International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 15 (2016) pp 8507-8510
© Research India Publications. http://www.ripublication.com
Experimental Investigation of Electrical Discharge Machining using
Dielectric Fluid with Surfactant and Different Carbon Additives
Pay Jun Liew a*, Muhammad Raziman Abdul Razak b, Nur Izan Syahriah Hussein c and Qumrul Ahsan d
a,b,c
Manufacturing Process Department, Faculty of Manufacturing Engineering,
d
Engineering Materials Department, Faculty of Manufacturing Engineering,
Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal,
Melaka, Malaysia.
*Corresponding author.
Abstract
In this paper, Electrical Discharge Machining of Reaction
Bonded Silicon Carbide (RB-SiC) was carried out using
dielectric fluid with different surfactant concentrations and
different type of carbon additives. Surfactant concentrations
and types of carbon additives were varied and the machining
performances such as material removal rate (MRR), electrode
wear ratio (EWR), surface roughness and spark gap were
investigated. The experiment results show that the surfactant
and carbon additives added dielectric fluid not only increases
the MRR and spark gap, but also reduces the EWR. In the
case of surface roughness, only 0.4 wt.% surfactant with CNF
produced smoother surface compared to the one obtained with
no surfactant. Among three carbon additives, CNF was more
effective to improve the machining efficiency of RB-SiC with
the optimum surfactant concentration at 0.6 wt.%.
fluids has been investigated extensively, all the previous
works have focused on the high conductivity materials.
Surprisingly, there is no report on a comparative study of
different size and shape of carbon additive on low
conductivity RB-SiC by EDM process.
Therefore, the primary aim of this paper is to compare the
machinability of RB-SiC using different types of carbon
additives, such as carbon nanofiber (CNF), carbon nano
powder (CNP) and carbon powder (CP) on the MRR, EWR,
surface roughness and spark gap. Based on the present
author’s work [8], the addition of surfactant span 80 can
improve the machining efficiency of RB-SiC, especially on
the MRR. Thus, in this study, surfactant span 80 was used to
disperse the various types of carbon additives and its
concentrations were also investigated.
Keywords: EDM, RB-SiC, Dielectric fluid, Surfactant,
Carbon additives
EXPERIMENTAL DETAILS
Sodick AQ35 EDM machine, type die-sinker was used to
conduct the experiments. The workpiece material was RB-SiC
with dimensions of 30 mm x 30 mm x 13 mm, and the tool
was copper electrode with a diameter of 6 mm. Span 80 was
used as a surfactant and mixed into EDM oil type Low Smell
(LS) to disperse the carbon additive. Four different
concentrations of surfactant were investigated, such as 0
wt.%, 0.4 wt.%, 0.6 wt.% and 0.8 wt.%.
There are three different carbon additives, namely carbon
nanofiber (CNF), carbon nano powder (CNP) and carbon
powder (CP) were added into dielectric fluid. The differences
between these three powders lay in their shape and size.
Figure 2 indicates the field emission scanning electron
microscopy (FE-SEM) micrograph of the CNF, CNP and CP,
respectively.
Before the EDM experiment, the required amount of
surfactant, carbon additive and EDM oil were measured and
mixed together. The process started by mixing the EDM oil
with surfactant for 5 minutes to dissolve the surfactant using
ultrasonic homogenizer. Then, carbon additive was added to
the mixture and subjected to ultrasonication process for
another 30 minutes. During the ultrasonic process, the sample
was immersed into ice bath to minimize the temperature rise.
Table 1 shows the experimental conditions and Figure 1
shows the EDM experimental setup. After the machining
process, MRR, EWR, surface roughness and spark gap were
measured as machining responses. An average of four
measurements for each parameter setting was taken.
INTRODUCTION
Electrical Discharge Machining (EDM) is one of the most
promising unconventional machining processes to fabricate
products with high hardness and complex geometrical
profiles. In this process, the workpiece material is removed by
means of repetitive spark discharges between the electrode
and workpiece that submerge in a dielectric fluid [1-2].
