m²·K)
- Ambient temperature: 800°C
- Cooling rate: Natural convection
| Level | A: Pouring Temp (°C) | B: Pouring Speed (mm/s) | C: Shell Preheat (°C) |
|---|---|---|---|
| 1 | 1550 | 200 | 900 |
| 2 | 1560 | 300 | 1000 |
| 3 | 1580 | 400 | 1100 |
4. Process Optimization Results
The L9(3³) orthogonal experiment revealed optimal parameters through range analysis:
$$R_j = \max(K_{ij}) – \min(K_{ij})$$
Where Rj represents the range value for each factor
| Test | A | B | C | Filling Time (s) | Shrinkage (%) |
|---|---|---|---|---|---|
| L1 | 1 | 1 | 1 | 3.92 | 1.85 |
| L2 | 1 | 2 | 2 | 3.70 | 1.94 |
| L3 | 1 | 3 | 3 | 3.38 | 1.85 |
| L4 | 2 | 1 | 2 | 3.17 | 1.88 |
| L5 | 2 | 2 | 3 | 3.74 | 1.80 |
| L6 | 2 | 3 | 1 | 3.60 | 1.82 |
| L7 | 3 | 1 | 3 | 3.52 | 1.90 |
| L8 | 3 | 2 | 2 | 3.38 | 1.92 |
| L9 | 3 | 3 | 1 | 3.07 | 1.89 |
5. Optimized Process Parameters
The precision investment casting process achieves optimal quality with:
- Shell thickness: 6 mm
- Shell preheating temperature: 1100°C
- Pouring temperature: 1560°C
- Pouring speed: 300 mm/s
This parameter combination reduces shrinkage defects to 1.80% while maintaining 3.74s filling time and 368.67s solidification duration. The precision investment casting process demonstrates significant improvements in defect control compared to initial parameters.
6. Industrial Implementation Considerations
For successful precision investment casting production:
- Maintain ceramic shell integrity during dewaxing
- Control furnace atmosphere with ≤ 50ppm oxygen content
- Implement post-casting heat treatment:
$$T_{austenitizing} = 850^{\circ}C \pm 10^{\circ}C$$
$$T_{tempering} = 560^{\circ}C \pm 10^{\circ}C$$ - Use automated shell coating with viscosity control:
$$\mu = 35 \pm 2 \, \text{cPs}$$
The developed precision investment casting methodology provides a reliable solution for complex automotive components, achieving 98.2% dimensional compliance and surface quality exceeding Ra 5.6μm in production trials.