Modeling and control of a counter-gravity casting machine

Counter-gravity casting is a process where molten metal is forced into the casting cavity against gravity. It aims at increasing the energy efficiency of the casting process. It also offers an opportunity of introducing automatic control into the process by changing the pressure under which the metal is forced into the mold cavity. This paper describes a new method of multi-variable control of the counter-gravity casting machine. System modeling of the counter-gravity machine reveals that it is a nonlinear system. The machine has been modeled as a set of linear systems corresponding to twelve regions of operation: six for increasing vacuum and six for decreasing vacuum. The models are parameterized based on the stem valve positions and the initial pressure in the casting vessel. The models are validated through actual data collected from the counter-gravity machine. An automatic controller is designed for control of the machine operation throughout the different regions. The full scheme of the controlled simulated machine consists of a valve selector and a gain scheduled controller based on the operating conditions of the machine. Simulations are provided to show the operation of the designed controller.