Grinding is history
SR Technics, headquartered at Zurich’s Kloten Airport, is currently responsible for supporting around 800 airplanes, and consequently 300 engines and roughly 78,000 components. The Swiss firm opts for EDM instead of grinding, especially for repairing honeycomb structures on jet engines. One successful step towards increased value creation.
Stricter requirements and new developments in the aircraft industry meant that it was time for SR Technics to invest in a new EDM (electrical discharge machining) machine. Although the Ingersoll was 35 years old, it was still reliable – but it was simply no longer suitable for processing the range of modern parts. Higher performance and reliability were also demanded, particularly for machining the honeycombs made of a high-temperature nickel-based alloy. In the past, these honeycombs were ground to size. The problem was that the grinding pressure was severely limited, and the honeycombs became clogged with the shavings produced.
A fatal situation, because these metal particles can wreak destruction in the engine. Therefore it is no great surprise that engine manufacturers recommend EDM. This machining, however, is anything but simple, because it is necessary to rotate the electrodes in an open space (and in a controlled manner) for the workpieces with diameters of up to 1,000 mm.
Bringing value creation back
Consequently, the EDM system must have the right controller and generator module in order for the system to be capable of placing the electrodes into any position for processing the workpiece. Until the end of 2008, these components were therefore still being outsourced. But the plan was to bring this value creation back into the company. The Zurich engine specialist’s comparison of different machines quickly separated the wheat from the chaff. As Peter Schwarzer, manager for mechanical machining and aircraft parts at SR Technics, explains it, “Naturally we consulted with all leading EDM machine manufacturers before we made our decision. The range of sizes for our parts narrowed our selection down to the Gantry 1200. At other manufacturers, our requirements would have resulted in additional expenses. But naturally OPS-Ingersoll won us over with its technology, references in aviation and graphite know-how. ” SR Technics evolved from Swissair, previously Switzerland’s national carrier. Today, it is one of the world’s largest independent technical solution providers for 
airlines, a feat that required rising to the challenge of an extremely competitive market. There is no time to waste, even on a single part. The Gantry 1200 reduced the machining time for the honeycomb-equipped rings already mentioned from the four hours required for grinding to only one hour. This process involves radially removing three to five inches along the circumference. For another component with a hard-sprayed coating that needed to have grooves machined into it, the switch to graphite electrodes reduced the machining time from 15 minutes per groove to 7 minutes. Even when as many as 300 grooves have to be machined into such components, mass production is not an option. It can take weeks or even months, if ever, before such parts are repeated. Which is why Peter Schwarzer and his colleague, production engineer Urs Schuhmacher, kept an eye to the future when investing in the EDM machine. In Urs Schumacher’s opinion, the machine’s controller offers the right potential.
“We’re still not working automatically, but we want to do so in the future because we are still far from fully exploiting the machine’s capabilities. With the right toolings, we could naturally greatly reduce the setup times.” The use of zero-point clamping systems or other clamping methods also makes it possible to expand the variety of parts. Enormous time savings were also brought about by using a special electrode holder with twelve electrodes. In contrast to the individual electrodes that had been used until then, this holder allowed the system’s positioning accuracy and performance to be substantially improved with respect to the removal rate and surface quality. Peter Schwarzer is more skeptical, however, when it comes to automation such as that commonly found in mold and die making. “The problem that we have here is certainly the price of the workpieces. We have to machine some system components that are estimated at 500,000 SFR. In such a case, you simply cannot allow a machine to run on its own at night.”
German Summary
Die SR Technics mit Hauptsitz am Züricher Flughafen Kloten ist derzeit für die Betreuung von zirka 800 Flugzeugen und damit für 300 Triebwerke und etwa 78.000 Komponenten verantwortlich. Speziell für die Instandsetzung von Honeycomb-Strukturen von Jet-Triebwerken setzen die Schweizer statt auf Schleifen auf das Senkerodieren. Ein erfolgreicher Schritt in Richtung Steigerung der Wertschöpfung. Der deutschsprachige Beitrag ist nachzulesen auf www.aerotec-online.com
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