EDM accepts the challenge
MTU Aero Engines is not only Germany’s leading engine manufacturer but globally the No. 1 independent provider of commercial aero engine maintenance services. At MTU’s Munich plant Electrical Discharge Machining (EDM) is used for high-precision machining of stator components and materials’ production.
Each one of the EDM machines was ordered after comparative machining tests involving various manufacturers. Hermann Peters, the man in charge of machine procurement at MTU, and Immanuel Schmidt-Streckenbach, a production engineer, applied strict standards in their evaluation of the machines. In 2003 MTU asked a number of EDM manufacturers to segment high-pressure compressor rims made of inconel. As Hermann Peters points out, “Makino was best prepared for the task at hand” and the Makino EU64 not only delivered the best results in quality terms but was also faster than the other machines, reducing the total machining time for rim segmentation by 32%.
Since March 2004 a Makino EU64 featuring 650 mm x 400 mm x 420 mm travels (X, Y, Z) has been segmenting these rims. As Immanuel Schmidt-Streckenbach explains, “we wire-erode the rims to an accuracy of ±0.075 mm. That means 15 to 32 individual segments, depending on the engine stage in question. One reason for this segmentation is that maintenance work can be carried out on these high-pressure compressor rims without having to take the entire turbine apart, another is to compensate for thermal expansion. We need to be able to adjust the flushing and wire guide with great precision because if the wire breaks while eroding, it is highly probable that the whole component will be ruined.”
A second Makino EDM machine – a U86 featuring 800 mm x 600 mm x 500 mm travels (X, Y, Z) – was also chosen after a benchmarking process. In 2004 MTU tested the performance of several manufacturers in machining titanium split-cases. The 420 mm high cases for the medium-pressure compressor of the TP400-D6 turboprop engine for the new Airbus A400M military transport aircraft are split into two halves for assembly reasons. This has to be done in a single cutting operation with strict tolerance compliance guaranteed. The difficulty lies in the height of the case and the distance between the wire guides. Here, again, the japanese machine delivered the best results and has been in operation since October 2004.
The third machine to be installed, another EU64 EDM, also had to pass through an extensive testing procedure, including machining the Haynes brush seals MTU manufactures for steam turbines, aero engines, industrial gas turbines and compressors as well as other mechanical engineering applications. These patented MTU brush seals replace reduce leakage (by up to 80%), wear and tear and fuel consumption compared with the widely used labyrinth-type seals. In the tests Makino came out top in technical and economical terms. Brush seals are manufactured in an extremely delicate process: thousands of ultra-fine wires are mechanically clamped in position around a core wire in a tube and then wire-eroded to the required length. If these ultra-fine wires are accidentally welded together during eroding, the entire brush seal is ruined. Here too, the EU64 has met all the requirements since its installation in January 2005.
MTU seems to be extremely satisfied with the Makino machines. As Immanuel Schmidt-Streckenbach explains, “they make a big contribution to the high quality of our output and the stability of our production processes”. Since their installation in 2004 and 2005, there have been no significant breakdowns or stoppages. As a high-tech company, MTU places great emphasis on the operational stability and reliability of its production machinery. Hermann Peters also testifies to the reliability of Makino and its EDM machines: “Their availability is above 95%, as was agreed, and Makino is a reliable and competent partner when it comes to support and maintenance.” On the basis of these experiences, MTU ordered another U86 from Makino and the machine was delivered on schedule just a year ago.
German Summary
MTU Aero Engines setzt zur Präzisionsbearbeitung von Triebwerks-Stator-Komponenten und im Betriebsmittelbau Drahterodieranlagen ein. Sie tragen mit zu hoher Fertigungsqualität und Prozessstabilität bei. Der deutschsprachige Beitrag ist nachzulesen auf www.aerotec-online.com
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