The manufacturing level of engine blocks serves as a critical indicator of a nation’s industrial capabilities and automotive development. Continuous improvements in engine power output, fuel efficiency, and emission reduction remain essential for both technological advancement and environmental compliance. Lost foam casting (LFC), a near-net-shape precision forming process, enables cleaner production by utilizing expandable polystyrene (EPS) patterns that vaporize during metal pouring. This study focuses on optimizing LFC for low-alloy HT250 diesel engine blocks, achieving a first-pass yield exceeding 95% and a process yield of 91%.
1. Mold Design and Pattern Formation
Horizontal layered segmentation with localized hollowing at the crankcase wall proved optimal for mold design. This approach balances pattern integrity, demolding efficiency, and glue joint quality. Critical mold parameters include:
| Parameter | Value |
|---|---|
| EPS Type | B107 (Jiachang) |
| Pre-expansion Density | 20–21 g/L |
| Final Pattern Density | 23–24 g/L |
| Aging Time | 20 days |
The relationship between pre-expansion density ($\rho_{\text{pre}}$) and final pattern density ($\rho_{\text{final}}$) follows:
$$
\rho_{\text{final}} = \rho_{\text{pre}} + \Delta\rho_{\text{aging}}
$$
where $\Delta\rho_{\text{aging}}$ accounts for residual gas diffusion during aging.
2. Coating and Gating System
A two-layer coating system (1.0–1.5 mm total thickness) from Sanmenxia Sunshine Materials demonstrated superior thermal stability. The gating ratio adheres to:
$$
F_{\text{runner}} : F_{\text{gate}} : F_{\text{sprue}} = (1.3\text{–}2) : (1\text{–}1.5) : 1
$$
Multi-point gating ensures uniform filling, with pouring time ($t$) calculated as:
$$
t = \frac{V_{\text{metal}}}{Q_{\text{pouring}}} \leq 40\,\text{s}
$$
3. Process Parameters
| Parameter | Value |
|---|---|
| Sand Grain Size | 40–70 mesh |
| Vibration Frequency | 10–20 Hz |
| Vacuum Pressure | −0.035 to −0.040 MPa |
| Pouring Temperature | 1480–1520°C |
4. Material Composition
The HT250 alloy composition strictly controls trace elements:
| Element | Range (wt%) |
|---|---|
| C | 3.10–3.30 |
| Si | 1.60–1.80 |
| Mn | 0.60–0.75 |
| Cu | 0.6–1.0 |
| Cr | 0.3–0.5 |
5. Quality Control
Three critical validation metrics confirm process stability:
- Pattern dimensional tolerance: ±0.3 mm
- Coating permeability: ≥2.0 cm4/(g·min)
- Mechanical properties post-aging:
$$
\sigma_b \geq 250\,\text{MPa},\quad \text{HB} = 187\text{–}255
$$
6. Conclusion
Lost foam casting demonstrates exceptional suitability for complex engine blocks through:
- 91% process yield via optimized gating
- 95% first-pass quality through precise pattern control
- Near-net-shape accuracy reducing machining by 40%
This research validates lost foam casting as a sustainable solution for high-performance castings, aligning with global trends in green manufacturing and precision engineering.