effect of aluminium powder addition in … i/ijaet vol i issue iii... · effect of aluminium powder...

International Journal of Advanced Engineering Technology E-ISSN 0976-3945

IJAET/Vol.I/ Issue III/Oct.-Dec.,2010/13-24

Research Article

EFFECT OF ALUMINIUM POWDER ADDITION IN

DIELECTRIC DURING ELECTRIC DISCHARGE MACHINING

OF HASTELLOY ON MACHINING PERFORMANCE USING

REVERSE POLARITY 1Saurabh Sharma, *

2Anil Kumar,

3Naveen Beri

4Dinesh Kumar

Address for Correspondence 1,4 Dept. of Mechanical Engineering, S.S.C.E.T Badhani Pathankot, (Pb.) India.

*2, 3 Dept. of Mechanical Engineering, BCET Gurdaspur, (Pb.) India.

E-mail: [email protected], [email protected],[email protected],

[email protected]

ABSTRACT The addition of powder particles suspended in dielectric fluid of electrical discharge machining (EDM) modifies

some process characteristics and creates the condition to achieve higher machining performance. In this paper

attempt has been made to study the effect of aluminium powder on the machining performance of conventional

EDM with reverse polarity. The machining performance is evaluated in terms of material removal rate, tool

wear rate, percentage wear rate, surface roughness. Concentration and grain size of aluminium powder are taken

as the input powder parameters and its effect are presented on machining performance. It is found

experimentally that powder characteristics significantly affect machining characteristics.

KEYWORDS: Electrical discharge machining, Powder-Mixed dielectric electrical discharge machining,

Aluminium powder, material removal rate, tool wear rate, percentage wear rate, surface roughness and polarity.

1. INTRODUCTION

Since 1940 considerable research efforts have

fostered a deep understanding, prediction and

control of the electric discharge machining

process (EDM). The development of the super

tough electrical conductive material such as

hastelloy, carbides, stainless steel, nitralloy

etc. resulted in development of the non-

traditional machining processes. These

materials are difficult to machine by

conventional machining process, & have wide

range of applications in industry. EDM has

been widely used is a removal process to

manufacture parts, dies & moulds for long

time now. In EDM thermal energy is used to

machine all electrical conductive materials of

any hardness & toughness. Since there is no

direct contact between the tool electrode &

work piece in EDM, machining defects like

mechanical stresses, clattering & vibration do

not create problem during machining. In the

past few years, powder-mixed dielectric

electric discharge machining (PMD-EDM)

emerges as a new technique to enhance the

process capabilities. In PMD-EDM a suitable

metal powder (aluminium, chromium, copper,

silicon carbide etc.) is mixed into the dielectric

used in EDM. When a voltage in the range of

80 to 320 V is applied between the tools and

the work piece placed close to each other an

electric field of the range 105 - 10

7 V/m is

generated. The additive particles suspended in

the dielectric has important influence on the

discharge process; increase both the gap

distance & the discharging rate. The high

electric field energises the conductive powder

particles. These conductive particles form

chains at different places under sparking area,

which bridges the gap between tool electrode

& work piece material. Due to this bridging

effect, the gap voltage & insulting strength of

the dielectric decreases, this causes easy short-

circuiting and hence early explosion in the gap

between the electrode and the work piece. At

the same time the suspended particles in the

dielectric enlarged the plasma channel,

because of which electric density decreases

and hence uniform distribution of the sparking

takes place. Very little literature is available

on PMD-EDM on reverse polarity.



Researchers have done work to improve the

surface finish and machining output

Parameters for various hard and tough

materials by adding different metal powder

during machining. However no work has been

reported on the machining characteristics of

hastelloy using reverse polarity on EDM. The

major applications of the Hastelloy are making

of pressure vessels of nuclear and chemical

industry and aerospace engine parts etc. The

objective of the present research work is to

examine the variation of material removal rate,

tool wear rate and surface roughness with

variation of the two input parameters i.e. grain

size of the aluminium Powder particles and

concentration of the aluminium powder in the

dielectric fluid of EDM using the reverse

polarity.

