This study investigates critical defects in 11L 6-cylinder engine cylinder block castings produced through horizontal flaskless molding, proposing an optimized gating system design validated through numerical simulation and production trials. The original process exhibited 11% scrap rate from upper crankshaft chamber porosity and inconsistent mechanical properties at bearing cap locations.
1. Defect Mechanism Analysis
The original 3-tier gating system with bearing cap gates created two fundamental issues:
1.1 Gas Entrapment Dynamics
Mold filling simulations revealed premature freezing of initial iron streams (1,440^{\circ}C → 1,230^{\circ}C liquidus) in thin-wall upper crankshaft regions (5mm thickness). The temperature decay followed:
$$ T(t) = T_0 – kt^2 $$
Where:
– $T_0$ = Initial pouring temperature (1,440^{\circ}C)
– $k$ = Heat loss coefficient (0.33^{\circ}C/s)
– $t$ = Time since pour
This created gas entrapment zones with oxygen concentrations reaching 30.48 wt% (EDS analysis):
| Element | Weight % |
|---|---|
| O | 30.48 |
| C | 3.93 |
| Fe | 35.63 |
1.2 Thermal Segregation in Bearing Caps
Continuous metal flow through bearing cap gates (original design) caused delayed solidification, producing coarse graphite (Type B >50%):
$$ \lambda = \frac{Q}{A\Delta T} $$
Where:
– $\lambda$ = Graphite spacing
– $Q$ = Heat input
– $A$ = Cross-sectional area
– $\Delta T$ = Temperature gradient
| Location | Tensile (MPa) | Hardness (HBW) |
|---|---|---|
| Original Bearing Cap | 223.1±9.8 | 182.7±4.2 |
| Required | >195 | 170-230 |
2. Gating System Optimization
The redesigned system features:
$$ \Sigma A_{gates} = 0.8\Sigma A_{sprue} $$
- Upper crankcase side gates (4 channels)
- Eliminated bearing cap gates
- Reduced oil pan flange gates (30% area reduction)
2.1 Fluid Dynamics Verification
MAGMASOFT® simulations confirmed:
$$ v_{new} = 2.3v_{original} \text{ at upper crankcase} $$
$$ \Delta T_{max} < 15^{\circ}C \text{ vs. }45^{\circ}C \text{ originally} $$
| Parameter | Original | Optimized |
|---|---|---|
| Fill Time (s) | 21 | 19 |
| Cold Shut Risk | High | Low |
3. Production Validation
500-engine trial demonstrated:
$$ \text{Porosity Rate} = \frac{0.1\%}{11\%} \times 100\% = 99.1\% \text{ Improvement} $$
| Property | Original | Optimized |
|---|---|---|
| Tensile (MPa) | 223.1 | 251.6 |
| Hardness (HBW) | 182.7 | 206.1 |
| Graphite Type | B >50% | A95 >90% |
4. Conclusion
The engine cylinder block casting process achieved:
- 99% reduction in upper crankcase porosity through controlled initial iron distribution
- 14% increase in bearing cap tensile strength via thermal profile optimization
- Consistent Type A graphite formation through directional solidification control
This gating design methodology provides fundamental principles for heavy-section engine cylinder block production, particularly for commercial vehicle applications requiring high reliability.