Choosing the Right Shielding Gases for Arc Welding

Arc welding is a process that uses an electric arc to join metal pieces together. The arc generates intense heat that melts the metal and forms a weld pool. To protect the weld pool from the surrounding air, which contains oxygen, nitrogen, and other elements that can cause defects and corrosion, a shielding gas is used. The shielding gas flows around the arc and creates a barrier that prevents contamination.

The choice of shielding gas is important because it affects the quality, appearance, and performance of the weld. Different shielding gases have different properties and characteristics that influence the arc stability, metal transfer mode, penetration, bead shape, spatter, fume generation, and alloying content of the weld.

In this article, we will discuss how to choose the right shielding gas for arc welding based on the welding process, material type, thickness of material, welding position, and cost and availability.

I. Welding Process

The most common arc welding processes are gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), flux cored arc welding (FCAW), and shielded metal arc welding (SMAW).

1. GMAW, also known as metal inert gas (MIG) welding, uses a continuously fed wire electrode that melts and forms the weld pool. The shielding gas can be either inert or active. Inert gases are non-reactive gases such as argon and helium. Active gases are reactive gases such as carbon dioxide (CO2) and oxygen (O2). Inert gases are typically used for non-ferrous metals such as aluminum, magnesium, and titanium. Active gases are typically used for ferrous metals such as steel and stainless steel.
   

   
   

2. GTAW, also known as tungsten inert gas (TIG) welding, uses a non-consumable tungsten electrode that creates the arc. The filler metal is added separately to the weld pool. The shielding gas is usually 100% argon or a mixture of argon and helium. Argon provides a stable arc and good penetration. Helium provides more heat input and better wetting of the edges of the weld.
   

   
   

3. FCAW, also known as flux-cored welding, uses a tubular wire electrode that contains a flux core. The flux core generates a shielding gas when it melts and reacts with the arc. There are two types of FCAW: self-shielded and gas-shielded. Self-shielded FCAW does not require an external shielding gas because the flux core provides enough protection. Gas-shielded FCAW requires an additional shielding gas such as CO2 or an argon-CO2 mixture to enhance the quality and appearance of the weld.
   

   
   

4. SMAW, also known as stick welding or manual metal arc welding (MMAW), uses a coated electrode that melts and forms the weld pool. The coating of the electrode also generates a shielding gas when it burns and reacts with the arc. SMAW does not require an external shielding gas because the coating provides enough protection.

II. Material Type

The type of material being welded determines the type of shielding gas that is suitable for the welding process. Different materials have different chemical compositions, melting points, thermal conductivities, and mechanical properties that affect the weldability and performance of the weld.

• For non-ferrous metals such as aluminum, magnesium, and titanium, inert gases such as argon and helium are preferred because they do not react with the metal and cause oxidation or porosity. Argon is more commonly used than helium because it is cheaper and more readily available. Helium is sometimes added to argon to increase the heat input and improve the weld penetration.
  

  
  

• For ferrous metals such as steel and stainless steel, active gases such as CO2 or O2 are often added to argon to increase the arc stability and improve the metal transfer mode. CO2 produces more spatter and fumes than O2 but also provides deeper penetration and higher deposition rates. O2 produces less spatter and fumes than CO2 but also reduces the penetration and increases the oxidation of the weld.
  

  
  

• For some special alloys such as nickel-based alloys or copper alloys, specific shielding gases are required to prevent cracking or embrittlement of the weld. For example, nickel-based alloys require argon-hydrogen mixtures to reduce oxidation and improve wetting. Copper alloys require helium or argon-helium mixtures to increase heat input and prevent porosity.
  

To learn welding solutions for different materials, read Laser Welding: Which Materials Can You Weld? and Welding Materials Unveiled: Understanding the Characteristics of Metals and Alloys.

III. Thickness of Material

The thickness of the material being welded affects the amount of heat input required to melt the metal and form a sound weld. Thicker materials require more heat input than thinner materials. Therefore, the choice of shielding gas should match the heat input requirement of the material thickness.

1. For thin materials (< 3 mm), low heat input is required to prevent burn-through or distortion of the metal. Inert gases such as argon or helium are suitable for thin materials because they have low thermal conductivity and ionization potential, which result in a narrow arc column and a low transfer of heat to the outer areas of the arc. This forms a deep and narrow penetration profile that is ideal for thin materials.
   
