Shielding gas practice carried over from arc welding gets laser welds wrong
Argon shields well and ionises easily. At laser power densities that becomes a plasma that absorbs the beam before it reaches the joint.
Welders moving from TIG or MIG to laser welding bring habits, and gas selection is one that does not transfer cleanly. Argon is the default shielding gas in arc welding for good reasons: it is inert, dense enough to provide coverage, and it stabilises the arc.
At laser power densities, the property that helps an arc becomes a problem.
Plasma shielding
Argon has a relatively low ionisation potential. Above the weld pool, in the plume of metal vapour, a high-power beam ionises argon readily, forming a plasma cloud. That plasma absorbs and defocuses the incoming beam, so less energy reaches the workpiece and penetration becomes unstable.
The effect worsens with power and with slower travel speeds, which is exactly where deep penetration welding operates.
Why helium behaves differently
Helium has a much higher ionisation potential, so it does not form an absorbing plasma as readily under the same conditions. It is the standard answer for high-power welding where plasma suppression matters.
The trade-offs are cost, which is substantial and has been volatile, and low density: helium rises, so shielding coverage requires higher flow rates and careful nozzle design.
Mixtures of helium and argon are common, balancing plasma suppression against cost and coverage.
The nozzle question
Arc welding delivers shielding through the torch, coaxially with the process. Laser welding often does not: the process head must keep its optics away from spatter, so shielding is frequently delivered through a separate side nozzle.
That means shielding geometry is a design decision rather than a given. A side nozzle aimed incorrectly can blow the plume across the joint, disturb the melt pool, or fail to cover the solidifying weld behind the beam.
The practical implication
Gas selection and nozzle geometry are process parameters that need developing for the specific joint, not settings carried across from an arc procedure. Shops that treated them as given have generally spent time chasing penetration inconsistency that turned out to be a gas problem.
This article was produced by the LasersNews AI desk and reviewed by our editors.
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