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Why do laser welding machines use shielding gas during welding?

Apr 19,2023 | TOPTEK

Why laser welding machines use shielding gas, the reasons can be divided into three points:

Reason 1: It can protect the focusing lens from metal vapor contamination and sputtering of liquid droplets
The shielding gas can protect the focusing lens of the laser welding machine from metal vapor pollution and sputtering of liquid droplets, especially in high-power welding, because the ejection becomes very powerful, and it is more necessary to protect the lens at this time.

Reason 2: Shielding gas is very effective in dissipating plasma shielding generated by high-power laser welding
The metal vapor absorbs the laser beam and ionizes into a plasma cloud, and the protective gas around the metal vapor is also ionized due to heat. If too much plasma is present, the laser beam is somewhat consumed by the plasma. Plasma exists on the working surface as a second energy, which makes the penetration shallow and the surface of the weld pool widen. The recombination rate of electrons is increased by increasing the three-body collisions of electrons with ions and neutral atoms to reduce the electron density in the plasma. The lighter the neutral atoms, the higher the collision frequency and the higher the recombination rate; on the other hand, only the protective gas with high ionization energy will not increase the electron density due to the ionization of the gas itself.

Reason 3: The shielding gas can protect the workpiece from oxidation during the welding process
The laser welding machine must use a kind of gas for protection, and the program should be set in such a way that the protective gas is emitted first and then the laser is emitted, so as to prevent the oxidation of the pulsed laser during continuous processing. The inert gas can protect the molten pool. When some materials are welded regardless of the surface oxidation, the protection may not be considered. However, for most applications, helium, argon, nitrogen and other gases are often used as protection to prevent the workpiece from being welded during welding. subject to oxidation.

The above is the reason why shielding gas is used when laser welding machine welding. Generally, helium is used as the protective gas, which can suppress the plasma to the greatest extent, thereby increasing the penetration depth and increasing the welding speed; and it is light in weight and can escape, and it is not easy to cause pores. Of course, from our actual welding effect, the effect of using argon protection is not bad.

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