Arc Welding 101: Globular-transfer mode for MIG

Q: I am employed as an AWS D.1.1-qualified welder at a machine shop. I was wondering why you can certify on 75 percent argon/25 percent CO₂ when you are not allowed to use a short-circuit transfer on materials over 3/16 in. You need at least 83 percent argon to obtain a spray transfer, yet I passed on a 1-in. test piece. Can you explain this?

A: Your question implies that if your shielding gas mixture is not argon-rich enough to obtain a spray-transfer mode, the only alternative is short-circuit transfer mode. That's just not the case.

When using a 75 percent argon/25 percent CO₂ mix, you would not be able to achieve a spray transfer, but you could achieve a globular-transfer mode. It is quite common to complete the test you described (Unlimited Thickness to D1.1) in the gas metal arc welding (GMAW) globular-transfer mode for all positions (3G and 4G) successfully. This is a fairly typical test given in today’s construction industry.

I think you will find that globular-transfer mode is preferred in industries that utilize a 75/25 mix.

As for short-circuit transfer mode, when I mentioned in an earlier article the possibility of incomplete fusion being a concern on materials thicker than 3/16 in., I prefaced that by including the phrase "in certain positions and progressions." Completing an open-root limited-thickness welder qualification in the vertical progression (root down and fill and cover up) is a very common transfer mode used during testing. In fact, a test of that nature—a root pass with short-circuit transfer mode and the fill-and-cover pass in globular-transfer mode—would successfully qualify a welder in two processes (GMAW-S and GMAW) in a single test.

That would be a good welder qualification to have in your wallet.