Journal of Materials Research and Technology (Sep 2022)
Investigating the effect of different tool electrodes in electric discharge drilling of Waspaloy on process responses
Abstract
Despite the wide application of electric discharge machining in the fabrication of holes in difficult-to-cut materials, the process's performance and accuracy are governed by the choice of an appropriate tool material and process parameters. Moreover, the process becomes less productive due to unstable machining and inadequate debris flushing while drilling high aspect ration holes, resulting in a low material removal rate (MRR) and high average surface roughness (Ra). Further, the holes' accuracy deteriorates due to a high tool wear rate (TWR). To overcome these issues, a rotary tool electrode setup is proposed for the drilling of Waspaloy. The influence of three different tool materials, viz. copper, brass, and graphite, along with various process parameters, was studied on the process performance. The electrical discharge drilling (EDD) operation was performed by varying the input process parameters, viz. current (I), pulse-on-time (TON), pulse-off-time (TOFF), tool electrode speed (TES), and voltage (V), using copper, brass, and graphite tool electrodes. The influence of machining conditions was investigated on response variables, namely, Ra, TWR, and MRR. Taguchi-based L16 orthogonal array was used to design the experiments, and results were analysed using Analysis of Variance (ANOVA). An improvement in the performance of rotary EDD was observed due to proper flushing, efficient debris evacuation, and steady machining condition. The current was found to be the most significant electrical parameter. The graphite tool electrode had shown the highest MRR of 32.056 mm3/min at 25 A current which was 13.09% and 131.32% higher than that of the copper and brass tool electrodes, respectively. However, the graphite tool resulted in a poor surface quality, and a high energy transfer coefficient, indicating the highest Ra value of 8.385 μm. The brass tool electrode, owing to a lower thermal conductivity and melting point, caused a higher TWR than the copper and graphite tools. Finally, the microscopic images for drilled holes with different electrodes at various energy settings were captured using field emission scanning electron microscopy (FESEM) and compared for surface quality. In addition, the surface elemental analysis was performed using Energy Dispersive X-Ray Analysis (EDX) to investigate material migration from the tool electrodes to hole's side walls.
