'Dry' [ 1 Argon 1 Argon gas 1 EN31 1 Electric discharge machining 1 Electric discharges 1 En31 1 Gap voltage 1 Gas medium 1 Gas pressures 1 Graphite 1 Graphite-argon gas medium 1 Microcracks 1 Microhardness 1 Multiobjective optimization 1 Surface roughness 1 Taguchi method 1 Taguchi methods 1 Taguchi's methods 1 WPM 1 Weight product method White layer thickness 1 gas pressure 1 graphite-argon gas medium 1