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.

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In the former reports, it was discussed that a TIG arc behavior was controlled by a CO₂ laser when the traveling speed of a base metal was fast and the arc length was long. In this case, the bead width was different, although the experimental conditions were same except the traveling direction of the base metal. In this report, the behavior of the TIG arc only was investigated using high speed video images when the traveling direction was changed. Furthermore, the reasonable spot of CO₂ laser was examined for stabilization of the arc. In this case, the backward direction meant that the traveling direction was same as the direction of a tungsten electrode. The opposite direction was called the forward direction. The main experimental conditions were as follows. The TIG arc current, 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), 150 mm/s, 1×10^-3 m³/s and 15 mm, respectively. When the base metal moved to the backward direction, a straight arc column bent smoothly at the point which was near to the base metal, and moved straightly to an anode spot. This spot existed in the circular molten pool and the shape of the pool did not changed. In this case, the bending point scarcely changed its position. On the other hand, in the case of the forward direction, the shape of the bending arc column, the position of the bending point and the shape of the melted part were different from ones of the backward direction. It was considered that arc stiffness at the bending point of the backward direction arc and preheat effect of arc plasma were less than the ones of the forward direction arc.

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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 CO₂ laser beam was scanned by a beam oscillator, and the shapes of melted parts of the base metal were investigated. Furthermore, the behavior of a TIG arc with a scanning CO₂ laser beam was investigated by high speed video-pictures. The main experimental conditions were as follows. The TIG arc current, the laser output, the scanning frequency and the scanning width of a laser beam, the traveling speed of a SUS304 base metal and the distance between the base metal and a tungsten electrode were 100 A (DCEN), 2 kw, 25 Hz, 8 mm, 20 mm/s and 15 mm, respectively.
As a result, the arc could be controlled by the scanning laser beam, and wide and shallow beads were made using this method under the suitable conditions. Therefore, it was found that the arc with scanning laser beam is excellent as heat source for surface treatment.
On the other hand, the arc voltage and the range of its change decreased according as the scanning frequency increased from 5 Hz to 20 Hz. According to the observation using high speed video-pictures, the arc went straight forwards from the electrode and bent toward the scanning laser plume, and the bending point of the arc became increasingly far from the tip of the electrode when the scanning frequency increased. It would be considered that the arc voltage was affected by the bending point of the arc column because of the arc stiffness.

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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.

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In order to develop a fast surface treatment method or a fast welding method using an electric arc with a laser beam, stabilizing effects of a CO₂ laser on a TIG arc were investigated. A TIG arc makes discontinuous molten pools even when the travelling speed of a base metal is high and the distance between a base metal and a tungsten electrode is large. In such a case, the behavior of an arc usually becomes unstable and the arc voltage changes in the range of 5-8 V. Whereas, the arc behavior became stable by using a CO₂ laser beam simultaneously, and good continuous weld beads were made on conditions that the TIG arc current, the laser output, the distance between a SUS304 base metal and a tungsten electrode, and the travelling speed of a base metal were 100 A (DCEN), 2 kW, 15 mm and 200 mm/s, respectively.
It was found that the anode spot was fixed on the molten pool formed by the laser beam, and, the molten pool, the laser plume and the metallic vapor affected the stabilization of the path of a TIG arc and its voltage. Therefore, it is effective to controle a long arc by a laser that the beam irradiates near the tip of the arc where the arc stiffness becomes weak.

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