In the process of laser welding, inert gas is often used to protect the molten pool. When some materials are welded, surface oxidation may not be considered, and protection may not be considered. However, for most applications, helium, argon, nitrogen and other gases are often used as protection to make the workpiece Avoid oxidation during welding.
Three functions of protective gas:
- prevent oxidation of the metal surface;
- Suppress the metal vapor pollution generated during the welding process and the spatter after the metal is melted;
- Dissipate the plasma shield produced by high-power laser welding, because this plasma shield will affect the laser transmission effect and reduce the laser power reaching the surface of the welded object.
The advantages and disadvantages of the three inert gases are as follows:
Helium: It is not easy to ionize (higher ionization energy), which allows the laser to pass smoothly, and the beam energy reaches the surface of the workpiece without hindrance. This is the most effective shielding gas used in laser welding, but it is more expensive.
Argon gas: It is cheaper and denser, so the protection effect is better. However, it is susceptible to high-temperature metal plasma ionization, which shields part of the beam from reaching the workpiece, reduces the effective laser power for welding, and also damages the welding speed and penetration. The surface of the weldment protected by argon is smoother than when protected by helium.
Nitrogen: It is the cheapest shielding gas, but it is not suitable for welding certain types of stainless steel, mainly due to metallurgical problems, such as absorption, which sometimes creates pores in the overlap area.
The first function of shielding gas is to isolate oxygen and air during welding, so as to reduce oxidation reaction during metal welding, so that blackening can be effectively reduced during welding.
The second function of using protective gas is to protect the focusing lens from metal vapor contamination and liquid droplet sputtering. Especially in high-power laser welding, because the ejection becomes very powerful, it is more necessary to protect the lens at this time.