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ANALYSIS OF ELECTROCHEMICAL MACHINING PROCESS PARAMETERS AFFECTING MATERIAL REMOVAL RATE OF HASTELLOY C-276

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  • Bharati vidyapeeth's Jawaharlal Nehru Institute of Technology,Pune

Abstract and Figures

The difficulties in machining super alloys and other hard materials by conventional processes are largely responsible for the development of non traditional machining processes. Electrochemical machining (ECM) is a non-traditional process used mainly to machine hard or difficult to cut metals such as Ni-base super alloys, composites, stainless steels etc. Three parameters are changed during experiments: feed rate, electrolyte flow rate and voltage. Taguchi L9 orthogonal array is used for parameter setting during the experimental runs. Aqueous solution of sodium nitrate (NaNO3) is used as an electrolyte of concentration 200 g/l. The results show that the high material removal rate is obtained at high feed rate (1 mm/min), minimum electrolyte flow rate (150 L/hr) and high voltage (16 V). The feed rate is observed to be the main parameter affecting the material removal rate.
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International Journal of Advanced Research in Engineering and Technology (IJARET),
ISSN 0976 6480(Print), ISSN 0976 6499(Online) Volume 5, Issue 1, January (2014), © IAEME
18
ANALYSIS OF ELECTROCHEMICAL MACHINING PROCESS
PARAMETERS AFFECTING MATERIAL REMOVAL RATE OF
HASTELLOY C-276
Suresh H. Surekar
1
, Sudhir G. Bhatwadekar
2
, Dayanand S. Bilgi
3
1
(Department of Production Engineering, Kolhapur Institute of Technology’s College of
Engineering, Kolhapur, Maharashtra, India)
2
(Department of Production Engineering, Kolhapur Institute of Technology’s College of
Engineering, Kolhapur, Maharashtra, India)
3
(Department of Mechanical Engineering, Bharati Vidyapeeth’s College of Engineering for Women,
Pune, India)
ABSTRACT
The difficulties in machining super alloys and other hard materials by conventional processes
are largely responsible for the development of non traditional machining processes. Electrochemical
machining (ECM) is a non-traditional process used mainly to machine hard or difficult to cut metals
such as Ni-base super alloys, composites, stainless steels etc. Three parameters are changed during
experiments: feed rate, electrolyte flow rate and voltage. Taguchi L9 orthogonal array is used for
parameter setting during the experimental runs. Aqueous solution of sodium nitrate (NaNO
3
) is used
as an electrolyte of concentration 200 g/l. The results show that the high material removal rate is
obtained at high feed rate (1 mm/min), minimum electrolyte flow rate (150 L/hr) and high voltage
(16 V). The feed rate is observed to be the main parameter affecting the material removal rate.
Keywords: Electrochemical Machining Process, Material Removal Rate, Optimization,
Taguchi Methodology
1. INTRODUCTION
The difficulties in machining super alloys and other hard materials by conventional processes
are largely responsible for the development of non traditional machining processes. Electrochemical
machining (ECM) is a non-traditional process used mainly to machine hard or difficult to cut metals
such as Ni-base super alloys, composites, stainless steels etc. The difficult to cut metals require high
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energy to deform material in chips resulting into thermal stresses due to the high temperatures. In
traditional processes, the heat generated during the machining is dissipated to the tool, chip,
workpiece and environment, affecting the surface integrity of the workpiece. [2, 4, 5, 6, 9]
In Electrochemical machining process the tool is not touching the workpiece [8]. Electrochemical
reactions (electrolysis) are responsible for the material removal mechanism. Main components of
ECM system are voltage, a high current power supply and an electrolyte. The electrolyte is normally
solution of inorganic salts, like sodium chloride (NaCl) or sodium nitrate (NaNO
3
), acids, bases or
combinations of salt, acid and base [10]. The objective of this work is to optimize and analyze the
process (cutting) parameters in electrochemical machining of Hastelloy C-276 (Ni-Base Superalloy)
to get high material removal rate. C-276 alloy is a nickel-molybdenum–chromium wrought alloy that
is generally considered a versatile corrosion-resistant alloy. This alloy resists the formation of grain-
boundary precipitates. Hastelloy C-276 alloy has excellent resistance to localized corrosion and to
both oxidizing and reducing media. It also has excellent resistance to pitting and stress- corrosion
cracking. It is one of the few materials that withstand the corrosive effects of wet chlorine gas,
hypochlorite and chlorine dioxide. Because of its versatility, C-276 alloy can be used where “upset”
conditions are likely to occur or in multipurpose plants [3]. A prototype specimen developed at the
laboratory is used for experimentation. Three parameters are changed during the experiments: feed
rate, electrolyte flow rate and voltage. Aqueous solution of sodium nitrate (NaNO
3
) is used as an
electrolyte of concentration 200 g/l of H
2
O to machine Hastelloy C-276 [10]. Twenty-seven
experimental runs are carried out using the equipment developed, with different parameter
combinations. Taguchi methodology is used for optimization of the process. To combine parameters
at different levels L9 orthogonal array is used [1, 7].
