Comparative study on variation of process characteristics on al and die steel process

International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN
0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 3, April (2013), © IAEME
170
COMPARATIVE STUDY ON VARIATION OF PROCESS
CHARACTERISTICS ON AL AND DIE STEEL COMPONENTS IN
SINK EDM PROCESS
1
K.L.Uday Kiran, 2
R.Rajendra, 3
G.Chandramohan Reddy, 4
A.M.K Prasad
1, 2, 4
University College of Engineering, Osmania University, Hyderabad, A.P, India
3
Mahatma Gandhi Institute of Technology, Hyderabad, A.P, India
ABSTRACT:
Electrical Discharge Machining (EDM) process is a well established non-traditional
machining option for manufacturing geometrically complex and hard material parts that are extremely
difficult to machine by conventional machining process. In this process the material removal is
occurred electro thermally by a series of successive discrete discharges between electrode and the
work piece.
This paper presents the results of experimental studies carried out to conduct a comprehensive
investigation on the influence of EDM parameter (current) on process characteristics in sink EDM
process. The studied process characteristics included material removal rate, tool wear ratio, and
surface roughness parameters of two work pieces (Al & Die steel) by using a common tool (Cu). The
variation of process characteristics at different currents was studied. The observation revealed that the
MRR, TWR, Surface roughness parameters and machining time of work pieces were influenced by
current and thereby improves the quality of surface finishing and rate of production. The results of
this study could be utilized in the selection of optimum process parameter (current) to achieve the
desired EDM efficiency and surface roughness when machining Al and Die steel.
Keywords: EDM, Machining time, Material removal rate, Surface roughness, Tool wear ratio.
1. INTRODUCTION
Electrical Discharge Machining (EDM) is one of the important non-traditional machining
processes and it is widely accepted as a standard machining process in manufacturing industries. The
theory of the process was established by soviet scientists in the middle of 1940’s. They invented the
relaxation circuit and a simple servo controller tool that helped to maintain the gap width between the
tool and the work piece. This reduced arcing and made EDM machining more profitable and
produced first EDM machining in 1950’s. Major development of EDM was observed when computer
numerical control systems were applied for the machine tool industry. Thus, the EDM Process
became automatic and unattended machining method. The process uses thermal energy to generate
heat that melts and vaporizes the workpeice by ionization within the dielectric medium. The electrical
INTERNATIONAL JOURNAL OF ADVANCED RESEARCH IN
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ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 4, Issue 3, April 2013, pp. 170-177
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International Journal of Advanced Research i
discharges generate impulsive pressure by dielectric explosion to remove the melted material. Thus,
the amount of removed material can be effectively controlled to produce complex and precise
machine components. However, the melted material is flushed away incompletely and the remaining
material re-solidifies to form discharge craters. As a result, machined surface has micro cracks and
pores caused by high temperature gradient which reduces surface finish quality.
There have been published studies continuing surface finish of machined materials by EDM. It was
noticed that various machining parameters influenced the
surface roughness and by setting possible combination of
material removal rate and tool wear ratio
surface roughness parameters are pulsed current, pulse time, pulse pause time, voltage, dielectric
liquid pressure and electrode material. The present study
removal rate, tool wear ratio and
maximum height of the profile -Rz & Maximum roughness depth
Components using copper tool in EDM
2 .MECHANISM OF EDM
The working principle of EDM process is based on the thermoelectric energy.
Discharge Machining (EDM) is a controlled metal
means of electric spark erosion. In this
electrode submerged in a dielectric fluid with the passage of
electrode are separated by a specific small gap
gap filled with an insulating medium, preferably a
(de-mineralized) water as in fig.1.a [2]
work piece to produce the finished part to the desired shape. The metal
by applying a pulsating (ON/OFF) electrical charge of high
the work piece. This removes (erodes) ver
controlled rate.
Fig. 1(a). Working principle of EDM
The polarity normally used is straight (or normal polarity) in which tool is
while in reverse polarity the tool is
tool is towards the work piece is controlled by a servomechanism. The sparking takes place over the
entire surface of the work piece hence the replica of the tool is produced on the work piece. Usually, a
component made by EDM process is machined in two stages, viz
poor surface finish and finish machining at low MRR with high surface finish.
6499(Online) Volume 4, Issue 3, April (2013), © IAEME
171
owever, the melted material is flushed away incompletely and the remaining
solidifies to form discharge craters. As a result, machined surface has micro cracks and
pores caused by high temperature gradient which reduces surface finish quality.
noticed that various machining parameters influenced the material removal rate, tool wear ratio
surface roughness and by setting possible combination of these parameters optimum surface quality
ool wear ratio was obtained. The machining parameters which influence
d electrode material. The present study deals with the effect of current on
surface roughness parameters (Average roughness
Rz & Maximum roughness depth –Rzmax) of Al a
EDM process.
The working principle of EDM process is based on the thermoelectric energy.
Discharge Machining (EDM) is a controlled metal-removal process that is used to remove met
means of electric spark erosion. In this process the energy is created between a work piece and an
ctric fluid with the passage of electric current. The work piece and the
by a specific small gap called spark gap. Pulsed arc discharges occur in this
insulating medium, preferably a dielectric liquid like hydrocarbon oil or de
as in fig.1.a [2]. The electric spark is used as the cutting tool to cut (e
work piece to produce the finished part to the desired shape. The metal-removal process is performed
by applying a pulsating (ON/OFF) electrical charge of high-frequency current through the electrode to
(erodes) very tiny pieces of metal from the work
Working principle of EDM Fig. 1(b) Normal and reverse polarity in
EDM
The polarity normally used is straight (or normal polarity) in which tool is –ve and work piece is +ve,
while in reverse polarity the tool is +ve and work piece is negative shown in fig 1.b. Movement of the
he work piece is controlled by a servomechanism. The sparking takes place over the
component made by EDM process is machined in two stages, viz. rough machining at high MRR with
poor surface finish and finish machining at low MRR with high surface finish.
n Engineering and Technology (IJARET), ISSN
6499(Online) Volume 4, Issue 3, April (2013), © IAEME
owever, the melted material is flushed away incompletely and the remaining
solidifies to form discharge craters. As a result, machined surface has micro cracks and
ool wear ratio and
these parameters optimum surface quality,
machining parameters which influence
the effect of current on material
(Average roughness -Ra, Average
of Al and Die-Steel
The working principle of EDM process is based on the thermoelectric energy. Electrical
removal process that is used to remove metal by
created between a work piece and an
The work piece and the
Pulsed arc discharges occur in this
dielectric liquid like hydrocarbon oil or de-ionized
spark is used as the cutting tool to cut (erode) the
removal process is performed
frequency current through the electrode to
work piece at a
Normal and reverse polarity in
ve and work piece is +ve,
ovement of the
he work piece is controlled by a servomechanism. The sparking takes place over the
machining at high MRR with

