微量酸素軸流局部添加によるAr-MIGアーク溶接特性

抄録

GMA welding under pure Ar shielding gas atmosphere (pure Ar-MIG arc welding) is effective to obtain a high-quality welded joint. However, the pure Ar-MIG arc welding cannot be applied practically because of arc instability. In order to perform stable pure Ar-MIG welding, a new welding process has been required.
We analyzed the cause of arc instability by high-speed video camera system. From video images, it was found that long column of liquid metal (CLM) formed at melting wire tip moves irregularly. Therefore, it was expected that unstable MIG arc is due to the behavior of the CLM, although the cathode spots moves irregularly in front of weld pool.
Next, new welding process was developed, in which the small amount of oxygen can be added near the melting wire tip through the wire contact tip. In the developed process, the relationship between arc instability and oxygen content mixed in shielding gas was discussed. In the case of the introduction of small amount of oxygen, the length of CLM becomes effectively short and arc becomes stable, but the cathode spot moving area is not decreasing enough. Therefore, it was concluded that pure Ar-MIG arc instability depended on the CLM behavior.
Finally, the oxygen content in weld metal was able to reduce to less than 100 ppm in the process, and then high ductility weld metal was successfully obtained with low transformation-temperature welding wire.