How do you mig weld exhaust?

[Scottsdale10]

I'm a half way decent mig welder, but for the life of me I can not weld exhaust piping and it's really disappointing me. I cleaned up the pipe (old oem stuff) really good to nice clean metal and still had no lucky. I know being in an awkward position under the car and doing overhead is a lot of it. I'd love some tips if anyone could help me out.

 

[csp]

How about some details on what isn't working or what the welds look like?

 

[BD1]

Are you using gas ?

 

[dogdog]

I just fit, tack weld the sections then take it to the bench for a full tig weld.

If you are planning on doing **** weld thin wall tubing with mig .... it's going to be hard using mig very easy to blow through... gas or gas-less....... If you can get an ex pander and slip one section into another... it would be lot easier as well.

You can look up stitch welding and do little at a time instead of trying for a full weld in one pass. Basically it's one tack stop then another over lay and stop...... I find that have good results (with .030 flux core wires better if you have .023 or something mig gas wires) . try that on some thin gauge metal and get used to it before gunho under the car on jack stands. First time was fun, and hoohaaasss all the way after second and third, it's more like I am getting too old for this shiz......

 

[pepi]

Here is an alternative you may like,
http://www.summitracing.com/parts/sum-692250/overview/

not a big fan of welding under a car myself, PIA

 

[Scottsdale10]

Yes on using gas with size 30 wire I know 23 would be a lot better here

 

[kazlx]

**** welding with a mig using .030 wire is going to ****. Not much to make it not ****. I would probably just tack and move.

 

[MP&C]

For exhaust on the vehicle, I've used small mirrors with a magnet epoxied on the back side, place above the weld area on the floor pan so you can better see what you wouldn't normally see on top.

 

[LumpyMusic]

Lots of individual spot welds. Place the gun where you want a tack, hit it for 1 sec. Go 180 degrees from that, repeat. Eventually you end up with dozens of overlapping spot welds.

Eastwood sells a modified nozzle to help get the spacing repeatable -

www.amazon.com/dp/B008J438YY

Turn the heat UP a little, tack very QUICKLY. That tends to make the tack flatter.


For me at least, it's the "upside down, reaching up, trying to hold the gun steady" stuff that makes weld boogers. Being able to get the gun into place and hold it STILL while applying a tack helps a bunch.


Sgt Lumpy

 

[LXCam]

Like other mentioned stitch weld and it'll come together. But you might be fighting another problem you may not be aware of. Stock tubing is no issue to weld when cleaned properly. But if you have aluminized steel or galvanized tubing you're in for a whole new learning curve.

 

[nickelTwin]

You may already know this about welding galvanized steel. Welding galvanized will give off toxic fumes. Best to weld with a respirator and in a well ventilated area.
Also grinding away galvanized from welding area.
I think it's called galvanic poisoning or something like that.
Be safe

 

[csp]

And we still don't know what the problems are or what the attempted results are looking like.

 

[rsanter]

How old and thin is this tubing?
I welded up most of my exhaust with 030 wire and standard exhaust tubing and but welded it just fine.
Some work was done under the car and some was taken to the bench

Bob

 

[sberry]

I don't have a before but it was a rusted out 4 bolt flange connector, in hindsight might have done it a bit different but it worked.
In pic 3 I hadn't welded it yet but the thing looked pretty good as with a couple tacks I can go around it in about 2 welds which keeps it from looking messy.
If I did this daily would have 023, as it is I use 030 cause I can handle the heat.

 

[sqaurelizard]

stitch weld works nearly every time even on the sh@ttyest of exhausts

 

[Zeke]

I've watched the guys down at the muffler shop weld exhaust in place. They definitely don't have time to stitch weld, they just tack a couple places and run it on out. I'd say that the technique is to lay the nozzle on the pipe about 3/8" back from the joint and at an angle you wouldn't normally use. Too much angle and too much stick out can be managed with the settings. You simply round the tubing over the top where you can't see but you know where the gun tips is and you know the wire is hitting the joint. The idea is to not get too much penetration. You just want to lay out a fat cold weld covering the joint. Not much structural welding needed here and the tacks are probably good enough to hold the tubing together for a long time. You just need to basically seal the joint.

