DIY Forged Carbon Fiber
Updated: Aug 24, 2018
Previously I wrote about my research into various carbon composites and how I was designing a mold to try my hand at "forging" carbon fiber (Link). So here is my first attempt at it, and the results were better than expected.
I decided to go ahead and make a decent molding platform that I could test with and reuse for future projects. The housing is three steel plates burned out on a plasma table, with a removable 3D printed mold shape inside. A fourth plate, aka "the ram," can be fixed to the lid via the 4 screw holes in the center, however I decided the screws wouldn't be necessary since the ram is constrained by the mold.
Lamborghini uses 1200 - 1500 psi to compress their carbon fiber, so I wanted the housing to be able to hold up to that. I wasn't sure how the 3D printed part would hold up to those forces, (I'm positive it won't) but my mold clearances are so loose that I figured any excess epoxy would squish outward and around, instead of deforming and bulging the plastic.
I also assumed that I would have to break the plastic mold to get the carbon fiber puck out, even though I sanded the layer ridges off the interior faces. Epoxy is pretty good at getting in nooks and crannies and holding fast. An acetone vapor bath would have been more ideal to get a nice smooth finish on the 3D print (It's printed in ABS), but I didn't have any, and I was in a hurry.
Filling the mold with chopped fibers and epoxy
Once all was set the ram and lid were placed on and the screws tightened down. I would have used a press to compact it all, but I wanted to do it by hand to feel how easy or hard it was to compress the fibers, giving me a vague gauge as to whether or not I used enough chopped fiber. Turns out it was very easy to squish what I had, leaving me to believe I should have put more fibers in.
12 hours later it was time to crack open the mold and see what happened.
Right off the bat I knew that I had used too much epoxy. It had squeezed through the bottom edge opposite the ram and had filled the entire surface between the plastic and the bottom platen and had started seeping up the edges too. On one hand, this let the plastic hold up to any forces exerted by the ram and didn't deform.
On the other hand, his pretty much meant that the carbon fiber and the plastic had become one solid piece.
I used a press to remove the plastic jig from the steel case, and then used a chisel and a vice to pry the plastic and carbon fiber apart. Completely destroying the plastic in the process.
3D printed molds aren't the best idea, but for a one off job like this it was fast and it did the job pretty well. The goal here isn't to make a production quality jig, but to learn the limits and what I can do with what I have available to me.
The shattered remains of the 3D printed mold, and a forged composite puck
Once the mold had been... removed... I trimmed the excess edges off and wet sanded the puck with 400, 1000, and 2000 grit to get a super smooth finish. The puck looks really cool when wet, but once it dried up it turns a little dull, so I wanted to add a final clear coat. I wasn't sure if a paint clear coat or another thin layer of epoxy would look the best, so I tried one on each side.
The clear coat didn't turn out the best, but the epoxy side looks great!
The forged carbon fiber puck with epoxy coat
I think some changes I will make in the future will be to chop the fibers up smaller than I did. I left some of the strands pretty long which made it more difficult when fitting into the mold. Also I need to work on better mold making practices than 3D printing and sanding. While it did work better than expected, it would be nice to not have to destroy the mold to get the part out.
I'll most likely refine my methods some more and then try to make an actual object instead of a coaster.