“Multifunctionality is the laser’s strength for the future”
Aircraft engines no doubt rank high among propulsion systems that must meet extremely exacting requirements, especially when the aim is to make them quiet and fuel efficient over a long service life. Gerhard Maria Backes, aircraft engine expert at the Fraunhofer Institute for Laser Technology ILT in Aachen, reports on the role lasers play in achieving these goals.
Mr Backes, what are you working on currently?
We are cooperating with Rolls-Royce Germany on the development of laser maintenance techniques, such as those for components of the secondary power system on the Tornado, as well as for the turboshaft engine on the Sikorsky H-3 Sea King multi-purpose helicopter. In the latter case, we use LMD to repair 14 different components. In the civil sector we have developed maintenance techniques for two components of the BR715 engine.
What are the general advantages of using lasers in aircraft construction, and where are they particularly useful?
Lasers almost always come into consideration when other processes cannot handle the job. Most enquiries come from the engine maintenance sector. The key advantage of the laser is its low input of energy or heat compared with conventional processes, which means that the component suffers little distortion. The user can repair minute cracks with pinpoint precision and perform tiny welds without affecting the component as a whole. What’s more, hardly any finishing work is required thanks to the accuracy of the deposition technique.
What is the situation with the materials?
LMD allows materials of different types to be adapted much more precisely to each other, which means that the material you use for repair work need not be the same as that from which the component was originally made – you can choose a better alternative. On bearing surfaces, for example, a harder material which does not require any further treatment would be a natural preference. What’s more, magnesium can be coated and welded using LMD techniques.
Are lasers then, in your opinion, an option in component manufacture?
I assume you are referring to laser generation: Our institute was conducting initial projects on this back in the 1990s – for example on engine blades. Back then, hollow blades were generated directly on a shaft for the first time. This saves production costs, because components do not have to be milled from the solid, but are instead generated in tailor-made form as an entire assembly. Component parts can be produced using different materials which are either more temperature-resistant or harder. This gives the components a longer service life.
Why is the technique not being used in series production?
Exhaustive material tests are still required to ascertain how the generated components would perform in actual practice.
What is the difference between laser metal deposition (LMD) and selective laser melting (SLM), which was developed at Fraunhofer ILT?
SLM is an additive technique that allows very complex but small parts to be built, and these are suitable for use as new components. To make larger parts using the SLM technique would call for large chamber systems, whereas LMD can be used to work on components that measure as much two meters in length, without the need for a chamber.
Why is the LMD technique so interesting for aircraft engine manufacturers?
The trend towards “power by the hour agreements” where service is paid according to operating hours, is prompting the manufacturers to consider how to repair components instead of replacing them with new ones. Another factor is the difficulty in repairing older engines for which spare parts are no longer available.
And what more do you hope to achieve on the LMD front?
We are conducting work on components made of magnesium and special Inconel alloys. We also want to establish laser metal deposition in applications where the technique represents a completely new technology for the user, even if it has become an everyday technology for us.
What is the difference between LMD and TIG welding?
LMD processes parts ten times faster and subjects them to less thermal loading. It also achieves better near-net-shape results than TIG welding.
What lies behind the Fraunhofer ILT’s success in the use of lasers in aircraft engine construction?
Fraunhofer ILT develops maintenance techniques not only for the customer but also with the customer. As a result, technology can be transferred very quickly and efficiently to the customer when the development is completed. We also assist our customers in the design of suitable facilities for laser metal deposition.
Does a technology transfer always take place?
No. If the work only involves repairing individual parts and the process is extremely complex, as is the case for example with some magnesium parts, a technology transfer would be too expensive. If, however, the quantity increases to a worthwhile batch size, we offer the customer a technology transfer.
You work closely with Rolls-Royce Germany. How could a different engine manufacturer benefit from your expertise?
Obviously it’s against the rules to transfer a technique developed in cooperation with Rolls-Royce Germany in identical form to the processes of a different engine manufacturer, and technically it’s not realistic. On the basis of our many years of experience with LMD, however, we could develop something independently to solve specific problems at other engine manufacturers.
What laser sources do you use?
We mainly use Nd:YAG or diode solid-state lasers for repair work with laser metal deposition. These systems work in a wavelength range of about one micrometer.
Looking ahead, how do you see the future of laser metal deposition?
One promising new area for LMD is coating at extremely high process speeds, where a rate of over 100 meters per minute is to be compared with up to three meters per minute using conventional methods.
And as far as the multifunctionality of lasers is concerned, what can be improved?
If we take a spare part for the Tornado as an example, with a single laser we can perform three processes in one setup – soldering, welding and coating. I see this multifunctionality as the laser’s strength for the future. A system with a bayonet catch would be ideal here as this would make it much quicker to change the processing heads.
Interview conducted by Nikolaus Fecht
German Summary
Kein Zweifel, Flugzeugtriebwerke zählen zu den anspruchsvollsten Antriebselementen. Sie sollen leise sein, wenig verbrauchen und lang halten. Welche Rolle der Laser dabei spielt, berichtet Gerhard Maria Backes, Experte für Laserauftragsschweißen an Trieb-werkskomponenten. Er ist wissenschaftlicher Mitarbeiter des Fraunhofer-Instituts für Lasertechnik ILT in Aachen. Der deutschsprachige Beitrag ist nachzulesen auf:
www.aerotec-online.com/aero0111ilt
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