To improve the machining capabilities of EDM, powder
mixed EDM (PMEDM) has emerged as one of the advance
method in the past thirty years. In this process, the fine
particles in the powder form are mixed into dielectric fluid to
reduce the insulating strength of dielectric fluid [3]. Many
previous researches have been done using PMEDM method
and pioneer work can be traced to Jeswani [4], who reported
that addition of 10 µm graphite powder can increase the
material removal rate (MRR) and reduce the electrode wear
rate (EWR). Tan and Yeo [5] added 45-55 nm silicon carbide
powders into dielectric fluid, and confirmed the reduction of
recast layer thickness on stainless mould steel. Liew et al. [6]
also tried suspending carbon nanofiber (CNF) in dielectric
fluid and they found that machining efficiency of reaction
bonded silicon carbide (RB-SiC) was improved significantly.
Recently, Marashi et al. [7] observed that after adding Ti
nano-powder to dielectric, the surface morphology, surface
roughness and material removal rate were notably enhanced.
Although the effect of powder additive in various dielectric
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 15 (2016) pp 8507-8510
© Research India Publications. http://www.ripublication.com
Table 1: Experimental conditions
Working Parameter
Workpiece Material
Description
Reaction Bonded Silicon Carbide
(RB-SiC)
Electrode Material
Copper
Diameter Electrode [mm] 6
Polarity
Positive (Workpiece)
Negative (Tool/electrode)
Voltage [V]
22
Peak Current, Ip [A]
6
Pulse On Time, Ton [µs] 10
Pulse Off Time, Toff [µs] 40
Machining Time [min] 15
Additive
Carbon nanofiber (CNF)
Carbon nano powder (CNP)
Carbon powder (CP)
Surfactant
Span 80
Concentration of
0, 0.4, 0.6 and 0.8
Surfactant [wt. %]
Figure 1: EDM experimental setup
RESULT AND DISCUSSION
Material Removal Rate (MRR)
Figure 3 shows the effect of three different additives on the
MRR of RB-SiC. It is clearly seen that the MRR increased
with the increasing of surfactant concentration, except for the
additive CP where there were no significant changes for all
surfactant concentrations. With the presence of a surfactant in
the dielectric fluid, the carbon particles were surrounded by
surfactant molecules which can reduce the electrostatic force
[9]. Due to this phenomenon, the particles can disperse evenly
and cause a better distribution of discharge energy, leading to
a higher MRR. The highest MRR was achieved at a
concentration of 0.6 wt.%, whereby this only occurred for the
additives CNF and CNP. However, the MRR tended to
decrease at the surfactant concentration of 0.8 wt.%.
For comparison, CNF was more effective at improving the
MRR for machining RB-SiC compared to CNP and CP. In
this case, the high electrical conductivity CNF might help to
increase the frequency of discharge, and resulting in an
improvement of MRR [6]. The addition of CNP, which has a
nano size, also induced a higher MRR compared to the CP,
which has a micro size. This result is consistent with that
reported by Chow et al. [10]. Due to the small machining gap
during the EDM process, it is difficult for the larger particles
to enter the gap between the electrode and the workpiece.
Therefore, the material removal rate is lower using the micro
powder grain size than that obtained when applying the nano
powder grain size.
(a)
(b)
(c)
Figure 2: FE-SEM micrographs of different types of additives
(a) carbon nanofiber (CNF), (b) carbon nano powder (CNP)
and (c) carbon powder (CP).
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 15 (2016) pp 8507-8510
© Research India Publications. http://www.ripublication.com
Surface Roughness
Figure 5 illustrates the effect on surface roughness using
different concentrations of the surfactant Span 80 and
different additive powders. The graph shows that without the
use of a surfactant, the value for surface roughness with CNF
was high. However, when a suitable amount of surfactant was
added (0.4 wt.% in this experiment), the surface roughness
showed a decrease. According to Wu et al. [13], when a
surfactant is added to the dielectric fluid, the hydrophilic head
group absorbs on the surfaces of the particles and the
hydrophobic tail will extend to the dielectric, causing these
agglomerated particles separated and well distributed within
the dielectric fluid. Therefore, the electrical discharges are
more distributed and lead to a better surface finish on the
machine surface.
