ME8073 Unconventional Machining Processes - By www.LearnEngineering.in.pdf

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ENGINEERING COLLEGES
2016 – 17 Even Semester
IMPORTANT QUESTIONS AND ANSWERS
Department of Mechanical Engineering
SUBJECT CODE: ME 8073
SUBJECT NAME: UNCONVENTIONAL MACHINING PROCESSES
Regulation: 2017 Year and Semester: IV and VII
Prepared by
Sl. No. Name of the Faculty Designation Affiliating College
1. Mr. M. Thomas Victor Asst. Prof SMTEC
2. Mr. V. Vignesh Asst. Prof SMTEC
Verified by DLI, CLI and Approved by the Centralised Monitoring Team
Visit & Downloaded From : www.LearnEngineering.in

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ANNA UNIVERSITY, CHENNAI AFFILIATED INSTITUTIONS R - 2017
SYLLABUS B.E. MECHANICAL ENGINEERING
SEMESTER VII
ME8073 UNCONVENTIONAL MACHINING PROCESSES L T P C
3 0 0 3
OBJECTIVES:
To learn about various unconventional machining processes, the various
process parameters and their influence on performance and their applications
UNIT I INTRODUCTION 6
Unconventional machining Process – Need – classification – Brief overview.
UNIT II MECHANICAL ENERGY BASED PROCESSES 9
Abrasive Jet Machining – Water Jet Machining – Abrasive Water Jet Machining -
Ultrasonic Machining. (AJM, WJM, AWJM and USM). Working Principles – equipment
used – Process parameters – MRR- Applications.
UNIT III ELECTRICAL ENERGY BASED PROCESSES 9
Electric Discharge Machining (EDM)- working Principle-equipments-Process
Parameters-Surface Finish and MRR- electrode / Tool – Power and control Circuits-
Tool Wear – Dielectric – Flushing – Wire cut EDM – Applications.
UNIT IV CHEMICAL AND ELECTRO-CHEMICAL ENERGY BASED PROCESSES
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Chemical machining and Electro-Chemical machining (CHM and ECM)-Etchants –
Maskant - techniques of applying maskants - Process Parameters – Surface finish and
MRR-Applications. Principles of ECM- equipments-Surface Roughness and MRR
Electrical circuit-Process Parameters- ECG and ECH - Applications.
UNIT V THERMAL ENERGY BASED PROCESSES 10
Laser Beam machining and drilling (LBM), plasma Arc machining (PAM) and
Electron Beam Machining (EBM). Principles – Equipment –Types - Beam control
techniques – Applications. TOTAL: 45 PERIODS
OUTCOMES:
Upon completion of this course, the students can able to demonstrate different
unconventional machining processes and know the influence of difference process
parameters on the performance and their applications.
TEXT BOOKS:
1. Vijay.K. Jain “Advanced Machining Processes” Allied Publishers Pvt. Ltd., New Delhi,
2007
2. Pandey P.C. and Shan H.S. “Modern Machining Processes” Tata McGraw-Hill, New
Delhi, 2007.
REFERENCES:
1. Benedict. G.F. “Nontraditional Manufacturing Processes”, Marcel Dekker Inc., New
York, 1987.
2. Mc Geough, “Advanced Methods of Machining”, Chapman and Hall, London, 1998.
3. Paul De Garmo, J.T.Black, and Ronald.A.Kohser, “Material and Processes in
Manufacturing” Prentice Hall of India Pvt. Ltd., 8thEdition, New Delhi , 2001.

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3. TABLE OF CONTENTS
S.NO TABLE OF CONTENTS
PAGE
NO
a. Aim and Objective of the subject 4
b. Detailed Lesson Plan 5
c. Unit I-Introduction-Part A 8
d. Unit I- Introduction -Part B 10
e.
Unit II- Mechanical energy based processes -Part
A
18
f.
Unit II- Mechanical energy based processes -Part
B
20
g. Unit III- Electrical Energy Based Processes -Part A 31
h. Unit III- Electrical Energy Based Processes -Part B 32
i.
Unit IV- Chemical And Electro-Chemical Energy
Based -Part A
43
j.
Unit IV- Chemical And Electro-Chemical Energy
Based -Part B
45
k. Unit V- Thermal Energy Based Processes - Part A 60
l. Unit V- Thermal Energy Based Processes - Part B 62
m. Question Bank 76

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ME 8073 UNCONVENTIONAL MACHINING PROCESSES 3 0 0 3
L T P C
1. Aim and Objective of the Subject
 To understand the need and the importance of unconventional machining
processes.
 To learn about various types of unconventional machining processes based on
the energy involved.
 To know the various process parameters and their influence on performances.
 To know the differences between the processes, advantages, limitations and
their practical applications.
2. Need and importance for study of the subject:
 Students will get a sound knowledge about the recent technologies in
Unconventional Machining Processes.
 It will be very much helpful if they are interested in doing research in non
traditional machining Techniques.
3. Industrial Connectivity and latest developments:
 It gives the knowledge about the product machining to the Industrial
standards.
 Recent techniques have been used for machining new innovative
materials.

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SCAD GROUP OF INSTITUTIONS
DEPARTMENT OF MECHANICAL ENGINEERING
DETAILED LESSON PLAN
Name of the Subject & Code: ME 8073 UNCONVENTIONAL MACHINING
PROCESSES
Text Books:
T1- Vijay.K. Jain “Advanced Machining Processes” Allied Publishers Pvt. Ltd., New
Delhi, 2007
Reference Books:
R1- Pandey P.C. and Shan H.S. “Modern Machining Processes” Tata McGraw-Hill,
New
Delhi (2007).
R2-Vijaya Ramnath ,M.Vijayan , “ Unconventional Machining Processes”
R3- R.K.Rajput, A textbook of Manufacturing Processes Edition 2010
T – Text book, R – Reference book
Sl.No Unit Topic
Hours
Required
/Planned
Cumulativ
e
Hrs
Books
Referred
Unit-I Introduction
1 1
Introduction to unconventional
machining processes
1 1 T1
2 1 The need of the process 1 2 T1, R2
3 1 Classification 1 3
T1, R3,
R2
4 1
Energies employed in the processes-
EDM,ECM,USM,LBM,PAM,AJM,WJM
etc.
1 4 T1
5 1
Features , principle of unconventional
machining processes
1 5 T1, R2
6 1
Advantages , disadvantages
,Applications of UCM
1 6 R2
7 1
Brief overview of all techniques-
overview of Unit-I
1 7 R1, R2

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Unit-II Mechanical Energy Based
Process
8 2 -AJM Processes- Operating Principle
Equipment of AJM
1 8
R1, R2
9 2
Metal removal rate-Mechanism of
material Removal process parameters
2 10 T1, R2
10 2
Applications, advantages,
disadvantages-AJM
1 11 R1, R2
11 2
WJM Process- Operating Principle
,Equipment of WJM
1 12
T1, R1,
R2
12 2
Effect of feed rate , machining
characteristics, Effect of exit pressure
1 13
T1, R1,
R2
13 2
Process parameters Applications,
Advantages, Disadvantages-WJM
1 14 T1, R1
14 2
AWJM Process- Operating Principle
,Equipment of AWJM
1 15 T1, R1
15 2
Metal removal rate-Mechanism of
material Removal process parameters -
disadvantages-AWJM
1 16 T1, R1
16 2 USM-Process- working Principles 1 17 T1, R2
17 2
Types of Transducers Concentrators,
Tool, nodal point clamping
1 18 T1, R2
18 2
Abrasive feed mechanism, abrasive
slurry
1 19 R1, R2
19 2
Tool feed mechanism, metal removal
rate ,work material
1 20 R1, R2
20 2
Process parameters of USM
Disadvantages. Overall review of Unit II
2 22 R1, R2
Unit – III Electrical Energy Based
Processes
21 3 EDM-Process, operating principles 1 23
T1, R1,
R2
22 3
Break down mechanism-Dielectric, fluid
Electrode material, Tool wear
1 24
T1, R1,
R2
23 3
Power generator circuits, Process
parameters, Metal removal rate
2 26
T1, R1,
R2
24 3
Flushing techniques, Wire Cut EDM-
operating principles
2 28
T1, R1,
R2
25 3
disadvantages and Recent
1 29
T1, R1,
R2

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developments in EDM Review of unit-III
Unit-IV – chemical and electro
chemical energy based processes
26 4
Introduction to Chemical machining
processes
1 30
T1, R1,
R3
27 4
Etchants-maskent, Techniques of
applying maskants, process parameter,
surface finish, Applications, advantages,
disadvantages
1 31
T1, R1,
R2
28 4
ECM -Process-principles Principles of
ECM- equipments-
1 32 T1 R1
29 4
Process parameters, surface
Roughness-Analysis of metal removal
rate -Tool material
2 34 T1, R1
30 4
ECH working principle, process
parameters ECG- advantages,
disadvantages & Applications
2 36 T1, R2
31 4
ECG working principle, process
parameters - advantages,
disadvantages & Applications
2 38
T1, R1,
R2
Unit-V Thermal Energy Based
Processes
32 5
LBM process, principle LBM process,
principles- pumping processes
2 40
T1, R1,
R2
33 5
Process characteristics & m/c rate,
Laser drilling, cutting, marking, welding,
disadvantages
1 41 T1, R2
34 5
EBM Processes, working principle,
process parameters
1 42 T1, R1
35 5
Gun construction- types of gun -vacuum
and non-vacuum technique Beam
control techniques Applications,
advantages, disadvantages
1 43 T1, R2
36 5
PAM-Introduction, construction,
Parameters affecting cutting
1 44 T1, R2
37 5
Plasma arc system ,types of torch
Advantages, disadvantages,
applications
1 45 R1 ,R2
38 All Over view of all 5 units 2 47 T1,R1R2

