Perfecting the Butt Weld

[mastorna]

I notice that every time I do a butt weld, it creates a noticeable warp in the panel where the weld occurred. I'm not sure if its due to my grinding or if its due to heat (I suspect the later). As such, I have to spend a bit of time trying to bang the metal back into shape. Is that normal?

What's the best technique to get the perfect butt weld on a panel? Lets say, on a corner of a bus?
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1959 Type II Mango SO-23
1962 Type II Kombi Light Gray
1963 Type II Standard Sunroof SWR\BG
1963 Type II Deluxe MG\PW

[supersuk]

How fast are you performing the welds? If you allow the weld to cool back to almost room temp, you shouldn't have any distortion. As long as you do a tack in one area and then move to another that is at minimum 4-6 inches away, you should be able to minimize the distortion or even eliminate it.

When I was first learning how to buttweld sheet metal, I had the same problem as you. Once I learned to tack and let the welds cool before starting another round of welds next to it, I got rid of the distortion.

Grinding the welds on the other hand is where most of the distortion comes from. Take your time when grinding and don't grind until it becomes so hot, the metal changes color. Its almost impossible to have no distortion when grinding. This is when I pound the metal a little and use a shrinking disc to get rid of the distortion.
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[Matt K.]

When I weld a butted panel I do the tack weld method as most do.....but I start at the top put on a couple of tack welds and immediately cool the weld with my air blower or a rag soaked in water........then I move to the middle do the same........move to the bottom do the same....back and forth so I do not stay in the same spot. Grinding the weld can warp the metal just as easy.....I grind a bit....then cool.....grind then cool. It all sounds like a lot of work and you might end up still with a little warpage but it will not be as extreme.
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[BIGMIKEY]

It's called "butt" welding, however, there should be a bit of gap between the panels too, correct?

Mike T
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BIGMIKEY

Deserter Series 1 project.
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1973 Beetle Driver, Marina Blue.

[eyetzr]

cooling works best. I was told a long time ago to use a heat sink near your welding area, damp rag, copper plate, commercial product (Kool Weld i think). You should also lightly tap above & below the weld to release tension in the area. It is hard to explain with out seeing it. A very clean body hammer & tap around the weld about 4-6 times. Do not try to dent the panel. There was a u tube video showing this.

[clarkster75]

H.Freight and east wood sell clamps that maintain the gap and hold the two sides together.
Although when you get a few tack welds in, the clamps are no longer needed.
But yes, less heat is better and if you can be patient and be slow that should keep you from overheating/warping anything.

[ritchiet002]

Are any of you running gas when you weld?
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[Chubber]

Having a spray bottle with water can be a quick way to cut most of the heat, as can an air hose.

But it's still going to take a long time to make a long butt weld. When I did the whole left center panel (from driver's door to rear wheel well) it took around 5 hours to do all the welding, one inch at a time, then move far away and do another 1/2 to 1 inch part. 4 or 5 of those and I let the whole panel cool to the touch, then did a couple of more.

It's slow, but it will keep it smooth.

You can either have no gap or a 1/16" gap. The larger the gap the better the heat penetration, so a little bit is fine, but if you are working upside down or something it can be hard to do that smoothly if the gap is large. I use those HF clamps, but you really need to have them close to your welds to get good alignment, maybe 1 inch on each side. Then move them between welds while your panels cool.

Don't rush. Once you pull that MIG trigger, it's only going to get harder to align flush if it's not right.
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Chubber
'71 Deluxe 7 Passenger Bus (Resto thread)
'72 Fastback
'74 Super Beetle Convertible (Sold)

[ritchiet002]

Someone told me I could use CO2 as a shield gas. Cheap and would help cooling?
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Somewhere there is a jar with your name on it!

From now on, I'm gonna connect the dots my own way!______________________________________

[Chubber]

Use the right Argon/CO2 mix for your metal. Any tiny savings in price is going to be more work when the metal warps from excess heat.
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Chubber
'71 Deluxe 7 Passenger Bus (Resto thread)
'72 Fastback
'74 Super Beetle Convertible (Sold)

[modok]

You can't weld thin metal with flux core
Straight co2 should work ok, but the argon mix is a bit less spatter and less fumes too.

I know a lot of advice is to use many clamps and tack welds and weld a little here, a little there. I won't say that's wrong but it does create UNEVEN distortion that is hard to correct.

If you are, for instance, welding in a straight line, and start at one end and just go straight across...........then it is all one bend and you can straighten that out EASY.

Also, weld circles not corners. Any square corners will be warped funky, but a circle is just a uniform shape and you can hammer that out no problem.

About the worst thing in the world would be a SQUARE patch panel
Try to avoid that, instead shoot for strips and circles.

[Crankey]

when I weld sheetmetal it's usually flat sheet for furniture or something. I have done very little bodywork. when it's finished product it's usually plated or raw metal with a clear coat. no bondo ever. there are alot of rich people that like steel or brass clad walls. nickel plated walls...go figure.

anyway, I fit the butt weld tight, no gap at all. and even 1/16 material I'll bevel/chamfer the edge just a little. if nothing else its a deburring process that allows the edges to be aligned and flat to each other.

I divide the whole seam up at least by eye. tac the ends and middle, then between those tacs then etc and etc and like others have said don't allow heat to build up. if it's a 2 ft long weld you may want to wait between rounds .

I don't use a wet rag because I've been told that force cooling encourages shrinking, and I actually use wet rags to help shrink a welded intersection in bar material. say for instance a corner pulled out of square, I might pull the joint open and run a bead on the outside of the joint nad quickly quench it with a wet rag. the joint will pull harder towards where the bead and quench happened.

anyway, whatever works I guess ?

I've welded a full stainless steel sink into a stainless counter top and have it remain dead flat. tacing small tacs in even divisions over and over all day long. seems like alot of time to spend welding a sink in, but if it warps the sink and counter top is total scrap so that's fine.

when it's possible I also use 1/4" aluminum plate behind the joint and along side the seam on the front too. clamped on with deep vice grip C's


as far as grinding goes, I'd grind a weld in sheet with fresh 36 grit and change discs as soon as they get a little dull.
dull abrasives create heat, you want that grinder to cut fast and clean. knock the weld down with 36 and when you close to flush switch to 60 or 80.
fresh sharp abrasives will not heat up the surface. if anything turns blue you are using WAY dull grit.
don't scrub back and forth with your grinder. skim the full weld with little pressure on the disc. keep skimming over it back and forth lightly knocking it down closer and closer to flush.

for what I do I typically use tig. but for bodywork I think I'd prefer mig. mainly because it's real fast, and a few small imperfections like small pits from all the start-stop and possible impurities from paint and dirty fenderwells or whatever...that will all get hidden in paint.