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Some anomalies in the experimental results of EDM

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In electro discharge machining (EDM) the metal removal occurs from the erosive effects of high frequency sparks. Consequently the erosion rate depends on spark energy, sparking frequency and the factors affecting them. However, the experimental results are highly random and sometimes unexpected. Material erosion rate and surface roughness were analysed for the effect of important factors like pulse parameters (voltage, current, on time and off time), polarity and work material. Taguchi method of experiment planning with orthogonal arrays was adopted to analyse the anomalies observed in the experimental results.
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Int. J. Manufacturing Technology and Management, Vol. 24, Nos. 1/2/3/4, 2011 57
Copyright © 2011 Inderscience Enterprises Ltd.
Some anomalies in the experimental results of EDM
K. Buschaiah*
Department of Mechanical Engineering,
University College of Engineering,
Osmania University,
Hyderabad – 500 007, India
E-mail: bkarrolla@gmail.com
*Corresponding author
P. Laxminarayana
University College of Technology,
Osmania University,
Hyderabad – 500 007, India
E-mail: laxp@rediffmail.com
V.S.R. Murti
Sree Visvesvaraya Institute of Technology and Science,
Mahabubnagar – 509 204, India
E-mail: drvsrmurti@yahoo.com
Abstract: In electro discharge machining (EDM) the metal removal occurs
from the erosive effects of high frequency sparks. Consequently the erosion
rate depends on spark energy, sparking frequency and the factors affecting
them. However, the experimental results are highly random and sometimes
unexpected. Material erosion rate and surface roughness were analysed for the
effect of important factors like pulse parameters (voltage, current, on time and
off time), polarity and work material. Taguchi method of experiment planning
with orthogonal arrays was adopted to analyse the anomalies observed in the
experimental results.
Keywords: metal removal rate; surface roughness; orthogonal array.
Reference to this paper should be made as follows: Buschaiah, K.,
Laxminarayana, P. and Murti, V.S.R. (2011) ‘Some anomalies in the
experimental results of EDM’, Int. J. Manufacturing Technology and
Management, Vol. 24, Nos. 1/2/3/4, pp.57–70.
Biographical notes: K. Buschaiah is a Research Scholar in the Department of
Mechanical Engineering, University College of Engineering (A), Osmania
University, Hyderabad, India. He is pursuing his PhD on EDM. Currently, he is
working as a Scientist in Osmania University. Previously, he has worked as
Technical Assistant in BDL, Hyderabad. He joined Osmania University as
Laboratory Assistant at Department of Mechanical Engineering, Osmania
University and later promoted as Scientist. He obtained his graduation from
JNTU, Hyderabad and post graduation from Osmania University. His research
interests are manufacturing technology and surface metrology.
58 K. Buschaiah et al.
P. Laxminarayana received his PhD in Mechanical Engineering from Osmania
University in 2003. He joined university service as an Assistant Professor in
1991 and became Professor in 2005. Currently, he is the Head, Department of
Mechanical Engineering, University College of Engineering (A), Osmania
University, Hyderabad. His research and teaching interest are in the area of
material science, manufacturing and metrology.
V.S.R. Murti received his PhD in the Mechanical Engineering from IIT
Madras, Chennai in 1988. He received the Best Teacher Award in the year
2000 from Osmania University. He published more than 100 technical papers
in various international and national journals and conference proceedings. His
research areas are materials and manufacturing science. He was a national
bridge player and represented A.P. many times. He won many awards at the
national level. He worked as a faculty for 34 years in Mechanical Engineering
Department, O.U. He also worked as the Head of the Department. After his
retirement, he worked as Professor Emeritus for two years in Department of
Mechanical Engineering, Osmania University, Hyderabad. Later, he moved to
SVITS, Mahabubnagar as the Director (Academic) and worked there till his last
breathe. He passed away on 29th March 2011.
