comparative study for mrr on die-sinking edm using electrode ... - ijater

International Journal of Advanced Technology & Engineering Research (IJATER) 

COMPARATIVE STUDY FOR MRR ON DIE-SINKING 

EDM USING ELECTRODE OF COPPER & GRAPHITE 

Authors 1 Nikhil Kumar, 2 Lalit Kumar, 3 Harichand Tewatia, 4 Rakesh Yadav 

Abstract 

Electrical discharge machining (EDM) is one of the nontraditional 

machining processes, based on thermo electric 

energy between the work piece and an electrode. In this 

process, the material removal is occurred electro thermally 

by a series of successive discrete discharges between electrode 

and the work piece. The per<strong>for</strong>mance of the process, to 

a large extent, depends on the Electrode material, Work 

piece material manufacturing method of the electrodes. A 

suitable selection of electrode can reduce the cost of machining. 

So in this paper Die- Sinker EDM using copper and graphite 

electrode experiment has been done <strong>for</strong> optimizing 

Per<strong>for</strong>mance parameters and reducing cost of manufacturing, 

finally it is found that a silver electrode give better per<strong>for</strong>mance 

in certain characteristics but the cost become high <strong>for</strong> 

machining so keeping in mind cost and other some characteristics 

a graphite electrode is more suitable than copper electrode 

in case of both MRR and TWR. 

Keywords: - Die -Sinker EDM, MRR, TWR 

1. Introduction 

In the Die -Sinker EDM Machining process, two 

metal parts submerged in an insulating liquid are connected 

to a source of current which is switched on and off automatically 

depending on the parameters set on the controller. 

When the current is switched on, an electric tension is 

created between the two metal parts. If the two parts are 

brought together to within a minimum gap, the electrical 

tension is discharged and a spark jumps across. Where it 

strikes, the metal is heated up so much that it melts. Sinker 

EDM, also called cavity type EDM or volume EDM consists 

of an electrode and work piece submerged in an insulating 

liquid such as, oil or, less frequently, other dielectric fluids. 

The electrode and workpiece are connected to a suitable 

power supply. The power supply generates an electrical potential 

between the two parts. As the electrode approaches 

the work piece, dielectric breakdown occurs in the fluid, 

<strong>for</strong>ming a plasma channel, and a small spark jumps. These 

sparks usually strike one at a time because it is very unlikely 

that different locations in the inter-electrode space have the 

identical local electrical characteristics which would enable 

a spark to occur simultaneously in all such locations. These 

sparks happen in huge numbers at seemingly random locations 

between the electrode and the work piece. As the base 

metal is eroded, and the spark gap subsequently increased, 

the electrode is lowered automatically by the machine so that 

the process can continue uninterrupted. Several hundred 

thousand sparks occur per second, with the actual duty cycle 

carefully controlled by the setup parameters. 

1.1 Why copper Electrode 

With development of the transistorized, pulse-type power 

supplies, Electrolytic (or pure) Copper became the metallic 

electrode material of choice. This is because the combination 

of Copper and certain power supply settings enables low 

wear burning. Also, Copper is compatible with the polishing 

circuits of certain advanced power supplies. Many shops in 

both Europe and Japan still prefer to use Copper as the primary 

electrode material, due to their tool making culture that 

is averse to the “untidiness” of working with graphite. Due 

to its structural integrity, Copper can produce very fine surface 

finishes, even without special polishing circuits. This 

same structural integrity also makes Copper electrodes highly 

resistant to DC arcing in poor flushing situations. Copper 

is frequently used to make female electrodes on a Wire 

EDM <strong>for</strong> subsequent use in reverse burning punches and 

cores in the Sinker EDM. The addition of 1-3% Tellurium to 

Copper improves its machinability to a level similar to brass, 

eliminating the “gummy” properties normally exhibited by 

Copper when it is machined. 

1.2 Why Graphite Electrode 

Graphite is the preferred electrode material <strong>for</strong> 90% of all 

sinker EDM applications. Thus, it is important that we expend 

considerable ef<strong>for</strong>t to understand its properties and 

application to EDM. 

Graphite was introduced to the EDM industry approximately 

50 years ago. One of the early well known brands of graphite 

was manufactured by General Electric, and known by 

the trade name of “Gentrode”. Graphite is made from Carbon 

derived from petroleum. The powdered Carbon is mixed 

with petroleum based binder material and then compacted. 

