Printing jet engines
Additive manufacturing could reduce the vast amount of waste produced by the aerospace industry. James Perkins reports on the recently completed MERLIN project.
Nickel powder alloy used in the additive manufacture of jet engine components can be reused at least 14 times without significant loss of quality.
That is one of the findings from MERLIN, a European Union-funded project, which looked into 3D-printing jet engine components and brought together some of the continent’s biggest names in aerospace research including, Rolls-Royce, Turbomeca, Fraunhofer ILT and TWI.
Additive manufacturing holds promise for the aerospace industry, which wastes a huge amount of material in the construction of its high-specification parts. It is estimated that 28 tonnes of high environmental impact, toxic and carcinogenic material is wasted to create a seven tonne aeroplane engine.
There is the potential for high materials use if unmelted powder in selective laser melting (SLM) can be reclaimed and reused/recycled for subsequent builds, but powder bed methods waste large amounts of metal because reused powder has not been validated to the standard required by manufacturers – until now. As MERLIN Project Manager, Dr Carl Hauser, explains, ‘That is one of the big cost drivers, or cost issues, for additive manufacture – the amount of waste material that is generated.’
Three types of Inconel (LPW-718-6), plus MAR-M-247LC, were used in SLM, while Inconel 718 was also tested in laser metal deposition (LMD), in both powder and wire form. Studies led by LPW Technology and the Lortek Research Centre found that Inconel 718 maintained its properties after 14 cycles during SLM.
Dr Hauser, who is also a principal project leader in the Joining Technologies Group at TWI Technology Centre Yorkshire, says, ‘In industries with less stringent quality control, the powder can often be reused, but aerospace and medical sectors are more wary of the use and reuse of powder, so tend to proceed with caution and dispose powder after a single use.
‘One of the outcomes of the project was that it is highly
likely you can reuse IN718 powder at least 14 times with no significant degradation from its initial quality, following proper recycling methods.
‘There was also no evidence of degradation of the quality of final parts made with reused powder, despite some minor changes in the powder properties relating to its particle size distribution and chemistry. The task now is trying to convince the aero manufacturers to consider outputs of this work in more detail and how it would impact on their business.’
The construction of a helicopter combustion casing using LMD was also a big moment for the team. It is difficult to build overhanging structures with this laser cladding process because there is no powder to support the part. To overcome this restriction, five-axis LMD CAM software and procedures were developed at TWI. Dr Hauser explains, ‘Ordinarily, for prototyping of this component, it would take a two month lead time for tooling and part manufacture. LMD reduced this to a seven-hour build while upholding the geometric requirements imposed by Turbomeca.’
Hauser would like to see the research continue. ‘There have been a lot of interesting developments to keep the momentum going,’ he says, ‘and there is an interest within the partnership to look for other opportunities to continue some of the MERLIN outputs.’