シールドガス組成制御によるGMA溶接プロセスの開発

—超狭開先GMA溶接プロセスの開発(第3報)—

抄録

In previous reports, an ultra-narrow gap CO₂ gas metal arc welding process has been developed in order to produce excellent welded joints. In the ultra-narrow gap (less than 5 mm gap) welding process, as the welding wire melting behavior was controlled by low frequency pulsated arc current waveform, the arc generating at the wire tip was widely oscillated in the direction of thickness and a good weld bead with large throat thickness was formed. In such a higher efficient welding process, the strong arc force of CO₂ arc is essential to obtain sound beads without lack of fusion at a groove bottom, however, the oxygen content of weld metal in CO₂ arc welding has to be reduced to obtain high-toughness at weld metal. In this report, a newly welding process is proposed in which an arc is widely oscillated along groove walls and oxygen content of welded metal is reduced as periodically controlling composition of CO₂ gas in shielding gas. As an arc length between the wire tip and groove wall is held constant in ultra-narrow I type gap joint, arc current at stable operating point of CO₂ arc essentially decreases less than that at stable operating point of Ar arc in constant potential characteristics of power source. It was confirmed from the numerical simulations on both wire melting and electric welding circuit that pulsated current waveform was produced as periodically alternating CO₂ arc with MIG arc. Using the developed welding torch locally introducing CO₂ gas into Ar+2%O₂ shielding gas, the welding was carried out under V-type groove with less than 30 degree in the bevel angle. It was shown that the arc was widely oscillated along V groove walls and sound bead was formed in one side welding. Furthermore, it was confirmed that the oxygen content of weld metal in the proposed process was reduced to the level of that in MIG arc welding, and absorbed energy of weld metal was the same level as the MIG arc welding.