Alternative Real-Time Control Strategies and Sensing Requirements for Improving Thermal Spray Performance

The plasma spray process is characterized by variations that occur over multiple time-scales and events such as over the life-time of the electrodes, changing of electrode sets, arc instabilities, and torch power cycling.  As a result, there can be large variations in coating thickness from part-to-part and even for a large single part.  In order to reduce the effects of these sources of process variation, a number of alternative control strategies have been proposed.  This paper discusses the requirements for implementing real-time control, and evaluates the performance of several alternative strategies in terms of maintaining desired coating thickness. This paper will also review the sensor requirements for implementing real-time control as well as the performance of several alterative sensing schemes in terms of how well they correlate to specific control objectives.