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MIG welding stainless

TerryD

TerryD

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I was wondering how critical the type of shield gas is when welding stainless. I need to make a couple 1" long welds but my shield gas is not what the chart in my welder recommends for stainless. I was wondering if it would have a huge effect on the quality of the weld anymore than my having never welded stainless before.
 
I have a C25 mix now, but the chart recommends a "Tri-Mix" (90%He/7.5%Ar/2.5%CO2).
 
I've only mig welded SS with whats recommended, whatever that is I don't know. But with it, it welds really nice. I haven't done a ton of MIG SS welding but enough to know it's a good quality weld vs any other weld process, just as good I mean. Sure it's a different looking weld vs tig, but just as quality in strength if welded correctly. I want to get into a lot more stainless sheetmetal fabrication so I plan on doing a lot of SS MIG welding in the future.
 
Well, it seems to work. It throws some spatter but that may be my lack luster welding ability.
 
Well, here's what I got. Not pretty by any means, but they appear to be attached.

uploadfromtaptalk1412962937517.jpg

uploadfromtaptalk1412962937517.jpg
 
Yes thats basically the outcome. Ive mig'd stainless with both. The trimix works way better and will give your weld better flow. Also on really thin stuff the co2 will promote burn through the trimix will prevent.
 
Good to know. I need to look into a tri-mix set up then cause I'd like to do some thin wall tube in the future.

It all held though! The tank never moved and I flogged the K5 pretty hard in the mucky goo the trail had turned into by the time we got there.
 
I weld a lot of stainless at work and I never switch to tri-mix when using MIG. That being said all of the thin stainless work I TIG while the heavier plate work I use the MIG. Like stomis said if you are going to MIG weld thin stainless you might want to try the tri-mix.
 
Avery4jc said:
I weld a lot of stainless at work and I never switch to tri-mix when using MIG. That being said all of the thin stainless work I TIG while the heavier plate work I use the MIG. Like stomis said if you are going to MIG weld thin stainless you might want to try the tri-mix.
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I actually noticed when I was using the straight CO2 that sometimes the arch would actually seem like it continued until the shielding gas dissipated. I couldnt figure out wtf was going on. Im not exactly a text book technical welder but I know I wasnt crazy because I actually blew through some **** after I had completely backed the gun away.

:confused:
 
For exhaust work I just load stainless wire in and use the regular C25. I just don't feel like buying into another tank. With this gas, the stainless doesn't lay down quite as nice as the mild, but it's acceptable for non-cosmetic welds.

PICT0715.jpg
 
I don't have any first hand experience MIG welding stainless, only TIG. But I did read somewhere in a technical manual or something a while back that MIG with the C25 on stainless can leave impurities on the surface and then the stainless can actually rust later, the tri-mix supposedly doesn't do this. However, I can't confirm if that is true.
 
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Everything I'm reading now says that to weld stainless tubes you need to fill the tube with shield gas while you weld. They usually use a dual-flow system for the gun and the purge. The other option is Solar Flux brushed onto the backside. Let's say I expand one pipe to slip over the other, then MIG with C20 and stainless wire. Is my exhaust really going to crack or rust later? Wouldn't it still be better than clamps? I'm planning to do a tailpipe and it will be like 5 different bends pieced together, so the joints need to at least hold the thing together.

I would try Solar Flux, but $50 a can is a lot for experimentation. Plus, it seems like a narrow window of that the mix is good for, so after all fitting was done, the tack welds would have to come off to get to the inside joints. So the risk of getting the final weld misaligned is pretty high.

Or am I overthinking this? That flex joint I posted above has been fine so far and I didn't do any special prep.
 
You do not NEED to back gas stainless steel. Back gassing stainless is a practice used a lot when you're trying to make a full penetration weld in a butt joint. We do it at work when doing no filler tig passed on tubing. It also allows you to get a beautiful weld with very nice color and zero impurities.

Theres a bagillion things made of stainless that literally can't be back gassed.



O and for the record you're already not doing it technically correctly using 75/25 to weld stainless so throw the back gassing out the window.
 
Stomis said:
Hobart Handler 140.
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Not sure how I missed this but that's good to know. I have the 187. No more stainless work for any foreseeable time so it's been dropped until I need it again. Other, more pressing things going on for the time being.
 
Stomis said:
Back gassing stainless is a practice used a lot when you're trying to make a full penetration weld in a butt joint. W

O and for the record you're already not doing it technically correctly using 75/25 to weld stainless so throw the back gassing out the window.
Click to expand...

That's part of why I planned to expand the tube ends and slide one over the other. Seems like the shield gas is going to pretty much cover everything. It's 16 gauge tube so I shouldn't be deforming the inside much. I can't believe that factory exhausts are all welded with a back gas.

I just haven't picked up another bottle of shield gas due to expense. If I could straight rent a bottle and pay for what I use I'd be all over that.
 
Blue85 said:
That's part of why I planned to expand the tube ends and slide one over the other. Seems like the shield gas is going to pretty much cover everything. It's 16 gauge tube so I shouldn't be deforming the inside much. I can't believe that factory exhausts are all welded with a back gas.

I just haven't picked up another bottle of shield gas due to expense. If I could straight rent a bottle and pay for what I use I'd be all over that.
Click to expand...


Its probably safe to say the factory exhaust was NOT welded with back gas. Unless maybe we're talking about a very high end low production number car. In which case they probably would back gas it. Just have a chamber purged with argon like a blast cabinet.
 
So I built an exhaust with 409 tube, Hobart .030 stainless wire, and regular C25 mix. This wire jams on the roll all the time and made it impossible to get longer continuous beads. The arc also wanted to wander all over the place, which is probably from using the wrong shield gas or maybe the machine had been drinking? Other than that, it seemed pretty clean with virtually no splatter. Not pretty, but I didn't find any leaks.
 
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