Abstract Scope |
Pipes are sometimes welded in the horizontal (2G) position. Its weld penetration sensing and control for critical application is of necessity. In the present work, the pulsed gas tungsten arc welding (GTAW-P) with filler wire, one of the high quality welding methods, is employed to assure the weld quality in 2G position. Pulsed current in the process, the introduction of filler wire and the welding position make the weld penetration sensing difficult. In the welding process, the torch was fixed in one position to observe the weld pool dynamic from partial penetration to burn through with the expectation to find a characteristic signal representing weld penetration status; and the filler wire was only fed for 1 s to avoid over accumulated molten metal and to eliminate the effect of filler metal on the volume of weld pool that affects the sensing signal. The weld pool dynamics was recorded by a high speed camera, which imaged the contours of molten pool from the top view, and simultaneously the welding parameters (welding current and arc voltage herein) were collected. Experimental results showed that the weld pool experiences the process that the amplitude of front weld pool surface became larger with the continuously feeding of filler wire, when the pipe is partial penetrated; at the moment that the pipe is penetrated, the front weld pool surface collapses, and backside weld pool surface rises suddenly; with further heating, the front weld pool surface springs back with the height of backside weld pool surface decreasing; with the increase in the backside weld width, both heights of the front and backside weld pool surface decreases, at which time the fluctuation of the front molten pool surface increased during the base current period; over penetration, with large volume of weld pool, results in that the oscillation amplitude reaches the maximum but the frequency drops; and then the workpiece is burnt through. Since the front weld pool surface dynamics can be represented by the arc voltage signal to some extent, arc voltage dynamics is proposed to control the backside width and backside reinforcement in 2G position in the GTAW-P process of pipe, as per the relationship between the front and backside weld pool surface behaviors from the foregoing weld pool growth process. |