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  • forming stainless

    I have a project I'm considering where I will need to form a 4" diameter stainless hemisphere. Gauge will be 24 or smaller. Alloy can be suited to forming method (meaning, best to fit manufacturing process).

    Anybody experienced in this? Am I going to have problems with that much stretch? Is this going to take a ridiculous amount of force?

  • #2
    I suspect you're going to get a lot of spring back. How many pieces do you need to make? While I've never seen spinning used for stainless, that does not mean it cannot be done.

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    • #3
      I can deal with springback, the accuracy of the hemisphere is not really all that important...it's just a general "shape"

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      • #4
        All I know is what I skimmed of this link. http://www.fanagalo.co.za/tech/tech_fab_form.htm

        The readers' digest is 304/308 alloys and the forces will be roughly double what you'd expect for similar operations in mild steel. Workhardening is a significant issue.
        Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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        • #5
          You can do it, but its a lot of work.
          I have made dome shapes from 16 gage stainless- I had to do it hot, heating it in a forge, or with a rosebud, then hammering. First round, I used a dishing die- I actually have a big bowl depression in my swage block, and I used ball end forming hammers, kind of like a double ended ball pein hammer.
          I blocked out the intitial shape, then planished cold over a big football stake. I actually did use the english wheel on it towards the end, but it required so much down pressure on the english wheel that it was crazy, and it took a lot of wheeling to get it to move much.
          Seems to me I annealed once or twice- with 300 series stainless, that means heating to red hot and quenching in water.

          These are my regular sheet metal forming tools, which work really easily on 16 gage 3003- and they were a real workout on stainless.

          I also did some dome shapes like that in 1/8"- again, hot. beat to shape in a ring die- thats a 6" circle made from 3/4" round, that has a yoke on the bottom so you can put it in a vise. When you pound on metal in it, the center, unsupported part of the metal moves.

          Unless you have a power hammer like a Yoder, I dont think you could do it cold.

          The toes of these boots are the 1/8" pieces-
          In the detail shot on the workbench, you can still see some hammer marks on the toe. I built it up from three pieces- the rounded toe piece, and two side pieces that are just curved in one direction, and are welded together in the middle.

          Last edited by Ries; 02-11-2010, 05:38 PM.

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          • #6
            What you really need is an Earth Shattering KABOOM.

            The faster you move the metal the more drastic the change in shape can be. When it is formed by explosives it doesn't bend to a new shape, it flows. Even with a much slower high capacity and high speed press it flows somewhat. But if you are going to do it by beating on it or some other equally crude technique you will hate the job long before you finish the first part.
            Free software for calculating bolt circles and similar: Click Here

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            • #7
              HERF (High Energy Rate Forming) might be fun. http://www.pageranknet.com/mechanica...e-Forming.html Do it away from the house if you're fond of your windows though.

              Here's a lecture on the process. Put on a pot of caffeinated bevvy though. The lecturer spends 3:48 in review, then defines HERF then discusses process selection.... Hardly a spellbinding presentation, but it is free.
              Last edited by camdigger; 02-11-2010, 07:02 PM.
              Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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              • #8
                Yeah, lets see how long it takes the Homeland Security guys to show up once you start using explosives...
                There are a couple of companies that do this commercially- and they are heavily regulated, and it is NOT a cheap process.
                There is one near me, in Port Townsend, Wa- I have a chunk of stainless steel that was explosive welded to aluminum sitting on my window sill. Its a very slick process, if you have the bucks. They use it a lot in salt water pumping equipment- a buddy of mine who runs tenders up in Alaska, and has pumps with 9" hoses that will vacuum out an entire 20,000lb hold of live salmon in about ten minutes, says his pumps are titanium explosively welded to aluminum inside.

                There was supposed to be a woman artist in Colorado or Wyoming a few years ago who was using explosives to make big plate steel sculptures- but I havent heard anything about her lately.

                But as a practical matter, the learning curve and time and money it would take you to get usable results would probably buy you a 30 hp CNC spinning lathe and leave you with change for a new pickup...

                Me, I actually really enjoy beating on metal. I just seldom can justify it for paying customers. I took a workshop from Ron Fournier years ago, and learned just enough to be dangerous.

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                • #9
                  These guys claim they're doing 318. No mention of gage, but seems pretty thin from the sound the finished products make. Seems to take the big machine they're using a while to do it too. http://www.youtube.com/watch?v=zzsUhaDSqzI

                  As far as the learning curve and Homeland security issues, well there are risks to any metal work. Some issues may be left to be resolved by the end user...

                  I wonder if a little prima cord over a hollowed out spot in the ground would work. How much ballast sand would need to be piled on top of the sheet?
                  Last edited by camdigger; 02-11-2010, 07:23 PM.
                  Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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                  • #10
                    304 plate or sheet works great.... great elongation, you can bend, shape it anyway you need it... cold or heat... won't crack... cleans up nice... shine it, buff it, paint it any way you like it....

                    Try it you'll like it

                    The Worm

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                    • #11
                      Well, since I'm fresh out of C4, I guess I'm going to have to do it the old fashioned way.

                      I had actually planned to do it on a hydraulic press, similar to the bonny doon type of press for jewelry work, but with some modifications to the process. I was planning to make a positive out of aluminum or scrap steel and use a combination of urethane and sand as the die "shoe". I figure for a few uses, the aluminum should hold up.

                      Ries...when you anneal the stainless, how does the discoloration/oxidation come out? Simply grinding and polishing?

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                      • #12
                        Sorry for this post being off the subject....


                        Ries,

                        How do you start a sculpture like the boot? Do you have a form you work around or do you just start welding each piece together and your artistic ability just "knows" how each piece fits? Maybe you could post some photos of the various stages of its construction.

                        Thanks...

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                        • #13
                          I sand, grind, wirebrush, and otherwise attack the stainless, but my secret weapon is Railmakers, in Everett Washington, who have a 4' x 4' x 8' tank of 120 degree heated phosphoric acid, and a 1000 amp 100 volt power supply. They electropolish the stuff for me. I made two of these cowboy boots, and they were 7' tall by 7' long- so they needed double dipping, at about a half hour each dip.

                          I do get pretty good success using stainless steel wire brushes on grinders, or using blue alumina zirconia flap discs on my 4 1/2" grinders, or using air powered DA sanders, or sometimes using scotchbrite belts on my portable belt sanders. I got a whole arsenal of tricks for this stuff. Depends on the finish you want- sometimes I even hit it with a needle scaler.

                          As for layout- I draw what I want, and then usually hand bend a framework, and work within it- on the boots, the bottom was the hardest-

                          here you can see the welt, bent from 3/8" x 2" flat bar the hard way, and the easy way, and the heel, built up, and I am beginning to lay out the outline of the boot itself, using 3/4" round bar, bent into the shape of where stitching would be on a real boot. I built the outline of the whole boot, then filled in all the little parts in 1/2" round bar.
                          On this piece, every part was hot textured first, except for the welt on the sole, which had stitching machined into it with a ball end mill on the milling machine.

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                          • #14
                            Ok now I got to try the explosive forming. I think I will put a water buffer between the SS and explosive. Who wants to lend me one half of a ball mold? a steel one would be preferred.

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                            • #15
                              The die into which the metal will be forced should be evacuated to a reasonable approximation of a vacuum.
                              Free software for calculating bolt circles and similar: Click Here

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