Continuous Fiber FDM

Continuous Fiber FDM 3D prints thermoplastic parts with in-situ laid continuous fibers, delivering high stiffness and strength along defined load paths.

Overview

Continuous Fiber FDM (continuous fiber reinforcement) is an FDM-based composite process that prints a thermoplastic matrix while placing continuous carbon, glass, or aramid fiber strands inside the part. Fiber is routed in specific regions and directions, so properties are highly anisotropic—very strong and stiff along the fiber path, much weaker across layers and where fiber cannot be placed.

Choose it for lightweight structural brackets, fixtures, and end-use parts where you can define clear load paths and want metal-like stiffness at low mass with short lead times. It’s most effective at low to medium quantities and for parts that benefit from localized reinforcement rather than full-solid material.

Tradeoffs: tighter design rules than standard FDM (minimum radii, fiber turn limits, keep-out zones), variable surface finish, and dimensional accuracy limited by FDM thermal behavior. Strength depends heavily on fiber continuity, layer adhesion, and avoiding stress risers at fiber start/stop and around holes.

Common Materials

  • Nylon (PA6/PA12)
  • Nylon-CF
  • Polycarbonate (PC)
  • PEEK
  • Continuous carbon fiber
  • Continuous glass fiber

Tolerances

±0.010–0.020 in (±0.25–0.50 mm), after stabilization; tighter with machining on critical features

Applications

  • Lightweight robotic end-effector brackets
  • Drone arms and equipment mounts
  • Composite jigs, fixtures, and assembly tooling
  • Machine guarding brackets and covers with stiffeners
  • Structural enclosures with integrated reinforcement
  • Replacement parts for legacy equipment with load-bearing ribs

When to Choose Continuous Fiber FDM

Pick Continuous Fiber FDM for load-bearing thermoplastic parts where stiffness and strength must be concentrated along known load paths. It fits low-volume production and rapid iteration when you can accept FDM-level accuracy and will post-machine critical interfaces if needed. It works best on geometries that allow continuous fiber routing without tight turns or frequent start/stop points.

vs Chopped Fiber Infusion Printing

Choose Continuous Fiber FDM when you need a step change in stiffness/strength in specific directions, especially for bending-dominated parts where continuous strands carry the load. Chopped fiber processes improve overall material properties but won’t match continuous reinforcement for beam-like features, straps, and reinforcement rings. Continuous fiber also lets you place reinforcement only where it pays off instead of reinforcing the whole volume.

vs Standard FDM (unfilled thermoplastics)

Choose Continuous Fiber FDM when basic FDM parts are failing in bending, creep, or fastener pull-through and you need a structural solution without moving to metal. Continuous reinforcement can reduce weight and bulk compared to simply thickening walls or increasing infill. Expect similar FDM-driven constraints on accuracy and surface finish, with added fiber routing rules.

vs CNC machining (aluminum)

Choose Continuous Fiber FDM when weight matters, lead time is tight, and loads align with reinforcement directions so you can get metal-like stiffness at lower mass. It’s also useful when you want integrated features (ribs, stiffeners) without multiple machining setups. Plan to machine holes, datums, and sealing surfaces if they drive fit or alignment.

vs Short-fiber injection molding

Choose Continuous Fiber FDM for low volumes or frequently changing designs where tooling isn’t justified. Continuous fiber can outperform short-fiber molded parts in targeted directions with reinforcement placed only where required. For high volumes or highly isotropic requirements, molded parts usually win on unit cost and consistency.

Design Considerations

  • Define primary load paths early and align continuous fiber with those directions; avoid designs that rely on across-layer strength
  • Use generous radii and smooth fiber routing; avoid tight corners that force fiber breaks or start/stop points
  • Add bosses, washers, or metal inserts for bolted joints; don’t rely on printed threads or bare polymer bearing surfaces for high clamp loads
  • Keep holes and precision interfaces oversized for post-machining; call out which datums must be machined in the drawing
  • Avoid thin, wide cantilevers without reinforcement continuity; use ribs or closed sections that let fiber run uninterrupted
  • Provide print orientation and fiber placement intent (or allowable orientations) to make quoting and performance predictable