When comparing the types of additives, it can be seen that
lower surface roughness can be achieved using CP particles.
This might be due to the fact that the material is removed
slowly (low MRR) through melting and evaporation, causing
a decrease in crater size; thus the surface finish is improved.
Figure 3: Effect of different carbon additive using different
concentrations of the surfactant Span 80 on the MRR
Electrode Wear Ratio (EWR)
The effect of different concentrations of the surfactant Span
80 with different carbon additives on EWR is shown in Figure
4. For all three additives used in this experiment, the EWR
tended to reduce with the addition of surfactant until a
concentration of 0.6 wt.%. Nevertheless, when the surfactant
further increased to 0.8 wt.%, the EWR tended to increase
again. As known from Rehbein et al. [11], during the
machining, the electron movement is intense, whereby a small
arc that is produced during machining may reverse the
direction of the feed to maintain a larger gap and, as a result,
most negative ions move easily through the machining gap,
resulting in a lower EWR.
In terms of additive powder, it was noticed that the EWR was
lowest when CNF was added to the dielectric fluid, compared
to CNP and CP. This might be related to the good dispersion
of CNF inside the dielectric fluid, producing a higher MRR,
thus decreasing the EWR. The addition of CNF might also
have prevented the ions that were produced by the ionization
of the dielectric fluid from hitting the tool electrode with a
high momentum and high energy, which causes a rapid
erosion of the tool electrode [6]. Moreover, CNP with a
smaller size also shows a lower EWR compared to that of the
micro sized CP. This is attributed to the combined effect of a
low MRR and a high tool wear by large particles [12].
Figure 5: Effect of different carbon additives using surfactant
Span 80 on surface roughness
Spark Gap
The results for the spark gap using different additive powders
and different surfactant Span 80 concentrations are illustrated
in Figure 6. The graph clearly shows that using a surfactant
affected the spark gap in contrast to a dielectric fluid without
surfactant. When surfactants were used, the spark gap
increased significantly. The addition of a surfactant might
prevent the agglomeration of particles, and cause the particles
to be well dispersed within the dielectric fluid. Therefore,
bigger spark gap was obtained.
Moreover, it is worth noting that the highest spark gap was
obtained using the CNF additive compared to CNP and CP.
Presumably, when CNF was added to the dielectric fluid, the
long and thin shape of its particles might be able to more
significantly bridge the gap between the electrode and the
workpiece by interlocking with each other, in contrast to
round-shaped particles of CNP and CP. In addition, when the
CNF was added to the dielectric fluid, the additive reduced the
insulating strength of the dielectric fluid [6] and due to this, a
bigger spark gap was produced between the electrode and the
workpiece.
Figure 4: Effect of different carbon additive using different
concentrations of the surfactant Span 80 on the EWR
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International Journal of Applied Engineering Research ISSN 0973-4562 Volume 11, Number 15 (2016) pp 8507-8510
© Research India Publications. http://www.ripublication.com
[2]
[3]
[4]
[5]
Figure 6: Effect of different carbon additives using surfactant
Span 80 on the spark gap
[6]
CONCLUSION
In this experimental works, EDM machining of RB-SiC was
carried out using dielectric fluid with surfactant and different
carbon additives. The effect of carbon additives in the
presence of different surfactant Span 80 concentrations on the
material removal rate, electrode wear ratio, surface roughness
and spark gap was investigated. The following conclusions
can be drawn:
MRR increases with the increasing of surfactant
concentration and the optimum MRR was achieved
at 0.6 wt.% of surfactant concentration using CNF as
an additive.
Surfactant concentration strongly effects the EWR.
The higher the concentration is, the lower the EWR.
However, there was only a marginal reduction of
EWR using CP additives.