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ME8073- UNCONVENTIONAL MACHINING PROCESSES
QUESTION BANK WITH ANSWER
UNIT-I- INTRODUCTION
Unconventional machining Process – Need – classification – Brief overview.
PART-A
1. What is the need for unconventional machining processes? (AP/MAY 2015,
NOV/DEC 2014, MAY/JUNE 2014, NOV/DEC 2012, DEC-2005, AP/MAY2010,
MAY/JUNE 2009)
High production rate, Low cost of production, Better surface integrity, High
surface finish.
2. What are the characteristics of UCM processes? (DEC-2004, NOV-2010)
 Performance is independent of strength barrier
 Use different kinds of energy in direct form
 In general, low MRR but better quality products
 Comparatively high initial investment cost
3. Differentiate the conventional and unconventional machining processes in
terms of principles. (AP/MAY 2015, MAY-2007)
 In conventional processes, the material is removed in the form of chips by
the advancing cutting tool that plastically deforms (shearing) the material
ahead. In the case of the UCM processes, energy (Electrical, Chemical,
Thermo-Electric, and Mechanical) in its direct form is utilized for the
material removal and so there is no physical contact between the work
piece and tool.
4. What are the various types of energy sources used in non-traditional
machining techniques? Give examples for each. (DEC-2007, MAY-2011)
Pneumatic pressure- AJM
Hydraulic pressure- WJM, USM, AWJM
Corrosion- CHM, CHB, PCM
High current density in electrolytes- ECM (creating avalanche in lazing medium)
High voltage- EDM (for sparking); IBM, EBM (ionizing); LBM
PAM (for ionizing the plasma gases)
5. Classify the different types of unconventional machining processes based
on the mechanical energy. (NOV/DEC 2013,DEC-2005, MAY-2009)
 Abrasive Jet Machining (AJM)
 Water Jet Machining (WJM)
 Ultrasonic Machining (USM)
 Abrasive Water Jet Machining (AWJM)

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6. Identify the mechanism of material removal, transfer media and energy
source for EDM. (NOV-2010)
 Mechanism of material removal- Fusion of materials by arcs
 Transfer media - Electron stream
 Energy source - High voltage
7. What are the points to be considered in selection of unconventional
machining process?
 Physical parameters
 Shapes to be machined
 Process capability
 Economic consideration
8. Write the limitations of unconventional machining process. (NOV/DEC 2012,
MAY-2011)
 More expensive
 Metal removal rate is slow
 AJM, CHM, PAM and EBM are not commercially economic processes.
9. Write advantages of unconventional machining process. (MAY/JUNE 2013,
NOV/DEC 2012)
 It increase productivity
 It reduces number of rejected components
 Close tolerance is possible
 The tool material need not be harder than work piece material as in
conventional machining
 Harder and difficult to machine materials can be machined by this process.
 The machined surfaces do not have any residual stresses.
10. Name the unconventional machining processes for machining following
materials.
 Non metals like ceramics, plastics and glass – USM,AJM,EBM,LBM
 Refractories –USM,AJM,EDM,EBM
 Titanium- EDM
 Super Alloys – AJM,ECM,EDM,PAM
 Steel – ECM,CHM,EDM,PAM

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PART-B
1. Classify the modern machining processes in detail.
(APR/MAY2015, NOV/DEC 2014, MAY/JUNE 2014, NOV/DEC 2010,
APR/MAY2011, 2013,NOV/DEC 2012,AP/MAY 2010,NOV/DEC 2009)
Classification of Material removal processes:
 The non-conventional manufacturing processes are not affected by hardness,
toughness or brittleness of material and can produce any intricate shape on
any work piece material by suitable control over the various physical
parameters of the processes.
 The non-conventional manufacturing processes may be classified on the basis
of type of energy namely, mechanical, electrical, chemical, thermal or
magnetic, apply to the work piece directly and have the desired shape
transformation or material removal from the work surface by using different
scientific mechanism.
 Thus, these non-conventional processes can be classified into various groups
according to the basic requirements which are as follows:
(i) Type of energy required, namely, mechanical, electrical, chemical etc.
(ii) Basic mechanism involved in the processes, like erosion, ionic
dissolution, Vaporization etc.
(iii) Source of immediate energy required for material removal, namely,
Hydrostatic pressure, high current density, high voltage, ionized
material, etc. (iv) Medium for transfer of those energies, like high
velocity particles, electrolyte, electron, hot gases, etc.

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Classification of Unconventional Machining processes:
Detailed Classification of Non conventional manufacturing Processes:
2. Explain the need of Unconventional machining processes. (MAY/JUNE 2014,
APR/MAY2009,MAY/JUNE 2013, APR/MAY 2010)
 Conventional machining sufficed the requirement of the industries over
the decades. But new exotic work materials as well as innovative
geometric design of products and components were putting lot of
pressure on capabilities of conventional machining processes to
manufacture the components with desired tolerances economically. This

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led to the development and establishment of NTM processes in the
industry as efficient and economic alternatives to conventional ones. With
development in the NTM processes, currently there are often the first
choice and not an alternative to conventional processes for certain
technical requirements. The following examples are provided where NTM
processes are preferred over the conventional machining process:
 Intricate shaped blind hole – e.g. square hole of 15 mmx15 mm with a
depth of 30 mm
 Difficult to machine material – e.g. same example as above in Inconel, Ti-
alloys or carbides.
 Low Stress Grinding – Electrochemical Grinding is preferred as
compared to conventional grinding
 Deep hole with small hole diameter – e.g. f 1.5 mm hole with l/d = 20
 Machining of composites.
3. Compare the mechanical and electrical energy processes in terms of physical
parameters. Shape capabilities, Process capability, and Process economy.
(same ANS)
4. Explain the reasons for the development of Unconventional Machining
Process.
Discuss about the criteria recommended in selection of these processes.
(APR/MAY 2015, NOV/DEC 2013, MAY/JUNE 2013,APR/MAY2009, NOV/DEC
2012,MAY/JUNE 2009)
 A comparative analysis of the various unconventional manufacturing
processes should be made so that a guide-line may be drawn to find the
suitability of application of different processes.
 A particular manufacturing process found suitable under the given
conditions may not be equally efficient under other conditions. Therefore,
a careful selection of the process for a given manufacturing problem is
essential.
 The analysis has been made from the point of view of: (criteria)
(i) Physical parameters involved in the processes;
(ii) Capability of machining different shapes of work material;
(iii) Applicability of different processes to various types of material, e.g.
metals, alloys and non-metals;
(iv) Operational characteristics of manufacturing and
(v) Economics involved in the various processes.
Physical parameters
The physical parameters of non-conventional machining processes
have a direct impact on the metal removal as well as on the energy
consumed in different processes.
From a comparative study of the effect of metal removal rate on the power
consumed by various non-conventional machining processes shown

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 It is found that some of the processes (e.g. EBM, ECM) above the mean
power
 Consumption line consumes a greater amount of power than the
processes (e.g. EDM, PAM, and ECG) below the mean power
consumption line. Thus, the capital cost involved in the processes (EBM,
ECM etc.) lying above the mean line is high whereas for the processes
below that line (e.g., EDM, PAM, MCG) is comparatively low.
CAPABILITY TO SHAPE:
 The capability of different processes can be analyzed on the basis of
various machining operation point of view such as micro-drilling, drilling,
cavity sinking, pocketing (shallow and deep), contouring a surface,
through cutting (shallow and deep) etc. For micro-drilling operation, the

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only process which has good capability to micro drill is laser beam
machining while for drilling shapes having slenderness ratio, l
 D< 20, the process USM, ECM and EDM will be most suitable. EDM
and ECM processes have good capability to make pocketing operation
(shallow or deep).For surface contouring operation, ECM process is most
suitable but other processes except EDM have no application for
contouring operation.
APPLICABILITY TO MATERIALS:
Materials applications of the various machining methods are summarized in the
table
For the machining of electrically non-conducting materials, both ECM and EDM
are unsuitable, whereas the mechanical methods can achieve the desired results.

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MACHINING CHARACTERISTICS:
 The machining characteristics of different non-conventional processes
can be analyzed with respect to: (i) Metal removal rate (ii) Tolerance
maintained (iii) Surface finish obtained (iv) Depth of surface damage (v)
Power required for machining.
 The process capabilities of non-conventional manufacturing processes
have been Compared in table, the metal removal rates by ECM and PAM
are respectively one- fourth and 1.25times that of conventional whereas
others are only a small fractions of it.
 Power requirement of ECM and PAM is also very high when compared
with other Non-conventional machining processes. This involves higher
capital cost for those processes.
 ECM has very low tool wear rate but it has certain fairly serious problems
regarding the contamination of the electrolyte used and the corrosion of
machine parts. The surface finish and tolerance obtained by various
processes except PAM is Satisfactory.
ECONOMICS OF THE PROCESSES:
The economics of the various processes are analyzed on the basis of following
factors are given in Table (i) Capital cost (ii) Tooling cost (iii) Consumed power
cost (iv) Metal removal rate efficiency (v) Tool wear.
* indicates cost of chemicals.
 The capital cost of ECM is very high when compared with traditional
mechanical contour grinding and other non-conventional machining
processes whereas capital costs for AJM and PAM are comparatively low.

