Optimization of process parameters on edm of ti 6 al-4v- materials today paper

Optimization of process parameters on EDM of titanium alloy
Bhiksha Gugulothu
Department of Mechanical Engineering, Malla Reddy Engineering College (Autonomous), Maisammaguda, Secunderabad, Hyderabad, Telangana 500100, India
a r t i c l e i n f o
Article history:
Received 6 September 2019
Received in revised form 28 September
2019
Accepted 26 October 2019
Available online xxxx
Keywords:
Electrical discharge machining (EDM)
Titanium alloy (Ti-6Al-4V)
Discharge current
Pulse on time
Pulse off time
Dielectric fluid
a b s t r a c t
In this research paper, the effect of process parameters on electrical discharge machining (EDM) of Ti-6Al-
4V has been investigated. The process parameters were discharge current, pulse on time, pulse off time
and three types of dielectric fluid were used, they were deionized water, drinking water and mixed (25%
deionized water with mixing of 75% drinking water) has been used for machining of Ti-6Al-4V.
Experiments were carried out using Taguchi L27 (313
) Orthogonal Layout. The output process performance
was material removal rate (MRR) and surface roughness (Ra) was evaluated. Taguchi methodology were
used to optimize the process parameters. It has been observed from the analysis, drinking water as
dielectric fluid shows maximum material removal rate and reduced the surface roughness. The maximum
material removal rate of Ti-6Al-4V was 5.46 mm3
/min and minimum surface roughness was 2.53 mm.
Ó 2019 Elsevier Ltd. All rights reserved.
Selection and Peer-review under responsibility of the scientific committee of the First International
Conference on Recent Advances in Materials and Manufacturing 2019.
1. Introduction
EDM is termed as Electrical Discharge machine which is a
machining process of combination of electro-thermal energy
whereas the electrical energy is utilized to generate an electrical
spark [1]. The purpose of using EDM is to remove the material
and to shape the material [2] from the work piece as we required.
The thermal energy is generated due to the high electrical energy
[3] of the machine. Using this generated thermal energy and elec-
trical energy [4], the material is to be molten and the unwanted
portion of the material is to be removed [5] from the work piece.
The material used in the EDM must have the high strength temper-
ature resistant alloys [6] and also electrically conductive. In EDM,
the work piece and tool should be [7] electrically conductive. Both
of these materials [8] were immersed in dielectric medium [9] like
deionized water or kerosene [10]. The workpiece and tool [11] is
separated by some distance. After this some voltage [12] or poten-
tial difference is applied between the tool and workpiece [13].
Based on the gap between workpiece and tool and the amount of
potential difference [14] applied, the electric field is to be estab-
lished [15]. Normally, this setup is having the positive terminal
[16] and also the negative terminal. The tool is connected to the
negative terminal of the generator and also the work piece is con-
nected to the positive terminal of the generator. Because the elec-
tric field is induced between the tool and workpiece, [17] the free
electrons created in the tool are applied to electrostatic forces. If
the bonding energy between material and work piece of the elec-
trons [18] is less, then a quantity of electrons is emitted from the
tool and this emitted electron is known as cold emission. Then
the emitted cold electrons are moving towards the work piece
via the dielectric medium and get the velocity and energy. After
moving towards the workpiece, [19] there is a collision is induced
between the electrons and dielectric molecule and this collision
may cause the ionization of the dielectric medium which is based
on the bonding energy of the molecule and an electron. Due to col-
lision, more amounts of negative and positive ions are accelerated
[20]. This process will enhance the concentration of the ions and
electrons in the dielectric medium between work piece and tool
[21]. The matter presented in the channel is known as plasma
and the electrical resistance [22] of this is very low. Then unfortu-
nately, huge quantity of electrons and ions are to be flow from the
tool and the workpiece [23]. This movement of electrons is called
as avalanche motion of electrons. Such movement is to be create
an electrical spark and the amount of energy is to be dissipated
in the form of heat in spark. The high velocity electrons are fall
on the workpiece and ions on the tool. The kinetic energy of the
ions and electrons are impact with the surface of the workpiece
and tool respectively and to be converted into thermal energy or
heat flux. Such intense localized heat flux leads to extreme instan-
taneous confined rise in temperature and to material removal
which would be in excess of 10,000 C [24]. The schematic diagram
https://doi.org/10.1016/j.matpr.2019.10.150
2214-7853/Ó 2019 Elsevier Ltd. All rights reserved.
Selection and Peer-review under responsibility of the scientific committee of the First International Conference on Recent Advances in Materials and Manufacturing 2019.
E-mail address: bhikshamg@gmail.com
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings
journal homepage: www.elsevier.com/locate/matpr
Please cite this article as: B. Gugulothu, Optimization of process parameters on EDM of titanium alloy, Materials Today: Proceedings, https://doi.org/
10.1016/j.matpr.2019.10.150

