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This paper deals with developments of Wire-EDM technologies for fir tree slot production. The aim of these developments is to substitute certain conventional processes within turbine manufacturing that have been identified as non-optimal like the critical broaching process. Thereby the negative characteristics like inflexible manufacturing processes, high machine tool investment costs and huge energy consumption can be abolished. The objective targets of the conducted research are to meet all safety requirements of the critical components and get an economic manufacturing process. In the first step a special brass wire technology for cutting Ni-based super alloys was developed. Main focus was to meet the requirements of fir tree production concerning aspects of surface integrity and geometry. To measure these aspects on the one hand non-destructive analyses have been performed to guarantee surface roughness and accuracy. On the other hand destructive analyses in terms of cross section polishing for showing thermal influenced rim zones have been prepared. A capable Wire-EDM process is presented.

Against the background of an increased importance of in-process quality measurement -especially for manufacturing of safety critical jet engine componets -this paper deals with the development of a process monitoring tool for process quality assessment and correlating surface integrity evaluation of Wire-EDM for fir tree slot production. For the last trim cut, which is the relevant cut for the final surface integrity, a correlation between process data and surface integrity aspects is set up. The process data are read out from the machine tool's controlling device to obtain a position depending signal of mean gap voltage for the quality assessment. Two demonstration runs showed the work capability of the monitoring tool for cutting the often applied nickel-based turbine alloy Inconel 718. On the one hand a failure free slot machining process and on the other hand a manipulated machining process with enforced short circuits were conducted. For the manipulated process these instabilities were successfully detected. A cross section view analysis of both fir tree slots results in best surface integrity qualities for the first run, which shows the potential to machine fir tree slots by Wire-EDM, and failures in the surface of the manipulated run due to short cuts. These failures were additionally correlated with the position depending signal. With the developed monitoring tool a first approach was designed to build up an in-process and position oriented quality assessment for the production of fir tree slots by Wire-EDM.