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 EDM has got higher tooling cost than other machining processes. Power
consumption is very low for PAM and LBM processes whereas it is
greater in case of ECM.
 The metal removal efficiency is very high for EBM and LBM than for other
processes. In conclusion, the suitability of application of any of the
processes is dependent upon various factors and must be considered all
or some of them before applying nonconventional processes.
5. Compare the conventional and Unconventional Machining Processes in detail.
(NOV/DEC 2014, NOV/DEC 2008, APR/MAY2011)
TRADITIONAL VS. NON-TRADITIONAL PROCESSES:
 A machining process is called non-traditional if its material removal
mechanism is basically different than those in the traditional processes,
i.e. a different form of energy (other than the excessive forces exercised
by a tool, which is in physical contact with the work piece) is applied to
remove the excess material from the work surface, or to separate the
work piece into smaller parts.
 The principal characteristics of traditional machining processes, and non-
traditional processes is presented to compare their advantages and
limitations: The cutting tool and work piece are always in physical contact,
with a relative motion against each other, which results in friction and a
significant tool wear.
 In non-traditional processes, there is no physical contact between the tool
and work piece. Although in some non-traditional processes tool wear
exists, it rarely is a significant problem;
 Material removal rate of the traditional processes is limited by the
mechanical properties of the work material. Non-traditional processes
easily deal with such difficult-to-cut materials like ceramics and ceramic
based tool materials, fiber reinforced materials, carbides, titanium-based
alloys;
 In traditional processes, the relative motion between the tool and work
piece is typically rotary or reciprocating.
 Thus, the shape of the work surfaces is limited to circular or flat shapes.
In spite of widely used CNC systems, machining of three- dimensional
surfaces is still a difficult task. Most non-traditional processes were
developing just to solve this problem.
 Machining of small cavities, slits, blind or through holes is difficult with
traditional processes, whereas it is a simple work for some non-traditional
processes; Traditional processes are well established; use relatively
simple and inexpensive machinery and readily available cutting tools.
 Non-traditional processes require expensive equipment and tooling as
well as skilled labor, which increases significantly the production cost;

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 From the above it follows that non-traditional processes generally should
be employed when there is a need to process some newly developed
difficult-to-cut materials, machining of which is accompanied by excessive
cutting forces and tool wear; there is a need for unusual and complex
shapes, which cannot easily be machined or cannot at all be machined by
traditional processes;
 The non-traditional processes are often classified according to the
principle form of energy used:
 Mechanical processes: the mechanical energy differs from the action of
the conventional cutting tool. Examples include ultrasonic machining and
jet machining; Electrochemical processes: based on electrochemical
energy to remove the material.
 Examples include electrochemical machining, and electrochemical
deburring and grinding; thermal energy processes: use thermal energy
generated by the conversion of electrical energy to shape or cut the work
piece.
 Examples include electric discharge processes, electron beam
machining, laser beam machining, and plasma arc cutting; Chemical
machining: chemicals selectively remove material from portions of the
Work piece, while other portions of the surface are mask protected.

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UNIT II- MECHANICAL ENERGY BASED PROCESSES
Abrasive Jet Machining – Water Jet Machining – Abrasive Water Jet Machining -
Ultrasonic Machining.(AJM, WJM, AWJM and USM). Working Principles –
equipment used – Process parameters – MRR- Applications.
PART-A
1. What is the principle behind abrasive jet machining? (NOV-2010, DEC-2006)
 A jet of inert gas consisting of very fine abrasive particles strikes the work
piece at high velocity (usually between 200-400 m/sec) resulting in
material removal through chipping / erosive action.
2. Name the abrasive materials that are used for the AJM. (AP/MAY 2010)
The common abrasives used for the AJM process are:
 Dolomite
 Sodium Bicarbonate
 Glass beads
 Silicon carbide
 Silicon Nitride
 Alumina
3. What are the process parameters affecting the material removal rate in AJM
process? (NOV/DEC 2013, NOV/DEC 2012)
The following factors will affect the material removal rate in AJM process.
a. Mass flow rate
b. Abrasive grain size
c. Gas pressure
d. Velocity of abrasive particles
e. Mixing ratio
f. Nozzle tip clearance.
4. What are the desirable properties of carrier gas in AJM? (MAY- 2009, 2012)
 It should be cheap
 It should be non-toxic
 It should be easily available.
 It should dry quickly
 N2, CO2, He, etc are normally used as carrier gas.
5. How does AJM differ from conventional sand blasting process?
(NOV- 2010, MAY-2011)
 AJM differ from the conventional sand blasting process in the way that the
abrasive is much finer and effective control over the process parameters and
cutting. Used mainly to cut hard and brittle materials, which are thin and
sensitive to heat.

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6. What is the operating principle of WJM? (MAY/JUNE 2013)
 If a jet of water is directed at a target in such a way that, on striking the
surface, the high velocity flow is virtually stopped, then most of the kinetic
energy of the water is converted into pressure energy. Erosion occurs when
this pressure exceeds the strength of the bond binding together the materials
making up the target.
7. Name the main elements of the WJM system. (MAY-2010)
 Hydraulic unit
 Intensifier
 Accumulator
 Filters
 Water transmission lines
 On/off valve
 Water jet nozzles
 Water jet catchers
 Fluid additives
8. List the applications of WJM process. (AP/MAY 2015, AP/MAY 2008, DEC-
2005)
 This process is very convenient for cutting relatively softer and non-metallic
materials like paper boards, plastics, wood, rubber, leather, fiber glass etc.
9. What is ultrasonic machining? (AP/MAY 2015, MAY-2007)
 USM is a mechanical material removal process in which the material is
removed by repetitive impact of abrasive particles carried in liquid medium on
to the
Work surface, by a shaped tool, vibrating at ultrasonic frequency.
10. What is magnetostriction effect?
 When a rod of ferromagnetic material such as iron or nickel is kept in a
magnetic field to its length, the rod suffers a change in its length. This
phenomenon is known as magnetostrictition effect.

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PART-B
1. (i) Explain the principle of AJM. Mention some of the specific applications. (6)
(NOV/DEC 2013, APR/MAY 2005)
PRINCIPLE OF AJM
 In Abrasive Jet Machining (AJM), abrasive particles are made to impinge
on the work material at a high velocity. The jet of abrasive particles is
carried by carrier gas or air. The high velocity stream of abrasive is
generated by converting the pressure energy of the carrier gas or air to its
kinetic energy and hence high velocity jet.
 The nozzle directs the abrasive jet in a controlled manner onto the work
material, so that the distance between the nozzle and the work piece and
the impingement angle can be set desirably. The high velocity abrasive
particles remove the material by micro-cutting action as well as brittle
fracture of the work material.
APPLICATIONS:
 Drilling holes, cutting slots, cleaning hard surfaces, deburring,
polishing,
and radiusing.
 Deburring of cross holes, slots, and threads in small precision parts
that require a burr-free finish, such as hydraulic valves, aircraft fuel
systems, and medical appliances.
 Machining intricate shapes or holes in sensitive, brittle, thin, or
difficult-to-machine materials.
(ii) Discuss in detail about the AJM process variables that influence the rate of
material removal and accuracy in the machining. (10)
PROCESS VARIABLES:
(APR/MAY 2015, NOV/DEC 2014, MAY/JUNE 2014, MAY/JUNE 2013, NOV/DEC
2012,NOV/DEC 2009, NOV/DEC 2008)
The process parameters are listed below:
 Abrasive
Material – Al2O3 / Sic / glass beads
Shape – irregular / spherical Size – 10 ~ 50 μm
Mass flow rate – 2 ~ 20 gm/min

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 Carrier gas
Composition – Air, CO2, N2
Density – Air ~ 1.3 kg/m3 Velocity – 500 ~ 700 m/s
Pressure – 2 ~ 10 bar
 Abrasive Jet
Velocity – 100 ~ 300 m/s
Mixing ratio – mass flow ratio of abrasive to gas
Stand-off distance – 0.5 ~ 5 mm
Impingement Angle – 600 ~ 900
 Nozzle
Material – WC / sapphire
Diameter – (Internal) 0.2 ~ 0.8 mm
Life – 10 ~ 300 hours
Effect of process parameters MRR
 MRR, machining accuracy, surface roughness and nozzle wear are influenced
by
 Size and distance of the nozzle.
 Composition, strength, size, and shape of abrasives
 Flow rate
 Composition, pressure, and velocity of the carrier gas.
ABRASIVE:
 Mainly two types of abrasives are used (1) Aluminum oxide and (2) Silicon
carbide. (Grains with a diameter 10-50 microns are readily available)
 For good wear action on the surfaces the abrasive grains should have
sharp edges.
 A reuse of the abrasive powder is normally not recommended because of
a decrease of cutting capacity and clogging of the nozzle orifices due to
contamination.
 The mass flow rate of the abrasive particles depends on the pressure and
the flow rate of the gas.
 There is an optimum mixing ratio (mass fraction of the abrasive) for which
the metal removal rate is the highest.
 When the mass flow rate of the abrasive increases the material removal
rate also increases.

22
GAS:
 The AJM unit normally operates at a pressure of 0.2-1.0 N/mm2
.
 The composition of gas and a high velocity has a significant impact on the
MRR even if the mixing ratio is not changed.
NOZZLE:
 The nozzle is one of the most vital elements controlling the process
characteristics.
 The nozzle material should be hard to avoid any significant wear due to
the flowing abrasive. [Normally WC (avg. life: 12-30 hrs.) or Sapphire
(Appr. = 300 hrs.) are used]
 For a normal operation the cross-sectional area of the orifice can be either
circular or rectangular and between 0.05- 0.2mm2
.
NOZZLE TO TIP DISTANCE: (Stand off distance)
 The nozzle tip distance (NTD) or the stand off distance is a critical
parameter in AJM.
 The NTD not only affects the MRR from the work surface but also the
shape and size of the cavity produced.
 As shown in the figure below, the velocity of the abrasive particles
impinging on the work surface increases due to their acceleration after
they leave the nozzle. This increases the MRR.
 With a further increase in the NTD, the velocity reduces due to the drag of
the atmosphere which initially checks the increase in MRR and then
decreases it.
2. (i) Explain the method of AJM with help of schematic diagram.
(10)
(MAY/JUNE 2013, APR/MAY 2012, APR/MAY 2010, APR/MAY 2008, NOV/DEC
2008)
 A stream of abrasive grains (Al2O3 or SiC) is carried by high pressure gas
or air (compressed).Impinges on the work surface at very high velocity
through a nozzle of 0.3 to 0.5 mm diameter. Material removal – by
mechanical abrasion action of the high velocity abrasive particles.
 Best suited for hole drilling in super hard materials. Typically used to cut,
clean, peen, deburr, deflash and etch glass, ceramics and other hard
materials.

