Filament winding is a very fast and efficient method of laying down resin and reinforcements to create strong, lightweight composite products. Windings are limited to the size of the machine and the rotating mandrel. Parts requiring mandrels of more than 30 m (100 ft) in diameter generally are wound at the site of the installation. Filament-wound parts provide high fibre volume fractions (up to 80%) and precisely controlled fibre orientation.
In the filament winding process, continuous strands of resin-impregnated glass fibre, carbon fibre or other reinforcements are wound under tension onto the mandrel in precise geometric patterns to build up the part. Once the desired winding thickness is achieved, the winder stops, the part is allowed to cure, and the mandrel is removed using an extractor. Mandrels can be left inside the winding to become an integral part of the component. Collapsible mandrels facilitate the job of extraction.
The rovings are fed from multiple spools positioned on a creel, through a tensioning system. A bath of catalysed low-viscosity thermoset resin is typically used to wet out the strands, although thermoplastic resin pre-impregnated tow preg materials can be used. For faster winding, dry fibres can be sprayed with resin as they are applied to the mandrel.
Multi-axis filament winding systems offer the ability to fabricate parts with up to six axes of motion control for the production of higher-performance pressure tanks and non-symmetrical components. Advances in winding software and computer numerical control enable the filament winding of such products as pipe elbows and other curved shapes.