Is there a solution for joints pulling in

**Michael G** · 18th January 2014, 10:30 PM

Today I was doing some TIG welding on a piece of 25 diameter Al tube (1mm wt) and to see if I could, welded up a mitre joint. (Haven't ever done on on material that thin).

The tube was cut at 45 degrees but once the weld was done it had pulled in by a degree or so (so a 90 degree joint was now 88 something). Looking at it, the inside of the joint is effectively a fillet while the sides and outside corner are effectively butt welds, so there is certainly more material there to contract. Due to the thin wall I had the ends of the tube butted up - I wouldn't like to try it with a small gap between the tube ends, but that's about the only way I can think of allowing for the contraction.

Has anyone any tips or thoughts on how to prevent the tube pulling in?

Michael

**WelderMick** · 19th January 2014, 10:31 PM

On the assumption that you are clamping it up firmly whilst welding (not just tacking), the next thing I'd try is welding the outside corner first, then the sides, then finally the fillet on the inside corner. That way your thicker fillet weld has something firm to pull against. The same goes for your initial tacks - do the outside corner first. Minimising the thickness of this fillet weld side will help - so a nice tight arc, highest AC frequency you have access to, and smaller filler rod. Also think about what direction you're welding the sides in. Are you starting from the outside and working towards the fillet? or vice versa? starting from the outside and working in will tend to sharpen the corner too.

You could go for the gap as you suggest and anticipate the pull, but you shouldn't have to, and it will just make it trickier with the 1mm stuff. I'd go for a nice tight fit up - so that you can minimise the overall heat and amount of filler metal you need to put into the weld.

Cheers

- Mick

**Michael G** · 20th January 2014, 07:30 AM

Thanks Mick. No jigging was involved as the pieces were only 70mm or so long.
However, a good point about weld location from outside to in but direction of travel from inside to out.
I must admit that I rarely weld on AC so I tend to leave the frequency where it is. Probably worth looking at though (I think I go up to 250Hz and it's around 150 to 200 at the moment)

Michael

**Karl Robbers** · 27th January 2014, 12:13 AM

I would echo what WelderMick has said. Traditional wisdom says you weld from the inside to the outside of a mitre to get the least distortion. I would also add that if you only got 2 degrees distortion, you did pretty well, so don't be too hard on yourself.

**Grahame Collins** · 27th January 2014, 08:57 PM

What about setting up another sample with an angle of 92 Degrees? Weld it and see what happens.

Then play about in reducing the fillet section leg length, if possible.

Grahame

**danielhobby** · 4th February 2014, 03:47 PM

I would imagine that pre setting an angle of 92 degrees inside as graham suggests would be successful.no gap would be essential and clamp solid if possible.Maybe trial and error will flush out the correct procedure.good luck

**brenton21** · 9th February 2014, 01:47 PM

Can't just straighten it? It'll only be kinked after the inside weld

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