Aqueous Solutions of Organic Compounds as Dielectrics for EDM Sinking

Abstract

Use of aqueous solutions of organic compounds as a medium for EDM sinking almost completely excludes any fire hazard, permitting safe operation of plant in the second and third shifts. Although addition of organic compounds often considerably increases the attainable removal rate as compared to that for pure deionized water, the removal rate at low concentrations remains significantly less than that possible with hydrocarbons. This drawback must be seen in relation to the advantage that relative wear at high discharge currents is practically halved. Additionally, surface roughness is lower when water dielectrics are used, although the corrosive effect of aqueous working media must be taken into account when processing steels. In the present study, the best results were obtained with a highly concentrated aqueous glycerine solution. Working media containing glycerine are at an advantage as compared to hydrocarbon dielectrics when working with long pulse durations and high pulse duty factors and discharge currents, i.e. in the roughing range with high open-circuit voltages and a positively polarised tool electrode. A change to graphite electrodes permitted a further significant improvement in working results. The glycerine dielectric proved superior to the hydrocarbon medium for roughing at optimised parameters in the parameter range under investigation.