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

69 into a given shape, in a process often likened to icing a cake. FDM machines range from very low cost (sub-£1000) ‘home printers’ to high-end industrial systems (more than £70,000) with generally a corresponding difference in quality, mechanical properties of the deposited material and productivity. The second technique, SLA, consolidates material from a liquid photopolymer resin contained in a build vat; a UV wavelength laser then cures the resin before submerging the cured layer into the vat by one-layer thickness and levelling the next layer of liquid resin over the top, ready for the next cycle. SLS is very similar in concept to SLA but instead it uses a thermoplastic powder feedstock and an infrared laser to sinter the powder particles together. Each technology has its own advantages and disadvantages with respect to the others, and choosing which is most suitable depends largely on the manufacturing requirement. For a one-off part, FDM is likely to be the most economic, while for large numbers of components, SLS can be very cost-effective as it is the only technology where multiple parts can be ‘nested’ or stacked together in all three dimensions, rather than being restricted to a footprint on the build platform (as with FDM and SLA). Although the design freedoms are certainly greater compared to traditional moulding processes, there is by no means total design freedom – certain manufacturing rules must still be observed. For example, both FDM and SLA require the use of supporting structures to build any down-facing surfaces below a critical angle relative to the build substrate. These structures must then be removed either by hand or, for FDM processes where a soluble support material has been used, by dissolving them from around or inside the final component. While SLS does not require any supports (and so perhaps provides the greatest design freedom), thought must still be given to the finishing of the rough semi-sintered surface, removal of unsintered Additive Manufacturing | Focus Unmanned Systems Technology | Spring 2015 Bespoke instrument housing for satellite application (Courtesy of CRP)