Electrochemical machining (ECM) is an anodic electrochemical dissolution process. Figure 1 illustrates its principles and basic equipment. A D.C. voltage (usually about 10 to 25 volts) is applied across the interelectrode gap between a pre-shaped cathode tool and an anode workpiece. The electrolyte (e.g. NaN03 aqueous solution ) flows at high speed (10 to 60 mls) through the gap (about 0.1 to 0.6 mm). With current density of 20 to 200 Alcm2, the anode workpiece is dissolved according to Faraday's law. The dissolved material (usually metal hydroxide) and other by-products
generated in the process such as cathodic gas are transported from the gap by the electrolyte flow. The final shape of the workpiece is approximately negative mirror image of the tool electrode, as the latter does not alter during the ECM process.