How to fix

[Maddog]

So I over heated a panel welding in a patch, now below it on a somewhat flat panel I have a approx 4" concave circle, what would be the best attack to "pull it' and shrink it back? Can not acces from the rear, its a Chevy truck bed with a double wall.

[chevynut]

You probably didn't overheat it. Any welding is going to cause shrinkage. If you can't get to the back of it, it's going to be hard to do much with it. If you try to shrink the "concave circle", it's probably just going to move lower on you.

If you really think you overheated it, I would cut out the welded patch and start all over. Then try to weld a new patch in being careful to prevent getting it too hot. Making a few MIG weld tacks at a time is the best way to do that.

[Maddog]

No reason to remove patch since the damage is adjacent to it. I'll pull it with my stud welder as near back to orig as possible and work it, just was wondering if someone might have any other ideas/experience, no metal men here?

[chevynut]

There is no "damage" next to your patch, unless it was there prior to patching it. What happened is that your weld shrunk the metal and "puckered" it. Imagine a piece of paper where you shrink the edge of it...you will get a "wrinkle" or "pucker" next to that edge. If you try to shrink out the pucker, you'll just chase it across the panel. I've done a lot of this and have seen exactly what you're taking about. It's difficult to fix if you can't get to both sides of the panel.

Why do you think you "overheated" the panel?

[BAM55]

The problem is the damage is caused by the welding area (HAZ or Heat affected zone) and pulling or hammering anywhere else is not the correct way to fix it. The welding caused the shrinkage and the damage and if you could hammer on dolly the HAZ area the problem would be resolved. You have to work the area that caused the damage. You said its a double sided panel. Could you cut and access hole to have access to backside of the panel? I have done that in the past with great results. Then I simply welded the access panel back very carefully. In my opinion you have two options one is to cut it out (it should release that tension that is causing the damage) and be more careful re welding it or cut an access hole to hammer on dolly if possible.

[Maddog]

So the weld across the horizontal line shrunk there and that caused the wave in the adjacent metal, makes sense as I can see a dip right at the weld line that extends down to the wrinkled area. No real way to access from rear. If I make a cut across(length wise with the weld) the welded area should that give relief to the stressd area?

[chevynut]

Yes, the shrinkage at the welded area caused the dip. The weld and the blued area around it is all affected. If you cut it, you will have to re-weld it. That will make a bigger mess. If you cut the panel behind it to access it, you will have to weld that too....again, I think that creates a bigger mess because you will have the same problem there after you try to weld it back in.

If you think you got it too hot, and can do it better without as much shrinkage, I would cut the patch out and try again.

[BAM55]

So the weld across the horizontal line shrunk there and that caused the wave in the adjacent metal, makes sense as I can see a dip right at the weld line that extends down to the wrinkled area. No real way to access from rear. If I make a cut across(length wise with the weld) the welded area should that give relief to the stressd area?

If there is no way to access the rear, in my opinion your only option is to cut the patch panel completely out and be very careful re welding it. Pulling and hammering on areas that has nothing to do with what caused the damage can create a bigger mess. Now remember all welding causes shrinkage you are just trying to minimize it as much as you can. When re welding just try to keep the metal cool as possible. What I do is tack the panel in place grind the tacks and tack again grind those tacks. I do that until the panel is completely welded. I find that while I'm grinding the tack welds it allows the metal to cool and I'm still continuously working. If I can't touch the area with my bare hand I don't welded until I can. This is just my way of doing it.

[Maddog]

Imagine a rectangular patch welded in, say 6"x3", the only heat affected area is on one side of the rectangle only, along the lower 6" length. The metal directly below this 6" line is wavy, the other 3 sides of the rectangle are fine. I would hope that cutting this weld line out would allow the lower stressed(wavy) panel to regain it's original shape, what say you? I just don't see how the other 3 sides would make a difference if i leave them as is. There are actually 2 additional panels behind this with the closest being about 1/4" away from the outer. This is a 73 truck bed at the wheel well, the wheel tub and inner panel all are behind my patch.

[BAM55]

I say that just because the wavy area is beneath one weld seam does not mean that is necessarily the area causing the shrinkage. I have had experiences where the the shrinkage or wave was nowhere near the patch panel I welded in. But once I hammered the welded area (HAZ) the shrinkage disappear in all areas of the panel.