of the Electrical Discharge Machining used in this research is illus-
trated in Fig. 1.
2. Selection of the work piece material, electrode material and
types of dielectric fluid
The workpiece material employed in this study is Ti-6Al-4V.
Copper was used as an electrode material, drinking water, deion-
ized water and combinations (25% deionized water + 75% drinking
water) were used as dielectric fluids. The chemical composition
and properties of Ti-6Al-4V were shown in Tables 1 and 2, respec-
tively. The dielectric fluid characteristics of drinking water, drink-
ing water properties and deionized water properties were shown
in Tables 3–5. The experimental setup used for conducting actual
experiments is given in Fig. 2.
2.1. Identification of the important EDM process parameters
The most important EDM Process parameters identified were
discharge current, pulse on time. Pulse of time and dielectric fluids
were used.
2.2. Determination of the levels for the process parameters and their
working range
The working range of the selected process parameters under the
present study is given in Table 6.
2.3. Selection of orthogonal array
In the present analysis, an L27 (31 3
) orthogonal array is selected.
The selected orthogonal array is presented in Table 7.
2.4. The response measures (i.e. MRR and SR)
The EDM responses was measured in terms of MRR, SR.
The MRR can be calculated as the following formulae.
Fig. 1. Schematic diagram of EDM machine.
Table 1
Chemical Composition of Ti-6Al-4V.
Element C Al V N O Fe H Ti
% Max. 0.08 5.5–6.5 3.5–4.5 0.05 0.13 0.25 0.01 Balance
Table 2
Properties of Ti-6Al-4V.
Property Quantity
Hardness (HRC) 32–34
Melting point (°C) 1649
Density (g/cm3
) 4.5
Ultimate tensile strength (MPa) 897–1000
Thermal conductivity (W/m°K) 7.2
Specific heat (J/kg°K) 560
Mean coefficient of thermal expansion 100 °C/°C 08.6x10-6
Volume electrical resistivity (ohm-cm) 170
Elastic Modulus (GPa) 114
Table 3
Characteristics of Drinking water.
Characteristic Value
Appearance Clear and Colorless
Specific gravity at 30 °C 1.0004
Flash point (°C) –
Pour point (°C) 3
Viscosity at 38 °C (cst) 0.78
Copper corrosion Not worse than 1
Dielectric strength (KV/min) –
Table 4
Drinking water properties.
Total dissolved solids 98 mg/l
Total Suspended solids 10 mg/l
Total solids 120 mg/l
Dissolved O2 7.0 mg/l
Dissolved CO2 9 mg/l
Dissolved N2 0.01 mg/l
Chlorides 20.7 mg/l
Sulphate 32.0 mg/l
Total alkalinity 34.0 mg/l
pH 6.55
Total hardness 55.1 mg/l
Resistivity at 25 °C 4000 O/cm3
2 B. Gugulothu / Materials Today: Proceedings xxx (xxxx) xxx
10.1016/j.matpr.2019.10.150

