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I am trying to figure out the best way to mould/ create a closed shape (It is a 500mm long quadcopter arm) that has a foam core, and a rigid good quality carbon fibre outer. Oh and to add to the fun, I need a hole through the center of the foam core.

Said shape must be structural and resistant to twist and bend.

My initial thought is to create 2 halves of the foam core on a 3 axis router, with the hole present, stick them together, then somehow wrap them with carbon... epoxy, jam into a mould?

Obviously there will be an amount of finishing involved, but thats OK.

The process muse be repeatable and yield a near-identical item each time.

ETA: Further reading suggests that Vacuum assisted resin transfer moulding may be the answer. I would need to create a (very stiff) mould slightly larger than the foam core, pre-attach/ wrap the core with carbon/kevlar fabric, and then mould around. I will need to somehow stop the central hole from filling with resin of course!

Digital Lightcraft
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  • VARTM is a solid answer, and would be my first suggestion. Feel free to answer your own question with that if it does work. – do-the-thing-please May 10 '16 at 14:28
  • Thank you - I would rather not answer it myself as it would be nice if someone with experience of the process could explain how i should go about it in better detail. – Digital Lightcraft May 10 '16 at 14:35

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If your part is above a certain diameter (the hole in the middle) you can fit a vacuum bag within the hole between the two parts of the foam core do your lay up on the core put it into the negative mold and close the vacuum bag (which has now a toroidal shape).

In each case the dimensions/tolerances of the foam core need to be adapted to the layup thickness / volume fraction of matrix/fibers.

Lageos
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If you can go with a circular cross-section, you could use a pre-manufactured CFRP tube, e.g. one of these.

If the cross-section shape is important, there is CFRP sleeves you could probably wrap around your custom core, working in "Positivbauweise" (positive design?).

If I understand correctly, the hole should be in longitudinal direction. For such a hole, I would apply the CFRP to a solid foam core and drill a hole in a second step. Use styrofoam or similar as core material that you can easily remove later. Also with some plastic cores, you can use acetone to remove the core entirely in case you don't need it.

If surface finish is really important, you will have to go with VARTM.

PS: Sorry for the links being from the same supplier, but those were the first ones I found. I'm sure you can get similar products from lots of other suppliers.

Robin
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