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Old 06-25-2012, 08:27 PM
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A little display on weld techniques and warping.

Back a while ago we were talking about methods of butt welding and the idea of using a gap came up, of cooling came up, hammer welding, there are many different methods to join two pieces of sheetmetal and most were mentioned.

I got to thinking how could you really test them, head to head? Without some sort of measuring method, how could you honestly say one is better than another? Sure you could feel it and know that one is better than another but how could you show the difference. I came up with this idea, to get a piece of 18 gauge mild steel bent into a 90 degree angle, cut a slice into it and butt weld it. Then check it with a straight edge and see how much your weld altered it.

Hmmm, this could work. It worked pretty well on this one little example.
I drilled a hole right at the bend in the metal so I could cut all the say to that hole at the bend. Using tin snips to cut the perfect tight butt weld that I believe in couldn't be done without putting that hole so I just put the hole in both of them so they would be the same. The other piece I cut with a 1/32" cut off wheel.

Both pieces were perfectly straight when I started, checked with an aluminum yard stick. I cleaned the metal on both sides as well so they would be exactly the same outside of the cut method.

I did a nice hot tack on my butt welded piece then let it cool naturally, no cooling what so ever with water or air or anything. Just a nice fast tack with the welder set hotter than recommended for sheetmetal. My thoughts are if you weld it fast you are creating less heat because you don't have to heat the metal with the weld to get it to penetrate. WHAM it's done this way, very little heat.

The other one I welded short tacks then cooled the weld with water. I did let it set between welds so it wasn't like a bead, just tack, cool then set it down and to the other one and even walk away for a bit. There was no rush, just weld and cool and let it set for a while.

You can barely see the results (it was hard to capture it in a photo) but the one with the tight gap and letting the welds cool naturally has zero shrinkage by the test. The piece remained perfectly straight. The other piece is noticeably bent with the yardstick resting on the center there is about an 1/8" inch gap on both sides!

Now, this is far from a scientific test, but I kept everything as close to perfect as I could with the metal being cut from the same piece and exactly the same length. I planned on doing a bunch of them with cooling and a gap and not cooling and a gap and so on but I only had the two pieces to use and thought I would do the both extremes and leave it at that for now.

Brian







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Old 06-25-2012, 10:33 PM
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Nice test. Good stuff. I think no gaps on corners can be an issue though if the patch panel or whatever you're butt welding in has square edges. What I mean is sometimes I'll let the metal get a little hot so the weld sinks slightly but doesn't do any warping, if I have backside access for a hammer and dolly. Then I hammer and dolly while you're presumably supposed to cool the weld. This is a quick way of doing it and ending up with straight metal, but you know that. Anyhow, when you do this that square corner CAN warp on you a tad even though nothing else warped, so I always make sure there's a slight gap on corners or maybe round it off a bit.

I had an episode on my video blog about how not to do things where I mudded a guy's quarter patch panel and it was shrunk to high hell and he didn't metal work the mangled quarter while the old metal was cut off and had access to it. I was kind of grumbling about it in the video and due to all the metal work and deciding to just peck down the highs and fill I overlooked one thing...the squared corner warped far beyond a couple inches. The rest of the weld zone was just sunk in bad but no real warpage to deal with but that corner had a tital wave coming out of it.


I never use water but sometimes if I'm in a rush I'll let it cool naturally for about two minutes and zap it lightly with some air. Most of the time I just let it cool naturally and game plan around it. It's never really an issue with time.
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Old 06-26-2012, 01:33 PM
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Is there a better shape than a square or rectangle for a patch like maybe 45 degree corners instead of 90 degrees? It seems like when I cut out square patches, they seem to want to warp more. Is this true or just me? 90 degree corners are easier to cut out but not if they warp more when welded.
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Old 06-26-2012, 02:25 PM
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I always use the largest radius corner that makes sense and never leave it square.

Brian
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Old 06-26-2012, 02:43 PM
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I use to have that problem also, and I heard its because the corner is getting heat from two directions and it is kind of like the stopping point, so the heat gets concentrated in the corners. I started making the corners round and that helps a lot.
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Old 06-27-2012, 07:26 AM
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using a copper backer will absorb the heat and add support strength while welding along with cutting down the burn throughs
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Old 06-27-2012, 08:09 AM
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I don't get the copper backing because frankly, if your gap is tight enough, you aren't going to have burn thrus, at least not many before you knock yourself in the head and stop doing it.

Brian
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Old 07-01-2012, 08:24 AM
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My problem is I always want to do just one more tack and "BAM" a burn throu.
patience IS a virtue...
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Old 07-01-2012, 08:28 AM
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Guess I am getting older and wobbly as my welds are sometime not so good..have to work on some settings and some patience..making round corners make a lot of sense..

Sam
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