Xem mẫu
Journal of Materials Processing Technology 191 (2007) 141–144
Examination of machining parameters on surface
roughness in EDM of tool steel
M. Kiyak a,∗ , O. Cakır b
¸
a
Department of Mechanical Engineering, Yildiz Technical University, 34349 Istanbul, Turkey
b Department of Mechanical Engineering, Dicle University, 21280 Diyarbakir, Turkey
Abstract
Electrical discharge machining (EDM) is one of the important non-traditional machining processes and it is widely accepted as a standard
machining process in the manufacture of forming tools to produce molds and dies. Since its introduction to manufacturing industry in late 1940s,
EDM became a well-known machining method. The method is based on removing material from a workpiece by means of a series of repeated
electrical discharges, produced by electric pulse generators at short intervals, between an electrode (tool) and a part being machined in dielectric
fluid medium. This paper is devoted to a study of the influences of EDM parameters on surface roughness for machining of 40CrMnNiMo864 tool
steel (AISI P20) which is widely used in the production of plastic mold and die. The selected EDM parameters were pulsed current (8, 16 and
24 A), pulse time (2, 3, 4, 6, 12, 24, 48 and 100 s) and pulse pause time (2 and 3 s). It was observed that surface roughness of workpiece and
electrode were influenced by pulsed current and pulse time, higher values of these parameters increased surface roughness. Lower current, lower
pulse time and relatively higher pulse pause time produced a better surface finish.
© 2007 Elsevier B.V. All rights reserved.
Keywords: EDM; Tool steel; Current; Surface roughness
1. Introduction
Electric discharge machining (EDM) is one of the most popular non-traditional material removal processes and has became
a basic machining method for the manufacturing industries of
aerospace, automotive, nuclear, medical and die-mold production. The theory of the process was established by two Soviet
scientists B.R. and N.I. Lazarenko in the middle of 1940s. They
invented the relaxation circuit and a simple servo controller tool
that helped to maintain the gap width between the tool and the
workpiece. This reduced arcing and made EDM machining more
profitable and produced first EDM machine in 1950s. 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 [1].
The process uses thermal energy to generate heat that melts
and vaporizes the workpiece by ionization within the dielectric
∗
Corresponding author.
E-mail addresses: kiyak@yildiz.edu.tr (M. Kiyak), ocakir@dicle.edu.tr
(O. Cakır).
¸
0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmatprotec.2007.03.008
medium. The electrical 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 resolidifies to form discharge craters. As a result,
machined surface has microcracks and pores caused by high
temperature gradient which reduces surface finish quality.
There have been many published studies considering surface
finish of machined materials by EDM. It was noticed that various machining parameters influenced surface roughness and
setting possible combination of these parameters was difficult
to produce optimum surface quality. The influences of some
machining parameters such as pulsed current [2–9], pulse time
[2–6,8,9], pulse pause time [2,5,9], voltage [4,6], dielectric liquid pressure [4,6,8,10] and electrode material [11] have been
examined. One study examined P20 tool steel and provided useful information the effects of some machining parameters on
surface roughness, but the selected of pulsed current values was
very low 1–8 A [12].
The present study examines the effects of pulsed current,
pulse time and pulse pause time on surface roughness in the
40CrMnNiMo864 tool steel (AISI P20) tool steel.
142
M. Kiyak, O. Cakır / Journal of Materials Processing Technology 191 (2007) 141–144
¸
Table 1
Properties of workpiece material
Chemical composition (%)
C
Cr
Mn
Mo
Ni
S
Si
0.37
2
1.4
0.2
1
Max. 0.01
0.3
Hardness
Elasticity module (E)
Thermal conductivity
290–341 HB
205 GPa
29 W/m K
Fig. 1. Effects of pulse time and pulsed current on surface roughness of workpiece (2 s pulse pause time).
