Leistritz AG, of Nurnberg, Germany, has focused its activities on the production of turbine blades for stationary gas and steam turbines and compressor blades for aero engines. Leistritz carries out all machining necessary to produce finished part, equipment for precision forging, profile drawing and for mechanical machining (milling, grinding), as well as facilities for electrochemical machining (ECM) of blades for the final surface treatment processes such as shot peening.
Leistritz applies its special ECM machines for the production of gas turbine compressor blades. This process, in a single operation, finishes the airfoil, including leading and trailing edge as well as the blade platform. The operating areas of the cathodes are shaped like modified negatives of the surfaces to be produced. In the gab between the tools and the workpiece, an appropriate electrolytic solution flows at a high rate to carry the electrolytic current and also to flush away particles from the areas being machined. A controlled movement of the tools towards the workpiece then accurately forms the complex shapes, in this case three-dimensional, twisted airfoils.
To form the blade platform, a third movement of the blade into the tool is superimposed on the movement of the two cathodes for the airfoil. The main advantages of he ECM method compared with other techniques, such as precision forging or milling, are its applicability regardless of material toughness, high accuracy and repeatability, with a superior surface quality and the absence of tool wear.
Modern ECM machines, devices and tools, as well as the use of appropriate quality control systems, can totally eliminate hand work on the airfoil, including the edges. The manufacturing sequence starts with an oversized forged blank. The airfoil and the platform of the part are ECM-machined and, finally, the root is finish-machined mechanically. All the materials commonly used for blades or vanes can be ECM-machined easily at impressively high metal removal rates. Even modern high temperature alloys that are especially difficult to machine by mechanical means are not an extra problem for the process. Because of this, the blade designer has the freedom to design even more complex, aerodynamically improved airfoil layouts and use any advanced material.
In the past, ECM was considered to be economical only for smaller aeroengine blades produced in large numbers. This method has been further developed by the Leistritz in-house design of special ECM machines for the production of single blades and vanes as well as for integrally-bladed rotors. Because of the envelopment advanced ECM machinery, the CM process has now become an alternative to forging or milling for larger blades and can be applied even for small order quantities of compressor blades for industrial gas turbines.
Presently, ECM produced blades are used in six compressor stages of the new ABB GT24 gas turbine. Leistritz is already looking forward to applying the same technique for the production of similar blades for the GT 26 gas turbine.