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A laser that mends microcracks

Repairing a damaged aircraft turbine or a worn injection mold for coffee machines or car instruments can be a very expensive business. At the Euromold trade show in Frankfurt, researchers presented a laser system that can quickly and accurately correct the damage.

Coffee machines, car instruments and aircraft turbines appear at first glance to have nothing in common, yet engineer Dr. Steffen Nowotny of the Fraunhofer Institute for Material and Beam Technology IWS mentions them all in the same breath: “The new laser welding robot is able to repair expensive components such as turbines or complex tools such as inserts for injection molding.” A flexible robot arm accurately focuses the laser beam on the damaged section of the component, i.e. the crack or chipped corner. The energy from the laser beam causes the surface to melt as the laser scans the component dot by dot, producing microscopic puddles no wider than a few tenths of a millimeter each. At the same time, powder is blown onto the surface by a stream of gas and bonds with the melt. As the powder granules are very small – with a diameter in the micrometer range – they are completely melted by the laser beam and rapidly form a tight bond with the base material. “This laser method is very flexible. Depending on the components and applications concerned, we can use metals such as titanium, nickel and cobalt, hard metals and even ceramics. This allows us to seal cracks in tools, or rebuild chipped edges,” explains Nowotny. “The process enables us to accurately reconstruct several millimeters of material. This is sufficient to repair damage such as that caused by a bird strike to the delicate blades or disks of aircraft turbines.” Laser beam deposition welding has already been in use for several years. However, the new system enables surfaces to be processed more accurately than before. The Fraunhofer researchers are using an innovative beam source: the fiber laser. This laser is able to deposit material with unprecedented accuracy, yet without putting any strain on the component. This makes it possible to produce metal structures at a resolution of as little as 100 micrometers, which is roughly equivalent to the thickness of a single hair.

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