Computational studies on the design of an electromagnetic pump for the process of aluminum investment casting

The mould filling process of aluminum investment casting consists basically of the liquid metal flow in a U-bend. It shows a high pouring velocity at the beginning and decreasing flow velocity values during the course of the process. The main problem is the occurrence of large velocity values at the beginning of the casting process, leading to an accumulated generation of vortices inside the pouring channel. A high rate of turbulence in the flow is supposed to entail the transported impurities, oxides or gas bubbles from the walls and the free surface, respectively, into the bulk of the casting patterns. As a result, the mechanical properties of the casting products are deteriorated.
We present results on the design and application of electromagnetic pumps to control the velocity of the aluminum melt during the pouring process. The induced electromagnetic force in the melt caused by the coil system were calculated using the commercial finite-element code OPERA-3d (Vector Fields Ltd.). The free surface problem which occurs in the riser of the casting unit was taken into account by a Volume-of-Fluids Method. Three-dimensional transient calculations using the commercial finite-element code FIDAP (FLUENT Inc.) were carried out for a simplified model system. Parallel to the simulations model experiments have been performed using the low melting eutectic GaInSn.
The casting unit was modeled by a perspex model [1], which also allows the monitoring of the filling process. Ultrasonic Doppler velocimetry measurements were applied in the model in order to validate the numerical calculations [2]. A comparison between numerical and experimental results showed an excellent agreement.
The main goal of this study is the optimization of the pump design depending on the geometry of the coil system in oder to achieve the best possible homogeneity in the electromagnetic force distribution with an integral flow rate of sufficient strength. Inhomogeneities in the force distribution can lead to undesirable fluid vortices in the melt, which on this part can induce a detriment of the material properties after solidification.

References

[1] A. Cramer, S. Eckert, V. Galindo, G. Gerbeth, W. Willers, W. Witke,
Liquid metal model experiments on casting and solidification processes
Journal of Materials Science 39 (2004) 7285-7294
[2] S. Eckert, G. Gerbeth, Th. Gundrum, F. Stefani, W. Witke,
New approaches to determine the velocity field in metallic melts,
Proceedings of the 4th Int. Conference on Electromagnetic Processing of
Materials (EPM 2003), Lyon (France), October 14-17, 2003, pp. 601-608