That which fits the mold: a braided composite wing

Abstract

In this design study, a model airplane wing, partially constructed from braided composite panels, was made for the purpose of demonstrating the applications of braided composites for aerospace components. Fibres of Kevlar® were braided together along a tubular surface, then subsequently cut and unrolled to form two planar sheets of interlaced yarns that could be laid down in a 3D printed mold to later be coated in resin. The mold consisted of four parts: two female parts to shape the composite wing panels and two male parts to compress the composite. When connected together they form a fused core. A fibre sheet was draped over each female part, and its extraneous edges were folded inward to form a second layer as reinforcement. Each sheet was then laid up with Ecopoxy® resin and allowed to cure while sandwiched between the female mold and its corresponding male component. Upon disassembly of the mold system, a braided composite wing panel had formed upon both halves of the 3D printed core. The external portion of each panel was found to be smooth with few irregularities that could potentially compromise their aerodynamic performance. The mold was constructed to facilitate the process of cold-curing rather than curing at an elevated temperature. For heated cure process, the use of metal would be recommended because it generally deforms negligibly through heating and cooling. A metal mold would also be used to ease the process of debonding from the composite materials. Care should be taken to ensure that fibre orientation is consistent. The results illustrate how a mold can be fabricated to facilitate the process of curing braided composites, and can serve to improve the quality of products that require a higher strength to weight ratio.