Unmanned Systems Technology 011 | C-Astral Bramor ppX | IMUs | Autonomous farming | UAV Turbines UTP50R | London Show report | Advanced materials | Las Vegas Expo report

70 Focus | Advanced materials AM also provides new and exciting opportunities for functional materials, for example designing part geometry on the scale of the laser beam’s diameter (less than 100 µm) in order to deliver the desired mechanical or thermal properties. However, as such processes form the material and geometry simultaneously, they are usually more inspection-intensive because, unlike machining from solid, the material’s composition and integrity are not a given and must be checked after manufacture. Typically the integrity of solid billet material is checked before the cost of forming the geometry is incurred. Polymers/composites The alternative to metals is to use polymer-based materials. Although the strength of most engineering polymers (such as ABS or nylon) is far lower than that of metallic alloys, their much lower density means that in many applications they remain competitive on a strength-to- weight basis – in fact polymers such as PEEK (poly-ether-ether-ketone) are able to compete with many aluminium alloys in terms of performance, particularly at high temperatures. To achieve higher strengths, polymers are typically combined with a reinforcing material such as carbon fibres to produce a composite. Composites typically consist of bundles of the fibres (known as tows) woven into flat sheets; depending on the design, several sheets of the fibres (known as plies) may be laid up in differing directions before being cured in a resin matrix. In service, the fibres carry the loads through the material, giving it most of its strength, while the matrix serves to transfer the load effectively to the fibres and hold the shape of the component. Depending on the expected service environment, different grades or types of carbon fibres or resins may be chosen; by varying the composition and manufacturing techniques, differing fibres and resins can deliver a wide range of performance. One of the most important properties for the resin is its glass transition temperature, which dictates its temperature resistance in service as well as the temperature needed to cure the material. In general, resins that provide higher temperature resistance in service will need to be cured at higher temperatures in an autoclave during manufacture. Resins can be infused into the plies using either a wet process or by using pre-impregnated fabrics (generally termed ‘pre-preg’). For wet lay-up, the reinforcing plies are laid into a mould and then sealed inside an airtight bag; a vacuum pump then removes the air from the plies, while drawing resin into the material. Wet lay-up is inherently less consistent than the use of pre-preg, as the resin might not travel to all areas of the component equally, potentially leaving small, resin-poor regions that will initiate premature failure of the part. That said, wet lay-up techniques are generally less expensive and more versatile for use during development stages. Pre-preg materials have the resin applied to the fibres mechanically when the fabric is manufactured, allowing a greater degree of control over the resin- to-fibre ratio as well as its consistency across the entire sheet. Pre-preg materials are then laid into a mould but typically cured in an autoclave. While most carbon composites December/January 2017 | Unmanned Systems Technology Additive manufacturing can allow the production of structural metal foams at resolutions down to 100 µm (Courtesy of Betatype) Thin-ply spread tow composites manufactured by tape laying provide high performance and consistency (Courtesy of North Thin Ply Technology)