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

72 are manufactured using tows of about 12,000 fibres, where each fibre is roughly 5-7 µm in diameter, some specialist manufacturers spread these tow bundles out into flat tapes (down to 30 µm thick) before weaving, resulting in a thinner ply. These thin plies reduce the kinking of fibres and improve resin impregnation, providing a more consistent product. By delivering a lower defect level, this allows reduced safety margins and therefore more weight-efficient structures compared to conventional composite technology. Conventional pre-preg material is typically manufactured and supplied in sheets of about 300 gsm with thicknesses of a few hundred microns, while thin-ply material can be defined as being below 75 gsm and can be as light as 15 or 30 gsm with a 30 µm thickness. For shapes that do not lend themselves to manufacture from plies of composite material, AM can offer alternative materials. For example, nylon matrix materials filled with short carbon fibre strands (a few hundred microns in length) are widely used in aerospace. An AM process route allows a high degree of geometric freedom and economic production of small batch sizes. Manufacturing methods Composite parts can be moulded in one of two ways, either directly from a tool designed to give the finished part or indirectly using a tool to form a carbon fibre mould that is then in turn used to give the finished part. To get the initial mould tool, epoxy or polyurethane is machined to give the tool geometry, and this is typically achieved on large- frame specialist CNC machines to a high tolerance and surface finish. Polyurethane moulds are very easy to machine and have excellent temperature stability but poor temperature resistance, so they are only used for moulding non- critical parts or jigs. Epoxy moulds are slightly harder to machine and have good temperature resistance, but their temperature stability falls as temperature resistance increases for different epoxies. Epoxy moulds can therefore be used either to form production parts directly or indirectly as a first step in forming carbon fibre moulds. Carbon moulds are made from cheaper tooling carbon, which has a lower curing temperature than performance composites, but they may be preferred to epoxy moulds as they will have a longer useful production life and a higher temperature resistance. December/January 2017 | Unmanned Systems Technology Additively manufactured carbon-reinforced nylon is used for the airframe of this small UAV (Courtesy of CRP Group) Specialist high-quality machining of carbon fibre components (Courtesy of Progressive Technology)