Infrared sensing of full penetration state in gas tungsten arc welding

The objective of this study is to present an applicable top-side infrared sensing technique for the prospective closed-loop control of weld penetration in gas tungsten arc welding (GTAW). A model is developed to calculate the full penetration state, which is specified by the back-side bead width, from the sensed infrared images. To ensure the model validity in the prospective closed-loop control, the experiments, which generate the data for the model identification, are conducted under the experimental conditions that will be encountered during practical closed-loop control of the welding process. The heat transfer condition and electrode tip angle may vary during welding or from case to case. Also, the control variables which are used to adjust the weld process in order to reach the required weld penetration will also change. In many cases, the current can be employed as an on-line adjustable control variable because of the implementation ease, when the welding speed and arc length are maintained at the preset values. Thus, different currents, workpiece sizes, and electrode tip angles are arranged in the experiments to emulate the possible current adjustments, case to case heat transfer variations, and electrode wear. The infrared characteristics of the effects of these parameters are extracted to regress the full penetration state. Finally, the back-side weld width (the full penetration state) is calculated using the resultant model from the sensed infrared data.