Vibration, tool-electrode

An alternative approach to constant tool vibration is to move the tool-electrode up and down at specific moments during drilling in order to allow fresh electrolyte to flush inside the hole [122]. A possible algorithm can be based on the measurement of the contact force between the tool-electrode and the workpiece. If this force is higher than a selected level, the tool-electrode is moved up in order to flush the microhole. 

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]. 

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]. 

The heat transfer through the electrolyte can be influenced by local hydrodynamic flows (by convection) or by changing the heat conductivity of the electrolyte. The first strategy can be implemented by adding the appropriate tool-electrode motion such as vibration or rotation. Both do not only promote the heat transfer but also the local high-temperature chemical etching of the workpiece as discussed in Section 7.2. 

The tool-electrode is mounted on a flexible structure that controls the vertical guidance of the tool. An optical sensor measures the tool displacement. An optional voice-coil motor can be added in order to control the force at which gravity-feed drilling is done. This motor can also be used to add vertical vibrations to the tool to promote the flow of the electrolyte inside the microhole. Rotation can also be included. 

TR-SFG seems to be an ideal tool to study the surface dynamics of adsorbed CO at solid/liquid interfaces. Although there are several reports of TR-SFG studies on an electrode, they are only of investigations of vibrational relaxation lifetime by IR excitation [34, 65, 67]. 

Over the past decades, smface enhanced Raman scattering (SERS) has became a valuable spectroscopic technique as a powerful smface diagnostic tool. In 1974 Fleischmann, Hendra, and McQuillan performed the first measurement of a surface Raman spectrum from pyridine adsorbed on an electrochemically roughened silver electrode. It has been explained that some vibrational bands of pyridine are selectively enhanced a million times. This increases the sensitivity of... 

SHG) [610], total internal reflection fluorescence (TIRF) spectroscopy [611], UV/Vis spectroscopy, IR spectroscopy, ellipsometry [612], quartz crystal microbalance (QCM) [613], STM [614], and AFM (see Refs. [618-623] for review of in sitn spectroscopies). From those, only the vibrational methods (SHG, SERS, and IR spectroscopy) are able to provide information on both the chemical composition and the strnctnre of the species adsorbed. The IR SEC experiment is simpler and more accessible than SHG and SERS, making IR spectroscopy the dominant tool for stndying electrochemical reactions at metallic electrodes [616, 617, 624-641]. 

---