Experimental study of continuous CO2 laser welding at subatmospheric pressures

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Abstract
A comparison between laser welding under vacuum and atmospheric pressure conditions was performed. By measuring plasma size, electron density, and electron temperature, plasma suppression at low pressure (below 20 Torr) is observed, associated with an electron density and temperature decrease with reduction of pressure. These microscopic parameters were then correlated to the ambient pressure according to Saha’s law. The electron density in the plasma plume is controlled by the ambient pressure. The influence of the plasma suppression on the welded seam was also studied. New information concerning the energy deposition process inside the keyhole was obtained: Under reduced pressure conditions, the laser light is mainly absorbed by Fresnel reflection and a constant energy deposition per unit length occurs. At atmospheric pressure the laser is absorbed by a combination of Fresnel effect and inverse bremsstrahlung plasma process. The power deposition can be approximated by an inverse exponential law.

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