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Improved control of smelt conditions and solidification for precisi on casting of non-ferrous metals

Exploitable results

Automatic monitoring and controlling of the smelt state in the casting process and of the solidification of the castings is important for all kinds of casting processes especially for precision castings of materials with high melting temperature. Due to the reactivity of the smelt and its interactions with the crucible material the melting time becomes an important process parameter influencing significantly the quality of the casting. The following results can be concluded: 1. The signal of power and the power describing measurements like voltage-or current signals showed very small changes during the melting process especially only at NRUs machine. Hence these signals could not be used in an easy way for smelt condition monitoring. Separating the dynamic part of the signal and its amplification could lead to a process, but this was not realised within the project. 2. Pre-calculation of the time needed for complete melting at a known power input and mass to be molten can be a rough mark for defining the start of casting and should be used to increase the reliability of the system. 3. Acoustic measurements showed changes in the signal especially caused by the movement of the solid inside the growing liquid phase (friction process and striking walls). This behaviour led to different changes in the signal. The low frequency range (vibration) was characterised by peaks and in most cases by increasing the signal level (up to 10 %) whereas the high frequency range (Acoustic Emission) mainly represents the power input and also in most cases showed a small change in the signals (increase or decrease of the signals and in some cases peaks). All these signals were not sharp enough to detect the best moment for casting. Increasing the sensitivity of the system reached limits due to the influence of the noise produced by the power input. 4. The application of optical methods showed results which could be used for definition and recognition of the complete smelt. 5. The metallo-graphical, mechanical and structural investigations showed no significant differences in the properties compared with the normal casting process checked visually and a certain degree of under heating (incomplete melting) on the one hand and a certain degree of overheating the smelt on the other hand. 6. A monitoring strategy using these sensors was derived and applied to the different casting machines and successful tested.

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