High Wycombe-based CRDM has provided rapid prototyping services since the mid-1990s. For Graham Bennett, the company’s technical director, the term “rapid prototyping” is now synonymous with ALM. He acknowledges that there is something of a war of words going on. “What we now call additive layer manufacturing used to be called rapid prototyping, and some are trying to lose that tag because they are thinking about production. ‘Additive layer manufacturing’ gives the sense that it’s come of age.”
The technologies of ALM machines are broadly the same as those of prototyping equipment, such as selective laser sintering and fused deposition modelling. But what has changed is the quality and range of materials available to make parts. Rapid prototyping in the early days relied on specialised materials that were difficult to process and did not produce particularly robust results. But now many types of plastic and metal can be used in ALM equipment. For example, EADS’s Meyer says: “We can process very high-strength titanium alloy, steel, and aluminium alloys, so from that point of view materials are not such a limitation – I think they are actually on a par with what you can get from other processes.”
James Bradbury of the University of Exeter says: “Additive manufacturing has been around for years but one of the limitations has been the materials. That limits the applications.” But Exeter’s new machine demonstrates the possibilities on offer – it’s for selective laser sintering of high-temperature thermoplastics, which can produce components as hard as metal. Flint points out: “They are much stronger than traditional nylon materials. They have good mechanical properties with high wear resistance, good chemical resistance – and they are also biocompatible so another new market opens up for ALM, medical.”
This high-temperature plastic would normally be used in injection-moulding machines. Bradbury says: “This is an existing thermoplastic that’s used in injection moulding. Aerospace, motorsport and the medical industry are all using this material – but not this method.”
If the range of materials available has improved, ALM also opens up an exciting new world for design engineers. This includes the opportunity to optimise designs without the constraints of traditional subtractive manufacturing technology, building many components as one part.
Aerospace engineers might be able to design lighter components as a result of the technology. The complex geometries that can be easily built are another advantage as is the ability to produce new iterations of designs without changing tooling. Showing off a metal chain that has been built as one piece, Bennett of CRDM says: “ALM gives you incredible design flexibility. If a design has to be changed, it can be changed from one build to the next. You don’t have to worry about modifying the expensive, capital-intensive injection-mould tool.”
He adds: “The price of the part is entirely independent of its complexity. Because the machine just builds layer by layer, it doesn’t care what the geometry looks like – in fact a piece that is hollow is a lot cheaper to make than if it were solid, simply because it uses less material.”
EADS estimates that ALM typically produces 5% swarf compared to 90% with some traditional manufacturing. So the technology certainly has potential to cut down on waste. Further, it could simplify the supply chain because the raw material is powder. There is no need for, say, steel or aluminium to be made into a billet, for that to be made into a component, for the component to be transported somewhere else – to be made part of a bigger structure. The raw material is stored where it will be used and the structure is created. EADS describes this approach as “green, clean and lean”.