Abstract: The manufacturing level of diesel and gasoline engine blocks reflects the development status of a country’s automotive industry. Continuously improving engine efficiency, reducing fuel consumption, and minimizing exhaust emissions are both internal demands of the automotive industry’s development and external environmental requirements. Lost foam casting is one of the advanced manufacturing processes featuring near-net-shape and precision forming, enabling green and clean production. This paper summarizes the application of lost foam casting in the production of engine block castings for automotive engines.
Introduction
Lost foam casting involves bonding foam patterns similar in size and shape to the castings into clusters, applying a refractory coating, drying them, burying them in dry sand for molding by vibration, pouring liquid metal under normal or negative pressure to gasify the patterns, and allowing the metal to solidify and cool to form the castings. This method simplifies the process flow, conserves raw and auxiliary materials, facilitates the recycling of used sand, and reduces environmental pollution while ensuring casting quality, achieving green casting production.
Table 1: Characteristics of Engine Block Castings
| Material | Chemical Composition (%) | Tensile Strength (MPa) | Hardness (HBS) | Hardness Difference (HBS) |
|---|---|---|---|---|
| HT250 | C: 3.10-3.30, Si: 1.60-1.80, Mn: 0.60-0.75, P: 0.040-0.050, S: 0.050-0.060, Cu: 0.6-1.0, Cr: 0.3-0.5 | ≥250 | 187-255 | ≤40 |
Casting Plan and Implementation
Table 2: Key Steps in the Lost Foam Casting Process
| Step | Description |
|---|---|
| Mold Design | Horizontal slicing and local solidification of the crankcase with equal-wall thickness hollowed-out concave processing on the outer wall. |
| Material Pre-expansion and Maturation | EPS material (Jiachang B107) with a density of 23-24 g/L, pre-expanded to a density of 20-21 g/L and matured for 4-8 hours. |
| Foam Shaping and Maturation | Hydraulic semi-automatic molding machine with optimized molds for one-time forming of cylinder liners and crankcase bodies, natural aging for 20 days. |
| Foam Drying | Drying in a separate chamber at 55°C ± 5°C and relative humidity less than 30%. |
| Foam Finishing and Bonding | Trimming, repairing, and bonding with cold and hot glue, sealed with double-sided tape. |
| Coating Application and Drying | Applying coating twice with a thickness of 1.0-1.5 mm, dried separately. |
| ** Gating System** | Closed gating system with F横 > F内 > F直 ratio of (1.3-2):(1-1.5):1, pouring two castings per system within 35-40 seconds. |
| Molding | Using 40-70 mesh dry sand, filling in two stages, compacting with a suitable frequency for 10-20 seconds. |
| Pouring and Cooling | Pouring under a vacuum of -0.035 to -0.040 MPa, pouring temperature above 1480°C, cooling for 1.5 hours before sand removal. |
Pouring and Results
The pouring process involves checking the sand layer thickness, pouring cup position, vacuum pump operation, and pouring temperature. The pouring temperature is controlled between 1600-1620°C, with a final casting temperature above 1480°C. After cooling for 1.5 hours, the sand is removed.
Table 3: Production Results
| Metric | Value |
|---|---|
| Yield of Engine Block Castings | >95% |
| Machining Qualification Rate | 99% |
| Casting Process Yield | 91% |
Conclusion
- Mold Optimization: Different mold structures are adopted for different engine block structures through mold optimization design and production verification.
- Process Analysis: Casting technicians must conduct process analysis, and other casting processes can be used to complement areas where lost foam casting alone cannot meet requirements.
By leveraging lost foam casting, engine block castings can be produced with high yields, quality, and efficiency, contributing to the advancement of the automotive industry.