Electro discharge machining for micro manufacturing
Due to the high precision and good surface quality that it can give, Electrical Discharge Machining (EDM) is potentially an important process for the fabrication of micro tools, micro components and parts with micro features. However, a number of issues remain to be solved before micro EDM can become a reliable process with repeatable results and its full capabilities as a micro manufacturing technology can be realised. This work presents some developments in advancing the state-of-the-art in the micro EDM process. EDM drilling and EDM milling are regarded as separate processes as they require different approaches in investigating and implementing the results of the study. At the beginning, special attention is paid to factors and procedures influencing the accuracy achievable, including positioning approaches during EDM and electrode grinding. In particular, the main parameters affecting the size and position of a machined feature are discussed and new techniques for minimising errors are proposed. The technological capabilities of different methods of setting up and dressing the electrode on the machine are analysed. Factors contributing to electrode wear, the main systematic cause for inaccuracy of the dimensions achieved, during the micro EDM process are studied. A method for calculating the volumetric wear ratio based only on geometrical information obtained from the process is proposed. This study investigates the suitability of micro EDM electrode wear compensation methods. Electrode shape deformation and random variations in the volumetric wear are also investigated as the two main factors affecting the applicability of the wear compensation methods as well as indicating the accuracy achievable with micro EDM. When producing features and parts on the micro scale, the phenomena that take place between the electrodes in EDM is not fully understood. A barrier to a complete exploitation of the potential natural tolerance of this process and to the further development of the process towards the production of components on the nano-scale is therefore in place. An analytical micro EDM model of electrode wear based on electrode shape deformation and wear ratio is suggested, verification of which requires experimental work with pure metals. Electrode-tool wear is studied during the micro EDM process of pure metals and the effect of electrode wear on the process accuracy and process variability. Objectives in this case are to advance the experimental knowledge of the electrical discharges during micro EDM operations which often conflicts with existent theoretical models of the EDM process. In particular, the remit of this investigation is to identify the effects that electrode materials have on selected electrical characteristics of the discharge process. An exploratory data analysis (EDA) approach is adopted in order to draw conclusions from the performed experimental activity. The material removal mechanism in the micro EDM process was confirmed to be mainly attributed to the melting and vaporisation phenomenon. Metal removal takes place as a result of the extremely high temperature generated by the discharge sparks. It was also found in this study that the volumetric wear ratio depends not only on the sparking conditions but also on the electrode materials. In addition, the research also proved that the electrode material severely influences the energy distribution between the electrodes during the sparks.
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