Filament winding is a continuous fabrication method that can be highly automated and repeatable with relatively low material costs. A long, cylindrical tool called a mandrel is suspended horizontally between end supports, while the “head” – the fiber application instrument – moves back and forth along the length of a rotating mandrel, placing fiber onto the tool in a predetermined configuration. Computer-controlled filament-winding machines are available, equipped with from 2 to as many as 12 axes of motion.
In most applications, the filament winding apparatus passes the fiber material through a resin “bath,” just before the material touches the mandrel. This is called “wet winding.” Towpreg – continuous fiber pre-impregnated with resin – also can be wound, eliminating the need for an onsite resin bath. In a slightly different process, fiber is wound without resin (“dry winding”). The dry shape is then removed and used as a preform in another molding process, such as RTM.
Automated tape laying (ATL), and its close relative automated filament placement (AFP) usually involve the placement of carbon fiber tape or filaments, prepreg or dry, in a tool or on a mandrel to build large composite structures, such as an aircraft fuselage or wings. The tape or filament may be continuously placed, but often the courses are relatively short and designed to meet specific strength and rigidity requirements. Machinery used for AFP and ATL has seen significant improvement since the late 1990s and is one of the fastest-evolving segments in composites processing.