Carbon Fiber R&D


Lately I've been doing some research and prototyping with carbon fiber. Everyone loves carbon fiber for one reason or another, and I am no exception. I'm definitely no expert on composites, but I've worked with custom carbon fiber molding in the past, though it was on a scale 100 times larger than the scale of the parts I'm concepting for BRACE.

Small scale carbon fiber is a lot harder than large scale.

Well, not to say that it's too much harder, you just need more specialized tools. Which I don't have.

But it also depends on what your application is and what look and feel you're going for. Since I don't know the answer to either of those questions yet, I'm just experimenting to see what I can achieve with what I have available.

One problem with carbon fiber is that everyone seems to expect the shiny checker board finish. Some to the extent that if it doesn't have that, is it really carbon fiber? This is great when the parts and smooth and uniform, but it's really hard to get that sweet pattern on tiny parts with irregular detail. It's doable to some extent, but it's hard. A stock piece of carbon fiber can be machined down to the part, preserving some of the pattern and that introduces new patterns as well, which can be interesting. You can cheat and use hydrographics to put the pattern on a finished part, but that's not what I'm after.

Another route I'm looking into is a composite carbon fibers. Basically this means using nylon (or a lot of other things) that is filled with small chopped up strands of carbon fiber, greatly increasing it's strength. That can then be combined with full carbon fiber strands either 3D printed or cast, yielding a part that has strength comparable to 6061 aluminum. There are a hundred different names and types of this material out there, Onyx, Aurum, Vespel, CarbonX, Carbonite... DuPont has been making new variations of this for a long time now, and these are used everywhere. You just don't mentally associate them with carbon fiber because they generally don't have the sweet pattern.

Composite bracelet links with stainless steel screws.

One experiment with composite carbon fiber are these bracelet links. They turned out pretty nice but I'm not quite content with the finish, so I've been doing multiple tests with sandblasting, clear coating, and epoxy finishes. This material is actually really nice in it's own right and I like it a lot, but it doesn't have quite the right look (or chatoyance, pinky finger out) and feel that I associate with carbon fiber.

Sandblasted and unpolished clear coated composite links.

Finally I've been looking into forged carbon fiber (or forged composite), which is a lot like regular carbon fiber, but it utilizes an irregular weave (more correctly, it uses no weave at all) to give it isotropic properties instead of the traditional two dimensional strengths along the carbon blanket's plane. It is pressed into a mold similar to injection molding as opposed to layering blankets like traditionally done, and then heated to cure the epoxy.

I haven't done this myself yet, but I have begun the process of designing an adjustable mold/jig that I can experiment with, and turn into a production mold if need be. It is massively overkill for what I would actually need for testing, but it can also be made in stages, testing as I go along.

Anyway, I'm learning a lot about the different methods out there, and learning what methods I'll be able to use in future projects. Hopefully I'll be able to make some forged composite in the near future. We'll see how that goes.

Got any carbon fiber tips and tricks? Leave a comment below.

#prototype #carbonfiber

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