Investigations on Vibration-Assisted EDM-Machining of Seal Slots in High-Temperature Resistant Materials for Turbine Components

Modern aircraft engines are nowadays designed with the aim of reducing fuel consumption and emission of pollutant gases as well as increasing reliability and competitiveness in the manufacturing and repair costs. These requirements on the engines result in new requirements on components and manufacturing processes, to know: application of new engineering materials, higher component temperatures, increased demands on tightness, 3-D complex shapes as well as new manufacturing technologies. EDM-machining is typically chosen for applications including complex geometries like high aspect ratio cavities in high-temperature resistant materials, since the EDM-process is independent from the mechanical properties of the processed material. This paper addresses the design and utilization of a unit composed of piezoelectric actuators for machining seal slots in turbine components. This aims the optimization of the flushing mechanisms through vertical vibration of the tool electrodes while manufacturing high aspect ratios cavities and therewith the optimization and/or reduction of both process time and electrode wear. Firstly, the piezo-unit was designed and components like piezoelectric actuators and charge amplifier were chosen, in accordance to previous defined requirements regarding vibration frequencies and amplitudes. During the experimental investigations graphite electrodes were applied. A total of twelve cavities with an aspect ratio of 12 are simultaneously machined in the material MAR-247. During the process, a harmonic longitudinal vibration of the electrodes overlapped to the machine's feed movement is realized. Both vibration amplitude and frequency were varied during the experiments, ranging from 2 μm to 16 μm and from 50 Hz to 1 kHz, respectively. The results are compared to the conventional process without vibration, while the EDM-parameters remain unaltered. By applying longitudinal vibration to the tool electrodes the material removal rate was increased by 11%. The relative tool electrode wear was reduced by 21%.