In laser welding a shielding gas plays very important role to obtain high quality welds. Especially Ar shielding gas has come into wide use, but it has the problem of plasma generation in high power laser welding.
This paper describes the formation of shielding gas plasma and its behavior. The authors observed plasma and molten pool directly by CCD camera, and detected the spectrum emission, acoustic emission and plasma potential at the same time. The plasma potential in this study was the potential difference between the insulated nozzle and specimen. It was generated from the difference between the mobility of electrons and the metallic ions. As for the direct observation of welding zone by CCD camera, both plasma and molten pool were seen in one flame picture by using the 25W-Ar-laser back light and original band pass filter which transmitted Ar laser light and partially plasma light pass.
For optical signal, the spectrum emission of Iron atom (298.4 nm) which is representation of metallic plasma behavior and that of Ar atom (738.4 nm) were detected.
According to these results, an optimum conditions for Ar shielding gas velocity and mixed ratio of shield gas were proposed.
This work was performed under the management of ALERI (Applied Laser Engineering Research Institute) as a part of "the Leasing Basic Research Practical Use of Research Facility Centers" supported by NEDO (New Energy and Industrial Technology Development Organization).
