Been busy for my employer today. Replies are on my available time.
The trimix gas inquired about (89%AR, 8.5%CO2, 2.5%O2) is a listed product offering of Airgas. That surprised me. My friend with 57 years as a welding supply distributor reminded me of that when I phoned him today on your behalf. Its intended use is spray-arc MIG to lower heat input on carbon and hardenable low alloy steels as Chris Hamilton has noted with O2 addition to 5% max. O2 is used to get spray arc transfer of filler droplets across the arc. The newer "pulse spray arc" is used with power sources that either have that function as a manual switch flip and control of pulse current pulse width and duration or those nice new fancy inverters that have that as a synergy function built in without the ability to adjust those parameters yourself. In that case--wire diameter is often the variable.
This gas is a liability for you to use with your small Lincoln MIG welder if indeed it does not have pulsed spray arc capabilities.
I only use spray or short-arc in my industrial work and forgot about pulsed spray MIG. I have qualified about a hundred welding procedures and thousands of welders to work under various legally required codes. Many of these welding code share similar ideas about welding outcomes. They are not perfect or Gospel--just the best for the moment to minimize problems.
So in my 31 years as a welding engineer/welding metallurgist what I can tell folks who are hobbyists etc. is:
"Strike and arc on it--you own it, it's good things and it's liabilities you might not be aware of---for better or worse."
It would seem from replies, Chris and Crashtech work or have worked where their employers became accredited to use I-CAR logo and various levels of accreditation that organization offers. None of it appears to be inexpensive. Welder training and then "welder performance qualification" testing in various levels is offered. A welder certification is simply a written attestment of whoever gave the tests to the person. The employer is always responsible to accept the welding work of his/her employees to meet any such accrediting requirements. My opinion is that the automotive collision sector has done a noble and admirable job with what I-CAR has today with using welding for repair work of "returning the vehicle to pre-accident factory approved repair". People who have these I-CAR welding Certs--I tip my hat to you. They are trying to steer you away from known dangers.
I will add another way--look at the wire spec you are using on the wire spool or box label. Should be AWS 5.18. ASME calls it SFA 5.18. Use only the gases listed within that and you have not strayed from how the wire was intended to be used. CO2 was used to qualify the wire--the worst case shielding gas can still meet the spec. and pass a radiographic soundness test as well. Please see attached.
