Electrochemical surface machining

FIGURE 2.14. Electrochemical surface machining current density distribution (left) and resulting hole (right). (See color insert.)... 

The electrochemical conversions of solid compounds and materials that are in direct contact with electrolyte solutions or liquid electrolytes (ionic liquids), belong to the most widespread reactions in electrochemistry. Such conversions take place in a wide variety of circumstances, including the majority of primary and secondary batteries, in corrosion, in electrochemical machining, in electrochemical mineral leaching, in electrochemical refining (e.g., copper refining), and in electrochemical surface treatments (e.g., the anodization of aluminum). 

D. Landolt, P.F. Chauvy, O. Zinger, Electrochemical micro machining, polishing and surface structuring of metals fundamental aspects and new developments, Electrochim. Acta 48 (2003) 3185-3201. 

Several electrochemical methods are employed in the metals-processing industry because of their ability to manufacture or surface-finish metal articles, fabric ations and components which are difficult or impossible to produce by tradition al mechanical workshop techniques. The most important methods are electrochemical forming, machining, grinding, debarring and etching. 

Electrochemical machining is performed in concentrated solntions of salts alkali chlorides, snlfates, or nitrates. Very high current densities are nsed hundreds or thousands of kA/m when referring to the surface area of the anodic working sections. At a current density of 10" mA/cm, the rate of iron dissolution is about 0.15 mm/min. This should also be the rate of advance of the cathode in the direction of the anode. High rates of solution flow through the working gap are used to eliminate the reaction products and heat evolved (e.g., flow rates of 10" cm/s). 

Surface-enhanced resonance Raman scattering (SERRS), 21 327-328 advantage of, 21 329 Surface Evolver software, 12 11 Surface excess, 24 135, 136 Surface extended X-ray absorption fine structure (SEXAFS), 19 179 24 72 Surface filtration, 11 322-323 Surface finish(es). See also Electroplating in electrochemical machining, 9 591 fatigue performance and, 13 486-487 Surface finishing agents, 12 33 Surface force apparatus, 1 517 Surface force-pore flow (SFPF) model,... 

Finally, metal objects can sometimes be fabricated in their entirety by electrodeposition (electroforming), with much the same considerations as electroplating. Conversely, portions of a metal specimen can be selectively electrolyzed away (electrochemical machining). This technique is especially useful where the metal to be shaped is too hard or the shape to be cut is too difficult for conventional machining. The sample is made the anode, a specially shaped tool the cathode, and electrolyte solution (e.g., aqueous NaCl) is fed rapidly but uniformly over the surface to be machined. Current densities may reach several hundred amperes per square centimeter across the electrolyte gap of a millimeter or so. Excellent tolerances can be achieved in favorable circumstances.16... 

When a jet of fluid submerged in a medium of that fluid strikes a surface perpendicularly, it spreads out radially over that surface. Original interest in these systems was due to mass transfer investigations of downward directed jets of vertical-take-off aircraft [41], though other applications such as electrochemical machining are important. 

Electrochemical machining (ECM) is a method of metal machining that aims at producing parts of specified shape, dimensions, and surface finish. The process is based on the removal of metal by electrochemical dissolution ([1-15] and references cited therein). Special machines have been developed to realize this aim. A complete ECM installation (Fig. 1) consists of the machine, the power supply, the electrolyte circulation system (tank, pump, heat exchanger, and sludge removal unit), and the control system (control of current, voltage, feed rate, gap width, and electrolyte temperature, pH value, pressure, and concentration short-circuit protection). 

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