Laser melting key to better aircraft engine parts
Manufacturing components for aircraft engines is not an easy task. The components must be lightweight yet strong enough to tolerate extreme conditions. They need to endure 1 000 rotations every second and withstand heat of up to 2 000°C, and above all, they need to meet stringent safety standards. EU-funded researchers have not only developed a way to produce parts that tick all of these boxes but they have discovered a way to produce them quickly and at a reasonable price. The FANTASIA ('Flexible and near-net-shape generative manufacturing chains and repair techniques for complex shaped aero engine parts') project was funded EUR 3.78 million under the 'Aeronautics and space' Thematic area of the Sixth Framework Programme (FP6).
The 20-member FANTASIA consortium, headed by researchers from the Fraunhofer Institute for Laser Technology (ILT) in Germany, has demonstrated how selective laser melting (SLM) can be used to make both super strong and efficient complex-shaped aircraft engine components and repair damaged ones. In fact, tests have shown that the quality of components produced using this method is equally as high (or better) than those manufactured using conventional processes.
With SLM, the part is built one layer at a time, using a metal powder that is applied to the substrate and instantly melted into place with a high-power laser beam, creating a permanent bond with rest of the object.
'With this process we cannot only make perfect repairs to damaged engine parts but also build complete components that cannot be produced using conventional methods such as milling or casting,' explained ILT's Dr Konrad Wissenbach and FANTASIA's coordinator. 'This also permits the kinds of geometries and designs we once could only dream of.'
Tests have also shown that manufacturing cycle times can be reduced by at least 40% using SLM and other laser-based generative methods. This would ultimately mean savings of a maximum of 50% of the material required, and a minimum of 40% of repair costs.
Dr Wissenbach said that the SLM approach is not, as yet, appropriate for use with every turbine material but that the team has already noted very good results with Inconel 718, a nickel-based superalloy, and with titanium alloys.
He also noted that there is still research that needs to be undertaken specifically on materials that are prone to cracking or splitting. The researchers are currently looking into ways of using melting or moulding to re-seal cracks developed by components during use. But since prevention is always better than cure, the engineers are also experimenting with ways to stop the cracking in the first place, such as by varying the laser output power or using beam geometry.
Currently, other areas of focus for the researchers are the effects that construction-platform preheating has on product quality, and the need to improve on the productivity of the method (with a coating thickness of between 30 and 100 micrometres, larger components can take too long to produce).
'[The latter] is an area where we can combine a larger beam diameter for large surfaces with a smaller diameter for the contours,' added Dr Wissenbach. 'By doing this, we want to increase our speeds by a factor of 10.'
Research for FANTASIA was undertaken by research institutes and industrial partners from France, Germany, Italy, Latvia, Spain, South Africa and Switzerland.