MIG Welding with Oxygen: A Comprehensive Guide

MIG (Metal Inert Gas) welding with oxygen is generally not recommended due to the risk of oxidation and reduced weld quality. Oxygen is a reactive gas that can cause various issues, such as excessive spatter, porosity, and poor weld integrity. This comprehensive guide will delve into the technicalities of MIG welding with oxygen, providing expert-level insights and a hands-on approach to help you navigate this complex topic.

Understanding Shielding Gases in MIG Welding

The primary purpose of shielding gas in MIG welding is to protect the molten weld pool from exposure to atmospheric gases, such as oxygen, nitrogen, and hydrogen, which can react with the weld pool and cause various problems. The four most common shielding gases used in MIG welding are:

  1. Argon (Ar): Argon is an inert gas that provides a stable arc and produces a narrow, deep weld profile. It is commonly used for welding non-ferrous metals, such as aluminum and stainless steel.

  2. Helium (He): Helium is also an inert gas that produces a wide, deep penetration profile. It is often used for welding thick materials and stainless steel.

  3. Carbon Dioxide (CO2): CO2 is a reactive gas that provides deep weld penetration but can also lead to a less stable arc and more spatter. It is typically used for welding mild carbon and low-alloy steels.

  4. Oxygen (O2): Oxygen is a reactive gas that can improve weld pool fluidity, penetration, and arc stability in mild carbon, low-alloy, and stainless steel. However, it also causes oxidation of the weld metal, making it unsuitable for use with aluminum, magnesium, copper, and other exotic metals.

Selecting the Optimal Shielding Gas Mixture

mig welding with oxygenImage source: Mig weld example

The choice of shielding gas mixture depends on the specific application and the desired weld characteristics. Here are some common shielding gas mixtures and their benefits:

Shielding Gas Mixture Benefits
75-95% Argon, 5-25% CO2 Provides a balance of arc stability, puddle control, and reduced spatter. Allows for spray transfer process.
25-75% Helium, 75-25% Argon Produces a wide, deep penetration profile, suitable for thick materials and stainless steel.
9% or less Oxygen Improves weld pool fluidity, penetration, and arc stability in mild carbon, low-alloy, and stainless steel.

It’s important to note that the specific ratios of the shielding gas mixture can be adjusted to achieve the desired weld characteristics, such as penetration, bead profile, and travel speed.

Ensuring Proper Shielding Gas Coverage

When selecting MIG gun consumables, it is crucial to ensure that the weld pool is properly protected by the shielding gas. Factors to consider include:

  1. Nozzle Size: The nozzle should be the appropriate size to provide adequate shielding gas coverage to the weld pool.
  2. Nozzle Condition: A clogged or damaged nozzle can restrict the flow of shielding gas, leading to excessive spatter, porosity, and weld contamination.
  3. Diffuser Design: The diffuser plays a crucial role in distributing the shielding gas evenly around the weld pool. A well-designed diffuser can help maintain a consistent gas coverage.
  4. Gas Flow Rate: The gas flow rate should be adjusted to ensure that the weld pool is fully protected, without excessive turbulence or gas waste.

Regularly inspecting and maintaining the MIG gun consumables is essential to ensure proper shielding gas coverage and optimal weld quality.

Potential Issues with MIG Welding with Oxygen

While oxygen can be used in small amounts (typically 9% or less) to improve weld pool fluidity, penetration, and arc stability in certain steel alloys, it is generally not recommended for MIG welding due to the following issues:

  1. Oxidation: Oxygen is a highly reactive gas that can cause oxidation of the weld metal, leading to reduced weld quality, increased spatter, and porosity.
  2. Weld Contamination: Oxygen can react with the molten weld pool, causing the formation of undesirable oxides and inclusions, which can compromise the weld’s mechanical properties and appearance.
  3. Limited Applications: The use of oxygen in MIG welding is primarily limited to mild carbon, low-alloy, and stainless steel. It is not recommended for welding aluminum, magnesium, copper, and other exotic metals, as it can cause severe oxidation and weld defects.

Alternatives to MIG Welding with Oxygen

If you’re looking to improve weld quality and productivity, consider the following alternatives to MIG welding with oxygen:

  1. Argon-based Shielding Gas Mixtures: As mentioned earlier, a mixture of 75-95% Argon and 5-25% CO2 can provide a balance of arc stability, puddle control, and reduced spatter, while allowing for the use of a spray transfer process.
  2. Helium-based Shielding Gas Mixtures: Helium-based mixtures, such as 25-75% Helium and 75-25% Argon, can produce a wide, deep penetration profile, making them suitable for welding thick materials and stainless steel.
  3. Flux-Cored Arc Welding (FCAW): FCAW uses a tubular wire filled with a flux, which can provide shielding and deoxidizing properties, eliminating the need for an external shielding gas. This process can be a viable alternative for certain applications.

By understanding the technicalities of shielding gas selection, proper MIG gun consumable maintenance, and the potential issues with using oxygen in MIG welding, you can make informed decisions to achieve high-quality, consistent welds in your projects.

References

  1. MIG Welding with 100% CO2 – YouTube
    https://www.youtube.com/watch?v=pTsithkxj8U
  2. mig welding while on medical oxygen – The Jalopy Journal
    https://www.jalopyjournal.com/forum/threads/mig-welding-while-on-medical-oxygen.193165/
  3. MIG Welding Shielding Gas Basics – Tregaskiss and Bernard
    https://www.tregaskiss.com/mig-welding-shielding-gas-basics/
  4. What is the effect of oxygen in welding? – Chemistry Stack Exchange
    https://chemistry.stackexchange.com/questions/98706/what-is-the-effect-of-oxygen-in-welding
  5. Oxygen in MIG gas mix??? – Miller Welding Discussion Forums
    https://forum.millerwelds.com/forum/welding-discussions/570242-oxygen-in-mig-gas-mix