OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 1 2024 scale with a minimum count of 0.001 g both before and after machining. The material removal rate was calculated using Eq. 1. 1 2 ñ W W MRR T æ - ÷ö = ç ÷ ç ÷ çè ´ ø , (1) where W1 is the mass of the workpiece before machining, (g); W2 is the mass of the workpiece after machining, (g); ρ is the density of the workpiece, (gm/cm3); T is the cycle time, (min). Fig. 1. Experimental set-up Ta b l e 1 Design variables Parameters Performance measures Gap current (A): 8, 10, 12,14 16 Material removal rate, white layer thickness, and crack length Magnetic strength (T): 0, 0.124, 0.248, 0.372, 0.496 Pulse on time: 38 μs Gap voltage: 55 V Pulse off time: 7 μs Dielectric: Commercial EDM oil Flushing pressure: 0.5 Kg/cm2 Polarity: Workpiece (-ve); Tool electrode (+ve) The thickness of the white layer of each specimen was examined at 850× magnifi cation using a scanning electron microscope. Next, the treated surfaces of the specimens were examined at 1000× magnifi cation and surface cracks on the bottom and walls of the holes were measured. Using electrolytic copper tool electrodes, square holes with a depth of 5 mm from the surface were created on untreated BeCu alloy parts. Figure 1 shows the experimental setup, which consisted of a BeCu workpiece, copper tool electrode, and magnets used for experimentation. A BeCu workpiece drilled with square holes with copper tool electrodes and magnets in the cutting zone. Experiments were carried out to understand the eff ect of cryogenic treatment of the workpiece and tool electrodes, along with the gap current and external magnetic strength, on the material removal rate. Thus, the experiments were carried out in two stages: a pilot study and main experiments based on the Box–Behnken design. To study the eff ects of the process parameters on the performance characteristics, the design variables are listed in Table 1.
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