Reinforce Your 3D Prints with Carbon Fibers and Epoxy

After seeing the success of my last video,
where I reinforced 3D printed parts with steel wire, it was clear to me that this needs a
follow up. And it only took me five months to come up
with this: Carbon Fiber reinforced prints. Now, I can already hear some saying: There
are printers out there, doing this automatically. Yeah, but just the material they use probably
cost more than the cheap chinese 3D printer most of us own. I want to find the cheapest and easiest way
to use carbon fiber in our 3D prints and for that, I bought some so called carbon fiber
roving. This one consists out of 24 thousand single
carbon fibers and it is fairly cheap. My first Idea was to use the fibers the same
way like the steel wire in the last part: Just use a soldering iron to press it into
the plastic. I quickly realized that this isn’t going
to work well. Problem number one: Its pretty hard to control
24 thousand individual fibers. They tend to spread apart and it’s just
a pain to work with them. A possible solution to this would be to twist
the fibers by hand or with a drill and use a drop of superglue to keep them together. Still, this wouldn’t solve the second problem:
While a steel wire absorbs the heat of a soldering iron and melts into the plastic, the carbon
fibers don’t really do this. Therefore we don’t get a nice bond between
the two materials and because of that I don’t expect any significant increase in strength. To solve this problem, we are going to use
the best friend of carbon fibers: Epoxy. This is just some cheap stuff I found online. It has a low viscosity and a very long curing
time of some hours up to a day. I definitely don’t want to use epoxy anywhere
near my 3d printers as I am certain that this is going to end in a big mess. Therefore I made the test parts hollow on
the inside and added two ports, one for adding the resin and another for the air to escape. During the print, I add the carbon fibers
by just loosely position them inside the model, fixed with some drops of superglue. After the print, I am using a syringe to inject
the resin. For comparison, I also made the exact same
part with epoxy only. Injecting the resin works very well and by
just pushing in more and more resin it’s easy to get rid of any air bubbles. Injecting resin into the carbon filled parts
needs more pressure on the syringe and creates a mess. There are two problems right here: First,
the hole for injecting the resin doesn’t seal the syringe. To prevent that, I made it higher and the
diameter a bit smaller, which turns out to work great. The second problem is the epoxy pushing through
the top layer. Here I would suggest to use a higher layer
number, something like at least 10 layers or 1.5 mm, as well as maybe turning up your
flow rate a bit to prevent any holes. Here you can see how easy it is to get rid
of remaining air bubbles by just pushing in more and more resin. For comparison, additional to the resin and
carbon fiber reinforced parts, I printed the hollow version of each part with plastic only
as well as a normal version with 3 perimeters and 50% infill. Next step: Breaking parts After breaking some parts, the whole process
became a lot scarier. It seems like the souls of the broken parts
are haunting me or something in my test setup is dying slowly and painfully First lets have a look at the results of the
normal plastic parts and compare them to the results of the test 5 months ago. You can see, that when the filament was new,
the parts were slightly stronger. After 5 months, the filament seems to have
become a little bit brittle. It was stored away from any sunlight, however
I haven’t dried it before testing. I didn’t notice any bubbles or similar symptoms
of moist filament but there is clearly something going on. So, always remember to store your filaments
the right way. These are the results of the test today. Interestingly, the normal plastic parts show
next to no difference to the epoxy reinforced parts. Maybe that’s because the cross section of
my test parts is relatively small and therefore the difference between plastic infill and
epoxy isn’t that big. Or, as this is the first time I am working
with epoxy, the one I chose just isn’t the right one for the job. I haven’t compared any datasheets and just
went with the cheapest one. This makes my idea of using epoxy to fill
the space between the infill of parts kind of unnecessary, but I still want to show it
to you real quick. Maybe this is going to make a difference on
bigger parts or someone can find a good use for it. While standard infill patterns create separate
chambers which don’t allow the epoxy to spread through the part, gyroid infill does
allow exactly that. So, after the print I drilled a hole all the
way to the bottom of the part and then used a syringe to inject the resin. You can see that the epoxy fills nearly the
entire part and it isn’t leaking. The carbon fiber reinforced parts show a significant
increase in strength compared to the normal parts. If we compare it to the steel wire reinforced
parts, we can see that it performs worse in bending as well as pulling situations. However the oval test part, which combines
pulling and bending, seems to favor the carbon fiber reinforcements. Keep in mind that the moist filament also
has an effect on these results, so comparing the exact numbers one to another might not
be a good idea. I would recommend to use steel wire when you
want to reinforce small parts. It’s easy to insert and a fast and cheap
method to increase strength. Carbon fibers are hard to align inside small
parts, so use these for bigger ones, where it would be very time consuming to insert
steel wire. Instead of the roving I used you could also
use a carbon fiber fabric. Cut it into the size of your part and insert
it during the print. Carbon fibers also give you the possibility
to add strength along the z axis, like I did here with this filament holder which you have
already seen in the beginning of this video. I just hollowed the original part and pushed
the carbon fibers inside while making sure they are oriented along the longitudinal axis. After that, I just poured in the epoxy slowly. I hope you found this video interesting. Thanks for watching and have a great day.

10 Replies to “Reinforce Your 3D Prints with Carbon Fibers and Epoxy

  1. The epoxy injected parts will probably be quite strong in compression.

    The carbon/epoxy matrix strength depends a lot on the ratio of carbon fibers to epoxy. A 50/50 layup is considered to be achievable for an amateur working with wet layups. With pre-preg carbons it is higher. (and you can go too high, and achieve an epoxy starved layup if consolidation is done with positive pressure instead of vacuum.

    From the videos I guess the ratio of carbon/epoxy was substantially below 50/50. That might be one variable explaining the measurements.
    Another variable is strand orientation. Twisting the fibers will cause the layup to be weaker as compared to straight fibers.

    If you could achieve similar weight between the epoxy/carbon layup and the steel wire, I would be interested in the results. The carbon/epoxy layup should be significantly stiffer than the steel/plastic fusion and thus take all loads instead of working as a composite steel/plastic part.

    The epoxy used, curing time and temperature are also some variables that might be influencing the measurements. "Cooking" the part in an oven for 8 hours at 80degC and then letting the part sit at 20degC for a day or two might change the results a bit. If it was the epoxy matrix, not the carbon/epoxy composite, that carried the tensile loads there might be significant changes.

    Cool experiment and video! You cerntainly thing outside the box 🙂

  2. For years i use abs with carbon fibre….i just put carbon fibre mid print , add a few drops of acetone and resume the print 🙂
    for method you use….i use it too 🙂 but for easier aplication i twist filament few times then aply it or aply resin before puting it in print and add rest of the resin after.

  3. Bravo! Very interesting video, I would suggest checking into Kevlar tow/fiber as it is very cheap and strong in large spools, similar to CF. I have tried both with success. I would also suggest it because it is much less messy and stays in a compact fiber very similar to string. Finally it would be worth checking into purpose-made CF epoxy resin since it is made specifically to bind to fiber and the stuff I got has a nice slow cure time and works well. You might try JB Weld alone since it is among the very strongest epoxies out there, it would be difficult to inject around fiber.

  4. Very interesting idea to mix carbon with epoxy. There are also additives for epoxy, like glass fibre from West System. This would make things easier (like your tests with pure epoxy) but maybe not as strong as the long carbon strings.

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