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Welding/Metalworking... Talk & Q&A Get your torch, braze, hammer, tig or mig on here!

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  #1  
Old 12-06-2016, 08:59 AM
serrata serrata is offline
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Default Help! Large panels warping after welding...

I'm just having a terrible time learning how to weld flat sheetmetal on bodywork.

I've done okay on the curved areas on the back of my 33 chevy, but the roof is giving me fits. When I tacked the main sheet on the roof, it lined up great and fit perfectly. Once I welded the seams, everything in the flat areas warped and rippled horribly. I've tried several things I've found on youtube videos:

- Heating spots in the middle of the rippled area and quenching it with cold water. This seems to have minimal effect, event when done over and over.

- Hammering the seam after grinding the bead down seemed to work somewhat in one area, but others doesn't seem to do anything to flatten out the buckled areas next to it.

The sheetmetal is 18 gauge mild steel.
What advice can you guys give me?
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  #2  
Old 12-06-2016, 09:39 AM
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I use the weld an inch and cool with an air nozzle, which works better for me along with, moving to a completely different area of the panel for the next weld bead.
If you have an english wheel available, you can pre-stretch the edges a little that will help too.
It takes quite awhile to get a panel welded in this way but warping is really minimal.

Last edited by Old Iron; 12-06-2016 at 09:52 AM.
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Old 12-06-2016, 06:08 PM
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to tackle that ,you need to understand what`s happening first. When the metal is heated ,it expands. Once cooled down the surface has shrunk more than it was before heating . That`s why you get the distortion. So if you want to get rid of the distortion, you need to stretch the shrunk areas. Rule of thumb is the colored metal is where the shrinking happend. Big problem is mig welds are thick and very hard and almost impossible to stretch, and when you grind them down to the same thickness as the surrounding sheetmetal, (another round of heat and shrink) there`s a big risk they crack when you hammer them. In your case the panels are even more difficult to fix because of the heating / cooling you did, because you tried to fix the problem in an area that wasnt the problem area. Cant help with that without the panel under my hands...
Now this is all hindsight , or looking a cow in the a$$ ,as we say here,, but it may help in the future... imo when you weld a panel ,you need to try to get a very even heat input (color) so you get very even distortion ,which will be much easier to remove. You also need a soft weld to be able to stretch it after cooling. In think the best way to weld panels is make it fit seamless and gas weld without use of wire, and weld all the way in one pass. Yea, it will distort ,and probably a lot too with a flat panel, but the metal and weld will be soft and uniform and easy to stretch. Downside is rusty panels on our crappy old rides tho never easy...

In your case, I think I`d hammer & dolly right along the welds ( not on them) but it`s not easy to "read" the panel. More coloring = more on dolly hammering. Using a heavy slapper instead of a hammer helps too, as you raise the low areas when hitting on dolly but at the same time shrink the high areas when hitting off dolly. Remember your problem is not where the ripples are, it`s where the welds are

Hope theres something in here that helps...
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Old 12-06-2016, 07:53 PM
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Quote:
Originally Posted by dutch View Post
to tackle that ,you need to understand what`s happening first. When the metal is heated ,it expands. Once cooled down the surface has shrunk more than it was before heating . That`s why you get the distortion. So if you want to get rid of the distortion, you need to stretch the shrunk areas. Rule of thumb is the colored metal is where the shrinking happend. Big problem is mig welds are thick and very hard and almost impossible to stretch, and when you grind them down to the same thickness as the surrounding sheetmetal, (another round of heat and shrink) there`s a big risk they crack when you hammer them. In your case the panels are even more difficult to fix because of the heating / cooling you did, because you tried to fix the problem in an area that wasnt the problem area. Cant help with that without the panel under my hands...
Now this is all hindsight , or looking a cow in the a$$ ,as we say here,, but it may help in the future... imo when you weld a panel ,you need to try to get a very even heat input (color) so you get very even distortion ,which will be much easier to remove. You also need a soft weld to be able to stretch it after cooling. In think the best way to weld panels is make it fit seamless and gas weld without use of wire, and weld all the way in one pass. Yea, it will distort ,and probably a lot too with a flat panel, but the metal and weld will be soft and uniform and easy to stretch. Downside is rusty panels on our crappy old rides tho never easy...

