Jeenkies! Warpage!

[JoshStratton]

I have been working with some 20 gauge sheet metal. I spot welded everything and began laying my tracks. This was all done in a concentrated area and I didnt wait long enough between welds. I now have some ugly warpage and need to correct it.

Can anyone offer some tips to correct my mistakes? I tried laying a few welds to heat up the metal (i dont have a torch) and then use a body hammer to tap them down, but that just made the bump pop out the other way. Can I cut groves into the warped area and then weld the cuts together? I am really not sure how to get it purty and straight again.

[parsonsj]

First, go buy a torch. Then pick up Ron Covell's metalworking book. It has some good instructions about how to shrink metal that can help ... but you'll still need to know where to shrink.

You might consider starting over with 18g, and taking your time. You'll probably get done more quickly that way.

jp

[astroracer]

Hey Josh,
One thing you never do on sheet metal is "pull" a weld... You have seen the results of that. The correct way to do this is to tack weld it, cooling every weld as you go. Tacking until the panel is completely welded. Some guys use air nozzles to cool the tacks, others use damp rags. I have done it both ways with mostly equal results. Skip around as you are tacking to keep from comcentrating to much heat in one area. Don't get carried away with tacking. Do ONE then cool it. It will take longer to do but it saves a ton of time trying to fix the ravaged steel when you are done.
The bulge you have created now needs to be shrunk. If you don't have a set of torches you can use a propane torch with decent results. Heat a quarter sized spot in the middle of the bulge to a dull cherry red then cool it quickly with a wet rag. You may have to do this a couple of times to shrink it back but this is the best way to do it. Cutting and welding will just make it worse.
Also, when you start grinding or dressing the welds, same thing, skip around, keep the metal as cool as possible. DON'T grind to long or to much in one area. It will stretch the metal and you will be back to shrinking again...
Mark

[JoshStratton]

Thanks guys! I will give the shrinking a try. If it doesnt seem to work, I can use the metal elsewhere. I will try it with 18 gauge in that case.

I was very careful with the tacking. It looked great until I started laying the beads. I did them in 1/2 inch strips waiting about 2 or 3 minutes between each, but it was in a small area and there were a lot to do. I think I should have waited longer or tried your cooling methods.

Which brings me to my next question. If you use a wet rag on a new weld, wont it pull the moisture into the metal and cause rust? I was always worried abou that.

[Rolling_Thunder]

I would think if you cooling the metal it is way over 100*... at which point it would cause any moisture to evaporate ---- this was my belief - correct me if im wrong somebody

[astroracer]

New HOT welds will make your wet rag sizzle and pop! No water will be pulled into a 1000* weld... Like R_T said it will just boil off. The rapid cooling forces the sheet metal back to it's (nearly) original shape. You definitely put too much heat into the steel. All of your welding should be done as I said in my first post. TACKS ONLY... and... 18 gage will warp just as quickly as 20 so changing gages will not fix the problem.
As an example:
When I filled the tailgate handle on my truck it took me almost three hours to tack it in. I would do a half dozen or so and then lay a wet rag on the patch and go do something else for a while. Get 95% of the latent heat OUT of the panel before you do any further welding. It can be warm but you should be able to comfortably lay your hands on it. Waiting 2 or 3 minutes between welds isn't enough. Without cooling ,the sheet metal is just getting hotter as the heat spreads into the surrounding material and all you did was make a bad situation worse. The hot metal has to expand somewhere and that is what made the bulge...
Mark

[JoshStratton]

Mark.

This is great information. Thank you very much. So do tacks only. No beads, no click and drags, no nuttin. I will just skip around a bunch of tacks until the whole thing is one continuous weld. I am on my way to get more steel so I will stick with the 20 since it is lighter. This time I will take a few days to get the whole thing done instead of rushing to get it all done in one day.

I must say though, my beads were looking much better than in the past. They were clean and had nice definition ))))))). I was very proud

On another note: I think I, and a few other welding newbs have started some pretty good posts trying to get to the bottom of this complicated art known as welding. I think we are gaining enough good information to start a sticky.

[Norwoodx55]

I don't know if this applies to what you are doing or not. If you have too wide a gap between the 2 pieces of sheet metal that you are welding, even the tacks you apply will pull the pieces together as it cools. This can distort the metal as well. I have had this problem before. As I got better fits and smaller gaps between pieces, the warpage problems lessened. Hope this helps.
Brett

[Matt@RFR]

The rapid cooling forces the sheet metal back to it's (nearly) original shape.

Mark, I don't want to be anal, but I will. Cooling a weld will make it shrink more than letting it air cool. This is a method used in the industry to shrink gaps in big plate butt welds. The reason it's benificial to sheetmetal work is, like you said, to keep the heat from making it's way out to the field where the sheetmetal isn't supported at all. Quenching a tack with water also doesn't effect it all that much because it's done quite a bit of cooling by the time you lift your hood up, grab the rag and apply.

You guys aren't welding with a wet rag in your hand, right?

One reason TIG sucks for sheetmetal.