The laser welding machine often uses helium, argon, nitrogen and other gases to protect the molten pool during the welding process (people call it shielding gas), but many people don’t know why a shielding gas is used. Next, Foshan Fulan Laser Technology Co., Ltd. The company tells everyone why the shielding gas is used?

One is that the shielding gas can protect the focusing lens from metal vapor pollution and liquid droplet sputtering. Especially in high-power welding, because the ejection becomes very powerful, it is more necessary to protect the lens at this time.

The second is that the shielding gas can dissipate the plasma shield produced by high-power laser welding. The metal vapor absorbs the laser beam and ionizes into a plasma cloud. The protective gas around the metal vapor will also be ionized by heating. If there is too much plasma, the laser beam will be consumed by the plasma to some extent, and the plasma exists as a second kind of energy. On the working surface, the penetration depth becomes shallower and the molten pool surface becomes wider. Increase the electron recombination rate by increasing the three-body collision of electrons with ions and neutral atoms to reduce the electron density in the plasma. The lighter the neutral atom, the higher the collision frequency, and the higher the recombination rate. On the other hand, only the shielding gas with high ionization energy will not increase the electron density due to the ionization of the gas itself.

The third is that the shielding gas can protect the workpiece from oxidation during the welding process. In most applications, shielding gas is used to protect the workpiece from oxidation during the welding process (the shielding gas may not be used when welding of some materials does not care about surface oxidation). When using shielding gas, you must set the shielding gas first, and then output the laser, which can prevent the pulse laser from oxidizing during the continuous processing of the laser welding machine.

The above is the reason why the shielding gas is used in the laser welding machine. Commonly used protective gases include nitrogen, argon, helium, a mixture of argon and helium. Under normal circumstances, argon should be used when welding carbon steel, nitrogen should be used for stainless steel, helium should be used for titanium alloy, and a mixed gas of argon and helium should be used for aluminum alloy.

Warm reminder from Fulan Laser: Because the shielding gas is injected through the nozzle opening with a certain pressure to reach the surface of the workpiece, the hydrodynamic shape of the nozzle and the diameter of the outlet are very important. It must be large enough to drive the sprayed shielding gas to cover the welding surface, but in order to effectively protect the lens and prevent metal vapor contamination or metal splash damage to the lens, everyone must pay attention: the size of the nozzle must be limited, and the flow rate must be controlled. Otherwise, the laminar flow of the shielding gas will become turbulent, and the atmosphere will be drawn into the molten pool, which will eventually form pores.