Selection and Use of Gases During Welding
1.The core role of gases in laser welding
·Protecting the molten pool: Preventing oxidation and nitriding reactions between the metal and oxygen, nitrogen, etc. in the air at high temperatures, and avoiding defects such as pores and cracks.
·Assisting the cooling of the molten pool: Controlling the solidification speed of the molten pool through airflow to improve the microstructure and properties of the weld seam.
·Removing splatter: Reducing the contamination of the lens or workpiece surface caused by metal splashing during welding.
·Regulating the plasma: During high-power laser welding, suppressing the absorption of the plasma cloud by the laser energy to improve energy utilization efficiency.
2.Common Gas Types and Characteristics Used in Laser Welding
·Inert gases (mainly used for protection)
Argon (Ar):High density, excellent protection effect, low cost; stable airflow, less prone to splashing.Suitable for welding of stainless steel, aluminum alloy, copper and other non-ferrous metals as well as thin plates, especially suitable for pulsed laser welding.
Helium (He):Low density and high thermal conductivity, which can effectively suppress plasma and enhance the penetration ability of deep fusion welding; however, the cost is high.Suitable for high-power continuous laser welding of thick plates (such as carbon steel, titanium alloy), or for scenarios where high welding speed is required.
·Active gas (used for specific materials or processes)
Carbon Dioxide (CO₂):
It reacts with metals to form CO, which can reduce the surface tension of the molten pool and improve the fluidity of the molten pool. However, it is prone to cause weld oxidation.
Applicable scenarios: Low-carbon steel welding (needs to be used in combination with other gases), or for laser-MIG composite welding.
Nitrogen (N₂):
It is cost-effective, but it easily forms hard and brittle nitrides with metals such as titanium and aluminum, affecting the toughness of the weld.
Applicable scenarios: Stainless steel surface sealing welding (for non-critical structures), or copper alloy welding (to inhibit oxidation).
3.The key factors for gas selection
·Welding material types
Aluminum alloy: Preferentially use pure argon (Ar), avoiding nitrogen-induced embrittlement; for thick plates, consider argon-helium mixture (e.g. Ar:He = 7:3).
Carbon steel / stainless steel: Thin plates use argon, medium-thick plates (>5mm) use helium or argon-helium mixture to increase penetration depth; for low-carbon steel, a small amount of CO₂ (<5%) can be added to improve the fluidity of the molten pool.
Copper / titanium alloy: Copper welding uses argon or nitrogen (to prevent oxidation), titanium alloy uses high-purity argon (to avoid nitriding).
·Welding process parameters
High-power continuous welding (>2kW): Use helium or argon-helium mixture, reducing plasma shielding;
Low-power pulsed welding (<1kW): Pure argon is sufficient, with low cost and stable protection effect.
·Welding quality requirements
Welds with high toughness (such as aerospace components): Avoid nitrogen, prefer argon or helium;
Welds with high surface smoothness requirements: Use argon or helium to reduce spatter and oxide scale.
4.Key points for the use of gases
·Gas purity control
The purity of inert gases should be ≥ 99.99% (impurities such as water and oxygen can cause weld porosity);
The purity of active gases (such as CO₂) should be ≥ 99.5%, and they need to be dried (to avoid moisture causing hydrogen pores).
·Gas flow regulation
Low flow rate: insufficient protection, prone to oxidation;
High flow rate: turbulent airflow, air is introduced, and it may blow away the molten pool metal.
Reference values:
Argon gas: Thin plate welding (1-3mm) 8-15L/min, Medium-thick plate (5-10mm) 15-25L/min;
Helium gas: The flow rate should be 30%-50% higher than that of argon gas (due to its low density, a larger flow rate is needed to form a protective gas layer).
·Nozzle design and position
Nozzle diameter: Usually 6-10mm, a larger diameter requires an increase in flow rate, and a smaller diameter is prone to clogging;
Distance between nozzle and workpiece: 5-8mm, too close can be easily contaminated by splashes, and too far reduces the protection effect.
·Airflow direction control
Blowing in the same direction as the welding direction: suitable for high-speed welding, reducing the interference of airflow on the molten pool;
Side blowing: suitable for deep penetration welding, better for blowing away plasma.
5.safety precautions
·The asphyxiation risk of inert gases
Argon and helium are colorless and odorless gases. At high concentrations, they will displace the oxygen in the air. During operation, ventilation must be maintained to avoid using them in enclosed spaces.
·The toxicity and explosion risk of reactive gases
Excessive CO₂ concentration can cause breathing difficulties. Nitrogen, when heated, reacts with metals and may produce toxic nitrogen oxides. A protective mask must be worn;
Avoid mixing reactive gases with flammable gases (such as acetylene) to prevent explosion.
·Gas cylinder management
Gas cylinders should be fixedly stored, kept away from heat sources and fire sources, and the output pressure should be controlled by a pressure reducer (usually 0.2-0.5 MPa)
--Rayther Laser Camila Wang