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  1. #1
    ctyleruf is offline Plastic
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    Default Milling Carbon Fiber Sheets

    Hi guys,

    I'm trying to machine some carbon fiber sheets to make CF wing frames. I've posted some pics of my first attempt. It went okay but I need a better way of fixturing the sheets. I begin with facing the 0.8mm sheets to 0.15mm with a 1/4" flat endmill. I then proceed with cutting the inner contours of each wing with a 1mm endmill; followed by the outer contours to release them from the sheet. I am using a small table top CNC Baron at 1500rpm. Each side is 1mm wide and 0.15 thick except for the triangular base; which is the original 0.8mm.

    I plan to try a double sided tape method to hold them down next. I would like to get a tape that holds, but also doesn't leave a residue on the frames. It's also necessary that they be removed easily, possibly with acetone.

    I thought of a vacuum chuck system but when I get to the through contours I wouldn't want to damage the chuck.

    Any fixturing suggestions would be helpful. Also, tool wear with eventually be a problem. Any suggestions regarding tooling would also be helpful. I don't know if diamond coated burrs will cut at these speeds (plus they're sort of expensive).

    Thanks.

    PS: I understand the hazards associated with the process. I'm taking the proper precautions.

    fixture_cf-wings_sized.jpgcf-wings_1_sized.jpgcf-wings_2_sized.jpg

  2. #2
    AeroE is offline Cast Iron
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    Get the parts water jetted.

  3. #3
    henrya is offline Stainless
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    Adhesive transfer is one thing you should try. Its like only the sticky part of tape without any tape.

    I'd think about molding these. You can make them stronger and lighter. And you can do all your cutting with scissors before the cured resin makes it difficult. Machine a mold from aluminum and lay bare carbon tow into the mold, then fill mold with resin. I think the parts produced would be superior to those you're making now.

  4. #4
    ctyleruf is offline Plastic
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    We don't really have the resources for water jet machining now. Ideally, that is what we'd like to do. Thanks

  5. #5
    ctyleruf is offline Plastic
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    Could you recommend some appropriate adhesive transfer?

    We've tried laying-up prepreg strips of cf into machined teflon molds previously. This wasn't as repeatable as we would like. Also, the joints were the first to break (couldn't apply enough pressure I think). We haven't tried carbon tow, however. That is something we could try fairly easily. I anticipate a bit of post processing (flashing removal) this way.

    Thanks.

  6. #6
    kustomizingkid is online now Hot Rolled
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    Waterjet.... I have machined CF and it does not like getting thin in the terms of the distance from two slots or the edge of the part and a cut.

  7. #7
    henrya is offline Stainless
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    Quote Originally Posted by ctyleruf View Post
    Could you recommend some appropriate adhesive transfer?

    We've tried laying-up prepreg strips of cf into machined teflon molds previously. This wasn't as repeatable as we would like. Also, the joints were the first to break (couldn't apply enough pressure I think). We haven't tried carbon tow, however. That is something we could try fairly easily. I anticipate a bit of post processing (flashing removal) this way.

    Thanks.
    Most any office supply or art supply store will have it. It comes in many varieties, some permanent, some removable, various thicknesses, all kind of industrial rated stuff.

    I don't have true expertise in carbon lay-up, just some hands on experience as a hack. That said, I'd add more tow material than I thought I needed in the corners, probably starting there and then laying in the straight sections on top of the corner pieces. (you know this already, carbon laminates develop their strength in tension so keep that in mind as you go about this work) Trimming off the flash will be a razor knife job as long as its only resin you're cutting. Mess up and have some fiber in the flashing and you'll going to be grinding. If you're super careful in metering your resin you could have zero or near zero flash. While I'm at it, where did you come up with that design? Does each little section have a purpose? I could see easier designs to build.

  8. #8
    specfab is online now Hot Rolled
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    Check the 3M product line for transfer adhesive, McMaster also carries a few varieties. I would look carefully at that application though, as you don't want the adhesive layer to be too thick. That will allow part motion. If I were doing it I would stick with the double sided tape to give the "stickum" more structure of its own. For removal, a little soak with some of that citrus gunk remover will get it loose easily. Regarding waterjetting, it's quite inexpensive in my experience, unless you have a whole bunch of onesey-twosey items.

  9. #9
    noobimachinist is offline Plastic
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    Im wondering, when you are milling carbon fiber, do you have a vacuum with a fine mesh filter or HEPA filter and do you wear face masks? Is it a breathing hazard the dust sorta like asbestos?

  10. #10
    maxh is online now Hot Rolled
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    I don't have much to add, and next to no carbon fiber experience, but was wondering, if you're milling the sheet so thin, is it not compromising the integrity of the material? It seems that after milling away most of the thickness, instead of long woven strands, you'd have many short, disconnected segments of carbon fiber filament suspended in the resin, and the overall material properties would be related more to the strength of the resin than the tensile strength of carbon fiber. I may be way off base, though, since I don't have any experience in the field. Is building the parts up instead of machining from stock out of the question? I picture a fixture/jig milled into aluminum, maybe with some pins, and you soak carbon fiber filament in resin and wrap it strategically, then squish with the top half of a mold while it cures.

  11. #11
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    Use diamond coated end mills for sure, they will last a lot longer, worth the $ for sure. There is a local water jet shop here, UPS your parts to them. PM me, I'll get you their info.

  12. #12
    AeroE is offline Cast Iron
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    Quote Originally Posted by maxh View Post
    I don't have much to add, and next to no carbon fiber experience, but was wondering, if you're milling the sheet so thin, is it not compromising the integrity of the material? It seems that after milling away most of the thickness, instead of long woven strands, you'd have many short, disconnected segments of carbon fiber filament suspended in the resin, and the overall material properties would be related more to the strength of the resin than the tensile strength of carbon fiber. I may be way off base, though, since I don't have any experience in the field. Is building the parts up instead of machining from stock out of the question? I picture a fixture/jig milled into aluminum, maybe with some pins, and you soak carbon fiber filament in resin and wrap it strategically, then squish with the top half of a mold while it cures.
    The parts appear to be for models. Whether they're intended to fly or not isn't known so far. In any case, your instinct is correct, and this is a misapplication of the material with all down side and no benefit as used in this example.

  13. #13
    henrya is offline Stainless
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    Quote Originally Posted by AeroE View Post
    The parts appear to be for models. Whether they're intended to fly or not isn't known so far. In any case, your instinct is correct, and this is a misapplication of the material with all down side and no benefit as used in this example.
    +1
    I alluded to this in my post but perhaps too politely.
    But it appears the OP has left the building.

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