Investigation on material removal mechanism in mechano-electrochemical milling of TC4 titanium alloy

Abstract

With the advantages of electrochemical milling (ECM) and conventional milling (CM), mechano-electrochemical milling (MECM) is effective for shaping titanium alloys. However, previous research failed to clarify the mechanism for material removal in MECM, seriously limiting its further application. This work focuses on an in-depth investigation of the material removal mechanism in the MECM of TC4 titanium alloy. There are three material removal processes in MECM, and a model for each is established. To generalize the MECM material removal mechanism, the first (vff) and second (vsf) critical feed speeds are defined: when the feed speed is less than vff, the MECM material removal process is that of ECM; when the feed speed is between vff and vsf, the process is that of ECM→CM→ECM; when the feed speed exceeds vsf, the process is that of CM→ECM. The surface morphologies of solid products during MECM at different feed speeds are also consistent with the proposed MECM material removal mechanism. When the MECM material removal process is ECM→CM→ECM, the difference in material removal rate between MECM and pure ECM is the largest, showing the higher machining efficiency of MECM. Also established is a mathematical model for calculating the relative contributions of ECM and CM during MECM. In addition, compared to 304 stainless steel, the machined surface of TC4 titanium alloy is poor; this is due mainly to the strong self-passivation of titanium in NaNO3 solution, and this aspect must be improved in future work.