This paper is a revised and expanded version of a paper entitled ‘Some
Anomalies in the Experimental Results of EDM’ presented at 3rd International
and 24th All India Manufacturing Technology, Design and Research
Conference-2010 (AIMTDR-2010), Vishakhapatnam, India, 13–15 December
2010.
1 Introduction
Electro discharge machining (EDM) employs high frequency sparks for machining
difficult to machine materials and contours. The tool and work piece form a pair of
electrodes, separated by about 20 to 200 µm in a liquid dielectric medium through which
the spark discharges occur (Figure 1). The volume of metal removed ranges between 2 to
400 mm3/min which in combination with associated frequencies of several kHz amount
to about 10–6 to 10–4 mm3 per spark discharge. The result of machining process is
material removal and the surface roughness. In EDM the erosion being thermal, i.e., by
melting from spark heat, the erosion rate and the surface roughness depend primarily on
the work material property (enthalpy of melting), sparking frequency and spark energy
(Jeelani and Pandey, 1983; Kunieda et al., 2005). The last one depends on pulse voltage,
current and pulse on and off times. Combining these one can write a generalised
relationship for material removal rate in EDM.
()
(
)
. .....
pm ps s on d o off d
mC T L CT fVI t t fVsI t t t
⎡⎤
++ = − = − −
⎣⎦ (1)
where m is the erosion rate in gram per second Tm, L and Ts are melting point, latent heat
of melting and superheat of eroded material respectively and Cp is the specific heat. f, Vs
and I are the frequency, sparking voltage and average current and to, ton, toff and td are
respectively pulse time, pulse on time, pulse off time and ignition delay. These terms are
illustrated in Figure 2 and Figure 3.
Some anomalies in the experimental results of EDM 59
The cycle time has two components, on time and off time. The spark occurs after a
time lag (td) called as ignition delay. Thus, effective sparking time is equal to
(to – toff td). The pulse energy is then equal to Vs.I.(to – toff td). There are two types of
pulse generators. One called as iso frequent, has constant frequency or pulse time
(ton + toff). Thus, the pulse energy varies from pulse to pulse depending on ignition delay
(td). The other one and more common is iso pulse generator which provides pulses of
constant energy, i.e., equal discharge times thus spark frequency will be variable
(cycle times t1, t2, t3, etc., are all different, Figure 3). The advantage of iso pulse generator
is that due to constant energy sparks the erosive effect of each spark will be similar
and a uniform surface roughness is produced which can be set as the control parameter
in the adaptive control system of EDM. In both the cases, the effective sparking
pulses are reduced by open circuit, arcing and short circuit pulses. The explanation on
voltage and current wave forms is to distinguish between effective pulses and ineffective
pulses.
Effective pulses are:
1 pulses with low ignition delay
2 pulses with medium ignition delay
3 pulses with large ignition delay.
Ineffective pulses are:
1 short circuit pulses
2 open circuit pulses
3 arcing pulses.
Figure 1 General features of EDM
Filter unit
Pump
Insulation
Column
Servo
control
Power
supply
+
Dielectric
Tool
Table
60 K. Buschaiah et al.
Figure 2 Ideal theoretical pulse shapes (iso frequent)
V
o
= Open cir cuit voltage
V
s
= Spark voltage
T
o
= Cycle time = t
on
+ t
off
V
V
o
V
s
t
on
t
off
t
d
Open Lar ge t
d
Small t
d
Arc Micro µ Sec
Circuit Short
Effective pulses
I
I
s
µ Sec
t
s
Figure 3 Ideal theoretical pulse shapes (iso pulse) showing only effective sparking pulses
t
1
t
2
t
3
µ Sec
t
d
t
on
t
off
small t
d
large t
d
V
I
µ
Sec
These are ineffective pulses and do not cause material erosion. Their occurrence is
explained in Figure 4. The inter electrode distance is the spark gap which is maintained
uniform by a servo control system which feeds the electrode at a uniform feed rate
compatible to erosion rate. Stable sparking requires spark gap to be maintained with
electrode position within zone 2 to 3. If the spark gap increases (zone 1 to 2), it results in
open circuit and sparks extinguish. This occurs if the electrode feed rate is lower than
erosion rate. On the other hand if the spark gap reduces (electrode position in the region 3
Some anomalies in the experimental results of EDM 61
to 4) short circuits occur due to bridging of electrodes by erosion debris (d). This occurs
when electrode feed rate exceeds erosion rate.
