OCTOBER 19-20, 2012 - YMCA University of Science & Technology

Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012
increase in concentration of impurities. It was reported that machining becomes unstable at an excessive additive
powder concentration due to the occurrence of short-circuits and occurrence of discharges at same spot. Since
then a lot of research work has been done in the area of additive mixed electrical discharge machining and have
shown great effect on process performance in terms of material removal rate, surface characteristics, wear ratio
etc.
Jeswani [13] investigated the effect of suspended fine graphite powder in dielectric medium of electrical
discharge machining on tool steel and reported that addition of about 4 g/l of fine graphite powder (10 μm in
average size) in kerosene increased metal removal rate (MRR) by 60% and tool wear rate by 15%. This was
attributed to better electrical discharge distribution between spark gap.
Mohri and co worker [14] studied the effect of silicon powder in dielectric medium and reported significant
improvement in machining performance. Kumar and Beri studied the effect of graphite powder on surface
quality and reported improved surface finish [15]. The aim of the present research work was to experimentally
evaluate on surface quality improvement in aluminium powder mixed AEDM of Nickel Based Super Alloy 718
with cryogenically treated copper electrode and to find best parametric settings to minimize SR.
2. Experimental Planning and Procedure
Taguchi methodology has been applied to plan and analyze the experiments. The Taguchi method can optimize
performance characteristics through the settings of process parameters and reduce the sensitivity of the system
performance to sources of variation.
Table 1 Process parameters and their levels
Symbol Process parameters units Levels
1 2 3
A Polarity +ve -ve
B Types of electrode Copper Cryogenically
treated copper
C Peak current amps 0.5 3 6
D Pulse on time µs 50 100 150
E Duty cycle τ 0.7 0.8 0.9
F Gap voltage volts 40 60 80
G Retract distance mm 1 2 3
H Concentration of Powder
(300 Mesh size)
g/l 0 6 12
The experimental parameters and their levels selected for present study are tabulated in Table 1 keeping other
parameters constant based on trial experiments and previous studies. In the present study experiments were
carried out on Electronica make electrical discharge machine; model SMART ZNC (S50).
A copper electrode of 8mm φ was subjected to deep cryogenic treatment which consists of a slow cool-down rate
(2.5°C/min) from ambient temperature to the temperature of liquid nitrogen. When the material reached
approximately at −193.15°C it was soaked for 24 hours.
Experiments were performed with O.A L 36 (2 2 x3 6 ). The results were analyzed for minimum surface roughness
with “smaller the better” quality characteristic with Minitab software 15.1.1.The SR was measured in terms of
arithmetic mean roughness of the evaluated roughness profile (Ra in µm) by using a Mitutoyo SJ 400 surface
testing analyzer.
3. Results and Discussions
The S/N ratios of SR for each trial run have been calculated from experimental data and response table for
smaller the better are summarized in Table 2 giving relative importance of each parameter on desired response.
The individual effects of input parameters on the S/N ratios for SR are shown in main effect plot (Fig.2).
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