Parametric Analysis of Electrochemical Discharge Micro-Machining ... · electrochemical machining...

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014,

IIT Guwahati, Assam, India

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Parametric Analysis of Electrochemical Discharge Micro-Machining

Process during Profile Generation on Glass 1B. Mallick*, 2M.N. Ali, 3B. R.Sarkar, 4B. Doloi, 5B. Bhattacharyya

1-5Production Engineering Department, Jadavpur University, Kolkata-32

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

Abstract

Electrochemical discharge micro-machining (micro-ECDM) has the ability to machine electrically non-

conducting materials as compared with different existing traditional and also non-traditional machining

processes. This paper deals with the effects of different process parameters like applied voltage (V), electrolyte

concentrations(wt%), pulse frequency and duty ratio on different machining performance characteristics such as

material removal rate (MRR), overcut (OC) and heat affected zone (HAZ) during micro-profile generation on

electrically non-conducting glass. Applied voltage has been set from 35-55 V and the electrolyte concentration,

pulse frequency and duty factor were varied from 10-30wt%, 200Hz-1kHz and 45-65% respectively during the

experimentation. A cylindrical shaped stainless tool of diameter 350 µm and NaOH solution as electrolyte were

used to conduct the experiments. Material removal rate is high for 55 V and 30 wt% electrolyte concentration

respectively. Overcut and HAZ area decreases with frequency whereas it increases with duty ratio after 50% and

55% of duty ratio respectively.

Keywords: µ-ECDM, µ-channel, MRR, OC, HAZ

1. Introduction

Electrochemical Discharge micro-machining

process is utilized as an advanced hybrid micro-

machining technique, which is combination of

electrochemical machining (ECM) and electro

discharge machining (EDM) proposed by Basak et al.

(1996). In ECDM process, the material removal takes

place due to the combined effects of electrochemical

(EC) reaction and electrical spark discharge (ESD)

action analyzed by Bhattacharyya et al. (1999), Jain et

al. (1999) and Jawalkar et al. (1999). Many

researchers have carried out researches to trounce the

various drawbacks associated with µ-ECDM process.

Cao et al. (2009) studied micro-electrochemical

discharge machining to improve the machining of 3D

micro-structures on glass and to obtain good surface

with minimized structures during drilling and milling

operations. Han et al. (2007) reported a new method

for improvement of the surface integrity in

electrochemical discharge machining (ECDM)

process by the use of fine graphite powder mixed with

electrolyte. Jui et al. (2013) fabricated in-house high

aspect ratio micro-tools, which have been used for

deep micro-hole drilling on glass using low

electrolyte concentration. An aspect ratio of 11 has

been achieved. Kim et al. (2006) studied the voltage

pulse frequency and duty ratio effects in an

electrochemical discharge micro-drilling process

using Pyrex glass materials. Sarkar et al. (2006)

showed the effects of various process parameters

during micro-drilling of silicon nitride ceramic using

electrochemical discharge machining (ECDM)

process.

Still, a little attention has been drawn in the area

of µ-profile or µ-channel cutting on electrically non-

conducting materials viz glass and ceramics with

ECDM process. Therefore, this paper includes the

basic experimental results of profile generation like

micro-channel on glass. This paper also deals with the

effects of different process parameters like applied

voltage (V), electrolyte concentrations(wt%), pulse

frequency and duty ratio on different machining

performance characteristics such as material removal

rate (MRR), overcut (OC) and heat affected zone

(HAZ) during micro-channel cutting on electrically

non-conducting glass.

2. Experimentation

2.1 Experimental set up

To accomplish the objectives of this research

work and to control the process parameters such as

machining voltage, duty ratio, pulse frequency,

electrolyte concentration etc an experimental ECDM


Process during Profile Generation on Glass

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set-up was indigenously designed and developed. The

set-up includes the following sub systems:

a) Mechanical hardware system

b) Electrolyte supply System

c) Electrical power supply unit

The mechanical hardware system is very

important parts of micro-ECDM set-up. The

mechanical hardware system is used to achieve the

goal of the present research work. It consists of the

main elements such as (i) Main machining chamber,

(ii) Job holding unit, (iii) Tool holding unit, (iv)

Auxiliary electrode unit and (v) Job feeding

arrangement etc.

