Investigating the Performance of EDM Process using Tool Rotation Methodology for Machining INCOLOY 800HT

Electrical discharge machining (EDM) being one of the most earliest and accepted nonconventional machining process is used in achieving intricate shapes in difficult to machine materials. Material removal rate (MRR) is one of the machining performances measures which are always discussed while adopting any machining process. In this paper tool rotation methodology has been adopted to observe the effect on MRR while machining INCOLOY 800HT using EDM. The experimental results show that tool rotation improves the MRR of the machined material. Keyword-Electric discharge machining (EDM), INCOLOY 800HT, Response surface methodology (RSM), Box-Behnken, Material removal rate (MRR)

shows the various input parameters at three different levels.  Total 30 numbers of experiments were performed, 15 each for stationary and rotary tool conditions. TABLE  3 and TABLE 4, shows the experimentally obtained values for material removal rate for stationary and rotational tool EDM process.  ( 1 ) III. DATA ANALYSIS AND DISCUSSION As per the experimental data obtained, it is clear that the MRR increases with the use of electrode rotation while machining the work piece with the help of EDM process. Rotation of the electrode helps in solving the flushing difficulty which arises during machining hole of small diameter with EDM process [8]. Flushing is improved by pumping effect of the dielectric through the gap. This not only increases the MRR but also produces hole of better quality compared to stationary electrode [9]. For better understanding of the experimental results, a comparative graph between MRR for stationary tool EDM and MRR for rotational tool EDM is plotted against the standard order of the experiment. From Fig. 2, it is seen that MRR during rotary EDM process is increased as compared to stationary process.

Fig.2. MRR vs Standard Order
Better MRR is obtained with the electrode rotation where molten material is frequently cleared from the melt pool. As due to better flushing during electrode rotation technique, there is no left over molten material between the work piece and the tool, spark intensity increases, which in turn causes more surrounding material to melt. Hence, material in the vicinity of the spark gets melted and frequent flushing by the flow of the dielectric helps in improved MRR.

A. Recast Layer Analysis for Stationary EDM
Recast layer Analysis for INCOLOY 800HT has been carried out using a scanning electron microscope. The images observed by the SEM process suggest that the recast layer thickness is not uniform. The obtained images are at a magnification level of 1000 times the original size. From the Fig. 3 it can be seen a lot more microcracks as compared to the rotary tool.

B. Recast Layer Analysis for Rotary EDM
From the Fig. 4 it is observed that there are less micro-crack on the work piece as compared to stationary EDM process. This is due to the fact that flushing system is improved in the rotary process carrying away the debris from the work piece with the dielectric flow, whereas, in the case of Stationary EDM debris remains on the surface and after hardening forms a recast layer with several micro-cracks on the work piece surface.

IV. CONCLUSION
In this research paper an attempt has been made to experimentally analyze the effect of tool rotation process over stationary tool process while machining INCOLOY 800HT using EDM. From the obtained results it is concluded that rotary tool EDM gives a better MRR with less micro-cracks on the machined surface. This happens due to better flushing of the debris which results in less molten material deposition on the work piece surface. As there is lesser molten material deposition on the work piece surface, the hardened layer after solidification is almost half of that in stationary tool EDM, hence minimizing the chances of micro-cracks to appear on the work piece surface.