172
3. DESCRIPTION OF EXPERIMENTAL SET-UP
3.1 Machine tool
The experimental setup consists of CR-6C Creator (SYCNC PC-60) Sink type Electro Discharge
Machine, Taiwan (shown in fig. 2) available at Department of Mechanical Engineering, University
College of Engineering, Osmania University, Hyderabad-500007. It is energized by a 50 A pulse
generator. Ruslic oil dielectric fluid was used during the experiments. The surface roughness was
measured by Handy surf Surface testing analyzer
3.2 Work piece material
The work piece materials in this work were Al and Die steel, having the properties shown in
Table.1
3.3 Electrode material
Electrode material considered for analysis was copper and its properties being shown in Table.2
Table.1: Work piece material properties
Material Al Die-Steel
Density(g/cm3
) 2.70 7.7-8.0
Thermal conductivity (W/m K) 237 19.9-48.3
Electrical resistivity (µΏ/cm) 26.50 72
Coefficient of thermal expansion (x 10-6 0
C-1
) 23.1 9.5-15.1
Melting point (o
C) 660 1435
Table.2: Electrode material properties (copper)
(g/cm3)
Thermal
conductivity
(W/m K)
Electrical resistivity
(µΏ/cm)
Coefficient of thermal
expansion (x 10-6 0
C-1
)
Melting
point
(o
C)
8.9 268-389 1.96 6.6 1083
3.4 Experimental Procedure
The Experimental study was carried out on CR-6C Creator (SYCNC PC-60) Sink type
Electro Discharge Machine using ruslic oil as a die electric fluid. The experiments on Die steel and Al
samples which were in the form of cylindrical shapes of diameter 50mm each were carried out using
different machining setting’s with Copper electrode. Cylindrical copper tool’s with a diameter of
12mm each ware used as electrode’s for machining both Al and die steel work pieces. The copper
electrodes ware finished ground before experimental study. Three work pieces of each Aluminum and
Die Steel were used and machined on EDM using separate copper electrodes giving 1mm depth at
three different currents (i.e. 10 A, 15 A & 20 A).
Fig. 2 Sink type Electro Discharge Machine Fig 3 shows the Tool (Cu) and Work
piece (Al)

