In the field of mechanical engineering, the demand for high-quality structural components is ever-increasing, and sand casting parts play a pivotal role in meeting these requirements. As a researcher focused on advancing casting technologies, I have extensively studied the challenges associated with producing complex sand casting parts, particularly those made from cast steel. These sand casting parts often face issues such as shrinkage porosity, hot tearing, and inadequate mechanical properties due to the inherent characteristics of steel, including high melting point, poor fluidity, and significant shrinkage during solidification. Traditional casting process design relies heavily on empirical knowledge and iterative trials, which are time-consuming and costly. Therefore, in this work, I employ numerical simulation as a powerful tool to optimize the process for sand casting parts, aiming to enhance efficiency, reduce defects, and ensure that the final sand casting parts meet stringent performance standards.
The specific component under investigation is a beam structure, a common sand casting part used in machinery like machine tools and cranes. This sand casting part must withstand substantial loads, necessitating excellent internal quality and mechanical properties. Cast steel, specifically ZG270-500 (similar to ZG35), was selected for its balance of strength, plasticity, and cost-effectiveness. However, the casting of such sand casting parts is complicated by factors such as a wide solidification temperature range and high volumetric shrinkage. To address these challenges, I initiated this study by designing an initial casting process based on conventional methods, followed by numerical simulation using ViewCast software to identify and mitigate potential defects. The goal is to achieve a robust process that enables smooth filling and directional solidification, thereby minimizing defects in these critical sand casting parts.
Before delving into the simulation details, it is essential to analyze the beam sand casting part. The component has a relatively simple geometry with uniform wall thickness, measuring approximately 1,900 mm in length, 260 mm in width, and 190 mm in height. It is classified as a medium-sized sand casting part, and for mass production, sand casting with self-hardening sodium silicate sand was adopted. A two-cavity mold layout was used to improve productivity. The material composition of ZG270-500 is critical, as it influences the solidification behavior and final properties of the sand casting parts. The chemical composition is summarized in Table 1.
| Element | C | Si | Mn | P | S | Mo | Cr | Ni | Fe |
|---|---|---|---|---|---|---|---|---|---|
| Content | 0.32–0.42 | 0.20–0.45 | 0.50–0.80 | ≤0.04 | ≤0.04 | ≤0.20 | ≤0.35 | ≤0.30 | Bal. |
The casting process design began with the gating system. For steel sand casting parts, an open gating system is preferred to ensure rapid and tranquil filling, given the use of a bottom-pour ladle that inherently offers slag-trapping capabilities. The ladle nozzle diameter was set at 45 mm based on the casting weight, and the cross-sectional areas of the gating components were determined using proportional ratios. Specifically, the ratio of the total area of the ladle nozzle (∑Anozzle) to the total area of the ingates (∑Aingate), cross gates (∑Across), and sprue (∑Asprue) was set as 1:1.9:1.9:2.2. The dimensions are illustrated in Table 2.
| Component | Dimensions (mm) | Cross-Sectional Area (mm²) |
|---|---|---|
| Sprue | Diameter: 70 | ≈ 3,848 |
| Cross Gate | Width × Height: 60 × 60 | ≈ 3,600 |
| Ingate | Width × Height: 50 × 50 | ≈ 2,500 |
Riser design is crucial for feeding sand casting parts to compensate for solidification shrinkage. The modulus method was applied to determine riser sizes. The modulus (M) is calculated as the volume (V) divided by the surface area (A) of the section: $$M = \frac{V}{A}$$. For the beam ends, the modulus was computed as 1.9 cm, leading to the selection of cylindrical top risers with a diameter of 120 mm and height of 180 mm. For the reinforcing ribs, which are thinner, side risers were employed with a diameter of 140 mm and height of 280 mm to feed both sand casting parts in the mold. The initial process layout included these risers, as shown in the 3D model.
Numerical simulation was conducted using ViewCast software to analyze the solidification process of these sand casting parts. The 3D model of the casting system was imported in STL format and discretized into approximately 2 million finite difference mesh cells to balance accuracy and computational time. The simulation parameters were set based on typical casting conditions for steel sand casting parts: pouring temperature of 1,550°C and initial mold temperature of 20°C. The governing equations for heat transfer during solidification include the energy conservation equation: $$\frac{\partial (\rho H)}{\partial t} = \nabla \cdot (k \nabla T)$$ where $\rho$ is density, $H$ is enthalpy, $t$ is time, $k$ is thermal conductivity, and $T$ is temperature. Additionally, the fraction of solid ($f_s$) evolution is modeled using Scheil’s equation for microsegregation: $$f_s = 1 – \left( \frac{T_m – T}{T_m – T_l} \right)^{1/(1-k)}$$ where $T_m$ is the melting point, $T_l$ is the liquidus temperature, and $k$ is the partition coefficient.
The simulation results for the initial process revealed the solidification sequence and defect formation. As shown in the temperature field plots, solidification initiated at the edges of the sand casting parts at 172 s, progressed through the thin sections, and eventually left isolated liquid pools in the central regions by 981 s. By 1,342 s, solidification was nearly complete, but shrinkage porosity was predicted at the junctions between the risers and the casting, as well as in areas beyond the effective feeding range of the risers. The defect distribution, visualized through porosity probability maps, indicated that the risers were partially effective but insufficient to fully compensate for shrinkage in these sand casting parts. This is quantified by the Niyama criterion, often used to predict shrinkage porosity: $$N_y = \frac{G}{\sqrt{\dot{T}}}$$ where $G$ is the temperature gradient and $\dot{T}$ is the cooling rate. Regions with $N_y$ below a critical threshold (e.g., 1 °C1/2·min1/2/mm) are prone to shrinkage defects.
