The use of a segmented tool for the analysis of electrochemical machining

A planar workpiece/planar segmented tool experimental configuration has been used to collect current-time data for the electrochemical machining (ECM) of Inconel 718 (In718) and stainless steel (SS316). As with previous measurements, theoretical analysis of the chronoamperometric data has been used to obtain values for the characteristic parameters of ECM under characteristic machining conditions, but the segmented tool allows this for each segment. These parameters are the valency, n, and k, from which the minimum voltage required to initiate machining, V-0, and the electrolyte conductivity, kappa can be obtained. The variation of n, V-0 and kappa between segments enables ECM conditions along the flow path length to be probed. Measurements on In718 in nitrate electrolyte have shown a small increase in electrolyte conductivity along the flow path. Tool segments which overlap the workpiece ends have been employed to measure edge effects in the ECM process; no significant edge effects were found when machining In718 in nitrate. The temporal and spatial dependences of a change in valency previously observed during the machining of SS316 have also been studied for the first time. Regions of low valency (n = 2.1) dissolution (downstream) and high valency (upstream, n = 3.0) dissolution were observed, with an intermediate region with monotonically decreasing valency where 3.0 > n > 2.1.