Additive manufacturing makes real headway as a valuable engineering tool

The mainstream media furore around 3D printing seems to have calmed somewhat since we last covered the subject in May. Indeed, just two months ago, the talk in newspapers was around the possibilities of making 3D printable firearms and the need to get this emerging technology swiftly under control.

For some perspective, the gun that has done the rounds on YouTube was not made by a £2000 home 3D printer, but an industrial machine that costs in the region of £100,000. Principally we are talking about the same technology that has been available for some 25 years. The plastic guns also unsurprisingly fail after just a few shots. "The things we are seeing in the press are ridiculous," says Professor Richard Hague, director of the EPSRC Centre for Innovative Manufacturing in Additive Manufacturing and head of additive manufacturing and 3D printing research group at the University of Nottingham. Speaking recently at the Advanced Manufacturing exhibition, he said: "There is nothing novel in this [gun] at all. It is a dreadful design that in no way maximises the design freedom of additive manufacturing and it could easily have been done 20 years ago. This is just an application that is feeding the hype. It is nothing novel." It serves as a good example to highlight that additive manufacturing is not going to change manufacturing as we know it. In this case, surely laser scanning and then using a micro CNC home machining centre would be more advantageous as you could make genuine established designs out of steel. This is the thing about additive manufacturing: it is misunderstood and most do not know when or how to use it. "It will not replace or overtake every other manufacturing process, but it will become a growing part of the manufacturing landscape," says Professor Hague. "For designers, it allows personalisation, more design freedom than ever before and potentially allows increasing functionality." Much of the coverage around additive manufacturing discusses it as a single technology and process. Of course, there are numerous processes and material possibilities that include plastic, metal, ceramic and increasingly, multi-material machines are coming to market. There is a great deal of potential for additive manufacturing going forward as the technologies mature and they begin to become more widely used by design engineers. However, many conventional design techniques and geometries don't really transpose to 3D printing, which makes it difficult to get the most from additive manufacturing today. "Standard CAD software such as Solidworks, Creo, CATIA, NX, Inventor; those kinds of design systems are excellent, but they have been designed for conventional manufacture," says Professor Hague. "They don't account for the design freedoms available from additive manufacturing. A lot of our work is about making new design tools. "Many of the complex geometries that are possible from additive manufacturing processes would be very difficult to produce in conventional CAD modelling software. At the moment there is a lot of geometry that we could easily print, but in many cases we don't as modelling that geometry would be so long-winded and difficult." Within the new tools being developed, Professor Hague and his team want to incorporate the ability to move from what he calls 'passive additive manufacturing' to, 'multifunctional additive manufacturing'. The theory is that different functional properties can be built in to printed objects such as electrical conductivity, flow patterns and even optical connections. To put this in to practical terms, the team wants to take the technology from being able to print a mobile phone case to be able to print an entire mobile phone. Design for additive The ability to print the complexity, and many materials, needed to produce a typical mobile phone is probably 10 years away or more. However, an interesting example of where more elaborate and complex geometry can be used is within internal fluid flow channels of components like heat exchangers. At the moment any flow through metallic parts has to be machined in and that restricts the possible geometry. However, additive manufacturing allows the flow to be optimised around the part rather than creating a part and machining the flow in to it. "It is a different way of designing things that gives you a different type of structure," says Professor Hague. "A good example of complex internal flow channels comes from 3T RPD when it produced a heat exchange system. This kind of design freedom would be almost unobtainable using conventional design and manufacturing techniques. "The heat exchanger was produced on an EOS 270 and that has very nice surface finish but there would have been various post-processing routines that would have happened." There is a lot more potential on the horizon as more valid design tools and techniques become available. One method that is likely to be increasingly used is topology optimisation. This is a complex mathematical approach that is able to optimise material layout within a structure for a given set of loading conditions. For example, it is traditionally used to remove weight from items such as bulkheads and crossbeams. The analysis highlights areas that can have material removed, while the part retains the necessary strength. Topology optimisation techniques can produce parts that are often difficult, expensive and even infeasible to make using traditional manufacturing processes. However, these constraints do not readily apply to additive manufacturing. "We have no manufacturing constraints and can pretty much produce any shape," says Professor Hague. "However, the surface finish is often terrible." Topologically optimised parts often yield peculiar geometric layouts that would never be acceptable as a visual part. Many design engineers use these optimised parts as a starting point, which they then tidy up and make more 'regular' in appearance. However, additive processes open up the possibility of having a topologically optimised structure that is then covered by a thin outside layer of material giving the best combination of appearance, weight and strength. "One of the challenges is getting people and companies to accept that this kind of topology analysis and resulting geometry is typical," says Professor Hague. "The weight reduction potential of using this technique is dramatic, and assuming loading conditions are correct, a weight reduction of 40 to 50% is not uncommon." An aerospace bracket that followed this analysis and was subsequently made by a selective laser melting (SLM) metal sintering additive manufacturing process yielded a weight reduction of over 40%. However, one of the issues around using metallic additive manufacturing processes is the fatigue life. It is a real issue and is holding back more widespread implementation. "Surface finish and fatigue are big issues," says Professor Hague. "There is a lot of work to be done in improving fatigue life, but it's not insurmountable. What we do at the moment is post heat treating [and annealing] of parts. "The ideal from an environmental point of view is to take the part off the machine, and there is your part. But at the moment the micro structure is terrible so you get this awful fatigue. However, there is a lot of work going on with various companies to enable control of the microstructure as a part is being built." Many consider the most interesting and relevant additive manufacturing technology to engineers and industrial applications is indeed using techniques around metals. At the moment there is much development towards higher power lasers to increase production speed to overcome the other major barrier to entry, cost. Varying layer thickness, particle size and laser power results in different surface finishes, but this is still a process that is being refined. Additive manufacturing has the potential to democratise manufacturing by making the production of components – using these processes – competitive with much lower labour cost countries. However, there is still a long way to go and it is likely to be sometime before genuine fears should be raised over the possibilities of 3D printing firearms.