The objective of this research is t

The objective of this research is to obtain a fundamental knowledge of generation behaviour andionised state of a plume or plasma induced during bead on plate welding of a 20 mm thick type304 stainless steel plate with a 10 kW fibre laser beam of 0?9 MW mm22 power density, on thebasis of 10 000 to 40 000 flames s21 high speed video observation and spectroscopic analysis.The high power fibre laser produced a partial penetration weld of 12 mm in depth at 50 mm s21welding speed. According to the high speed observation pictures, the laser induced plume wasrepeatedly generated from a keyhole at the interval of about 0?5 ms period to reach 12 mm inmaximum height. The spectroscopy indicated the line spectra of neutral atoms of alloyingelements of type 304 such as iron (Fe), chromium (Cr) and manganese (Mn). However, ionisedspectra of alloying elements and line spectra of argon (Ar) neutral atom were not apparentlydetected under these welding conditions. Furthermore, the temperature and the ionisation degreeof the laser induced plume were calculated to be approximately 6000 K and 0?02 respectively, bythe Bolzman plots and Saha’s equation. Consequently, the plume induced with the 10 kW fibrelaser beam of the ultra high power density was judged to be weakly ionised plasma from theseexperimental results.