2. Experimental procedures
The experimental study was carried out on AJAN EDM 982 machine. The
dielectric liquid was a brand of Cuttex Fel Ultra. The viscosity of dielectric fluid was 2.2–2.7 at 40 ◦ C and the lightning point was 105 ◦ C/min. The
selected workpiece material was 40CrMnNiMo864 (AISI P20) that was widely
used in die and mold manufacturing industry. The properties of workpiece
material were presented in Table 1. The workpiece specimen was prepared
20 mm × 70 mm × 315 mm of dimension and the surfaces of workpiece were
milled and finish ground before EDM method application. The possible more
influential machining parameters were selected according to literature review.
The list of selected machining parameter values was given in Table 2.
A cylindrical pure copper with a diameter of 22 mm was used as an electrode
which was finish ground before experimental study. It was mounted axially in
line with workpiece.
The surface roughness of the machined surface was measured by using Taylor
Hobson Surtonic 3+ surface test equipment. The surface roughness, which is
measured by central line average (Ra ) was employed to asses the quality of the
machine surface quantitatively. Each surface roughness value was obtained by
averaging five measurements at various positions of workpiece and electrode
surfaces for each machining condition. The surface measurement filter of this
equipment was 2CR type. The cut-off length was set as 2.5 mm. The evaluation
length was selected as the maximum value which was 2.5 mm. Stylus type was
diamond with 5 m radius.
3. Experimental results and discussion
First part of the experimental study carried out for machined
workpiece surface finish quality.
Fig. 1 gives the experimental result of surface roughness when
2 s pulse pause time was used with different pulsed current and
pulse times. It was observed that surface roughness increased
when higher pulse time was used. Similar result was noticed
for pulse current values, higher currents produced poor surface
finish.
When pulse pause time increased from 2 to 3 s, similar
results were obtained (Fig. 2). Higher pulse time and pulsed
current produced poor surface finish. However, up to certain
pulse time (6 s), surface roughness was different comparing to
2 s pulse pause time results. For the same machining conditions, surface roughness was 2–3 m for 2 s pulse pause time
and 6 m for 3 s pulse pause time. Pulsed current showed a
similar trend, increasing current gave high surface roughness.
Table 2
Parameters of examinations
Number of test
1
Pulsed current (A)
Pulse time (s)
Pulse pause time (s)
Surface roughness (Ra ) (workpiece)
Surface roughness (Ra ) (electrode)
2
3
4
5
6
7
8
9
10
11
12
13
8
2
2
1.8
1.8
8
4
2
3.8
2.2
8
6
2
5.3
2.6
8
12
2
5.7
3.0
8
24
2
7.2
3.1
8
48
2
8.1
3.3
8
100
2
8.7
3.4
8
3
3
1.8
2.1
8
4
3
2.4
2.6
8
12
3
5.0
3.0
8
24
3
6.3
3.1
8
48
3
8.0
3.2
8
100
3
8.9
3.3
Number of test
1
Pulsed current (A)
Pulse time (s)
Pulse pause time (s)
Surface roughness (Ra ) (workpiece)
Surface roughness (Ra ) (electrode)
2
3
4
5
6
7
8
9
10
11
12
13
16
2
2
2.5
2.2
16
4
2
5.0
3.4
16
6
2
6.4
3.6
16
12
2
6.7
3.7
16
24
2
8.4
4.3
16
48
2
9.3
4.6
16
10
2
10.4
4.7
16
3
3
2.3
2.5
16
4
3
3.0
3.0
16
12
3
5.7
3.8
16
24
3
7.0
3.9
16
48
3
8.6
4.3
16
100
3
10.1
4.3
Number of test
1
Pulsed current (A)
Pulse time (s)
Pulse pause time (s)
Surface roughness (Ra ) (workpiece)
Surface roughness (Ra ) (electrode)
2
3
4
5
6
7
8
9
10
11
12
13
16
2
2
3.1
3.0
16
4
2
5.2
3.5
24
6
2
6.7
3.6
24
12
2
8.5
3.9
24
24
2
9.4
4.4
24
48
2
9.7
4.7
24
100
3
11.3
4.8
24
3
3
3.0
3.0
24
4
3
3.2
3.1
24
12
3
6.6
3.8
24
24
3
7.5
4.2
24
48
3
9.0
4.4
24
100
3
10.9
4.4
M. Kiyak, O. Cakır / Journal of Materials Processing Technology 191 (2007) 141–144
¸
143
Fig. 2. Effects of pulse time and pulsed current on surface roughness of workpiece (3 s pulse pause time).