How the graphite is compacted in this stage of production is 

vitally important to its ultimate properties. All early graphites 

were made by compressing the powder/binder mixture 

ISSN NO: 2250-3536 VOLUME 2, ISSUE 2, MAY 2012 170


in only one direction, resulting in properties or “grain” similar 

to wood, that varied relative to the direction of pressing. 

As an outgrowth of the space program, methods were developed 

to isostatically press graphite such that its properties 

became “isotropic”, that is the same in all directions. All 

high quality, high per<strong>for</strong>mance graphites are now manufactured 

this way. After compacting, the “green” compacted 

material undergoes a series of thermal treatments that convert 

the Carbon to graphite. Graphite has certain properties 

quite different than wrought metal based electrode materials: 

• Graphite has an extremely high melting point. Actually, 

graphite does not melt at all, but sublimes directly from a 

solid to a gas (just as the Carbon Dioxide in dry ice) at a 

temperature thousands of degrees higher than the melting 

point of Copper. This resistance to temperature makes graphite 

an ideal electrode material. 

• Graphite has significantly lower mechanical strength properties 

than metallic electrode materials. It is neither as hard, 

as strong, nor as stiff as metallic electrode materials. However, 

since the EDM process is one of relatively low macro 

mechanical <strong>for</strong>ces, these property differences are not often 

significant. Due to the significant differences between metallic 

electrodes and graphite, there are certain properties, 

unique to graphite that are commonly specified and controlled. 

Fig. 1 Die-Sinker EDM Set-up 

1.3 Characteristics of die-Sinker 

EDM 

The characteristics necessary <strong>for</strong> die-sinker EDM are given 

below in the table 

Table 1 Process Parameters of Die-Sinker EDM Process 

Mechanism of Processes Controlled erosion (melting 

Spark gap 

Spark frequency 

Peak voltage across the gap 

Metal removal rate (max.) 

Specific power consumption 

Dielectric fluid 

Tool material 

Machine-able materials 

Shapes that can be produced 

Limitations 

and evaporation) 

0.010 – 0.500 mm 

200 – 500 KHz 

30 – 250 V 

5000 mm3/min. 

2 – 10 W/mm3/min. 

EDM oil, Kerosene liquid, 

Silicon oil, Deionised water 

etc. 

Copper, Brass, Graphite, Ag- 

W alloy, Cu-W alloy 

All conducting metals and 

alloys 

Micro holes, Narrow slots 

High energy consumption, 

can’t machined nonconducting 

materials 

2. Literature Review 

In this paper few selected research paper related to Diesinker 

EDM with effect of metal MRR, surface roughness 

(SR), workpiece material 

2.1 Workpiece and tool material- 

Dhar and Purohit evaluates the effect of current (c), pulseon 

time (p) and air gap voltage (v) on MRR, TWR, ROC of 

EDM with Al–4Cu–6Si alloy–10 wt. % SiCP composites. 

This experiment can be using the PS LEADER ZNC EDM 

machine and a cylindrical brass electrode of 30 mm diameter. 

And three factors, three levels full factorial design was 

using and analyzing the results. A second order, non-linear 

mathematical model has been developed <strong>for</strong> establishing the 

relationship among machining parameters. The significant of 

the models were checked using technique ANOVA and finding 

the MRR, TWR and ROC increase significant in a nonlinear 

fashion with increase in current. 

Karthikeyan et .al has presented the mathematical molding 

of EDM with aluminum-silicon carbide particulate composites. 

Mathematical equation is Y=f(V, I, T). And the effect 

of MRR, TWR, SR with Process parameters taken in to 

consideration were the current (I), the pulse duration (T) and 

the percent volume fraction of SiC (25 μ size). A three level 

full factorial design was choosing. Finally the significant of 

the models were checked using the ANOVA. The MRR was 

found to decrease with an increase in the percent volume of 

SiC, whereas the TWR and the surface roughness increase 

with an increase in the volume of Sic. 

B.Mohan and Satyanarayana evolution the of effect of the 

EDM Current, electrode marital polarity, pulse duration and 

rotation of electrode on metal removal rate, TWR, and SR, 

and the EDM of Al-Sic with 20-25 vol. % SiC, Polarity of 

the electrode and volume present of SiC, the MRR increased 

with increased in discharge current and specific current it 

decreased with increasing in pulse duration. Increasing the 



speed of the rotation electrode resulted in a positive effect 

with MRR, TWR and better SR than stationary. The electric 

motor can be used to rotate the electrode(tool) AV belt was 

used to transmit the power from the motor to the electrode 

Optimization parameters <strong>for</strong> EDM drilling were also developed 

to summarize the effect of machining characteristic 

such as MRR, TWR and SR. 

