The use of cold liquid metal modeling exemplified at the magnetic field control of the aluminum 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. Special attention is given on model experiments using the low melting point eutectic melt GaInSn. Ultrasonic Doppler velocimetry was applied to carry out detailed velocity measurements in the model. In addition, high-speed video camera observation of the incoming melt front was performed revealing the key importance of the initial flow structure for the final casting product quality.
Based on this modelling knowledge, a DC magnetic field has been developed in order to control the mould filling process. This DC field has been tested under industrial conditions. The primary action of the magnetic field, i.e. the reduction of the velocity peaks at the beginning of the process, was clearly demonstrated. 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. Eventually, a remarkable diminishment of defects in the casting products was achieved. A multitude of investment casting units have been produced showing a significant improvement of the casting properties due to the magnetic field control of the filling process.