Fig. 4. Effects of pulse time and pulsed current on surface roughness of electrode
(3 s pulse pause time).
Surface finish quality was better when applying smaller
pulsed current and pulse time. This is because of small particle size and crater depths formed by electrical discharge. As a
result, the best surface finish will be produced. The selection of
these machining parameters for EDM of any material should be
used for a higher surface quality is required.
It was observed that when pulsed current and particularly
pulse time increased, machined workpiece surface exhibited a
higher surface roughness due to irregular topography. Pulsed
current had an effect on surface roughness at low pulse time,
but the influence of pulse time was more significant than pulsed
current at higher pulse times.
It was noticed that excellent machined surface quality could
be obtained by setting machining parameters at a low pulse current and short pulse time. This combination will unfortunately
produce low material removal rate and cause high machining
time, in total high machining cost. When high material removal
rates are needed, high pulsed current and pulse times should
be selected. However, this selection will produce a poor surface finish due to deeper and wider crates on the machined
surface. There is also an influence on dielectric fluid at high
pulsed current; the properties will be lost because of high
temperature.
Second stage of the experimental study considered to examine the surface roughness of electrode. The bottom surface
of the electrode, which is continuously contacted to workpiece, was investigated. For the same machining conditions,
the experimental results were given in Figs. 3 and 4. Low
pulse times and pulsed currents provided a better surface quality for both duration times. It was observed that pulse pause
time was an influential parameter; 2 s of pulse pause time pro-
vided better surface quality comparing to 3 s of pulse pause
time.
Similar surface roughness results were noticed for electrode
surface roughness. It was observed that the surface roughness
of electrode was better when applying smaller pulsed current
and pulse time. When pulsed current and pulse time increased,
electrode surface presented a higher surface roughness. Pulsed
current had an effect on surface roughness of electrode at low
pulse time, but the influence of pulse time was more significant
than pulsed current at higher pulse times. The effect of pulse
pause time was insignificant.
Fig. 3. Effects of pulse time and pulsed current on surface roughness of electrode
(2 s pulse pause time).
4. Conclusion
The experimental study of the EDM of 40CrMnNiMo864
tool steel (AISI P20) tool steel provided important quantitative
results for obtaining possible high surface finish quality and
machining outputs as follows:
a. Surface roughness increased with increasing pulsed current
and pulse time. Low current and pulse time with high pulse
pause time produced minimum surface roughness that means
good surface finish quality. The selection of these machining
parameters is not useful because machining process generally becomes very slow. Material removal rate will be low
and thus machining cost increases. This combination should
be used in finish machining step of EDM process.
b. High pulsed current and pulse time provide low surface finish
quality. However, this combination would increase material
removal rate and reduce machining cost. As a result, this
combination (high pulsed current and pulse time) should be
used for rough machining step of EDM process.
c. From power point of view, rough and finish machining steps
require different level of machine power. For rough EDM
application, the machine power should be one-fourth of the
produced power with 16 A of current, 6 s of pulse time and
3 s of pulse pause time. Finish machining should be carried
out at one-half level of power at 8 A of current as well as 6 s
of pulse time and 3 s of pulse pause time.
d. Increasing wear on electrode surface is unavoidable during
EDM process. Therefore, workpiece surface roughness will
be increasing due to wear rate on electrode.
e. Wear on electrode surface is unavoidable during EDM
process. Surface roughness of machined workpiece would
144
M. Kiyak, O. Cakır / Journal of Materials Processing Technology 191 (2007) 141–144
¸
increase when surface quality of electrode decreases due to
pulsed current density.
f. For the same pulse pause time, the trends of surface roughness on the workpiece and electrode are similar. Thus, there
will be a relation between wear on electrode and increase of
surface roughness from workpiece surface quality point of
view.