J. Simao et al was developed the surface modification using 

by EDM, details are given of operations involving powder 

metallurgy (PM) tool electrodes and the use of powders suspended 

in the dielectric fluid, typically aluminum, nickel, 

titanium, etc. experimental results are presented on the surface 

alloying of AISI H13 hot work tool steel during a die 

sink operation using partially sintered WC / Co electrodes 

operating in a hydrocarbon oil dielectric. An L8 fractional 

factorial Taguchi experiment was used to identify the effect 

of key operating factors on output measures (electrode wear, 

workpiece surface hardness, etc.). With respect to micro 

hardness, the percentage contribution ratios (PCR) <strong>for</strong> peak 

current, electrode polarity and pulse on time. Even so, the 

very low error PCR value (<strong>for</strong> micro hardness ~6%) implies 

that all the major effects were taken into account. 

Thus after going through literature we have taken two electrodes 

i.e copper and graphite <strong>for</strong> experimental setup and 

P20 steel as the workpiece and a <strong>comparative</strong> <strong>study</strong> has been 

made. 

3. Experimental Set-up 

For this experiment the whole work can be down by Electric 

Discharge Machine, model ELECTRONICA- ELECTRA- 

PULS PS (die-sinking type) with servo-head (constant gap) 

and positive polarity <strong>for</strong> electrode was used to conduct the 

experiments. Commercial grade EDM oil (specific gravity= 

0.763, freezing point= 94°C) was used as dielectric fluid. 

With internal flushing of pin-shaped cu tool with a pressure 

of 0.2 kgf/cm2 .Experiments were conducted with positive 

polarity of electrode. The pulsed discharge current was applied 

in various steps in positive mode. It is capable of machining 

of hard material component such as heat treated tool 

steels, composites, super alloys, ceramics, carbides, heat 

resistant steels etc. The higher carbon grades are typically 

used <strong>for</strong> such applications as stamping dies, metal cutting 

tools, etc. AISI grades of tool steel is the most common scale 

used to identify various grades of tool steel. Individual alloys 

within a grade are given a number; <strong>for</strong> example: A2, 

O1, D2, P20 etc. 

In this experiment using AISI P20 tool steel material this P- 

20 tool steel material is a pre hardened high tensile tool steel 

which offers ready machine ability in the hardened and tempered 

condition, there<strong>for</strong>e does not require further heat 

treatment. Subsequent component modifications can easily S 

N 

be carried out. The workpiece material composition is given 

in table below. 

Table 2 Chemical composition of work piece material 

Elements Weight Limit 

(%) 

Actual Weight 

(%) 

C 0.28 – 0.40 0.40 

Mn 0.60 – 1.00 1.00 

Si 0.20 – 0.80 0.40 

Cr 1.40 – 2.00 1.20 

Mo 0.30 – 0.55 0.35 

Cu 0.25 0.25 

P 0.03 0.03 

S 0.03 0.03 

Table 3 Mechanical and Thermal Properties of Steel AISI P20 

S. Properties 

Condition Unit 

No 

T(oC) 

1 Density (ρ) 7.85 X 103 25 Kg/m3 

2 Poission’s 0.27 – 0.30 25 - 

Ratio (ν) 

3 Elastic 190 - 210 25 GPa 

Modulus (E) 

4 Thermal 

Expansion 

(α) 

12.8 X 10-6 20 - 425 / oC 

4. Calculation and Results of MRR 

and TWR 

MRR = Wwb – Wwa/ t x ρ 

TWR = Wtb – Wta/ t 

Where 

Wwb = Weight of the workpiece be<strong>for</strong>e machining 

Wwa = Weight of the workpiece after machining 

Wtb = Weight of the tool be<strong>for</strong>e machining 

Wta = Weight of the tool after machining 

t = Maching time (1hr) 

ρ = Denisty of the material (7.85 x 1000 kg/m3) 

Dc 

mm 

Table 4 Material removal <strong>for</strong> copper electrode 

I Ton Weight 

Weight 

(A) 

Of 

Of 



. μsec work piece 

(gm) 

Tool 

(gm) 

Wwb Wwa Wtb Wta 

1 4 1 50 354.760 354.470 28.923 28.921 

2 4 2 50 354.470 353.595 28.921 28.919 

3 4 3 50 353.595 352.103 28.919 28.918 

4 4 4 50 352.103 350.662 28.918 28.916 

5 4 5 50 350.662 349.415 28.916 28.914 

D C = Diameter of copper electrode, 

I = Current, 

Wwb = Weight of the workpiece be<strong>for</strong>e machining 

Wwa = Weight of the workpiece after machining 

Wtb = Weight of the tool be<strong>for</strong>e machining 

Wta = Weight of the tool after machining 

N. (mm) (A) (μsec) (mm3/min) (gm/min) 

1 4 1 50 0.743 1.67E-05 

2 4 2 50 1.942 1.67E-05 

3 4 3 50 3.199 1.67E-05 

4 4 4 50 3.144 3.33E-05 

5 4 5 50 2.800 3.33E-05 

Table 5 MMR and TWR <strong>for</strong> Copper electrode 

S.N. 

