Workpiece electrochemical machining

FIGURE 16.5 Electrochemical machining of metals (1) workpiece (anode) (2) tool (cathode). 

Electrochemical machining is a process based on the same principles used in electroplating except that the workpiece is the anode and the tool is the cathode. Electrolyte is pumped between the electrodes and a potential is applied, resulting in rapid removal of metal. 

Another technique used in metal finishing is electrochemical machining, which employs anodic current densities of up to 5 MA rrT2 The principle of this technology is to advance a shaped tool, which serves as the cathode, towards the anodic workpiece. As the interelectrode separation narrows, the workpiece dissolves... 

Schematic diagram of (a) an electrochemical micromachining apparatus, (b) configuration of the tungsten workpiece being machined [15].

Electrochemical machining (ECM) is a material removal process into which pulsed current is dissipated through a conductive electrolytic solution between the tool and the workpiece (Fig. 2). Such chemical interaction causes material to be removed from the workpiece according to the shape of the tool. ECM is based on thermal effects by extremely quick heating, melting, and vaporizing. The heat sources are the energy... 

D machining of electrochemically active materials, including the construction of unconventional island patterns on a surface with nanoscale resolution, was also realized by this method [95, 115-117]. Thus, electrochemical machining can be applied to microelectromechanical systems (MEMS] [118] and even in the nanoelectromechanical systems (NEMS]. Electrochemical methods can realize the nanofabrication in a selective place and make the complicated 3D nanostructures. Conducting polymers can also be fabricated in this way. Similar to the electrochemical machining, by application of short voltage pulses to the tool electrode in the vicinity of the workpiece electrode, the electropolymerization... 

The total system is shown in Figs 8.6 and 8.7 and it can be seen that the cell (tool + workpiece) is but a small part of the equipment necessary for electrochemical machining. 

Static electrode electrochemical machining techniques are limited in the form and accuracy of their machined products as metal is removed from the workpiece, the interelectrode gap increases and the metal removal rate falls. This problem may be overcome by continuously moving the tool (or the workpiece) in order to maintain a constant gap. This is the principle behind electrochemical forming (sometimes called electrochemical sinking), which is perhaps the most important and versatile application of electrochemical machining. 

The process is conducted in the working chamber (electrochemical cell) of the machine, where a workpiece (WP) and a tool electrode (TE) are placed. The WP is connected to the positive pole of a power supply, and the TE serves as the cathode. The interelectrode distance is typically 0.02-0.8 mm. The electrolyte (usually an aqueous solution of an inorganic salt, 15% NaNC>3 or NaCl, for example) is... 

SACE makes use of electrochemical and physical phenomena to machine glass. The principle is explained in Fig. 1.1 [128]. The workpiece is dipped in an appropriate electrolytic solution (typically sodium hydroxide or potassium hydroxide). A constant DC voltage is applied between the machining tool or tool-electrode and the counter-electrode. The tool-electrode is dipped a few millimetres in the electrolytic solution and the counter-electrode is, in general, a large flat plate. The tool-electrode surface is always significantly smaller than the counter-electrode surface (by about a factor of 100). The tool-electrode is generally polarised as a cathode, but the opposite polarisation is also possible. 

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). 

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