Based on this analysis, I optimized the process to enhance the quality of the sand casting parts. The key modifications included adding chill blocks at strategic locations to increase cooling rates and extend the feeding range of risers, and replacing conventional risers with insulating sleeves risers to improve feeding efficiency. The chill blocks, made of cast iron, were placed in the thin-walled sections between the ribs and ends to promote directional solidification. The insulating risers reduce heat loss, maintaining a longer liquid state for effective feeding. The optimized layout was re-simulated to validate the improvements. The addition of chills alters the heat extraction rate, which can be described by the Fourier number: $$Fo = \frac{\alpha t}{L^2}$$ where $\alpha$ is thermal diffusivity, $t$ is time, and $L$ is characteristic length. This ensures faster solidification in targeted areas of the sand casting parts.
The simulation of the optimized process showed significant improvements. The filling process was smooth and complete within 12.7 s, meeting the requirement for fast pouring of steel sand casting parts. The solidification sequence became more orderly, with chills accelerating cooling in critical zones and the insulating risers remaining liquid longer. By 1,598 s, the last regions to solidify were successfully shifted into the risers, eliminating isolated liquid pockets in the sand casting parts. The defect prediction maps confirmed a substantial reduction in shrinkage porosity, with only minor defects remaining on the bottom surfaces, which could be easily repaired during machining. A comparative summary of defect volumes is provided in Table 3.
| Process | Predicted Shrinkage Volume (cm³) | Critical Defect Locations | Niyama Criterion Compliance (%) |
|---|---|---|---|
| Initial | ≈ 15.2 | Riser junctions, mid-sections | 65 |
| Optimized | ≈ 2.1 | Bottom surfaces only | 92 |
To verify the simulation results, the optimized process was implemented in actual production for these sand casting parts. The cast beams were inspected using ultrasonic testing according to MC2000 standards, and no significant internal defects were detected. Furthermore, samples from attached test blocks were analyzed for microstructure and mechanical properties. The average hardness was measured as 50.8 HRC, exceeding the required specifications. The metallographic structure, etched with 4% nitric alcohol solution, revealed a typical hypoeutectoid steel microstructure consisting of ferrite and pearlite, with some Widmanstätten morphology due to coarse as-cast grains and rapid cooling. Although Widmanstätten structure can reduce toughness, it can be eliminated through subsequent heat treatments like normalizing. This confirms that the optimized process yields high-quality sand casting parts with desirable properties.
The success of this optimization highlights the importance of numerical simulation in designing processes for sand casting parts. By integrating simulation into the workflow, I was able to identify defect-prone areas, test modifications virtually, and achieve a robust process without costly physical trials. The final process achieved a yield of 72%, demonstrating efficiency gains. For future work, I plan to explore advanced simulation features, such as coupled fluid-flow and stress analysis, to further enhance the performance of sand casting parts. Additionally, the principles applied here—such as using chills and insulating risers—can be generalized to other complex sand casting parts, contributing to broader advancements in casting technology.
In conclusion, this study underscores the value of numerical simulation for optimizing the manufacturing of sand casting parts. Through iterative simulation and process adjustments, I successfully reduced defects and improved the mechanical properties of cast steel beams. The methodology presented here—combining traditional design rules with modern simulation tools—offers a reliable pathway for producing high-integrity sand casting parts. As industries continue to demand lighter, stronger, and more reliable components, such approaches will be indispensable for advancing sand casting parts production. The integration of simulation not only saves time and resources but also ensures that sand casting parts meet the rigorous standards required in critical applications.
To further elaborate on the technical aspects, the solidification behavior of sand casting parts can be modeled using the following energy equation that accounts for latent heat release: $$\rho c_p \frac{\partial T}{\partial t} = \nabla \cdot (k \nabla T) + \rho L \frac{\partial f_s}{\partial t}$$ where $c_p$ is specific heat, $L$ is latent heat, and $f_s$ is solid fraction. This equation is solved numerically in ViewCast to predict temperature fields. For the sand casting parts in this study, the cooling curves at various locations were analyzed to ensure directional solidification toward the risers. The temperature gradient $G$ and cooling rate $\dot{T}$ are critical parameters; for effective feeding, $G$ should be high and $\dot{T}$ moderate. In the optimized process, the use of chills increased $G$ in thin sections, as calculated by: $$G = \frac{\Delta T}{d}$$ where $\Delta T$ is temperature difference and $d$ is distance. This helped maintain a positive temperature gradient toward the risers in the sand casting parts.
Moreover, the feeding capacity of risers for sand casting parts can be evaluated using the feeding distance formulas. For steel castings, the effective feeding distance ($L_f$) of a riser can be estimated as: $$L_f = 4.5 \sqrt{T} \cdot M$$ where $T$ is section thickness and $M$ is modulus. In the initial design, some areas of the sand casting parts exceeded this distance, leading to shrinkage. By adding chills, the effective feeding distance was extended by localizing cooling and creating favorable thermal gradients. This is a key strategy for large sand casting parts where riser placement is constrained.
The economic impact of optimizing sand casting parts should not be overlooked. By reducing defect rates, material waste is minimized, and productivity increases. For instance, the reduction in shrinkage volume from 15.2 cm³ to 2.1 cm³ per casting translates to significant savings over mass production runs. Additionally, the improved mechanical properties reduce the need for post-casting treatments, further cutting costs. These benefits make numerical simulation an essential investment for foundries producing high-value sand casting parts.
In summary, the journey from initial design to optimized process for these sand casting parts involved a blend of empirical knowledge and computational analysis. The iterative simulation approach allowed me to refine riser and chill designs effectively, ensuring that the final sand casting parts exhibit superior quality. As casting technologies evolve, I believe that simulation-driven design will become the standard for manufacturing complex sand casting parts, enabling faster innovation and higher reliability in diverse industrial applications.