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Table 1. Increase in Yield Strength Relative to the Baseline and the Corresponding Performance Index for the Flow Rates


nifi cant decrease in elongation (Fig. 6). T e cooling rate during dendrite formation increased by about 100% at locations near the helium supply. T e average SDAS in the helium- assisted castings at a fl ow rate of 4 L/minute was 46 µm compared to 60 µm in the baseline castings (Fig. 7). Surface fi nish was not aff ected. According to Saleem and


Makhlouf, the test results showed that beyond a certain helium fl ow rate, the benefi ts began to show diminishing returns, so they defi ned a “performance index” as a ratio of the increase in yield strength to the cost penalty of using helium (Table 1). T ey found that a 2.6 L/minute fl ow rate (parallel to each face) was the optimum helium fl ow rate that maximizes the performance index. During the testing and analysis,


the researchers recorded a thermal gradient in the parts cast via helium assisted sand casting with parallel fl ow. T e gradient was insignifi cant in the small plates but might be more signifi cant in larger parts. Sal- eem and Makhlouf recommend in- troducing helium at more than one location, which can be determined with casting process modeling. Or, helium could be used for localized cooling or to induce directional solidifi cation, replacing chills to simplify the mold design. According to the authors of


“Helium-Assisted Sand Casting,” a cost analysis not discussed in the paper showed that helium-assisted sand casting in the parallel-flow mode compares favorably to tra- ditional sand casting up to a flow rate of 4 L/minute. 


T is article is based on the paper “Helium-Assisted Sand Casting,” which fi rst appeared in the International Journal of Metalcasting.


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Jan/Feb 2013 | METAL CASTING DESIGN & PURCHASING | 29


Fig. 7. Secondary dendrite arm spacing decreased with helium-assisted sand casting via the parallel-fl ow mode.


Helium fl ow rate (parallel to each face) % Increase in yield strength* Performance Index 1


4 8


*With regard to the baseline casting


0.085 0.344 0.264


0.085 0.086 0.033


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