Materials Today: Proceedings xxx (xxxx) xxx

Contents lists available at ScienceDirect

Materials Today: Proceedings

journal homepage: www.elsevier.com/locate/matpr

Drilling investigations on Inconel alloy 625 material of material removal

rate using micro electrochemical machining
Udhayakumar Gobikrishnan ⇑, Periyagoundar Suresh, Paramasivam Kumaravel
Department of Mechanical Engineering, Sona College of Technology, Salem 636005, India

a r t i c l e i n f o a b s t r a c t

Article history: Electrochemical machining (ECM) is one of the unconventional machining processes used to cut only the
Received 28 June 2020 electrically conductive and hard materials with different shapes. It can be used in several applications
Accepted 8 July 2020 such as turbine blades, aerospace, and aeronautical industries. Compare to conventional machining,
Available online xxxx
unconventional machining gives a better result. In an Unconventional Machining, only ECM machines
offer the best Material Removal Rate, because due to an electrolyte concentration. In an
Keywords: Electrochemical Machining, Electrolyte concentration is one of the primary roles of removing the material
Electro chemical machining
removal rate. The input parameters were chosen as Current, Voltage and Electrolyte concentration. The
Material removal rate
Orthogonal array
output parameters were obtained as the Material Removal Rate. In this paper, the experimental value
Analysis of variance was taken as an L9 orthogonal array based on the Taguchi technique. Scanning Electron Microscope
Scanning electron microscope (SEM) was chosen to study the micro holes. From the obtained results, the optimal results were current
4 amps, voltage 18 V, Electrolyte concentration 60 g/lit, and to maximize the Material Removal rate. In
this paper, the Current is the most critical parameter for removing material in the work piece.
Ó 2020 Elsevier Ltd. All rights reserved.
Selection and peer-review under responsibility of the scientific committee of the International Confer-
ence on Newer Trends and Innovation in Mechanical Engineering: Materials Science.

1. Introduction t = Time (secs).

F = Faraday’s constant.
Electro-chemical machining (ECM) is an unconventional Jain et al. [1] In the field of electrochemical machining, genetic
Machining processes, which is used to remove the materials from algorithms were used to optimize process parameters. Since the
the work piece. Normally, work piece will be taken as anode and input parameters and their main purpose were to minimize geo-
tool is taken as cathode. And then finally the two components, metric inaccuracies during machining, the tools were used for feed
one is the work piece electrodes, and other is the tool electrodes rate, voltage and electrolyte flow rate. C. Senthilkumar et al. [2]
immersed in an electrolytic bath solution and removing the mate- Reducing electrolyte concentrations and increasing the tempera-
rials. It is a Non-contact method process, which is tool and Work ture of non-passivation electrode systems improves surface perfor-
pieces are not contact with each other. It maintains some gap mance. Chakradhar et al. [3] Using feed rate, application voltage
between tool and Electrode, that gap is called as Inter Electrode and electrolyte concentration as ECM process parameters in steel
Gap. It is a reverse of an electroplating process. It is based unit EN31 and optimized output functions. Habib et al. [4] used
on the Faraday’s law of electrolysis, mathematically, Figs. 1 & 2 Taguchi technique to performance Electro chemical Machining
and Table 1 process investigation. As the machining variables for optimizing
Material Removal rate and Surface Roughness, they have selected
EIt the current, voltage, tool feed rate and electrolyte concentration
W¼
F and suggested that the Ra and MRR responses are improved when
Where, W = mass of ions dissolved (kg). current and voltage was improved. Da silva et al. [5] studied the
E = Equivalent amount of material dissolved. ECM using four parameters, such as electrolyte flow rate, feed rate
I = Current (amperes). and voltage, and also they observed the effect of these affecting
parameters with reactions such as Material Removal Rate, showing
⇑ Corresponding author. that the feed rate is the important parameter distressing the
E-mail address: U.gobikrishnan@gmail.com (U. Gobikrishnan). response. Goda et.al. [6] Precise ECM conducted in fixed electrolyte

https://doi.org/10.1016/j.matpr.2020.07.173
2214-7853/Ó 2020 Elsevier Ltd. All rights reserved.
Selection and peer-review under responsibility of the scientific committee of the International Conference on Newer Trends and Innovation in Mechanical Engineering:
Materials Science.

Please cite this article as: U. Gobikrishnan, P. Suresh and P. Kumaravel, Drilling investigations on Inconel alloy 625 material of material removal rate using
micro electrochemical machining, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.07.173
2 U. Gobikrishnan et al. / Materials Today: Proceedings xxx (xxxx) xxx

Fig. 1. EMM Power Supply.

Fig. 2. Effect of S/N Ratios for MRR.

Table 1
Chemical composition of inconel alloy 625 material.

