Unmanned Systems Technology 002 | Scion SA-400 | Commercial UAV Show report | Vision sensors | Danielson Trident I Security and safety systems | MIRA MACE | Additive manufacturing | Marine UUVs

SLS parts are capable of high performance, complex internal geometries and integrated moving parts (Courtesy of 3T RPD and the University of Southampton) 70 Focus | Additive Manufacturing powder and to thermal warpage/ shrinkage effects, which may be an issue in large components for example. The materials available also differ between each process. FDM offers different thermoplastics, including ABS, polycarbonate, polyamide, polyphenylsulphone and polyetherimide (PEI), providing a wide range of material properties (and cost) which allows production of anything from prototypes to functional end-use parts. In particular, PEI- based materials have a high temperature and chemical resistance as well as good Flame, Smoke and Toxicity (FST) ratings, allowing their use in demanding engineering and aerospace applications. SLA materials also include ABS-based polymers, often mixed as a composite material with fillers such as ceramic particulates for improved properties in certain applications. However, the greatest limitation with SLA is the need to work with a specialised liquid feedstock, which typically results in a much higher material cost/kg. SLA materials were once known for continued UV ageing after the manufacturing process, but modern resins have gone a long way to improving this behaviour. SLS materials are most usually based on a Nylon (polyamide 12) powder, which may also be mixed with different fillers such as glass, aluminium or short-strand carbon fibres to improve properties; special flame-retardant mixtures are also available which fulfil aerospace FST standards. Polyether ether ketone-based materials are also available – although typically they require a dedicated machine – and offer exceptional mechanical properties as well as temperature and chemical resistance, but they are more difficult and costly to process. These plastic-based AM technologies have great potential for the manufacture of parts for unmanned vehicles. The design freedom they offer enables components to be made with lower weight and increased functionality (for example by fulfilling two or more functions with one well-designed part). The essentially low-volume, batch-based manufacturing process also reduces the cost of otherwise expensive plastic parts where tooling would be required, and allows increased design flexibility as no moulds or tools need to be committed to manufacture, meaning design iterations are easily possible without a high cost. Coupled with reasonable functional material properties, this makes plastic AM technologies ideal for producing small volumes or even one-off components for a range of unmanned vehicles, ranging from low cost to high value. Plastic AM technologies are also ideally suited to small UAVs for the manufacture of most structural parts or aero surfaces, although polishing processes such as vibro/tumbling are typically conducted to smooth SLS parts. SLA parts or soluble FDM materials are also often used to make complex moulds or cores as tooling for carbon fibre parts, which would otherwise be very difficult or impossible to manufacture. Metal AM Two primary technologies are available for the direct manufacture of metallic components, and while they have many differing trade names they are fundamentally based on either laser beam melting (LBM) or electron beam melting (EBM) of metallic powders. Unlike SLS or SLA, where material is either sintered or cured, LBM Spring 2015 | Unmanned Systems Technology Small UAVs can be built using functional SLS materials (Courtesy of Graphite Additive Manufacturing)