Welding Stainless exhaust tubing with a MIG

[bjhines]

I am poking through the available options for fabricating my own exhaust.

I am thinking about mandrel bends in stainless.

 

I have considered purchasing one of the Elcheapo $300 light duty TIG welders. I am open to anyone's opinions or stories about these.

 

I currently have a MM 140. I now have 2 tall Argon cylinders. I have considered trading one cylinder in for a different gas mix.

 

What would it take to convert my MIG over to weld stainless. Is it just wire and gas mix that needs to change.

 

I have read that Pulsed arc uses Argon with a tiny amount of O2.

I have read the Short Circuit welding uses Helium/Argon/CO2.

 

I tend to use the pulsed method now for thin stuff. Could I use the same gas mix that I used for the regular steel on stainless steel?

 

 

This is a picture of 20g sheet metal MIG-welded with the pulsed method.

[JMortensen]

After reading some of the threads on stainless I think I would try it with a mig. I'd just get 100% argon (seems to be the recommended gas for mig and stainless) and take it slow. I guess the question is how perfect does it need to be? Yours is a race car, so I'd figure if it doesn't leak that's the important thing.

 

I have actually welded stainless to regular steel on accident with a 220V Miller and I had no idea that it was stainless until the guy who was loaning me the welder told me. Welded just like regular metal in that limited experience. Probably did 20 welds like that, they all came out fine.

 

Also with regards to the MM and sheet metal welding, I usually run my 135 between 2.5 and 3 on the voltage and 25 to 35 on the wire speed and I can run a nice bead on sheet without blowing through. I wonder if you might be doing something else wrong that was causing your previous blow-throughs, like maybe pointing the wire directly at the work instead of coming in at an angle...

[bjhines]

I think that most of the problems with improper gas mix on stainless are related to the tendancy for the welded areas to rust afterwards. I was under the imprression that stainless "welds" easily, but the anti corrosion properties are easily lost in the welded area.

[Nismo280zEd]

I think that most of the problems with improper gas mix on stainless are related to the tendancy for the welded areas to rust afterwards. I was under the imprression that stainless "welds" easily, but the anti corrosion properties are easily lost in the welded area.

 

This was my impression as well. I'm interested to find out the answer.

 

Where do you buy your welding supplies?

[tannji]

I can look into this at work tomorrow, but there are two options that I am aware of for restoring Stainless properties to welded joints, one being an incredibly expensive little machine that dresses the joint, and another being a pickeling agent. The thing that I have wondering is, how would you dress the inside portion of joints that join long pieces?

I will try to follow on this from work tomorrow, unless someone here beats me to it....

[madkaw]

That's one reason I didn't do my exhaust in SS. I wasn't sure what I was doing as far as welding SS and those SS pieces are to expensive to be screwing up. I just did mine in mild steel and later after i study and practice with SS I might duplicate my exhaust in SS. This exhaust stuff sure gets expensive quick. I've got 250$ in mine in mild steel so I figure it would be 500$ in SS. And I am running 12$ glasspacks . I guess dual exhaust makes it a little more $$$$$

[Roostmonkey]

Straight argon and SS wire is all you'll need.As for the welds rusting,you may get some mild surface oxidation from the iron coming to the top of the weld bead but its not anything to be overly concerned with.I use both the expensive electro/passivation machine and a nitric acid pickling paste depending on the application.The paste is nasty zhit but it does a great job of eating the iron off the surface. I tig weled mine and didnt treat it with anything and theres no rust to speak of.I used mandrel 304 el's from Mcmaster's ( 4-90's ) from turbo to tail.

[johnc]

Personally and for most of my club racing customers, a stainless exhaust is overkill unless they are taking advantage of the heat strength advantage stainless has over regular steel. That allows a thinner wall which gives a slight weight savings. An .049" wall mild steel exhaust will weigh less then a .049" stainless steel exhuast, but with stainless you can use .035" wall exhaust tubing without heat related problems.

 

So far, the first 3" OD .049" wall racing exhaust I did is working like a champ 5 years after I made it. The customer pulls it off the car at the end of each racing season and wipes it down with WD 40. It has some surface rust but nothing serious.

 

FYI... this is a car that's raced all across California, Nevada, and Arizona.

 

Use 309L filler to weld stainless to mild steel and 100% argon. Purge the tubing or use a flux like Solar Flux B.

[BirdmanZ]

I use a tri-mix of 90% helium, 7.5% argon, and 2.5% CO2 when MIG welding stainless. Roberts Oxygen recomended it for use with the MIG machine. I have used 100% argon before, but i figured they would know better than I.

[CableSrv]

just curious what do you mean by pulse welding ? I have a miller 140 and it has no settings for pulse welding.... I could just be totally lost tho.. still learning alot of this welding stuff after just getting my 140

[bjhines]

I have been using the technique of starting the arc and letting one drop of filler fall onto the surfaces. then I release the trigger and wait ~1 second for the area to cool. You press and release the trigger repeatedly to form a bead.

 

The wire starts the arc and shrinks back while the arc melts the parent metals. then the drop of molten filler sticks them together. This does a very good job on thin metals when you get the timing right.

[Roostmonkey]

as for timing, wait for the orange glow to disapear from sight with your helmut down.

[SHO-Z]

One thing that you want is full penitration on the weld. On SS you get "Sugaring" on the back side. Sugaring will cause turbulance and reduce your exhaust flow.You can either purge the tubing with argon or your weld gas or use Solar Flux.