Thixoforming : Semi-solid Metal Processing

382j 10 Thixoforging and Rheoforging of Steel and Aluminium Alloys
Figure 10.7 Experimental results with pyrometer control, surface
temperature and power of the converter over time.
induced into the billet. The steady-state temperature shows a difference between the
surface and the axis temperature. The assumption that the energy is only fed into the
outer scale yields this deviation. Furthermore, the material data were not adjusted
exactly. However, taking into consideration that open-loop control will always have
some deviations, the results achieved are very good. Further improvements of the
results could be obtained by using a model-based controller for the converter.
Additionally, optimization could be used to adjust the material properties [30]. In
order to reduce the deviation between the inner and outer temperatures of the billet, it
could be considered in the open-loop control that the energy is not only fed into the
Figure 10.8 Experimental results with flatness-based control, desired and measured coil current.