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Numerical modeling of gravity die casting processes with solidification present during filling
Hunt, Spencer J.
Hunt, Spencer J.
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2025
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Computational modeling of U-10wt.%Mo (U-10Mo) and Al-5wt.%Si (Al-5Si) was performed, simulating alloy casting mold filling and solidification with FLOW-3D CAST®’s gravity die casting workspace. Simulations and instrumented castings in the literature have shown casting into a thin plate, monolithic mold cavity using top-gated gravity die casting produces an undesirable temperature gradient in the fluid after filling, which results in porosity formation. Increasing the pouring temperature (TPour) and/or mold temperature (TMold) to reduce porosity formation results in long solidification times, which can cause other casting issues. In the present study, a mold was designed to reproduce simulated fluid flows, solidification evolution, and porosity distributions observed in previous work. TPour, TMold, and filling time (tFill) were varied to determine the sensitivity of these parameters on predicted porosity distributions and solidification times of thin U-10Mo plate castings. Between TPour and TMold, TPour has a greater influence on porosity formation, while TMold has a greater influence on solidification time for the temperature ranges investigated. These results suggest that to decrease porosity while minimizing solidification time, TPour should be increased preferentially over TMold. Reducing tFill reduces the extent of solidification during filling and subsequent porosity formation without increasing solidification time, potentially providing an effective method for minimizing defects associated with the interaction of convection and solidification during filling.
To provide insights into the modeling of defect formation using commercial computational fluid dynamics (CFD) packages, instrumented castings of Al-5Si were performed to compare with model predictions, including temperature evolution in the fluid and defect formations (e.g., porosity) during filling. Applying interfacial heat transfer coefficients (IHTC) from the gravity die casting literature results in an underestimation of the heat transfer between the fluid and mold, preventing accurate predictions of filling-related defects observed in experiments. Increasing the IHTC improves predictions of temperatures and cooling rates observed during casting, but even so, small discrepancies between the modeling and experiments prevent accurate defect predictions during filling. In particular, porosity predictions in the model do not match well with experiments, which is likely due to other mechanisms not considered here such as solid feeding and oxide entrapment. Future casting models should pay special consideration to the IHTC values, as these values determine the amount of solidification that occurs during filling and subsequent defect formations. To improve porosity predictions, future models should include additional porosity formation mechanisms (e.g., oxide entrapment).
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