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Discussion Starter #1
Hello all.
I hope i can describe my problem properly.
but when ever im tig welding whether it be a lap joint or a tee joint in the middle of larger sheets of alloy, usually 3mm sheet. Whilst im working on developing even the slightest puddle to get the weld started. the big flat section will warp to the point where there can be anywhere up to 10mm gap between the two once tight pieces of material.

As an example. Ive folded up 2 doors for my work truck and im trying to weld on a inner folded rib to give strength and also somewhere to mount lights and stuff to. But when ever im trying to weld this rib on the thing warps like no tomorrow and i just end up cracking the ****s and trying to break stuff (think the hulk) surely its something im doing wrong as i see fabricators putting lap joints on this kind of stuff all the time and they look perfect.

specs as follows.
3mm alloy both pieces.
sheet size is about 1100mm square. rib has a double folded edge so it has a flat on flat section to weld.
i probably should be hitting it all with a wire brush before welding but realised this after my last attempt.
machine details
everlast 200dx tig.
bout 100amps
cant remember the gas settings.
frequency i realised last time was up over 200
balance about 40%
2.5mm tungston and filler rod.
pedal run so no up or down slope.
short of trying to put the whole thing in a press. or buying a 20 million dollar pulse mig how the hell can i stop this?
 

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nissan/swb gq
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if I'm following what your saying correctly .
you could try to clamp it all nice and flat , preferably down to a steel bench or similar , the backing will help to stop that warp and as a bit of a heat sink as well . mark out where you want all of your stitch welds to be and place a tac at either end of you stitch before you them weld them out . those Long C-vise grips are really handy for this or you can use 2 pieces of rhs / shs and clamp them at either end to hold it all together nice and tight . if you have some spare , use an off cut off ally between rhs and the door sheet to stop is scratching or impregnating the ally with steel .
 

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Yep, always a pain. That's why now I've designed all the strengtheners in our canopies to be riveted on and treat them as a feature. Takes so much longer to weld them on properly and even then if he canopy is smooth and gets painted you need to sand the pull marks on the outside for a great finish.

As Shan said the key is tack each end of every stitch before welding them out and clamp at every one as you go. Often even on both sides of the tack spot. Or if not possible sit the panel on a hard surface and with a helper or by yourself if you can press down hard beside the tack point with the handle end of a hammer. Then if necessary and quickly before the tack completely cools give it a tap with the hammer to close any gap (carefully mind you). When you are welding and tacking sheet metal you should always have a hammer close by. A small cross pein or panel hammer.

Clamping on a large panel can still be a pain. In Shan's example clamping some RHS etc at each end of the panel can still allow it to sink away when working more towards the centre. If I have to weld against a sheet, especially if the outside is seen and it needs to look good, I will clamp either side of the tacks first and I'll clamp a small thick backer on the outside where the weld is. I'll often then do the full weld (stitch) with the backer clamped in place. I have a selection of backers for this purpose most 10mm plate. Ally for stainless or carbon steel panels and stainless for ally panels. Something like some 50 x 10 flat bar, say 100mm long.

And that's why we now do so much more riveting and gluing on our canopies.

Oh and 100 amps for my liking is too cold for tacking and even the welding, especially if you add the backing bar. Everyone welds differently but on stuff like this you have to get in and get out. I would be more likely 120-130 amps.
 

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Liking this thread, taught myself how to TIG ally while off work with me buggered knee last year, question for you guru's does Beno's lack of wire brushing/cleaning cause increased temperature to get weld started?
Like the ability to weld ally but so much to learn!
 

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To a degree as you have to burn through the oxidised layer but the most of it is just the nature of the weld.
We don't sit there and clean every single weld point on something like a canopy especially.in the days when welding stiffeners on. It would blow the time out significantly. And don't forget al that brushing will leave ugly scratches everywhere.
Acetone will clean all the grease and muck off the area which helps but won't get through the oxidation layer. Some of this all depends on the expectation of the finished product. That's why I started bead blasting my manifolds before and after, couldn't be bothered stuffing around with trying to keep them looking all shiny and polished.
 

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Pretty normal either big long c grips or get somone to push on the other side worse when your doing it with a mig and it opens up while the tack is soft and it welds it with a big gap under it

Sent from my SM-G950F using Tapatalk
 

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Discussion Starter #7
thanks for the help guys
im going to be having a bit more of a crack at these today so see how we go. might even see if if i can weld 3 sides and just glue the long and extremely difficult one just to save the hassle. but its still mechanically fastened around the edges closer to the sides of the sheet.
ill keep you posted.
thanks all
 
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