In your case, I think I`d hammer & dolly right along the welds ( not on them) but it`s not easy to "read" the panel. More coloring = more on dolly hammering. Using a heavy slapper instead of a hammer helps too, as you raise the low areas when hitting on dolly but at the same time shrink the high areas when hitting off dolly. Remember your problem is not where the ripples are, it`s where the welds are

Hope theres something in here that helps...
Great explanation Dutch
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  #5  
Old 12-07-2016, 12:29 AM
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Thank you Dutch. I'm going to reread that and reread that.
My '34 Plymouth is a botched project that I thought I could save. All of the patch panels and the roof insert were welded in quickly, so the whole car is warped. I will use your advice.
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  #6  
Old 12-08-2016, 05:19 AM
King Herald King Herald is offline
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I was gob-smacked when I welded a lug onto the nice flat floor of my old rod. the whole floor turned to a rippled wave pool! It calmed down a little as the weld cooled, but was still a big of an eye sore.

I've seen guys flattening distorted panels with a gas torch and heating small circles in strategic places. It is a bit of an art, but works incredibly well.....when you know what you are doing....

Heated metal doesn't really shrink per se, as it cools, just it has compressed some material around the area you welded as it expanded, and that is what causes the distortion afterwards. But the effect is exactly the same.
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Old 12-09-2016, 12:56 AM
serrata serrata is offline
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Thanks guys. This helps. I'm going to try some more this weekend to see if I can flatten things out a bit with the above advice!
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  #8  
Old 12-09-2016, 01:46 AM
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Quote:
Originally Posted by King Herald View Post
I was gob-smacked when I welded a lug onto the nice flat floor of my old rod. the whole floor turned to a rippled wave pool! It calmed down a little as the weld cooled, but was still a big of an eye sore.

I've seen guys flattening distorted panels with a gas torch and heating small circles in strategic places. It is a bit of an art, but works incredibly well.....when you know what you are doing....

Heated metal doesn't really shrink per se, as it cools, just it has compressed some material around the area you welded as it expanded, and that is what causes the distortion afterwards. But the effect is exactly the same.

heated metal does shrink, period. actually ,it already does when you can see small puffs of steam appear when the metal is cooled with water, before temperatures are high enough to color the metal. If the distortion would be caused by compression from expansion, it would be flat again when cooled.

There are 2 ways to remove distortion. You either stretch where the metal has shrunk, or you shrink where it didn`t shrink, which is why heating with a torch helps flattening panels too. When a panel has impact damage ,and therefor is stretched, working with a torch to shrink that area sure helps, but you do need to know what you`re doing.
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Old 12-09-2016, 12:07 PM
Willowbilly3 Willowbilly3 is offline
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I would take a cutoff and cut most of those welds out. I'm with Dutch on the wire feed welds but that's the tool and skill most of us have. I used to be able to hammer weld and that is the best because done right, the work is all done while it's being welded in.
With my wire feed, I like to use a heat sink where I can. I would cut most of the welds, get things straightened back up. Then bend a piece of flat bar to the roof contour and cleco it right next to the weld, just enough room so you don't weld to it. Then take your time and move around, a little here and a little there allowing cool down in between
I also have some big thick copper bus bars I clamp up right behind the weld on old thin parent metal. It is a great heat sink and allows you to not blow holes.
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Old 12-14-2016, 10:49 PM
serrata serrata is offline
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What you say makes sense. I'm going to try some trial and error to see what works best on the ugly welds I made. Worst case, I'll just cut the welds and do small lengths at a time.

Quote:
Originally Posted by dutch View Post
heated metal does shrink, period. actually ,it already does when you can see small puffs of steam appear when the metal is cooled with water, before temperatures are high enough to color the metal. If the distortion would be caused by compression from expansion, it would be flat again when cooled.

There are 2 ways to remove distortion. You either stretch where the metal has shrunk, or you shrink where it didn`t shrink, which is why heating with a torch helps flattening panels too. When a panel has impact damage ,and therefor is stretched, working with a torch to shrink that area sure helps, but you do need to know what you`re doing.
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