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Fold and weld fabrication with 5/16" steel.

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  • Fold and weld fabrication with 5/16" steel.

    I've built several things out of 1/8", 3/16" and 1/4" steel by laying out the patterns, making interrupted cuts with the plasma torch, folding along the interrupted cuts, and welding the joints. Some of the assemblies required 90-degree folds. I haven't had any problems with the joiner tabs breaking when folded......Until now.

    I'm building a rectangular hopper out of 5/16" mild steel plate. It will have a flat bottom and four sloping sides with a vertical band around the top. The cut lines are laid out on a sheet that's six feet wide and eight feet long. There are eight fold lines with interrupted cuts where I left 3/8" tabs about 16" apart. Two folds need to be 60 degrees, two need to be 30 degrees, and the rest need to be 45 degrees. I've got the sheet positioned on a support under what will be the bottom of the hopper, and I plan to bend the sides down so I can tack the corner joints, then make the other bends to form the band around the top.

    I also laid out and cut some smaller parts that need 90-degree folds on another sheet. When I tried to fold the first one, the joiner tabs broke at about 45-degrees of bend. That doesn't bode well for folding up the larger assembly.

    What's the best way to keep the joiner tabs from breaking as they're being bent?

    I know I could just cut the parts loose, but then I'd have to figure out a way to hold them in position to tack them together. They're pretty heavy, and I don't have much good help available right now.
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  • #2
    Could you use an angle grinder to cut about half way through the tabs? That would/could make them thinner and less likely to break.
    Paul A.

    Make it fit.
    You can't win and there is a penalty for trying!

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    • #3
      Sounds like a too tight radius for bending that thick. Either grind it thinner or bend with a larger radius
      Amount of experience is in direct proportion to the value of broken equipment.

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      • #4
        Heat it before you bend it!

        Jim

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        • #5
          Hang it over the edge of a table and clamp one side to the table. Then heat all the tabs with a torch and let gravity bend it for you. You migh need to hang some weight on the outboard end. Be ready to hold it in position when it reaches the angle you wish. You could have some blocks of the right height to use as a stop. You don't need "red Hot", just enough heat that it bends under its own weight.

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          • #6
            Some of the fold lines are over six feet long with five tabs, so it's going to be hard to heat them all at the same time.

            Grinding will leave small grooves across the top surface of the tabs being bent. I've seen a lot of cases where stress risers like that cause welds to fail in bend tests, so I'm a little hesitant to try that.

            What do you think about making about 30 degrees of the bend, and then putting a small weld next to each joiner tab? The weld would be at the bottom of the V formed by the bending. The fresh weld metal might hold for the rest of the bend even if the original tabs break. Any chance that would work?
            Any products mentioned in my posts have been endorsed by their manufacturer.

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            • #7
              You want to grind the tabs on the side your bending to, you are welding the inside aren't you?

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              • #8
                Ahh, yes. Grinding the tabs on the inside of the bend makes more sense.

                As for the welding, I was planning on chain welding the outside of the V-shaped openings along the fold lines and joints. There's no reason to weld the inside. The finished hopper doesn't need to be smooth on the inside or leakproof.
                Any products mentioned in my posts have been endorsed by their manufacturer.

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                • #9
                  If the tabs are not too long you can play with the heat on all of them. If you have weight on the outboard ends and the heat get close it will slowley make your bend. I beleive the temp is only close to 800F maybe less. Definitly not in the "red heat " category. With just the tabs to heat it should go easy.

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                  • #10
                    I'd build myself a "roof" shape w appropriate angles and stops out of wood (2x4 ?) and use that as a "buck" as well as a support for said sheet for the flat bottom and sloping sides portion. Sorry but actually what I would do would be to cut the parts completely loose and then place them on the previously mentioned shape. My gut feeling is a problem in the making with trying to control the bend of the tabs with such a large/heavy sheet.

                    The way I am reading the OP plan you would have tabs at the bottom edge where the sides would slope but also at the top of those sides for the vertical band and, given the way my projects usually "go", this could get complicated IF those tabs don't all fold exactly correct...its usually on the last corner and given size/thickness/weight getting the last bit aligned could be tough (it would be for me for sure)

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                    • #11
                      Bending the tabs should produce some pretty good stress risers on it's own. If they are thinner, the stress level should be less I would think. And I guess I was figuring you would weld over where you grind.


                      Originally posted by winchman View Post
                      Some of the fold lines are over six feet long with five tabs, so it's going to be hard to heat them all at the same time.

                      Grinding will leave small grooves across the top surface of the tabs being bent. I've seen a lot of cases where stress risers like that cause welds to fail in bend tests, so I'm a little hesitant to try that.

                      What do you think about making about 30 degrees of the bend, and then putting a small weld next to each joiner tab? The weld would be at the bottom of the V formed by the bending. The fresh weld metal might hold for the rest of the bend even if the original tabs break. Any chance that would work?
                      Paul A.

                      Make it fit.
                      You can't win and there is a penalty for trying!

                      Comment


                      • #12
                        Here's a question I just thought of.

                        When I make part of the bend, I'll be putting some stress in the tabs. Will heating the partially-bent tabs and allowing them to cool release that stress, so that I can continue bending without reaching the breaking point?

                        I realize it's an ambitious project and there are other ways to do it, but I really want to make this fold-and-weld idea work on thicker metal.
                        Any products mentioned in my posts have been endorsed by their manufacturer.

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                        • #13
                          Oops. DP.
                          Any products mentioned in my posts have been endorsed by their manufacturer.

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                          • #14
                            I believe that if you heat the partially bent tabs, they will then bend further without cracking.

                            My first thoughts on this was that you have probably hardened the tabs by the plasma cutting. Re-heating each tab and playing the torch to allow a much slower cooling of each tab would probably help resolve the problem.

                            Another thought was that since this is thicker material, the length of the tab vs the width of the plasma cut slots is now shorter. You don't want to widen the slots to make the tabs longer and thus more able to bend without cracking, but you could lengthen the tabs by plasma cutting a bit of a T at the ends of each slot. That will probably allow the bend to take place without cracking, but it might also leave the width of the slot wider than you'd like it after the bend is done. Could be worth an experiment.

                            I like the idea of angle grinding some material out of the inside of the tabs. That would tend to keep the edges closer together after they're bent, and it would leave a clean look on the outside. Again, I think an experiment would be in order.
                            Last edited by darryl; 06-01-2013, 05:28 AM.
                            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                            • #15
                              Just an uneducated guess, but bend to a little less than 45 degrees, then heat each tab to near red heat to anneal them. Even mild steel will work harden and CRS (cold rolled steel) will start out harder than HRS.

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