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  • Hydroforming

    Just watched a vid where a guy made some domed hubcaps from aluminum. Typical of many vids these days, the whole process is shown about making the apparatus, but at high speed. I'm getting kind of tired of that, so I skip ahead to the final product. Sometimes I'll miss something, but much of the time the end result is ho hum, and I've just wasted a few more minutes of my life.

    But whatever- skipping through this one to the final result gave me a question- could I hydroform a lexan dome without heat? To some extent you can bend it cold, and that's stretching it, so I'm thinking that doming should be possible. The method used to make the hubcaps was grease under pressure from a grease gun. With lexan, I'd think you'd be using water- maybe with a bit of dish soap, or not. City water pressure would probably not be near enough, so perhaps an adaptation of a pressure washer would be the way.

    At any rate, the question is whether cold forming would give a decent result, without clouding the lexan. Any ideas?
    I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

  • #2
    Originally posted by darryl View Post

    At any rate, the question is whether cold forming would give a decent result, without clouding the lexan. Any ideas?
    I think it might craze and not even budge. Its a tricky beast.

    Maybe try with less expensive the other clear plastic, brain fart. Cant remember.

    Saw the mythbusters do hydro-forming with a pressure washer or some pump. Came out nice in metal.

    I dont thing polycarb will move much. If it does might not stay that way. I do like the plastic. JR

    My old yahoo group. Bridgeport Mill Group

    https://groups.yahoo.com/neo/groups/...port_mill/info

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    • #3
      You will need to heat it.

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      • #4
        Polycarb is not the same as acrylic- polycarb can be bent cold, acrylic will break. Either one can be hot formed, and I've done that with both. The worst thing that happened to me with polycarbonate is that I didn't properly dry it before heating to forming temperature. If you dry it first, it forms nicely- I used a bicycle pump to form a few domes, basically clamping the material in an appropriate frame and pumping the air in, reaching and maintaining the rise I wanted until it cooled. It worked fine AFTER I pre-dried it. I've never had that problem with plexiglass.

        I know that doming polycarb cold will take a lot more pressure than a bicycle pump can muster. Forming it hot, there was some springback, but cold- well there might be a lot of springback, and maybe there will be more over time, making it a virtually useless effort. I don't know.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #5
          Originally posted by darryl View Post
          I know that doming polycarb cold will take a lot more pressure than a bicycle pump can muster. Forming it hot, there was some springback, but cold- well there might be a lot of springback, and maybe there will be more over time, making it a virtually useless effort. I don't know.
          Well, either way. Im kinda digging it mostly to see the carnage, I mean progress

          Heat deff but I do want to see your experiment cold forming. Umm? What type of blast chamber do you make to protect you from that hahaa.

          Lets go. What thickness? JR

          My old yahoo group. Bridgeport Mill Group

          https://groups.yahoo.com/neo/groups/...port_mill/info

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          • #6
            The carnage- ha ha. Yes, there will be a blast shield of some kind when I get to this experiment. I'll try to point it eastward, so JR if you find a chunk of lexan in your yard you'll know where it came from

            I would likely be using 2 or 3 mm thickness, as anything thicker would probably be over stressed at the clamping ring.

            My first hot forming was in 1/4 inch material, and bubbled it badly. I saved that piece all these years, but threw it out last year. After that I needed windows for a combo vacuum/pressure chamber, and that was 3/8 thick material. I made 4 domes, two about 8 inches across, the other two a bit larger. This material I baked at about 150F or so for several hours before clamping it in the frame and heating to forming temperature. Those came out beautifully clear and well formed- still using a bicycle pump, though at the edge of the pressure capability of the pump.

            This was all in lexan- I have made several domes in plexiglass, the largest of which was just under 22 inches in diameter, and had to go in the oven at an angle to fit. Ah, the smell of cooking mdf- . One pair of these became a lens- they were siliconed together, then filled with water. The water outgassed of course, and it was a while before I could knock all the bubbles off and get a clear visual through it. I nearly burned the house down with that lens. Those were the days, experimenting with large lenses and space blanket reflectors- I made a 4 ft diameter reflector once, and vacuum shaped it. That one would set a 2x4 on fire in 2 seconds.

