In the competitive landscape of V-type engine block manufacturing, the demand for lightweight, integrated structures with high quality and rapid delivery has intensified. This paper presents our research on a 3D printing casting process for a V16 engine block featuring complex nested cavities, thin walls, and stringent internal quality requirements. By leveraging additive manufacturing for sand cores, we optimized the core design to minimize the number of cores, improved dimensional consistency, and eliminated hard-to-clean flash and veining. The process includes a bottom-side gating system, riser and chill placement, and a tailored melt chemistry. Production results demonstrate that the castings meet all technical specifications, including UT Grade I, dimensional accuracy DCTG9, and mechanical properties per QT450-10, confirming the efficacy of the approach.
Introduction to the Challenge
The engine block under investigation is a V16 configuration with overall dimensions of 1650 mm × 800 mm × 590 mm, a casting weight of 986 kg, and a nominal wall thickness of 8 mm. The material is ductile iron QT450-10. The geometry features a water jacket and tappet chamber that are interleaved, and above the camshaft bore there is a full-length double-layer cavity only 20 mm wide at the narrowest point, extending 1580 mm. Only eight 37 mm diameter core prints are available on the top face for cleaning access. Such intricate internal cavities, if contaminated with sand or flash, cannot be mechanically cleaned. Furthermore, the thin walls (8 mm) between cavities demand high core strength and dimensional stability. Traditional sand casting with multiple cores would introduce parting lines inside these inaccessible regions, leading to unacceptable defects. Therefore, we adopted 3D printing casting as the core manufacturing method to achieve a monolithic core structure that eliminates parting lines and ensures casting integrity.
Product Specifications and Quality Requirements
The engine block must conform to the following specifications:
| Material | Overall Dimensions (mm) | Mass (kg) | Max Wall (mm) | Min Wall (mm) | Nominal Wall (mm) |
|---|---|---|---|---|---|
| QT450-10 (GB/T 5612–2008) | 1650 × 800 × 590 | 986 | 62 | 8 | 8 |
| Parameter | Standard / Value |
|---|---|
| Material Grade | QT450-10 (GB/T 5612–2008) |
| Dimensional Tolerance | DCTG9 (GB/T 6414–2017) |
| Tensile Strength (MPa) | ≥450 (GB/T 228.1–2021) |
| Hardness (HBW) | 160–210 (GB/T 231.1–2002) |
| Nodularity (%) | ≥70 (GB/T 9441–2009) |
| Ferrite Content (%) | ≥80 (exhaust port area ≥90) (GB/T 9441–2009) |
| UT Inspection | Grade I (critical areas) (GB/T 34904–2017) |
| Surface Roughness Ra (μm) | ≤50 (GB/T 6060.1–1997) |
| Section Examination | No defects within bearing cap and cylinder bore zones (layer milling ≤3 mm) |
Casting Process Analysis and Challenges
The major technical difficulties include:
- Interleaved water jacket and tappet chamber cores with low self-strength, prone to deformation. The double-layer cam cavity is extremely narrow (20 mm) and long (1580 mm), making core coating and cleaning nearly impossible if flash or veining occurs. Therefore, an integral core design is essential.
- Large wall thickness variations: nominal 8 mm, with local thick sections (e.g., bearing caps, foot pads) acting as hot spots. Critical areas require UT Grade I, demanding a well-designed feeding system with chills and risers to ensure directional solidification and shrinkage-free structure.
3D Printing Casting Core Strategy
3D printing casting allows maximum flexibility in splitting the core assembly. Our principle was to reduce the number of cores while ensuring adequate strength, ease of coating, and safe handling. We divided the core package into six pieces:
- Lower outer core (base core): Integrates the water jacket, tappet chamber, oil gallery, and camshaft bore into one monolithic core. This eliminates all internal parting lines within the nested cavities, ensuring no flash in inaccessible regions.
- Inner core: Contains cylinder bores, camshaft bores, and crankcase cavities.
- Upper outer cores (left and right sides, free end, and damper end): These cores carry the external geometry of the engine block and also form the side water jackets. They are designed to allow easy placement of chills and to provide access for coating.
The resulting sand-to-metal ratio was 2.2. The 3D printing casting core scheme is illustrated conceptually by the following image showing a typical sand-core assembly for a complex engine block.
Gating System Design for 3D Printing Casting
The gating system was designed to ensure smooth, non-turbulent filling to avoid slag entrapment and reoxidation. We adopted a bottom-gated, open system with a U-shaped runner layout to balance flow to both cylinder banks. The cross-sectional area ratio was:
$$ \Sigma F_{\text{直}} : \Sigma F_{\text{横}} : \Sigma F_{\text{内}} = 1 : 1.59 : 2.08 $$
The in-gate velocity was kept below 0.9 m/s. A ceramic foam filter (silicon carbide) was placed between the runner and the ingate to further trap inclusions. Flow simulation verified that the metal filled the runners rapidly and then rose smoothly into the cavity without splashing or air entrapment.
