In the precise world of laser welding, high-energy beams are undoubtedly the leading role. However, without the precise coordination and protection of suitable gases, the welding quality will be greatly reduced or even fail. These seemingly simple gases actually play multiple crucial roles:
Isolation protection: At high temperatures in the molten pool, it isolates air, effectively preventing metal oxidation and nitriding, and avoiding weld embrittlement, porosity, and inclusions.
Plasma suppressor: The dense plasma cloud generated by high-power welding will scatter and absorb laser energy. Specific gases can suppress plasma, ensuring that laser energy can reach the workpiece efficiently.
Optical protection shield: Blow away welding fumes and spatter, protect expensive focusing lenses from contamination and damage, extend equipment life and maintain beam quality.
Molten pool stabilizer: Appropriate airflow can stabilize the flow of the molten pool and improve the weld formation (such as reducing undercut and hump).
Cooling assistant: (Auxiliary gas) cools the heat-affected zone and protects the lens holder.
Detailed explanation of Core Gas types
Laser welding mainly uses two types of gases, and their functions and selection criteria are different:
I. Protective Gas: The direct "shield" of the molten pool
Argon (Ar) :The ionization energy of Ar is relatively the lowest. Under the action of laser, its ionization degree is relatively high, which is not conducive to controlling the formation of plasma cloud and will have a certain impact on the effective utilization rate of laser. However, the activity of Ar is very low and it is difficult to undergo chemical reactions with common metals. Moreover, the cost of Ar is not high. In addition, the density of Ar is relatively large, which is conducive to sinking above the weld pool. It can better protect the weld pool, and thus can be used as a regular shielding gas.
Nitrogen (N₂) : The ionization energy of N2 is moderate, higher than that of Ar and lower than that of He. Under the action of laser, its ionization degree is average, which can effectively reduce the formation of plasma clouds and thereby increase the effective utilization rate of laser. Nitrogen can undergo chemical reactions with aluminum alloys and carbon steels at certain temperatures, generating nitrides, which will increase the brittleness of the weld seam, reduce its toughness, and have a significant adverse effect on the mechanical properties of the weld joint. Therefore, it is not recommended to use nitrogen to protect the weld seams of aluminum alloys and carbon steels. The nitrides produced by the chemical reaction between nitrogen and stainless steel can enhance the strength of the weld joint, which is conducive to improving the mechanical properties of the weld. Therefore, nitrogen can be used as a protective gas when welding stainless steel.
Helium He: He has the highest ionization energy and a very low degree of ionization under the action of laser, which can effectively control the formation of plasma clouds. Laser can act well on metals, and He has very low activity and basically does not undergo chemical reactions with metals, making it an excellent protective gas for weld seams. However, the cost of He is too high, and this gas is generally not used in large-scale production products. He is generally used in scientific research or for products with very high added value.
Ii. Auxiliary Gas: The "Invisible Guardian" of the Equipment
The auxiliary gas is ejected from an independent nozzle, mainly protecting the optical system:
Function
Strongly remove the smoke and metal splashes generated during welding to prevent their deposition and contamination of the protective lenses.
Cool the lens holder and the surrounding area.
Common gases: Dry and clean compressed air is the most economical and commonly used. Inert gases (such as Ar) can also be used when the requirements are extremely high or the materials are special.
Key points: The direction, flow rate and pressure of the airflow need to be carefully set, ensuring effective cleaning without interfering with the main protective airflow and the stability of the molten pool.
How to choose the most suitable gas?
Welded material
Stainless steel, titanium, aluminum: Argon gas is preferred (anti-oxidation).
Copper and high thermal conductivity alloys: Helium gas or high helium mixture gas is often selected.
Carbon steel: Argon and helium-argon mixtures can be used, but pure nitrogen should be avoided.
Specific austenitic stainless steel: Can be tested with nitrogen.
Welding requirements
For deep penetration and high-power welding, helium gas or high-helium mixture gas is the preferred choice.
High surface quality requirements: Helium and argon gases usually work better.
Extremely high anti-oxidation requirement: argon gas.
Cost consideration: Helium is expensive. Under the condition of meeting the process requirements, argon, nitrogen or a mixed gas (reducing the proportion of helium) can be considered.
Laser power and welding speed: High-power and high-speed welding rely more on helium to suppress plasma.
Joint form and nozzle accessibility: Complex joints or confined Spaces may affect the gas protection effect.
Gas conveying parameters
Flow rate: If it is too low, the protection will be insufficient; if it is too high, it may disrupt the molten pool, waste gas and increase costs.
Nozzle type and height: They directly affect the gas coverage and protection effect.
Air supply mode: Coaxial/side-axis air supply selection.
Gas is by no means a supporting role in laser welding, but a core element ensuring high-quality, high-efficiency and high-stability production.