23
 In the machining system shown in Fig., a gas (nitrogen, CO2, or air) is
supplied under a pressure of 2 to 8 kg/cm2. Oxygen should never be used
because it causes a violent chemical reaction with workpiece chips or
abrasives. After filtration and regulation, the gas is passed through a
mixing chamber that contains abrasive particles and vibrates at 50 Hz.
 From the mixing chamber, the gas, along with the entrained abrasive
particles (10–40 μm), passes through a 0.45-mm-diameter tungsten
carbide nozzle at a speed of 150 to 300 m/s. Aluminum oxide (Al2O3) and
silicon carbide powders are used for heavy cleaning, cutting, and
deburring.
 Magnesium carbonate is recommended for use in light cleaning and
etching, while sodium bicarbonate is used for fine cleaning and the cutting
of soft materials. Commercial-grade powders are not suitable because
their sizes are not well classified.
 They may contain silica dust, which can be a health hazard. It is not
practical to reuse the abrasive powder because contaminations and worn
grit will cause a decline of the machining rate.
 The abrasive powder feed rate is controlled by the amplitude of vibrations
in the mixing chamber. The nozzle standoff distance is 0.81 mm. The
relative motion between the work piece and the nozzle is manually or
automatically controlled using cam drives, pantographs, tracer
mechanisms, or using computer control according to the cut geometry
required.
 Masks of copper, glass, or rubber may be used to concentrate the jet
stream of abrasive particles to a confined location on the work piece.
Intricate and precise shapes can be produced by using masks with
corresponding contours. Dust removal equipment is incorporated to
protect the environment.
(ii) Mention the advantages and limitations of AJM. (6)
Advantages: NOV/DEC 3013
 Because AJM is a cool machining process, it is best suited for machining
brittle and heat-sensitive materials like glass, quartz, sapphire, and ceramics.
 The process is used for machining superalloys and refractory materials.
 It is not reactive with any work piece material.
 No tool changes are required.
 Intricate parts of sharp corners can be machined.
 The machined materials do not experience hardening.
 No initial hole is required for starting the operation as required by wire
EDM.
 Material utilization is high.
 It can machine thin materials.
Limitations: NOV/DEC 3013
 The removal rate is slow.
 Stray cutting can‟t be avoided (low accuracy of +0.1 mm).
 The tapering effect may occur especially when drilling in metals.
 The abrasive may get impeded in the work surface.
 Suitable dust-collecting systems should be provided.
 Soft materials can‟t be machined by the process.
 Silica dust may be a health hazard.
 Ordinary shop air should be filtered to remove moisture and oil

24
3. Explain the working principle and process parameters in WJM processes.
List the applications, advantages and limitations of WJM (16)
(NOV/DEC 2014, MAY/JUNE 2013, NOV/DEC 2010, APR/MAY 2012,NOV/DEC
2012, NOV/DEC 2009, APR/MAY 2008,NOV/DEC 2008 )
Water Jet Cutting:
 Water jet cutting (WJC), also known as water jet machining or
hydrodynamic machining, uses a high-velocity fluid jet impinging on
the work piece to perform a slitting operation.
 Water is ejected from a nozzle orifice at high pressure (up to 60,000
psi). The jet is typically 0.076 to 0.5 mm in diameter and exits the
orifice at velocities up to 900 m/sec.
 Key process parameters include water pressure, orifice diameter,
water flow rate, and working distance (distance between the work
piece and the nozzle). Nozzle materials include synthetic sapphire due
to its machinability and resistance to wear. Tool life on the order of
several hundred hours is typical.
 Mechanisms for tool failure include chipping from contaminants or
constriction due to mineral deposits. This emphasizes the need for
high levels of filtration prior to pressure intensification.
Jet nozzle:
 The standoff distance, shown in Fig. 2.20, is the gap between the jet
nozzle (0.1–0.3 mm diameter) and the work piece (2.5–6
mm).However for materials used in printed circuit boards, it may be
increased to 13 to 19 mm.
 For a nozzle of 0.12-mm diameter and cutting rate of 1.1 millimeters
per second (mm/s), McGeough (1988) reported the decrease of the
depth of cut at a larger standoff distance. When cutting fiber-reinforced
plastics, reports showed that the increase in machining rate and use of
the small nozzle diameter increased the width of the damaged layer.
Jet fluid:
 Typical pressures used are 1500 to 4000 MPa to provide 8 to 80 kW of
power.
 For a given nozzle diameter, increase in pressure allows more power to be
used in the machining process, which in turn increases the depth of the
cut.
 Jet velocities range between 540 to 1400 m/s.

25
 The quality of cutting improves at higher pressures by widening the
diameter of the jet and by lowering the traverse speed.
 Under such conditions, materials of greater thicknesses and densities can
be cut.
 Moreover, the larger the pump pressure, the greater will be the depth of
the cut.
 The fluid used must possess low viscosity to minimize the energy losses
and be noncorrosive, nontoxic, common, and inexpensive.
 Water is commonly used for cutting alloy steels.
Work piece:
 Brittle materials will fracture, while ductile one will cut well.
 Material thicknesses range from 0.8 to 25 mm or more.
 Table below shows the cutting rates for different material thicknesses
APPLICATIONS:
 Water jet cutting is mostly used to cut lower strength materials such as
wood, plastics and aluminium.
 When abrasives are added, (abrasive water jet cutting) stronger materials
such as steel and tool steel can be cut.
ADVANTAGES OF WATER JET CUTTING:
 There is no heat generated in water jet cutting; which is especially useful
for cutting tool steel and other metals where excessive heat may change
the properties of the material.
 Unlike machining or grinding, water jet cutting does not produce any dust
or particles that are harmful if inhaled.
DISADVANTAGES OF WATER JET CUTTING:
 One of the main disadvantages of water jet cutting is that a limited number
of materials can be cut economically.
 Thick parts cannot be cut by this process economically and accurately
 Taper is also a problem with water jet cutting in very thick materials. Taper
is when the jet exits the part at different angle than it enters the part, and
cause dimensional inaccuracy.

26
4. Explain the USM machine setup, working principle, advantages and
limitations. (16)
(NOV/DEC 2014, NOV/DEC 3013, MAY/JUNE 2013, NOV/DEC 2004, APR/MAY
2013, MAY/JUNE 2013)
 Ultrasonic machining is a non-traditional machining process. USM is grouped
under the mechanical group NTM processes. In ultrasonic machining, a tool
of desired shape vibrates at an ultrasonic frequency (19 ~ 25 kHz) with an
amplitude of around 15 – 50 μm over the work piece. Generally the tool is
pressed downward with a feed force, F.
 Between the tool and work piece, the machining zone is flooded with hard
abrasive particles generally in the form of water based slurry. As the tool
vibrates over the work piece, the abrasive particles act as the indenters and
indent both the work material and the tool.
 The abrasive particles, as they indent, the work material, would remove the
same, particularly if the work material is brittle, due to crack initiation,
propagation and brittle fracture of the material. Hence, USM is mainly used
for machining brittle materials {which are poor conductors of electricity and
thus cannot be processed by Electrochemical and Electro-discharge
machining (ECM and ED)}.
 Ultrasonic machining (USM), sometimes called ultrasonic impact grinding,
employs ultrasonically vibrating tool to impel the abrasives in slurry at high
velocity against work piece. The tool is fed into the part as it vibrates along an
axis parallel to the tool feed at amplitude on the order of several thousandths
of an inch and a frequency of 20 kHz.
 As the tool is fed into the work piece, a negative of the tool is machined into
the work piece. The cutting action is performed by the abrasives in the slurry
which is continuously flooded under the tool.
 The slurry is loaded up to 60% by weight with abrasive particles. Lighter
abrasive loadings are used to facilitate the flow of the slurry for deep drilling
(to 5mm deep). Boron carbide, aluminum oxide, and silicon carbide are the
most common used abrasives in grit sizes ranging from 400 to 2000.
 The amplitude of the vibration should be set approximately to the size of the
grit. The process can use shaped tools cut virtually any material but is most
effective on materials with hardness greater than Rc 40 including brittle and
non-conductive materials such as glass.

27
 Ultrasonic Machining is a non-traditional process, in which abrasives
contained in a slurry are driven against the work by a tool oscillating at low
amplitude (25-100 μm) and high frequency (15-30 KHz):brittle fracture
caused by impact of abrasive grains due to the tool vibration; cavitation
induced erosion; chemical erosion caused by slurry.
 The ultrasonic machining process can be used to cut through and blind holes
of round or irregular cross-sections. The process is best suited to poorly
conducting, hard and brittle materials like glass, ceramics, carbides, and
semiconductors.
 There is a little production of heat and stress in the process, but work may
chip at exit side of the hole. Sometimes glass is used on the backside for
brittle materials. The critical parameters to control the process are the tool
frequency, amplitude and material, abrasive grit size and material, feed force,
slurry concentration and viscosity. Limitations of the ultrasonic machining
include very low material removal rate, extensive tool wear, small depth of
holes and cavities.
 The acoustic head is the most complicated part of the machine. It must
provide a static constant force, as well as the high frequency vibration. Tools
are produced of tough but ductile metals such as soft steel of stainless steel.
 Aluminum and brass tools wear near 5 to 10 times faster. Abrasive slurry
consists of a mixture of liquid (water is the most common but oils or glycerol
are also used) and 20% to 60% of abrasives with typical grit sizes of 100 to
800. The common types of abrasive materials are boron carbide, silicon
carbide, diamond, and corundum (Al2O3).

