| Laser induced plasma(LIP) and its effect on weld penetration were discussed in this paper. High power carbon dioxide laser system was used to make bead-on-plate weld on structural steel. LIP formation sequence was recorded by a rotating prism type high speed camera 16㎜ tine film was loaded and the filming rate was 5,000 fps. Average elapse time for emerging, expanding and fading out of a LIP was about 1.4 msec. Effect of assist gas blowing on the reduction of LIP column height was remarkable especially when the rate was 101/min at the straight nozzle of 5mm orifice diameter. In accordance with increase of the assist gas blowing rate, the upper side of key hole was elongated and, at the same time, the shape of LIP showed small cone instead of round column. The calculated temperature of LIP column, based on the spectrum analysis results and black body radiation theory, was 11,290K or more. |
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