Acknowledgements
Authors would like to thank two companies (OPAS and
ERDEM) for kind encouragement and technical support. They
are also thankful to Mech. Eng. Ca˘ atay ACAR for his sincere
¸ g
help throughout this research.
References
[1] K.H. Ho, S.T. Newman, State of the art electrical discharge machining
(EDM), Int. J. Mach. Tools Manuf. 43 (2003) 1287–1300.
[2] P.V. Ramarao, M.A. Faruqi, Characteristics of the surfaces obtained in
electro-discharge machining, Prec. Eng. 4 (1982) 111–113.
[3] C.C. Wang, B.H. Yan, H.M. Chow, Y. Suzuki, Cutting austempered ductile iron using an EDM sinker, J. Mater. Process. Technol. 88 (1999)
83–89.
[4] S.H. Lee, X.P. Li, Study of the effect of machining parameters on the
machining characteristics in electrical discharge machining of tungsten
carbide, J. Mater. Process. Technol. 115 (2001) 344–358.
[5] H.S. Halkacı, A. Erden, Experimental investigation of surface roughness
in electric discharge machining (EDM), in: Proceedings of the 6th Biennial
Conference (ESDA 2002), Istanbul, Turkey, 2002, pp. 1–6.
[6] S.H. Lee, X. Li, Study of the surface integrity of the machined workpiece
in the EDM of tungsten carbide, J. Mater. Process. Technol. 139 (2003)
315–321.
[7] Y.H. Guu, H. Hocheng, C.Y. Chou, C.S. Deng, Effect of electrical discharge
machining on surface characteristics and machining damage of AISI D2
tool steel, Mater. Sci. Eng. A 358 (2003) 37–43.
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[8] C. Co˘ un, B. Kocabas, A. Ozgedik, Experimental and theoretical investi¸ g
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gation of workpiece surface roughness profile in EDM, J. Fac. Eng. Arch.
19 (2004) 97–106 (in Turkish).
[9] Y. Keskin, H.S. Halkacı, M. Kızıl, An experimental study for determination of the effects of machining parameters on surface roughness in
electrical discharge machining (EDM), Int. J. Adv. Manuf. Tech. 28 (2006)
1118–1121.
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[10] A. Ozgedik, C. Co˘ un, An experimental investigation of tool wear in
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electric discharge machining, Int. J. Adv. Manuf. Tech. 27 (2006) 488–500.
[11] S. Singh, S. Maheshwari, P.C. Pandey, Some investigations into the electric discharge machining of hardened tool steel using different electrode
materials, J. Mater. Process. Technol. 149 (2004) 272–277.
[12] F.L. Amorim, W.L. Weingaertner, The influence of generator actuation
mode and process parameters on the performance of finish EDM of a tool
steel, J. Mater. Process. Technol. 166 (2005) 411–416.
