Fig. 4. Illustrations show that the porosity defects on the middle-plane longitudinal cross section of the steel casting: a) porosity defects on the test casting; b) predicted microporosity by the rapid solidification model; and c) predicted microporosity by the first principles model.
weighed 301.6 lbs. (136.8 kg) and measured 28.1 x 8.7 x 9.3 in. (0.715 x 0.22 x 0.235 m). Te core was a polyurethane cold
box silica sand core. To simulate an extreme case, no venting was allowed at the print surfaces. Te grain size of the core was 180 µm, and the binder weight fraction was 1%. Te core and the mold had the same thermal con- ductivity and density-specific heat, which were temperature dependent and shown in Figs. 2 and 3. The meshed domain was 43.3 x 25.5 x 23.6 in. (1.1 x 0.65 x 0.6 m). The simulations were set to finish after all metal was solidified. To test the correctness of the param- eter settings, the simulations were first run with a rapid solidification shrinkage model. Te porosity defects in the
three main porosity regions on the middle-plane longitudinal cross section of the casting are shown in Fig. 4. Te calculated result of the rapid solidification shrinkage model is shown in Fig. 4b. As can be seen from the figure, the model provides qualitatively satisfactory results for regions A and B. The same parameters were used
to run full simulations with the first principles shrinkage model and core gas model. For the rapid solidification shrinkage model, total solidification time was 6,040 seconds, whereas the first prin- ciples model took 2,500 seconds. The first principles model took less time because the liquid metal convection transfers heat more efficiently. For castings with large cross sections, convective heat transfer has to be considered. If the
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