Determining welding shielding gas ratios

Q: For years we have used 75/25 argon/carbon dioxide during gas metal arc welding (GMAW). I was told by my supplier that I needed to change to 90/10. Will one gas mixture provide better welding penetration than the other? Most of our work is mild steel (A-36), 0.1875 to 0.25 in. thick, although we do go thinner and heavier. Which gas is the best for us?

Choosing the Right Gas Ratio

A: One gas mixture will provide more weld penetration than the other, and equally important, one will provide a better penetration profile than the other. The mix you are currently using should serve you well for the 0.1875- to 0.25-in. material that you’ve noted. You will probably experience more burn-through when welding thinner materials with 75/25. Do you weld out-of-position? If so, the 75/25 will be easier to control when welding vertical-up and overhead.

Typically, the 75/25 will give you more weld penetration and a better penetration profile than 90/100. That’s why it burns through thin material. On the other hand, if you’re trying to reduce weld spatter, rarely weld out-of-position, and tend to weld thinner material (less than 0.25 in.), the 90/10 is a good choice. You will still get good penetration when welding on thicker materials (greater than 0.375 in.), but the penetration profile might be less than desirable (less side-wall fusion).

Testing the Ratio

Advice from suppliers can be helpful, but don’t make significant changes to your weld process without conducting your own tests. Weld samples that represent your common weld joints and cut and etch them to see if they have the profile that you are comfortable with.