Nickel Chromium Molybdenum Iron Niobium Carbon Manganese Silicon Phosphorus Sulphur Aluminum Titanium Cobalt
58.0 min. 20.0–23.0 8.0–11.0 5.0 max 3.15–4.15 0.10 max 0.50 max 0.50 max 0.015 max. 0.015 max. 0.40 max. 0.40 max. 1.0 max.

by unvarying high voltage pulses superimposed on low voltage Removal Rate (MRR) of stainless steel material and also Analysis
pulses. As the high-voltage pulses increased the removal rate even of variance (ANOVA) is carried out to observe the influence of each
at low concentrations of electrolytes, narrow lateral gaps of 20 mm parameters and their level of factors. Micro holes were found by
were obtained at the shortest. As the diameter of the system elec- using with the help of Scanning Electron Microscope (SEM). An
trode was no more than 300 mm, however, it is not clear in their orthogonal Array (OA) L9 is generated using the Taguchi techniques
investigation if this method can be applied to large-scale machin- to carry out the experiments on Inconel Alloy 625 Material.
ing. de silvaa et al. [7] Furthermore, there is an increase in gap
resistance due to different causes during the micro-ECM processes.
Kurita et al. [8] Electrolyte concentration also plays a major role in 2. Experimental investigation
the production of a high-precision micro hole during the removal
of ECM processes. Hewidy et al. [9] analyzed the ECM cost compo- In the above diagram, it has shown all the necessary parts of the
nents such as machining and concentration of electrolytes in order set up where the machining of the tool and workpiece is to be car-
to establish the basic standards for selecting a suitable electro- ried out. The experimental setup consists of stepper motor, pulse
chemical machine to meet the local production requirements of a generator, filter, tool feeding arrangement and machining cham-
company. For this purpose, the authors talked about the impossi- ber. The workpiece is fixed inside the machining chamber and
bility of generalizing a model. U. Gobikrishnan et al. [10] analysed the tool is attached with main screw which is driven by the stepper
the two different electrodes through SEM Microscope images and motor. The process parameters like current, voltage and electrolyte
finally suggested that the stainless-steel electrode gives good concentration are varied by the control panel. The output result is
results in terms of MRR and overcut performance. used to calculate the Material Removal Rate (MRR). Here, the tool
The aim of the present paper is to analyse the effects of Current, is considered as the cathode and the workpiece is taken as Anode.
Voltage and Electrolyte concentration to Maximize the Material The Tool Material has been taken as Stainless steel and the work-

Please cite this article as: U. Gobikrishnan, P. Suresh and P. Kumaravel, Drilling investigations on Inconel alloy 625 material of material removal rate using
micro electrochemical machining, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.07.173
 U. Gobikrishnan et al. / Materials Today: Proceedings xxx (xxxx) xxx 3

piece material is taken as Inconel Alloy 625. Here the electrolyte Y = Weight of the workpiece after machining
concentration was taken as Sodium Chloride (NaCl). The weight of the workpiece can be calculated from the elec-
tronic weighing balancing machine
2.1. Material selection
3. Experimental results and discussion
Inconel alloy 625 workpiece materials chosen in the present
study. It is a Nickel-based super alloy that possesses high strength 3.1. Effect of MRR using electrolyte concentration of sodium chloride:
adequate properties and excellent uniform high corrosion resis-
tance to elevated temperatures. These types of material are suit- The material removal rate in electrochemical process is very
able for pipe fittings parts, petroleum pipe valve parts and sea low as compared to the conventional machining process but it is
water parts type applications. Stainless steel material selected as preferable option for machining to such kind of exotic materials
tool components in this paper. Sodium chloride is chosen as elec- (difficult to cut materials) as Inconel 625 is a nickel based alloy
trolyte concentration, and it can use for common types of materi- which comes under exotic materials category. Here, the Material
als. The electrolyte has unique properties such as composition, Removal Rate was found on using electrolyte concentration as
concentration; temperature and PH value for the variables have sodium chloride. The below tabular column shown the effect of
been chosen. Both the workpiece and tool material should be elec- MRR using Sodium chloride solution as Electrolyte concentration
trically conductive materials for the reaction to happen. in Micro ECM. The changing variable at a time approach of the
Chemical composition by % selected parameters in the table shows changes on the other two
variables on the machining response. The table clearly shows the
2.2. Process parameters and their levels: influence of machining parameters on the material removal rate.
Their import values can be found by Analysis of Variance (ANOVA)
In this study, the experimental setup has 3 controllable param- using Minitab software. For getting the Better Removal rate,”
eters namely current, voltage and electrolyte concentration which Higher the better” characteristics have been chosen. The equation
are the variables to be changed considering one variable at a time for S/N ratios shown as
approach. The feasible range for machining parameters has been
defined at three different levels. The Table 2 shows that the three S=N ratio ¼ 10log½sumð1=Y 2 =nÞ
levels and three parameters have been chosen for the experiment
by using L 9 Orthogonal Array (OA).
3.2. Effects of parameters on MRR:
2.3. Machining parameters
The effect on the MRR can be seen with the change in the three
The performance of machining is largely dependent on machin- of the above parameters. As seen from the above graph, the MRR is
ing parameters. So the selection of parameters is the most impor- increased with the increase of the current and the voltage. The
tant predominant role in Micro ECM. From the literature survey, Material Removal Rate should be maximum with the highest cur-
the input parameters like current, Voltage and Electrolyte concen- rent, Voltage and Electrolyte concentration as shown in the Table 3
tration have been chosen for the current research article. The MRR (i.e.) A1-B1-C1 have the significant value. The increase in the cur-
can be defined as the rate of dissolution of metal removal from the rent increases the voltage in the electrode gap helping in removing
work piece. MRR can be found as output parameters and calculated the material fast. Thus the highest MRR is achieved at the maxi-
as using the formula. mum value of the current parameter where simultaneously the
voltage parameter is also at the optimum point.
XY On the basis of the different combination of parameters
MRR ¼
time obtained by the Taguchi method, the corresponding values of S/N
Where X = Weight of the workpiece before Machining
Table 4
Response table for signal to noise ratios of MRR (Larger is better).
Table 2
Levels and parameters. Level Current (A) Voltage (V) Electrolyte Concentration (g/lit)

