Filament winding is a fabrication technique for manufacturing composite material, usually in the form of cylindrical structures. The process involves winding filaments under varying amounts of tension over a male mould or mandrel. The mandrel rotates while a carriage moves horizontally, laying down fibres in the desired pattern. The most common filaments are carbon or glass fibre and are coated with synthetic resin as they are wound. Once the mandrel is completely covered to the desired thickness, the mandrel is placed in an oven to solidify (set) the resin. Once the resin has cured, the mandrel is removed, leaving the hollow final product.
Filament winding is well suited to automation, where the tension on the filaments can be carefully controlled. Filaments that are applied with high tension results in a final product with higher rigidity and strength; lower tension results in more flexibility. The orientation of the filaments can also be carefully controlled so that successive layers are plied or oriented differently from the previous layer. The angle at which the fibre is laid down will determine the properties of the final product. A high angle “hoop” will provide crush strength, while a lower angle pattern (known as a closed or helical) will provide greater tensile strength.
Products currently being produced using this technique range from golf clubs, pipes, oars, bicycle forks, power and transmission poles, pressure vessels to missile casings, aircraft fuselages and lamp posts and yacht masts.
Filament Winding can also be described as the manufacture of parts with high fibre volume fractions and controlled fibre orientation. Fibre tows are immersed in a resin bath where they are coated with low or medium molecular weight reactants. The impregnated tows are then literally wound around a mandrel (mould core) in a controlled pattern to form the shape of the part. After winding, the resin is then cured, typically using heat. The mould core may be removed or may be left as an integral component of the part(Rosato, D.V.).This process is primarily used for hollow, generally circular or oval sectioned components, such as pipes and tanks. Pressure vessels, pipes and drive shafts have all been manufactured using filament winding. It has been combined with other fibre application methods such as hand layup, pultrusion, and braiding. Compaction is through fibre tension and resin content is primarily metered. The fibres may be impregnated with resin before winding (wet winding), pre-impregnated (dry winding) or post-impregnated. Wet winding has the advantages of using the lowest cost materials with long storage life and low viscosity. The pre-impregnated systems produce parts with more consistent resin content and can often be wound faster.
Glass fibre is the fibre most frequently used for filament winding, carbon and aramid fibres are also used. Most high strength critical aerospace structures are produced with epoxy resins, with either epoxy or cheaper polyester resins being specified for most other applications. The ability to use continuous reinforcement without any breaks or joins is a definite advantage, as is the high fibre volume fraction that is obtainable, about 60% to 80%. Only the inner surface of a filament wound structure will be smooth unless a secondary operation is performed on the outer surface. The component is normally cured at high temperature before removing the mandrel. Finishing operations such as machining or grinding are not normally necessary.
- Resins: Any, e.g. epoxy, polyester, vinylester, phenolic.
- Fibres: Glass, aramid, carbon and boron fibres. The fibres are used straight from a creel and not woven or stitched into a fabric form.
- Cores: Any, although components are usually single skin.
- Uses a continuous length of fibre strand, roving, or tape
- Results in a shell of materials with a high strength-to-weight ratio
- Requires thermal curing of workpieces
- Patterns may be longitudinal, circumferential, or helical