Dielectric fluid with the addition of CNF and 0.4
wt.% of surfactant concentration can lower the
surface roughness of machined surface. For the
additive comparison, both CNF and CNP produced
rougher surfaces than CP.
Adding surfactant in the dielectric fluid can
significantly improve the spark gap, particularly
using CNF additive.
[7]
[8]
[9]
[10]
[11]
[12]
ACKNOWLEDGEMENT
The authors would like to thank the Ministry of Higher
Education Malaysia and Universiti Teknikal Malaysia Melaka
(UTeM) for technical, educational and financial support
through the grant FRGS/1/2014//TK01/FKP/02/F00220.
[13]
REFERENCES
[1]
Kibria, G., Sarkar, B. R., Pradhan, B. B. and
Bhattacharyya, B., 2010, “Comparative Study of
Different Dielectrics for Micro-EDM Performance
during Microhole Machining of Ti-6Al-4V Alloy,”
The Int. J. Adv. Manuf. Tech., 48(5-8), pp. 557-570.
8510
Zeid, O. A., 1997, “On the Effect of
Electrodischarge Machining Parameters on the
Fatigue Life of AISI D6 Tool Steel,” J. Mater.
Process. Tech., 68(1), pp. 27-32.
Kansal, H. K., Singh, S. and Kumar, P., 2007,
“Effect of Silicon Powder Mixed EDM on
Machining Rate Of AISI D2 Die Steel,” J. of
Manuf. Processes, 9(1), pp. 13-22.
Jeswani M.L., 1981, “Effect of the Addition of
Graphite Powder to Kerosene used as the Dielectric
Fluid in Electrical Discharge Machining,” Wear, 70,
pp. 133-139.
Tan, P. C. and Yeo, S. H., 2011, “Investigation of
Recast Layers Generated by a Powder-Mixed
Dielectric Micro Electrical Discharge Machining
Process,” P.I. Mech. Eng., Part B: J. of Eng.
Manuf., 225(7), pp. 1051-1062.
Liew, P. J., Yan, J. and Kuriyagawa, T., 2013,
“Carbon Nanofiber Assisted Micro Electro
Discharge Machining of Reaction-Bonded Silicon
Carbide,” J. Mater. Process. Tech., 213(7), pp.
1076-1087.
Marashi, H., Sarhan, A. A. and Hamdi, M., 2015,
“Employing Ti Nano-Powder Dielectric to Enhance
Surface Characteristics in Electrical Discharge
Machining of AISI D2 Steel,” Appl. Surf. Sci., 357,
pp. 892-907.
Abdul Razak, M. R., Liew, P. J., Hussein, N. I. S.,
and Ahsan, Q., 2016, “Effect of Surfactant on EDM
of Low Conductivity Reaction-Bonded Silicon
Carbide,” Key Eng. Mat., Vol. 701, pp. 107-111.
Feng, J. Q. and Hays, D. A., 2003, “Relative
Importance of Electrostatic Forces on Powder
Particles,” Powder Technol., 135, pp. 65-75.
Chow, H. M., Yang, L. D., Lin, C. T. and Chen, Y.
F., 2008, “The use of SiC Powder in Water as
Dielectric for Micro-Slit EDM Machining,” J.
Mater. Process. Tech., 195(1), pp. 160-170.
Rehbein, W., Schulze, H. P., Mecke, K.,
Wollenberg, G. and Storr, M., 2004, “Influence of
Selected Groups of Additives on Breakdown in
EDM Sinking,” J. Mater. Process. Tech., 149(1), pp.
58-64.
Tzeng, Y. F. and Lee, C. Y., 2001, “Effects of
Powder Characteristics on Electrodischarge
Machining Efficiency,” The Int. J. Adv. Manuf.
Tech., 17(8), pp. 586-592.
Wu, K. L., Yan, B. H., Lee, J. W. and Ding, C. G.,
2009, “Study on the Characteristics of Electrical
Discharge Machining using Dielectric with
Surfactant,” J. Mater. Process. Tech., 209(8), pp.
3783-3789.