Parameters Level 1 Level 2 Level 3 1 10.77 13.18 13.20

2 14.84 14.56 14.64
Current (A) 4 6 8 3 17.63 15.50 15.41
Voltage (B) 17 18 19 Delta 6.86 2.32 2.21
Electrolyte Concentration (C) 40 50 60 Rank 1 2 3

Table 3
Result of MRR using Sodium Chloride electrolyte concentration.

S. No A B C MRR S/N ratio for MRR

1 4 17 40 2.489 7.9205
2 4 18 50 3.619 11.1718
3 4 19 60 4.579 13.2154
4 6 17 50 5.125 14.1939
5 6 18 60 6.012 15.5804
6 6 19 40 5.459 14.7423
7 8 17 60 7.432 17.4221
8 8 18 40 7.028 16.9366
9 8 19 50 8.456 18.5433

Please cite this article as: U. Gobikrishnan, P. Suresh and P. Kumaravel, Drilling investigations on Inconel alloy 625 material of material removal rate using
micro electrochemical machining, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.07.173
4 U. Gobikrishnan et al. / Materials Today: Proceedings xxx (xxxx) xxx

Table 5
ANOVA for MRR.

Parameters DOF Sum of Squares Variance F-Value P-Value percent (%)

Current 2 24.9341 12.4671 748.73 0.001 87.16
Voltage 2 1.9842 0.9921 59.58 0.017 6.94
Electrolyte Concentration 2 1.6564 0.8282 49.74 0.020 5.78
Error 2 0.0333 0.0167 0.12

Table 6 been calculated and displayed in Table 5. The Sum of Squares

Optimum values for MRR.
and Percent contribution for all process parameters on MRR has
Parameters calculated from the ANOVA. From the table, the result showed that
Current(A) Voltage(V) Electrolyte conc.(g/lit) MRR(g/min) the Current is the most contribution parameter to this work. It
8 19 60 8.668 shows that the current, voltage, and electrolyte concentrations
parameters for their contributions obtained as 87.16%, 6.94% &
5.78%, respectively. It shows that the current is the most predom-
inant role in improving the Material Removal Rate (MRR). In the
Table 5, shows that the values of Sum of squares, variance, F-
value, P-value and the percentage contribution of varying parame-
ters as Current, Voltage and Electrolyte concentration and the
response parameters calculated as Material Removal Rate. There-
fore from the Table 5, shows that the p-value has smaller value
means that the stronger evidence in the favour of the Material
Removal Rate.
From Table 6, it is showing the optimum value for setting a bet-
ter Material Removal Rate was to be current (8A), Voltage (19 V),
and Electrolyte Concentration (60 g/lit).

3.4. Photographic images for optimum Parameters:

From the Fig. 3, shows that the Scanning Electron Microscope

image for the optimum values as Current (8A), Voltage (19 V)
and Electrolyte Concentration (60 g/lit). The main aim of the SEM
images is to study the micro holes of the optimum parameter val-
ues. In the optimum values, the result of the images shows a good
removal of material from the workpiece. The removal of Material
shows the good result for the optimum parameter values based
on L9 orthogonal Array.
Fig. 3. Scanning Electron Microscope (SEM) with current (8A), Voltage (19 V),
Electrolyte Concentration (60 g/lit).
4. Conclusion:

