International Journal of Engineering Trends and Technology (IJETT) – Volume 26 Number 4- August 2015
Analysis on the effects of machining parameters on the
performance characteristics in the EDM process of Ti-6Al-4V
G.Kumanan1, D.Kanagarajan2, R.Karthikeyan3
1
Assistant Professor, Directorate of Distance Education Annamalai University, Annamalainagar, Tamil Nadu,
India
2
Assistant Professor, Department of Manufacturing Engineering, Annamalai University, Annamalainagar,
Tamil Nadu India
Department of Mechanical Engineering, Birla institute of technology, Dubai.
Abstract — Electrical discharge machining (EDM) is
a process for shaping hard metals and forming deep
complex shaped holes by arc erosion in all kinds of
electro-conductive materials. The objective of this
paper is to study the influence of operating
parameters such as peak current(I), pulse on
time(Ton), electrode rotational speed(S) and flushing
pressure(P) of Ti-6Al-4V on the machining
characteristics of material removal rate(MRR) and
surface roughness (Ra). The effectiveness of EDM
process with
Ti-6Al-4V is evaluated in terms of the
material removal rate and the surface roughness of
the work piece produced. It is observed that copper is
most suitable for use as the tool electrode in EDM of
Ti-6Al-4V. The experiments were performed on a
newly designed experimental setup developed in the
laboratory. The response surface methodology is used
to identify the most influential parameters for
maximizing the metal removal rate and for minimizing
the surface roughness. The surface was also explored
by a scanning electron microscope (SEM) to evaluate
the effects of the electrical discharge machining.
Moreover, a pertinent EDM process with high
efficiency and high quality of machined surface could
be accomplished to satisfy modern industrial
applications.
Keywords: EDM, Ti-6Al-4V, MRR, Ra, RSM, SEM
I. INTRODUCTION
Titanium alloys have received considerable
interest recently due to their excellent corrosion
resistance, high strength-to-weight ratio, high strength
at elevated temperatures and biological compatibility.
In this manner, they are used in a wide range of
applications in the aerospace, automotive, chemical
and medical industries. However, the main reason for
the increase in demand for titanium in the past few
years has been the large consumption in the aerospace
sector. The excellent strength-to-weight ratio of
titanium alloys provides a decrease of aircraft weight
and, therefore, a reduction in fuel consumption and
emissions[1-2]. However, titanium and its alloys are
very difficult to machine materials owing to several
inherent properties of the material.
ISSN: 2231-5381
Electro discharge machining is very good
tool for machining of this type of material, It has been
widely applied in the modern metal industry for
producing complex cavities in moulds and dies, which
are difficult to manufacture by conventional
machining. The use of electrical discharge machining
in the production of forming tools to produce plastics
mouldings, die castings, forging dies etc. The EDM is
a well- established machining choice for
manufacturing geometrically complex, hard material
parts that are extremely difficult to cut by
conventional machining process. This is because
proper selection of the machining parameters can yield
the best performance with a particular machining
setup. It is in general observed that out of the two
main performance characteristics, MRR and surface
roughness (Ra) have traditionally received greater
research attention in comparison to surface roughness
even though EDM is largely used for its high precision
quality [3-4].
In this study four design factors; peak
current(I), pulse on time(Ton), electrode rotational
speed(S) and flushing pressure(P) of EDM, were
chosen as variables in order to study the process
performance in terms of MRR and surface
roughness(Ra). The experiments were performed on a
newly designed experimental setup developed in the
laboratory. The response surface methodology is used
to identify the most influential parameters for
maximizing the metal removal rate and for minimizing
the surface roughness. Accordingly, mathematical
models have been developed, using design of
experiments (DOE) technique to select the optimum
machining conditions for machining of Ti-6Al-4V
using electro discharge machining.
II. EXPERIMENTAL TECHNIQUE
2.1. Equipments used
The experiments were carried out using a die
sinking EDM (Electronica-M100 MODEL) machine.
