Development and application of weld pool oscillation sensing for front-face penetration control of gas tungsten arc welding

Control of penetration in welding has received considerable attention from researchers over the last few years. Ideally, a penetration control system should be robust and reliable, capable of operating with a variety of materials over a wide range of welding parameters, require access only from the front face of the weld, and should not need extensive additional equipment in the vacinity of the welding torch. The system which at present seems to come closest to meeting these requirements is the generation and detection of oscillations in the weld pool. Weld pool oscillations were shown to be related to weld pool size more than 10 years ago and since then a number of researchers have utilized the pool oscillation phenomenon to monitor the state of penetration during gas tungsten arc welding (GTAW). The technique involves inducing oscillations in the weld pool by pulsing the welding current to a higher level for a few milliseconds. A series of experiments were conducted on stainless steel sheet from 0.015{emdash}0.120 in. thickness and two methods of detecting oscillations were compared. Arc voltage can be used to monitor oscillations which cause changes in arc length and hence in arc voltage. However, monitoring of arc light hasmore » been shown in this work to give better signal-to-noise ratios: the length of the plasma column changes as the pool oscillates and provides a sensitive technique to detect oscillations. Recent efforts at EWI have concentrated on the development of penetration control for practical applications. A computer control system has been developed which allows simultaneous monitoring of the voltage, light, and sound signals. possible mechanisms for changes in signal-to-noise ratio in the three detection systems are discussed.« less