2. DESIGN OF EXPERIMENTS
Fig. 1 shows a schematic diagram of the electrochemical machining system used in this work.
The workpiece is held in fixture containing two metal plates; one fixed and other movable. The
fixture is kept in a plastic box to avoid loss of current and shock during experimentation. A nut and
bolt assembly is used to move the plate for tightening the workpiece. During the process, tool
electrode moves according to feed movement while the workpiece is stationary. A threaded shaft is
used to provide linear motion to the tool with a gear mounted to rotate shaft through a pinion and a
stepper motor. It is welded to steel frame by means of bearing assembly. The shaft is supported in
two ball bearings at the ends to ensure free rotation of the shaft. Feed is given manually as well as
automatically by means of stepper motor. The tool is of copper and used to supply current through
negative pole of power supply. The electrolyte is supplied for machining through the hole drilled at
its centre. Acrylic plate of 10 mm thickness is used to hold the tool and to avoid loss of current and
shock during manual feeding. The electric unit is used to supply voltage and current at desired level
during experiments. It supplies current in regulated DC mode and has calibrated voltmeter and
ammeter to set values of voltage and current in the range 0-30 V and 0-60 A respectively. The
hydraulic unit is used to supply electrolyte at high and desired pressure or flow rate to facilitate
removal the material. It consists of a pump, PVC pipes, fittings and a rotameter. Rotameter is used to
measure electrolyte flow rate in liters per hour. To calculate material removal rate an electronic
weight balance with a least count of 10 mg is used.
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Figure 1: Experimental Set up
The metal removal rate (MRR) is given by,
(1)
Where Wb = weight before machining and
Wa = weight after machining and
T = machining time.
During experimentation (1) is used for calculation of the material removal rate (MRR).
3. RESULTS AND DISCUSSION
Optimization of parameters is done by means of Taguchi method. The first step in
this method is to select the number of parameters and their levels. The methodology for optimization
is given below: (i) Selection of number of parameters and their levels (ii) Selection of orthogonal
array (iii) Selection of criteria (Higher-The- Better, Lower-The-Better, Nominal-the-Best)
(iv) Determination of signal to noise ratio (S/N ratio), (v) Selection of best combination of
parameters for maximum material removal rate. In case of the material removal rate the Higher-The-
Better criterion is selected. For increasing productivity of the process the material removal rate needs
to be high hence this criterion is selected. S/N ratio for Higher-The-Better criterion is calculated by
means of (2).
(2)
International Journal of Advanced Research in Engineering and Technology (IJARET),
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Table 1 shows general results for MRR. From the table the optimized combination of
parameters high feed rate, minimum flow rate and high voltage is seen. S/N ratio is calculated from
(2) and S/N7 has highest value and hence results into optimized combination of parameters for high
material removal rate. For this condition, the voltage is 16V and the flow rate of the electrolyte is
150 L/hr.
Table 1: Experimental Results and S/N ratio
Sr.
