Composite printing covers two technologies whose results differ by an order of magnitude. Chopped fibre filled filaments produce a stiffer, more dimensionally stable plastic. Continuous fibre printing places unbroken strands along the load path and produces something that genuinely behaves like a composite. Both are sold as composite printing.
Chopped fibre reinforcement
Short carbon, glass or aramid fibres are mixed into a base polymer, usually nylon. The result is stiffer and warps less than the unfilled polymer and is more brittle. The fibres are far too short to carry load between layers, so the anisotropy of the printing process is unchanged and in some respects worse. It is a better plastic, not a composite.
Continuous fibre placement
A second head lays an unbroken strand of fibre inside the part while the polymer is printed around it. Because the fibre is continuous it carries tensile load along its length, and stiffness and strength in that direction rise dramatically. The part is only strong where the fibre goes, so the design is a fibre routing exercise rather than a shape one.
What it competes with
Continuous fibre printed parts compete with machined aluminium for jigs, fixtures, brackets and end of arm tooling, where they win on weight and often on lead time. They do not compete with autoclave cured laminates on structural performance, because fibre volume fraction is much lower and the resin is a thermoplastic rather than a cured thermoset.
Practical constraints
Filled filaments are abrasive and require hardened nozzles and feed paths. Filled nylons absorb moisture and must be dried. Continuous fibre machines are proprietary and the material comes from the machine maker, so the supply chain is closed. And fibre cannot turn a sharp corner, so the geometry has to accommodate the minimum bend radius of the strand.
Questions people ask about composite 3d printing
Is filled filament a composite?
Not in the structural sense. The fibres are too short to carry load between layers, so it is a stiffer, more stable plastic rather than a composite.
What does continuous fibre printing achieve?
Substantially higher stiffness and strength along the fibre direction, enough to replace machined aluminium in fixtures, brackets and end of arm tooling.
Can printed composites replace laminates?
Not for structural laminates. Fibre volume fraction is far lower and the matrix is thermoplastic, so autoclave cured prepreg remains a different class.
What do filled filaments do to a printer?
They abrade brass nozzles quickly. A hardened nozzle is essential and a hardened feed path helps on machines that run them regularly.