Filament winding

Resin-wet fiber wound onto a spinning mandrel

Filament winding wraps resin-wet fiber around a spinning core called a mandrel, layer after layer, like thread on a spool. A moving carriage guides the fiber so it lands at an exact angle. Pipes, gas cylinders, hydrogen tanks and rocket motor cases are made this way.

Photo: Gdipasquale1, CC BY-SA 4.0, via Wikimedia Commons

Filament winding machine, side view, with the three winding patterns and the cureCircled numbers match the steps below. The lower row shows the three basic winding patterns and the final cure.

How it works

Feed the fiber. Rovings (untwisted bundles of continuous fiber) unwind from spools and pass through tensioners, which keep them evenly taut.
Wet it with resin. The fiber runs over a drum turning in a resin bath. Alternatively, towpreg (fiber already soaked in resin, like a thin prepreg tape) is wound dry.
Guide it onto the spinning mandrel. A carriage with a delivery eye (the guide the fiber leaves from) travels back and forth while the mandrel turns. A computer links the two motions.
Build up the layers. The speed of the carriage compared with the spin sets the fiber angle: near 90° for hoop layers, a set angle for helical layers, near 0° for polar layers over the ends. Layers are stacked until the wall is thick enough.
Cure, then remove the mandrel. The part cures (the resin hardens), often in an oven while still turning. The mandrel is then pulled out, or it stays inside as a liner, as in most pressure tanks.

Key facts

Materials: Glass fiber (most common), carbon or aramid (a tough synthetic fiber); epoxy, polyester or vinyl ester resin
Typical parts: Pipes, pressure vessels, gas and hydrogen tanks, drive shafts, poles, rocket motor cases
Part size: From tubes a few centimeters across to tanks and pipes several meters in diameter
Precision: Inner surface as accurate as the mandrel; fiber angle and wall thickness controlled layer by layer
Surface finish: Inside smooth; outside ridged by the fiber bands unless sanded, wrapped or coated
Batch size it suits: One-off large tanks to tens of thousands of cylinders a year on multi-spindle machines
Tooling and machine cost: Mandrels from hundreds to hundreds of thousands of dollars; machines from tens of thousands to millions
Speed: Minutes for a small tube; hours for a large tank, plus curing time

Strengths and limits

Strengths

Fibers stay continuous and are placed at exact angles: very high strength for the weight
Ideal for parts under internal pressure, such as tanks and pipes
Highly automated and repeatable
Low material waste

Limits

Only shapes that can spin: tubes, cylinders, domes and near-round bodies
Concave shapes are hard, because the fiber bridges across hollows
The outside surface is rough unless finished
The mandrel must come out, unless it stays as a liner

Where it's used

Energy and gasHydrogen and natural-gas tanks for vehicles, LPG cylinders
Chemical and waterCorrosion-proof pipes and storage tanks
Aerospace and defenseRocket motor cases, launch tubes, pressure bottles
Automotive and industryCarbon drive shafts, rollers, hydraulic cylinders
Sports and leisureGolf club shafts, bike parts, scuba and paintball air tanks

How to recognize it

Crisscross diamond pattern of fiber bands on the outside, sometimes visible under clear resin.
Round or capsule shapes with domed ends and a small opening at one or both poles.
A smooth, exact inside surface and a slightly ridged outside.