Electrochemical Micromachining of Stainless Steel by Ultrashort Voltage Pulses

Abstract

Stainless Steel / Microstructures / Microfabrication / Electrochemistry / Short Voltage PulsesApplication of ultrashort voltage pulses to a tiny tool electrode under suitable electrochemical conditions enables precise three-dimensional machining of stainless steel. In order to reach submicrometer precision and high processing speed, the formation of a passive layer on the workpiece surface during the machining process has to be prevented by proper choice of the electrolyte. Mixtures of concentrated hydrofluoric and hydrochloric acid are well suited in this respect and allow the automated machining of complicated three-dimensional microelements. The dependence of the machining precision on pulse duration and pulse amplitude was investigated in detail.

Discussion of ultrashort voltage pulses electrochemical micromachining: a review

“…The time of double layer charging to the activation overpotential depends on gap thickness, therefore, the voltage pulse length can define the spatial resolution of machining (pulse time determine how far from the tool workpiece surface reach activation overpotential). According to the Butler-Volmer equation (valid only in an active state of dissolution), the current density i is exponentially related to the overpotential, therefore, a small change of the electrode potential leads to a large change of the current density, thus the additional effect of dissolution localization occurs [6,18,19,40]. Such an effect is irrelevant in machining with a longer pulse time (t i > 0, 5 μs) because the double layer is charged uniformly over the machining surface, and machining is carried out in the diffusionlimited state (the current density is determined by transport phenomena in the gap).…”

“…For example, for 1.4301 steel thickness of lateral gap ≈200 nm and edge radius ≈1 μm was obtained [6]. Therefore, the amount of research works in this field have increased significantly.…”

“…Moreover, for pH < 2 oxide layers do not form and with change of electrode potential during dissolution a change of iron dissolved ions valence from Fe 2+ to Fe 3+ take place. For these reasons, application of acid electrolyte is one of the main condition for correct ns-PECM process [6,16]. To prevent corrosion is such a system anode and cathode have negative potential (−200 mV) in relation to reference electrode.…”

Design of a pulse power supply unit for micro-ECM

“…Most of the solutions implemented for that purpose, measure the current flowing through the system via a sensing resistor in series with the gap. Moreover, the measured current can be used to control the IEG [7,22,[28][29][30][31].…”

“…The dissolution process can be accurately confined by setting the pulse duration according to the charging time of the EDL [2][3][4][5][6]. The frequency and the pulse duration are respectively higher and shorter than in initial PECM [7,8]. This process requires a pulse power supply unit (PSU) that is able to deliver pulses at very high frequency with an adjustable pulse duration.…”