A Filament Winder Buyer\'s Guide
Specifying that new machine with your process and product in mind.
By Nancy Pottish, Contributing Writer | August 2005
Filament winding is an automated composites manufacturing process in which a mobile placement device wraps continuous fiber reinforcements (resin-impregnated or dry) around the outer surface of a rotating mandrel (male tool) in a controlled pattern to form hollow structures. It can form cylindrical, tapered and spherical shapes; tubes with rectangular or multi-faceted (pentagonal, hexagonal, etc.) and even irregular cross-sections. Part diameter can be as small as a golf shaft, as large as a 38m/125 ft holding tank or as long as an oilfield down-hole drilling pipe.
Filament winding can be done with thermoset or thermoplastic resins and most continuous fiber forms. Fiber may be pre-impregnated (towpreg), pulled through a resin bath before being applied to the mandrel (wet winding) or wound dry and then infused with resin in a secondary process. While towpreg is more expensive than resin and dry fiber, it can be cost-effective for carbon fiber-reinforced parts because it can be wound at higher speeds without throwing resin off the mandrel. Moreover, the resin content of a towpreg part can be more tightly controlled than for a wet-wound part, and for some parts with complex geometries, wet fibers will not stay in place as readily as towpreg. Wet winding, however, is an easier process to master and permits cost-effective winding of hybrid laminates (e.g., combinations of glass and aramid fibers).
Given this varied capability, the process serves a very wide range of markets. High-end winders produce tight-tolerance parts with superior mechanical properties (e.g, rocket fairings and nose cones, helicopter blades, cryogenic tanks and satellite structures). At the other end of the market, volume products, such as light poles, water and sewer pipe, pressure vessels and bike frame tubing, are turned out at relatively high speeds at costs competitive with steel or aluminum.
SYSTEM ANATOMY
In its most common form, wet winding, the process requires five main subcomponents: a creel, a resin bath, a fiber delivery system, a winder and a control system. (Towpreg and dry fiber winding do not require the bath.) A number of individual rovings/tows are pulled from the creel through the resin bath and then through a delivery head, which is mounted on a carriage that can be moved back and forth along the length of the mandrel. The tows are secured to a spiked band called a pin ring on one end of the mandrel, which is supported by spindles on the winder. The mandrel is then rotated, pulling the fiber through the system in a continuous process. The delivery head moves down the mandrel length, placing the tow on the mandrel according to a user-determined pattern. When the head reaches the mandrel's end, another pin ring secures the fibers and the head is moved back along the mandrel to complete one "circuit." The number of circuits determines part wall thickness. The speed of the mandrel rotation with respect to the carriage movement determines the fiber angles and winding pattern. The control system can vary fiber angle from near-axial (as acute as 6°) to radial (90°) orientation, depending on mandrel diameter and the amount of fiber band overlap, to accommodate changes in mandrel shape down the length of the part. The part is then cured and the mandrel typically is removed with extraction equipment.