The electrode was fed downwards using servo-control
into the work piece. A copper cylindrical electrode of
12 mm diameter was used as the tool. Kerosene was
used as a dielectric fluid and the dielectric fluid was
circulated by lateral flushing. The experiments were
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International Journal of Engineering Trends and Technology (IJETT) – Volume 26 Number 4- August 2015
performed with peak current (I), pulse on time (Ton),
electrode rotational speed(S) and flushing pressure (P)
as variables. The studies have been undertaken to
investigate the effects of on MRR and Ra. The
selected work piece material for the research work is
Ti-6Al-4V. The ranges of these parameters are
selected on the basis of preliminary experiments
conducted by using one variable at a time approach.
The process parameters and their levels selected for
the study are listed in Table 1.
Table 1 Process parameters and their levels
Levels
Process parameters
-2
-1
0
1
2
5
7.5
10
12.5
15
Pulse on time (μs)
100
200
300
400
500
Rotational speed(rpm)
50
100
150
200
250
0.5
1
1.5
2
2.5
Peak current (A)
2
Flushing pressure(kg/cm )
Table 2 Experimental design matrix and results for MRR and Ra
Experiment No
Peak current (I)
(A)
Pulse on
time(T) (µs)
Electrode rotational
speed(S) (rpm)
Flushing pressure (P)
(kg/cm2)
MRR (g/min)
Ra (µm)
1
7.5
200
100
1
0.3676
0.0667
2
12.5
200
100
1
0.4170
0.0652
3
12.5
400
100
1
0.4840
0.0850
4
12.5
400
100
1
0.5650
0.0879
5
7.5
200
200
1
0.4009
0.0520
6
12.5
200
200
1
0.3960
0.0670
7
12.5
400
200
1
0.4917
0.0606
8
12.5
400
200
1
0.5130
0.0610
9
12.5
200
100
2
0.4080
0.0670
10
12.5
200
100
2
0.4616
0.0670
11
7.5
400
100
2
0.4720
0.0700
12
12.5
400
100
2
0.6360
0.0712
13
7.5
200
200
2
0.5355
0.0758
14
12.5
200
200
2
0.5180
0.0742
15
7.5
400
200
2
0.6358
0.0700
16
12.5
400
200
2
0.6914
0.0480
17
5
300
150
1.5
0.4410
0.0620
18
15
300
150
1.5
0.5721
0.0620
19
10
100
150
1.5
0.3558
0.0682
20
10
500
150
1.5
0.5721
0.0801
21
10
300
50
1.5
0.4948
0.0880
22
10
300
250
1.5
0.5909
0.0712
23
10
300
150
0.5
0.4320
0.0590
24
10
300
150
2.5
0.5719
0.0590
25
10
300
150
1.5
0.5205
0.0571
26
10
300
150
1.5
0.5224
0.0520
27
10
300
150
1.5
0.5205
0.0571
28
10
300
150
1.5
0.5205
0.0571
29
10
300
150
1.5
0.5000
0.0560
30
10
300
150
1.5
0.5250
0.575
31
10
300
150
1.5
0.5205
0.0571
ISSN: 2231-5381
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International Journal of Engineering Trends and Technology (IJETT) – Volume 26 Number 4- August 2015
Experiments were conducted according to DOE
concept covering the full range of input variables. For
each experiment, a new set of tool and work piece has
been used. The response variable calculated for this
study are metal removal rate(MRR) and surface
roughness(Ra).
MRR, Ra are used to evaluate machining
performance. The MRR is expressed as the ratio of the
difference of weight of the work piece before and after
machining to the machining time,
(g/min)
(1)
Where
and
are the weights of the
work piece before and after machining, and ‘t’ is the
machining time.
The surface roughness is measured on a surf
coder SE1200 surface testing analyzer. For each
sample, five set of readings on surface roughness have
been taken and the average value of those five
readings has been considered as the final reading and
the results are presented in Table 2.
2.2. Procedure of response surface methodology
Response surface methodology (RSM) is a
collection of statistical and mathematical techniques
useful for design of experiments and optimizing
process parameters. In this work, RSM is utilized for
establishing the relations between the different EDM
process parameters with a variety of machining
criteria and exploring their effects on MRR and Ra.
