Gases for laser welding are used for surface laser welding and treatment. Heated material surface and a welding puddle must be protected against contact with ambient air.
Moreover, in welding with high-power CO2 lasers, excessive plasma generation should be prevented. Helium and helium-argon mixtures are the main welding gases for welding with CO2 laser. Helium shall be a component of the mixture as it prevents plasma generation under a blowhole. Argon usually supports plasma generation; thus, this gas should not used for lasers with power exceeding 3 kW. Helium-argon mixtures are usually recommended for welding of aluminum.
For some applications, argon-oxygen mixtures or CO2 can be used, but in order to prevent excessive plasma creation, CO2 should not be supplied via the central nipple. For more powerful lasers, argon-oxygen mixtures provide high efficiency and acceptable welding quality.
Argon-hydrogen mixtures ensure high efficiency and acceptable seam shape in welding of austenitic stainless steels. It should be considered that hydrogen may result in brittle behavior of ferrite steels! Gases and gas mixtures are supplied in cylinders.
Argon is the best gas for welding with Nd:YAG lasers, though acceptable weld seams can be also obtained with the use of nitrogen CO2 (if CO2 is used, the seams are usually slightly oxidized). In contrast to argon, helium requires a high flow of a very light gas to protect a welding point. This causes turbulence in a welding puddle. Thus, usage of helium is undesirable.
Shielding gases for surface treatment
Commonly, the shielding gases used for surface treatment are the same used for laser welding.
Neutral gases, such as argon and helium, ensure full protection against ambient air. Sometimes, nitrogen can be also used. Argon-hydrogen mixtures ensure good surface appearance due to a blanketing effect and prevention of plasma generation in the presence of hydrogen.
Gas for blowdown of laser beam transmission cabinet
A laser beam transmission cabinet is equipped with mirrors guiding a laser beam into a treatment zone. Obstacles along a beam path may influence the beam, for example, expanding it. In addition, they may cause contamination of water-cooled mirrors. Argon, oxygen, water vapors and hydrocarbon impurities influence both the beam and an optic system; therefore, such gases should be avoided.To blowout the laser beam transmission cabinet, it is recommended to use nitrogen for laser cutting or laser nitrogen; the flow is: 2.0-5.0 m3/h (70-175 cubic feet per hour).