Linear-Quadratic-Gaussian (LQG) Controller for Liquid Pool Profile in Vacuum Arc Remelting

Process control for vacuum arc remelting is a challenging and interesting problem that has captured the attention of the metallurgy and control communities for decades. The main goal of the process is the production of homogeneous ingots with an appropriate chemistry, physical size, and grain structure. Traditionally, this process has been controlled by applying a desired current to the furnace expecting to control the solidification profile and, therefore, the microstructure of the ingot. It is believed that the final ingot grain microstructure is strongly influenced by the molten metal pool profile. Thus, if pool profile was controlled during the melt then defect-free microstructures would be obtained. However, there was no controller capable of performing such a task. The recent development of a reduced-order model of solidification in vacuum arc remelting allowed the design of the first pool profile controller. A Linear-Quadratic-Gaussian (LQG) controller was designed to account for inaccuracies in the reduced-order model and the measurements. Simulation and experimental results show the accurate performance of the controller.