 Open Access
 Total Downloads : 198
 Authors : Suresh H. Surekar, Sudhir G. Bhatwadekar
 Paper ID : IJERTV5IS010503
 Volume & Issue : Volume 05, Issue 01 (January 2016)
 DOI : http://dx.doi.org/10.17577/IJERTV5IS010503
 Published (First Online): 27012016
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Experimental and Theoretical Investigation of Electrochemical Machining Process
Suresh H. Surekar
Department of Production Engineering KITs College of Engineering Kolhapur, India
Sudhir G. Bhatwadekar
Department of Production Engineering KITs College of Engineering Kolhapur, India
Abstract Electrochemical Machining (ECM) has proven to be very effective in machining difficulttocut materials because of high removal rates. It is a relatively new and important method of removing material from the surface or drilling the hole in workpiece and offers a number of advantages over other machining methods. Material removal from the workpiece is done by means of Principle of Electrolysis. It is an electrolytic process and its basis is the phenomenon of electrolysis, whose laws were established by Faraday. Metal removal is effected by a suitably shaped tool electrode, and the parts thus produced have the specified shape, dimensions, and surface finish. Experimentally material removal rate is calculated by measuring weight of the workpiece before and after machining. In theoretical material removal rate the process control parameters are not considered. Electrochemical drilling is affected by number of parameters such as tool feed rate, voltage, electrolyte flow rate, electrolyte concentration etc. Taguchi method of optimization is used for parameter combinations and to carry out experimentations to calculate material removal rate. The input parameters are termed as Signal and error in the response/result is termed as Noise (S/N). Workpiece used in the electrochemical machining process is Hastelloy C276 (Ni Base Superalloy) because of its high hardness and special applications such as aerospace chemical etc.
Keywords Electrochemical Machining Process, Material Removal Rate, Hasetlloy C276, Taguchi Me

INTRODUCTION
Electrochemical Machining Process is a nontraditional, non conventional, nonmechanical machining process in which material removal from the workpiece is done by means of Principle of Electrolysis [15]. It is an electrolytic process and its basis is the phenomenon of electrolysis, whose laws were established by Faraday in 1833. Electrolysis is the name given to the chemical process which occurs when an electric current is passed between two conductors dipped into a liquid solution. The system of electrodes and electrolyte is referred to as the electrolytic cell and the chemical reactions which occur at the electrodes are called the anodic or cathodic reactions or processes respectively.
The principle of electrochemical machining process is shown in fig.1. The process of electrochemical machining is developed on the principle of Faradays law and Ohms law. In this process an electrolytic cell is formed by the anode (work piece) and the cathode (tool) in the static or flowing electrolyte. The metal is removed by the controlled
dissolution of the anode according to the well known Faradays law of electrolysis when the electromotive force (emf) is applied across electrodes, flow of current in the electrolyte is established due to positively charged ions being attracted towards the cathode and negatively ions are attracted towards anode. Current/current density depends on the rate at which ions arrive at respective electrodes which are proportional to the applied voltage, concentration of electrolyte, the gap between the electrodes and tool feed rate.
The material removal rate (MRR) is affected by various parameters which are controllable as well as non controllable. Metal removal is achieved by electrochemical dissolution of an anodically polarized workpiece which is one part of an electrolytic cell in ECM. Hard passive alloys, such as nickelbase superalloys (Hastelloy C276) [6] are widely used in various industries, such as chemical, aircraft and automotive industries can be shaped electrolytically by using ECM and the rate of machining does not depend on their mechanical properties.
Electrochemical Machining is a relatively new and important method of removing material from the surface or drilling the hole in workpiece and offers a number of advantages over other machining methods (conventional / unconventional). Metal removal is effected by a suitably shaped tool electrode, and the parts thus produced have the specified shape, dimensions, and surface finish. Being a nonmechanical metal removal process, ECM is capable of machining any (high strength high temperature alloys) electrically conductive material with high stock removal rates regardless of their mechanical properties such as hardness. ECM is employed in many applications, for example, for automotive, offshore petroleum, and medical engineering industries, as well as by aerospace firms, which are its principal user. ECM leaves no burrs; one ECM operation can replace several operations of mechanical machining. Hard passive alloys are widely used in various industries, such as chemical, aircraft and automotive industries. Electrochemical Machining (ECM) has proven to be very effective in machining difficulttocut materials because of high removal rates, ability to generate complicated contours and profiles, no tool wear, no burrs and no scratches left on the machined surface. The passivation effect can negatively influences the productivity of the ECM process. Theoretically material removal rate is calculated by means of Faradays laws.
(4)
Fig.1: Principle of Electrochemical Machining
Experimentally material removal rate is calculated by measuring weight of the workpiece before and after machining Electrochemical drilling is affected by number of parameters such as tool feed rate, voltage, electrolyte flow rate, electrolyte concentration etc. Taguchi method of optimization is used for parameter combinations and to carry out experimentations to calculate material removal rate [7]. The input parameters are termed as Signal and error in the response/result is termed as Noise (S/N). Workpiece used in the electrochemical machining process is Hastelloy C276 (NiBase Superalloy) because of its high hardness and special applications such as aerospace chemical etc.