To perform this task second order polynomial
response surface mathematical models can be
developed. In the general case, the response surface is
described as (2).
(2)
Where, y is the corresponding response of
MRR and Ra yield by the various EDM process
variables and the xi (1, 2 , , , , n) are coded levels of n
quantitative process variables, the terms C0,Ci,Cii and
Cij are the second order regression coefficients. The
second term under the summation sign of this
polynomial equation is attributable to linear effect,
whereas the third term corresponds to the higher-order
effects; the fourth term of the equation includes the
interactive effects of the process parameters. Equation
(3) can be rewritten according to the four variables
used as in(3).
(3)
ISSN: 2231-5381
Where: x1, x2, x3 and x4 are peak current (I),
pulse on time (Ton), electrode rotational speed(S) and
flushing pressure (P) respectively.
MRR=0.51757+0.027696I+0.059038Ton+0.023471S
+0.041788P+0.015081ITon0.018344IS+0.00680625IP-0.00133125
TonS+0.00249375TonP+0.027194SP-0.00346057I20.014111Ton2+0.00561443S2-0.00461057P2g/min.
(4)
Ra=0.056943-0.000233333I+0.00351667Ton0.004375S
+0.00240833P+0.0006625ITon0.000675IS+0.00005IP-0.00235TonS0.004.275TonP+0.0060625SP+0.00134554I 2
+0.00449554Ton2+0.00574554S2-0.000654464P2µm.
(5)
III. RESULTS AND DISCUSSION
3.1 Effect of current (I) and pulse on time (Ton) on
MRR and Ra
The Material removal rate in EDM mainly
occurs by melting, evaporation, and spalling. Spalling
is typical for some ceramic materials. This spalling
effect is most often related to the generation of large
micro cracks (perpendicular and parallel to the top
surface) generated during EDM. These larger micro
cracks make the separation of a small volume of
material during successive discharges much easier [6].
The effect of parameters on MRR and Ra has been
analysed through contour plots. A contour plot shows
how a response variable relates to two factors based
on a model equation 4 and 5. The surface roughness of
an electro discharge machined product can be defined
as a chip-forming process where the chips are
spherical debris melted by sparks [7]. So the surface
roughness is depending on the size of spark crater. A
large discharging energy causes violent sparks and
impulsive forces and results in deeper and larger
erosion, sand large size of the crater was produced on
the machined surface [8].
The optimum pulse current and pulse on
time is obtained as 12.5 amps and 400 μs. As the pulse
current increases, the MRR, and the Ra increases. The
increase in current intensity increases the pulse energy
and hence, the MRR increases with current intensity.
The increase in MRR increases the debris in the gap.
This event is due to the increase in discharge energy,
which subsequently causes a larger crater on the
surface of the body. The MRR decreased with an
increase in the pulse duration. Short pulse duration
would cause less surface vaporization, whereas long
pulse duration could cause the plasma channel to
expand and to decrease the energy density for the
workplace. The longer the spark is sustained to more
material removal rate. Consequently, the resulting
craters will be broader, deeper and therefore, the
surface finish will be rougher. Obviously, with shorter
duration of sparks, the surface finish will be better.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 26 Number 4- August 2015
Design-Expert® Software
Factor Coding: Actual
Ra µm
Design points above predicted value
Design points below predicted value
0.0929
With a positively charged work piece the spark leaves
the tool and strikes the work piece resulting in the
machining. Except during roughing, all the sparks that
leave the tool will result in a microscopic removal of
particles from the surface. Hence, the increase in pulse
on time has negative effects in all the objectives and
the optimum value obtained is close to the minimum
value of pulse on time.
