Electromagnetic flow control in the process of aluminium investment casting

The mould filling process of aluminium investment casting consists basically of the flow in a U-bend showing a high pouring velocity at the beginning and decreasing velocity values during the course of the process. The high velocities during the starting phase are supposed to cause distinct problems like bubble or inclusion entrapment.
We present results on the design and application of a DC magnetic field to control the pouring velocity. Numerical 3d transient calculations were performed to simulate the filling process and the effect of the magnetic field. In parallel, model experiments with a plexiglas model have been performed using the low melting eutectic GaInSn. Ultrasonic Doppler velocimetry was applied to carry out detailed velocity measurements in the model. These measurements served for the validation of the numerical calculations, thus allowing to scale up the simulations to the realistic aluminium casting process.
The developed DC field system has been tested under industrial conditions. The amplitude of the DC field was tuned during the process as the braking action is only needed during the first part of the process. In this way, a clear reduction of the peak velocities is obtained without a significant prolongation of the overall filling time. A multitude of investment casting units have been produced showing a significant diminishment of defects due to the magnetic field control of the pouring process.