Figure 4 Theoretical configuration of spark gap and working pulses
Other ineffective pulses occur from arcing whereby successive sparks occur at the same
spot due to poor deionisation of spark gap during pulse off time. As soon as short circuit
occurs it is detected by servo control system which retraces the electrode to open circuit
condition (location 1) whence the electrode is again fed forward at the preset speed. The
spark gap for effective sparking depends on the size and density of erosion debris present
(d). The number of pulses resulting in effective erosion is thus reduced by ineffective
pulses from open circuit, short circuit and arcing pulses. The erosion rate is thus further
dependent on servo response characteristics and the extent of contamination of spark gap
by erosion debris.
The actual surface after EDM has a typical appearance with characteristics features of
spark erosion. The machined specimens were studied under SEM to analyse the
morphology and metallurgical characteristics of spark eroded surfaces. The severity and
rapidity of spark discharges result in certain induced effects like cracking residual
stresses and enhanced micro hardness which are also studied.
2 Experimental plan
The machining of specimens was carried out on a CHARMILLES EDM (Sinker EDM,
Model: Robo Form-54) with the copper electrode and kerosene dielectric. The process
variable were pulse current, voltage, pulse on time, pulse off time, type of work material
and polarity setting where as the process characteristics analysed were machining rate
and surface roughness. The selected L8(26) Orthogonal array of Taguchi method (Tzeng
62 K. Buschaiah et al.
and Chen, 2003) is listed in Table 1. The associated factors and the coded levels are listed
in Table 2. For better accuracy, randomisation and replication were adopted.
Table 1 L
8(26) orthogonal array
Factors
Expt.
no.
A
Current
B
Voltage
C
TON
D
TOFF
E
Work
material
F
Polarity
1 1 1 1 1 1 1
2 1 1 1 2 2 2
3 1 2 2 1 1 2
4 1 2 2 2 2 1
5 2 1 2 1 2 1
6 2 1 2 2 1 2
7 2 2 1 1 2 2
8 2 2 1 2 1 1
Table 2 Factor levels classification
Levels
S no. Factor 1 2 Remarks
1 Current 8 Amp 16 Amp Peak current
2 Voltage 120 V 160 V Open circuit voltage
3 TON 100 μs 200 μs Pulse on time
4 TOFF 12.8 μs 50 μs Pulse off time
5 Work material A1 Steel Based on melting point and
enthalpy of melting
6 Polarity Straight Reverse Based on electrode polarity
Straight: electrode negative
Reverse: electrode positive
Table 3 Nominal composition of HSS-PM (Wt%)
Cr Fe Cu Zn Mo Sn W Total
5.75 67.66 0.00 0.00 12.69 0.00 3.90 100.00
3 Results and discussion
3.1 Material removal rate
The machining rates (MR) estimated in terms of mm3/min. for the selected factors and
their levels are listed in Table 4 with graphical display in Figure 5 under it. The effect of
work material properties is considerable. In EDM the erosion being from melting from
spark energy, two contradictory effects come into play. Lower enthalpy of melting leads
to higher erosion rates but higher thermal conductivity reduces heat concentration.
Whichever of these effects is more; the erosion rate is affected likewise. Relative to HSS,
Some anomalies in the experimental results of EDM 63
aluminium has considerably lower enthalpy of melting and its effect is more compared to
its higher conductivity and the net result is higher erosion rates. With higher current and
pulse on times the erosion rates are higher for both aluminium and HSS. Their effect of
increasing pulse energy also results in higher erosion rates (Bhattacharya, 1981). But the
effect of current is more compared to pulse times. The reason being the reduction of
energy concentration due to expansion of plasma channel with higher pulse times.