0.041
0.1
X1 = A: Peak current(I) A
X2 = B: Pluse on Time (Ton) µs
0.09
Design-Expert® Software
Factor Coding: Actual
MRR g/min
Design points above predicted value
Design points below predicted value
0.6914
Fig.1(a) presents the influence of peak current
and pulse on time on material removal rate. The
experimental results evidence that increasing peak
ampere increase the material removal rate for pulse on
time. In EDM process, the material removal rate is a
function of electrical discharge energy. The increase
of peak current generates high energy intensity and
due to this energy melts more material from the work
piece. Thus the material removal rate increases with
increases of peak current. In general, the power of the
spark and frequency defined by the number of pulses
per second determine the process performance. The
low frequency and high power combination results in
high metal removal. As pulse on time increases the
frequency reduces and consequently longer pulse
duration increases material removal rate. It is revealed
from the results that the combination of high pulse on
time and high power conceive more material removal
rate. The same results are achieved by the researches
of [7-9]. Fig.1(b) shows the interaction effect of the
pulse on time with current on Ra. It predicts the Ra
value increases with increasing pulse on time at any
value of current. The machining rate is proportional to
the current intensity. High amperage generally
requires a large machining area and produces greater
Ra. This will be observed at high peak current and
long pulse on time; the reason for the larger roughness
values with higher pulse duration can be explained by
the generation of the large craters owing to large
amounts of energy. Fig.1(c) shows the surface
contains larger craters, cavities and cracks, which
would result in a poor surface finish.
0.3558
g /m in
Actual Factors
C: Rotational Speed (S) rpm = 150.00
D: Flushing Pressure (P) kgf/cm2 = 1.50
µ m
0.07
0.05
0.06
0.04
0.03
500.00
15.00
400.00
12.50
300.00
B: Pluse on Time (Ton) µs
.
10.00
200.00
7.50
100.00 5.00
A: Peak current(I) A
Fig.1(b).Effect of peak current and pluse on time on Ra
Fig1(c) .SEM micrographs of machined surface obtained by EDM
3.2 Effect of current (I) and electrode rotational
speed(S) on MRR and Ra
0.8
0.7
0.6
0.5
M RR
X1 = A: Peak current(I) A
X2 = B: Pluse on Time (Ton) µs
0.08
R a
Actual Factors
C: Rotational Speed (S) rpm = 150.00
D: Flushing Pressure (P) kgf/cm2 = 1.50
0.4
0.3
500.00
15.00
400.00
12.50
300.00
B: Pluse on Time (Ton) µs
10.00
200.00
7.50
100.00
5.00
A: Peak current(I) A
Fig.1(a).Effect of peak current and pluse on time on MRR
ISSN: 2231-5381
The optimum electrode rotational speed is
obtained as 200rpm .The increase in electrode rotation
would increase the MRR decrease the surface
roughness. When the cylindrical electrode rotates, due
to the centrifugal action, a new layer of dielectric fluid
is drawn into the machining gap. This induces a
conductive atmosphere for effective discharge and
encourages process stability. The rotation of the
electrode also contributes to better heat transfer from
the electrode, thus bringing down the electrode’s
surface temperature. With an increased peripheral
speed of the electrode, the ignition time delay
increases, thus bringing down the energy transferred
through the individual discharges for material
removal. This diminishes the crater dimensions to give
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International Journal of Engineering Trends and Technology (IJETT) – Volume 26 Number 4- August 2015
a better roughness value. Fig.2(a) and 2(b) depicts the
influence of peak current and rotational speed on
MRR and Ra. Also shows that the value of MRR
increases with increasing of rotational speed.
Design-Expert® Software
Factor Coding: Actual
MRR g/min
Design points above predicted value
Design points below predicted value
0.6914
roughness improved gradually for all current levels,
with certain levels after that it will decrease
0.3558
0.8
g /m in
X1 = A: Peak current(I) A
X2 = D: Flushing Pressure (P) kgf/cm2
Actual Factors
B: Pluse on Time (Ton) µs = 300.00
C: Rotational Speed (S) rpm = 150.00
Design-Expert® Software
Factor Coding: Actual
MRR g/min
Design points above predicted value
Design points below predicted value
0.6914
0.7
0.6
0.3558
M R R
0.5
0.8
g /m in
X1 = A: Peak current(I) A
X2 = C: Rotational Speed (S) rpm
Actual Factors
B: Pluse on Time (Ton) µs = 300.00
D: Flushing Pressure (P) kgf/cm2 = 1.50
0.4
0.3
0.7
0.6
2.50
M R R
0.5
15.00
2.00
12.50
1.50
0.4
10.00
D: Flushing Pressure (P) kgf/cm2 1.00
0.3
Design-Expert® Software
Factor Coding: Actual
Ra µm
Design points above predicted value
15.00 value
Design points below predicted
0.0929
250.00
200.00
12.50
100.00
7.50
0.1
0.09
Actual Factors
0.08
A: Peak current(I) A
50.00 5.00
Ra
Pluse on Time (Ton) µs = 300.00
Fig. 2(a)Effect of peak current and rotational B:C:speed
on MRR.
