In the realm of automotive manufacturing, the production of engine cylinder heads through sand casting processes presents significant challenges due to the complex geometry and stringent performance requirements of these components. As a critical part that seals the combustion chamber and endures high thermal and mechanical loads, cylinder heads must be free from defects that could compromise their integrity. Among the common issues encountered in sand casting, shrinkage defects, particularly shrinkage holes, are prevalent in thick-walled sections and can lead to failures such as leakage. This study focuses on investigating the influence of key process parameters—pouring temperature and mold temperature—on the formation of shrinkage holes in cylinder heads produced via sand casting. Using advanced numerical simulation software, we aim to quantify these effects and provide insights for optimizing the casting process to minimize defects.
The sand casting method is widely employed for manufacturing cylinder heads due to its versatility and cost-effectiveness. However, the inherent complexities of the process, including variations in material properties and environmental conditions, often result in quality inconsistencies. In our research, we utilize the InteCAST CAE system, a powerful tool for simulating casting processes, to analyze how changes in pouring and mold temperatures affect shrinkage defect formation. By conducting a series of simulations across a range of temperatures, we seek to establish correlations that can guide practical improvements in sand casting operations.
To begin, we outline the materials and methods used in this study. The cylinder head castings are made from compacted graphite iron, specifically grade RU450, which is known for its excellent thermal conductivity and mechanical strength, making it suitable for high-performance engine applications. The molding sand consists of reclaimed sand mixed with bentonite, coal dust, and other additives, while the cores are produced using a cold-box process with silica sand or regenerated sand and cold-cure resins. The key process parameters under investigation include pouring temperature and mold temperature, with ranges set from 1360°C to 1400°C for pouring temperature and 20°C to 40°C for mold temperature. These ranges were selected based on typical industrial practices in sand casting to ensure relevance and applicability.
For the numerical simulations, we employed the InteCAST CAE software, which specializes in predicting shrinkage and porosity defects during the solidification phase of sand casting. The software’s gravity feeding module was utilized to model the formation of shrinkage holes, providing a quantitative assessment of defect severity. In the pre-processing stage, the three-dimensional models of the cylinder head, gating system, and risers were discretized into a uniform mesh to facilitate accurate computations. The meshing scheme is summarized in Table 1, detailing the total number of elements, element sizes, and other relevant parameters.
| Mesh Type | Total Elements | Casting Elements | Max Edge Length (mm) | Min Edge Length (mm) | Pouring Weight (kg) | Casting Weight (kg) | Yield Rate (%) |
|---|---|---|---|---|---|---|---|
| Uniform Mesh | 13,296,465 | 960,627 | 3.5 | 3.5 | 408 | 283 | 69.33 |
The experimental design involved 15 simulation runs, as detailed in Table 2, covering all combinations of pouring temperatures (1360°C, 1370°C, 1380°C, 1390°C, and 1400°C) and mold temperatures (20°C, 30°C, and 40°C). This full factorial approach allows for a comprehensive analysis of the main effects and interactions between these parameters in the context of sand casting. Each simulation was conducted under identical conditions to ensure consistency, with a focus on monitoring the number and location of shrinkage holes post-solidification.
| Simulation ID | Pouring Temperature (°C) | Mold Temperature (°C) |
|---|---|---|
| 1 | 1360 | 20 |
| 2 | 1370 | 20 |
| 3 | 1380 | 20 |
| 4 | 1390 | 20 |
| 5 | 1400 | 20 |
| 6 | 1360 | 30 |
| 7 | 1370 | 30 |
| 8 | 1380 | 30 |
| 9 | 1390 | 30 |
| 10 | 1400 | 30 |
| 11 | 1360 | 40 |
| 12 | 1370 | 40 |
| 13 | 1380 | 40 |
| 14 | 1390 | 40 |
| 15 | 1400 | 40 |
Moving to the results and analysis, the solidification simulation outputs revealed a sequential cooling pattern from the bottom to the top of the cylinder head, consistent with the use of a bottom-gating and top-riser system in sand casting. This pattern is critical for understanding how thermal gradients influence defect formation. The color temperature maps from the simulations illustrated the progression of solidification, highlighting areas prone to shrinkage due to slower cooling rates in thick sections.