2. LITERATURE SURVEY

Erden A., et al., [1] Reported during the

machining of mild steel that the machining

rate increases by the addition of powder

particles (aluminium, copper, iron) in the

dielectric fluid of dielectric machining. Here

improvement in the Break Down

characteristics of the dielectric fluid is

observed with the addition of powder particles,

but after a certain critical concentration of

powder short circuiting take place which

causes poor machining. Jeswani M.L., et al.,

[2] 1981 Study the effect of addition of

graphite powder to kerosene used as dielectric

fluid in the EDM. He concluded that addition

of about 4gm/litre of fine powder having

average size of particle as 10µm increases the

MRR (Material Removal Rate) by 60% and

TWR (tool wear rate) by 15% in electrical

discharge machine. Wear ratio is also reduced

by 30%. He concluded that there is 30%

reduction in the breakdown voltage of

kerosene at spark gap of 50µm was observed.

Narumiya H., et al., [3] used silicon,

aluminium and graphite as powder materials.

The concentration range of the powder was

between 2gm/l to 40gm/l. Their conclusion

showed that the gap distance increases with

the powder concentration and is larger for the

aluminium powder but there is no direct

relation between the surface roughness and the

gap distance. The best results concerning the

surface finish were achieved for low powder

concentrations levels and that also for silicon

and graphite powders. Kobayashi K., et al., [4]

have concluded that silicon powder mixed in

the dielectric improves the surface finish of

SKD-61 tool steel. It has also been observed,

however, that at specific machining conditions

in the EDM of steel the aluminium and

graphite powders generate better surface

roughness than silicon powder. Wong Y.S., et

al., [5] Study the powder mixed dielectric

electric discharge machining (PMD-EDM) by

employing a current of 1A and pulse on time

as 0.75µs to produce a near mirror finish on

SKH-54 tool steel. The conclusion was that

the resulting machining surface was composed

of well defined, uniformly sized, smoothly

overlapped and shallow craters. The analysis

was carried out by varying the silicon powder

concentration and the flushing flow rate.

Furutani K., et al., [6] Used titanium powder

in dielectric fluid (Kerosene) and found that

the layer of titanium carbide of hardness

1600HV (Vickers hardness number) on a

carbon steel with negative polarized copper

electrode, peak current 3A and 2 µs pulse

duration. Titanium and titanium Carbide are

found in X-Ray diffraction (XRD) analysis of

machine surface. It was concluded that the

breakdown of dielectric takes place and carbon

came from it. Tzeng Y.F., et al., [7] examines

the effect of powder characteristics on

machining efficiency of electrical discharge

machining. They reach to a conclusion that 70-



80nm powder suspended in dielectric produces

the greatest material removal rate and least

increase in the spark gap. Yan BH., et al., [8]

studied the electric discharge machining with

powder suspended working media and

reported that the gap length become shorter

regardless of a mixed powder with a decrease

of the pulse duration at a duty factor of 0.5.

Kozak J., et al., [9] Reported that the material

removal rate and tool wear rate were decreased

by addition of powder. Consequently the

machined surface becomes smooth. Peças P,

Henriques E., et al., [10] studied the

relationship between the roughness and pulse

energy under a few sets of the conditions in

the removal process. However, the influence

of the energy was not systematically analysed.

Klocke F., et al., [11] Used HSFC high speed

forming camera technique to find out that in

comparison to standard electrode, the

aluminium mixed dielectric forms larger

plasma channel. It was concluded that

discharge energy distribution is on the larger

part on the work piece surface. The type and

concentration of the powder mixed in the

dielectric fluid also found to have direct effect

on the machining performance output. Wu

KL., et al., [12] Study the problem of powder

settling by adding a surfactant with aluminium

powder in dielectric fluid and observed that a

surface roughness (Ra value) of less than

0.2µm. This is because of more apparent

discharge distribution. It was also reported that

negative polarity of the tool resulted in better

hardness of the surface. Kansal H.K., et al.,

[13] reported that the addition of Silicon

powder into the dielectric fluid of EDM and an

enhanced rate of material removal and surface

finish. Yeo S H., et al., [14] The experiments

were conducted using dielectric with and

without additive and at low discharge energies

of 2.5µJ, 5µJ and 25µJ, and was observed that

a considerable difference in crater

morphology is seen between craters in

dielectric with and without the powder at low

discharge energy of 2.5µJ, 5µJ and 25µJ. More

circular shapes with smaller diameters are

produced with powder additive as compared to

without powder additive. Craters with the

additives are smaller and have more consistent

depth than in dielectric without additive. They

reported that dielectric with additive in it

lower the amount of discharge flowing

between the work piece and the tool electrode

and slows down the rate at which these

charges flow. Peças P., et al., [15] Study the

effect of silicon powder particles suspended in

dielectric fluid. The powder concentration and

flushing flow rate are two input parameters.

