Strategies for Re-Heating Steel Billets for Thixoforming
Inductive re-heating of billets is the state-of-the-art method to enable the desired liquid fraction for thixoforming. In laboratory experiments the temperature might be directly controlled since it is usually possible to apply thermocouples for temperature measurements. Due to technical restrictions temperature measurements especially in the interior of a billet are difficult in industrial heating processes. For this reason, thixoforming billets are heated without temperature monitoring by using proven heating functions. Such functions are usually obtained by trial-and-error or on the basis of FEA simulations. In both cases exhaustive experimental work is usually necessary. Moreover, FEA simulations require thermo-physical material data that is difficult to obtain for industrial relevant heating processes. In this paper an alternative method of experimentally obtaining optimized heating functions by using a fuzzy logic controller is introduced. Under steady-state environmental conditions this method allows a quick and reproducible re-heating. The main advantages of the fuzzy logic based approach are that no specific material data is required, system specific properties such as the efficiency have not be explicitly determined and that the practical implementation could be realized with a minimum of experimental work.
G. Hirt, A. Rassili, A. Bührig-Polaczek
B. A. Behrens et al., "Strategies for Re-Heating Steel Billets for Thixoforming", Solid State Phenomena, Vols. 141-143, pp. 121-126, 2008