Exhaust flange and my traction bar

[David230]

Hi everyone, Thought I'd post up a picture of a 3" stainless exhaust pipe to flange that I attempted to weld today. I hav'nt welded anything for ages and most of what I have welded in the past has been mild steel. This was my first attempt at stainless. I used .8mm 308lsi welding wire with argon/co2 mix. Admittedly I wasn't expecting great results but one thing I did find difficult was maintaining consistent weld pattern. I think it has something to do with the way I'm trying to weld around the pipe. I also managed to warp the flange in the process.

Anyway please tell me where I'm going wrong or what I can try to improve.

Here is a little something else I've fabricated for my car although I wont be seam welding this as its a much more critical part. I will be sending off to Rick so he can weld it properly for me safe in the knowledge I have some decent welds.

Hope you dont mind all the pics


cheers
David

 

[David230]

ok, I'm now using a different method, trying to minimise heat with big pauses between welding tacks but high power for high penetration and flatter welds. This is the join I attempted to weld today straight pipe to elbow. I'm going to redo the flange join using the same method.. What do you think?

 

[Engineer]

To minimise distortion you need to back step weld, and on welds where you are joining thick to thin, its a good idea to clamp the thicker part down to something substantial to lessen the chances of distortion.

Main problem with MIG welding an SS exhaust though is the possibility of cracks close to the welds, and this is the main reason commercially made systems are either TIG welded, or MIG'ed using mild steel wire.

 

[keith19]

Your first pics don't look bad to me, aside from the reported slight flange distortion; caused by following it around close tacking in one go, I guess? Bolting the flange down tightly might have helped, as Engineer says.

I don't do much s/s pipe, just exhausts now and then, but I'd say your second method is best, less to clean up on sections, and far less likely to get distortion in a flange. I use this method myself particularly if the pipe is pretty thin.

Just have to make sure the overlap on the tacks is good to ensure no holes, and keep gas pressure up if you're in a draughty place.
These pro guys use this method too:
http://www.youtube.com/watch?v=JohBHzhOyPg

 

[David230]

Tried the same method on the flexi pipe today but this time with a slightly tighter overlap.

 

[Wozzaaah]

Very tidy!
Almost looks like it's been tig welded.

 

[keith19]

That looks excellent mate, a really pro job. Congrats.

 

[David230]

thanks alot guys, I'm reasonably pleased with it. Although tried to weld in a lambda boss today and blew a hole into one side of the boss. oops! Got half of it welded ok and the other half is ugly so I have decided to cut that out and put in another one. This time I will keep the weld more towards the bass of the lambda boss as its quite thin wall.

I'm still very much a newb with the mig and I am not 100% confident with it yet. Enjoying the fabricating aspect alot though.

 

[Delgado]

Hi David, not trying to be funny, but you might want to re-think the design of that crossmember, as you've efectively built a can opener. The gusset/s that go between the angle and the box section need to be on the outside faces/edges of the box, not in the centre (maybe a better way to do it, would be to cut some gussets from the same box?).Also, grind off the mill scale before you tack it all together to ensure decent welds, as it's a pain to do it after.

Apart from that, looking good welding wise, although instead of using a series of tacks, you could try welding the thin tube vertical down (rolling it if you can).

Ps. Where abouts in Bucks are you?

 

[David230]

Hi Delgado, not funny at all you make perfect sense. I'm not sure why I didn't do it like that to begin with. I will cut a corner piece out of the box section I think and do it that way. Like you say minimise the stress by loading up the face edge of the bar.

 

[^neo^]

Looks spot on to me!
Only thing i would suggest is putting your tack welds on the end of the box instead of the middle, then you can just join between the tacks rather than stop starting in the middle of the box or grinding them off before fully welding

 

[David230]

Ok, taking into consideration everything that Delgado and neo have said I decided to make a few changes to the bar.

Cleaned up the metal a bit and flattened down the tack welds in the middle and put them in each corner of the box section.

Corner piece of box section or single gusset raised so that its inline with the edge of the box section face?? Not decided what to do for the best. Now the traction bar I have built is based upon and replicates a tried and tested bar that is sold in the states. The gusset on these were welded in the place I had mine originally and there are no known failures to date. That said I dont mind making it a better design and I think what Delgado suggests is a good idea. J

Made the tabs for the tie bars, still got to tack these in place too.

 

[^neo^]

Box section gusset looks much better and you should be able to flush the welds right off on the faces to pretty it up.