REAL-TIME CONTROL OF THE PLASMA-ARC CUTTING PROCESS BY USING INTENSITY MEASUREMENTS OF EJECTED PLASMA

Abstract

In the plasma arc cutting process, faster cutting speeds are achievable on up to 1-in. (25-mm) thick plate when compared with the oxyfuel gas cutting process, since the plasma arc supplies a high energy density. Therefore, automatic cutting machines with a NC or CNC system are often used, and in-process monitoring and control could be used to improve the cut quality and also to overcome the difficulties that may lie in varying cutting conditions. The cut quality in plasma arc cutting can be evaluated using various parameters. In this study, the cut thickness and dross attached at the bottom cut edge were considered for the process evaluation. In order to improve the cut quality in plasma arc cutting of plates with varying thicknesses, the intensity of the plasma arc exiting the bottom of the plate was measured using a photo darlington sensor, and the cutting speed was controlled to maintain the uniform intensity of the ejected plasma arc. As a result, with a simple speed control, the amount of the attached dross was substantially reduced, and a plate with gradually varying thicknesses was cut successfully. But for cutting of plates with sharply varying thicknesses, a more sophisticated control scheme would be required.