A Discharge Separation Model for Powder Mixed Electrical Discharge Machining

Abstract

Added powders in a dielectric medium substantially influence the features of electrical discharges due to altered interelectrode conditions during the electrical discharge machining (EDM) process. The main discharge channel is disturbed due to the added powders in dielectric liquid and leads formations of secondary discharges. Such altered discharge conditions generate a unique topography on the machined surface and consequent subsurface microstructure beneath it. Ti6Al4V work material machined using SiC powder mixing in de-ionized water for an extensive set of pulse-on duration and pulse currents. Then, different forms of secondary discharges were identified from the resultant surface features and corresponding subsurface microstructures. The results pointed out that generation of unevenly separated secondary discharges increased the material transfer rate from the powder mixed dielectric liquid to the machined surface by means of the decomposed ions in the plasma channel. Complete separation of the main discharge channel into evenly distributed secondary discharges is possible under specific machining conditions that suggested minimal deformation of the machined surface regarding microcracks, roughness, and heat affected layer thickness. Under such machining conditions, another means of material transfer mechanism is activated that lead a powder particle build-up process on the machined surface. Consequently, five different discharge forms were proposed to describe the resultant surface topographies and subsurface microstructures. The material migration phenomena and the mechanisms are discussed in relation to the pulse-on time and pulse current.

Particle migration and surface modification on Ti6Al4V in SiC powder mixed electrical discharge machining

“…Therefore, it could be concluded that the changes on the machined surface are directly associated powder concentration in the dielectric liquid as well as the electrical parameters such as pulse on time and current. In the previous study [19] several discharge channel separation forms were suggested in the view of surface textural changes and subsurface heat affected layers for a wide variety of electrical parameters but constant powder concentration in PMEDM. The thickness of the re-solidified layer increases with the generation of single or unevenly distributed discharges during machining.…”

“…SiC powder addition in water dielectric liquid revealed various types of topographical features on Ti-6Al-4V surfaces suggesting machining is accompanied by subdivided electrical discharges in different forms [18,19]. Moreover, the material migration phenomenon from the dielectric liquid and the built up to the machined surface was also closely related to the forms of discharges.…”

A comprehensive review on metallic implant biomaterials and their subtractive manufacturing

“…Therefore, researchers have attempted to develop manufacturing processes that can produce miniaturized medical parts and assemblies in recent years, leading to relatively quicker healing and greater patient comfort [ 234 ]. Hence, the researchers were led to establish the powder mixed-micro-EDM (PM-µ-EDM), a downscaled form of PM-EDM with a smaller process variables’ domain including tool electrode diameter in the submillimeter range, for obtaining miniaturized components of various complex to machine materials, including Ti and Ti alloys [ 235 ]. The most recent study on PM-µ-EDM of TiNi SMA presented the favorable effect of TiC powder at 5 g/l powder particle concentration on the recast layer of improved microhardness 438.7 HV, suggesting its use in orthodontic applications [ 236 ].…”

Study on Powder Mixed Elecrtical Discharge Machining Process: A Review

“…The stirring system ensures the proper mixing of powder particles in dielectric and avoids settlement of powder at bottom of tank (Ekmekci et al, 2016;Rajendra and Rao, 2014;Rouniyar and Shandilya, 2019a). Figure 3 (Gugulothu et al, 2015;Marashi et al, 2015;Rouniyar and Shandilya, 2019a).…”