Just thinking out loud, is it feasible to infuse chop carbon fiber into one of the resin(maybe the tough one) and have it print successfully? If I could find the right ratio of resin to carbon fiber would the prints be much stronger?
I would be surprised if you could achieve acceptable results with anything more coarse than a fine powder. And a fine powder wouldn’t make the print any stronger.
See if you can procure some carbon chop used to fill plastic resins, it will be the smallest stuff you can get. If it allows the part to print properly, then yes you will be much stronger particularly in the x/y directions. The fibers would mostly get squished out of the z axis so i don’t think you will get much there.
Then you will have to deal with these little fibers sticking out EVERYWHERE. Filled resins are very common in injection molding but the process is such that there is a usually a resin rich layer on all surfaces and the mold itself keeps things contained so you don’t have frills of the fiber sticking out.
While this may be true for a FDM printer, it is not for a SLA printer (and other similar printing processes like SLS).
FDM prints are “anisotropic”, they are weaker in Z than in X/Y because the adhesion between layers is weaker than the continuously-extruded bead of plastic comprising each layer.
SLA prints don’t exhibit this weakness. The prints are “isotropic”, equally strong in all directions because each new layer seamlessly fuses to the previous layer when the laser cures the resin (or in the case of SLS, melts the powder).
You probably won’t have the same strength with fiber reinforcements in a SLA print. As stated above the strands will tend to orient flat in the layers causing them to act more like a FDM print in that direction.
You do need to check that the resin will adhere to the material being added. In the composites world some materials just don’t stick together (some epoxys and fiberglass for instance).
I’ve printed with a a few different materials added to resins (on my Form 1). You would be amazed at what will print. Aluminum, copper, microspheres, and tungsten powder will all print. Not exactly functional but they will print.
The prints themselves may be isotropic, but I was talking about the addition of chopped fiber. The fibers may not bridge the build direction well so it could be weaker.
On this note, I just printed some dogbones using 5% chopped glass fiber mixed with Clear V2 and it printed without any issue. I used open mode on the Form 2 so that resin dispensing wouldn’t change the mix ratio. I am not sure if the wiper would help or hurt either. It could end up pushing the fiber out of the build zone but it could also help agitate the resin and keep things mixed properly, as i noticed significant settling of the fiber after the build completed. I used 0.1mm resolution to maximize layer height and minimize the risk of fibers not bridging the z axis. If you look closely you can see fibers sticking out of the surface of the part.
Now you just need to print a set of dogbones without the fiber and compare their strength! Cured resin seems to stick to glass pretty good, so maybe this has made it stronger. Be interesting to see.
and a tensile tester…
Carbon does not form a strong bond with acrylic resins. In fact, it does not form a bond at all, in contrast with glass fibres. I have witnessed more than 120% strength increment by adding less than 5% w/w glass fibres in clear resin.
I’m actually interested in how the parts fail with the added glass fiber.
Is the impact strength increased? How much stiffer is the print?
Also, what length was the chopped strand you used?
I didn’t use chopped strands rather than full length fibres. I printed dog - bone specimens adding carbon, glass fibres and also UHMWPE. I paused the printing procedure in order to add the fibre. The final result was a composite specimen, which was later tested using an Instron UMT. Specimens with carbon fibres had the worst behaviour; carbon fibres could easily pull from the printed specimen by hand. GF had the best behaviour followed by UHMWPE. During failure, GF specimens had an explosive behaviour. On the other hand, UHMWPE fibres did not fail and continued to withstand loading after resin rapture. Did not test impact strength yet, but UTS increased by 120% (from 60MPa it reached 135MPa).
I have a lot of resin which is going to expire soon…I’m willing to test some of this stuff out. I’d rather use it to test than go to waste.
I also work for a water manufacturer. We literally have 10 tons of carbon in our warehouse, although I imagine it is in the wrong form. ours is for water filters and looks like this:
Obviously that won’t work as-is…it has a size/consistency about that of sand. Would I be able to mill that down further into a powder form and try? Or are we talking different materials at the molecular level?
I think it would take a bit to process the carbon granules into something useful for reinforcement.
I was looking at a couple of things.
milled glass fiber. It’s milled so the fiber lengths vary quite a bit but they do have a max length. I was looking at 1/32" fibers but this might be good enough to test (and reasonably cheap). https://www.amazon.com/System-Three-3135S16-White-Milled/dp/B013K2WGGA/ref=sr_1_1?ie=UTF8&qid=1505475248&sr=8-1&keywords=milled+glass+fiber
Microfibers. these aren’t glass but I was wondering if they would adhere or even add any strength to our resins. West sells this for epoxy but it may work with acrylic resins. https://www.amazon.com/gp/product/B0000AY1NY/ref=ox_sc_act_title_1?smid=A9HNR4I8RXLVW&psc=1
@kevinduhe I have tried graphene nanoplatelets with disappointing results. Based on my experience, acrylic resins do not like carbon.
@FredB I’m also interested in using milled glass fibre. I’m in search of a producer in EU. Also, glass wool could be an interesting option, but you have to stop the printing in order to apply a thin sheet of wool.
That’s what I figured…as they are they would either block the laser or provide nothing but a hinderance to any resin bonding process.
Here are some results from a FL test a while back with carbon sheet. Carbon Sheet
You can see my results above for 1/32 milled glass fiber. The print went without issue and there appears to be a good amount of fiber in the part itself. Just have to do the testing still. This is where I got it, not sure about international supply sorry. Fibre Glast
I wouldn’t expect the same UTS increase as FredB since this is chop and not continuous strands. If you orient continuous strands in your load direction then as long as you get good bonding you will get the tensile strength of the fiber. My goal was to allow the fiber to give added strength in multiple directions by allowing random orientation. See Markforged
Thanks for the info. I’ll keep the forum informed about my findings.
@FredB Can you elaborate a little on your experiments with things like aluminum particles and what you meant by “not exactly functional”? Did you ever try the milled glass fibers?
5% is 5vol% or 5wt%?
I know this is an old thread, but has anyone had any more interesting results with including glass or carbon fibers with their builds?
The sizing / surface treatment of carbon fibers has a large role in determining interfacial strength between the fiber and matrix. Carbon fibers with sizing that is suited to the common 2-part epoxy resins may not be suitable for an SLA resin (I think the clear Formlabs resin is an acrylated urethane?).
So maybe finding the right sizing / surface treatment would solve the low interfacial strength issue that was observed when using carbon fibers? Or is the problem the opacity and high absorptivity of the carbon itself that inhibits curing at the interface of the resin and the fibers?
I’d love to know if there have been any more developments with this concept.