(Signal to Noise) ratio were generated. With the help of response The outcome of the variables in the process such as current,
table, the influences of each machining parameter was determined voltage and electrolyte concentration of machining of Inconel
which helps to understand the most important parameter factor. 625 have been analysed. In the present study, the optimization of
The response table helps to provide rank to the three variable the machining process parameters is carried out using the S/N
parameters which decides the most important influencer for ratios approach and Analysis of Variance (ANOVA) to get the
increasing the MRR. Based upon the Delta value as shown from response values.
the table, rank 1 is given to the current variable, rank 2 is given
to the voltage variable and at last rank 3 goes to electrolyte con-  From the results, the optimal parameter as Current (8A), Volt-
centration variable. The Material removal rate is ‘‘Larger the Bet- age (19 V) and Electrolyte concentration (60 g/lit).
ter” having the significant value is the current. It clearly shows  The current (A), Voltage (19 V) and Electrolyte Concentration
that the current is the most influential parameter for removing (60 g/lit) influenced the MRR by 87.16%, 6.94%, 5.78% respec-
the material from the workpiece, followed by Voltage and Elec- tively for the electro chemical machining of Inconel 625 alloy.
trolyte Concentration.  The main factor for material Removal Rate initially increases
From the Table 4, shows the response table for Material with increases in current and later also increases with voltage
Removal Rate is” Larger is better ‘‘and concluded that the optimum and Electrolyte concentration.
values as the level 3 for current, voltage and Electrolyte Concentra-  As the current parameter increases are going on, the removal of
tion. The optimum value has been calculated using minitab soft- material from the workpiece will be higher in the workpiece
ware 18 version. material due to affecting parameters of Voltage and Electrolyte
concentration.
3.3. Analysis of Variance  The effect of all response parameters on MRR has found using
the ANOVA table.
Analysis of Variance (ANOVA) is a mathematical operation used  From Table 4, it is showing the current is the most influential
to find the significance parameters from the experiments. It has parameter on removing the workpiece material.

Please cite this article as: U. Gobikrishnan, P. Suresh and P. Kumaravel, Drilling investigations on Inconel alloy 625 material of material removal rate using
micro electrochemical machining, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.07.173
 U. Gobikrishnan et al. / Materials Today: Proceedings xxx (xxxx) xxx 5

 The Experiment results have obtained from the optimum val- [3] D. Chakradhar, A. Venu Gopal, ‘‘Multi-objective optimization of electro-
chemical machining of EN31 steel by grey relational analysis”, Vol. 1, No. 2,
ues. The micro-holes had studied with the help of Scanning
pp. 113 – 117, 2011..
Electron Microscope (SEM) images. [4] S. Habib, ‘‘Experimental Investigation of Electrochemical Machining Process
using Taguchi Approach”, Vol. 1, Issue: 6, pp. 93-105, 2014..
[5] J.C.d.S. Neto, E.M.d. Silva, M.B.d. Silva, Intervening variables in electrochemical
Declaration of Competing Interest machining, J. Mater. Process. Technol. 179 (1-3) (2006) 92–96, https://doi.org/
10.1016/j.jmatprotec.2006.03.105.
[6] H. Obara, M. Isogai, T. Goda, T. Sasaki, Y. Ikemoto, High-voltage pulse- assisted
The authors declare that they have no known competing finan- electrochemical machining, IJEM 17 (2012) 15–21.
cial interests or personal relationships that could have appeared [7] K.P. Rajurkar, D. Zhu, J.A. McGeough, J. Kozak, A. De Silva, New developments in
to influence the work reported in this paper. electro-chemical machining, CIRP Ann. 48 (2) (1999) 567–579.
[8] T. Kurita, K. Chikamori, S. Kubota, M. Hattori, M (in press) A study of three-
dimensional shape machining with an ECM system. Int. J. Mach. Tool. Manuf..
References: [9] M.S. Hewidy, M. Fattouh, M. Elkhabeery, Some economical aspects of ECM
processes, Int. Conf. Appl. Mech. Mech. Eng. 1 (1) (1984) 87–94, https://doi.org/
[1] N.K. Jain, V.K. Jain, Optimization of electro-chemical machining process 10.21608/amme.1984.49203.
parameters using genetic algorithms, Mach. Sci. Technol. 11 (2) (2007) 235– [10] S. Dr, U. Ramesh, K. Gobikrishnan, Umnath” micro Drilling Studies on Titanium
258, https://doi.org/10.1080/10910340701350108. alloy using Micro Electro Chemical Machining’, Aust. J. Basic & Appl. Sci 99110
[2] C. Senthilkumar, G. Ganesan, R. Karthikeyan, Study of electrochemical (2015) 934–941.
machining characteristics of Al/SiCp composites, DOI: 10.1007/ s00170-008-
1704-1..

Please cite this article as: U. Gobikrishnan, P. Suresh and P. Kumaravel, Drilling investigations on Inconel alloy 625 material of material removal rate using
micro electrochemical machining, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.07.173