On-line monitoring of welding processes is a crucial factor for its further development. Many different approaches are used for this purpose, and optical emission spectroscopy is considered the most promising method. This paper deals with laser welding of thin sheets (1.5 mm) of austenitic steel. A continuous-wave CO2 laser with a power range between 1 to 3 kW was used as the laser beam source. Time resolved spectroscopy (wavelength range 530-1000 nm) of the time evolution of laser-induced plasma was applied for assessing the optional welding conditions and presence of welding defects. The experiments were performed by fluently varying the focal position of the laser beam. Experimental results show that a typical emission spectrum of laser-induced plasma emits strong emission lines when the welding process is off-balance. In the case of optional and stable conditions, in contrast, these emission lines are suppressed and the spectrum shows a typical curve of black body radiation with a maximum around 675 nm. [References: 5]
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