Welding stainless exhaust

[VenturaII]

I was told I could weld stainless with my mig with the proper wire and gas. Is there any reason I cant or shouldnt buy a kit and cut and weld up an exhaust system this way?

[Matt@RFR]

You bet. Find out what alloy the material is (probably 304) and buy the correct alloy wire:

304 base - use 308 wire
321 base - use 347 wire

And you can use your 75/25, but it'll spatter. "Tri-mix", which has some helium in it, works much better.

[VenturaII]

I was hoping it would work. Thanks Matt!!

[airrj1]

Ventura,

Can I tag onto your question? I wanted to know what gauge pipe you can use for exhaust pipe? If you were using 304 in a 2 1/2" or 3" pipe, what gauge would be suggested?

Thanks.

[Matt@RFR]

16ga is the most common. Some use 18ga to save "weight" (mostly from your wallet). And when you order tubing, it's .065 wall, not 16ga.

[Restomod]

Let me throw a wrench in the mix.....what about welding Titanium??? For exhaust that is......

[Matt@RFR]

What do you want to know?

[parsonsj]

Yep, just get the right wire, tri-mix gas and weld away. My cheap Lincoln MIG works just fine with stainless.

I've found the stainless doesn't penetrate as much as ordinary steel, so you'll need to make some minor setup adjustments, weld a bit more slowly, etc.

jp

[BRIAN]

Hey Matt 2 questions: I always have problems with distributor in regards to gas. I swear it is different with each fill as weld looks different with all other factors being the same. Back to the question can you use the tri mix with steel and stainless?? 2nd I never attempted titanium? What is involved??

[RobM]

i know ti has to be tiged in a clean enviroment aka a bag filled with gas. i think a full exhaust would be difficult to impossible for the average fabricator. but that would be very cool. you need some serious equipment though to weld ti as far as i know

[Matt@RFR]

Brian, invision one of today's finest minimum wage employee's filling up your argon bottle...because that's how it happens. Industrial grade argon (what you have) is supposed to be 98.5% pure argon if I remember correctly, so the mix has a little room to be different fill to fill. "Pure" argon is 99.99% argon, and is surprisingly more expensive.

Do you check the flow rate after every fill? Have you checked the entire gas system for leaks? What signs are you seeing that makes you feel the gas is different?

You might just be one of the few that's persceptive enough to see the difference from fill to fill.


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Titanium can be TIG and MIG welded. True, it's best to weld Ti in a "glove box", but it can be welded in open air with some accessories.

A glove box is an air tight chamber that is first pulled down to about 5" of vacuum, and then is purged with pure argon to inflate it back up. They have integral gloves inside them, and are clear.

To weld Ti in open air, you have to provide a trailing shield of argon to the cooling weld. Ti can react with the atmosphere until it's below about 800ºF, so it has to be covered with gas until then. You can make your own out of thin sheetmetal (make a 5 sided rectangle that attaches to the torch) and provide a gas inlet. Then fill it with sintered bronze packing to distribute the argon. An assortment of curved trailing shields are needed to do pipe and tubing.

Welding Ti is a lot like welding stainless. Just like stainless, shiny silver and light blue is perfect. But depending on the application, orange, gold, dark blue and purple could be fine. (color is a direct indicator of contamination, heat, and gas coverage. The further away from perfect, color wise, the less corrosion resistance it will have, and the more brittle it may be.)

Weld prep is where Ti is different than stainless. It needs to be perfectly clean to get an acceptible weld. Most shops will degrease it, wire brush it or machine it and handle it with Ti-only gloves. Most shops will also keep their filler in an argon chamber until it's used, and they have a set limit to the maximum time the filler and base matel can be exposed to atmosphere before it has to be re-prepped.

As far as the physical act of welding titanium, it's really not that different. It's all in the prep and gas coverage.



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Tri-mix can be used on steel, but it's a lot more expensive than 75/25, so you'd be ahead of the game to either buy one of each, or buy a bottle of 75/25 for normal use, and just rent a bottle of tri-mix if all you need it for is a couple weekends.

I want to reiterate that 75/25 is ok to use with stainless wire, but it will spatter quite a bit, and you'll have to run alittle hotter to make up for the missing helium that would be in the tri-mix.

[BRIAN]

Matt I fear answering any welding question to a REAL welder as I usually get ripped a new one. I know you gys are super techincal and touchy about welding. With that said my stupid answer is: I feel that when welding 1/8" and up that sometimes I can achieve what has been described to me as Spray Arc? type weld. I beleive that is the term. I had discussed with one of the fabricators at S&W after I questioned the cleanliness of the wleds on brackets they did for me on a 9". Othertimes using evey other variable the same I can't reproduce this type of weld. Ok am I right?

[Matt@RFR]

MIG transfer modes:

Short circuit or short arc: That's what most of us use every day. Associated with the "frying bacon" sound (which never has made any sense to me!)

Spray transfer: This is reserved for the heaviest of weldments (1/2" and up usually). It takes lots of amperage, and a high CO2 content gas like 90/10, 95/5, or 98/2 (as opposed to the normal 75/25). By nature, it gets excellent penetration and fusion, and can be run in all positions, except vertical down. You mainly just run stringer beads, and you'll know when you're spraying by the sound; all you'll hear is a "hiss".

It's been awhile, but I'm pretty sure that you need to be at around 28 volts to get into spray mode, so I highly doubt anyone is using it on rear end brackets...especially since short arc is cheaper (less wire used and a standard gas), and is more than adequate for that type of weldment.

Anyway, Brian, I'm still not exactly sure why you can't get consistency out of every bottle of gas, but for sure you'll never get into spray mode with 75/25.

[BRIAN]

Like I said I feared that answer. Hey maybe it is in my head or welding technique but it appeared to be gas to me? All I can tell you is what I was told regarding the technique used.

[BRIAN]

If I was given different gas combo what would the effects be??? There has to be a difference, right?