Mig Welding HELP stainless to mild steel; exhaust systems.

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Okay so I'm just starting out with a new welder, finally decided to retire my old gasless flux core mig welder for a lincoln 140t.  Now I want to start doing cleaner welds for my light duty projects so I need to set this mig machine up accordingly.The first task I'm going to do will be the exhaust system on my truck.  I have a header and y-pipe system that's stainless steel (304 non-magnetic) that doesn't fit just right.  So what I need to do exactly is weld some areas of this stainless steel as I modify the pipes, as well as weld this stainless steel piping to mild steel flanges and aluminized 16 gauge steel piping.What setup will be best for this for my 140 lincoln?  It's a new machine so I just wish to set it up once for all around usage.  This will be only one of many small (usually mild steel) projects I'm going to be doing.  I read up about 309lsi lincoln mig wire that may suit my needs, but will a wire like this work for most of my mild steel project needs?  And how about an all around gas setup??You're help is very much appreciated, I will accept it as knowledge of the trade
Reply:I can save you a lot of trouble.Trying to weld stainless with GMAW (wire feed with gas) with that smallwire feed will be just about impossible.You will need expensive tri mix gas and with thin 16 ga  or thinner the stainless just barely works. the weld bead will have a high build up and the travel speed of your hand movement will have to be high.To get the stainless set up to work you will have to turn up the travel speed of the wire ALL THE WAY UP. 309 is the correct filler material for stainless to steel. What you really need to do this job is TIG. To have ANY control and workmanship like results, that is the best solution.You may not listen to this, but after you go thru the whole experiment you will then fully understand.You can go to a muffler shop and they use wire feed, and some the new exhaust systems are stainless. Ask them what they do and believe me they do not get good appearence.
Reply:i agree that TIG would be the way to go if you can, but if appearance and emissions are not a concern, then you can TIG it without any problem. tou can even use steel wire... the RIGHT way to do it is with the 309 and the tri-mix, but you can stick them metals together, and they will hold for a while, by using your MIG. in short, is it code? no. is it the right way? no. can it physically be done? yes.Later,Andy
Reply:Okay, so it doesn't sound like a good idea?  Well if muffler shops just use standard mig for mild steel to weld even stainless, then is it just the poor appearance of it that results?  I would imagine that since there's not high stress loads on 16 gauge exhaust systems, using the standard mild steel setup with .025 wire, 75/25 gas may be sufficient.  I know cleanliness counts too but if I can get away with this setup then I think that would be great??  That's what most muffler shops do right?  If it holds for the life of the exhaust system then that will be more than satisfactory.What do you think?Last edited by turbosean; 05-07-2008 at 05:33 PM.
Reply:Making stainless stick together with mild steel filler isn't too much of a problem.  It's just that the places you weld will not be stainless and prone to rust.  Nothing I have has a stainless exhaust...but, my understanding is that one of the bigger benefits of SS exhausts is it will last the life of the car...they are REALLY durable.  By welding it up with mild steel filler, you will have pieces that will last, but they may not stay connected.You can weld SS with wire.  There is a company here in my area that does a bunch of the countertops and dishwashers for a major waffle producing restaurant that specializes in waffles and...well, waffles...they use mig exclusively...however, I know that the primary reason is that it costs less in labor and time and not because it's cheaper in other ways.  I talk with the owner occasionally (our kids are on the same swim team) and he has indicated that setup is crucial for getting acceptable welds.  Just some more to think on.Smithboy...if it ain't broke, you ain't tryin'.
Reply:I did tons and tons of exhausts' with my Lincoln 100. Use the same gas you use for steel, and use .030 308 filler. It bonds to regular steel just fine. No problems whatsoever. You will get a slightly humped weld bead with SS filler, but you will be fine. If you want a nicer apperance, maybe forego the SS filler and use mild steel filler. 309 is nice, but a bit harder to locate sometimes. And mig is just fine, no need for tig unless you are really trying to sell it to somebody who is picky. The special tri mix gas is a waste of money for an exhaust. You are not backpurging, nor cleaning the inside of the old exhaust tube, headers, etc., so sugaring and such is already going to happen a bit. It's not a problem for that application.And then, after so much work...... you have it in your hand, and you look over to your side...... and the runner has run off. Leaving you holding the prize, wondering when the runner will return.
Reply:Originally Posted by turboseanOkay, so it doesn't sound like a good idea?  Well if muffler shops just use standard mig for mild steel to weld even stainless, then is it just the poor appearance of it that results?  I would imagine that since there's not high stress loads on 16 gauge exhaust systems, using the standard mild steel setup with .025 wire, 75/25 gas may be sufficient.  I know cleanliness counts too but if I can get away with this setup then I think that would be great??  That's what most muffler shops do right?  If it holds for the life of the exhaust system then that will be more than satisfactory.What do you think?
Reply:Hey rojo, thanks a lot.  I think I'm going to just use the mild steel .025 wire that came with my lincoln 140 for the job.  I was just worried about stainless steel bonding issues to aluminized piping or mild steel flanges?  But from the sounds of it, it should be just fine.  The truck does go through stresses of supercharged towing, causing high exhaust temps, this shouldn't be a problem right?
Reply:when i did my car's exhaust, i directly welded the SS mufler (stock) onto aluminized 14 ga tube (2" dia.). i used flux core (NR-211MP Lincoln InnerShield) and the lowest settings i could with my machine. i found that the aluminized coating messed with the wire a little. i ground off the rest of the joints and they turned out much better than the first. a flap disk works great for this.sure you will have increased ET's, but unless you are running at about 5,000*F (impossible), you shouldn't have any problem.Later,Andy
Reply:Okay, thanks for everyone's help!
Reply:I used to use a filler rod when tigging stainless steel legs of sinks to ship steel decks with what if I remember correctly was called Everdear rod. Was very strong and welded nicely.