Saving big with patch repair

CF6-80C2 turbofan rear frame
Progressive technology

CF6-80C2 turbine rear frame: The Engine Parts and Accessories Repair (EPAR) business unit of Lufthansa Technik has obtained certification for another repair procedure that offers customers enormous savings: an oversize patch repair for the turbine rear frame of the CF6-80C2 turbofan engine that makes use of state-of-the-art repair technology. 

More than a standard procedure

When damaged, the turbine rear frame of the CF6-80C2 typically exhibits cracking next to a strut. This type of damage is not found that often, but due to the size, loading and complex geometry of the part, it is not repairable by a standard procedure so that the damaged component has to be replaced by an expensive new part. On top of this, there is no certainty that a spare part will be available on the market when required. Although a simple patch repair has been available in the past, because of the limit on the extent of the cracking for which it could be used Lufthansa Technik decided to develop and arrange for the certification of an oversize patch repair in collaboration with the manufacturer. The new repair allows the turbine rear frame to be restored at a fraction of the cost of a spare part. 

Individuality of each repair

The repair work is customized to the circumstances of each individual case. The first step is to digitize the site of the damage (picture 1) and determine the patch geometry. A patch cutout (picture 2) completely removing the damage is then created in a special adaptive milling procedure.
The patch cutout is now measured precisely using optical measuring techniques, the data is digitized and a CAD model of the repair patch is created. In this connection it has to be borne in mind that the repair patch must be inserted with minimum oversize. A check is therefore carried out in a simulation on the CAD screen to ensure that this condition is satisfied. Only if this is the case is the repair patch fabricated on the CNC milling machine (picture 3). An unfinished block of material of the desired material quality is used here as the starting material.
The repair patch is then inserted into the cutout in the turbine rear frame under carefully controlled conditions and secured in position by electron beam welding. The final step is to perfectly integrate the patch contour into the original contour of the rear frame (picture 4).
 

Outstanding significance of Lufthansa Technik

This new repair reflects closely Lufthansa Technik's philosophy that it is better to perform an efficient repair than to install a purchased replacement part. Today Lufthansa Technik is the only company with formal approval to perform this repair.
It goes without saying that customers also benefit: the new repair brings a significant cost saving while avoiding replacement cost by purchasing a new part.