Predicting radial overcut in deep holes drilled by shaped tube electrochemical machining

Shaped tube electrolytic machining (STEM) is a versatile and relatively low cost process for drilling deep, high aspect ratio holes. Since the radius of a drilled hole is the sum of the tool radius and radial overcut, one crucial aspect of dimensional accuracy is radial overcut. However, models of overcut in the literature are scarce and have primarily been restricted to shallow holes. Moreover these models were purely empirical and therefore restricted in scope. A fundamental mathematical model that uses STEM operating parameters (voltage, tool diameter and feed rate, bare tip length and electrolyte composition) as inputs to predict radial overcut has been developed. Predictions from the proposed radial overcut model are much closer to experimental data compared to those from the models available in the literature. A novel contribution of this study has been the formulation of a methodology to determine the magnitude of current flowing out radially from the bare tip length using experimentally measured total current values.