what gas is used for welding

Shielding Gases in Fusion Processes

Role of Shielding Gases

Gases are employed to protect the molten weld pool and the electrode (if applicable) from atmospheric contamination. These contaminants include oxygen, nitrogen, and hydrogen, which can lead to porosity, embrittlement, and other weld defects. The shield prevents these issues, ensuring a strong and ductile weld.

Categories of Shielding Gases

  • Inert: Chemically unreactive gases that provide a protective barrier.
  • Active: Gases that participate in the welding process, influencing arc characteristics, weld penetration, and weld metal properties.

Commonly Utilized Gases

Inert Gases

  • Argon (Ar): Widely used for various fusion techniques, including GTAW (TIG) and GMAW (MIG). It's heavier than air, providing excellent shielding coverage. Generally produces a smooth, quiet arc. Suitable for ferrous and non-ferrous alloys.
  • Helium (He): Lighter than air and provides deeper penetration than argon. Often mixed with argon to increase heat input and welding speed. Commonly used for welding aluminum, magnesium, and copper alloys. Produces a hotter, more forceful arc.

Active Gases

  • Carbon Dioxide (CO2): An inexpensive option, particularly in GMAW (MIG). It promotes deeper penetration but can lead to spatter and a less stable arc compared to inert alternatives. Often used for carbon steel welding.
  • Oxygen (O2): Typically added in small percentages to argon to stabilize the arc and improve droplet transfer in GMAW (MIG) of carbon steel and stainless steel. Too much oxygen can lead to oxidation and porosity.

Gas Mixtures

Specific combinations are frequently employed to optimize weld characteristics. These mixtures can tailor the arc properties, penetration profile, and weld metal composition.

  • Argon/Carbon Dioxide (Ar/CO2): A common mixture for GMAW (MIG) of carbon steel, offering a balance between arc stability, penetration, and cost.
  • Argon/Oxygen (Ar/O2): Used for GMAW (MIG) of stainless steel and low-alloy steels, providing good arc stability and weld bead appearance.
  • Argon/Helium (Ar/He): Employed for welding aluminum, magnesium, and copper alloys, offering improved heat input and weld penetration compared to using only argon.
  • Argon/Hydrogen (Ar/H2): Used in specialized applications such as plasma arc operations.

Considerations for Selection

The choice of shielding atmosphere depends on several factors, including:

  • Base Metal: The material being joined significantly influences the gas selection.
  • Fusion Process: Different methods (GTAW, GMAW, SAW, etc.) have specific requirements.
  • Weld Properties: Desired mechanical properties, corrosion resistance, and aesthetic appearance impact gas selection.
  • Cost: The cost of different options is a factor in selecting a shielding solution.