They reach to a conclusion that even for small

level of powder concentration there is evident

amount of reduction in crater depth, crater

diameter and the white layer thickness. They

reported that for a particular experimental

configuration used, we can find the powder

concentration that generates better surface

morphology. It was observed that there is

dielectric flow rate that minimises the surface

roughness for each electrode area and for

larger flow rates, no positive effect on the

surface morphology. Furutani K., et al., [16]

the conditions for deposition machining by Ti

powder suspended EDM was investigated with

respect to discharge current and pulse duration

in this paper. They concluded that the

discharge energy affected the deposit able

condition range. TiC could be deposited in the

case that both discharge energy and powder

density was small. They reported that the

hardness of the deposition achieved was

2000Hv. The matrix surface was also

hardened. Kumar S., et al., [17] found that

significant amount of material transfer takes

place from the manganese powder suspended



in dielectric fluid to the machined surface

under appropriate machining conditions which

changes the surface composition and its

properties. They reported that percentage of

manganese increased to0.95% from 0.52% and

that of carbon to 1.03% from 0.82% that result

in increase in the micro hardness. For surface

alloying favourable machining conditions

were found to be low peak current (4 A),

shorter pulse on-time (5µs), longer pulse off-

time (85µs), and negative polarity of the tool

electrode.

3. EXPERIMENTAL SETUP

Experiments were conducted on smart ZNC

EDM machine Electronica make. The

dimensions of the working tank of ZNC EDM

are 800mm X 500mm X 350mm. Working

tank contains the dielectric fluid and with

these dimension the tank contains large

amount of dielectric. So it requires large

amount of aluminium powder to get the

desired amount of concentration of powder. To

avoid this problem a new container was

developed with a capacity of 6.5liter for the

EDM oil. The container was filled with EDM

oil and placed in the empty working tank.

Experiments were performed in that container.

Hastelloy Steel was used as a work material

and standard EDM oil was used. To hold the

work piece a special type fixture was made.

Container was filled with EDM oil and the

fixture was placed in it with the work piece

fixed on it. A small dielectric circulation pump

was placed in the container to achieve the

proper circulation of the powder mixed

dielectric through the gap between the work

piece and the electrode tool. Proper distance

was maintained between the nozzle of the

pump and the discharge gap for proper

circulation. A magnet was also placed in the

container to hold the fixture with the work

piece. Mitutoyo SJ-400 surface roughness

tester was used for the measurement of surface

roughness of holes.

Table1. Chemical composition of Hastealloy steel

Element Ni Co Cr Mo Fe Si Mn C Ti

% 65 2 16 16 3 0.08 1 0.01 0.7

Table2. Chemical properties of aluminium metal powder

Powder Density

(g/cm3)

Thermal

conductivity (300 K)

Electrical

resistivity

(20 °C)

Melting

point

Specific heat

capacity

(25 °C)

(25 °C) 2.70 237 W·m−1·K

−1 28.2 nΩ·m 933.47 K 24.200 J·mol

−1·K

−1

Table3. Grain size of the aluminium powder

Type Mesh size (µm)

Fine 300 – 400

Medium 200 – 300

Coarse 100 - 200



3.1 Experimentation

The experiments were conducted with the

Reverse Polarity on the EDM. Two input

process parameters decided are concentration

of aluminium powder and the grain size of the

powder particles. Output parameters decided

are MRR, TWR, %WR, SR.

Table4. Experimental settings

Polarity Negative (-)

Machining time 20 min.

Electrode lift time 0.2 sec.

Total nine numbers of experiments were

conducted. During the first five experiments

Current, voltage, pulse on time, duty cycle and

grain size was kept at a known constant value

and the concentration of the powder was

changed after certain intervals for different

experiments. In the next four experiments the

concentration of powder was kept constant

along with current, voltage, and pulse on time,

duty cycle and grain size of the powder is

changed for each experiment. Output

parameters were calculated accordingly by

taking necessary observations.

