Abstract
The light emissions of the plasma plume in the deep penetration laser welding of metals typically have the character of irregular short-time pulses. Their nature indicates that the size of the plume significantly fluctuates and the plasma flows out of the keyhole in the form of short bursts rather than a continuous flow. In this paper, the authors study the plasma plume light emissions using an autocorrelation analysis. The authors show that it is an efficient tool for the detection of the plasma bursts period which is typically in the order of milliseconds. The authors compare the autocorrelation characteristics and the geometry of the welds made on a 2 kW ytterbium-doped yttrium aluminium garnet (Yb:YAG) fiber laser welding machine for the X5CrNi 18-10 stainless steel and the S235JR carbon steel. The welding parameters settings is varied over a range of laser power (1–2 kW) and welding speed (10–30 mm/s) usually used in industry. As a result, the authors identify a linear dependence between the plasma bursts period and the weld depth.
Highlights
The deep penetration laser welding of metals is accompanied by the formation of the keyhole filled with the laser induced plasma and the bright plasma plume above the keyhole opening.1 The light emissions generated by the plasma plume have pulsing character that indicates continuous fluctuations of its brightness and size.2the keyhole oscillations have different degree of influence in the plasma bursts generated by different laser sources.9,10In our previous papers,11,12 we have studied the light emissions using the short-time frequency analysis
We study the plasma plume light emissions using an autocorrelation analysis that is more feasible for the recognition of the repetitive patterns in the noise-obscured signal
The plasma bursts were detected for all chosen welding parameters settings except for the combination of the S235JR carbon steel, the laser power of 1.0 kW, and the welding speed of 20 and 30 mm/s
Summary
The deep penetration laser welding of metals is accompanied by the formation of the keyhole filled with the laser induced plasma and the bright plasma plume above the keyhole opening. The light emissions generated by the plasma plume have pulsing character that indicates continuous fluctuations of its brightness and size.. The light emissions generated by the plasma plume have pulsing character that indicates continuous fluctuations of its brightness and size.. We have studied the light emissions using the short-time frequency analysis. We have detected the presence of the plasma bursts through a significant peak in the frequency spectrum that corresponds to the frequency of the short-time pulses observed in the waveforms of the light emissions. The complex time series of the plasma bursts limit the use of the Fourier transform suitable rather for the periodic signals. We study the plasma plume light emissions using an autocorrelation analysis that is more feasible for the recognition of the repetitive patterns (such as the pulses corresponding to the plasma bursts) in the noise-obscured signal. We identify a direct relationship between the plasma bursts period and the weld depth
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