MATERIAL REMOVAL RATE (MRR)
Material removal rate (MRR) in ECM is calculated by means of Faradays laws [8]. Faradays laws state that: (1) the amount of chemical change produced by an electric current i.e. the amount of any material dissolved or deposited is proportional to the quantity of electricity passed. (2) The amount of different substances dissolved or deposited by the same quantity of electricity are proportional to their chemical equivalent weights. From faradays two laws,
Material Removed/Dissolved (M) I x t x (1) (2)
Where, M Mass of material dissolved, gm (gram) I current, A (ampere)
T Time, hr (hour)
– gram equivalent weight
F Faradays constant, (A hr)
The gram equivalent weight of the metal is given by = A/Z where A is atomic weight and Z is the valancy of the ions produced. Therefore
(3)
Equation (2) contains constant and variable parameters, in this current/voltage and valancy are variable and remaining all parameters are constant for single element. To calculate material removal rate for workpiece containing number of elements equation (3) is used.
Where, I – Current (A)
F – Faradays constant (26.8 A hr)
– Density of material, (8.89 g/cm3) A – Atomic weight of element
Z – Valancy of element
X – Percentage composition of element
The chemical composition of Hastelloy C276 along with percentage and valancy and atomic weight is given in table
 From table 1 it is clear that each element of the workpiece is having multiple valancies and valancy changes as temperature changes. Therefore temperature and pH of electrolyte is considered constant. To calculate material removal rate theoretically voltage has been taken as e.g. 12 V, 14 V and 16 V. From this voltage current required for calculation of MRR is calculated by considering materials and electrolytes conductivity by means of Ohms law. While calculating MRR other process parameters are not taken into consideration. Accurate material removal rate has not been calculated theoretically as every element has multiple valancy (Z) and valancy changes as temperature changes. As well as the percentage of each element has been given in the range ant it is impossible to add exact percentage. Hence for calculating MRR values are taken as minimum (1), intermediate (0) and maximum (+1). Taguchi methodology is used for parameter combinations at different levels as the parameter affecting MRR to the large extent is impossible to predict directly. Therefore L9 orthogonal array has been taken for parameter combinations at different levels. The L9 orthogonal array along with parameter values is given in the table 2.
TABLE 1: CHEMICAL PROPERTIES OF HASTELLOY C276 [9, 10]
S.
N.
Name of Element
Percentage (X)
Valancy (Z)
Atomic weight (gm)
1
Nickel
57
2,3
58.693
2
Molybdenum
1517
3,4,6
95.96
3
Chromium
14.516.5
2,3,6
51.996
4
Carbon
0.01
1,2,4
12.011
5
Manganese
1.0
2,3,4,6,7
54.938
6
Silicon
0.08
2,3,4
28.085
7
Iron
47
2,3,
55.845
8
Tungsten
34.5
6,8
183.54
9
Cobalt
2.5
2,3,
58.933
10
Vanadium
0.35
3,5
50.94
11
Phosphorous
0.025
3,4
30.97
12
Sulphur
0.01
2,4,6
32.07
Experimentally material removal rate is calculated as a difference in weight i.e. weight before drilling/machining weight after drilling/machining. To calculate material removal rate electronic weight balance is used with least count of 10 mg.
TABLE 2:L9 ORTHOGONAL ARRAYS WITH THEORETICAL VALUES
S.N.
Voltage
Percentage
valancy
1
12
1
1
2
12
0
0
3
12
1
1
4
14
1
0
5
14
0
1
6
14
1
1
7
16
1
1
8
16
0
1
9
16
1
0
(5)
Where Wb : weight (gm) before machining/drilling Wa : weight after machining/drilling
T : time of machining/ drilling
To calculate material removal rate experimentally only weight of the workpiece before after drilling or machining is considered. The process control parameters are not considered hence Taguchi method of optimization is used to carry out experimentations and to combine parameters at different levels. The parameters considered for experimentation are voltage, feed rate and electrolyte flow rate. L9 orthogonal array along with parameter combinations at different levels is given in table 3. To carry out experimentations a set developed and fabricated as shown in figure 2.
 From table 1 it is clear that each element of the workpiece is having multiple valancies and valancy changes as temperature changes. Therefore temperature and pH of electrolyte is considered constant. To calculate material removal rate theoretically voltage has been taken as e.g. 12 V, 14 V and 16 V. From this voltage current required for calculation of MRR is calculated by considering materials and electrolytes conductivity by means of Ohms law. While calculating MRR other process parameters are not taken into consideration. Accurate material removal rate has not been calculated theoretically as every element has multiple valancy (Z) and valancy changes as temperature changes. As well as the percentage of each element has been given in the range ant it is impossible to add exact percentage. Hence for calculating MRR values are taken as minimum (1), intermediate (0) and maximum (+1). Taguchi methodology is used for parameter combinations at different levels as the parameter affecting MRR to the large extent is impossible to predict directly. Therefore L9 orthogonal array has been taken for parameter combinations at different levels. The L9 orthogonal array along with parameter values is given in the table 2.