The analysis of shrinkage holes showed that these defects predominantly occurred in the thick-walled regions of the cylinder head, where thermal contraction during solidification is most pronounced. The number of shrinkage holes varied significantly across the different temperature combinations, as summarized in Table 3. For instance, at a mold temperature of 20°C, the number of shrinkage holes decreased initially with increasing pouring temperature, reaching a minimum of 22 at 1370°C, before rising again at higher pouring temperatures. Similarly, at mold temperatures of 30°C and 40°C, the lowest shrinkage counts were observed at the lower end of the pouring temperature range (1360°C), with values of 24 and 22, respectively. This indicates that optimal temperature settings can mitigate defect formation in sand casting processes.
| Mold Temperature (°C) | Pouring Temperature (°C) | Number of Shrinkage Holes |
|---|---|---|
| 20 | 1360 | 28 |
| 1370 | 22 | |
| 1380 | 25 | |
| 1390 | 27 | |
| 1400 | 30 | |
| 30 | 1360 | 24 |
| 1370 | 26 | |
| 1380 | 28 | |
| 1390 | 29 | |
| 1400 | 31 | |
| 40 | 1360 | 22 |
| 1370 | 24 | |
| 1380 | 26 | |
| 1390 | 28 | |
| 1400 | 30 |
To quantify the relationships between the process parameters and shrinkage defects, we performed a correlation analysis using Pearson’s correlation coefficient. The formula for the correlation coefficient \( r \) between two variables \( X \) (e.g., pouring temperature) and \( Y \) (e.g., number of shrinkage holes) is given by:
$$ r = \frac{\text{Cov}(X, Y)}{\sqrt{\text{Var}[X] \cdot \text{Var}[Y]}} $$
where \( \text{Cov}(X, Y) \) is the covariance, and \( \text{Var}[X] \) and \( \text{Var}[Y] \) are the variances of \( X \) and \( Y \), respectively. Applying this to our sand casting data, we calculated the correlation coefficients for different scenarios. For a mold temperature of 20°C, the correlation between pouring temperature and shrinkage hole count was \( r = 0.7251 \), indicating a moderate positive relationship. At mold temperatures of 30°C and 40°C, the correlations were stronger, with \( r = 0.9199 \) and \( r = 0.9105 \), respectively, suggesting that higher pouring temperatures tend to increase shrinkage defects in these conditions. Conversely, when examining the effect of mold temperature at fixed pouring temperatures, the correlations were generally weaker or negligible. For example, at a pouring temperature of 1360°C, the correlation was \( r = -0.9934 \), showing a strong negative relationship, while at other pouring temperatures (e.g., 1370°C and 1380°C), the variance in shrinkage counts was zero, implying no correlation. This analysis underscores that pouring temperature has a more pronounced impact on shrinkage defects compared to mold temperature in sand casting.
Further sensitivity analysis reinforced these findings. The changes in shrinkage hole numbers with respect to pouring temperature were more consistent and significant across all mold temperature levels, whereas variations in mold temperature had a limited effect, especially at higher pouring temperatures (1370°C to 1400°C). This can be expressed mathematically by considering the sensitivity coefficient \( S \), defined as the partial derivative of the defect count \( D \) with respect to a parameter \( P \) (e.g., pouring temperature \( T_p \) or mold temperature \( T_m \)):
$$ S_{T_p} = \frac{\partial D}{\partial T_p}, \quad S_{T_m} = \frac{\partial D}{\partial T_m} $$
From our data, the magnitude of \( S_{T_p} \) was generally larger than that of \( S_{T_m} \), confirming that shrinkage defects in sand casting are more sensitive to changes in pouring temperature. For instance, at a mold temperature of 30°C, increasing the pouring temperature from 1360°C to 1400°C resulted in a steady rise in shrinkage holes, with an average sensitivity of approximately 1.75 holes per 10°C increase. In contrast, varying the mold temperature from 20°C to 40°C at a fixed pouring temperature of 1400°C led to minimal changes, with a sensitivity close to zero.
In conclusion, this study demonstrates that optimizing pouring temperature is crucial for reducing shrinkage defects in the sand casting of cylinder heads. The use of numerical simulation software like InteCAST CAE provides valuable insights into the solidification behavior and defect formation, enabling manufacturers to fine-tune process parameters for improved quality. Based on our findings, we recommend maintaining pouring temperatures at the lower end of the range (e.g., 1360°C to 1370°C) and ensuring consistent mold temperatures to minimize shrinkage holes. Future work could explore additional factors in sand casting, such as gating design and alloy composition, to further enhance defect prediction and control. Overall, the integration of CAE simulations into the sand casting workflow holds great potential for advancing the reliability and efficiency of automotive component production.