Aachen, Germany – Selective laser melting can produce complex-shaped components in aircraft engines quickly and at a reasonable price, as demonstrated by researchers at the Fraunhofer Institute for Laser Technology (ILT) in the EU-sponsored FANTASIA project. The experts presented their latest findings at the International Laser Technology Congress (AKL'10), May 5-7, 2010, in Aachen, Germany.
Aircraft engine components must perform under extreme conditions: they must rotate more than 1000 times in a single second, withstanding temperatures of up to 2000 degrees C and extreme pressures. At the same time, they should be as lightweight as possible and yet satisfy the most stringent standards for safety. Given all of these factors, the tasks of developing and servicing aircraft engines pose major challenges for engineers.
The photo shows laser cladding with a telescopic optical system, courtesy of Fraunhofer ILT.
Using the selective laser melting (SLM) method, researchers at ILT build up the part, layer by layer, on a building platform using a powder-based material. In essence, this process is comparable to that of a computer printer except that it takes place in three dimensions. Based on computer-generated design data for the planned part, the metal powder is applied to the appropriate areas of the substrate and then immediately melted into place with a high-power laser beam. This forms a permanent bond with the portion of the object that is already complete. Materials tests have found that the quality of components produced using SLM is at least as high as that of parts manufactured using conventional methods.
SLM has great potential. "With this process, we can not 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," observes Dr. Konrad Wissenbach of ILT. "This also permits the kinds of geometries and designs we once could only dream of." Indeed, the figures speak for themselves: with this and other laser-based generative methods, manufacturing cycle times can be reduced by 40 percent or more. In the future, this will mean savings of up to 50 percent of the material required, and at least 40 percent of repair costs.
The SLM approach is not suitable for every turbine material just yet. "We have already seen very good results with Inconel 718, a nickel-based superalloy, and with titanium alloys as well," Wissenbach remarks. "We are not quite as far along with other fissure-prone materials."
ILT researchers are continuing the search for ways of using melting or molding to reseal any cracks a part may have developed during use. Of course it would be even better if cracking could be prevented altogether. This is why the engineers are experimenting with different parameters, varying laser output power, beam geometry and the structure strategy. They are also investigating the effects of construction-platform preheating on product quality.
The productivity of the method needs to be further improved as well, because with a coating thickness of 30-100 micrometers, larger components can take quite a long time to produce. “This is an area where we can combine a larger beam diameter for large surfaces with a smaller diameter for the contours,” Wissenbach says. “By doing this, we want to increase our speeds by a factor of ten.”