Electrochemical micromachining of passive electrodes

The electronic model describing the electrochemical micromachining (ECMM) of passive electrodes utilizing the transpassive dissolution is discussed. Numerical simulations are performed on a machining model circuit using measured electrochemical properties of the model system which consisted of a tungsten tool electrode, a 1 M H2SO4 electrolyte and a stainless steel work piece electrode. The results of these simulations were verified by performing machining experiments applying the same model system. For a passive stainless steel electrode it is shown that it can be treated like an actively dissolving electrode with high reaction overpotential. The efficiency of the machining process can be enhanced by polarizing the steel work piece electrode close to the transpassive potential region. Three different ways of achieving this polarization are discussed: by polarizing the work piece electrode only, by polarizing both electrodes and by adding oxidizing species to the electrolyte solution.