The EDM process plays an important role in the manufacturing of parts for gas turbine (jet) engines and static turbines used to obtain large scale electrical energy production. These include turbine vanes, turbine blades, impellers and so on.
Industrial gas turbines differ from aeronautical designs in that the frames, bearings, and blades are of heavier construction. A turbine is made up of several blade and nozzle guide vane (NGV) stages. Each of the NGV stages comprises between 18 and 38 segments that are joined to form rings. The seal slots of these joints are produced by EDM and ONA has developed technologies specifically suited to produce these.
Some types of turbine vanes also have cylindrical and shaped cooling air holes, running from the inner to the outer edge of the shroud or from the trailing edge to the core, produced by EDM. Honeycomb seals usually manufactured from Hastelloy and Inconel nickel alloys are also produced using the EDM process.
The development of blisks (blades integrated on disc) has been an area of rapid change for the aero engine sector, as one blisk can substitute up to 120 different pieces in one turbine. ONA’s NX range fitted with a single axis rotary table provide the ideal solution.
Turbine impellers are some of the most complex parts of the turbines to be manufactured. The first stage in the manufacturing process is often achieved by milling. EDM is then used at the final stage to obtain a homogenous final surface finish.
Location housing for the vanes and blades that are placed inside turbine rings is achieved using wire EDM. ONA has developed a family of wire EDM machines especially designed to machine large cylindrical pieces ranging up to 2,000 mm.
Due to the high costs and low flexibility of broaching operations, wire EDM is being used as an alternative method to produce the fir tree shaped slots of the turbine blade holder. Roughing is done using wire EDM and finishing can be achieved either by broaching or by a finish pass with the wire.