Multi-objective optimization of hole dilation at inlet and outlet during machining of CFRP by μEDM using assisting-electrode and rotating tool

Machining of carbon fiber-reinforced polymers (CFRP) by traditional processes is quite challenging as damages namely breakage of fibers, delamination, and fiber pull-out occur during machining. Therefore, non-traditional machining process namely micro-electrical discharge machining (μEDM) is emerging to produce precise and high-quality features in CFRP. In this work, for machining CFRP, μEDM method coupled with rotary tool and assisting-electrode was used for efficient spark generation. Grey relational analysis (GRA) was performed to optimize the machining parameters viz. voltage (100, 130, 160, and 190 V), pulse duration (10, 20, 30, and 40 μs), and tool speed (200, 300, 400, and 500 RPM) that affect the output responses namely hole dilation at inlet (HD_in) and outlet (HD_out). The optimal condition of input parameters was found to be V1/T1/S1 (100 V/10 μs/200 RPM). The voltage was observed to be the most affecting factor with a contribution of 90.95% while tool speed and pulse duration had a contribution of 5.91% and 1.48%, respectively. It was also found that the material removal mechanism was a complex phenomenon where sparking occurred both at end face and side surface of the tool. The deposition of pyrolytic carbon particles that helps in continuing the sparking was observed in the micrographic images obtained through field emission scanning electron microscope (FESEM). The burning of the matrix due to thermal effect and spalling was also evident which led to the removal of the material from the composite.