Long, aligned strands of carbon fiber add rigidity. Chopped up, small bits at random angles does not.
3D printed "carbon fiber" PLA (which is small chopped up bits like you said) actually does not a lot to increase the strength of the plastic. Parts just break around the individual CF bits.
IMO, it's primarily a marketing gimmick. And it chews up your hotend very quickly during extrusion compared to normal PLA, because the material is so abrasive.
If you want stronger prints, you're better off printing in ABS or nylon.
Re:Plastic Gears Are the Future (2017)
by defterGoose on Monday June 03, 2019 @01:22AM
(#20080586)
The samples I got from Markforged refute your point. They are identical parts, one in plain nylon and one in their chopped CF nylon. The CF filled one is noticeably stiffer. I'm not sure anyone is making the claim that the CF filled parts are comparable to traditional composite parts.
Completely agree. You also run into strength issues at the layer interfaces if they’re not aligned properly in relation to your parts stresses. Fibers do nothing to help this since they don’t cross layers.
One of the interesting ideas mentioned is putting some chopped carbon fiber into the plastic to give it more tensile strength and hardness. That's being used in 3D printing now. See the current issue of Machine Design. Finally, decent tensile strength from hobbyist-type FDM 3D printing.[1]
[1] https://ultimaker.com/en/blog/52718-our-complete-solution-3d...