Advanced Composites - Manufacturing
Filament Winding Process
Precision high-speed positioning of continuous fiber in a pre-determined pattern is the basis of the filament winding process. The filament winding process enables the designer to custom engineer components by placing the exact mechanical characteristics where needed, allowing the roller design to be optimized for strength, stiffness and thermal stability. This means Addax engineers have the ability to modify the variables necessary to meet our customer's performance specifications.
Filament winding equipment comes in a variety of sizes and configurations characterized by capacity, single/multiple spindles and a multi-axis carriage and payout eye. These filament winding machines are computer numerically controlled (CNC) machines, highly automated and may be set-up and operating in a matter of minutes. Filament winders are not limited to producing cylindrical shapes, in fact, the flexibility of these machines allow for the manufacturing of almost any geometric shape imaginable. Addax operates multi-spindle-winding machines that will produce a part as large as 60 inches in diameter and 46 feet in length, and as small as 1/2" in diameter and just a few inches in length.
Tooling used in the filament winding process can be manufactured from a variety of materials including steel, aluminum, ceramics, and composites. One primary tool used in the filament winding process is a precision ground mandrel that the fiber and resin matrix is wound upon. On completion of the filament winding process, the fiber and resin matrix is cured, either at room temperature or in an oven with a controlled heat profile depending upon the type and style of resin matrix used. After cure, the mandrel is removed leaving a hollow composite structure. Mandrel diameter and runout are strictly controlled to maintain bond interfaces between the composite structure and other components of the overall assembly while providing the ability to control the overall straightness and concentricity of the final composite product.
Often referred to as "wet winding", the process begins with spools of dry fiber (tows) supported by a creel and threaded around tension bars. The signals returned from these bars are interpreted by a closed-loop, servo driven system that maintains constant fiber tension as spools unwind. The amount of applied tension is dependent on the fiber material, part diameter and the pattern being wound. The tension can directly affect the void content and fiber volume, which are factors in the strength and stiffness of the composite tube.
Next, the fiber is directed into a resin wet dip or drum bath system where the tows are impregnated with the resin matrix. Fiber "wet out" takes place as the fiber tows are "spread" across face of the resin bath system. The tow package is now ready for placement onto the mandrel by the filament winding equipment upon exit from the resin bath system.
After exit from the wet bath system, the resin impregnated fiber tow package is fed through a comb and payout eye located on the carriage of the winding machine. The impregnated fiber is then wrapped by hand onto a clean, well mold released mandrel. The operator then initializes the start sequence of the CNC filament winding machine and the winding machine takes over and the process begins.
The CNC filament winding machine lays the resin impregnated fibers on the mandrel in a geometrical pattern predefined by the design engineer. A typical filament-winding pattern consists of helical and circular layers. The filament winding machine operator is responsible for measuring and correcting the fiber bandwidth, monitoring the part diameter and removing excess resin from the composite structure during the process. Other than these relatively small tasks, fiber placement is performed entirely by the filament-winding machine.
The curing of the resin matrix has a direct impact on the overall performance of the composite structure. Just as the fiber tows are laid in a predefined orientation, the cure sequence and temperatures are controlled to optimize the performance of the filament wound structure. After completion of the filament winding process, the composite structure is then most commonly removed from the filament-winding machine and placed into an oven while remaining on the precision ground mandrel. Preprogrammed heating profiles are loaded into electronic control units of the oven. These control units incrementally ramp and hold the oven temperature throughout various temperature cycles until the composite is fully cured. The electronic control unit is capable of identifying abnormalities in the cure cycle, issuing alarms and disabling the oven if so required. This function ensures that the composite structure is cured to exactly as required in the design specifications.
The last step in the filament winding process requires pulling or "stripping" the mandrel out of the cured composite structure. While supporting the composite structure, the mandrel is attached to an extractor carriage and slowly removed from the center of the part, leaving behind a lightweight, high performance composite structure that is ready for assembly.
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