RESULTS AND DISSCUSSION
Theoretical material removal rate is calculated by means of (4) and is given in table 3. From the table it is clear that large volume of material is removed at high voltage, intermediate percentage and minimum valancy as MRR is directly proportional to the voltage and inversely proportional to the valancy.
S.N.
Voltage
Percentage
valancy
MRR
x106 mm3/min
1
12
1
1
1.66
2
12
0
0
1.49
3
12
1
1
1.45
4
14
1
0
1.79
5
14
0
1
1.68
6
14
1
1
1.87
7
16
1
1
1.97
8
16
0
1
2.12
9
16
1
0
2.00
S.N.
Voltage
Percentage
valancy
MRR
x106 mm3/min
1
12
1
1
1.66
2
12
0
0
1.49
3
12
1
1
1.45
4
14
1
0
1.79
5
14
0
1
1.68
6
14
1
1
1.87
7
16
1
1
1.97
8
16
0
1
2.12
9
16
1
0
2.00
TABLE 3 THEORETICAL MATERIAL REMOVAL RATE
Fig. 2: ECM Set up
TABLE 4: L9 ORTHOGONAL ARRAYS WITH EXPERIMENTAL VALUES
350
S.N.
Feed Rate
Electrolyte Flow Rate
Voltage
1
0.5
150
12
2
0.5
250
14
3
0.5
350
16
4
0.7
150
14
5
0.7
250
16
6
0.7
350
12
7
1.0
150
16
8
1.0
250
12
9
1.0
14
Experimental material removal rate at different levels of parameters is given in table 5. From the table 5; large amount of material is removed at combination 1 mm/min feed rate, minimum electrolyte flow rate and maximum voltage. Tool feed rate and voltage are directly proportional to MRR and electrolyte flow rate is inversely proportional. As flow rate increases MRR decreases.
ANOVA and regression analysis has been done to validate the obtained results. Theoretical and experimental ANOVA and regression have been given in table 6 and table 7 respectively. From the ANOVA and Regression analysis it is clear that all the results are valid for the given parameter values and levels. To validate the results the values of R square and F (from table 6 and table 7) are considered at 95
% of confidence level. If the value of R square is 1 more accurate the results as well as higher the value of F more accurate the results.
TABLE 5: EXPERIMENTAL MATERIAL REMOVAL RATE
S. N
.
Fee d Rat e
Electroly te Flow Rate
Voltag e
Material Removal Rate
Initial Weight( g)
Final Weight( g)
mg / 5
min
mg/ min
1
0.5
150
12
214.060
213.910
150
30
2
0.5
250
14
213.910
213.710
200
40
3
0.5
350
16
213.710
213.570
140
28
4
0.7
150
14
213.570
213.280
290
58
5
0.7
250
16
213.280
213.000
280
56
6
0.7
350
12
213.000
212.820
180
36
7
1.0
150
16
212.820
212.430
390
78
8
1.0
250
12
212.430
212.170
260
52
9
1.0
350
14
212.170
211.930
240
48
TABLE 6: THEORETICAL ANOVA AND REGRESSION ANALYSIS
Regression Statistics
Multiple R
0.995775688
R Square
0.991569221
Adjusted R Square
0.986510754
Standard Error
0.026791375
Observations
9
ANOVA
df
SS
MS
F
Significance F
Regression
3
0.4221
0.1407
196.021
7
1.32552E05
Residual
5
0.00358
9
0.00071
8
Total
8
0.42568
9
TABLE 7: EXPERIMENTAL ANOVA AND REGRESSION ANALYSIS
Regression Statistics
Multiple R
0.951936074
R Square
0.906182288
Adjusted R Square
0.849891661
Standard Error
6.138175053
Observations
9
ANOVA
df
SS
MS
F
Significance F
Regression
3
1819.61
4
606.538
16.0982
8
0.005304633
Residual
5
188.386
37.6771
9
Total
8
2008
Fig.3: Combined effect of parameter (experimental)
Fig.4: Combined effect of parameter (theoretical)

CONCLUSION
In electrochemical machining process material removal rate is calculated by means of Faradays laws of electrolysis. While calculating MRR the process parameters such as tool feed rate, electrolyte concentration, electrolyte flow rate etc. are not considered. Only one parameter i.e. current has been taken into consideration. Experimentally material removal rate is calculated by measuring the weight of workpiece before and after machining as difference. For conducting experiments numbers of parameters are combined instead of considering each parameter separately by means Taguchi methodology. To validate the theoretical as well as experimental results ANOVA and Regression analysis has been performed. From ANOVA and Regression analysis it is concluded that the selected parameters are giving desired results. For that purpose values of R square and F are considered. Large values R square and F are desirable and are obtained. Main effect graphs are plotted to check interrelation of parameters and it is found that all the parameters are interrelated and affects each other as each line is crossing through other two lines.
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