Argon Mixes and Specialty Welding Gases

MIG (GMAW) welding with shielding gas and a solid wire electrode produces a clean, slag-free weld without the need to continually stop welding to replace the electrode, as in Stick welding. Increased productivity and reduced clean up are just two of the benefits possible with this process.

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The primary purpose of shielding gas is to prevent exposure of the molten weld pool to oxygen, nitrogen and hydrogen contained in the air atmosphere. The reaction of these elements with the weld pool can create a variety of problems, including porosity (holes within the weld bead) and excessive spatter.

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Different shielding gases also play an important role in determining weld penetration profiles, arc stability, mechanical properties of the finished weld, the transfer process you use and more.

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Choosing the Right Gas

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Argon, Helium, Carbon Dioxide and Oxygen are the four most common shielding gases/mixtures used in MIG welding, with each providing unique benefits and drawbacks in any given application.

 

Carbon Dioxide (CO2) is the most common of the reactive gases used in MIG welding and the only one that can be used in its pure form without the addition of inert gas.

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For many companies, including those that place an emphasis on weld quality, appearance and reducing post-weld clean up, a mixture of between 75% and 95% percent Argon and 5% to 25% percent CO2 will provide a more desirable combination of arc stability, puddle control and reduced spatter than pure CO2. Argon also produces a narrower penetration profile, which is useful for fillet and butt welds. If you’re welding a non-ferrous metal — aluminum, magnesium or titanium — you’ll need to use 100 percent Argon.

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Oxygen, also a reactive gas, can improve weld pool fluidity, penetration and arc stability in mild carbon, low alloy and stainless steel, oxygen mixes are typically in the amounts of 1 to 8 percent. Mixtures of 98 percent argon/2 percent oxygen and 92 percent argon/8 percent oxygen are common gas mixtures.

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Helium, like pure Argon, is generally used with non-ferrous metals, but also with stainless steels. Because it produces a wide, deep penetration profile, Helium works well with thick materials and is usually used in ratios between 25% and 75% Helium to 75% and 25% percent Argon. Helium creates a ‘hotter’ arc, which allows for faster travel speeds and higher productivity rates. However, it is more expensive and requires a higher flow rate than Argon, so you’ll need to calculate the value of the productivity increase against the increased cost of the gas. With stainless steel, Helium is typically used in a tri-mix formula of Argon and CO2.

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Choosing the right shielding gas for your specific application will require a careful analysis of the type of welding you are doing as well as your operational priorities. Using the guidelines above should provide a good start to the learning process, but be sure to consult your local welding supply distributor prior to making a final decision.

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