Plasma blowing in deep penetration CO2 laser welding

Abstract

The deep penetration laser welding is limited by the presence of a plasma on the working piece. This plasma absorbs a part of the power and defocuses the beam. The consequences are a loss in penetration and a wider weld. In order to avoid these phenomena, one can blow the plasma with a transverse gas jet. A model of deviation by jet has been developed and experimentally validated after a study on the gas jet behaviour. Tests on gas blowing during laser welding on different materials show that the plasma can be suppressed using a lower gas flow rate than with the usual shielding systems. Furthermore, other gas than helium, such as argon, nitrogen and even air could be used with the same performances. If they are mixed with an inert gas, the use of air or nitrogen does not increase the oxidation or nitriding rate of the weld. The main effect of the blowing is a reduction of the weld width on its upper part, due to a decrease of the radiated heat and the defocusing. The heat affected zone is also reduced, which should involve an increase of the mechanical resistance of the weld.The deep penetration laser welding is limited by the presence of a plasma on the working piece. This plasma absorbs a part of the power and defocuses the beam. The consequences are a loss in penetration and a wider weld. In order to avoid these phenomena, one can blow the plasma with a transverse gas jet. A model of deviation by jet has been developed and experimentally validated after a study on the gas jet behaviour. Tests on gas blowing during laser welding on different materials show that the plasma can be suppressed using a lower gas flow rate than with the usual shielding systems. Furthermore, other gas than helium, such as argon, nitrogen and even air could be used with the same performances. If they are mixed with an inert gas, the use of air or nitrogen does not increase the oxidation or nitriding rate of the weld. The main effect of the blowing is a reduction of the weld width on its upper part, due to a decrease of the radiated heat and the defocusing. The heat affected zone is also reduced, wh...