Two quite different things are sold as carbon fibre printing. One is a polymer filled with short chopped fibres, which is stiffer and more dimensionally stable than the base polymer and not structurally comparable to a composite. The other lays continuous fibre inside the part, which genuinely produces a composite. The gap between them is enormous.
Chopped fibre filled filament
Short carbon fibres are mixed into nylon, polycarbonate or another base polymer. The result is stiffer, more dimensionally stable, less prone to warping and a good deal more brittle than the unfilled material. It prints on ordinary machines, provided they have a hardened nozzle, because the fibre is abrasive enough to wear a brass one out quickly.
Continuous fibre printing
A second print head lays a continuous strand of carbon, glass or aramid fibre inside the part while a conventional head prints the polymer around it. Placing fibre along the load path produces genuine composite stiffness and strength, at a fraction of the weight of an equivalent metal part, and it is used for fixtures, brackets and end of arm tooling.
What the marketing conflates
Chopped fibre gives perhaps a moderate improvement in stiffness and no meaningful improvement in strength between layers, which is where printed parts fail. Continuous fibre changes the answer entirely, and only along the direction the fibre was laid. A part described simply as carbon fibre printed tells you almost nothing about which of these it is.
Practical notes
Hardened nozzles are mandatory for filled filaments and hardened feed paths help. Filled nylons still absorb moisture and must be dried. Surface finish is matte and slightly fuzzy. And for continuous fibre, the design has to be laid out around where the fibre can physically go, which is a composites design problem rather than a printing one.
Questions people ask about carbon fiber 3d printing
Is carbon fibre printing as strong as real composite?
Chopped fibre filled filament is not; it is a stiffer plastic. Continuous fibre printing produces a genuine composite, but only along the direction the fibre was placed.
Can you 3D print carbon fibre?
Yes, in two senses: filled filament on ordinary machines with a hardened nozzle, or continuous fibre on machines built to lay it inside the part.
Does filled filament damage printers?
It wears brass nozzles quickly. A hardened nozzle is essential, and a hardened feed path helps on machines that see a lot of it.
Where is continuous fibre printing actually used?
Jigs, fixtures, brackets and end of arm tooling, where a light stiff part replaces machined aluminium and the fibre can be laid along the load path.