   

2. For thick materials (> 6 mm), high heat input is required to ensure adequate fusion and penetration of the metal. Active gases such as CO2 or O2 are suitable for thick materials because they have high thermal conductivity and ionization potential, which result in a wide arc column and a high transfer of heat to the outer areas of the arc. This forms a wide and shallow penetration profile that is ideal for thick materials.
   
   

3. For medium materials (3-6 mm), a balanced heat input is required to achieve a good weld quality and appearance. A mixture of inert and active gases such as argon-CO2 or argon-O2 is suitable for medium materials because they provide a moderate arc column and a moderate transfer of heat to the outer areas of the arc. This forms a well-balanced width-to-depth penetration profile that is ideal for medium materials.
   

To learn welding solutions for different thicknesses of materials, read How to Weld Thin Metal: Types, Welders, and Techniques (2023).

IV. Welding Position

The welding position refers to the orientation of the weld joint relative to the horizontal plane. There are four basic welding positions: flat, horizontal, vertical, and overhead.

1. For a flat position, the weld joint is parallel to the horizontal plane, and the weld pool is supported by gravity. Any shielding gas can be used for the flat position because there is no risk of the weld pool sagging or falling.
   

   
   

2. For horizontal position, the weld joint is perpendicular to the horizontal plane and the weld pool is partially supported by gravity. A shielding gas that provides good arc stability and low spatter is preferred for the horizontal position because there is a risk of weld pool sagging or rolling.
   

   
   

3. For vertical position, the weld joint is parallel to the vertical plane, and the weld pool is not supported by gravity. A shielding gas that provides good arc stability and low spatter is preferred for the vertical position because there is a risk of the weld pool falling or dripping.
   

   
   

4. For the overhead position, the weld joint is opposite to the horizontal plane, and the weld pool is not supported by gravity. A shielding gas that provides good arc stability and low spatter is preferred for the overhead position because there is a high risk of the weld pool falling or dripping.
   

For more welding position tips, read What are the 4 Basic Welding Positions and How to Choose the Right One?

V. Cost and Availability

The cost and availability of shielding gas are also important factors to consider when choosing the right shielding gas for arc welding. The cost of shielding gas depends on the type, purity, quantity, and delivery method of the gas. The availability of shielding gas depends on the location, supply, and demand of the gas.

In general, inert gases such as argon and helium are more expensive and less available than active gases such as CO2 and O2. This is because inert gases are extracted from air by cryogenic distillation, which is a complex and energy-intensive process. Active gases are produced by chemical reactions or combustion, which are simpler and cheaper processes.

Therefore, when cost and availability are major concerns, active gases or mixtures of active gases are preferred over inert gases or mixtures of inert gases. However, when quality and performance are more important than cost and availability, inert gases or mixtures of inert gases are preferred over active gases or mixtures of active gases.

VI. Conclusion

Choosing the right shielding gas for arc welding is not a simple task. It requires careful consideration of various factors such as the welding process, material type, thickness of the material, welding position, cost, and availability. The choice of shielding gas can have a significant impact on the quality, appearance, and performance of the weld.

The following table summarizes some common shielding gases and their applications for different welding processes and materials:

The above table is only a general guideline and does not cover all possible combinations of welding processes, materials, and shielding gases. The optimal choice of shielding gas may vary depending on the specific welding conditions and requirements. Therefore, it is advisable to consult with a welding expert or refer to a welding handbook before selecting a shielding gas for arc welding. You can also read the article Which Shielding Gas Should You Use for MIG/MAG Welding? to choose welding gases for MIG/MAG welding.

☆ Notice: Importance of Gas Purity and Flow Rate

1. Gas Purity Considerations: Ensuring the purity of shielding gases is crucial for preventing weld contamination and achieving consistent results.

2. Optimal Gas Flow Rates: Proper regulation of gas flow rates is essential for maintaining a stable arc and protecting the weld pool from atmospheric contamination.

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2. Shielded Metal Arc Welding (SMAW): The Beginner's Guide

3. Which Shielding Gas Should You Use for MIG/MAG Welding?

4. Gas-shielded arc welding processes (TIG/MIG/MAG)

5. Complete Basics of Gas Shielded Arc Welding