Mehmet Can ÇAPAR, 030070131 6th week definitions


1-Chemical Engraving (Manufacturing method)
(old answer)
This is a closely related process in which chemical machining techniques are used to remove metal from selected areas of nameplates or other components to produce the lettering, figures, or other nomenclature required. Chemical engraving is a substitute for mechanical pantograph engraving. Lettering can be either deprressed or raised.
Typical parts produced by chemical engraving are instrument panels, nameplates, printing plates, signs, and pictures. Parts require engraving with fine detail are especially suitred to chemical engraving.


 (DFM Handbook, 2nd Edition, Bralla, p.4.227)


(new answer) (better)

    SACE (spark-assisted chemical engraving) makes use of electrochemical and physical phenomena to machine glass. The principle is explained in figüre 1.1. 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.
     When the cell terminal voltage is low (lower than a critical value called critical voltage, typically between 20 and 30 V), traditional electrolysis occurs  (Fig.  1.2). Hydrogen gas bubbles are formed at the tool-electrode and oxygen bubbles at the counter-electrode depending on their polarisation and the
electrolyte used. When the terminal voltage is increased, the current density also increases and more and more bubbles are formed. A bubble layer develops around the electrodes.The density of the bubbles and their mean radius increase with increasing current density. When the terminal voltage is increased above the critical voltage, the bubbles coalesce into a gas film around  the tool-electrode. Light emission can be observed in the film when electrical discharges, the so-called electrochemical discharge,occur between the tool and the surrounding electrolyte. The mean temperature of the electrolytic solution increases in the vicinity of the tool-electrode to about 80-9o degrees C.Machining is possible if the tool-electrode is in the near vicinity of the glass sample (Fig.  1.3). Typically,the tool-electrode has to be closer than  25 micrometre from the workpiece for glass machining to take place
     However, thing are not simple as they seem. The gas film around the tool-electrode is not always stable. Microexplosions may occur destroying the machined structure locally. During drilling of holes, the local temperature can increase to such an extent, resulting in heat affected zones or even cracking.

 (Rolf Wüthrich, Micromachining using electrochemical discharge phenomenon, pg:2-3)