This study investigates the optimization of casting processes for ZG07Cr19Ni10 stainless steel self-priming pump bodies using numerical simulation and orthogonal experimental methods. The research focuses on addressing critical casting defects through systematic process improvements while maintaining production efficiency.
1. Fundamental Theories and Numerical Simulation
The filling and solidification processes were analyzed using fluid dynamics and heat transfer principles. Key governing equations include:
Continuity equation:
$$ \frac{\partial \rho}{\partial t} + \nabla \cdot (\rho \mathbf{U}) = 0 $$
Navier-Stokes equations:
$$ \rho \left( \frac{\partial \mathbf{U}}{\partial t} + \mathbf{U} \cdot \nabla \mathbf{U} \right) = -\nabla p + \mu \nabla^2 \mathbf{U} + \rho \mathbf{g} $$
Energy conservation equation:
$$ \rho c_p \frac{\partial T}{\partial t} + \rho c_p \mathbf{U} \cdot \nabla T = \nabla \cdot (k \nabla T) + Q $$
The RNG k-ε turbulence model was employed to analyze flow characteristics:
$$ \frac{\partial}{\partial t}(\rho k) + \frac{\partial}{\partial x_i}(\rho k u_i) = \frac{\partial}{\partial x_j}\left(\alpha_k \mu_{\text{eff}} \frac{\partial k}{\partial x_j}\right) + G_k – \rho \epsilon $$
$$ \frac{\partial}{\partial t}(\rho \epsilon) + \frac{\partial}{\partial x_i}(\rho \epsilon u_i) = \frac{\partial}{\partial x_j}\left(\alpha_\epsilon \mu_{\text{eff}} \frac{\partial \epsilon}{\partial x_j}\right) + C_{1\epsilon} \frac{\epsilon}{k} G_k – C_{2\epsilon} \rho \frac{\epsilon^2}{k} $$
2. Process Optimization Strategy
The initial casting process exhibited multiple casting defects including shrinkage porosity (2.6% of total volume) and cold shuts. Key improvements included:
| Parameter | Initial Design | Optimized Design |
|---|---|---|
| Gating System Type | Open | Semi-closed |
| Riser Quantity | 5 | 3 |
| Process Yield | 55.9% | 77% |
| Defect Volume | 3.0×10⁵ mm³ | 1.0×10⁵ mm³ |
3. Orthogonal Experimental Analysis
An L9(3⁴) orthogonal array was implemented to optimize process parameters:
| Level | A: Pouring Temp (°C) | B: Mold Preheat (°C) | C: Pouring Time (s) |
|---|---|---|---|
| 1 | 1530 | 100 | 10 |
| 2 | 1560 | 200 | 15 |
| 3 | 1590 | 300 | 20 |
Significance analysis revealed:
$$ F_{\text{pouring time}} = 87.8 \quad (\text{p}<0.01) $$
$$ F_{\text{pouring temp}} = 21.1 \quad (\text{p}<0.05) $$
$$ F_{\text{mold preheat}} = 2.4 \quad (\text{p}>0.05) $$
4. Defect Formation Mechanism
The Niyama criterion was applied to predict shrinkage defects:
$$ NY = \frac{G}{\sqrt{\dot{T}}} $$
where $G$ is temperature gradient (K/m) and $\dot{T}$ is cooling rate (K/s). Critical NY values <1.0 K1/2·s1/2/mm indicated high-risk defect zones.
5. Validation and Production
Optimized parameters achieved:
- Shrinkage porosity reduction: 69%
- Mechanical properties enhancement:
$$ \sigma_b = 557\ \text{MPa},\ \delta = 56.5\% $$ - Pressure test performance: 3MPa hydraulic/2.2MPa pneumatic
This systematic approach demonstrates effective casting defect control through numerical simulation-guided process optimization, providing valuable insights for complex stainless steel castings production.