Measurement of Material Removal Rate:

MRR = Work piece weight loss (g)

Machining Time (min)

Measurement of Tool Wear Rate:

TWR = Work piece weight loss (g)

Machining Time (min)

Measurement of % age Wear Rate:

%WR = TWR X 100/MRR

Measurement of Surface Roughness:

The arithmetic surface roughness value (Ra)

was used to measure the surface finish.

Various measurements of roughness were

carried out at the bottom of holes by using

Mitutoyo SJ-400 Surface Roughness tester.

4. RESULTS AND DISCUSSIONS

Total nine numbers of experiments were

performed on hastelloy steel with powder

mixed EDM process using reverse polarity. At

the end of each experiment; calculations were

done for MRR, TWR, Percentage WR, and

SR. The final phase of experimental work has

been analysed and results have been discussed.

The variations of all the four output

parameters have been plotted against the

variable input parameters

Table 5.Parametric variation chart

Exp

No.

Current

(A)

Voltage

(V)

Pulse on

time (µs)

Duty cycle

(µs)

Concentration

(g/lt) Type of powder

1 5 60 150 9 00 Without powder

2 5 60 150 9 03 Medium

3 5 60 150 9 06 Medium

4 5 60 150 9 09 Medium

5 5 60 150 9 12 Medium

6 5 60 150 9 00 Without powder

7 5 60 150 9 06 Fine

8 5 60 150 9 06 Medium

9 5 60 150 9 06 Coarse

.



Table 6.Observation chart

Exp.

No.

Work piece

weight loss

(g)

Electrode

weight

Loss (g)

Time of cut

(min)

MRR

(g/min)

TWR

(g/min) % WR

Ra

(µm)

1 0.006 0.008 20 0.0003 0.0004 133.33 2.13

2 0.064 0.012 20 0.0032 0.0005 18.76 1.97

3 0.082 0.02 20 0.0041 0.001 24.3 1.67

4 0.03 0.01 20 0.0015 0.0005 33.33 1.806

5 0.09 0.018 20 0.0045 0.0009 20 1.43

6 0.006 0.008 20 0.0003 0.0004 133.33 2.13

7 0.06 0.018 20 0.003 0.0009 30 2.87

8 0.082 0.02 20 0.0041 0.001 24.39 1.67

9 0.092 0.019 20 0.0046 0.00095 21.73 1.59

Analysis of Material Removal Rate (MRR)

Fig.1 Graph between concentration and MRR

Fig.2 Graph between grain size of powder and MRR

Concentration

It was seen that material removal rate is very

low in conventional EDM with reverse

polarity. With the addition of aluminium

powder in the dielectric fluid material removal

rate increases sharply. It is because of the fact

that with addition of powder particles in

dielectric, the spark gap is filled up with

additive particles. The powder particles

reduces the insulating strength of dielectric



fluid and increases the spark gap distance

between tool and work piece This increases

the material removal rate with the increase in

concentration. However, with further increase

in concentration, MRR lowers down, it may be

due to short circuiting with increase in powder

density. Again at concentration of 12gm/lt the

value of MRR rises it can be explained by the

fact that with the more powder particles more

erosion from the work piece.

Grain Size of the powder

It was observed that material removal rate is

very low without any grain size of particles.

However, with the addition of fine grain size

of aluminium powder the value of MRR

increases sharply. With future addition of

medium and coarse grain size powder particles

the value of MRR increases, but not as sharp.

This may be defined by the reason that the

density of suspended fine particles is higher

than that of medium and coarse particles.

Analysis of the Tool Wear Rate (TWR)

Fig3. Graph between Concentration and TWR

Fig4. Graph between Grain size of the powder and TWR



Concentration

It was observed that the tool wear rate is more

than the material removal rate with zero

concentration of powder and tool wear rate

increases with the addition of powder particles

in the dielectric. This can be explained by the

fact that during reverse polarity more heat is at

the tool electrode than the work piece. With

the addition of powder concentration in fluid

due to erosion of electrode the tool wear rate

increases. A little change in the trend may be

due to the more erosion of tool at

concentration of 9gm/lt. It may be due to the

reason that higher concentrations of powder

particles block the path of ions to hit the

electrode surface. Again at 12gm/lt

concentration the TWR increases. It may be

due to the reason that at higher concentration

more particles hit the electrode during reverse

polarity.