28
ADVANTAGE OF USM:
 USM process is a non-thermal, non-chemical, creates no changes in the
microstructures, chemical or physical properties of the work piece and offers
virtually stress free machined surfaces.
 Any materials can be machined regardless of their electrical conductivity
 Especially suitable for machining of brittle materials
 Machined parts by USM possess better surface finish and higher structural
integrity.
 USM does not produce thermal, electrical and chemical abnormal surface
DISADVANTAGES OF USM:
 USM has higher power consumption and lower material-removal rates than
traditional fabrication processes.
 Tool wears fast in USM.
 Machining area and depth is restraint in USM.
5. Discuss the influence process parameters and applications of USM (16)
PROCESS PARAMETERS:
(NOV/DEC 2014, APR/MAY 2013, NOV/DEC 2012, NOV/DEC 2004,)
1. Tool Oscillation or Vibration – Amplitude & Frequency
 Amplitude of the tool oscillation has the greatest effect of all the process
variables.
 MRR increases with a rise in the tool vibration amplitude.
 Vibration amplitude determines the velocity of the abrasive particles at the
interface between the tool and workpiece.
 Under such circumstances the kinetic energy rises, at larger amplitudes,
which enhances the mechanical chipping action and consequently increases
the MRR.
 A greater vibration amplitude may lead to the occurrence of splashing, which
causes a reduction of the number of active abrasive grains and results in a
decrease in the MRR.
2. Abrasive Grains
 Both the grain size and the vibration amplitude have a similar effect on the
removal rate.
 According to McGeough (1988), MRR rises at greater grain sizes until the
size reaches the vibration amplitude, at which stage, the MRR decreases.
 When the grain size is large compared to the vibration amplitude, there is a
difficulty of abrasive renewal.
 Because of its higher hardness, B4C achieves higher removal rates than
silicon carbide (SiC) when machining glass.
 The MRR obtained with silicon carbide is about 15 % lower when machining
glass, 33 % lower for tool steel, and about 35 % lower for sintered carbide.
3. Work piece Impact Hardness
 MRR is affected by the ratio of tool hardness to work piece hardness.
 In this regard, the higher the ratio, the lower will be MRR.
 For this reason soft and tough materials are recommended for USM tools.
4. Tool Shape
 Increase in tool area - decreases the machining rate; due to inadequate
distribution of abrasive slurry over the entire area.

29
 McGeough (1988) reported that, for the same machining area, a narrow
rectangular shape yields a higher machining rate than a square shape.
 Rise in static pressure - enhances MRR up to a limiting condition, beyond
which no further increase occurs.
 Reason - disturbance in the tool oscillation at higher forces where lateral
vibrations are expected.
 According to Kaczmarek (1976), at pressures lower than the optimum, the
force pressing the grains into the material is too small and the volume
removed by a particular grain diminishes.
 Measurements also showed a decrease in MRR with an increase in the hole
depth.
 Reason - deeper the tool reaches, the more difficult and slower is the
exchange of abrasives from underneath the tool.
5. Accuracy (oversize, conicity, out of roundness) - affected by
 Side wear of the tool
 Abrasive wear
 Inaccurate feed of the tool holder
 Form error of the tool
 Unsteady and uneven supply of abrasive slurry
Other parameters:
 Amplitude of vibration (ao) – 15 – 50 μm
 Frequency of vibration (f) – 19 – 25 kHz
 Feed force (F) – related to tool dimensions
 Feed pressure (p)
 Abrasive size – 15 μm – 150 μm
 Abrasive material – Al2O3 – Sic- B4C – Boron silicarbide – Diamond
 Flow strength of work material
 Flow strength of the tool material
 Contact area of the tool – A
 Volume concentration of abrasive in water slurry – C

30
EFFECT OF MACHINING PARAMETERS ON MRR:
APPLICATIONS: MAY/JUNE 2013
 Used for machining hard and brittle metallic alloys, semiconductors, glass,
ceramics, carbides etc.
 Used for machining round, square, irregular shaped holes and surface
impressions.
 Machining, wire drawing, punching or small blanking dies. Machining of
shallow slots and holes in brittle materials, e.g. ceramics, glass, diamond,
tool steel.

31
UNIT III- ELECTRICAL ENERGY BASED PROCESSES
Electric Discharge Machining (EDM)- working Principle-equipments-Process
Parameters-Surface Finish and MRR- electrode / Tool – Power and control Circuits-
Tool Wear – Dielectric – Flushing – Wire cut EDM – Applications.
PART-A
1. Define electrical discharge machining? (AP/MAY 2015, NOV-2010, MAY-2011)
EDM is the controlled erosion of electrically conductive materials by the initiation
of rapid and repetitive spark discharge between the electrode tool to the cathode and
work to anode separated by a small gap kept in the path of dielectric medium. This
process also called spark erosion.
2. What are functions of dielectric fluid used in EDM? (MAY/JUNE 2014,MAY-
2011, DEC-2004)
It acts as an insulating medium
It cools the spark region and helps in keeping the tool and work piece cool.
It maintains a constant resistance across the gap.
It carries away the eroded metal particles.
3. What the dielectric fluids commonly used in EDM? (MAY-2010)
Petroleum based hydrocarbon fluids.
Paraffin, white sprite, transformer oil.
Kerosine, mineral oil.
Ethylene glycol and water miscible compounds.
4. Name some of the tool material used in EDM? (MAY-2009)
Copper, brass, alloys of Zinc &tin.
Hardened plain carbon steel
copper tungsten, silver tungsten, tungsten
Copper graphite and graphite.
5. What is the process parameter efficiency the MRR? (MAY-2011)
Energy discharge
Capacitance.
Size of work piece.
M/c tool design
6. Write the formula for finding the energy discharge in EDM? (MAY-2009)
W = (1/2) X EIT, W-discharge energy
I-Current
T-time
E-voltage
7. Define W/T (Tool wear) ratio?
It is the ratio of volume of work removed to the volume of tool removed.
8. Define over cut? (NOV-2010)
It is the discharge by which the machined hole in the work piece exceeds the
electrode size and is determined by both the initiating voltage and the discharge
energy.
9. Why the servo controlled system is needed in EDM? (NOV/DEC 2014, MAY-
2011)
EDM requires that a constant arc gap be maintained between the electrode and
the work piece to obtain maximum machining efficiency. Therefore EDM tool in
corporate some form of servo control.
10. List the applications of wire-cut EDM. (MAY-2013)
Production of gears, tools, dies, rotors, turbine blades and cams for small to
medium size production.

32
PART-B
1. Explain the construction and principle of electrical discharge machining
with neat sketch. (16)
(MAY/JUNE 2014, NOV/DEC 2009, MAY/JUNE 2009, APR/MAY 2008,
NOV/DEC 2008, APR/MAY 2005)
Electro Discharge Machining (EDM) is an electro-thermal non-traditional
machining process, where electrical energy is used to generate electrical spark and
material removal mainly occurs due to thermal energy of the spark.
Introduction:
 It is also referred to as spark machining, spark eroding, burning, die sinking or
wire erosion
 Its a manufacturing process whereby a desired shape is obtained using electrical
discharges (sparks).
 Material is removed from the workpiece by a series of rapidly recurring current
discharges between two electrodes, separated by a dielectric liquid and subject
to an electric voltage.
 One of the electrodes – „tool-electrode‟ or „tool‟ or „electrode‟.
 Other electrode - workpiece-electrode or „workpiece‟.
 As distance between the two electrodes is reduced, the current intensity
becomes greater than the strength of the dielectric (at least in some points)
causing it to break.
EDM components:
The main components in EDM:
 Electric power supply
 Dielectric medium
 Work piece & tool
 Servo control unit.

33
 The work piece and tool are electrically connected to a DC power supply. The
current density in the discharge of the channel is of the order of 10000 A/cm2
and power density is nearly 500 MW/cm2
.
 A gap, known as SPARK GAP in the range, from 0.005 mm to 0.05 mm is
maintained between the work piece and the tool. Dielectric slurry is forced
through this gap at a pressure of 2 kgf/cm2
or lesser.
Working Principle:
 It is a process of metal removal based on the principle of material removal by an
interrupted electric spark discharge between the electrode tool and the work
piece. In EDM, a potential difference is applied between the tool and workpiece.
 Essential - Both tool and work material are to be conductors. The tool and work
material are immersed in a dielectric medium. Generally kerosene or deionised
water is used as the dielectric medium.
 A gap is maintained between the tool and the workpiece. Depending upon the
applied potential difference (50 to 450 V) and the gap between the tool and
workpiece, an electric field would be established.
 Generally the tool is connected to the negative terminal (cathode) of the
generator and the workpiece is connected to positive terminal (anode).As the
electric field is established between the tool and the job, the free electrons on the
tool are subjected to electrostatic forces.
 If the bonding energy of the electrons is less, electrons would be emitted from
the tool. Such emission of electrons are called or termed as „cold emission‟. The
“cold emitted” electrons are then accelerated towards the job through the
dielectric medium. As they gain velocity and energy, and start moving towards

34
the job, there would be collisions between the electrons and dielectric molecules.
Such collision may result in ionization of the dielectric molecule.
 Ionization depends on the ionization energy of the dielectric molecule and the
energy of the electron. As the electrons get accelerated, more positive ions and
electrons would get generated due to collisions. This cyclic process would
increase the concentration of electrons and ions in the dielectric medium
between the tool and the job at the spark gap.
 The concentration would be so high that the matter existing in that channel could
be characterised as “plasma”. The electrical resistance of such plasma channel
would be very less. Thus all of a sudden, a large number of electrons will flow
from tool to job and ions from job to tool. This is called avalanche motion of
electrons. Such movement of electrons and ions can be visually seen as a spark.
Thus the electrical energy is dissipated as the thermal energy of the spark
 The high speed electrons then impinge on the job and ions on the tool. The
kinetic energy of the electrons and ions on impact with the surface of the job and
tool respectively would be converted into thermal energy or heat flux. Such
intense localized heat flux leads to extreme instantaneous confined rise in
temperature which would be in excess of 10,000o
C.Such localized extreme rise
in temperature leads to material removal.
 Material removal occurs due to instant vaporization of the material as well as due
to melting. The molten metal is not removed completely but only partially.
Additional Diagram:

