Fiber laser improves micro-crack repairs

27 Nov 2006

Laser welding of microcracks is an established technique but a new fiber laser-based process from Germany gives such repairs an unprecedented degree of accuracy.

At this week's Euromold trade show, which runs until 2 December at Frankurt Exhibition Centre, researchers from the Fraunhofer Institute for Material and Beam Technology (IWS) in Dresden are demonstrating a laser system that they say can better repair microscopic damage to welded metal pieces as varied as aircraft turbines or a worn injection mold.

Weld better

Coffee machines, car instruments and turbines might appear at first glance to have nothing in common, yet engineer Steffen Nowotny of the IWS says they can have common faults - and a common solution: "Our new laser welding robot can repair expensive components such as turbines or complex tools such as inserts for injection molding."

The flexible robot arm accurately focuses the laser beam on the damaged section of the component, which may be cracked or chipped. The energy from the laser beam causes the surface to melt as the laser scans the component dot by dot, producing microscopic puddles, each no larger than a few tenths of a millimeter.

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 - typically, 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 flexible," adds Nowotny. "We can employ weld-assist metals such as titanium, nickel and cobalt, hard metals and even ceramics, which allows us to seal cracks in tools, or rebuild chipped edges.

"The process enables us to accurately reconstruct several millimeters of material, sufficient to repair damage such as that caused by a bird strike to the delicate blades of aircraft turbines."

Laser beam deposition welding has already been in use for several years. However, the new IWS system enables surfaces to be processed more accurately than previously. 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 µm, equivalent to the thickness of a single hair.