MRRðmm3
=minÞ ¼
WWL gð Þ Â 1000
qðg=cm3Þ Â machining timeðminÞ
q = Density of work piece material
The SR is referred to the roughness or smoothness and it was
measured by surface roughness tester. MRR and SR was evaluated
for all the conditions and presented in Table 8.
MINITAB 17 software was used to prepare mean of response
tables and mean of S/N graphs for MRR and SR.
Taguchi method allows evaluation of individual parameters
effects independent of the other parameters for process parame-
ters optimization. The design parameters prominently affecting
the performance measures were determined by using analysis of
variance (ANOVA).
In Fig. 3. Where S/N ratio was larger to better was considered
for MRR. In Fig. 4 S/N ratio was lower to better was considered
for SR.
Fig. 4 shows the S/N response graph for surface roughness.
Significance of each parameter were found by using percentage
of contribution of each parameters in ANOVA table. High percent-
age contribution of process parameters on EDM has prominent
effect on the response. ANOVA was applied to find out the signifi-
cance of main factors and the percentage of contribution were used
to analysis the process parameter significantly effects on the MRR
and SR. The results of ANOVA for MRR and SR were presented in
Tables 9 and 10 respectively.
3. Results and discussions
3.1. Analysis of variance (ANOVA)
The ANOVA were performed to find the effect of process
parameters on various performance measures. Percentage of con-
tribution were used to determine the relative significance of var-
ious process parameters. From the ANOVA analysis shown in
Tables 9 and 10, it is observed that the dielectric fluid (A), dis-
charge current (B) pulse on time (C) were the most significant
factor affecting to MRR and SR. It was observed from the ANOVA
tables that discharge current (B) and pulse on time (C) have a
high percentage of contribution on various performance measures
as compared to pulse off time (D).
Table 5
Deionized water properties.
chloride 6.7 mg/l
Alkalinity Nil mg/l
pH 4.96
Total Hardness 22.4 mg/l
Resistivity at 25 °C 33333 O/cm3
Fig. 2. Experimental set up.
Table 6
Working range of the process parameters and their levels.
Parameters Levels
Dielectric fluid (A) Deionised
water
Drinking
water
Mixed (25% deionised
water + 75% drinking
water)
Discharge current (B) 10 15 20
Pulse on time (C) 25 45 65
Pulse off time (D) 24 36 48
Table 7
Experimental layout using an L27 (313
) OA.
Exp. No. Dielectric fluid (A) Discharge current (B) Pulse On Time (C) Pulse Off Time (D)
1 Deionized 10 25 24
10 Drinking 10 25 24
19 Mixed (25% deionised water + 75% drinking water) 10 25 24
B. Gugulothu / Materials Today: Proceedings xxx (xxxx) xxx 3
10.1016/j.matpr.2019.10.150

3.2. Effect of machining parameters on MRR
S/N graphs of MRR was presented in Fig. 3 and the ANOVA was
shown in Table 9. It is observed that for deionized water and drink-
ing water, the MRR increases and after that it decreases in the
mixed condition (25% deionized water + 75% drinking water) due
to decrease in thermal conductivity. It is also observed that, as
the current (I) increases from 10A to 20A, the MRR increases signif-
icantly. Discharge current controls the heat energy supplied for
metal removal, as the discharge current enhances, heat energy also
enhances. Thus the MRR increased from 10A current to 20A. The
discharge current is sharing 79% and it is the first significant factor.
The material removed is directly proportional to the amount of
energy supplied in this. Thus it is the most important factor as
far as sharing and importance is concerned. As the pulse on time
increases from 25 ms to 65 ms, the MRR also increases almost non-
linearly. Its contribution is 10%. Pulse off time is the least signifi-
cant factor and shows minimum contribution. Its contribution
towards MRR is 0.7%. It is observed that as the pulse off time
increases from 24 ms to 48 ms, the MRR is improved by very small
amount. At minimum pulse off time i.e. 24 ms, the dielectric fluid
gets less time to deionize and flush away the debris.
Table 8
Average results of MRR and SR.
Exp.
No.
Dielectric (A) Discharge current
(B)
Pulse On Time
(C)
Pulse Off Time
(D)
Average MRR (mm3
/
min)
Average SR (Ra)
mm
1 Deionized 10 25 24 1.6957 2.25
2 Deionized 10 45 36 2.1310 2.49
3 Deionized 10 65 48 2.46345 3.00
4 Deionized 15 25 36 2.5608 2.51
5 Deionized 15 45 48 4.0500 3.48
6 Deionized 15 65 24 3.2522 3.22
7 Deionized 20 25 48 3.4784 3.47
8 Deionized 20 45 24 4.4352 2.78
9 Deionized 20 65 36 4.5760 3.63
10 Drinking 10 25 24 2.2988 2.68
11 Drinking 10 45 36 2.4922 2.95
12 Drinking 10 65 48 2.6334 2.94
13 Drinking 15 25 36 3.7856 2.61
14 Drinking 15 45 48 4.1169 2.72
15 Drinking 15 65 24 4.0691 3.06
16 Drinking 20 25 48 4.2823 2.93
17 Drinking 20 45 24 4.5074 3.10
18 Drinking 20 65 36 5.4258 3.22
19 Mixed (25% deionised water + 75% drinking
water)
10 25 24 1.8950 2.91
water)
10 45 36 2.2254 3.03
water)
10 65 48 2.7238 3.18
water)
15 25 36 3.0563 2.72
water)
15 45 48 3.4300 2.89
water)
15 65 24 3.6542 3.40
water)
20 25 48 3.7967 3.12
water)
20 45 24 4.5128 3.48
water)
20 65 36 4.6655 3.49
Fig. 3. Influence of EDM parameters on S/N graph for material removal rate.
10.1016/j.matpr.2019.10.150

