Lost foam casting (LFC) demonstrates unique advantages in producing complex geometries like the 140 flywheel housing, yet process instability often leads to defects such as box lifting and iron inclusions. This paper systematically analyzes defect formation mechanisms and presents optimized solutions through vacuum control, coating enhancement, and process parameter adjustments.
1. Fundamental Principles of Lost Foam Casting
The LFC process follows three-phase dynamics:
$$ \frac{\partial (\rho \phi)}{\partial t} + \nabla \cdot (\rho \phi \mathbf{v}) = S_{\phi} $$
Where:
ρ = metal density
φ = phase fraction (liquid/solid/gas)
v = velocity vector
Sφ = source term for phase change
2. Defect Formation Mechanisms
| Defect Type | Critical Factors | Control Parameters |
|---|---|---|
| Box Lifting | Vacuum pressure (P), Solidification time (t) | P ≥ 0.04 MPa, t ≥ 75s |
| Iron Inclusion | Coating thickness (δ), Sand compactness (C) | δ ≥ 1.2mm, C ≥ 85% |
3. Process Optimization Strategy
The vacuum-pressure relationship follows:
$$ P_v = P_0 – \frac{\mu Q}{2\pi k h} \ln\left(\frac{r_e}{r_w}\right) $$
Where:
Pv = vacuum pressure at mold surface
P0 = atmospheric pressure
μ = gas viscosity
Q = gas flow rate
3.1 Vacuum Control Parameters
| Stage | Pressure (MPa) | Duration (s) |
|---|---|---|
| Pre-pouring | -0.025 | 30 |
| Pouring | -0.035 | 60 |
| Post-solidification | -0.015 | 75 |
4. Coating Performance Requirements
The optimal coating thickness satisfies:
$$ \delta_{opt} = \sqrt{\frac{2k(T_m – T_0)t_p}{\rho L}} $$
Where:
k = thermal conductivity
Tm = metal melting point
T0 = initial mold temperature
tp = pouring time
5. Production Validation
Implementing these optimizations in lost foam casting:
- Defect rate reduced from 40% to 1.2%
- Dimensional accuracy improved by 38%
- Production efficiency increased by 22%
6. Conclusion
This study demonstrates that precise control of vacuum parameters and coating characteristics in lost foam casting significantly improves product quality while maintaining production efficiency. The established mathematical models provide theoretical guidance for process optimization of similar castings.