Laser Welding

The laser resonator gases for CO₂ lasers usually consist of a mixture of helium, nitrogen and carbon dioxide. There are a number of reasons for adding helium to the laser gas mixture:
1. Helium helps to remove CO₂ molecules from the lower laser level by speeding up relaxation ransitions.
2. Helium has a very high thermal conductivity. Helium then helps to conduct heat away from the electric discharge.
Helium is added in order to reach very high laser powers.

The laser resonator gases for CO₂ lasers usually consist of a mixture of helium, nitrogen and carbon dioxide. Carbon dioxide (CO₂) is the gas which is active in generating the laser light itself, i.e. infrared radiation. The radiation is created by transitions between different vibrational energy levels in the carbon dioxide molecule. In this way it would be possible to run a CO₂ laser using only carbon dioxide as the laser gas. However, in order to reach the very high laser powers which are necessary for laser cutting and welding it is necessary to add nitrogen and helium to the laser gas.

The laser resonator gases for CO₂ lasers usually consist of a mixture of helium, nitrogen and carbon dioxide. By using an electric discharge it is very easy to excite a nitrogen molecule to its first vibrational energy level, which has almost the same energy as the upper laser level of CO₂. The vibrational energy is easily transferred from N₂ to CO₂ by collisions between the two molecules. Altogether it is far easier to excite the upper laser level of CO₂ by using nitrogen as an intermediate than to use only CO₂. Nitrogen is added in order to reach very high laser powers.

Tailor-made mixtures for all brands of lasers resonators are available at Air Products. The composition of the gas mixture varies depending on laser type, power and manufacturer. The laser resonator gases are usually delivered in separate gas cylinders but they can also be delivered premixed.

Argon is part of a range of pure elemental gases and gas mixtures that can be used for laser welding. Argon is suitable for laser powers up to 3 KW. However, the plasma suppression properties of argon can be improved by admixing helium, oxygen or carbon dioxide. The most commonly used gases are argon and helium.

Carbon dioxide and nitrogen are reactive gases which can form oxides, carbides or nitrides with the weld metal. The mechanical properties of the welds may therefore be impaired, and for some applications this disqualifies the use of carbon dioxide and nitrogen as welding gases. However, in some cases, reactive welding gases can be tolerated or even be advantageous. For some stainless steels, for example, nitrogen gives a better corrosion resistance and microstructure of the welds.

Air Products' shielding gases are commonly used in several welding processes, mainly MIG/MAG and TIG weldings. The selection of a suitable welding gas is essential for the welding process. The welding gas not only protects the weld metal from the surrounding air, it can also contribute to a higher productivity and to better mechanical properties of the weld. But the welding gas has other roles too. It protects the focusing optics against fumes and spatter and, in the case of CO₂ lasers, it controls plasma formation. What welding gas to use depends on the type of laser, the laser power, nozzle arrangement, the material to be welded, workpiece thickness, mechanical requirements on the weld and costs. The emphasis is on welding gases for CO₂ laser welding because CO₂ lasers are still the predominant type of laser in the manufacturing industry, at least in the higher power ranges. In addition, the selection of the welding gas is of critical importance for CO₂ laser welding whereas it is less demanding for Nd:YAG laser welding.

Impurities in the laser gas mixture can decrease the performance of a CO₂ laser by lowering the output power, making the electric discharge unstable or increasing the consumption of laser gases. The quality of the laser gases is not only decided by the purity as such but by what type of impurities they contain and in what levels. Therefore, the use of BIP cylinders is advisable for reaching a longer life time of your resonator and mirrors.

Impurities in the laser gas mixture can decrease the performance of a CO₂ laser by lowering the output power, making the electric discharge unstable or increasing the consumption of laser gases. The quality of the laser gases is not only decided by the purity as such but by what type of impurities they contain and in what levels. Therefore, the use of BIP cylinders is advisable for reaching a longer life time of your resonator and mirrors.

Our applications engineers can work with your plant personnel to analyse and understand your entire process. Based on that analysis and your needs, they can recommend process improvement solutions that can help you enhance product quality and consistency, plus optimise gas use. Air Products' services include leak-checking, furnace profiling, analytical calibration, gas analysis process troubleshooting and overall process review.

Training can include gas atmosphere safety, properties of gases, metal treating applications, NFPA 86, piping and flow control panel requirements and troubleshooting for atmosphere problems. This information can help keep your furnace operations safe and help prevent accidents.