35
2. Explain the classification and characteristics of various spark erosion
generators.
(16)
(NOV/DEC 2014, NOV/DEC 2013, MAY/JUNE 2013, NOV/DEC 2012,
APR/MAY 2010, NOV/DEC 2009, APR/MAY 2008,)
EDM – Power & Control Circuits:
 Commercially available: RC circuits based, Rotary impulse generator, transistor
controlled pulses.
Types of circuits used in EDM can be classified into three groups:
1) Resistance – Capacitance (RC) relaxation circuit with a constant dc source.
2) Rotary Impulse Generator
3) Controlled Pulse Circuit
 Two broad categories of generators (power supplies) are in use on EDM. In the
first category, the main parameters to choose from at setup time are the
resistance(s) of the resistor(s) and the capacitance(s) of the capacitor(s). In an
ideal condition, these quantities would affect the maximum current delivered in a
discharge.
 Current delivery in a discharge is associated with the charge accumulated on the
capacitors at a certain moment. Little control is expected over the time of
discharge, which is likely to depend on the actual spark-gap conditions.
 Advantage: RC circuit generator can allow the use of short discharge time more
easily than the pulse-controlled generator.
 Also, the open circuit voltage (i.e. voltage between electrodes when dielectric is
not broken) can be identified as steady state voltage of the RC circuit.In
generators based on transistor control, the user is usually able to deliver a train
of voltage pulses to the electrodes. Each pulse can be controlled in shape, for
instance, quasi-rectangular.
 In particular, the time between two consecutive pulses and the duration of each
pulse can be set.The amplitude of each pulse constitutes the open circuit
voltage. Thus, maximum duration of discharge is equal to duration of a voltage
pulse.
 Maximum current during a discharge that the generator delivers can also be
controlled. Details of generators and control systems on EDMs are not always
easily available to their user. This is a barrier to describing the technological
parameters of EDM process. Moreover, the parameters affecting the phenomena
occurring between tool and electrode are also related to the motion controller of
the electrodes.

36
 A framework to define and measure the electrical parameters during an EDM
operation directly on inter-electrode volume with an oscilloscope external to the
machine has been recently proposed by Ferri et al.This would enable the user to
estimate directly the electrical parameter that affect their operations without
relying upon machine manufacturer's claims.
 When machining different materials in the same setup conditions, the actual
electrical parameters are significantly different.When using RC generators, the
voltage pulses, shown in Fig. are responsible for material removal.A series of
voltage pulses (Fig.) of magnitude about 20 to 120 V and frequency on the order
of 5 kHz is applied between the two electrodes.

37

38
 Rotary Impulse Generator: MRR is not high in case of RC relaxation circuit. To
increase MRR impulse generator is used.
 The capacitor C is charged through the diode during the first half of the cycle and
during the following half the sum of the voltages generated by the generator and
the charged capacitor is applied to the work – tool gap.
 The operating frequency is the sine wave frequency that depends on motor
speed. Though the MRR is higher surface finish is not good.
3. Explain the Process parameters, characteristics, advantages, limitations
and applications of the EDM process.
(NOV/DEC 2013, MAY/JUNE 2013, NOV/DEC 2012, NOV/DEC 2008,APR/MAY
2005)
The process parameters - mainly related to the waveform characteristics
EDM is mainly used to machine difficult-to-machine materials and high strength
temperature resistant alloys. EDM can be used to machine difficult geometries in
small batches or even on job-shop basis. Work material to be machined by EDM
has to be electrically conductive.
The waveform is characterized by the
 The open circuit voltage - Vo
 The working voltage - Vw
 The maximum current – Io
 The pulse on time – the duration for which the voltage pulse is applied – ton
 The pulse off time – toff
 The gap between the work piece and the tool – spark gap – δ
 The polarity – straight polarity – tool (-ve)
 The dielectric medium
 External flushing through the spark gap.
CHARACTERISTICS OF EDM :
 The process can be used to machine any work material if it is electrically
conductive
 Material removal depends on mainly thermal properties of the work
material rather than its strength, hardness etc
 In EDM there is a physical tool and geometry of the tool is the positive
impression of the hole or geometric feature machined
 The tool has to be electrically conductive as well. The tool wear once
again depends on the thermal properties of the tool material

39
 Though the local temperature rise is rather high, still due to very small
pulse on time, there is not enough time for the heat to diffuse and thus
almost no increase in bulk temperature takes place. Thus the heat
affected zone is limited to 2 – 4 μm of the spark crater
 However rapid heating and cooling and local high temperature leads to
surface hardening which may be desirable in some applications
 Though there is a possibility of taper cut and overcut in EDM, they can be
controlled and compensated.
Advantages of EDM:
1. The process can be applied to all conducting metals and alloys irrespective of
their melting points, hardness,
toughness or brittleness.
2. Any complicated shape that can be made on the tool can be reproduced on the
work piece.
3. Machining time is less compared to conventional machining.
4. No mechanical stress is present in the process. Physical contact between the tool
and work piece is eliminated.
Fragile and slender work pieces can be machined without distortion.
5. Hard and corrosion resistant surfaces essentially needed for die making can be
developed.
6. Cratering type of surface finish automatically creates accommodation for
lubricants causing the die life to improve.
Disadvantages:
1. Profile machining of complicated contours is not possible at required tolerances.
2. Machining time is slow
3. Machining heats the work piece and hence causes changes in surface and
metallurgical properties.
4. Excessive tool wear.
5. High specific power consumption.
Typical EDM applications:
 Fine cutting with thread shaped electrode.
 Drilling of micro holes.
 Thread cutting.
 Helical Profile Milling.
 Rotary Forming.
 Curved hole drilling.
4. Explain the flushing techniques in detail on EDM process.
(MAY/JUNE 2013, APR/MAY 2010, NOV/DEC 2008, 2010)
 One of the important factors in a successful EDM operation is the removal
of debris (chips) from the working gap.
 Flushing these particles out of the working gap is very important, to
prevent them from forming bridges that cause short circuits.

40
 EDMs have a built-in power adaptive control system that increases the
pulse spacing as soon as this happens and reduces or shuts off the
power supply.
 Flushing – process of introducing clean filtered dielectric fluid into spark
gap.
If flushing is applied incorrectly, it can result in erratic cutting and poor
machining conditions.
 Flushing of dielectric plays a major role in the maintenance of stable
machining and the achievement of close tolerance and high surface
quality.
 Inadequate flushing can result in arcing, decreased electrode life, and
increased production time.
 Four methods:
1. Normal flow 2. Reverse flow
3. Jet flushing 4. Immersion flushing
 Normal flow (Majority)
 Dielectric is introduced, under pressure, through one or more passages in
the tool and is forced to flow through the gap between tool and work.
 Flushing holes are generally placed in areas where the cuts are deepest.
 Normal flow is sometimes undesirable because it produces a tapered
opening in the workpiece.
 Reverse flow
 Particularly useful in machining deep cavity dies, where the taper
produced using the normal flow mode can be reduced.
 The gap is submerged in filtered dielectric, and instead of pressure being
applied at the source a vacuum is used.
 With clean fluid flowing between the workpiece and the tool, there is no
side sparking and, therefore, no taper is produced.
 Jet flushing
 In many instances, the desired machining can be achieved by using a
spray or jet of fluid directed against the machining gap.
 Machining time is always longer with jet flushing than with the normal and
reverse flow modes.

41
 Immersion flushing
 For many shallow cuts or perforations of thin sections, simple immersion
of the discharge gap is sufficient.
 Cooling and debris removal can be enhanced during immersion cutting by
providing relative motion between the tool and workpiece.
 Vibration or cycle interruption comprises periodic reciprocation of the tool
relative to the workpiece to effect a pumping action of the dielectric.
 Synchronized, pulsed flushing is also available on some machines.
 With this method, flushing occurs only during the non-machining time as
the electrode is retracted slightly to enlarge the gap.
 Increased electrode life has been reported with this system.
 Innovative techniques such as ultrasonic vibrations coupled with
mechanical pulse EDM, jet flushing with sweeping nozzles, and electrode
pulsing are investigated by Masuzawa (1990).
 For proper flushing conditions, Metals Handbook (1989) recommends:
 Flushing through the tool is more preferred than side flushing.
 Many small flushing holes are better than a few large ones.
 Steady dielectric flow on the entire workpiece-electrode interface is
desirable.
 Dead spots created by pressure flushing, from opposite sides of the
workpiece, should be avoided.
 A vent hole should be provided for any upwardly concave part of the tool-
electrode to prevent accumulation of explosive gases.
 A flush box is useful if there is a hole in the cavity.
5. Describe the wire cut EDM equipment, its working and applications.
(APR/MAY 2015, NOV/DEC 2014, NOV/DEC 2013, NOV/DEC 2012, APR/MAY
2010, NOV/DEC 2009, MAY/JUNE 2009, NOV/DEC 2008)
 The Wire Electric Discharge Machining (WEDM) is a variation of
EDM and is commonly known as wire-cut EDM or wire cutting. In
this process, a thin metallic wireisfed on-to the work piece, which is
submerged in a tank of dielectric fluid such as deionized water.
This process can also cut plates as thick as 300mm and is used for
making punches, tools and dies from hard metals that are difficult
to machine with other methods.
 The wire, which is constantly fed from a spool, is held between
upper and lower diamond guides. The guides are usually CNC-
controlled and move in the x–y plane.
 On most machines, the upper guide can move independently in the
z–u–v axis, giving it a flexibility to cut tapered and transitioning
shapes (example: square at the bottom and circle on the top). The
upper guide can control axis movements in x–y–u–v–i–j–k–l–.This
helps in programming the wire-cut EDM, for cutting very intricate
and delicate shapes.
 In the wire-cut EDM process, water is commonly used as the
dielectric fluid. Filters and de-ionizing units are used for controlling
the resistivity and other electrical properties. Wires made of brass

42
are generally preferred. The water helps in flushing away the
debris from the cutting zone. The flushing also helps to determine
the feed rates to be given for different thickness of the materials.
WIRE EDM:
 Wire EDM, involves the use of a continuously moving conductive wire as
the tool electrode. The tensioned wire of copper, brass, tungsten, or
molybdenum is used only once, travelling from a take-off spool to a take-
up spool while being "guided" to produce a straight narrow kerf in plates
up to 75 mm thick.
 The wire diameter ranges from 0.05 to 0.25 mm with positioning accuracy
up to ± 0.005 mm in machines with NC. The dielectric is usually deionized
water because of its low viscosity.
 This process is widely used for the manufacture of punches, dies, and
stripper plates, with modern machines capable of routinely cutting die
relief, intricate openings, tight radius contours, and corners.
Applications of Wire-Cut EDM
 Wire EDM is used for cutting aluminium, brass, copper, carbides,
graphite, steels and titanium.
 The wire material varies with the application requirements. Example: for
quicker cutting action, zinc-coated brass wires are used while for more
accurate applications, molybdenum wires are used.
The process is used in the following areas:
 Aerospace, Medical, Electronics and Semiconductor applications
 Tool & Die making industries.
 For cutting the hard Extrusion Dies
 In making Fixtures, Gauges & Cams
 Cutting of Gears, Strippers, Punches and Dies
 Manufacturing hard Electrodes.
 Manufacturing micro-tooling for Micro-EDM, Micro-USM and such other
micromachining.

