Geometry and surface damage in micro electrical discharge machining of micro-holes

Abstract

Geometry and subsurface damage of blind micro-holes produced by micro electrical discharge machining (micro-EDM) is investigated experimentally to explore the relational dependence with respect to pulse energy. For this purpose, micro-holes are machined with various pulse energies on plastic mold steel samples using a tungsten carbide tool electrode and a hydrocarbon-based dielectric liquid. Variations in the micro-hole geometry, micro-hole depth and over-cut in micro-hole diameter are measured. Then, unconventional etching agents are applied on the cross sections to examine micro structural alterations within the substrate. It is observed that the heat-damaged segment is composed of three distinctive layers, which have relatively high thicknesses and vary noticeably with respect to the drilling depth. Crack formation is identified on some sections of the micro-holes even by utilizing low pulse energies during machining. It is concluded that the cracking mechanism is different from cracks encountered on the surfaces when machining is performed by using the conventional EDM process. Moreover, an electrically conductive bridge between work material and debris particles is possible at the end tip during machining which leads to electric discharges between the piled segments of debris particles and the tool electrode during discharging.

Influence of discharge energy on machining characteristics in EDM

“…It is used for machining complex geometry workpieces and difficult-to-machine materials, for which conventional methods are not applicable. The use of EDM is especially essential for the accurate production of forming tools, prototype parts, micro parts and other highly specialized products [2,3].…”

Experimental Investigation on the Electrode Specific Performance in Micro-EDM of Die-Steel

“…A numerical model has been developed, and it has been concluded that increase in pulse on-time shows increase in white layer thickness and depth of HAZ. Ekmekci et al [13] reported that when deionized water is used as dielectric fluid only minimum amount of retained austenite phase and the intensity of microcracks are identified in the white layer of the plastic mold steel than with kerosene as dielectric. It is possible that pickup of carbon can induce brittleness=cracking, sulphur in kerosene can also cause damage in HAZ.…”

Research on Shape Changes in Cylinder Electrodes Incident to Micro-EDM

“…End-tip concavity under specific machining conditions is first encountered [14]. Such concavities are also measured [15], and similar tip formations have been observed with low pulse energy [16].…”