nguon tai.lieu . vn
Examination of machining parameters on surface
roughness in EDM of tool steel
M. Kiyak a,∗ , O. Cakır b
¸
a
Department of Mechanical Engineering, Yildiz Technical University, 34349 Istanbul, Turkey
b Department of Mechanical Engineering, Dicle University, 21280 Diyarbakir, Turkey
Abstract
Electrical discharge machining (EDM) is one of the important non-traditional machining processes and it is widely accepted as a standard
machining process in the manufacture of forming tools to produce molds and dies. Since its introduction to manufacturing industry in late 1940s,
EDM became a well-known machining method. The method is based on removing material from a workpiece by means of a series of repeated
electrical discharges, produced by electric pulse generators at short intervals, between an electrode (tool) and a part being machined in dielectric
fluid medium. This paper is devoted to a study of the influences of EDM parameters on surface roughness for machining of 40CrMnNiMo864 tool
steel (AISI P20) which is widely used in the production of plastic mold and die. The selected EDM parameters were pulsed current (8, 16 and
24 A), pulse time (2, 3, 4, 6, 12, 24, 48 and 100 s) and pulse pause time (2 and 3 s). It was observed that surface roughness of workpiece and
electrode were influenced by pulsed current and pulse time, higher values of these parameters increased surface roughness. Lower current, lower
pulse time and relatively higher pulse pause time produced a better surface finish.
© 2007 Elsevier B.V. All rights reserved.
Keywords: EDM; Tool steel; Current; Surface roughness
1. Introduction
Electric discharge machining (EDM) is one of the most popular non-traditional material removal processes and has became
a basic machining method for the manufacturing industries of
aerospace, automotive, nuclear, medical and die-mold production. The theory of the process was established by two Soviet
scientists B.R. and N.I. Lazarenko in the middle of 1940s. They
invented the relaxation circuit and a simple servo controller tool
that helped to maintain the gap width between the tool and the
workpiece. This reduced arcing and made EDM machining more
profitable and produced first EDM machine in 1950s. 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 [1].
The process uses thermal energy to generate heat that melts
and vaporizes the workpiece by ionization within the dielectric
∗
Corresponding author.
E-mail addresses: kiyak@yildiz.edu.tr (M. Kiyak), ocakir@dicle.edu.tr
(O. Cakır).
¸
0924-0136/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmatprotec.2007.03.008
medium. The electrical 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 resolidifies to form discharge craters. As a result,
machined surface has microcracks and pores caused by high
temperature gradient which reduces surface finish quality.
There have been many published studies considering surface
finish of machined materials by EDM. It was noticed that various machining parameters influenced surface roughness and
setting possible combination of these parameters was difficult
to produce optimum surface quality. The influences of some
machining parameters such as pulsed current [2–9], pulse time
[2–6,8,9], pulse pause time [2,5,9], voltage [4,6], dielectric liquid pressure [4,6,8,10] and electrode material [11] have been
examined. One study examined P20 tool steel and provided useful information the effects of some machining parameters on
surface roughness, but the selected of pulsed current values was
very low 1–8 A [12].
The present study examines the effects of pulsed current,
pulse time and pulse pause time on surface roughness in the
40CrMnNiMo864 tool steel (AISI P20) tool steel.
142
M. Kiyak, O. Cakır / Journal of Materials Processing Technology 191 (2007) 141–144
¸
Table 1
Properties of workpiece material
Chemical composition (%)
C
Cr
Mn
Mo
Ni
S
Si
0.37
2
1.4
0.2
1
Max. 0.01
0.3
Hardness
Elasticity module (E)
Thermal conductivity
290–341 HB
205 GPa
29 W/m K
Fig. 1. Effects of pulse time and pulsed current on surface roughness of workpiece (2 s pulse pause time).
2. Experimental procedures
The experimental study was carried out on AJAN EDM 982 machine. The
dielectric liquid was a brand of Cuttex Fel Ultra. The viscosity of dielectric fluid was 2.2–2.7 at 40 ◦ C and the lightning point was 105 ◦ C/min. The
selected workpiece material was 40CrMnNiMo864 (AISI P20) that was widely
used in die and mold manufacturing industry. The properties of workpiece
material were presented in Table 1. The workpiece specimen was prepared
20 mm × 70 mm × 315 mm of dimension and the surfaces of workpiece were
milled and finish ground before EDM method application. The possible more
influential machining parameters were selected according to literature review.
The list of selected machining parameter values was given in Table 2.