Similarly with higher voltage, though the pulse energy increases, the erosion rate exhibits
reduction owing to increase in spark gaps with higher voltage (Cook, 1973). The longer
spark gaps lead to expansion of plasma channel due to mutual repulsion of similar charge
carriers which causes lower energy density of sparks. The effect of pulse off time is not
surprising. Lower off time leads to improved utilisation of spark energy and increase in
erosion rates. On the other hand it can also lead to poor deionisation and produce arcing.
Low off times also hinder effective gap flushing thus leading to short circuits. Higher
pulse off time can lead to superior results by effective deionisation and gap flushing.
Thus depending on the net results of these contradictory effects, the erosion rate can be
higher with higher pulse off time as in the present case. Of all the factors the polarity
setting has most profound effect. Electrode positive (anode) leads to higher MR. Though
the charge carriers have same energy, and release at respective electrodes, their density
levels are very different. Sparks are ionic discharges with electrons being absorbed at
anode and ions at cathode through the plasma channel. Being similar charge carriers there
is mutual repulsion, which is very high for electrons compared to ions due to their
negligible mass. Therefore the energy concentration at cathode (work electrode) is very
high due to very low expansion of ions of higher mass. Naturally this leads to very high
erosion rates of cathode and accordingly electrode positive and work piece negative
polarity is preferred.
Table 4 Response table for MR (mm3/min)
Current Voltage TON T
OFF Work
material Polarity
S. no.
M
achining
rate
1 2
1 2 1 2 1 2 1
A1
2
HSS
1 SP
(–)
2 RP
(+)
1 8.33 8.33 8.33 8.33 8.33 8.33 8.33
2 20.68 20.68 20.68 20.68 20.68 20.68 20.68
3 22.46 22.46 22.46 22.46 22.46 22.46 22.46
4 9.06 9.06 9.06 9.06 9.06 9.06 9.06
5 12.32 12.32 12.32 12.32 12.32 12.32 12.32
6 34.48 34.48 34.48 34.48 34.48 34.48
7 26.76 26.76 26.76 26.76 26.76 26.76
8 10.66 10.66 10.66 10.66 10.66 10.66 10.66 26.76
Total 144.75 60.53 84.22 75.81 68.94 66.43 78.32 69.87 74.89 75.93 68.82 40.37 104.38
Average 18.09 15.13 21.05 18.95 17.23 16.61 19.58 17.47 18.72 18.98 17.2 10.09 26.09
Estimated main
effect
+5.92 –1.72 +2.97 +1.25 –1.78 +16
Slope 2.96 0.86 1.49 0.625
64 K. Buschaiah et al.
Figure 5 Graphic display of factor effects on machining rate corresponding to Table 4
3.2 Surface roughness
The results in surface roughness are shown in Table 5 and Figure 6 and follow the same
pattern as MR as expected with any machining process. Higher erosion rates in EDM are
generally associated with higher spark energy. The electrical sparks cause local melting
and erosion in the form of atomised particles leaving behind spherical craters. This is the
widely put forth and accepted erosion mechanism in EDM (Ho and Newan, 2003; Kumar
et al., 2009). The final surface is Matty as a result of overlapping spark craters. Larger
pulse energies produce larger spark craters and result in higher surface roughness.
However, the effects of higher current and pulse on time are different.
