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Abstract:

In this dissertation, the application of micro-EDM to machine ceramic composites like Si3N4-TiN, Silicon infiltrated silicon carbide (SiSiC) and sintered SiC (SSiC) is investigated. These ceramic composites are difficult to be machined at microscale by conventional processing techniques. More specifically, the influence of process parameters on machining performances such as machining speed, tool wear and surface quality is studied in detail with the aid of the statistical Design of Experiment methods. Also, an in-depth analysis of the micro-EDM pulse generator is conducted to derive optimised machining strategies leading to maximum efficiency as well as to optimal machining accuracy. Each ceramic composite shows distinctive material removal mechanisms under variable machining conditions. Therefore, the correlation between material properties, machining results and input discharge pulse shapes has been investigated by extensive experiments. Furthermore, by exploring the process limits, it is experimentally proven that these ceramic composites can be shaped by micro-EDM process. Tool wear of the electrodes proves to be one of the critical factors affecting the dimensional and geometrical form accuracy of the micro-EDM milling process. The existing technology (e.g. the combination of in-process discharge detection and anticipating tool wear compensation) is able to accurately predict the tool wear for long prismatic tool electrodes. However, accurate tool wear compensation is not available in case of a change of workpiece geometry, tool dimension, tool path variation or extended machining time. In this work, the variables which are affecting the wear mechanisms are investigated and a more comprehensible model for tool wear is presented. Using this tool wear model, different milling conditions are evaluated by analysing the discharge pulses in order to further elevate the machining accuracy and production efficiency. Finally, the capabilities of the developed micro-EDM technology are illustrated by machining complex and three-dimensionally shaped micro structures, such as turbine impellers, compressors and micromoulds.