In our work, we focused on the design and numerical simulation of a sand casting foundry process for a ZL114A aluminum alloy impeller with a symmetric structure. The impeller had a diameter of 936 mm and a height of 210 mm, featuring 16 blades with thicknesses ranging from 6 mm to 100 mm. The casting required high-quality microstructure and mechanical properties at the spoke plane, while production cost was also a critical factor. Through systematic analysis and multiple simulation iterations using Anycasting software, we developed an optimized sand casting foundry solution that integrated gating and riser systems, filter placement, and mold design to achieve uniform filling, effective slag removal, and defect-free castings.
1. Casting Position and Parting Surface Design
We selected the pouring position with the large spoke plane facing downward, as shown in the conceptual layout. This orientation ensured that the critical planar region solidified under favorable conditions, minimizing gas porosity and slag entrapment. Although this required careful core placement, the use of cold-box resin sand cores provided sufficient strength and precision. The parting surface was placed at the maximum cross-section of the impeller to simplify mold handling and core setting. The resulting sand casting foundry layout allowed for easy assembly and alignment.
2. Gating System and Riser Design
After comparing multiple configurations including bottom-gating, side ring-gating, and center-gating systems, we adopted a low-position center-gating system that combined the sprue with a riser. A flow diverter cone was placed at the bottom of the sprue to spread the molten metal evenly and reduce turbulence. The gating system featured a stepped design that allowed smooth filling from bottom to top. To enhance slag removal and flow stabilization, we installed two layers of filters: a ceramic foam filter at the annular step in the runner and a refractory fiber filter at the junction between the upper mold and the core. This dual-filter arrangement effectively trapped impurities and promoted laminar flow. The filling time was calculated using the relationship:
$$ t_f = \frac{V}{A_{avg} \cdot v} $$
where \( V \) is the casting volume, \( A_{avg} \) is the average cross-sectional area of the gating system, and \( v \) is the average filling velocity. For our design, we obtained \( t_f \approx 18.74 \, \text{s} \), which provided rapid yet stable filling. The gating system parameters are summarized in Table 1.
| Parameter | Value |
|---|---|
| Sprue height (mm) | 190 |
| Sprue top diameter (mm) | 100 |
| Diverter cone angle (°) | 10 |
| Number of filters | 2 |
| Filter type | Ceramic foam + refractory fiber |
| Calculated filling time (s) | 18.74 |
3. Riser and Chills
Initial simulation results indicated potential hot spots at the junction between the blade tips and the curved transition surface. To eliminate shrinkage porosity, we designed six open risers with a slight taper (10° draft) positioned around the top of the impeller. The riser dimensions were 100 mm in diameter and 190 mm in height. These risers provided directional solidification and served as reservoirs to feed the casting during solidification. The volume of the risers was determined using the modulus method. The modulus of the critical section was:
$$ M_c = \frac{V_c}{A_c} \approx 0.85 \, \text{cm} $$
where \( V_c \) is the volume of the hot spot region and \( A_c \) is its cooling surface area. The riser modulus was set to 1.2 times \( M_c \), giving a riser diameter of 100 mm. The final solidification sequence showed that the center runner and risers were the last to solidify, ensuring effective feeding.
4. Mold and Core Design
We used self-hardening resin sand for both the mold and the core, which offered high strength and dimensional accuracy suitable for single-piece or small-batch production. The core was designed as a single monolithic piece to simplify assembly. A flow diverter cone was also integrated into the bottom mold to cushion the impact of molten metal and guide the flow radially. Four alignment holes were drilled in the top mold to reduce weight and facilitate handling. The core and mold assembly are shown schematically. The key sand casting foundry parameters are listed in Table 2.
| Parameter | Value |
|---|---|
| Sand type | Cold-box resin sand |
| Core material | Resin sand (monolithic) |
| Diverter cone radius (mm) | 50 |
| Core draft angle (°) | 2 |
| Pouring temperature (°C) | 710 – 730 |
| Mold preheating temperature (°C) | 150 |
5. Simulation and Optimization
We performed numerical simulations using Anycasting to evaluate filling and solidification behavior. The filling pattern was uniform, with the metal flowing from the center outward and rising gradually. The simulation confirmed that the dual filters effectively reduced turbulence and slag inclusion. Solidification analysis predicted no significant shrinkage defects in the casting, with porosity confined to the runner and riser base. The temperature gradient during solidification was monitored, and the cooling rate was evaluated using:
$$ \frac{dT}{dt} = k \cdot (T – T_{amb}) $$
where \( k \) is the heat transfer coefficient and \( T_{amb} \) is the ambient temperature. The calculated cooling rates were within acceptable limits to avoid hot tearing. A comparison of alternative gating systems is presented in Table 3, highlighting the advantages of our center-gating approach.
| System type | Filling uniformity | Slag removal | Simplicity | Defect risk |
|---|---|---|---|---|
| Bottom-gating (side) | Good | Moderate | Moderate | Low |
| Side ring-gating | Moderate | Low | Complex | Moderate |
| Center-gating (this work) | Excellent | High | Simple | Very low |
6. Results and Discussion
The final sand casting foundry process produced castings that met stringent quality requirements: X-ray inspection showed no cracks, cold shuts, or misruns, and the porosity level was below Grade 4. The use of a low-position center gating system combined with dual filters effectively prevented slag and gas defects. The six open risers provided adequate feeding, eliminating shrinkage in the critical spoke plane. The monolithic resin sand core simplified core setting and reduced assembly time. Overall, the sand casting foundry design achieved an optimal balance between casting quality, material yield, and production cost. The process demonstrated robustness for medium-to-large aluminum alloy impellers in a sand casting foundry environment.
7. Conclusion
We successfully designed a sand casting foundry process for a ZL114A aluminum alloy impeller. The key innovations include the integration of a center gating system with a flow diverter cone, dual-layer filters for slag removal, and open risers for directional solidification. Numerical simulations guided the optimization, confirming uniform filling and defect-free solidification. The final sand casting foundry solution is well-suited for single-piece or small-batch production of symmetric impeller castings, offering high quality and cost efficiency.