First of all, nitrogen and argon protection can isolate oxygen, nitrogen and hydrogen in the air to prevent weld oxidation and porosity;
Another effect of using protective gas is to protect the focusing lens from sputtering damage during welding, although fiber laser welding machine now have protective lenses in front of the focusing lens. However, in high-power laser welding, because the ejection becomes very powerful, it is very necessary to protect the lens at this time.
The third function of the shielding gas is to dissipate the plasma shielding produced by high-power laser welding.
The continuous radiation of the laser to the molten pool will form a plasma cloud on the upper part of the molten pool, which limits the passage of the laser and has a scattering effect on the laser. If it is not restricted, it will affect the penetration depth and reduce the strength of the weld. In the process of laser welding, the blowing of shielding gas to the weld can not only prevent the oxidation of the weld and the generation of pores, but also blow away the plasma cloud and increase the absorption of laser energy by the molten pool. The gas used should have a large ionization energy and prevent the protective gas itself from being ionized to generate plasma. Thereby increasing the efficiency with which the laser reaches the workpiece performance.
Helium has the smallest ionization and can quickly drive out the rising metal vapor generated from the molten metal pool. Using helium as a protective gas can suppress the plasma to the greatest extent, thereby increasing the penetration depth and increasing the welding speed. Light and able to escape, not easy to cause pores.
However, due to the high price, considering the cost reduction, and from the effect of our actual welding, the effect of nitrogen and argon protection is also good, so there are still more occasions for nitrogen and argon use.