Comparative Analysis of the Process Mechanics in Micro-Electrical Discharge Machining (EDM) and Reverse Micro-EDM

Abstract

The objective of this paper is to study the time-evolution of the process mechanics for micro-electrical discharge machining (MEDM) and reverse-micro-electrical discharge machining (R-MEDM), as a function of key system parameters, viz., voltage, capacitance, and threshold of the spark circuit. Full factorial experiments have been performed to quantify the aforementioned system parameters on the MEDM and R-MEDM processes. The process monitoring voltage and current signals, material erosion rate and the surface roughness values are the machining responses of interest. The voltage and current (V-I) signals reveal information about the material erosion rate and the extent of debris-interference associated with the corresponding process. Analysis of the V-I signals shows that R-MEDM is more stable than MEDM and can therefore be operated at aggressive conditions of capacitance and voltage. R-MEDM also results in higher material erosion rates but the resulting surface has a higher surface roughness value than that generated by MEDM. A debris deposition mechanism is proposed for R-MEDM that suggests debris entrapment and subsequent welding to the machined feature to be the reason for the increased surface roughness.

Experimental investigation into the micro-EDM characteristics of conductive SiC

“…Figure 26 shows superimposed element maps of machined workpiece. It is clear from maps that distribution of copper and carbon was uniform on the surface and no segregation was found on the machined 13 surface. The Si being a constituent element of workpiece was distributed uniformly.…”

“…6) obtained during machining cycle indicate the dynamically changing machining conditions at toolworkpiece interface. Mastud et al [13] obtained the current and voltage signals after 5 min into the machining cycle with machining parameters of 120 V, 10 nF and 20 %. In Figure 6, region AB denotes open circuit condition when the tool is approaching towards the workpiece.…”

“…The timing of the next spark is determined by threshold value. A higher threshold value results in more number of charging-discharging cycles of the capacitor over a fixed time interval and vice versa [13].…”

“…On the contrary, in EDM process, material removal is maximized by adjusting process parameters. The effective process parameters in micro EDM are gap voltage, capacitance and threshold [13]. Furthermore, electrodes do not come into contact during the process which makes it possible to use miniature electrodes to perform micro machining on difficult to cut materials.…”

“…Furthermore, Figure 19 (b) and (c) show that at higher threshold; combination of low voltage and low capacitance gives low residual stresses. This could be due to the fact that at higher threshold value, number of capacitor discharges will be more [13] but at the same time each spark will have less energy due 12 to low voltage and capacitance. Hence, sudden local expansion and contraction of material is prevented due to less spark energy and thus, lower residual stresses are observed.…”