In the first report, stabilizing effects of a CO2 laser on a TIG arc were discussed from the arc voltage. It was made evident that the unstable arc which formed discontinuous weld beads was stabilized and good beads were made with the laser beam. In such a case, the laser plume played the role as a path of electrons, and the anode spots of the arc were formed around the hot spot by the laser beam.
In this report, the effect of Ar gas flow rate on shapes of weld bead sections will be investigated. In the case of the conditions that the TIG arc current, the quasi-single mode laser output, the traveling speed of a base metal and the distance between a SUS304 base metal and a tungsten electrode were 100 A (DCEN), 2 kW, 150 mm/s and 15 mm, respectively, the beads width increased with the Ar shielding gas whose flow rate was from 0.67 × 10-3 to 1.33 × 10-3 m3/s. When the gas flow rate was 1.33 × 10-3 m3/s, the value of the ratio of beads width by the arc with the laser to ones by the laser only was 2.15. On the other hand, the penetration depth increased 22% under the same conditions. The arc voltage became high when the gas flow rate was large. The same phenomena were recognized under the multi mode laser.
When the base metal-electrode distance and the gas flow rate was large, the arc path became long and the arc column was bent easily. Therefore, the anode spot rolled from side to side of the laser spot and the bead width was increased by the arc. In such a case, the penetration depth was scarcely increased compared with the one by the laser only. When the gas flow rate was large, the absorption coefficient of the laser increased, because the melted surface was irradiated with the laser beam.
As the result, it would be considered that the role of the arc in this surface treatment process is extension of the beads width, and the penetration depth is increased by the laser.