Investigation of temperature control parameters for inductively heated semi-solid light alloys using infrared imaging and inverse heat conduction
In semi-solid die-casting, a metallic billet is first heated in an induction furnace until it reaches a semi-solid state (partially liquid and partially solid). Then, it is injected into a die and kept there until it is solidified. Subsequently, the die opens, the part is ejected and the cycle starts again. The liquid-solid fraction and its spatial distribution within the billet at the end of the heating phase are of prime importance for the success of the process and the quality of the final product. These parameters are strongly correlated with temperature gradients within the billet and their evolution in time through the heating cycle. There is presently no inspection method that could reasonably be used to control the billet temperature in a production environment. In this work, we investigate the suitability of using infrared thermography to meet the heating requirements. With this technique, it is possible to non-intrusively monitor the temperature distribution on the entire surface of the billet and to obtain information on how thermal energy is dissipated. Moreover, with the combination of surface infrared measurements and inverse heat conduction formalism, it is also possible to recover some information about the temperature distribution inside the billet. Effects of some process operating conditions such as heating power magnitude, power input cycles, location of the billet inside the induction coil, and the coil overhang are considered and discussed.