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Old 06-26-2010, 11:01 AM   #1
Koji
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Default Exhaust Welding - Why TIG?

In the not to distant future I've got an exhaust to weld for a non-Subaru application. I've got a ton of raw materials in terms of pipes of different diameters, and a combination of stainless and mild steel.

I've got both an Oxy-Acetylene setup and a MIG welder. The oxy I'm mostly using to join sheet metal and MIG I'm using as general use.

I've read at least a couple of articles that say that you can MIG weld an exhaust but TIG is preferred. Why? I haven't tried TIG welding yet so I have no idea how different it is or what applications I'd use it for.

Also I assume I can't oxy-weld it because the flame that's joining one side would be blowing a hole in the other. That sound about right?

Cheers,
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Old 06-26-2010, 03:02 PM   #2
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Tig welds are way stronger, but you need a tig machine and there not cheap. Im not a professional but i tig and mig weld from time to time. Tig takes some time to get the form down smooth. Its a lot more intricate but the way the metal puddles and beads makes it overlap and bond better than just a mig weld.
Also the wire in your mig welder is harder than the rod used in tig welding, and ive found that in high stress areas of force or high heat areas the harder mig wire seems to crack easier. Thats basically a basic overview but i hope it made some sense.
You can still mig weld your exhaust and it should be fine as long as its not headers

Last edited by Leadsled124; 06-26-2010 at 03:03 PM. Reason: grammer
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Old 06-26-2010, 04:56 PM   #3
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TIG welding is usually much slower, so you end up with much more precise, clean, and penetrating welds.
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Old 06-26-2010, 06:04 PM   #4
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There is nothing wrong with mig welding an exhaust system. TIG is a lot cleaner and more precise and will look a million times better if you know how. But if you already know how to mig weld, that will be easier and prob come out better than trying to learn how to TIG weld while doing it. TIG takes a while to get down, and years to master.
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Old 06-27-2010, 08:59 AM   #5
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If you're welding up mild steel, just MIG it. If you're working with stainless, you'll want to TIG it for stronger welds. I've done it both ways, including MIG for tacking and TIG for final welding.

Jay
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Old 06-27-2010, 01:02 PM   #6
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If you are proficient with Oxy welding you will probably be able to pick up TIG without too much problem if you do start working with it.

The strength of the welds and cleanliness of the welds are the real reason to use TIG.
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Old 06-27-2010, 10:41 PM   #7
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OP:
Try to ignore some of what was written above...some people are just misinformed.

People like TIG because it is pretty. You are welding an exhaust (that no one will see) so we really don't care how pretty it is.

You will be able to use your MIG just fine. I assume it is a 110V welder that runs .030" wire. Go to your nearest welding supply company and tell them you are wanting to weld some stainless exhaust pipe and you need a suitable wire for the job. More than likely they will have small (5lb) spools of .025" or .030" 308L (for SS to SS) and 309L (SS to carbon steel) welding wire. Use that. You will also need a different shielding gas for this job (98%Argon 2% Oxygen would be the most preferred). The wire will be ~$8 per pound and the gas will be not too bad for a small bottle (5-10 cubic feet). Once you have what you need you need to just play with the machine until you get the desired weld bead (nice and flat with no overlapping edges and enough penetration).

If you have any more questions feel free to ask. I am a new Subaru owner but not new to welding (B.S. in Welding Engineering in fact).

Hope that helps!
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Old 06-27-2010, 11:17 PM   #8
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Quote:
Originally Posted by bigusnickus View Post
OP:
Try to ignore some of what was written above...some people are just misinformed.

If you have any more questions feel free to ask. I am a new Subaru owner but not new to welding (B.S. in Welding Engineering in fact).

Hope that helps!
Now we're talking.

This exhaust is for a car that makes the exhaust even less visible than it is on your average Subaru. I absolutely don't care what it looks like as long as it functions.

Welder wise I've got a Hobart 110v with an 80/20 mix of Argon and CO2. I got it off of CL and it came with a 10lb spool of .23 wire. It's been fine so far for what I'm using it for.

The exhaust is for a single turbo setup on a V6. I've been collecting bits and pieces of Subaru exhaust for years now (seriously) and I've got a ton of stuff saved up. The turbo is going to be a Subaru pattern turbo because I've got several laying around so they're a sunk cost.

Most guys who turbo this motor do it with the stock manifolds and I don't have a good reason not to use them. They've already got 02 sensor bungs for dual widebands which is what I plan to use for tuning along with a stand alone.

So...I've got to get from two pipes down to one (could use a Subaru uppipe with a Y), then a downpipe out the back to a cat and a short exhaust system.

I've got both stainless steel and mild steel uppipes and downpipes. Given I've got basically four flanges to weld would it be worth it to get a different shielding gas? I'm fine with buying a bottle of something different I just don't want to waste money. Would that level of oxygen content be a non-starter for use with mild steel?
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Old 06-27-2010, 11:56 PM   #9
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Quote:
Originally Posted by Koji View Post
Now we're talking.