I can't find the info but I think there's a wire made for this. It's a high deposition wire like the SMAW rods known as "jet rod" or 7024.

 

[vintagespeed1956]

with a wire feed, fast in short sections. dont stack dimes or weave, move deliberately down the joint at the "right" pace, you'll know it when you get there.

if you adjust to the right speed for your heat, feed & flow, it'll lay down a nice bead all the way around. keep moving.

 

[2ndGearRubber]

We have a 120 argon/nitrogen mix welder at work, MIG. Almost all use is "under" the car, although we can stand to do so. Unless I'm making a tiny sleeve adapter for a flex pipe or something like that, it's all done in place.


Slip the pipes over one another, or into one another. Getting a pretty gap/flush weld can be tough, doable, but not time efficient.

If there's a larger gap, use wire feed to fill it, turn down the voltage a tad, unless it's a hackjob on a junk car, in which case you can blow through some of the over lapping pipe to create more fill that the welder can produce via wire feed.

I use tiny circles to keep it flowing and smooth, but that's more a shaky hand problem than a technique. Get it hot and move quickly. Tack the sides, then use the muscle memory of the curve to do the top blind if necessary. Mirrors are a PITA. Turn down the heat on the bottom if you have a big gap (common as people learn to use the expander, or are being lazy), or else your weld will just start falling off in cherrys on the floor.

 

[2ndGearRubber]

You will never have perfect results welding cheap aluminized/galvanized pipe onto OE semi-stainless pipe with 100k miles on it. Accepting that, is part of the process, it's not TIG welding on a bench.

 

[welder4956]

This:

 

[sberry]

Right, its not a structural problem, sealing is the deal. Most of the time no one cares about extreme beauty here. People don't want to pay for that either. I also do under car, I will take advantage when I can of easier ways and will take good fit with lap and it does take more effort when it gets down to **** joints.
Another thing, the day one welds this it looks comparatively sloppy, when it all rusts together the welding looks pretty good.

 

[nonhog]

I used this technique on my kids mini bike exhaust.....

I just ran beads on the Volvo exhaust. Ground would look better but its tucked pretty tight so I'm not worried about people pointing and laughing.

 

[CJ7VFR]

I have a buddy who works on cars all the time, and I had him weld a larger flange/pipe onto a Cat-Back stainless steel exhaust for me.

The flange that came with the exhaust was a 2 inch diameter into the three inch exhaust piping so it would fit on the stock cat converter. Since I was replacing the cat converter with a 2.5 inch version, I did not want the 2 inch diameter flange/pipe to be a bottle neck.

So I got a 2.5 inch flange and some 2.5 inch diameter pipe and had my friend do the welding with my old Clarke mig welder with some stainless steel wire.

My buddy tacked the flange into place while everything was on the car, and then removed it to weld the flange into place. When he was done he said to me, dude, I don't think it came out that great. I thought oh no, and looked.

Below is his work. The old 2 inch flange/pipe he cut off is on the left and the 2.5 inch flange/pipe he welded to the 3 inch cat-back exhaust is on the right weld to the exhaust.

I told him it looks like a damn machine did it, and what the heck was talking about that it did not look good? It looks a million times better than the factory welds on the cut off 2 inch flange/pipe.

Jim

 

[MarkG]

A series of overlapping tacks. It goes pretty quick. That's how I've done it------I like this way better than making a 'cold weld' just on principal! :S Looks better, too.

 

[Kensgarage]

On used pipe with a **** weld I take a sandpaper roll on the die grinder and clean up the insides too.You'll get a cleaner weld for your effort.I use .023 and straight CO2 on thin stuff.

 

[sberry]

I used this technique on my kids mini bike exhaust.....

I just ran beads on the Volvo exhaust. Ground would look better but its tucked pretty tight so I'm not worried about people pointing and laughing.

That looks dandy and it will look 10x better as it ages a little and the welding doesn't stand out and it becomes obvious it doesn't leak, nice job.