Abstract
This paper presents a methodology for studying weld pool oscillation by measuring its oscillation frequencies using both the welding voltage signal and analysis of weld pool profile images. The intense brightness from the arc is reduced using the technique of shadowgraphy, and the images are obtained at 1000 fps with a high-speed CMOS camera. The geometry of the pool is viewed in profile and frequency spectra are obtained by fast Fourier transform by processing the images in MATLAB. The methodology was applied to analyse the oscillatory behaviour of the weld pool resulting from a pulsed gas metal arc welding process. Two different types of welding current pulse were tested: (a) the conventional trapezoidal pulse (with only one level of peak current) and (b) the trapezoidal pulse with the ‘detaching current’ (the welding current has a modified trapezoidal shape in which, at the end of the peak current time, the welding current is reduced to an intermediary level where it is maintained some time, after which it is further reduced to the background current level). The results show that it is possible to measure oscillation of the weld pool using this methodology, and that its measurement by images is more reliable than analysis of the voltage signal.
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