Development of Casting Process for Ductile Iron Differential Housing with Enhanced Internal Integrity

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This paper presents the systematic development of a ductile iron casting process for a differential housing with stringent internal defect requirements. The component features asymmetrical flanges (8.3 mm thickness) and multiple functional windows, demanding exceptional dimensional accuracy (misalignment ≤0.5 mm) and internal soundness (D3/1 criteria: defects occupying <3% of inspected cross-section with maximum defect diameter ≤1 mm).

1. Material Specifications & Process Constraints

The ductile iron casting (QT600-M grade) requires precise chemical composition control:

Table 1. Chemical Composition Requirements (wt.%)
C Si Mn Cu Mg S P Ti Sn
3.3-3.9 1.8-3.0 0.2-1.0 0.2-1.0 0.027-0.06 ≤0.02 ≤0.06 ≤0.06 ≤0.06

Mechanical properties must satisfy:

$$ \sigma_b \geq 650\ MPa,\ \sigma_{0.2} \geq 405\ MPa,\ \delta \geq 3\% $$
$$ 200 \leq HBW \leq 265,\ \text{Nodularity} \geq 80\% $$

2. Gating System Optimization

The initial ductile iron casting process employed a 3-riser system (2 dedicated + 1 shared) with multi-stage gating:

Table 2. Riser Design Parameters
Riser Type Dimensions (mm) Neck Section (mm²) Weight (kg) Modulus (mm)
Dedicated 120×43×50 423 2.1 6.0
Shared 120×55×50 580 2.8 6.5

The gating system featured three-stage overlap connections to enhance slag retention:

$$ Q = \frac{W}{\rho t} $$

Where Q = flow rate (kg/s), W = casting weight (3.32 kg), ρ = molten iron density (7.1 g/cm³), t = pouring time (optimized to 10.3s).

3. Solidification Simulation & Defect Control

Numerical simulation revealed critical shrinkage areas in pin holes and flange junctions. The modified process achieved defect-free solidification through:

  1. 60% axial head filling (29mm of 48mm total height)
  2. 0.5mm flange thickness compensation
  3. Φ6×25mm chill pins in pin holes
Table 3. Defect Reduction Comparison
Parameter Initial Design Optimized Design
Max Shrinkage Volume (mm³) 80.0 0
Process Yield 36.7% 42.7%
Pouring Time (s) 13-16 10.2-10.3

4. Production Validation

Key improvements for ductile iron casting production:

$$ \eta = \frac{W_{casting}}{W_{total}} \times 100\% $$

Where η = process yield, improved from 36.7% to 42.7% through:

  • Horizontal runner weight reduction (15-20%)
  • Integrated exhaust sheets (0.5mm thickness)
  • Top-feeding gate redesign

Batch production achieved 96.71%合格率 with defect distribution:

Table 4. Defect Distribution in Mass Production
Defect Type Frequency Rate (%)
Sand Inclusion 37 1.96
Handling Damage 18 0.95
Marking Defects 7 0.37

5. Conclusion

The developed ductile iron casting process successfully meets stringent internal quality requirements through:

  1. Multi-stage overlap gating design
  2. Modulus-optimized riser system
  3. Strategic use of chills and axial filling
  4. Integrated exhaust system for gas escape

This case demonstrates that proper simulation-guided design combined with process parameter optimization can achieve high-integrity ductile iron castings even for complex geometries with thin-wall sections.

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