173
The material removal rate of Al and die steel work pieces were determined by the following equation
MRR = (Wb-Wa ) /Tm , where Wb =Weight of the work piece before machining
Wa =Weight of the work piece after machining
Tm = Machining time in min
The tool wear rate of copper tool for machining Al and Die steel work pieces ware determined by the
following equation [3].
TWR = (Wtb-Wta ) /Tm, where Wtb =Weight of the tool before machining
Wta =Weight of the tool after machining
Tm = Machining time in min
The surface roughness parameters (Ra, Rz & Rz max) of machined surfaces of each material at
corresponding currents (10A, 15A & 20 A) were measured by Handy surf Surface testing analyzer
(made in Japan). The sampling length of machined surface was taken as 1.25mm.
Electronic weighing machine was used to find the weights of work samples before and after
machining.
The machining time were also recorded for carrying out analysis.
4. RESULTS AND DISCUSSION
4.1 Effect of current on material removal rate: When the current is increased from 10A to 20A, the
corresponding MRR shown in fig. 4 for Al increases from 6.22 to 10.87(x 10-3
gm/min) and from 9.20
to 17.99 (x 10-3
gm/min) for Die steel respectively. The MRR values for Al and Die steel are shown in
the Table. 3.
Table.3: MRR values of Al and Die steel work samples
The peak current increases the input power by which the increase of MRR is expected due to more
spark energy flowing from tool into work piece. This causes craters and pits on the sample and
machining becomes faster.
4.2 Effect of current on tool wear rate: When the current increases from 10A to 20A, the
corresponding TWR shown in fig.5 for machining Al increases from 1.70 to 7.80 (x 10-3
gm/min) and from 2.20 to 9.60 (x 10-3
gm/min) for Die steel. The TWR values are shown in the
table.4. Higher current causes a strong spark which results in more eroded material from the tool.
Current
(Amps)
Aluminum Work Sample Die Steel Work Sample
Weight(gms) Time
(min)
MRR×10-3
(gm/min)
Weight(gms) Time
(min)
MRR×10-3
(gm/min)
Before After Difference Before After Difference
10 213.40 212.08 1.32 212 6.22 589.24 586.4
6
2.78 302 9.20
15 212.40 210.90 1.50 162 9.25 587.04 583.6
4
3.40 231 14.71
20 218.30 216.50 1.74 160 10.87 575.48 571.3
6
4.12 229 17.99

174
Table.4: TWR values of copper tool for machining Al and Die steel work samples
Fig .4 Material Removal Rate vs Current for Al & Die steel samples
Fig .5 Tool Wear Rate vs Current of Copper Tool for Machining Al & Die steel samples
4.3 Effect of current on surface roughness parameters: Average roughness (Ra), average
maximum height (Rz) and maximum roughness depth (Rzmax) of the profile parameters variation on
surface of Die steel and Al work samples for variation of current parameter at 10, 15, 20 Amps for 1
mm depth erosion. When the current is increased from 10A to 20A, the corresponding average
roughness, average maximum height and maximum roughness depth values shown in fig. 6(a) for Al
increase from 1.62 to 1.97 µm, 9.03 to 10.86 µm and 10.96 to 14.54 µm respectively. Similarly for
Die steel as shown in fig. 6(b), the corresponding average roughness, average maximum height and
maximum roughness depth values increases from 1.99 to 2.55µm, 10.02 to 13.43µm and 10.90 to
15.40 µm respectively. The surface roughness parameter values for Al and Die steel are shown.
At a low current, a small quantity of heat is generated and a substantial portion of it
is absorbed by the surroundings. As a result, the amount of utilized energy in melting and vaporizing
Current
(Amps)
For Machining Aluminum Work Sample For Machining Die Steel Work Sample
Weight(gms) Time
(min)
TWR×10-3
(gm/min)
Weight(gms) Time
(min)
TWR×10-3
(gm/min)
Before After Difference Before After Difference
10 96.68 96.32 0.36 212 1.70 96.32 95.64 0.68 302 2.20
15 95.16 94.74 0.42 162 2.60 93.04 91.66 1.58 231 5.97
20 98.02 96.76 1.20 160 7.80 94.60 92.40 2.20 229 9.60

175
the electrodes is not so intense. However, with an increase in pulse current and with a constant
amount of pulse on-time, a stronger spark with higher thermal energy is produced, and a substantial
quantity of heat will be transferred into the electrodes. Furthermore, as the pulse current increases,
discharge strikes the surface of the sample more intensely, and creates an impact force on the molten
material in the crater and causes more molten material to be ejected out of the crater, so the surface
roughness of the machined surface increases [4].
Fig .6 (a) Surface Roughness Parameters (Ra, Rz & Rzmax) vs Current for Al samples
4.4 Effect of current on machining time: When the current is increased from 10A to 20A, the
corresponding machining time was decreased from 212 to 160 min for Al and 302 to 229 min for Die
steel samples as shown in fig.7. The machining time for both samples at corresponding currents as
depicted in Table.6.
Table.6: Machining Time for Al & Die steel work pieces:
.
Fig .7 Machining Time vs Current for Al & Die steel samples
Current
(Amps)
Machining Time in min
Al Die steel
10 212 302
15 162 231
20 160 229

176
5. CONCLUSIONS
Analysis from an experimental investigation on the effect of current on material removal rate,
tool wear ratio and surface roughness parameters in EDM process have been presented. The leading
conclusions are drawn as follows:
1. The increase in pulse current leads to a sharp increase in the MRR and surface roughness of
both Al and Die steel samples, low currents produce good surface finish quality.
2. At higher currents the surface finishing quality will be low, but the MRR will be high which
leads to improve the rate of production.
3. It was evident that the tool wear ratio increases by the increase in the pulse current, but was
less compared to MRR values for same currents.
4. It was experimental that for same currents the material removal rate, tool wear ratio and
surface roughness parameters of Die steel work samples were more than that of Al samples.
5. There was a high increase in material removal rate for Die steel compared to Al work pieces
for same machining time.
6. It was observed that the machining time decreases as the current increases and the machining
time of Die steel work samples were more than that of Al samples.
ACKNOWLEDGEMENTS
The authors are thankful to the managements of their respective institutions for their
encouragement during the course of this work.
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