Classical Control of Gas Metal Arc Welding

This paper presents results using classical control techniques to regulate the output of the gas metal arc welding process (GMAW). Using data obtained from open-loop step response tests, a linear, multivariable, lumped-parameter model of the process is derived. This model is used to design first a single-input, single-output controller for current and then a multi-loop controller to simultaneously control current and measured arc voltage to desired setpoints. The multi-loop controller is designed using the relative gain array, which suggests loop pairings that match wire feed speed with current and open-circuit voltage with measured arc voltage. Experimental results, including a disturbance rejection test involving a step change in contact tube-to-workpiece distance, verify the effectiveness of the controller designs.