The relationship between total current, applied potential, electrolyte flow rate, electrolyte conductivity, and electrode gap in electrochemical machining was investigated experimentally and analytically. An electrolytic cell was designed permitting the electrode gap to be observed and photographed. A 0.25 × 0.375-in. rectangular 1100F aluminum anode was used. Electrode gap varied between 0.013 and 0.033 in. The electrolyte was potassium chloride in concentrations from 0.67 normal to 1.7 normal. Current density range was 40–450 amp/in. and electrolyte flow rate was 0.22 to 0.98 gal/min. The photographs taken of the electrode gap during operation clearly show development of a hydrogen bubble layer next to the cathode. Based upon a mathematical model incorporating the bubble layer, an equation in a nondimensional form has been derived describing the functional relationship between process variables. This equation correlates the experimental data within plus or minus 15 percent. An equation which predicts the local current distribution, and hence anode dissolution rate, along the electrode gap in the direction of electrolyte flow is also presented. Based on the theoretical analysis, optimum operation in electrochemical machining from the standpoint of uniformity of metal removal is discussed.
In electrochemical machining the evolution of gas and heat in the electrolyte results in local variation of the gap between the electrodes. The ability to predict these variations for any given operating condition is a prerequisite of proper design of the cathode tool. This paper provides analytical predictions of the change in gap geometry for the one-dimensional steady-state case. Employing the basic conservation laws, a system of coupled nonlinear differential equations is derived for the gas-electrolyte mixture which flows between the electrodes. The assumption of homogeneity of the two-phase mixture is employed throughout the analysis. Numerical results from the solution of the equations are presented graphically and compared with experimental data. The local variation in gap and the relation between current, gap, and applied voltage compare favorably with the experimental data within the ranges of parameters investigated: current density 45–400 amps per sq in., electrolyte flow rate 0.22–0.98 gpm, entrance gap size 0.015–0.020 in., potassium chloride electrolyte normality 0.67–1.14.
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