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Managing distortion in steel

General welding questions that dont fit in TIG, MIG, Stick, or Certification etc.

Managing distortion in steel

Postby clavius » Fri Dec 29, 2017 8:12 pm

So I am planning to make up a steel box. Picture something like a small lock-box or a gun locker. It will be about 24" x 18" x 18" rectangular box, made of 1/8" steel plate. Nothing exotic.

I have both MIG and TIG capabilities here but plan on TIG welding it. Partly because I can, partly for the practice and partly because it is like 6 degrees F outside here so I have to do my welding in my toasty warm garage, and I don't like MIG welding indoors. (before anyone says it: yes, I'm a wimp...)

Anyhow, I don't have extensive experience welding stuff like this to maintain accurate dimensions. I know there are techniques and an order that one can make welds and such to help minimize the effects of distortion. I've done some research and I have some general idea of the principles involved, so I guess I'm looking for some input from people with actual experience doing stuff like this.

What are some smart ways to end up with a rectangular box instead of a steel rhombus? I very much appreciate any input.
Thanks!
-Al

PS - Nobody will die or be gravely injured if this does not come out perfect, nothing will suffer but my ego. Just trying to get it as good as I can with what I have to work with.
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Re: Managing distortion in steel

Postby Farmwelding » Fri Dec 29, 2017 9:05 pm

Clamps. Lots of clamps. If you have some bar clamps you can cut a 2x4 or other piece to fit in between and then clamp it with the bar clamp for that dimension. You can always heat it afterward with a torch if you've got it.
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Re: Managing distortion in steel

Postby cj737 » Sat Dec 30, 2017 8:19 am

Both MIG and TIG want to be performed "indoors" so I'm unclear as to why don't want to MIG weld? But, I too would probably TIG it...

Your piece will distort, know that going in. Tack every corner of every piece. Then tack again at the center of each piece. Then tack again at the new mid points, constantly switching which edge you are tacking on. When you get tacks about every 6", then you can weld.

Do you plan to weld outside or inside? If outside, do you intend to have a finished, fully welded edge? If so, ONLY weld about 2-4" on a given edge at one time. Stop and let the part cool. Swap edges, weld 2" and stop. Let it cool. Controlling distortion is far more about self-control than heat control. We get going, we want to weld, we want to finish. But heat in metal takes time to dissipate. If you can manage your own urgency, you will do far better.

The places where your box will suffer most are on the long edges, that are "spans" and not supported/bound. You can tack in some temporary angle bars inside the 18" span, every 6" along the 24" length. This will help hold those panels from become a "taco" and help maintain their shape. Let the thing fully cool. Then cut them out, gently grind away the tacks.

If you only stitch welded the panels, you'd be far better off, but I suspect you'd prefer the fully welded edge? Clamping 2x2x1/4 angle iron on the inside of the seams while you weld would help with distortion and alignment. This trick is pretty dang useful for lots of carbon welding.
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Re: Managing distortion in steel

Postby cj737 » Sat Dec 30, 2017 8:25 am

Another trick you can try: instead of using ER70 wire, use Silicon Bronze wire in 3/32. You can TIG it just like ER70, but you need much less amperage to do so. It will be plenty strong too. After you weld, you can polish it up quickly with a ScotchBrite and have a shiny, gold weld against your steel.

When you assemble the panels, do so that each thickness leaves an exposed edge from both surfaces. This "notch" is where you put the weld. It allows better weld strength and creates a shelf for the puddle. Outside corners are tough, so this little fitment trick really helps create a consistent weld seam.
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Re: Managing distortion in steel

Postby clavius » Sat Dec 30, 2017 9:41 am

Guys, thank you for chiming in.

My comment about doing this indoors is in reference to the fact that I'm doing this is a rather crowded garage shop in my house. MIG does a bit more sparking and such than I care for in there. I typically do any MIG welding I want to do by opening up my garage door and pulling my table out into the driveway. It's a bit restrictive(can't be raining or windy, or single digit temps like it is now, etc..), but is preferred to burning my house down. :)

I'd not considered silicon bronze, that's not at all a bad idea. I'll see if I can pick some up and experiment with it a bit.

I was thinking to weld the outside edges only because I figured they would be easier to access. If my welds aren't beautiful (most likely won't be...) I have no problem grinding them to dress them up, this is a utility thing, not an art piece. That said, it would be nice to not have to.
Your comment: " Controlling distortion is far more about self-control than heat control. We get going, we want to weld, we want to finish. But heat in metal takes time to dissipate. If you can manage your own urgency, you will do far better."
is a very interesting and insightful one. I'd never thought about it that way. This is SO true. Thanks for that.

I have some angle around here I could tack in as you suggest, and a few bar clamps to get things aligned. I would prefer a full welded seam.

I appreciate you both taking the time to reply. Lots to digest here. Info like this is gold for us less experienced guys, thanks for sharing.
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