            Anyway, I guess the jury is out on the cold forming of lexan- I'll just have to give it a shot one day.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #7
              I bend polycarbonate in my 4’ folder, seems ok, never thought of hydroforming, make an interesting experiment at the least, I’ve done sheet steel as it’s one of the tests for steel destined for pressing, though only on a small scale, the 8” diameter bumps were useful for all sorts of things, I really can’t think of a way it won’t work unless instead of an even “ bulge” it has some sort of local embolism or hernia like a big blister?
              Mark

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              • #8
                Originally posted by darryl View Post
                The carnage- ha ha. Yes, there will be a blast shield of some kind when I get to this experiment. I'll try to point it eastward, so JR if you find a chunk of lexan in your yard you'll know where it came from
                Hey now!! Umm, can I keep it

                !/4" is thick. You had some 3/8" stuff? Sweet, that wasnt free. I have a few sheets of 1/4" that is waiting for a job. My CNC machine cabinet wont be happening.

                Line my car windows maybe. JR


                My old yahoo group. Bridgeport Mill Group

                https://groups.yahoo.com/neo/groups/...port_mill/info

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                • #9
                  3/8 lexan- I can't remember what I paid for it, but it definitely wasn't free. That's probably why I'm still limping- gave part of a leg for it.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                  • #10
                    My guess is that polycarbonate has too much "spring back" . Press brake or folder works for thin sheets as it puts enough sharp deformation to the plastic to yield it permanently.
                    Maybe cold forming could work if you make the mold shapes exaggerated to account for spring back?

                    Local plastics shops has lexan cutouts up to 1/2" thickness sold per kilo basis... I always scrounge their cutout bin for large lexan pieces when visiting
                    And its not just some 3x12" size leftovers, they have pretty often sizes up to something like 2x4 feet in the leftovers!
                    Location: Helsinki, Finland, Europe

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                    • #11
                      I don't think there's a question of whether you can form it cold and have it hold some of the resulting shape- my big question is can you retain the optical clarity and mechanical strength when you push it past the 'springy' stage, in other words into permanent deformation?
                      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                      • #12
                        Darryl-The lens story is hilarious....I wouldn’t have thought of such a construct in a million years.

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                        • #13
                          The space blanket reflectors were formidable- much, much respect paid to focusing sunlight with a 4 ft diameter reflector.

                          That lens that I almost burned the house down with- I got home from work and smelled something burning. Looked over to where the lens was leaning against the wall, and there was smoke coming off the wall when the sun was focused. It had burnt a track following the setting of the sun. Luckily, because the lens was leaning against the wall, it was closer to the wall than the actual focal distance.

                          Keep in mind this was two domes made from plexiglass, stuck together and filled with tap water- so not a really good lens shape, and not a particularly transparent filler medium. It was too thick, and poorly shaped to work really well, but it was nearly two feet across and I could easily burn things with it. But it was nothing compared to the space blanket reflectors. One difference being the size, the other being the depth of curvature. I could only draw the mylar film down to about an inch before it bottomed out on the frame, so that means a longer focal length, but also a tighter focus point. It wouldn't hold vacuum very well either, so I had to suck the air out before using it, and then I'd only have a couple minutes with it. Couldn't keep a set focal distance. A 4 ft diameter particle board disc is not particularly air tight. Probably a good thing-

                          By the way, the plexiglass lens was converted to a fish tank at one point- I separated the halves, spaced them apart about 4 inches and surrounded the perimeter with a decorative array of hardwood blocks. One side of one lens was cut down for access to the inside, which I had waterproofed with an epoxy. I removed a window in my friends house and mounted this in its place. It actually looked quite cool, but I always wondered what the fish saw through the sides-
                          Last edited by darryl; 09-18-2020, 08:39 PM.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                          • #14
                            Originally posted by darryl View Post
                            That lens that I almost burned the house down with- I got home from work and smelled something burning. Looked over to where the lens was leaning against the wall,
                            Ahhh I missed that story, probably before I got here.

                            Sounds like a good heart pounder. "Neighbor, hey, does yer house always smoke like that?" lol

                            Dang, that could have been a Darwin Award!!

                            Headlines read:
                            Mr in BC burns his house down while making fish bowls

                            Glad you didnt... JR

                            My old yahoo group. Bridgeport Mill Group

                            https://groups.yahoo.com/neo/groups/...port_mill/info

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