A comparative study on the surface integrity of plastic mold steel due to electric discharge machining

Abstract

The violent nature of the electric discharge machining (EDM) process leads to a unique structure on the surface of a machined part. In this study, the influence of electrode material and type of dielectric liquid on the surface integrity of plastic mold steel samples is investigated. The results have shown that regardless of the tool electrode and the dielectric liquid, the white layer is formed on machined surfaces. This layer is composed of cementite (Fe 3 C) and martensite distributed in retained austenite matrix forming dendritic structures, due to rapid solidification of the molten metal, if carbon-based dielectric liquid is used. The intensity of cracking increases at high pulse durations and low pulse currents. Cracks on the EDM surfaces have been found to follow the pitting arrangements with closed loops and to cross perpendicularly with radial cracks and continue to propagate when another discharge takes place in the neighborhood. The amount of retained austenite phase and the intensity of microcracks have found to be much less in the white layer of the samples machined in de-ionized water dielectric liquid. The number of globule appendages attached to the surface increased when a carbon-based tool electrode material or a dielectric liquid was used during machining.

White Layer Composition, Heat Treatment, and Crack Formation in Electric Discharge Machining Process

“…[14] The crack density is inversely proportional to the thermal conductivity of the work material, [15] and as the content of carbon within the white layer increases from the dielectric liquid, surface crack intensity increases very rapidly. [16] Surface cracks initiate from the surface and propagate in a vertical direction toward the parent material. While the majority of these cracks terminate within the recast layer, or at the interface between the recast layer and the base material in severe instances, cracks may penetrate into the parent material itself.…”

Surface Morphology of Die-Steel Machined with Al Powder Mixed Distilled Water and Kerosene in Edm A Comparison

“…During machining of Ti-6A-4V, TiClayer formed with kerosene and TiO layer with distilled water distilled water dielectric fluids 12 . It is also found that machining with de-ionized water the intensity of micro-cracks are less in the white-layer than the base material 13 .…”

Micro Eletro Discharge Milling for Microfabrication

“…The presence of high crack density is not desirable because it leads early product failure. Investigation of EDM parameters showed that higher pulse-on duration increased both the average white layer thickness and the induced stress (Lee and Tai, 2003;Ekmekci et al, 2005). These two conditions tend to promote crack formation.…”