Tuesday, April 29, 2014

GMAW Globular Transfer

I work at a machine shop where I am employed as a qualified welder to AWS-D.1.1. I was wondering why it is that you can certify 75% argon and 25% CO2 when you are not allowed to use a short circuit transfer on materials over 3/16". I read your article every month and in order to obtain a spray transfer you need at least 83% Argon but yet I passed on a 1 inch test piece.

Thanks K. B.

Your question insinuates that if your shielding gas mixture is not Argon rich enough to obtain a Spray Transfer mode the only alternative is Short Circuit Transfer, that's just not the case.
When using a 75% Argon and 25% Co2 mix you would not be able to achieve a Spray Transfer, but achieving a Globular Transfer would be no problem. It is quite common to complete the test you discribed (Unlimited Thickness to D1.1) in the GMAW Globular Transfer mode for all positions (3G/4G) successfully.  This is a fairly typical test commonly given in todays construction industry.  I think you will find Globular Transfer a prefered transfer mode in industries that utilize a 75/25 mix.
As for Short Circuit, when I mentioned in an earlier article, the possibility of incomplete fusion being a concern on materials greater than 3/16th inch, I prefaced that by including, "... in certain positions and progressions...".  Completing an open root limited thickness Welder Qualification in the Vertical progression (Root Down/Fill & Cover Up) is a very common transfer mode used during testing.  In fact, a test of that nature, Root Pass with Short Circuit, Fill and Cover Pass in Globular, would successfully qualify a Welder in 2 processes (GMAW-S & GMAW) in a single test.
That would be a good Welder Qualification to have in your wallet.

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