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Manufacture of Arbitrary Cross-Section Composite Honeycomb Cores Based on Origami Techniques

In recent years, the use of composite materials has drastically increased in the construction of aerospace components. In the case of sandwich panels, they have been extensively used as face sheets with aluminum honeycomb cores. Currently, space structures are increasing in size and require greater degrees of accuracy; hence, the use of composites as a core material is a natural progression. However, these composite core materials are not regularly used in sandwich construction. Compared to standard aluminum honeycombs, their manufacturing costs are very high and they have limited applications. Another problem is difficulty of machining. In the manufacture of complex-shaped parts, the cores must have some degree of curvature. For aluminum honeycombs, this can be done using a contour cutter, a 3-D tracer, and numerically controlled machines. However, burrs and buckling of cell walls present a difficult problem for surface accuracy. It is clear that the machining of composite cores requires more expensive and sophisticated systems. This study illustrates a new strategy to fabricate arbitrary cross-section honeycomb cores with applications of advanced composite materials. These types of honeycombs are usually manufactured from normal flat honeycombs by curving or carving, but the proposed method enables us to construct objective shaped honeycombs directly. The basic idea originates from the fold-made paper honeycombs proposed by authors, in which they attempted to apply origami and kirigami techniques to the creation of sandwich structures. Origami is the traditional Japanese art of paper folding. Kirigami is a variation of origami. We first introduce the concept of the origami honeycomb, which is made from single flat sheets with periodical slits resembling origami. In previous studies, honeycombs having various shapes were made using this method, and were realized by only changing folding line diagrams (FLDs). In this study, these 3D origami honeycombs are generalized by numerical parameters and fabricated using a newly proposed FLD design method, which enables us to draw the FLD of arbitrary cross-section honeycombs. Next, we describe a method of applying this technique to advanced composite materials. For partially soft composites, folding lines are materialized by silicon rubber hinges on carbon fiber reinforced plastic. Complex FLD patterns are then printed using masks on carbon fabrics. Finally, these foldable composites that are cured in corrugated shapes in autoclaves are folded into honeycomb shapes, and some typical samples are shown with their FLDs.