Transitions of micro-EDM/SEDCM/micro-ECM milling in low-resistivity deionized water

• Criteria for transitions of micro-EDM/SEDCM/micro-ECM milling are identified.
• SEDCM milling is only attained at moderate feedrate.
• Material removal mechanisms of three typical machining modes are demonstrated.

Owing to its slight conductivity, deionized water has been used as a bi-characteristic fluid to combine micro-EDM and micro-ECM milling in a unique machining process which has been named as SEDCM milling. To attain both electrical discharge and electrochemical reaction during machining, selection of machining parameters such as feedrate and layer depth has been empirically observed to be of prime importance. This paper presents an analytical model to identify the critical conditions for transitions of material removal mechanisms in this hybrid machining process. The criteria for three distinct machining modes micro-EDM/SEDCM/micro-ECM milling are determined based on the thickness of material layer that electrochemical reaction could dissolve when the electrode scans over the surface. The critical feedrate for transitions of material removal mechanisms are then predicted using double layer theory, Butler–Volmer equation and Faraday's law of electrolysis. Experimental tests were also performed to validate the proposed model. It has been established that the SEDCM milling is only attained at moderate feedrate. For high feedrate, machining mode is changed to micro-EDM milling alone when the thickness of material layer that electrochemical reaction could dissolve is smaller than the roughness of micro-EDMed surface. On the contrary, for low feedrate, material removal mechanism is converted to pure micro-ECM when the thickness of layer dissolved by electrochemical reaction is higher than the preset layer depth. In addition, it is also found that lower feedrate is required for SEDCM milling when higher layer depth is used because more material needs to be removed by the sparks in every feed.