A cylindrical pure copper with a diameter of 22 mm was used as an electrode
which was finish ground before experimental study. It was mounted axially in
line with workpiece.
The surface roughness of the machined surface was measured by using Taylor
Hobson Surtonic 3+ surface test equipment. The surface roughness, which is
measured by central line average (Ra ) was employed to asses the quality of the
machine surface quantitatively. Each surface roughness value was obtained by
averaging five measurements at various positions of workpiece and electrode
surfaces for each machining condition. The surface measurement filter of this
equipment was 2CR type. The cut-off length was set as 2.5 mm. The evaluation
length was selected as the maximum value which was 2.5 mm. Stylus type was
diamond with 5 m radius.
3. Experimental results and discussion
First part of the experimental study carried out for machined
workpiece surface finish quality.
Fig. 1 gives the experimental result of surface roughness when
2 s pulse pause time was used with different pulsed current and
pulse times. It was observed that surface roughness increased
when higher pulse time was used. Similar result was noticed
for pulse current values, higher currents produced poor surface
finish.
When pulse pause time increased from 2 to 3 s, similar
results were obtained (Fig. 2). Higher pulse time and pulsed
current produced poor surface finish. However, up to certain
pulse time (6 s), surface roughness was different comparing to
2 s pulse pause time results. For the same machining conditions, surface roughness was 2–3 m for 2 s pulse pause time
and 6 m for 3 s pulse pause time. Pulsed current showed a
similar trend, increasing current gave high surface roughness.
Table 2
Parameters of examinations
Number of test
1
Pulsed current (A)
Pulse time (s)
Pulse pause time (s)
Surface roughness (Ra ) (workpiece)
Surface roughness (Ra ) (electrode)
2
3
4
5
6
7
8
9
10
11
12
13
8
2
2
1.8
1.8
8
4
2
3.8
2.2
8
6
2
5.3
2.6
8
12
2
5.7
3.0
8
24
2
7.2
3.1
8
48
2
8.1
3.3
8
100
2
8.7
3.4
8
3
3
1.8
2.1
8
4
3
2.4
2.6
8
12
3
5.0
3.0
8
24
3
6.3
3.1
8
48
3
8.0
3.2
8
100
3
8.9
3.3
Number of test
1
Pulsed current (A)
Pulse time (s)
Pulse pause time (s)
Surface roughness (Ra ) (workpiece)
Surface roughness (Ra ) (electrode)
2
3
4
5
6
7
8
9
10
11
12
13
16
2
2
2.5
2.2
16
4
2
5.0
3.4
16
6
2
6.4
3.6
16
12
2
6.7
3.7
16
24
2
8.4
4.3
16
48
2
9.3
4.6
16
10
2
10.4
4.7
16
3
3
2.3
2.5
16
4
3
3.0
3.0
16
12
3
5.7
3.8
16
24
3
7.0
3.9
16
48
3
8.6
4.3
16
100
3
10.1
4.3
Number of test
1
Pulsed current (A)
Pulse time (s)
Pulse pause time (s)
Surface roughness (Ra ) (workpiece)
Surface roughness (Ra ) (electrode)
2
3
4
5
6
7
8
9
10
11
12
13
16
2
2
3.1
3.0
16
4
2
5.2
3.5
24
6
2
6.7
3.6
24
12
2
8.5
3.9
24
24
2
9.4
4.4
24
48
2
9.7
4.7
24
100
3
11.3
4.8
24
3
3
3.0
3.0
24
4
3
3.2
3.1
24
12
3
6.6
3.8
24
24
3
7.5
4.2
24
48
3
9.0
4.4
24
100
3
10.9
4.4
M. Kiyak, O. Cakır / Journal of Materials Processing Technology 191 (2007) 141–144
¸
143
Fig. 2. Effects of pulse time and pulsed current on surface roughness of workpiece (3 s pulse pause time).
Fig. 4. Effects of pulse time and pulsed current on surface roughness of electrode
(3 s pulse pause time).
