Hollow composite structures like air- and cable ducts are typically produced by bladder molding, use of retractable cores or bonding of two half-shells. Other methods for removing lost solid cores like mechanical carving, low melting alloys/salts or chemical dissolving do not meet modern requirements regarding environmental and personal safety. Water-soluble core materials have been used for years for coreless aerospace products like ducts but also structural elements like stringers and beams, door hinges and pressure vessels. Especially complicated geometries with undercuts, changes in cross-section and diameter or multiple branches are suitable for/require the use of washable cores during manufacturing. Further developments in this class of tooling material enable the use of production technologies for higher volumes and automation like winding, fibre placement, resin transfer molding (RTM) and pressing processes. New high-pressure resistant base material and suitable sealer system allow to create water soluble cores with higher pressure resistance, stiffness and improved surface quality at reasonable washout performance, even on long length and narrow cross-sections. Innovative design features permit also mandrels for large bended and curved structures which can be produced in high volumes by a cost-effective semi-automated core manufacturing process. Versatile form of delivery like machinable blocks and 3D-printed mandrels enable also the use for prototypes and small series.
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