Sometimes, repurposing proven technology can provide big payoffs. That's precisely what happened when Industries Engineering and Maintenance brought electron beam welding to bear on repairing a critical engine part for 's -80C2. The powerplant propels , and MD-11s.
The part in question is the fan mid-shaft tang, which comes with a list price of around $400,000, says Rene Scholten, the MRO's program manager for repair and industrialization. Contrast that with the price of an electron beam repair. That can cost $30,000-35,000 says Miranda Oele, AFI KLM E&M's program manager for aeroderivatives.
The tangs are situated on each end of the powerplant's fan mid-shaft, locking the coupling nuts on the low-pressure turbine rotor side and on the low-pressure compressor rotor side. Those tangs can crack, such as from “light impact during transportation,” says Scholten. Then, because the nut is secured with a locking ring, “We [also] suspect damage occurs during the removal of this ring. It's very tight. You have to be very cautious.”
Scholten says most of the time “the entire tang is gone.” It chips off. The maintenance manual says a maximum of two tangs can be cracked—as long as they are not located next to one another. After that, the shaft has to be scrapped—assuming there is no repair option available.
Now there is. AFI KLM E&M began fan mid-shaft tang replacement repairs employing Sciaky-built electron beam gear this past spring. The MRO did so in an application Scholten calls unique to the industry, with machines that cost roughly $2 million each.
“It's an expensive technology to establish in your repair process,” says Oele. Since spring, AFI KLM E&M has performed “something like 15 tang replacements,” she adds.
Electron beam welding “is not a new technology,” says Scholten, but he asserts it is particularly suited to fan mid-shaft tang replacement because it produces “a very nice weld” with a small heat-affected area. The weld itself takes place in a vacuum chamber.
The electron beam welder tackles repairs not just on airborne engines at AFI KLM E&M, but a stationary one as well. The MRO performs fan mid-shaft replacement on the stationary gas turbine LM6000 aeroderivative. Asked if the addition of the LM6000 repair renders the CF6-80C2 repair more economic, Oele says no: “I don't think we need [that extra] volume.” While the addition of the LM6000 to the mix “adds up,” what drives the CF6 repair is the availability of new parts. “The tang mid-shaft, that's not a typical stock item,” she says.
AFI KLM E&M performs fan mid-shaft tang replacement repairs at its Amsterdam Schiphol facility. Oele says operators can receive a serviceable assembly “within the turn time of an average shop visit.” That way, Scholten says, “Customers don't need to have a spare shaft or a replacement.”
The fix itself is comparatively fast. It's the initial setup that can be painstakingly time-consuming. “We have to measure everything correctly,” says Scholten, as well as meticulously clean surfaces where the welds will take place. But “once you have set the parameters, then you can perform the same quality weld over and over.”
Repeatability is the key, and it is accomplished robotically. Once the computer numeric control operator has programmed the Sciaky device, once the process has been tested a couple of times, Scholten says, “we can produce the actual weld [in] less than an hour.”
Oele says it is difficult to estimate the overall market for such fan mid-shaft-replacement electron-beam-weld repairs. “The volume we've been seeing up till now is not a backlog. It's our actual operational shafts.” Those shafts belong to a number of operators.
To increase the catchment basin of eligible powerplants, Scholten says AFI KLM M&E is exploring the possibilities of mid-shaft tang replacements for the CF6-80E. Its configuration is close to that of the -80C2. Before work begins, he says, “we have to prove to GE that we are able to [accomplish it].”
In the future, the MRO could move to electron beam repairs on the ubiquitous, a powerplant it currently overhauls. It's all a matter of demand. “We are problem driven,” says Scholten. “We will only start developing this type of repair for different mid-shafts if the same problem occurs, if there's a demand for it.” That said, the AFI KLM E&M executive adds, “we're the only [MRO] that can perform these repairs in the world. Once we've got the setup, we'd like to perform one every week.”