Table 5 Response table for surface roughness (µm)
Current Voltage TON T
OFF Work
material Polarity
S. no.
R
oughness
‘Ra’
1 2
1 2 1 2 1 2 1 2
1 2
1 1.46 1.46 1.46 1.46 1.46 1.46 1.46
2 1.94 1.94 1.94 1.94 1.94 1.94 1.94
3 1.72 1.72 1.72 1.72 1.72 1.72 1.72
4 2.11 2.11 2.11 2.11 2.11 2.11 2.11
5 2.63 2.63 2.63 2.63 2.63 2.63 2.63
6 3.06 3.06 3.06 3.06 3.06 3.06 3.06
7 3.55 3.55 3.55 3.55 3.55 3.55 3.55
8 3.18 3.18 3.18 3.18 3.18 3.18 3.18
Total 19.65 7.23 12.42 9.09 10.56 10.13 9.52 9.36 10.29 9.42 10.23 9.38 10.27
Average 2.45 1.80 3.10 2.27 2.64 2.53 2.38 2.34 2.57 2.35 2.55 2.34 2.56
Estimated main
effect
+1.3 +0.37 –0.15 +0.23 +0.2 +0.22
Slope 0.65 0.18 –0.075 0.11
Figure 6 Graphic display of factor effects on surface roughness corresponding to Table 5
Some anomalies in the experimental results of EDM 65
A higher magnitude of current causes a corresponding high pulse energy producing a
large depth of crater for the same pulse times. But for same pulse energy a higher pulse
on time leads to expansion of plasma column and larger crater diameter. If one constructs
a model of overlapping spark craters of equal volume (spherical segment) with varying
depth (effect of current) and diameter (effect of pulse times). One can observe the effects
on the roughness height. A 12 mm diameter electrode is considered for the construction
of a model of overlapping spark craters (spherical segment) and it is illustrated in
Figure 7 along with the estimated roughness height. ‘Ra’ is the average roughness created
by a set of overlapping spherical craters is shown at Figure 7(a). At Figure 7(b) is the
average roughness ‘Rb’ generated by a set of overlapping spherical craters of larger
diameter but smaller depth (effect of higher pulse time) and at Figure 7(c) is the average
surface roughness ‘Rc’ generated by spherical craters of larger depth (effect of higher
current) and lower diameter. The roughness Rc is more than Ra which in turn higher than
Rb. This demonstrates that the effect of current in generating craters of larger depth and
effect of pulse times in increasing crater diameter. The former leads to higher roughness
heights and the latter to smaller ones.
Figure 7 Schematic mechanism of surface roughness generation in EDM Rc > Ra > Rb,, (a) over
lapping spark craters (b) over lapping spark craters with larger diameter and lower depth
(c) over lapping spark craters with smaller diameter and larger depth
R
a
= 0.6190
(a)
R
b
= 0.5973
(b)
R
c
= 0.6431
(c)
3.3 Morphology and integrity of EDM surfaces
The actual surface after EDM has a typical appearance with characteristic features of
spark erosion. The machined specimens were studied under SEM to analyse the
morphology and metallurgical characteristics of the spark eroded surfaces. The severity
and rapidity of spark discharges result in certain induced effects like cracking, residual
stresses and enhanced micro hardness which are also studied. Owing to restricted
availability of SEM as well as similarity in the observations only representative
photomicrographs are presented.
The SEM photographs of the EDM surfaces with inherent characteristic features in
the form of overlapping craters, frozen droplets, pin holes and debris particles
incorporated in the surface (Figure 8). Melting of crater metal and its violent expulsion
and the associated turbulence are clearly evident. The surface formed by the overlapping
craters, their forms and the metal in the crater rims are clearly indicated.
66 K. Buschaiah et al.
The pock marks or burst blisters caused by the burst of supersaturated absorbed gases
shows the shell type of structure of the top surface of the frozen layer [Figure 9(a) and
Figure 9(b)]. The EDM surface exhibits the existence of a network of fine cracks on the
machined surface. Figure 9(c) and Figure 9(d) show the dendritic nature of the cracks on
the surface like draught affected land. Thermal stress cracking occurs due to high
temperature gradients. If phase transformation occurs or new phases form then additional
transformation stresses are created. Steep temperature changes create thermal shock
cracking. In the region near the surface, tensile stresses arise during cooling with
compressive stresses in the deeper lying regions (Laxminarayana et al., 2006). The stress
in the thin surface layer is very high since the deeper lying regions permit only a limited
amount of deformation to occur. The cracks are generally limited to the shell type of the
structure of the top surface, which is generally the recast layer.
