Unmanned Systems Technology 020 | Alpha 800 I Additive Manufacturing focus I USVs insight I Pegasus GE70 I GuardBot I AUVSI Xponential 2018 show report I Solar Power focus I CUAV Expo Europe 2018 show report

36 Focus | Additive manufacturing Carbon fibre materials are much more abrasive than standard thermoplastics so the nozzle has to be hardened and optimised to control the geometry of deposition as well as managing the complex thermodynamics of the heated material moving through the extruder to the nozzle tip and then the print bed. The largest FDM printers on the market are used by aircraft and space launcher builders, and allow a build volume of 1 x 1 x 0.66 m. That is being extended however by adding a build area on the side of the printer so that a component is built on its side rather than the base of the printer. A demonstration system has allowed parts as long as 5 m to be built. Another demonstration machine provides limitless printing. It uses robotic arms with deposition heads and a thermoplastic composite. However, this approach cannot use an oven to control the part’s temperature, so a new heating technology is needed for active thermal management of the part, rather than being limited by an oven or heated build bed. There are a number of approaches being tested out for this thermal management. One approach could be to use materials that print without an oven, but the machine maker doesn’t want to constrain its manufacturing partners to having to use particular materials, so other thermal techniques such as laser heating can be used. As FDM systems that can print larger objects come onto the market they will also need to deposit material faster, so screw-based extruders are being developed that can be ten times faster than existing systems, delivering 2 kg of material per hour. These allow the printers to use plastic pellets directly from a hopper feed, in the same way as that in the injection moulding industry, which would dramatically reduce costs as the material doesn’t need to be turned into filament first. It also removes issues around quality control of the filament diameter. FDM is also not just about thermoplastics or carbon additives; extruded metal and even ceramic pastes can also be used. One application here is a monolithic 3D motor. Powder bed fusion Powder bed fusion processes include a number of commonly used printing techniques that are all based, as the name suggests, on the use of a bed of powder made of metal or thermoplastic. Structures are built up by repeatedly heating the powder in layers. The choice of heating technique determines the name of the particular process, such as direct metal laser sintering, electron beam melting, selective heat sintering, selective laser melting and selective laser sintering (SLS). One of the risks of changing materials is the contamination of the powder June/July 2018 | Unmanned Systems Technology Prototype 3D printers can now avoid the constraints of the build bed and construct parts in free space (Courtesy of Stratasys) Metal AM can create dense meshes to retain strength while reducing weight (Courtesy of Renishaw)