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Physical principle of electrochemical processing

The physical principle of electrochemical machining (ECM) is based on high-speed anode dissolution of metals and alloys under the electrolysis current of high density in the flowing electrolyte at small interelectrode gaps. Thus according to Faraday's law, weight of the material removed from the workpiece is proportional to current density and processing time.

In domestic practice of industrial application of ECM the greatest distribution was received by electrolyte fluids representing water solutions of neutral non-toxic and fireproof mineral salts. From the point of view of high accuracy of processing the most rational choice is low concentrated (to 15 %) water solutions of oxygen-containing salts among which 8 %water solution of NaNO₃ had the greatest distribution. By this example, we will consider the essence of the ECM method.

For realisation of the ECM process two metal electrodes (the tool and blank), having electrolyte fluid in the space between them, are connected to opposite poles of technological current supply. The negative pole of supply connected to the EDM electrode (cathode), shifts its potential to the negative side owing to increase of electrons concentration. The positive pole selects electrons from the electrode-blank (anode) connected to it that shifts its potential to the positive side. Such deviation of potentials of electrodes from equilibrium values generates electrode processes: cathions recovery at the cathode, metal oxidation starts at the anode.

In case of the ECM of steel parts in water solution oxygen-containing neutral salt NaNO₃ which molecules are dissociated for nitrates-ions NO₃ ^- and sodions Na ⁺ the process of dissolution of a material of the blank (anode) proceeds in the following sequence. There is a process of ionisation of metals Me = {Fe, Cr, Ni...} at the anode which in the simplified form looks like this:

Me → Me^z+ + z · e^-.

Metal ions Ме^{z +} co-operate with OH ^- ions with formation of hydroxide of Me (OH) _n type which are besieged in the form of sludge. It is taken out from the interelectrode gap by a stream of electrolyte fluid and is removed by means of filters or separators.

Also the oxygen evolution reaction takes place at the anode in which result the anode layer of electrolyte fluid is acidified.

Decomposition reactions of water molecules with formation of gaseous hydrogen proceed at the cathode.

Sodions Na ⁺ because of very low electronegative values of their equilibrium potentials are not restored and formally do not take part in the process.

In theory, only water is consumed except the electric power during the ECM.