Tool-electrode material

The larger part of this book has been devoted to studies related to electrochemical measurements away from equilibrium. As demonstrated, these permit the determination of kinetic and thermodynamic parameters of the electrode processes, whereas measurements at equilibrium furnish only thermodynamic data. So, whilst potentiometric analysis is a powerful tool in the determination of activities or concentrations, the specificity arising from the electrode material, amperometric or voltammetric analysis permits other parameters besides these to be obtined. 

Kulkarni et al. [75] showed by various measurements that after each discharge, the temperature of the workpiece increases above the melting temperature and sometimes even above the vaporisation temperature of the machined material. They estimated that about 77-96% of the energy supplied to the process is used to heat the electrolyte and tool-electrode and only 2-6% is used for heating up the workpiece. However, it should be emphasised that the experiments by Kulkarni et al. were performed on metallic workpieces that have very different heat conductivities compared with materials that are machined traditionally using electrochemical discharges (e.g., glass or ceramics). 

Figure 5.5 shows the expected material removal rate as a function of the normalised heat power k for various tool-electrode radii b. In order to determine the relation between k and the machining voltage U, one has to compare these results with experimental data. 

The tool-electrode feeding rate has to be selected properly. Feed rates faster than the mean material removal rate of the process will result in breaking either the workpiece or the tool-electrode. On the other hand, very slow feed rates will increase drilling times and may result in large heat affected zones around the microhole. So far only a few studies have been carried out on the optimal feeding rate. Typical values reported in the literature are, depending on the tool-electrode... 

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