MIG Welding 20 ga sheet metal, argon or CO2

[Samckitt]

Which do you use?

[Motorcitydak]

I always use the same 75/25 gas for mig welding mild steel and stainless

[SShep71]

75/25 or 92/8

[parsonsj]

You shouldn't use 75/25 to MIG weld SS. It leaves enough carbon in the weld to allow oxidation. But to answer the OP's question, I use 75/25 for mild steel MIG welding.

[Samckitt]

Well welding this thin ***** is kicking my @ss. Today I got one of those copper spatula things to put behind it to try.

[jlcustomz]

Straight co2 is cheapest, but dirtiest welding. 75/25 most common , but not meant for stainless. Tri-mix, which contains helium is for stainless, but some use it for regular steel also because it can weld a little cleaner & hotter. I used to buy it before I got a tig for stainless, but it has gotten EXPENSIVE since it has helium. Straight argon is for tig or aluminum with mig, which requires spool gun.

So Scot, I say 75/25 gas at 20 -22 on flow, 023 -025 wire set properly with good fitment & mostly spot welds jumping around for warp control. Stainless wire brushing between spot weld passes won't hurt either.Some even snip the blob off the wire before each start.

Shut off main tank valve if stopping for more than a few minutes, ABSOLUTELY shutoff when done. Empty, barely used tanks suck, especially when welding supply shops usually run near bankers hours.

Also beware using any galvanized steel. It welds nasty, even with a little grinding to remove galvanizing, & emits poison gas. I mention this because galvanized is much easier to get in my (damp) location.

Mig is one of the easiest forms of welding to make a weld on steel, But takes some extra practice, skill, & patience to do a nice, neat, & properly penetrated without being burned through job. Use extra care also when grinding thin stuff not to overheat.


Do you have small wire & did you practice on samples first??? NOBODY is an expert overnite. I don't weld everyday & usually get better again after a little more useage each time.

[Motorcitydak]

Thanks for the info on the SS welding. I should have mentioned that I only needed to weld a patch or two on a SS exhaust. That was the first and probably last time Ill be doing SS, 1018 for me the rest of the time

If you are having the metal melt away, its not the gas. You are putting in too much heat. As mentioned above on 20ga you need to stitch weld. Just miles of tack welds until they finally join up and make 1 long complete seam. Jump around a few inches at a time then back track and throw down another tack

[raustinss]

Jlcustomz has some good info but from someone who does it everyday we use 85/15 or 75/25..either is good...as far as using a stainless brush..dont bother as soon as you use a s.s brush on carbon steel you have ruined, try a brass brush or a regular old carbon steel brush. if you can find one for a die grinder or angle grinder get it...your arm will thank you later. also a piece of brass or copper or even aluminum can be a great aid for a novice sheet metal welder, it will act as a heat sink and help with burning thru. If you want a cheap source for locating something to use. Check out any local fab shops, machine shops,even foundries. I used to work a a foundry and grabbed a few 2x1/4 flat bars about 18" . absolutely perfect. I just hammer them to conform to my work piece and go to town.
Best of luck ryan

[RobNoLimit]

C25, or 75/25 is pretty standard. More help may be the wire. Try running .023 dia. with the correct tip. The fit of your material will be more critical, and the material will tend to spread and warp more, so take your time. Secure clamping, and/or liberal use of cleco's will help. Also, weld up a small section, 1" or so, then use a hammer and dolly to close up the seam again.