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Penetration characteristics in YAG laser and TIG arc hybrid welding, and arc and plasma /plume behaviour during welding. Welding phenomena in hybrid welding using YAG laser and TIG arc (First Report)

The hybrid welding process, which combines both laser and arc, has received much attention in recent years as a high speed/highly efficient/high quality welding process which compensates drawbacks of the individual welding processes. A range of advantages has been reported to date, such as an increase in the groove gap tolerance, porosity reduction and arc stability in addition to an increase in the penetration depth and an increase in the welding speed. The YAG laser is capable of transmission using optical fibre and a marked increase in high power has become possible in recent years; however, for the use of this device, there are few detailed reports concerning the effects of welding parameters upon penetration, of the correlation of arc behaviour with melting characteristics or of detailed investigation on the fabrication process. For example, Beyer and others explain that the arc penetrates the inside of the keyhole and reaches the tip zone so the penetration increases not only at the upper zone of the weld but also at the root during hybrid welding using a YAG laser and a TIG arc; however, there are no examples of reports confirming this experimentally. Furthermore, Abe and others reported that, during hybrid welding with a CO 2 laser and a MIG, the distance between the laser and the arc affects consequential molten pool formation position due to each, the arc extreme point position, the penetration depth and the initiation of weld defects. It has not yet been confirmed whether the above can be applied to hybrid welding using a TIG arc combined with a YAG laser. Accordingly, in this study, welding was carried out upon austenitic stainless steel with a YAG laser alone, a TIG arc alone and also hybrid welding where the TIG arc was in the lead and where the laser was in the lead; the penetration characteristics, propensity for porosity formation and welding phenomena of each welding process were compared and studied. First, hybrid welding was carried out with varied range of parameters and the effects of the laser power, arc current, defocused distance and distance between the laser and arc upon the penetration characteristics and porosity formation were studied. The arc and plasma/plume behaviour was observed using CCD and high speed cameras and the position where the arc was concentrated, the dispersion and refraction of YAG laser beam and the effects of arc upon absorption were studied. The reason for the employment of a TIG arc welding source without a filler wire was to avoid the complicated welding phenomena.