Tool-electrode rotation, effect

As in the case of tool-electrode vibration, the electrolyte flow can be promoted by tool-electrode rotation. An example combining gravity-feed drilling with tool-electrode rotation is shown in Fig. 7.6. A tungsten carbide flat sidewall tool-electrode (Fig. 7.3b) with pulsed voltage supply was used [136]. The drilling time for the fixed depth of 450 p,m increases with the tool-electrode rotation rate due to the reduced heat power. The entrance diameter shows an inverse volcano dependence on the tool-electrode rotation rate. This effect was attributed by the authors to the competition between the promotion of the electrolyte flow and the increased drilling time [136]. 

Figure 7.6 Effect of tool-electrode rotation in gravity-feed drilling. Reprinted from [136] with the permission of the Journal of Micromechanics and Microengineering.

A further increase in the tool-electrode rotation improves the channel quality (Fig. 7.14). The sidewall taper angle of the microchannel profile decreases to almost 0° and the machining over-cut is also reduced. This effect is due to the improved electrolyte flow, promoting chemical etching of the glass. 

Adding abrasive material to the electrolyte does not itself promote the local chemical etching. This effect can, however, be achieved in combination with the appropriate tool-electrode motion (e.g., rotation or vibration). In this way, machining quality is improved by reducing the surface roughness [133]. 

One way to overcome this difficulty was proposed by Jain et al. [62]. They used abrasive cutting tools. The feed of the tool-electrode was chosen in such a manner so as to always keep contact between the tool and the workpiece. Thus, the machining gap is of the same order of magnitude as the size of the abrasive particles on the tool-electrode (a few micrometres). The researchers showed that the material removal rate achieved with the abrasive tools is higher than that obtained with the conventional tools. This effect may be attributed to the increased gap, but, at the same time, as tool rotation (20 rpm)... 

For a research on the electrode reaction mechanism and kinetics, particularly those of oxygen reduction reaction (ORR) (O2 + 4H+ + 4e -> 2H2O in acidic solution, or 02 + 2H20 + 4e -> 40H in alkaline solution), it is necessary to design some tools that could control and determine the reactant transportation near the electrode surface and its effect on the electron-transfer kinetics. A popular method, called the rotating disk electrode (RDE) technique has heen widely used for this purpose, particularly for the ORR. 

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