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Why You Can't Use the Same Gas for All Welders

Mr. TIG from drops by the studio gets the video started by greeting Kevin, who explains he was just about to do a how-to video based on questions from viewers who have a MIG welder and get a TIG. They want to know if they need to get another bottle of welding gas. Why can't they just use the bottle of mixed gas they are already using on their MIG welders?

Mr. TIG explains that, many years ago, CO2 was the only gas used with MIG. It worked fine for steel except when you pulled the welding torch trigger and the wire hit the part, you would get a lot of spatter. By mixing in argon gas, you get a much nicer weld with deeper penetration.

If you have a bottle of mixed, or blended, gas, which is 75% argon and 25% CO2, you'd think the argon would work great for TIG. It doesn't. The CO2 is an active gas. When you pull the trigger on your MIG welder and the wire comes out, it's live, very much like arc welding. With TIG welding, it has to be 100% inert. It can't be active at all, with any volatility.

So when somebody tries to use mixed gas they know right away. They will have set up their new TIG machine just right, but when they light an arc on steel, it starts a puddle then flares up. The first thing Mr. TIG asks is if they are using their MIG mixed gas. They often ask, "What's that?" He says it happens every day.

With TIG welding, you can use argon for everything. It's a completely inert gas that transfers the arc. You need a nice flood of argon gas to get the arc initiation right. Sometimes Mr. TIG will hit the foot pedal just to get the argon flowing, then hit it again, and the arc will initiate beautifully on almost every machine.

Argon is good for welding steel, stainless steel, inconel, titanium - all metals. For 95% of all the welding Mr. TIG does today, he uses straight argon. For the rest of the projects, he might use a specialty mix with a little helium or other gas.

To test what happens, Kevin has a piece of 1/8" plate off of which he's ground all the mill scale. He's going to use his Longevity ProMTS 200, which has TIG, MIG and stick (arc) to run a bead with argon, then switch it to the mixed gas to show the difference. He set the machine at 104 amps and uses a little filler rod.

Then he keeps everything the same except he switches to the mixed gas. Immediately you can see the sparks flying like fireworks on the 4th of July. Mr. TIG said that is the first sign that something was wrong. You also can see there was a problem when you look at the two welds. The first weld, made with 100% argon, looked like a regular TIG weld. The second weld, for which he used the MIG gas mix, is ugly: there's smoke, a big crater, and it almost looks like it rusted.

What if you used just argon with the MIG, though? Mr. TIG explains you can weld aluminum just fine. The argon allows the material to wet out - not nicely, but it does wet out.

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