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88 so when layer after layer is laid down, the excess powder is shaken off and a batch of components is moved into the furnace. Binder jet developers are also looking at aluminium, where there is less risk than with SLS as no high temperatures are used during the building of a component. However, aluminium forms a shell of oxide that restricts the traditional sintering process. But sintering is still possible by precisely breaking the shell for aluminium to touch aluminium, and this process is under development. Titanium is also of interest for binder jetting, as its growing use by laser systems means the cost of titanium powder is falling. The falling cost means it could be used in a binder jetting system with an appropriate binder and physical model for the shrinkage. Components made from it would be half to a third lighter than the same-size component currently made in steel. Liquid metal The liquid metal technique is a digital alternative to die casting, and uses 356 casting-grade aluminium that is supplied in standard welding wire format. It uses a strong magnetic field to control the stream of melted metal, and has a deposition rate four times faster than SLS-based systems. Its main limitation is that there is not the same geometric freedom as with SLS. For example, it is not possible to create a mesh or designs with the same level of complexity, but the advantage in using aluminium gives inherently lighter components. Structure removal Another issue in automating the AM process is removing support structures. These are used to hold parts of a component to allow complex geometric shapes to be created. In one development, a UK project called Separation of Additive-Layer Supports by Automation is using a collaborative robot (cobot) to remove the support structures when a part comes out of an SLS printer. It could reduce the average cost per part by 25%, making AM a cost-effective option for large- volume production. The cobots use machine learning to identify what is a support structure and what is part of the component. Automating the support removal and finishing changes the economics completely when scaling AM up, and makes it feasible for manufacturers to adopt this technology for rapid production. The digitising of AM also comes with an increase in quality, traceability and repeatability, which are key issues. On average, almost two- thirds of post-processing costs are in the finishing and support structure removal stages, and it is tackling this that could cut the cost by 25%. That is attractive to laser machine makers as well, as an automated manufacturing process could make AM adoption more appealing to manufacturers operating large-volume production lines. Composites Another approach is to use carbon fibre from the aerospace industry, slice it into ribbons and use a robot arm to build it into chopped fibre. Using a continuous strand polymer- impregnated fibre, the process requires exact temperature and pressure to create a pore-free lamination. This is well-defined in the material specification, and scaling down to thin ribbons allows less force to be used to apply the required level of pressure. It then goes through a curing stage so that all the polymers bind and cross-link. The robot lays down tape with a polymer binder from a spool. The build area for the February/March 2021 | Unmanned Systems Technology Combining a robot arm with SLS printing (Courtesy of Renishaw) Combined AM components for the Skydio UAV in a composite process (Courtesy of Arris Composites)