No.
Feed Rate
Mm/min (P1)
Electrolyte Flow Rate
L/hr (P2)
Voltage
V (P3)
MRR
mg/min
S/N ratio
1 0.5 150 12 30 29.54 S/N1
2 0.5 250 14 40 32.04 S/N2
3 0.5 350 16 28 28.49 S/N3
4
0.7
150
14
58
35.26
S/N
5 0.7 250 16 56 34.96 S/N5
6 0.7 350 12 36 31.12 S/N6
7
1.0
150
16
78
37.84
S/N7
8
1.0
250
12
52
34.32
S/N8
9
1.0
350
14
48
33.62
S/N9
The mean effect of parameters on material removal rate is shown in the following figures.
Graphs are plotted to show relation between mean S/N and process parameters from Table 2.
Table 2: Mean S/N values of MRR
Level Feed Rate Electrolyte flow rate Voltage
-1/1 30.02 34.21 31.66
0/2
33.78
33.77
32.8
+1/3 35.26 31.07 33.76
3.1 Effect of Feed Rate
In Fig. 2 the effect of feed rate is shown. As feed rate increases material removal rate
increases because tool is forwarding fast towards the workpiece and removes more material. Material
removal rate increases because the gap between tool and workpiece is maintained and thus current
efficiency are increased which results in high material removal.
Figure 2: Effect of Feed Rate on MRR
International Journal of Advanced Research in Engineering and Technology (IJARET),
ISSN 0976 – 6480(Print), ISSN 0976 – 6499(Online) Volume 5, Issue 1, January (2014), © IAEME
22
It is the main parameter which affects MRR on large extent because it is varied in fractions
(0.2 mm/min).
3.2 Effect of Electrolyte flow rate
In Fig. 3 effect of electrolyte flow rate is shown. As flow rate increases material removal rate
decreases because the electrolyte is flowing at fast rate without contacting surface of workpiece.
Contact of the electrolyte is needed to react with the material hence at minimum flow rate material
removal rate is high.
Figure 3: Effect of Flow Rate on MRR
3.3 Effect of Voltage
In Fig. 4 effect of voltage is given and it has almost linear relation with material removal rate.
The effect of voltage on material removal rate is negligible because it is varied by two units as
compared with feed rate.
Figure 4: Effect of Voltage on MRR
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4. CONCLUSIONS AND FUTURE SCOPE
In this case the best combination is high feed rare at minimum electrolyte flow rate and
maximum voltage. The input parameters are termed as Signal and Error in the response/result is
termed as Noise. The main component which needs to be tight controlled is feed rate. As voltage and
feed rate increases MRR increases. It requires low flow rate to complete the reaction between
electrolyte and workpiece to remove maximum material.
It is concluded that:
(i) The MRR is affected by tool feed rate to the greater extent.
(ii) At low feed rates irregular removal of material is more likely to occur.
(iii) The effect of voltage on MRR is almost linear.
(iv) At low electrolyte flow rate (150 L/hr) more material is removed from the workpiece due to
longer contact with the workpiece.
In this paper only cutting parameters are optimized and analyzed. Along with these
controllable parameters some non controllable parameters are affecting the process characteristics
(MRR) and hence optimization of those parameters is challenging. Study of reaction kinetics is broad
area for research to increase productivity.
REFERENCES
[1] Design and analysis of experiments, http://www.doe.soton.ac.uk/elearning/13/10/2012.
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Engineering & Technology (IJMET), Volume 4, Issue 3, 2013, pp. 47 - 53, ISSN Print:
0976 – 6340, ISSN Online: 0976 – 6359.
ResearchGate has not been able to resolve any citations for this publication.