Figure 8 SEM photographs of EDM surfaces illustrating the effect of work material and polarity
on the morphology of the eroded surfaces, (a) HSS surface (electrode negative)
(b) HSS surface (electrode positive) (c) aluminium surface (electrode negative)
(d) aluminium surface (electrode positive)
(a) (b)
(c) (d)
The morphology of the spark eroded surfaces clearly indicates the erosion to have
occurred in molten state from the spots of spark impingement. There is a possible
mechanism of erosion in vapour form also but is doubtful owing to the high cooling
effect of liquid dielectric surrounding the spark spot. The expulsion is not complete or
perfect from the molten zone of the spark impingement (Laxminarayana et al., 2004).
Some anomalies in the experimental results of EDM 67
There is a residual layer of metal, which appears to have resolidified. The surface formed
by overlapping craters and the resolidified metal has some other characteristic features
also in the form of pinholes and solidified layer. The pinholes or pockmarks are caused
by the burst of escaping supersaturated gases. The EDM sparks produce craters from
which the metal could have been ejected in any of the three possible modes of melting,
evaporation and thermal spalling of their combination. The actual mechanism of spark
erosion is difficult to formulate. But the observations of spark craters point to the
dominant mode being melting as erosion mechanism as already discussed. The presence
of hollow spherical debris may be due to metal removal in vapour form. Thermal spalling
is a possibility particularly in PM work materials. To investigate this possibility PM
(Al-SiC MMC) specimens were also machined and observed under SEM (Figure 10).
Melting of surrounding binders can cause thermal spalling of refractory SiC grains
(Figure 11). The large cavities seen are indicative of such physical expulsion of SiC
grains. Owing to melting from sparks, the voids however get filled up in PM materials
and the surfaces appear more uniform and exhibit similarity to conventional material
erosion.
Figure 9 Some typical characteristic features of EDM surfaces, (a) and (b) pock marks appearing
like burst blisters formed by escaping dissolved gases (c) and (d) a nature of
microcracks owing solidification shrinkage giving an appearance of a draught affect
land
(a) (b)
(c) (d)
Note: The cracks being limited to tip layer only.
68 K. Buschaiah et al.
Figure 10 SEM photographs showing the relative features of wrought and PM surfaces
before and after EDM, (a) HSS surface before EDM (b) MMC surface before EDM
(c) HSS surface after EDM (d) MMC surface after EDM (see online version
for colours)
(a) (b)
(c) (d)
Figure 11 (a) SEM photographs showing large erosion pits (b) schematic illustration of ejection
of a grain owing to melting of surrounding metal matrix (see online version
for colours)
(a)
(b)
Some anomalies in the experimental results of EDM 69
The morphology of MMC (Al-SiC alloy) parts show remarkable similarity between
unmachined and machined surfaces because of the melting of binder metal matrix during
sintering. However the machined surfaces exhibit more even melting and resolidification
of the metal matrix. Melting is clearly seen as the major mode of spark erosion of both
types of metals and is manifest also as the resolidified layer of the residual metal in the
overlapping spark craters and the cracking witnessed therein. Metal also causes filling up
of pores in PM and MMC materials. Compressive force of spark can cause lateral
expansion of grains causing dislodgement of adjacent grains. In case of MMC the metal
matrix may melt and may promote spalling of the embedded hard particles. The cracks
that occur in the resolidified layer can promote mechanical separation. Evaporation as a
mode of spark erosion is unrealistic owing to high thermal conduction of metals and also
quenching by the dielectric. However the suspended debris in the spark gap is subjected
to extremely high temperatures of the spark channel, which can cause their evaporation
and coalescence. This can also be the cause of the relatively large size of erosion debris
(Rajurkar et al., 1983; Patel et al., 2009; Puertas and Luis, 2011) a factor put forth in
support of vaporisation mechanism of erosion.