43
UNIT IV- CHEMICAL AND ELECTRO-CHEMICAL ENERGY BASED
PROCESSES
Chemical machining and Electro-Chemical machining (CHM and ECM)-Etchants
– Maskant - techniques of applying maskants - Process Parameters – Surface finish
and MRR-Applications. Principles of ECM- equipments-Surface Roughness and
MRR Electrical circuit-Process Parameters-ECG and ECH - Applications.
PART-A
1. What is the principle of Chemical Machining (CHM)?
 Chemical attacks metals and etch them by removing small amounts of
material from the surface using reagents or etchants.
2. What is the purpose of etchant used in CHM? Give some examples. (MAY-
2011)
 Purpose: to dissolve a metal by turning it into a metallic salt, this then goes
into solution. Many chemical are available as etchants: FeCl3, Chromic acid,
FeNO3, HF, HNO3.
3. What is the purpose of Maskant and how is it classified? (APR/MAY 2015,
MAY/JUNE 2013)
 Maskants (chemically resistant coatings) are used to cover the surfaces
which are not to be machined – does not allow the etchant to react reach and
react with work piece to dissolve it.
Butyl rubber
Neoprene rubber
Polymers
Polyethylene
3. Please identify the principle of ECM. How does it differ from electroplating?
(APR/MAY 2010, MAY/JUNE 2009, NOV/DEC 2008)
 Principle of ECM - electrolysis. When a D.C potential is applied across two
electrodes separated by a small gap and an electrolyte is pumped through
the small gap, the constituents of the anode work piece material goes into the
solution and not plate on the cathode tool.
 Electroplating is the reverse of ECM where the cathode is plated by the
depleted metal from the anode.
4. What are the various process characteristics of the ECM? (NOV-2010)
 Material Removal Rate – the MRRs with ECM are sufficiently large and
comparable with that of the conventional methods. MRR of 16m3
/min for
10,000 A is generally obtained in ECM
 Surface finish – under certain conditions, ECM can produce surface finishes
of the order of 0.4μm
 Accuracy – under ideal conditions and with properly designed tooling, ECM is
capable of holding tolerance of the order of 0.02mm and less.

44
5. What are the various tool materials that can be used effectively with ECM?
(MAY-2011, 2005)
 Generally aluminium, copper, brass, titanium, cupro-nickel and stainless
steel are used as tool materials.
6. What are the various process parameters of ECM? (MAY-2005, 09)
 Feed rate, current density, voltage, electrolyte concentration
 Electrolyte temperature
 Velocity and flow of electrolyte.
7. What are the different types ECM operations? (MAY-2007)
 Electro Chemical Milling (ECM)
 Electro Chemical Grinding (ECG)
 Electro Chemical Honing (ECH)
 Electro Chemical Deburing (ECD)
 Electro chemical turning (ECT)
8. What is ECG? Identify its applications. (NOV/DEC 2014, MAY-2011, NOV-/DEC
2010, NOV/DEC 2009)
 ECG is a process that combines the ECM with the mechanical grinding
operation to remove material. It uses a grinding wheel with an electrically
conductive abrasive bonding agent.
Applications:
 Single largest use for ECG is in the manufacturing and remanufacturing of
turbine blades and vanes for aircraft turbine engines
 Grinding of tungsten carbide tool inserts
 Re-profiling worn locomotive traction motor gears
 Burr-free sharpening of hypodermic needles
 Machining of fragile or very hard and tough material – honey comb, thin
walled tubes and skins High MRR‟s when grinding hard, tough, stringy, and
work-hardenable or heat sensitive materials.
9. What is ECH? Identify its applications. (APR/MAY 2015, APR/MAY 2010, MAY
2010)
 ECH is a process in which the metal removal capabilities of ECM are
combined with the accuracy capabilities of honing. The process consists of a
rotating and reciprocating tool inside a cylindrical component.
 Applications: the process is easily adaptable to cylindrical parts for truing
the inside surfaces.
10. What are the functions served by the electrolyte in the ECM process?
(NOV/DEC 2014, MAY/JUNE 2014, NOV/DEC 2013, DEC-2005)
 Medium for current to flow
 Takes away heat generated
 Removes reaction products

45
PART-B
1. Describe the working principle, elements, advantages, limitations and
applications of chemical machining (Chemical milling).
(APR/MAY 2015, NOV/DEC 2013, APR/MAY 2010,NOV/DEC 2009, APR/MAY
2005)
 This process is also called etching. The mechanism is to use chemical
reaction between the material of the work piece and some chemical
reagent, so that the products of the reaction can be removed easily. Thus
the surface of the work piece is etched away, exposing the lower layers,
and the process is continued until the desired amount of material is
removed.
 The chemical machining processes include those wherein material
removal is accomplished by a chemical reaction, sometimes assisted by
electrical or thermal energy applications. This group includes chemical
milling, photochemical machining, and thermo chemical machining.
 Chemical machining or Chemical milling (CHM) is a well known
nontraditional machining process is the controlled chemical dissolution of
the machined work
 piece material by contact with a strong acidic or alkaline chemical
reagent.
 Special coatings called maskants protect areas from which the metal is
not to be removed. The process is used to produce pockets and contours
and to remove materials from parts having a high strength-to-weight ratio.
CHM consists of the following steps:
1. Preparing and pre-cleaning the work piece surface. This provides good adhesion
of the masking material and assures the absence of contaminants that might
interfere with the machining process.
2. Masking using readily strippable mask, which is chemically impregnable and
adherent enough to stand chemical abrasion during etching.
3. Scribing of the mask, which is guided by templates to expose the areas that
receive CHM. The type of mask selected depends on the size of the work piece, the
number of parts to be made, and the desired resolution of details. Silk-screen masks
are preferred for shallow cuts requiring close dimensional tolerances.
4. The work piece is then etched and rinsed, and the mask is removed before the
part is finished.
 During CHM (Fig.), the depth of the etch is controlled by the time of
immersion. In order to avoid uneven machining, the chemicals that
impinge on the surface being machined should be fresh. The chemicals
used are very corrosive and, therefore, must be handled with adequate
safety precautions. Both the vapors and the effluents must be suitably
controlled for environmental protection.
 Agitation of the work piece and fluid is usual; however, excessive solution
flow may result in channeling, grooves, or ridges. Inclination of the
workpiece may prevent channeling from gas bubbles.

46
 Bellows (1977) and the Metals Handbook (1989) reported that dishing of
the machined surface occurs due to the uneven heat distribution resulting
from the chemical action. Typical reagent temperatures range from 37 to
85°C. Faster etching rates occur at higher temperatures, but must be
controlled within ±5°C of the desired temperature in order to attain uniform
machining.
 When the mask is used, the machining action proceeds both inwardly
from the mask opening and laterally beneath the mask thus creating the
etch factor shown in Fig. The etch factor is the ratio of the undercut d to
the depth of etch T. This ratio must be considered when scribing the mask
using templates.
Etch factor after CHM.
Contours cut by CHM

47
 A typical etch factor of 1:1 occurs at a cut depth of 1.27 mm. Deeper cuts can
reduce this ratio to 1:3. The radii of the fillet produced will be approximately
equal to the depth of etch. For simultaneous machining of multiple parts,
racks or handling fixtures are frequently used to facilitate the submersion of
the work in the chemical reagent and for subsequent rinsing.
 After rinsing the chemicals from the workpiece, the demasking is
accomplished by hand stripping, mechanical brushing, or chemical stripping.
Some chemicals leave a film of smut on the machined surface, which can be
removed by other chemicals or frequently by brushing.
 CHM will not eliminate surface irregularities, dents, scratches, or waviness.
Successive steps of mask removal and immersion as shown in Fig. can
achieve stepped cuts. Tapered cuts (Fig.), can also be produced without
masking the work piece by controlling the depth and rate of immersion or
withdrawal and the number of immersions. Continuous tapers, as great as
0.060 mm/mm for aluminum and 0.010 mm/mm for steel alloys, have been
machined on a production basis.
ADVANTAGES: (MAY/JUNE 2013)
 Weight reduction is possible on complex contours that are difficult to
machine using conventional methods.
 Simultaneous material removal, from all surfaces, improves productivity
and reduces wrapping.
 No burrs are formed.
 No stress is introduced to the workpiece, which minimizes the part distortion
and makes machining of delicate parts possible.
 A continuous taper on contoured sections is achievable.
 The capital cost of equipment, used for machining large components,
is relatively low.
 Design changes can be implemented quickly.
 A less skilled operator is needed.
 Tooling costs are minor.
 The good surface quality in addition to the absence of burrs eliminates
the need for finishing operations.
 Multiple parts having fine details can be machined by the gang method.
 Decorative finishes and extensive thin-web areas are possible.
 There are low scrap rates (3 percent).
LIMITATIONS:
CHM does have limitations and areas of disadvantage:
 Only shallow cuts are practical: up to 12.27 mm for sheets and plates,3.83 mm
on extrusions, and 6.39 mm on forgings.
 Handling and disposal of chemicals can be troublesome.
 Hand masking, scribing, and stripping can be time-consuming, repetitive,
and tedious.
 Surface imperfections are reproduced in the machined parts.
 Metallurgical homogeneous surfaces are required for best results.
 Deep narrow cuts are difficult to produce.
 Fillet radii are fixed by the depth of cut.
 Porous castings yield uneven etched surfaces.
 Welded areas frequently etch at rates that differ from the base metal.
 Material removal from one side of residually stressed material can