The main machining chamber is made of Perspex

material having rectangular shape. In job holding unit

the job is placed on a plate, which itself rests on four

springs guided by four stainless steel rod located at

four different corners of the plate. The feed to the job

is given by spring feed mechanism in the upward

direction so that the job can always be in touch with

the micro-tool. The tool holding unit is fitted with the

cover plate by means of screw-nut mechanism so that

the position of the µ-tool can be adjusted according to

the requirements to generate the different shapes of

the micro-channel. A flat rectangular graphite

auxiliary electrode plate is placed parallel to the job

holding table. The schematic diagram of main

machining chamber of the experimental µ-ECDM set-

up is shown in Fig. 1.

Fig. 1 Schematic diagram of main machining

chamber of µ-ECDM set-up

2.2 Experimental Planning

To investigate the influences of above process

parameters on different machining criteria such as

Material Removal Rate (MRR), Heat Affected Zone

(HAZ) and Overcut (OC) a cylindrical shaped with

flat end stainless tool of diameter 350µm were used

for each experiment and the experiments were

conducted in a NaOH solution. The process

parameters i.e. voltage, electrolyte concentration,

pulse frequency and duty ratio have been varied as

35-55 V; 10-30wt%; 200-1000 Hz and 45-65 %

respectively. Other parameters such as inter-electrode

gap and length of tool length have been kept fixed as

50mm and 10mm respectively. Glass slide was chosen

as workpiece material to cut µ-channel. During

experimentations one parameter has been varied while

other process parameters were fixed at low levels

within their respective ranges in order to expect

minimum effects of these parameters. As the tool

material is worn out due to generation of high heat

during ECDM process a new identical tool was

always used for each experiment. The machining

conditions for cutting micro-channel on glass have

been shown in Table 1. Machining rate in terms of

material removal rate (MRR) has been calculated by

weight difference. The width of cut (WOC) and HAZ

area of µ-channel were measured using a Leica

measuring microscope and overcut was calculated by

subtracting the diameter of tool from WOC.

Table 1 Machining conditions during µµµµ-channel

cutting on glass

Expt.

No

Voltage

(V)

Elect

Conc.

(wt %)

Pulse

Freq.

(Hz)

Duty

Ratio

(%)

1 35 10 200 45

2 35 10 200 50

3 35 10 200 55

4 35 10 200 60

5 35 10 200 65

6 35 10 400 45

7 35 10 600 45

8 35 10 800 45

9 35 10 1000 45

10 40 10 200 45

11 45 10 200 45

12 50 10 200 45

13 55 10 200 45

14 35 15 200 45

15 35 20 200 45

16 35 25 200 45

17 35 30 200 45

3. Results and Discussion

The data input parameters are applied voltage,

electrolyte concentration, pulse frequency and duty

ratio and machining characteristics are material

removal rate (MRR), overcut (OC) and heat affected

zone (HAZ) area. Each experiment was conducted

three times at every machining parametric

combination. The average values of the experimental

results thus obtained were used and plotted in graph to

analysis the influences of the various process

parameters on various machining characteristics.



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Table 2 shows the average values of various

machining characteristics recorded during the

experimentations.

Table 2 Experimental results obtained at different

parametric combinations

Expt.

No

MRR

(mg/hr)

Overcut

(µm)

HAZ

(µm2)x103

1 12.13 198.826 327.323

2 14.53 45.842 438.461

3 18.53 86.356 232.298

4 19.06 84.878 264.316

5 23.87 133.443 352.374

6 11.06 112.780 525.679

7 11.87 92.241 554.657

8 11.6 132.299 318.508

9 8.53 116.617 294.514

10 24.13 165.009 392.858

11 30.27 259.524 452.955

12 31.6 264.494 714.806

13 51.33 457.347 1048.131

14 36.8 119.431 760.221

15 70.93 309.583 706.739

16 74.27 342.867 908.92

17 105.47 273.210 894.771

Fig. 2 Effect of applied voltage on MRR

Fig. 3 Effect of electrolyte concentrations on MRR

Fig. 4 Effects of pulse frequency on MRR

Fig. 5 Effects of duty ratio on MRR

3.1 Influences of process parameters on

Material Removal Rate (MRR)

The influences of applied voltage, electrolyte

concentration, pulse frequency and duty ratio on

average material removal rate for fixed inter-electrode

gap when micro-channel is cut on glass using NaOH

electrolyte are shown in Fig. 2, 3, 4 and 5

respectively. These figures show that MRR for

NaOH electrolyte solution increases with the increase

of applied voltage, electrolyte concentration and duty

ratio but decreases with increase of pulse frequency.

