Filament Winding

Filament winding builds high-strength composite cylinders and pressure vessels by wrapping continuous fiber under tension over a mandrel with controlled fiber angles.

Overview

Filament winding (fiber winding) places continuous glass, carbon, or aramid tows under tension onto a rotating mandrel, typically with wet resin or prepreg tow. The CNC-controlled winding pattern sets fiber angle and thickness, giving excellent strength and stiffness in the hoop and axial directions on axisymmetric parts.

Choose it for tubes, pipes, drive shafts, and pressure vessels where performance comes from aligned continuous fibers and repeatable laminate architecture. It scales well from prototypes to production once tooling is built, and delivers high fiber volume with good consistency.

Tradeoffs: geometry is constrained—best for cylindrical, spherical, and some tapered shapes; features like flat panels, deep ribs, sharp corners, and complex cutouts usually require secondary machining and local reinforcement. Surface finish and final dimensions depend on mandrel quality and post-processing (trim, bore, machine ends). Tooling and setup cost can be significant, especially for removable or collapsible mandrels.

Common Materials

  • Carbon fiber/epoxy
  • E-glass/epoxy
  • S-glass/epoxy
  • Aramid/epoxy
  • Vinyl ester (glass fiber)

Tolerances

±0.010" to ±0.030" (as-wound), ±0.005" with secondary machining

Applications

  • Composite pressure vessels (COPV)
  • Composite pipe and chemical tanks
  • Carbon fiber drive shafts
  • Rocket motor cases
  • Roller and idler tubes
  • High-pressure composite overwrapped cylinders

When to Choose Filament Winding

Filament winding fits axisymmetric parts where you want high directional properties from continuous fibers and controlled winding angles. It’s a strong choice when the part can be built on a mandrel and you can tolerate post-trim/machining for interfaces and openings. It becomes cost-effective when you can reuse tooling across multiple parts or sizes in a family.

vs Resin Transfer Molding

Choose filament winding when the part is primarily cylindrical and performance depends on continuous fiber alignment (hoop/axial) rather than complex 3D features. It typically achieves higher directional strength and repeatability for tubes and pressure vessels without designing a full closed mold for the entire laminate.

vs Vacuum-Assisted Resin Transfer (VARTM)

Choose filament winding when you need precise fiber angles and high fiber volume in an axisymmetric structure. VARTM is more flexible on shape, but it’s harder to control fiber orientation and compaction to the same level on thick-walled tubes and vessels.

vs Prepreg Layup with Autoclave

Choose filament winding when the geometry is a tube/vessel and you want automated laydown with consistent fiber placement at scale. Autoclave prepreg excels for complex shells and tight surface/void requirements, but labor and layup time rise quickly on long tubes compared to automated winding.

vs Pultrusion

Choose filament winding when you need variable fiber angles, local thickness build-ups, or closed-end vessel shapes. Pultrusion is best for constant cross-section profiles and typically can’t match winding’s ability to tailor hoop vs axial properties along the length.

vs Hand Lay-Up

Choose filament winding when repeatability, fiber alignment, and production throughput matter on cylindrical parts. Hand lay-up can handle varied shapes, but it’s labor-heavy and less consistent for thick, high-performance tubes and pressure-rated structures.

Design Considerations

  • Design the part to be mandrel-removable: add draft/taper where possible and plan for collapsible or sacrificial mandrels when needed
  • Call out fiber angle(s), laminate thickness, and structural load directions; winding patterns drive performance and cost
  • Minimize cutouts and interrupts in the wound region; plan openings at ends or add local reinforcement pads for machined ports
  • Define machined interfaces clearly (bores, faces, threads, bond surfaces) and leave machining allowance in the wound thickness
  • Specify end fittings/liners early for pressure vessels (metal bosses, polymer liners) because they control process flow and qualification
  • Provide target OD/ID, straightness, and concentricity requirements separately; achievable tolerances depend on mandrel quality and post-machining scope