Dc 

(mm) 

I 

(A) 

Ton 

(μsec) 

MRR 

(mm3/min) 

TWR 

(gm/min) 

S 

N 

1 4 1 50 0.616 3.33E-05 

2 4 2 50 1.858 3.33E-05 

3 4 3 50 3.168 1.67E-05 

4 4 4 50 3.059 3.33E-05 

5 4 5 50 2.647 3.33E-05 

Dg 

mm 

I 

(A) 

Table 6 Material removal <strong>for</strong> graphite electrode 

Weight 

Weight 

Of 

Of 

Ton work piece 

Tool 

μsec (gm) 

(gm) 

Wwb Wwa Wtb Wta 

1 4 1 50 349.415 349.065 19.781 19.780 

2 4 2 50 349.065 348.15 19.780 19.779 

3 4 3 50 348.15 346.643 19.779 19.778 

4 4 4 50 346.643 345.162 19.778 19.776 

5 4 5 50 345.162 343.843 19.776 19.774 

D g = Diameter of graphite electrode, 

I = Current, 

Fig. 2 

Comparison of MRR using electrode of copper and graphite 

5. Conclusion 

The Die-sinker EDM is widely used machine <strong>for</strong> machining 

of hard material with high precision, high surface finish, 

complex profiles. The cost incurred <strong>for</strong> machining of hard 

and complex profile parts is less than the other methods of 

machining. From the results it is found that graphite electrode 

is more favourable than the copper electrode <strong>for</strong> the 

machining of steel work piece <strong>for</strong> MRR and TWR. It is also 

found that overall cost <strong>for</strong> machining of hard material with 

the use of graphite electrode is <strong>comparative</strong>ly less than copper 

electrode. 

Table 7 MMR and TWR <strong>for</strong> graphite electrode 

S. Dg I Ton MRR TWR 

References 



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Biographies 

1 NIKHIL KUMAR (MAIN AUTHOR) received the 

B.Tech. degree in Mechanical Engineering from Guru 

Jambheshwar University of Science & Technology, Hisar of 

Haryana State, in 2009, M.Tech. degree in Manufacturing 

and Automation from Maharishi Dayanand University, Rohtak. 

His research areas include Manufacturing and Automation 

field. 

gju.nikhil@gmail.com 

2 LALIT KUMAR, Assistant Professor, Rawal Institute of 

Engineering & Technology, Faridabad 

lalitkumar_m@rediffmaill.com 

3 HARICHAND TEWATIA, Assistant Professor, Rawal 

Institute of Engineering & Technology, Faridabad 

harichand88@gmail.com 

4 RAKESH YADAV, Assistant Professor, Al-Falah School 

of Engineering & Technology, Faridabad 

rkyadav2005@gmail.com 

[7] Zhou, M. And Han, F., 2009. Adaptive control <strong>for</strong> EDM 

process with a self-tuning regulator. International Journal of 

Machine Tools and Manufacture, 49(6), 462-469. 

[8] Izquierdo, B., Sánchez, J.A., Plaza, S., Pombo, I. And 

Ortega, N., 2009. A numerical model of the EDM process 

considering the effect of multiple discharges. International 

Journal of Machine Tools and Manufacture, 49(3-4), 220- 

229. 

[9] Kung, K.-., Horng, J.-. and Chiang, K.-., 2009. Material 

removal rate and electrode wear ratio <strong>study</strong> on the powder 

mixed electrical discharge machining of cobalt-bonded 

tungsten carbide. International Journal of Advanced Manufacturing 

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[10] Ding, S. and Jiang, R., 2004. Tool path generation <strong>for</strong> 

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of Machine Tools and Manufacture, 44(14), 1493-1502 

[11] Bleys, P., Kruth, J.-., Lauwers, B., Zryd, A., Delpretti, 

R. And Tricarico, C., 2002. Realtime tool wear compensation 

in milling EDM. CIRP Annals - Manufacturing Technology, 

51(1), 157-160.

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