The number of sparking increases with the increase of

voltage and electrolyte concentration since the

number of sparking increases with the increase of

current density and rate of electro-chemical reactions,

which increase with increase of voltage and

electrolyte concentration respectively. Fig. 2 and 3

reveal that material removal rate is high for 55 V and

30 wt% electrolyte concentration respectively. Also

MRR increases with increase of duration of pulse on-



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time, which increases with duty factor. As the

discharge duration increases, the removal rate

increases since the temperature of the glass channel

rises. MRR falls down with increase of pulse

frequency because the duration of the discharge

increases as the frequency decreases, even though the

total time that voltage is applied stays the same.


Overcut (OC)

Fig. 6 and 7 exhibit the influences of applied

voltage and electrolyte concentration respectively on

average overcut using NaOH as electrolyte.

Generally, rate of sparking increases with the increase

of both applied voltage and electrolyte concentration

and consequently increases not only MRR but also

width of cut due to side wall sparking from the tool

electrode and thereby increases overcut. Fig. 8 and 9

show the variation of overcut with varying pulse

frequency and duty ratio respectively. These show

that overcut increases with increase of duty ratio and

decreases with increase of pulse frequency. One

possible reason is that the discharge gets more

powerful because the current density on the tool’s side

surface rises. Photographic views of µ-channel taken

using optical microscope at applied voltage 50V and

35V are shown in Fig. 10 and 11 respectively.

Fig. 6 Effects of applied voltage on Overcut

Fig. 7 Effects of Electrolyte Conc. on Overcut

Fig. 8 Effects of Pulse frequency on Overcut

Fig. 9 Effects of Duty Ratio on Overcut



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Fig. 10 µ-channel at 50V/10wt%NaOH/200Hz/45%

Fig. 11 µ-channel at 35V/10wt%NaOH/200Hz/45%


Heat Affected Zone (HAZ) area

In ECDM process a large amount of heat is

generated during the machining of a glass material. A

portion of this heat is radiated to atmosphere, some is

lost to the electrolyte by convection and remainder is

conducted to the workpiece. Fig. 12 and 13 show the

influences of applied voltage and electrolyte

concentration on average heat affected zone (HAZ)

area. From the figures it is clear that that HAZ area

almost gradually increases with increase of applied

voltage and electrolyte concentration and it becomes

higher at 55 V and 30 wt% electrolyte concentration.

Variations of HAZ area with pulse frequency and duty

ratio are shown in Fig. 14 and 15 respectively. It is

obvious from the figures that initially HAZ area

increases and then it decreases with frequency

whereas it increases with duty ratio after 55% of duty

ratio. The discharge heat value is greater for long,

slow pulses because the duration of the discharge

increases. As a result HAZ grows larger. Fig. 10 and

11 show the photographic views of micro-channels

indicating the HAZ area and average HAZ is observed

641500.8354 µm2 and average width of cut (WOC) is

found 476.234 µm.

Fig. 12 Effects of Applied voltage on HAZ area

Fig. 13 Effects of Electrolyte Concentrations on

HAZ area

Fig. 14 Effects of Pulse frequency on HAZ



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Fig. 15 Effects of Duty Ratio on HAZ area

4. Conclusions

From the present parametric analysis, it can be

evident that ECDM can be used with great potential to

machine electrically non-conducting harder brittle

materials such as glass and can also be employed for

micro-channel cutting applications. Within the

limitations of the developed ECDM system, the

following conclusions can be drawn:

(i) MRR increases with the increase of applied

voltage, electrolyte concentration, duty ratio

but decrease with pulse frequency when NaOH

electrolyte is used for micro-channel cutting on

glass with ECDM process.

(ii) Overcut always increases with increase of

applied voltage but it increases with increase of

concentration upto 25wt% and with duty ratio

from 55%. Also it decreases with increase of

pulse frequency.

(iii) HAZ area increases with increase applied

voltage and with electrolyte concentration upto

25wt%. Initially HAZ area increases and then it

decreases with frequency whereas it increases

with duty ratio after 55% of duty ratio.

Hence, this research work will be very helpful to

manufacturing engineers during µ-profile generation

on electrically non-conducting materials such as glass

using advanced modern manufacturing processes.

Acknowledgement The authors acknowledge the financial assistance

provided by the CAS Ph-IV programme of the

Production Engineering Department of Jadavpur

University under the University Grants Commission,

New Delhi.

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