Rotational Speed (S) rpm = 150.00
0.1
X1 = A: Peak current(I) A
X2 = C: Rotational Speed (S) rpm
0.07
0.06
0.05
0.04
0.03
0.09
µm
0.08
Ra
Actual Factors
B: Pluse on Time (Ton) µs = 300.00
D: Flushing Pressure (P) kgf/cm2 = 1.50
10.00
X1 = A: Peak current(I) A
X2 = D: Flushing Pressure (P) kgf/cm2
µm
C: Rotational Speed (S) rpm
0.041
A: Peak current(I) A
Fig.3(a) Effect of peak current and flushing pressure on MRR.
0.041
150.00
Design-Expert® Software
Factor Coding: Actual
Ra µm
Design points above predicted value
Design points below predicted value
0.0929
7.50
0.50 5.00
2.50
0.07
15.00
2.00
0.06
12.50
1.50
0.05
10.00
D: Flushing Pressure (P) kgf/cm2 1.00
0.04
7.50
0.50
5.00
A: Peak current(I) A
Fig.3(b) Effect of peak current and flushing pressure on Ra
0.03
250.00
15.00
200.00
IV. Conclusion
12.50
150.00
C: Rotational Speed (S) rpm
10.00
100.00
7.50
50.00
5.00
A: Peak current(I) A
Fig.2(b) Effect of peak current and rotational speed on Ra
3.3 Effect of current (I) and electrode flushing
pressure(P) on MRR and Ra
The optimum flushing pressure is obtained as
2Kg/cm2. As the flushing pressure increases, it helps
to move away the debris from the workpiece, which is
removed by the spark discharges. The machining
performance is improved since the removed particles
in the machining gap are evacuated more efficiently,
so the MRR increases. It can be seen that when
flushing pressure is less than a certain pressure, it is
impossible to do any machining. The improved
flushing pressure results in maximum MRR as well as
improved surface finish.
Fig.3 (a) depicts the influence of peak current
and flushing pressure on MRR. Also shows that the
value of MRR increases with increasing of flushing
pressure. The flushing pressure of the dielectric fluid
enhances the MRR, with increase in pressure of the
dielectric fluid, the MRR tends to increase. This is
because the machining performance has been
improved, as the removed particles in the machining
gap are evacuated more efficiently. The Fig.3(b)
shows that the value of Ra increases with increase in
peak current at least up to the maximum level, and it
tends to increase the high valve of flushing pressure.
Along with increased flushing pressure the surface
ISSN: 2231-5381
In this work, the Ti–6Al–4V alloy was machined
by an electrical discharge machining process with
different machining conditions and copper
electrode as the tool material. Summarizing the
main features of the results, the following
conclusions may be drawn.
EDM characteristics of Ti-6Al-4V have
been studied.
RSM revealed that the all four input
parameters such as peak current(I), pulse on
time(Ton), electrode rotational speed(S) and
flushing Pressure(P) are the most influential
parameters for MRR and Ra.
When the increase the flushing pressure to
the dielectric fluid, the surface roughness
deteriorated with an increase in peak
current. Since an increase in the peak
current increased the discharge energy and
the impulsive force, removing more molten
material and generating deeper and larger
discharge craters.
Hence, the surface
roughness became coarser.
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International Journal of Engineering Trends and Technology (IJETT) – Volume 26 Number 4- August 2015
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