Work at TWI has demonstrated the feasibility of using argon instead of helium to reduce running costs in CO2 laser welding.
When CO2 laser welding thick (over 10mm) materials at high power and low welding speeds (less than 1m/min) the welding process may be adversely affected by formation of laser induced plasma above the work piece surface.
Several techniques have been developed to suppress or eliminate plasma formation above the weld and hence increase CO2 laser welding performance. In the technique that has received most attention a jet of gas is blown at the top of the weld to disrupt plasma formation. In most cases, the gas employed in the plasma control jet and associated weld shielding devices is helium. Although effective, helium is an expensive gas and its use can significantly increase production costs.
The TWI project assessed the feasibility of substituting argon for helium in both the plasma control jet and the weld shield when making partial penetration CO2 laser melt runs in 25mm thickness and full penetration melt runs in 12mm thickness structural steels.
Argon could be substituted for helium in the weld shield without adversely affecting melt run penetration, profile or top bead width, provided that helium was used in the plasma control jet.
Argon could be substituted for helium in the plasma control jet in a plasma control device with an open front, provided that helium at sufficient flow rate (over 20 litre/min) was used in the weld shield.
The detailed design of the plasma control device influenced the tendency for plasma formation when using argon in the plasma control jet and helium in the shield. An open-fronted plasma control device proved most effective with this gas combination.
So, for thick section CO2 laser welding at low speeds, argon can be used in either the plasma control jet or the shield. Successful use of argon may need fine tuning of gas flow rates, or redesign of existing plasma control equipment, to suit specific applications.
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