Dressing of Graphite Electrodes for EDM of Seal Slots in Nickel-base Alloy MAR-M247

The die-sinking EDM-technology, applied at the turbine industry for the fabrication of seal slots in turbine components, is addressed at this work. The objective was the development of a new technology to dress graphite electrodes inside the machine tool with the aim of reducing the set-up times and of enabling process automation with respect to all quality requirements. The wear pattern development of graphite electrodes during the EDM-machining of seal slots in nickel base alloy MAR-M247 was determined, followed by the analysis of the influence of dressing plate materials and dressing parameters. The process results analyzed were dressing time, dressing length and material removal rate. This enabled the understanding of tool electrode wear development, followed by the determination of influencing dressing parameters and their effects. The optimization of the dressing technology was conducted, including the variation of statistically high significant influencing dressing parameters. This enabled the determination of optimized dressing parameters applying the dressing plate materials graphite and cemented carbide. Finally, the dressing technology was integrated into the process chain, whereas five sets of 12 cavities were machined successively, with a dressing step between the EDM-machining steps. The analysis of all five sets of cavities proved that the form accuracy, arithmetical surface roughness and affected sub-surface remained within the tolerances for all pats.