4 Concluding remarks
EDM is a highly complex as well as unpredictable process. The experimental results
broadly follow the expected lines but the process is highly random with several factors
whose interaction effect coupled with noise factors in the EDM process can produce on
occasions quite a few anomalous results as listed below.
1 An increase in voltage increases spark energy which should lead to increased
machining rate, but here the opposite occurs.
2 Toff or pulse off time reduces effective sparking time which should reduce the
machining rate, but here the MRR increases with Toff.
3 Electrode negative is considered to produce higher erosion rate. However, here
electrode positive leads to higher MRR.
4 Similarly in the case of surface roughness, higher Ton (Pulse on time) leads to lower
roughness though it is expected otherwise since it produces higher MRR.
5 Aluminium with higher MRR compared to steel should have higher roughness also
but it is not so.
6 A non-conducting ceramic can be made conductive by doping with a conducting
metal. MMCs by nature are conductive therefore can be easily machined by EDM,
where as conventional method would be very difficult.
The metal removal rate and surface roughness have analogous pattern and depend on
spark energies. Thus, they increase with pulse voltage, current and duration. However,
their net effect depends on the final result from the corresponding effect of reduction
in spark energy densities due to increase in the plasma channel dimension from mutual
repulsion of similar charge carriers.
Large spark gaps from higher voltage and pulse times promote this phenomenon.
Accordingly, one finds lower erosion rates and roughness at higher voltage and pulse
70 K. Buschaiah et al.
time. Similarly, the effect of work material properties on the erosion rates and surface
roughness depends on the net effect of enthalpy of melting and conductivity (thermal and
electrical). Of all the factors, electrode polarity is most significant. The reverse polarity,
i.e., electrode positive leads to most effective machining. This is followed by work
material, pulse duration, current and voltage.
Acknowledgements
The authors are thankful to the organisers of AIMTDR 2010 Conference, in which the
original paper was presented.
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ResearchGate has not been able to resolve any citations for this publication.
Article
Electric discharge machining (EDM) has been proven as an alternate process for machining complex and intricate shapes from the conductive ceramic composites. The performance and reliability of electrical discharge machined ceramic composite components are influenced by strength degradation due to EDM-induced damage. The success of electric discharge machined components in real applications relies on the understanding of material removal mechanisms and the relationship between the EDM parameters and formation of surface and subsurface damages. This paper presents a detailed investigation of machining characteristics, surface integrity and material removal mechanisms of advanced ceramic composite Al2O3–SiCw–TiC with EDM. The surface and subsurface damages have also been assessed and characterized using scanning electron microscopy (SEM). The results provide valuable insight into the dependence of damage and the mechanisms of material removal on EDM conditions.
Article
This paper aims to show the prospects of electrical discharge machining (EDM) technology by interrelating recent achievements in fundamental studies on EDM with newly developed advanced application technologies. Although gap phenomena in EDM are very complicated and hence not yet very well understood, recent improvements in computers and electronic measuring instruments are contributing to new discoveries and inventions in EDM technology. Such newly acquired insight sometimes raises questions on the validity of the established theories of EDM phenomena, and EDM processes once believed to be impossible or unrealistic are now becoming practical.
Article
The last decade has seen an increasing interest in the novel applications of electrical discharge machining (EDM) process, with particular emphasis on the potential of this process for surface modification. Besides erosion of work material during machining, the intrinsic nature of the process results in removal of some tool material also. Formation of the plasma channel consisting of material vapours from the eroding work material and tool electrode; and pyrolysis of the dielectric affect the surface composition after machining and consequently, its properties. Deliberate material transfer may be carried out under specific machining conditions by using either composite electrodes or by dispersing metallic powders in the dielectric or both. This paper presents a review on the phenomenon of surface modification by electric discharge machining and future trends of its applications.
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