3.3. Effect of machining parameters on SR
Fig. 4 presents the S/N graph and Table 10 presents ANOVA for
SR. It is observed that for the dielectric fluid as deionized water and
drinking water the SR decreases and after that it increases in the
mixed condition (25% deionized water + 75% drinking water)
which is due to lower thermal conductivity of water. Fig. 4 show
that as the discharge current increases from 10A to 20A, the SR
increases. As the discharge current increases the bombarding
impulsive force of electrons also increases. In case of negative
polarity, the bombardment of electrons takes place from work
piece to electrode. The SR is higher at 10A as the amount of mate-
rial deposited is less. When the discharge current is increased to
20A, the larger impulsive force produces deeper and greater craters
with more amount of material being deposited. Hence the surface
roughness is more. The contribution of dielectric fluid on the SR is
12% and it is the third largest. The contribution of discharge current
is 23% and its significance is the second highest. The material
removed by using the electrode is directly proportional to the
amount of energy supplied. Thus it is the most significant factor.
As the pulse on time increases from 25 ms to 65 ms, the SR also
increases. Its contribution is 33%. Pulse off time is the least signif-
icant factor and shows minimum contribution as far as SR is con-
cerned. Its contribution towards SR is 6%. It is observed that as
the pulse off time increases from 24 ms to 48 ms, the SR becomes
Fig. 4. Influence of EDM parameters on S/N graph for SR.
Table 9
ANOVA analysis for material removal rate (MRR).
Factor Sum square Degrees of freedom Mean sum of square Per. contribution (%)
(A) 10.78 2 5.39 5.58
(B) 153.72 2 76.86 79.69
(AXB) 0.67 4 0.16 0.34
C 19.33 2 9.66 10.02
AXC 2.45 4 0.61 1.27
D 1.45 2 0.72 0.75
AXD 1.02 4 0.25 0.53
Error 3.44 6 0.57 1.78
St 192.88 26 100
Table 10
ANOVA analysis for surface roughness (SR).
Parameter Sum square Degrees of freedom Mean sum of square Per.contribution
(A) 4.510561504 2 2.25 12.22
(B) 8.579256394 2 4.28 23.25
(AXB) 3.730956924 4 0.93 10.11
C 12.35823198 2 6.17 33.49
AXC 0.048866944 4 0.012 0.13
D 2.352982883 2 1.176 6.37
AXD 1.635441424 4 0.408 4.43
Error 3.678515757 6 0.613 9.97
St 36.89481381 26 100
Table 11
Optimum values of the machining performance evaluation parameters.
Parameters Optimum condition Predicted Optimum value
MRR (mm3
/min) A2B3C3D3 5.46
SR (mm) A2B1C1D2 2.53
B. Gugulothu / Materials Today: Proceedings xxx (xxxx) xxx 5
10.1016/j.matpr.2019.10.150

low. At minimum TON of 24 ms, the dielectric fluid employed rela-
tively less time to de-ionize and flush away the debris. Thus stabil-
ity of the machining process and SR is influenced the optimum
values of the machining performance evaluation parameters were
given in Table 11 and the optimum results were given in Table 12.
4. Conclusions
In this study, the influence of dielectric fluid i.e. deionized
water, drinking water and mixed (25% deionized water + 75%
drinking water), the process parameters and optimization of tita-
nium alloy (Ti-6Al-4V) in the die sinking EDM was studied by using
Taguchi method. From the results it was found that drinking water,
discharge current, pulse on time and pulse off time have been
found to play significant role in EDM operations. Also, it was found
that the optimal levels of the factors for MRR and SR are differing
from each other. From ANOVA, pulse on time is more significant
than discharge current for SR whereas discharge current is more
significant than pulse on time for MRR. On the other hand, interac-
tion between dielectric fluid and discharge current is also signifi-
cant in case of SR.
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Table 12
The optimum results.
Parameter Optimum
condition
Predicted
Optimum value
Experimental
values
MRR (mm3
/min) A2B3C3D3 5.46 5.90
SR (mm) A2B1C1D2 2.53 2.98
10.1016/j.matpr.2019.10.150

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