This exhaust is for a car that makes the exhaust even less visible than it is on your average Subaru. I absolutely don't care what it looks like as long as it functions.
Just because it isn't going to be visible to everyone, doesn't mean you should care what it looks like, or at least try to make it look good. Thats not the best attitude to have about it.

I am a welder, I currently work @ 3 different places. my full time job is mostly structural steel, and some railings and what not. All the welds need to be done right, but, don't always have to look that amazing, in fact a few of us get told quite often not to make the stuff look so good because it doesn't matter. My part time job is mostly ornamental and has to look good. My 3rd welding job is @ my friends fabrication shop. (my user name) there we deal mostly with TIG, chrom-moly roll cages, stainless exhaust and turbo headers, and aluminum intercoolers and intercooler plumbing, so, everything welded there needs to look as good as it can possibly look while being as strong as it can be. And no matter what I am welding at any of the places i work i always try and make it look as good as my ability will allow me. It's good practice, and the more you weld, the better you get. If you always go into it with the attitude of, ohh, this cant be seen, it doesn't matter, then you are gonna start bad habits. but if you treat every single weld like it's in a visible area on a show car, then when it comes time to weld something that everyone CAN see you will just be able to weld it like you weld everything else.

thats my opinion anyways, i hate when people half ass and cut corners. if you just take the time to try to make it look good and fit good it will just make you a better welder/fabricator overall in the end. it's time well spent if you ask me.

but as for your exhaust, MIG is fine, my whole exhaust is MIG welded (it's all 3" Mild Steel) and it looks pretty good.
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Old 06-28-2010, 03:19 AM   #10
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I think you queued in on the wrong thing dude. It doesn't mean I want my welds to look like hell I just don't care if the weld rises to the level of art (which some TIG welds do) as opposed to looking just sort of OK but being strong (like my current MIG welds). If you're doing the process right any weld is going to look at least decent because inherent in the process is creating a good bead, weld pool, and join between the two materials.

In any event, almost all my exhausts end up wrapped in exhaust wrap anyway - or at least the manifold and downpipe sections. So it will literally be impossible to see no matter what I do.
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Old 06-28-2010, 08:42 AM   #11
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Koji,

You are much better off going 98/2 for gas. There are just too many chances for porosity and possible cracking with 80/20 and SS. See if you can even go as far as renting the bottle AND gas from the supply company.

EDIT: 80/20 is just fine for Mild Steel, so you should have zero issues if just welding mild steel to mild steel.

-Nick

Last edited by bigusnickus; 06-28-2010 at 08:44 AM. Reason: added mild steel info
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Old 06-30-2010, 04:41 PM   #12
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Quote:
Originally Posted by bigusnickus View Post
OP:
Try to ignore some of what was written above...some people are just misinformed.

People like TIG because it is pretty. You are welding an exhaust (that no one will see) so we really don't care how pretty it is.

You will be able to use your MIG just fine. I assume it is a 110V welder that runs .030" wire. Go to your nearest welding supply company and tell them you are wanting to weld some stainless exhaust pipe and you need a suitable wire for the job. More than likely they will have small (5lb) spools of .025" or .030" 308L (for SS to SS) and 309L (SS to carbon steel) welding wire. Use that. You will also need a different shielding gas for this job (98%Argon 2% Oxygen would be the most preferred). The wire will be ~$8 per pound and the gas will be not too bad for a small bottle (5-10 cubic feet). Once you have what you need you need to just play with the machine until you get the desired weld bead (nice and flat with no overlapping edges and enough penetration).

If you have any more questions feel free to ask. I am a new Subaru owner but not new to welding (B.S. in Welding Engineering in fact).

