Abstract
The manufacturing level of diesel and gasoline engine cylinder blocks reflects the developmental progress of a nation’s automotive industry. Increasing engine efficiency, reducing fuel consumption, and minimizing emissions are intrinsic demands for industrial advancement and environmental sustainability. Lost foam casting, as a near-net-shape and precision-forming technology, enables green and eco-friendly production. Compared to traditional methods, its application in engine cylinder block manufacturing shortens process flows, conserves raw materials, facilitates sand recycling, and reduces environmental pollution while ensuring casting quality. This study explores the technical implementation, challenges, and outcomes of lost foam casting for engine cylinder blocks, demonstrating its viability through industrial case studies.
1. Introduction
Lost foam casting (LFC) is an advanced casting method where foam patterns—matching the final part’s geometry—are assembled into clusters, coated with refractory material, embedded in dry sand, and replaced by molten metal during pouring. The foam vaporizes, leaving a precise metal replica. This process eliminates complex steps like core-making and sand preparation, streamlining production for intricate components like engine cylinder blocks.
The engine cylinder block, a critical automotive component, integrates complex features such as cooling jackets, oil passages, and reinforced ribs. Traditional casting struggles with these geometries, but lost foam casting excels due to its design flexibility and reduced post-processing. A case study from Chengdu Xinyi Co., Ltd., achieving a 95% first-pass qualification rate, underscores its industrial applicability.
2. Characteristics of Engine Cylinder Block Castings
Engine cylinder blocks are typically made of HT250 low-alloy cast iron, with strict compositional and mechanical requirements.
Table 1: Chemical Composition of HT250 Alloy
| Element | C | Si | Mn | P | S | Cu | Cr |
|---|---|---|---|---|---|---|---|
| Range | 3.1–3.3% | 1.6–1.8% | 0.6–0.75% | 0.04–0.05% | 0.05–0.06% | 0.6–1.0% | 0.3–0.5% |
Table 2: Mechanical Properties
| Property | Value |
|---|---|
| Tensile Strength | ≥250 MPa |
| Hardness (HBS) | 187–255 |
| Hardness Variation | ≤40 HBS |
Stress-relieving heat treatment ensures dimensional stability and uniformity.
3. Implementation of Lost Foam Casting
3.1 Foam Pattern Design
The foam pattern’s quality determines 50–60% of casting success. Key considerations include:
- Parting Design: Horizontal layering for easy demolding, optimized for intake/exhaust passages.
- Mold Structure: Localized reinforcement at the crankshaft housing to prevent deformation.
Table 3: Foam Material Specifications
| Parameter | Value |
|---|---|
| EPS Type | Gaojing B107 |
| Pre-expansion Density | 20–21 g/L |
| Final Pattern Density | 23–24 g/L |
| Aging Time | 20 days (ambient) |
3.2 Pattern Assembly and Coating
- Drying: 55°C ±5°C, humidity <30%.
- Coating: Two-layer refractory coating (1.0–1.5 mm thickness).
Table 4: Coating Process Parameters
| Step | Specification |
|---|---|
| Coating Layers | 2 |
| Drying Time per Layer | 4–8 hours |
| Coating Supplier | Sanmen Shuguang Co. |
3.3 Gating System Design
A closed gating system (Fm>Fn>Fn−1Fm>Fn>Fn−1) ensures smooth metal flow. Key parameters:
- Ratio: (1.3–2) : (1–1.5) : 1
- Pouring Time: 35–40 seconds
- Ingate Positions: Multi-point feeding (Figure 2).
3.4 Molding and Pouring
- Sand Type: 40–70 mesh dry sand.
- Vacuum Pressure: -0.035 to -0.040 MPa.
- Pouring Temperature: >1480°C.
Table 5: Pouring Parameters
| Parameter | Value |
|---|---|
| Melting Equipment | 1.5-ton induction furnace |
| Cooling Time | 1.5 hours |
| Castings per Batch | 4 blocks/sandbox |
4. Results and Discussion
Table 6: Production Outcomes
| Metric | Value |
|---|---|
| Yield Rate | >95% |
| Machining Pass Rate | 99% |
| Process Yield | 91% |
The high yield and precision validate lost foam casting as superior for engine cylinder blocks.
5. Conclusion
- Lost foam casting resolves geometric challenges in engine cylinder blocks through optimized pattern design and process control.
- Hybrid approaches (e.g., combining lost foam casting with other methods) address localized casting limitations.
- Sustainability benefits—reduced waste, energy efficiency—align with global green manufacturing trends.