In modern industrial applications, double-suction impellers are critical components in turbomachinery, such as pumps and compressors, designed to handle high flow rates and pressures. Compared to single-suction impellers, they offer superior efficiency and capacity, making them indispensable in sectors like energy, petrochemicals, and water treatment. The material of focus here is C95820 aluminum bronze, known for its narrow crystallization temperature range, excellent fluidity, and resistance to segregation and dispersed shrinkage, which makes it ideal for producing dense castings. However, aluminum bronze is prone to defects like oxide inclusions, gas porosity, and concentrated shrinkage during melting and pouring, posing challenges in traditional sand casting processes. The advent of 3D printing technology has revolutionized sand casting by enabling rapid, high-precision mold production with reduced lead times and material waste. This study explores the integration of sand mold 3D printing with simulation-driven design to overcome these challenges, focusing on a double-suction impeller with complex geometry and uneven wall thickness.
The double-suction impeller under investigation features a large outer diameter of 1015 mm and a height of 630 mm, with a central through-hole and asymmetric双层叶片布局. Key structural aspects include varying wall thicknesses, with minimum sections as thin as 5 mm, and连接板 widths of 15 mm between blade layers and 19 mm between cover plates and blades. This complexity increases the risk of sand core damage during demolding in conventional sand casting, alongside issues like oxide formation and gas entrapment due to aluminum bronze’s properties. To address this, we employed a sand mold 3D printing approach, which allows for monolithic core designs and optimized gating systems, ensuring dimensional accuracy and defect minimization.
In the initial phase, we analyzed the component’s geometry to identify potential defect zones. The impeller’s asymmetric blades and thin sections necessitated a careful浇注位置 selection to facilitate sequential solidification and reduce turbulence. We chose a bottom-gating system to promote steady metal flow, minimizing air inclusion and oxide formation. The gating design involved four bottom-entry gates connected directly to four blind risers, enhancing feeding efficiency and reducing shrinkage defects. Risers were strategically placed, including six腰形明冒口 at the top ring, cylindrical明冒口 for the central hole, and additional small risers at blade tips to act as vents and feeders. This design was iteratively refined using ProCAST simulation software to validate fluid dynamics and thermal behavior.
The simulation parameters were set to replicate industrial conditions: the mold material was resin-bonded sand, with a pouring temperature of 1150°C and initial mold temperature of 80°C. The heat transfer coefficient between the casting and mold was defined as 500 W/m²·K, and the pouring time was 120 seconds. The filling process simulation demonstrated laminar flow with no splashing or backflow, as metal entered through the gates and filled the cavity uniformly. Velocity magnitudes during filling were monitored, with values ranging from 0 to 14.36 m/s, confirming stable ascent and reduced defect risks. The solidification analysis showed that thin sections, like blades and连接板, solidified first, followed by thicker areas, with risers solidifying last to enable effective feeding. Defect prediction indicated that shrinkage porosity was concentrated in the risers and gating system, with no significant defects in the impeller itself, validating the design.
To quantify the material properties and process parameters, we incorporated key formulas and tables. For instance, the fluid velocity during filling can be described by the equation: $$v = \frac{Q}{A}$$ where \(v\) is the velocity, \(Q\) is the volumetric flow rate, and \(A\) is the cross-sectional area. This relates directly to the sand casting process, as controlling velocity minimizes turbulence. Additionally, the solidification time for a casting can be approximated using Chvorinov’s rule: $$t = B \left( \frac{V}{A} \right)^2$$ where \(t\) is the solidification time, \(V\) is the volume, \(A\) is the surface area, and \(B\) is a mold constant. This highlights the importance of geometry in sand casting design.
| Element | Cu | Al | Ni | Fe | Mn |
|---|---|---|---|---|---|
| Content | ≥77.5 | 9.0–10.0 | 4.5–5.8 | 4.0–5.0 | ≤1.5 |
The sand casting process was further enhanced through 3D printing of the molds. We designed the sand cores as monolithic structures to preserve blade accuracy, incorporating定位装置 for assembly. A critical aspect was the integration of ventilation channels to handle gas evolution from the resin-bonded sand. For simpler core sections, straight channels sufficed, but for complex blade areas, we utilized conformal channels that followed the曲面结构, ensuring efficient gas expulsion. This approach leverages the flexibility of sand mold 3D printing to overcome traditional sand casting limitations.
Printing parameters were optimized for the覆膜宝珠砂 material, as summarized in the table below. Post-printing, the molds underwent curing with flame treatment and oven heating to 180°C, followed by cooling to room temperature. Assembly involved sequential positioning of cores, preheating the cavity to 80°C, and inserting vent ropes for ignition during pouring. The actual pouring was conducted at 1150°C over 120 seconds, resulting in a sound casting with minimal defects, as confirmed by visual inspection.
| Parameter | Value |
|---|---|
| Laser Power (W) | 900 |
| Beam Spot Size (mm) | 1.1 |
| Scanning Speed (mm/s) | 2900 |
| Layer Thickness (mm) | 0.3 |
| Material | Coated Ceramic Sand |
The success of this sand casting process is evident in the final impeller, which exhibited no major defects such as shrinkage or porosity in critical areas. The use of ProCAST simulations allowed for precise optimization of the gating and riser system, ensuring that defects were confined to the feeders. Moreover, the integration of 3D printing facilitated the production of complex cores without partitioning, maintaining dimensional integrity. The conformal ventilation channels effectively managed gas release, a common issue in resin sand casting. Overall, this approach demonstrates how sand mold 3D printing can transform traditional sand casting, enabling the fabrication of high-integrity components like aluminum bronze impellers with reduced costs and lead times.
In conclusion, the combination of simulation-driven design and additive manufacturing provides a robust framework for advancing sand casting processes. For the double-suction impeller, this resulted in a defect-free casting that meets industrial standards, highlighting the potential for broader application in complex turbomachinery components. Future work could focus on refining material models for aluminum bronze and expanding the use of conformal cooling in sand casting molds to further enhance efficiency.