Feeding and Solidification Control
Hot spots were identified using modulus analysis. The main thermal centers are the bearing caps and foot pads (interconnected by thick walls), and the cylinder bore region where ribs and bosses intersect. For the bearing cap area, we placed insulating risers on the top of the foot pads and applied chills on the bearing cap sides to accelerate local solidification. For the cylinder bore zone, which is closer to the gating system, we used chills of appropriate thickness to create a favorable temperature gradient. The overall feeding system was verified by MAGMA simulation; the solidification sequence showed that the risers remained liquid while the casting solidification progressed directionally toward them.
Melt Process Design
The challenge was to achieve the required mechanical properties in both separately cast test bars and in coupons cut from the actual casting (bearing cap sections). We selected copper as the primary alloying element (0.45–0.8 wt%) to strengthen the matrix without increasing the carbon equivalent too much. The carbon equivalent was controlled to promote self-feeding in the thin-wall structure. The target chemical composition is given in Table 3.
| C | Si | Mn | P | S | Cu | Mg |
|---|---|---|---|---|---|---|
| 3.55–3.95 | 2.15–2.75 | ≤0.5 | ≤0.045 | 0.010–0.018 | 0.45–0.8 | 0.02–0.05 |
Charge materials consisted of 50–70% Q10 pig iron, 15–25% returns, and 15–25% steel scrap. Sulfur content was controlled between 0.025% and 0.080% before nodulization to ensure stable nodulization. The Q10 pig iron specification is listed in Table 4.
| C | Si | Mn | P | S | Mg |
|---|---|---|---|---|---|
| 3.5–4.0 | ≤0.4 | ≤0.1 | ≤0.035 | ≤0.035 | ≤0.010 |
Nodulization was performed using the cored-wire feeding process. Mg15 wire (Mg 14–16%, Si 42–46%, Ca 1.5–2.5%, MgO ≤1%) and inoculation wire (Si 73–77%, Al ≤1%) were fed at controlled rates. Immediately before pouring, 0.1–0.2% sulfur-oxygen inoculant was added as a stream inoculant to enhance nodule count and improve mechanical properties in the casting sections.
Simulation and Verification
We used MAGMA software to simulate both filling and solidification. The filling simulation confirmed that the gating system provided laminar flow with no air entrapment. The solidification simulation indicated that all hot spots were effectively fed by risers or cooled by chills, with shrinkage porosity confined to risers. A summary of the feeding system design is given in Table 5.
| Location | Feeding Element | Purpose |
|---|---|---|
| Bearing cap / foot pad | Insulating riser on foot pad top | Compensate shrinkage of thick sections |
| Bearing cap side | Chill | Accelerate solidification to avoid shrinkage |
| Cylinder bore region | Chills at rib intersections | Create directional solidification toward risers |
Production Results
The castings produced using the 3D printing casting process were subjected to full inspection. Figure below shows the microstructures obtained from coupons cut from the casting.
The graphite morphology was predominantly Type V and VI according to ISO 945-1:2019, with nodularity ≥84%. The matrix consisted of ≥90% ferrite and ≤1% carbides. Mechanical properties from attached test blocks are summarized in Table 6.
| Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Hardness (HBW) | Nodularity (%) | Pearlite (%) |
|---|---|---|---|---|---|
| 567 | 350 | 13.5 | 179 | 84 | 45 |
All castings passed UT inspection at Grade I in critical zones. Dimensional measurement confirmed DCTG9 tolerance. Surface roughness met the Ra ≤ 50 μm requirement. Sectioning of bearing cap and cylinder bore zones revealed zero shrinkage defects. The 3D printing casting approach successfully delivered a lightweight integrated engine block with high quality and repeatability.
Conclusion
Through systematic application of 3D printing casting technology, we developed a robust process for a complex V16 engine block. The key innovations include: (1) a monolithic core design that eliminated internal flash and veining, (2) an optimized gating and feeding system verified by simulation, and (3) a tailored melt practice ensuring both laboratory and cast-in properties. The production results demonstrate that 3D printing casting is an effective solution for lightweight, integrated engine blocks, offering improved dimensional consistency, reduced defect rates, and shorter development cycles. This study provides a reference for similar complex castings where traditional core-making is inadequate.
Acknowledgments: The authors thank the foundry team for their collaboration in implementing the 3D printing casting process.