Surface finish quality was better when applying smaller
pulsed current and pulse time. This is because of small particle size and crater depths formed by electrical discharge. As a
result, the best surface finish will be produced. The selection of
these machining parameters for EDM of any material should be
used for a higher surface quality is required.
It was observed that when pulsed current and particularly
pulse time increased, machined workpiece surface exhibited a
higher surface roughness due to irregular topography. Pulsed
current had an effect on surface roughness at low pulse time,
but the influence of pulse time was more significant than pulsed
current at higher pulse times.
It was noticed that excellent machined surface quality could
be obtained by setting machining parameters at a low pulse current and short pulse time. This combination will unfortunately
produce low material removal rate and cause high machining
time, in total high machining cost. When high material removal
rates are needed, high pulsed current and pulse times should
be selected. However, this selection will produce a poor surface finish due to deeper and wider crates on the machined
surface. There is also an influence on dielectric fluid at high
pulsed current; the properties will be lost because of high
temperature.
Second stage of the experimental study considered to examine the surface roughness of electrode. The bottom surface
of the electrode, which is continuously contacted to workpiece, was investigated. For the same machining conditions,
the experimental results were given in Figs. 3 and 4. Low
pulse times and pulsed currents provided a better surface quality for both duration times. It was observed that pulse pause
time was an influential parameter; 2 s of pulse pause time pro-
vided better surface quality comparing to 3 s of pulse pause
time.
Similar surface roughness results were noticed for electrode
surface roughness. It was observed that the surface roughness
of electrode was better when applying smaller pulsed current
and pulse time. When pulsed current and pulse time increased,
electrode surface presented a higher surface roughness. Pulsed
current had an effect on surface roughness of electrode at low
pulse time, but the influence of pulse time was more significant
than pulsed current at higher pulse times. The effect of pulse
pause time was insignificant.
Fig. 3. Effects of pulse time and pulsed current on surface roughness of electrode
(2 s pulse pause time).
4. Conclusion
The experimental study of the EDM of 40CrMnNiMo864
tool steel (AISI P20) tool steel provided important quantitative
results for obtaining possible high surface finish quality and
machining outputs as follows:
a. Surface roughness increased with increasing pulsed current
and pulse time. Low current and pulse time with high pulse
pause time produced minimum surface roughness that means
good surface finish quality. The selection of these machining
parameters is not useful because machining process generally becomes very slow. Material removal rate will be low
and thus machining cost increases. This combination should
be used in finish machining step of EDM process.
b. High pulsed current and pulse time provide low surface finish
quality. However, this combination would increase material
removal rate and reduce machining cost. As a result, this
combination (high pulsed current and pulse time) should be
used for rough machining step of EDM process.
c. From power point of view, rough and finish machining steps
require different level of machine power. For rough EDM
application, the machine power should be one-fourth of the
produced power with 16 A of current, 6 s of pulse time and
3 s of pulse pause time. Finish machining should be carried
out at one-half level of power at 8 A of current as well as 6 s
of pulse time and 3 s of pulse pause time.
d. Increasing wear on electrode surface is unavoidable during
EDM process. Therefore, workpiece surface roughness will
be increasing due to wear rate on electrode.
e. Wear on electrode surface is unavoidable during EDM
process. Surface roughness of machined workpiece would
144
M. Kiyak, O. Cakır / Journal of Materials Processing Technology 191 (2007) 141–144
¸
increase when surface quality of electrode decreases due to
pulsed current density.
f. For the same pulse pause time, the trends of surface roughness on the workpiece and electrode are similar. Thus, there
will be a relation between wear on electrode and increase of
surface roughness from workpiece surface quality point of
view.
Acknowledgements
Authors would like to thank two companies (OPAS and
ERDEM) for kind encouragement and technical support. They
are also thankful to Mech. Eng. Ca˘ atay ACAR for his sincere
¸ g
help throughout this research.
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