A low-pressure turbine blisk in an Eurofighter EJ200 engine damaged by foreign object debris has been repaired by MTU Aero Engines using a process called patching, which involves cutting off the damaged blade area and welding on a replacement section.
Munich-based MTU claims to be the first company to successfully do this on a production basis. It was commissioned by the German air force to develop a solution for blisk blades needing repair due to FOD damage.
The two-stage repair involves patching the blade using a welding process specifically developed for the purpose. Then adaptive milling restores the blade to its original contour.
"We're the first company able to perform and offer this blisk repair technique on a production basis," says MTU senior vice-president and chief operating officer Rainer Martens. The blade repair took place in December 2007. The company has received European Aviation Safety Agency approval for the repair technique.
Under the European Union's Fifth Framework Programme, MTU was involved in the €6 million ($8.7 million), four-year advanced welding technologies For repair and salvage (AWFORS) research project, for nickel and titanium-based alloy engine components.
Direct laser deposition (DLD) and capacitive discharge welding (CDW) techniques were evaluated for engine blade repairs, including blisks. CDW is similar to friction welding and DLD involves the deposition of a metal powder that is melted into place with the laser. A conclusion of AWFORS was that DLD would be used to repair blisk blades. The AWFORS project had 10 partners, including Aachen University of Technology, Rolls-Royce Deutschland, the Swiss Federal Institute of Technology Lausanne, Turbomeca and Italy's Universita Degli studi di Lecce.
Source: Flight International
