new to Stainless steel welding with MIG

[geordiesworld]

Hello to all.

Been browsing this forum for some time and very impressed with the depth of knowledge, quite humbles me ..
Anyhoo, I have been welding since I was 14 odd i think (over double that age now!) on our farm. We have used an old arc welder from ancient times and more recently in the last decade 2 different MIG welders with our current machine a 200amp single phase MIG with Cougar 5 gas, 0.8mm mild steel wire. We also have a propane and oxy gas setup for cutting and heating, etc, no acetylene now .. All our work has been normal mild steel gates, tractor parts / implement repairs, etc. My welds are good and pretty neat with the MIG now.
Recenty I have embarked on a project to include the construction of a stainless steel assembly to act as a structural tie in a sandstone barn conversion. I have a concept / design for this and would like to weld it up myself. It will be 3.2 m etre sin length consisting of two tubes with a flat bar piece between them, cross section like a dumbbell. Each end will have a mounting flange plate welded for resin anchor bolts through into the stone.

My question / seeking advise on is using 304 stainless and 308L wire in the MIG with the Cougar 5 gas would I get a finish that i could clean up with pickling paste or similar to be asthetically pleasing enough to the eye, as this piece is to be exposed and admired .. ! ??

I know TIG may be better but that would require me to purchase such equipment and then learn how to use it which as far as I can gather is far from easy ..

Stabilising the pieces as I weld them to stop distortion will be a challenge. I will weight it down and bolt it or its jig to a concrete floor, and surely as long as i weld in bursts / stiches moving around the piece from tack to tack spreading the heat should limit this ? ANy other ideas ?

Just your thoughts ladies and gentlemen ..

Many Thanks in advance

Geordie

 

[TechnicAl]

ideally you want Argon + 2.5% CO2....I think Cougar 5 is 5% and that often results in a "Black" weld that doesnt clean up too well.

 

[knoba]

I had a go (first & last time) on a 304L 2.0mm stainless project of mine, on a 200 amp mig (transformer type). Gas was BOC's "Stainsheild light". Wire was murex 0.8mm 316L. New teflon liner, tips, etc. Immaculate prep, dedicated consumables, recommended settings, etc!

Even with all that, I sometimes had to do the welds 2 or 3 times to get proper fusion along the joint lines. When I dressed back the welds, flush after welding, there were gaps...

Still, might just have been me...

Stainless deforms easily if it gets too hot. This can include polishing & dressing. If the structure is heavy, or stressed, it can deform under its own weight while welding it. Plan the job well, lots of tacks & lots of tea breaks to let it cool between welding sessions.

Tig's the way to go, it's not that hard, just more expensive really.

HTH

Oh... I forgot to mention; I'm on pretty good terms with my gas dealer. He let me take away & try the stainsheild (for nothing). Worth asking if you can 'try before you buy'!

 

[Tino]

If the stuff your using is more than a couple of mm thick you could stick weld it. Some rods wouldn't cost much and usually give nice looking welds. Would save messing with liner, gas, settings or T.I.G, a few practice runs and away you go.

 

[backpurge]

It is hard to get stainless MIG to look pretty, as stated you need a gas with low CO2 content such as 2.5% and you want to be welding it in spray transfer if the material thickness will take it and remember to travel as fast as you can with no weaving

As Tino says if you can I would stick weld it

 

[Drains]

Got to agree with Backpurge and Tino- go for rods. Most stainless rods are very easy to use, but make sure of the open circuit voltage on your arc set and the rods before you buy! Some stainless rods need over 50v.

 

[TechnicAl]

usually best on DC+