In the first report, stabilizing effects of a CO2 laser on a TIG arc behavior were discussed from the point of the arc voltage and of the interaction between the arc and the laser plume.
In this report, the TIG arc behavior was investigated using high speed video images when the traveling direction of the base metal was changed. In this case, the backward direction meant that the moving direction of the base metal was same as the direction of a tungsten electrode, and in the case of the forward direction, the metal moved to the opposite direction. The main experimental conditions were as follows. The TIG arc current, the laser output, the traveling speed of a SUS304 base metal, Ar gas flow rate and the distance between the base metal and a tungsten electrode were 100 A (DCEN), 2 kw, 150 mm/s, 1×10-3 m3/s and 15 mm, respectively.
In the case of the backward direction, the bead width was smaller than one which was formed under the same experimental conditions except the traveling direction of the base metal. In this case, the temperature of the base metal remained normal in front of the combined heat source of the laser and the arc, and rose rapidly just before the heat source. In the case of the forward direction, the temperature rose slowly at the far point from the heat source and rapidly at the near point of it. Furthermore, two or three bonds were observed in the beads. On the other hand, it was appeared that anode spots were observed mainly in the area of the laser spot, and sometimes on the bead at the same time using high speed video images.
As a result, the bead width under the backward direction was narrower than the forward one, and the TIG arc melted not only the area arround the laser spot on the base metal but also the solidified bead.