Welding Corrugations

TRR · Feb 6, 2013

I welded 2 pieces of 1/8" sheet together today and ended up with one of them with more corrugations than I want. I welded each end, then went to the middle and worked to one end with 4" welds then skip a foot and another 4" weld until I got to the end then back to the middle and worked to the other end. Then repeated this until the entire seam was welded. When it cooled it had more of a corrugation than I expected. I obviously did something wrong. So I have 2 questions:
1) What do I need to do differently next time to keep this from happening?
2) Is this salvagable - meaning can it be flattened? And how would I do it. I'm going to look up the process to take bends out with torches to see if that would work. Otherwise I'll need to cut it out and try again. (This seam has to be rain proof, but could be done via bondo, caulk, etc., but I was trying to extend my welding abilities with this project.)

Gary Fowler · Feb 6, 2013

It is almost impossible to keep warps like that out of thin gauge sheet metal. Welding from alternate sides and skip welding as you did will help but it wont keep all of the corrugation as you call it out. If you had a long piece of angle iron to tack each end to and tack both sides in a few spots it may help but I doubt it.
Try taking a hammer to it with an anvil on the back side and see if you can stretch the low areas a bit to match

nuffer460 · Feb 7, 2013

1/8" steel is like welding automotive sheet metal. The next time try 2" welds or even shorter, and jump around allot. Stop and get a drink of water, coffee, or a soft drink. Start in the middle and work both ways, come back and fill in open areas. Shorter welds make for less heat. Now, to get you out of this issue. Gary is right. It's hammer and dolly time. Use the dolly on the lower areas and hammer down the high spots. I would like to tell you there is a faster way. There's not. When welding on a car quarter panels. I have taken all day to weld and grind one panel. Automotive panels can't be stitch welded. It's like welding one dot at a time. Patients a vertue when welding. Thin metal or structural steel.

Brad_Blazer · Feb 7, 2013

When metal gets hot enough, it will weaken and the internal stresses will relax and it will reach equilibrium in the hot state. As it cools, it gets it strength back while it's still pretty hot and further cooling will cause shrinkage. If the whole part is hot, it will shrink as a unit with no problems. If not, the heat affected zone will shrink relative to the cool portion and cause warpage. Welding the way you did helped to prevent uneven shrinkage but a 4" weld still creates a pretty big heat affected zone. Keeping the HAZ as small as possible and heating the whole part as warm as possible will help.

For a fix, try heating the whole part and hammer along the seam to stretch it until flat, then let it cool slowly. Build a long campfire or use bag charcoal to form a nice bed of coals to heat your part. Lay your "anvil" at one end and beat the seam as you pull it out of the fire.

SPIKER · Feb 8, 2013

A BUTT weld like this when welding requires a LOT of Tacks. the TACKS are done by jumping around end to end and middle out and in between each tack. You can then grind off some of the extra metal left from the tack. These TACKS then add a bit extra strength and align the 2 parts for welding. the tacks should be down to less than half inch with a small gap in the 2 sections being welded that weld will fill. The Weld in the photo appears to have been totally tightly butted together with no gap.

The 4" like other said is also a bit long for butt welding, 1~2" at a time and move/jump around the heavier the material the longer you can go but still even in 1/2" you dont want to weld much over 3" at a time without some preheating & post cooling.

One other item you welded a narrow 2" wide to a 4" wide part which those two parts have different structural "Strengths" so one will pull/shrink more that the other one causing these warped panels.

There is a Auto Body Term called Hammer Welding where you weld a 1" or so section then hammer the still hot/glowing weld to prevent this type of shrink/warping. This is not most Older Guys would weld in body panels but with NEW stuff at is 22gauge it is near impossible to do as well as getting to the back side for the dolly that you are hammering next to. (note hammering ON the dolly with stretch the metal.) New stuff is welded on using 1000's of spot welds and never really a WELD as most people would call it.

Mark

TRR · Feb 10, 2013

Thanks to everyone. I did look up heat shrinking on Utube and tried that with a Mapp gas torch. It didn't do much - not sure it helped and not sure that it made it worse. I got my big 3# hammer out and by the time I was finished pounding on it, I'd managed to straighted it out so that it was "good enuf". I've got another weld similar to this to do later in the week - I'll use shorter welds and take more breaks.

In the interest of providing accurate information for everyone. I know it looks like a butt joint, but I'm not that good at fitting - at least not yet. That is actually a lap joint with about 1.5 inch overlap.