Book
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What is New in this Edition? Although through this book I tried to encompass most of the manufacturing technologies, but not all of them, many educators felt the need to add more depth to make this text suitable for a majority of the Indian universities. So, to that extent, the following changes were made: • All the chapters were thoroughly checked to see that written material was in line with current practices and some of the obsolete details were removed. • Many illustrations were simplified to help students have a better understanding of the concepts in tune with the text. • Discussion on Unconventional Machining Processes: EBM, USM and PAM has been enhanced. • Topics on Shaper Construction, Dynamometer, Cutting Tools Geometry and Comparison of Reciprocating Machine Tools along with their figures have been added. • In-depth discussion on Broaching and Internal Centre-less Grinding has been incorporated. • Each chapter is provided with multiple-choice questions in view of the changing trends in examination systems in India. • Pedagogy: o 480 figures (33 new figures added) o 324 Review Questions (46 new questions added from University Question Papers) o 40 Numerical Problems o 175 MCQs added (present as a web supplement in the previous edition) o Section on Solved Examples added as part of OLC Available from Amazon in kindle edition and Google Books http://www.amazon.com/Manufacturing-Technology-Metal-Cutting-Machine-ebook/dp/B00H1Q21BW/ref=sr_1_2?s=digital-text&ie=UTF8&qid=1390994021&sr=1-2 https://play.google.com/store/books/details/P_N_Rao_Manufacturing_Technology_Metal_Cutting_and?id=b4FSAgAAQBAJ&hl=en
Article
To the end of 1974 the scientific literature contained over 1200 articles on electrochemical machining (ECM) [1]. Additionally approximately 100 papers appeared in 1975. Although a large number of those references appeared in what might be described as ‘non-learned’ journals, this still leaves the potential student with a difficult task if he wishes to review the state of the art. This is the first attempt to review thoroughly the literature in this field, although only a small proportion of those contributions are considered pertinent. The review will take the following form: after an introductory chapter there will be two chapters on dissolution kinetics, the second concerned with the kinetics as affected by the physical characteristics of the electrolyte; this will be followed by a section on the effects of electrochemically machined surface on the physical properties of a metal. Chapters 5 and 6 will deal with tool design and the optimizing of process parameters, after which will be a review of topics concerned with the application of ECM.
Metals Handbook-Machining, 8 th Edition
  • F John
  • Kahls
John F. Kahls, Metals Handbook-Machining, 8 th Edition,Vol.3 (ASM International, Metals park, Ohio, United States of America,pp-233-240, 1997).
  • J Kozak
J. Kozak, 2004, Electrochemical Machining, http://www.unl.edu/nmrc/ecmreferences.htm, 18/6/2004.
Metals Handbook-Machining, 9 th Edition
  • L Tery
  • Lievestro
Tery L. Lievestro, Metals Handbook-Machining, 9 th Edition, Vol.16, (ASM International, Metals park, Ohio, United States of America,pp-533-541, 1989).
  • E Paul Degarmo
  • J T Black
  • Ronald A Kohsher
E. Paul DeGarmo, J. T. Black, Ronald A. Kohsher, Materials & Processes in Manufacturing, 8 th Edition,Vol.8, (Prentice Hall of India private Limited, New Delhi, India,pp-947, 1997).
Electrolyte for electrochemically machining Nickel base superalloys
  • Us -Patent
US -Patent No. 3975245, Electrolyte for electrochemically machining Nickel base superalloys(17 th August 1976).
Application of Taguchi Method and Anova in Optimization of Cutting Parameters for Material Removal Rate and Surface Roughness in Turning Operation
  • Vishal Francis
  • Ravi S Singh
  • Nikita Singh
  • Ali R Rizvi
  • Santosh Kumar
Vishal Francis, Ravi.S.Singh, Nikita Singh, Ali.R.Rizvi and Santosh Kumar, "Application of Taguchi Method and Anova in Optimization of Cutting Parameters for Material Removal Rate and Surface Roughness in Turning Operation", International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 3, 2013, pp. 47 -53, ISSN Print: 0976 -6340, ISSN Online: 0976 -6359.