Hope that helps!
+5 billion! Ive MIG'd probably 20 plus exhaust systems and five or so were all stainless. Never had any welds crack. Just make sure you wire brush all your connections before you weld em up and dont forget to turn on the gas!
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Old 06-30-2010, 04:49 PM   #13
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and remember to keep your dedicated stainless/al brush out of mild steel's way
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Old 06-30-2010, 07:53 PM   #14
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+5 billion! Ive MIG'd probably 20 plus exhaust systems and five or so were all stainless. Never had any welds crack. Just make sure you wire brush all your connections before you weld em up and dont forget to turn on the gas!
just out of curiosity... when you say "wire brush all your connections" are you talking about where the flange/materials meet? Are you also talking about for stainless? Just curious... cause im a stainless sheetmetal working and ive never wire brushed stainless before welding....stainless as far as i know is not like aluminum and doesnt require brushing/cleaning before welding... assuming you dont get any dirt and greese where you are welding lol
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Old 06-30-2010, 09:06 PM   #15
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^^^ I would think it's not a bad idea, to expose some homogeneous material. Stainless is typically passivated after manufacture which changes the surface's composition a bit.
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Old 07-01-2010, 01:05 AM   #16
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What's the purpose of separating the AL/Stainless brushes from the mild steel brushes? Can I use the same brushes on AL and Stainless or do those need to be separate as well?
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Old 07-01-2010, 10:37 AM   #17
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Quote:
Originally Posted by Deathclutch View Post
just out of curiosity... when you say "wire brush all your connections" are you talking about where the flange/materials meet? Are you also talking about for stainless? Just curious... cause im a stainless sheetmetal working and ive never wire brushed stainless before welding....stainless as far as i know is not like aluminum and doesnt require brushing/cleaning before welding... assuming you dont get any dirt and greese where you are welding lol
At my shop pretty much all the metal I fab with has either been sitting outside in the scrap pile in the Oregon weather or I purchase it from a remnant yard, so its dirty. I wire brush everything I am going to weld to be on the safe side. Just make sure your welding area is clean and free from debris/contaminants.
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Old 07-01-2010, 11:12 AM   #18
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What's the purpose of separating the AL/Stainless brushes from the mild steel brushes? Can I use the same brushes on AL and Stainless or do those need to be separate as well?
you use stainless bristled brushes for cleaning al or ss, and mixing it with mild steel contaminates the brush and you're done.
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Old 07-01-2010, 10:00 PM   #19
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At my shop pretty much all the metal I fab with has either been sitting outside in the scrap pile in the Oregon weather or I purchase it from a remnant yard, so its dirty. I wire brush everything I am going to weld to be on the safe side. Just make sure your welding area is clean and free from debris/contaminants.

i can completely understand that then! I work in a shop making custom stainlesss kitchens/hood systems/whatever the customer wants shop! So when the stainless comes in it is covered in vinyl, we mainly use 18ga, 16ga and 14ga. In that scenario there is no reason for me to brush it... in fact it would only make my job harder polishing out the scratches lol
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Old 07-01-2010, 10:54 PM   #20
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Also the wire in your mig welder is harder than the rod used in tig welding,
The wire is exactly the same, 308/309/316 is the same if it comes in 36" lengths or 44# spools. Same goes with steel and aluminum. Now, the finished weld might have more or less ductility, but that is dependant on the parameters and the weldor.

Quote:
Originally Posted by bigusnickus View Post
OP:
You will also need a different shielding gas for this job (98%Argon 2% Oxygen would be the most preferred).
Im not so sure about that... 98/2 generally is used on heavier sections. Tri-mix will give a much nicer bead appearance with the small machine.

One last thing, if both welds are of sound quality under identical conditions then TIG and MIG are equal in strength. However it is MUCH easier to F-up a MIG weld.

Finishing up my B.S. in Welding Engineering.
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Old 07-02-2010, 09:31 AM   #21
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Im not so sure about that... 98/2 generally is used on heavier sections. Tri-mix will give a much nicer bead appearance with the small machine.
Ah yes, I forgot about tri-mix...we do all heavier sections and tri-mix is more $$$ so I put the blinders on.
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Old 07-04-2010, 03:06 AM   #22
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if you mix up the two, your in for a world of wandering arc.

BTW, how do you all sharpen your tungsten? I think I contaminated mine..
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Old 07-04-2010, 03:22 AM   #23
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I have always run C25 on my welder. I like it better than the tri-mix. Never heard of 98/2 even.

Never went to school for it, but have been welding for almost 20 years.
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Old 07-04-2010, 10:53 AM   #24
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# 100% CO2 -Lowest price, generally greatest penetration, and higher levels of spatter. Limited to short circuit and globular transfer.
# 75% Argon - 25% CO2 -Higher price, most commonly used by home hobbyist and light fabricator, lower levels of spatter and flatter weld bead than 100% CO2. Limited to short circuit and globular transfer.
# 85% Argon - 15% CO2-Higher price, most commonly used by fabricators, with a good combination of lower spatter levels and excellent penetration for heavier plate applications and with steels that have more mill scale. Can be used in short circuit, globular, pulse and spray transfer.
# 90% Argon - 10% CO2- Higher price, most commonly used by fabricators, with a good combination of lower spatter levels and good penetration for a wide variety of steel plate applications. Can be used in short circuit, globular, pulse and spray transfer.
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Old 07-05-2010, 10:32 AM   #25
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if you mix up the two, your in for a world of wandering arc.
If you mix what two?

As for sharpening the tungsten the only thing you really need to pay attention too is that the grind marks should be running parallel with length of the tungsten. This will help to focus the arc and help make the point last longer. Most people use bench grinders, I have a coarse and a fine wheel at the shop, use the coarse wheel to rough it out and finish it on the fine wheel. They also make dedicated sharpeners but you dont need one of those.
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