Grain size of the powder

As per (figure 4) graph between Grain size of

the powder and TWR, it is observed that with

the addition of powder with fine particles the

tool wear rate increases. It is due to the reason

that ions produced by the ionization of

dielectric fluid, hits the tool electrode with

high momentum and high energy during the

reverse polarity setup. And hence more tool

material is eroded.

Analysis of percentage wear rate (%WR)

Fig5 Graph between Concentration and % wear rate

Fig6. Graph between grain size of powder and %wear rate

Concentration



It was observed that the value of percentage

wear rate is high with no powder suspended;

this can be explained that more heat is at the

tool during reverse polarity. As the powder is

suspended in the dielectric the value of MRR

increases more than that of TWR and hence

the value of percentage wear rate decreases

sharply. A little change in trend can be

explained by the fact that tool wear rate

increase due to erosion of tool electrode due to

more concentration of powder particles.

Grain size of the powder

With the change in the grain size of the

powder particles the percentage wear rate

decreases continuously. This can be explained

by the fact that MRR increases with change in

the grain size of the powder particles more

than the increase in the tool wear rate. Hence

decrease in the percentage wear rate.



Concentration

From the graph drawn between the

concentration of the powder & surface

roughness figure7 , it is clear that the value of

surface roughness keeps on decreasing with

increasing the concentration of the powder in

dielectric. This may be explained by the fact

that this improvement in surface quality is due

to the reason that suspended powder particles

enlarge and widen the discharge passage

which helps easy evacuation of produced

debris from the spark gap. The suspended

powder particles lead to uniform dispersion of

discharge energy in all directions, which

results in shallow and small craters on the

machining surfaces. Due to this, surface

roughness reduces. Moreover during reverse

polarity more heat is at the electrode and less

heat is at the work piece. Reverse polarity

helps to attain better surface quality.

Grain size of powder

From the graph drawn between the

concentration of the powder & surface

roughness figure8, it is seen that surface

roughness increases when we add fine powder

particles. This can be explained by the fact that

densities of the fine powder particles are very

high so these particles come in the spark gap

and clog the discharge passage. Because of

this short circuiting takes place and process

became unstable. Moreover not easy

evacuation of debris produced leads to

somewhat rough surface. As we add powder

with medium grain size particles and then

coarse size powder particles the surface

roughness decreases continuously. This can be

explained by the reason that these particles are

not as dense as the fine particles. So these

powder particles easily enlarge and widen the

discharge passage which further facilitates

easy evacuation of produced debris from the

spark gap and lead to uniform dispersion of

discharge energy in all directions. Due to this,

better surface finish is achieved.

5. CONCLUSION

The experimental research work carried out on

reverse polarity on EDM are intended to

contribute to the generation of knowledge

related to the effect of aluminium powder

particles suspended in the EDM dielectric in

the quality of the final surface. The input

parameters have been taken as concentration

of the powder and the grain size of the powder

and the output parameters are MRR, TWR,

Percentage wear rate, Surface roughness.

Within the experimental range following

conclusions can be drawn:

1. The surface roughness of the work

material continuously decreases with the

increase in the concentration of

aluminium powder and with change in

the grain size of the powder particles.

2. With the increase in the concentration of

the powder, percentage wear rate

decreases sharply.

3. With change in the grain size of the

powder, the percentage wear rate

decreases continuously.

4. With the increase in the concentration of

additive powder in the dielectric fluid,

the tool wear increases.

5. With the addition of aluminium powder

in the dielectric fluid of EDM, the

material removal rate increases.



6. With increase in the grain size of the

aluminium powder particles in the

dielectric, the material removal rate

increases continuously.

ACKNOWLEDGEMENTS

The authors would like to acknowledge the

support of the Department of Mechanical

Engineering, Beant College of Engineering

and Technology, Gurdaspur, Punjab, India and

All India Council for Technical Education,

New Delhi, India, for supporting and funding

the research work under research promotion

scheme (F. No.: 8023/BOR/RID/RPS-

129/2007-2008 and F. No.:

8023/BOR/RID/RPS-144/2008 - 2009) in this

direction.

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effect of aluminium powder addition in … i/ijaet vol i issue iii... · effect of aluminium powder...

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