Structural change

Groundbreaking technique will allow components to be custom-made, and could reduce the weight and improve fuel economy in aircraft and cars. Stuart Nathan explains.

Metal components with the strength of a solid block but a structure containing 70 per cent air could result from a new manufacturing process being developed at the University of Liverpool.

Known as selective laser melting (SLM), the system transforms powders of titanium, stainless steel and other metals into a light, strong lattice structure. The Liverpool team, led by Chris Sutcliffe, claims to have developed the first commercial-scale SLM machine.

The technique will allow engineers to specify and design the precise shape and structure of the component they need — something that is currently not possible. Starting with a powder of the metal or alloy to be used, the system uses an infrared laser to melt the powder and build up the components in a series of layers which can be as thin as 25 microns. The result is a structure consisting of flat layers supported by ‘poles’, around 50–100 micron in diameter, which channel the loads applied to the structure, giving it strength.

Although methods for making metal lattices and foams have existed for some time, they tend to make a block of material which then has to be machined into the required shape. Moreover, the lattices themselves tend to be random; it isn’t possible to ‘design-in’ structural features.

With SLM, however, internal features to provide properties such as thermal absorption and impact resistance can be specified and constructed during the layer-by-layer building phase. The system can also be used to make composite components.

The research is being carried out in collaboration with the Anglo-German firm MCP (Mining and Chemical Products) Group, which specialises in rapid prototyping techniques, and is funded by the EPSRC.

Possibilities for the system include lightweight components for aircraft and cars to reduce the weight and improve fuel economy. It also has potential in electronics, in the design of heat-sink components for microprocessors and other computing components, where the lattices will be optimised to remove heat more efficiently. This would improve processor reliability and reduce the frequency of computer crashes.

The medical field could also benefit, with the system being used to build complex 3D porous structures for bone implants. Using MRI and X-ray tomography data from individual patients, the implants could be built to fit precisely the shape needed, but with the porous structure needed for bone cells to colonise and grow within the structure, thus incorporating it into the body.

Sutcliffe believes that the system could also be used to manufacture microreactors for use in the synthesis of complex pharmaceuticals and speciality chemicals. These could be made from the specialised alloys needed to withstand the corrosive and explosive chemicals often used in these applications, and to cope with the energy produced by the reactions. With microreactors already beginning to make headway in process development, refinements in design could improve their efficiency considerably.

‘There is worldwide interest in developing a standard rapid manufacturing process based on SLM,’ Sutcliffe said. ‘Our system will produce optimised engineering components that can’t be made in any other way, and will give the industry that supported us a significant advantage in future markets.’

The research group expects to have its commercial-scale system functioning during this year, with the larger version scheduled for commissioning in 18 months.