In precision investment casting, the elimination of shrinkage defects in complex thin-walled components remains a critical challenge. This study focuses on optimizing the casting process for a stainless steel bracket used in agricultural machinery through numerical simulation and experimental validation. We employed ProCAST software to analyze filling patterns, solidification behavior, and defect formation mechanisms, subsequently improving both the gating system and process parameters.
1. Component Characteristics and Process Design
The stainless steel bracket (304L grade) features heterogeneous wall thicknesses (average 4 mm) with multiple geometric discontinuities. The casting dimensions (141 mm × 81.8 mm × 60.84 mm) and complex topology create inherent challenges for directional solidification. Key chemical composition ranges include:
| Element | C | Si | Mn | Cr | Ni |
|---|---|---|---|---|---|
| Content (%) | ≤0.03 | ≤1.0 | ≤2.0 | 18-20 | 8-11 |
The initial gating system employed a top-feeding design with single sprue and runner. Pouring velocity was determined using the empirical Kalgin equation:
$$v_{\text{pour}} = \frac{h \cdot \delta \cdot T}{1000}$$
where \(v_{\text{pour}}\) represents pouring velocity (cm/s), \(h\) is casting height (cm), \(\delta\) denotes wall thickness (cm), and \(T\) indicates pouring temperature (°C). Calculated parameters yielded:
| Parameter | Value |
|---|---|
| Pouring Temperature | 1,500°C |
| Shell Preheat | 1,000°C |
| Filling Velocity | 240 mm/s |
2. Numerical Simulation and Defect Analysis
Finite element analysis revealed critical solidification issues in the initial design:
| Location | Shrinkage Porosity (%) |
|---|---|
| Rectangular Junction (A) | 8.2 |
| U-shaped Housing (B) | 6.9 |
| Arc Contact Zone (C) | 6.4 |
Thermal analysis demonstrated premature runner solidification (1,042 s complete solidification time), creating isolated hot spots with insufficient feeding. The original shrinkage porosity rate reached 21.45%, primarily concentrated in geometric transitions.
3. Gating System Optimization
Two modified gating configurations were proposed:
| Design | Modification | Shrinkage Reduction |
|---|---|---|
| Scheme A | Additional secondary runner | 61% |
| Scheme B | Secondary runner + vent channels | 70% |
Scheme B demonstrated superior performance with:
$$v_{\text{optimized}} = 230\ \text{mm/s}$$
$$T_{\text{shell}} = 1,050°C$$
$$T_{\text{pour}} = 1,650°C$$
4. Orthogonal Experimentation for Parameter Optimization
An L9(3³) orthogonal array evaluated three critical parameters:
| Factor | Level 1 | Level 2 | Level 3 |
|---|---|---|---|
| A: Pouring Temp (°C) | 1,530 | 1,600 | 1,650 |
| B: Filling Velocity (mm/s) | 200 | 230 | 250 |
| C: Shell Preheat (°C) | 1,000 | 1,050 | 1,100 |
Optimal parameters reduced shrinkage porosity to 1.34% through enhanced thermal management:
$$Q_{\text{shrinkage}} = \alpha \cdot \Delta T \cdot V_{\text{casting}}$$
where \(\alpha\) represents thermal contraction coefficient (11.5×10⁻⁶/°C for 304L), \(\Delta T\) is temperature gradient, and \(V_{\text{casting}}\) denotes casting volume.
5. Industrial Validation
Production trials confirmed:
- Defect rate reduction from 21.45% to 1.34%
- Improved dimensional accuracy (IT12 to IT10)
- Reduced scrap rate (32% → 4.7%)
This systematic approach demonstrates the effectiveness of combining precision investment casting simulation with statistical optimization for complex thin-walled components. The methodology provides a replicable framework for similar applications in automotive and aerospace industries.