This study details our comprehensive approach to optimizing the casting process for a critical excavator casting part – the rear axle housing. Using numerical simulation and empirical validation, we identified and resolved defects in the original manufacturing process, significantly improving quality and yield.
Introduction
Excavator rear axle housings are safety-critical components subjected to heavy cyclic bending moments during operation. Failures typically originate from casting defects like inclusions, shrinkage porosity, and hot tears. Traditional trial-and-error methods for process design are costly and time-consuming. We employed AnyCasting simulation software to analyze and optimize the production of this excavator casting part, achieving a 10% increase in yield while eliminating major defects.
Casting Characteristics
The excavator casting part measures 1,548 mm × 431 mm × 362 mm with a mass of 215 kg, manufactured in ZG270-500 steel. Its complex geometry features significant wall thickness variations (minimum 20 mm, maximum 100 mm), creating inherent solidification challenges. Key functional zones include:
| Feature | Dimension | Function |
|---|---|---|
| Central Hub | Ø390 mm cavity | Axle mounting point |
| End Journals | Ø100 mm × 2 | Bearing surfaces |
| Rib Network | 20-30 mm thickness | Structural reinforcement |
Original Process Defect Analysis
Initial simulations predicted defect distributions matching actual production failures. Key findings included:
Filling-Related Defects: The original top-gating system caused turbulent metal entry:
$$v = \frac{Q}{A}$$
where \(v\) = flow velocity (m/s), \(Q\) = flow rate (m³/s), \(A\) = cross-sectional area (m²). High velocities (>1.2 m/s) at ingates led to oxide entrainment and sand erosion.
| Defect Type | Location | Simulation Probability |
|---|---|---|
| Oxide Inclusions | Mid-section junction | 0.75 |
| Gas Porosity | Thin-wall base regions | 0.65 |
Solidification Defects: Thermal analysis revealed inadequate feeding:
$$ \frac{V_{casting}}{V_{riser}} < 0.2 $$
indicating undersized risers. Critical areas showed shrinkage susceptibility >0.6:
| Location | Solidification Time (s) | Shrinkage Severity |
|---|---|---|
| Central Hub | 420 | High (0.85) |
| Journal Transitions | 380 | Moderate (0.60) |
Optimization Strategies
Four key modifications were implemented for this excavator casting part:
1. Gating System Redesign: Changed to a bottom-fed, 5-ingate system:
$$ t = \left( f \sqrt{G} + \frac{1}{5} \delta \cdot \sqrt[3]{G^2} \right) \cdot \sqrt[3]{\frac{2}{n-1}} $$
where \(t\) = pouring time (s), \(f\) = material factor (0.7 for steel), \(G\) = casting weight (kg), \(\delta\) = dominant wall thickness (mm), \(n\) = number of gates. Calculated optimal pouring time: 19s.
2. Riser System Upgrade: Replaced conventional risers with insulated neck risers:
| Riser Type | Quantity | Volume Reduction |
|---|---|---|
| Conventional | 8 | 0% (Baseline) |
| Insulated | 6 | 32% |
3. Chilling & Geometry Modifications:
- Added end-journal chills (100 mm × 150 mm)
- Increased fillet radii from 15 mm to 30 mm at stress-concentration zones
4. Coating Process Enhancement: Implemented automated flow coating achieving uniform thickness (0.3±0.05 mm) versus manual application (0.2–0.6 mm).
Results and Validation
Optimized process simulations showed defect probabilities reduced by 80%:
| Defect Type | Original Probability | Optimized Probability |
|---|---|---|
| Shrinkage Porosity | 0.85 | 0.12 |
| Hot Tears | 0.70 | 0.08 |
| Inclusions | 0.75 | 0.10 |
Production trials confirmed:
- Yield increased from 55% to 65%
- X-ray inspection pass rate: 98.2% vs original 83.5%
- Fatigue life improvement: +40% (per ASTM E606)
Conclusion
Our integrated simulation-physical validation approach successfully optimized this critical excavator casting part. Key achievements include:
- Defect reduction through controlled filling (\(v\) < 0.8 m/s)
- Improved yield via optimized riser-to-casting volume ratio:
$$ \frac{V_{riser}}{V_{casting}} = 0.28 $$ - Elimination of thermal cracks through strategic chilling and geometry modifications
This methodology demonstrates significant potential for complex steel castings across heavy machinery sectors, particularly for high-stress excavator components requiring stringent quality standards.