Help! I've warped my roof skin

[Torqu-E-Cycles]

First time I've ever welded in the centre of a big, flat (actually slightly curved) panel and its gone horribly wrong!

I cut out a rust patch, the surrounding steel was good no surface rust etc, I made the repair patch to fit with about a 0.5mm gap all the way round and put it in flush with lots of small spots keeping it cool as I went, then pretty much at the last 5 spots it just bent in front of me!

Cut it out hope it returns to the correct form then lap a patch underneath and fill?

 

[Barking Mat]

Hmm, body filler ?

Gentle application of a BFH ?

 

[Torqu-E-Cycles]

Its bent the entire roof and created a horrible memory, if you poke one dent with your finger the whole roof moves in strange ways! I'm hoping by cutting it out 5mm larger past the welds it'll return to normal

 

[500e]

Doubt it will, start by grinding the welds down, keep it cold.
Then see what you have.
Patch a different guage to roof?

 

[Torqu-E-Cycles]

Oh dear.... I don't understand what I've done wrong? I didn't get it hot or weld for too long or put pressure on anywhere, the patch is the same thickness as the roof, I'm confused

 

[finyuk2005]

Oh dear.... I don't understand what I've done wrong? I didn't get it hot or weld for too long or put pressure on anywhere, the patch is the same thickness as the roof, I'm confused

i think you need to hammer the weld with a dolly on the other side if you can get to it,
the heat of the weld contracts the surrounding steel, and hammering the weld should sort it in theory....in practice i havent ever managed to get it 100% right!!
bit of a dark art i think!!

 

[500e]

Big panels are not the thing to start with.
Get an old door and do the same cut and weld then learn to shrink the panel, you have oil canning, a common problem but a hard thing to get sorted.
You don't need much heat left in the panel to start it of.
Look at some yt vids on shrinking it is not easy it is an art.
Finish the weld first.

 

[Morrisman]

You've basically shrunk that area of the panel, which causes the buckling. You need to 'stretch' it out again, by hammering along the welds with a hammer and dolly.

 

[Torqu-E-Cycles]

Could I not cut the patch out about an inch larger all the way round to see if it will go back to original shape? Basically reverse what I've done... I can't believe the heat would have passed that far through the panel as I didn't get it hot, I'm not a complete newbie, I get the feeling the welds have caused it to shrink as they cooled so hopefully its reversible? I'm working with 3 broken fingers on my left hand so battering hammers and dollies isn't an option sadly

 

[minimutly]

Big panels are not the thing to start with.
Get an old door and do the same cut and weld then learn to shrink the panel, you have oil canning, a common problem but a hard thing to get sorted.
You don't need much heat left in the panel to start it of.
Look at some yt vids on shrinking it is not easy it is an art.
Finish the weld first.

Oil canning? That's a term I've not heard before..

 

[AVI_8]

Could I not cut the patch out about an inch larger all the way round to see if it will go back to original shape? Basically reverse what I've done... I can't believe the heat would have passed that far through the panel as I didn't get it hot, I'm not a complete newbie, I get the feeling the welds have caused it to shrink as they cooled so hopefully its reversible? I'm working with 3 broken fingers on my left hand so battering hammers and dollies isn't an option sadly

Look at some you tube videos before cutting anything, there’s quite a few on the subject, yours looks particularly bad though.

 

[500e]

I am afraid you are in a world of hurt.
Practise on something else.
There is no shortcut, this is just an idea there are other ways, (shrinking discs) finish the weld you have started before doing anything else, buggering about with body work and broken fingers not good

 

[Morrisman]

Could I not cut the patch out about an inch larger all the way round to see if it will go back to original shape? Basically reverse what I've done... I can't believe the heat would have passed that far through the panel as I didn't get it hot, I'm not a complete newbie, I get the feeling the welds have caused it to shrink as they cooled so hopefully its reversible? I'm working with 3 broken fingers on my left hand so battering hammers and dollies isn't an option sadly

Then you're left with a hole in the panel.
The heat doesn't need to have passed through the panel, just the immediate area around the weld.

I am afraid you are in a world of hurt.
Practise on something else.
There is no shortcut, this is just an idea there are other ways, (shrinking discs) finish the weld you have started before doing anything else, buggering about with body work and broken fingers not good

What needs shrinking? If anything the patch welds needs stretching, to restore the geometry to the panel.

 

[500e]

Best of luck
Both will be needed.
Finish the weld first, then look at it

 

[Torqu-E-Cycles]

I am thinking if I cut it out past the heat soak it may hopefully return to form, at which point I will then work out what to do after that, if it doesn't, its having a whole new roof skin because there are 3 holes to deal with and I don't want tons of filler in my roof!

 

[Burdekin]

Ok don't shrink anything! Don't panic! Again don't shrink anything, that is NOT the problem.

Grind the welds flatter and you need to stretch the metal at the welds. Only at the welds! You want to hammer and dolly the welds, so press up with a dolly and hammer onto the dolly on the weld. Not easy with a hard mig weld so take your time. The last bit you might need a file slapper on dolly to lift it up to get nice.

 

[Burdekin]

If in the end you still have some tin canning the best way to sort that is to make a brace to go in under the area and glue in with polyurethane adhesive and tack weld it to other roof structure.

 

[Onoff]

Is it as bad as this? Look close.

 

[Torqu-E-Cycles]

Ok I will give it a go, fingers crossed! Onof thats insane!!

 

[Burdekin]

Ok I will give it a go, fingers crossed! Onof thats insane!!

For the next patch if using mig, do the tac stop tac method but only weld about 3/4" to 1" then stop and grind straight away. Watch the roof and if it's starting to shrink and distort then hammer and dolly the weld lightly to stretch back to the correct shape. Don't do another weld until it is back in shape. Then continue like this until all welded. It is much slower to weld but you should get to the end and have minimal distortion. You're minimising the distortion and then removing it as you go.