48
result in a considerable distortion.
 The absence of residual stresses on the chemically machined surfaces
can produce unfavorable fatigue strength compared with the processes
that induce compressive residual stresses.
 Hydrogen pickup and intergranular attack are a problem with some
materials.The straightness of the walls is subject to fillet and undercutting
limitations.
 Scribing accuracy is limited and complex designs become expensive.
Steep tapers are not practical.
APPLICATIONS:
 All the common metals including aluminum, copper, zinc, steel, lead, and
nickel can be chemically machined. Many exotic metals such as titanium,
molybdenum, and zirconium, as well as nonmetallic materials including glass,
ceramics, and some plastics, can also be used with the process.
 CHM applications range from large aluminum airplane wing parts to minute
integrated circuit chips. The practical depth of cut ranges between 2.54 to
12.27 mm. Shallow cuts in large thin sheets are of the most popular application
especially for weight reduction of aerospace components.
 Multiple designs can be machined from the same sheet at the same time.
CHM is used to thin out walls, webs, and ribs of parts that have been produced
by forging, casting, or sheet metal forming.
2. Explain in detail the ECM process with neat sketch and also mention the
advantages, limitations and applications.
(APR/MAY 2015, NOV/DEC 2013, MAY/JUNE 2013,APR/MAY 2008,NOV/DEC
2008, NOV/DEC 2005)
 Electrochemical Machining (ECM) is a non-traditional machining (NTM)
process belonging to Electro chemical category. ECM is opposite of
electrochemical or galvanic coating or deposition process. Thus ECM can
be thought of a controlled anodic dissolution at atomic level of the work
piece that is electrically conductive by a shaped tool due to flow of high
current at relatively low potential difference through an electrolyte which is
quite often water based neutral salt solution.
Principles of electrolysis:
 Electrolysis occurs when an electric current passes between two
electrodes dipped into an electrolyte solution. The system of the

49
electrodes and the electrolyte is referred to as the electrolytic cell. The
chemical reactions, which occur at the electrodes, are called the anodic or
cathodic reactions. ED of the anodic workpiece forms the basis for ECM
of metals.
 The amount of metal dissolved (removed by machining) or deposited is
calculated from Faraday‟s laws of electrolysis, which state that
1. The amount of mass dissolved (removed by machining), m, is directly
proportional to the amount of electricity.
m ∞ It
2. The amount of different substances dissolved, m, by the same quantity of
electricity (It) is proportional to the substances‟ chemical equivalent weight e.
m ∞ є
ECM equipment
 Figure shows the main components of the ECM machine: the feed control
system, electrolyte supply system, power supply unit, and work piece
holding device. As shown in Fig. the feed control system is responsible for
feeding the tool at a constant rate during equilibrium machining.
 The power supply drives the machining current at a constant dc
(continuous or pulsed) voltage. The electrolyte-feeding unit supplies the
electrolyte solution at a given rate, pressure, and temperature.
 Facilities for electrolyte filtration, temperature control, and sludge removal
are also included. ECM machines are capable of performing a wide range
of operations such as duplicating, sinking, and drilling. Semiautomatic and
fully automated facilities are used for large-size machining, such as
deburring in the automotive industry. ECM machines, in contrast to
conventional machine tools, are designed to stand up to corrosion attack
by using nonmetallic materials. For high strength or rigidity, metals with
nonmetallic coatings are recommended

50
Power supply:
The dc power supply for ECM has the following features:
1. Voltage of 2 to 30 volts (V) (pulsed or continuous)
2. Current ranges from 50 to 10,000 amperes (A), which allow current densities of 5
to 500 A/cm2
3. Continuous adjustment of the gap voltage
4. Control of the machining current in case of emergency
5. Short circuit protection in a matter of 0.001 s
6. High power factor, high efficiency, small size and weight, and low cost
Electrolytes.
EDM SYSTEM COMPONENTS:

51
The main functions of the electrolytes in ECM are to
1. Create conditions for anodic dissolution of work piece material
2. Conduct the machining current
3. Remove the debris of the electrochemical reactions from the gap
4. Carry away the heat generated by the machining process
5. Maintain a constant temperature in the machining region
The electrolyte solution should, therefore, be able to
1. Ensure a uniform and high-speed anodic dissolution
2. Avoid the formation of a passive film on the anodic surface (electrolytes
containing anions of Cl, SO4, NO3, ClO3, and OH are often recommended)
3. Not deposit on the cathode surface, so that the cathode shape remains
unchanged (potassium and sodium electrolytes are used)
4. Have a high electrical conductivity and low viscosity to reduce the power loss due
to electrolyte resistance and heat generation and to ensure good flow conditions in
the extremely narrow inter electrode gap
5. Be safe, nontoxic, and less erosive to the machine body
6. Maintain its stable ingredients and pH value, during the machining period
7. Have small variation in its conductivity and viscosity due to temperature rise
8. Be inexpensive and easily available
ADVANTAGES OF ECM:
The components are not subject to either thermal or mechanical stress.
 No tool wear during ECM process.
 Fragile parts can be machined easily as there is no stress involved.
 ECM deburring can debur difficult to access areas of parts.
 High surface finish (up to 25 μm in) can be achieved by ECM process.
 Complex geometrical shapes in high-strength materials particularly in the
aerospace industry for the mass production of turbine blades, jet-engine parts
and nozzles can be machined repeatedly and accurately.
 Deep holes can be made by this process.
LIMITATIONS OF ECM:
 ECM is not suitable to produce sharp square corners or flat bottoms because
of the tendency for the electrolyte to erode away sharp profiles.
 ECM can be applied to most metals but, due to the high equipment costs, is
usually used primarily for highly specialised applications.
APPLICATIONS:
 Dies and glass-making molds, turbine and compressor blades for gas-turbine
engines, round or non-round holes, passages, cavities and slots in parts.
ECM is also used for deburring of gears, hydraulic and fuel-system parts.
 Die sinking • Profiling and contouring • Trepanning • Grinding • Drilling

52
3. Describe the chemistry involved in ECM process and explain the process
parameters. (16)
(NOV/DEC 2012, NOV/DEC 2005)
Theory of ECM- chemistry involved
 ECM uses a direct current at a high density of 0.5 to 5 A/mm2 and a low
voltage of 10 to 30 V. The machining current passes through the
electrolytic solution that fills the gap between an anodic workpiece and a
preshaped cathodic tool.
 The electrolyte is forced to flow through the interelectrode gap at high
velocity, usually more than 5 m/s, to intensify the mass and charge
transfer through the sublayer near the anode.
 The electrolyte removes the dissolution products, such as metal
hydroxides, heat, and gas bubbles, generated in the interelectrode gap.
McGeough (1988) claimed that when a potential difference is applied
across the electrodes, several possible reactions occur at the anode and
the cathode.
 Figure illustrates the dissolution reaction of iron in sodium chloride (NaCl)
water solution as an electrolyte. The result of electrolyte dissociation and
NaCl dissolution leads to
The negatively charged anions OH− and Cl− move toward the anode, and the
positively charged cations of H+ and Na+ are directed to the cathode.
At the anode, Fe changes to Fe++ by losing two electrons.
At the cathode, the reaction involves the generation of hydrogen gas and the
hydroxyl ions.
The outcome of these electrochemical reactions is that iron ions combine with other
ones to precipitate out as iron hydroxide, Fe(OH)2.
The ferrous hydroxide may react further with water and oxygen to form ferric
hydroxide, Fe(OH)3.

53
With this metal-electrolyte combination, electrolysis has involved the dissolution of
iron, from the anode, and the generation of hydrogen, at the cathode.
PROCESS PARAMETERS:
Power Supply Type direct current
Voltage 2 to 35 V
Current 50 to 40,000 A
Current density 0.1 A/mm2 to 5 A/mm2
Electrolyte Material NaCl and NaNO3
Temperature 20oC – 50oC
Flow rate 20 lpm per 100 A current
Pressure 0.5 to 20 bar
Dilution 100 g/l to 500 g/l
Working gap 0.1 mm to 2 mm
Overcut 0.2 mm to 3 mm
Feed rate 0.5 mm/min to 15 mm/min
Electrode material copper, brass, bronze
Surface roughness, Ra 0.2 to 1.5 μm
4. (i) Explain the principle of ECG with sketch. list out the advantage of ECG.
Also mention the product application of ECG.
(16)
(APR/MAY 2015, APR/MAY 2010, MAY/JUNE 2009, NOV/DEC 2008, APR/MAY
2004, 2012)
 Electrochemical grinding is a process that removes electrically conductive
material by grinding with a negatively charged abrasive grinding wheel, an
electrolyte fluid, and a positively charged workpiece.
 Materials removed from the workpiece stay in the electrolyte fluid.
Electrochemical grinding is similar to electrochemical machining but uses
a wheel instead of a tool shaped like the contour of the workpiece.
 Electrochemical grinding (ECG) utilizes a negatively charged abrasive
grinding wheel, electrolyte solution, and a positively charged workpiece,
as shown in Fig.The process is, therefore, similar to ECM except that the
cathode is a specially constructed grinding wheel instead of a cathodic
shaped tool like the contour to be machined by ECM.
 The insulating abrasive material (diamond or aluminum oxide) of the
grinding wheel is set in a conductive bonding material. In ECG, the
nonconducting abrasive particles act as a spacer between the wheel
conductive bond and the anodic workpiece.
 Depending on the grain size of these particles, a constant inter electrode
gap (0.025 mm or less) through which the electrolyte is flushed can be
maintained.

54
 The abrasives continuously remove the machining products from the
working area. In the machining system shown in Fig., the wheel is a rotating
cathodic tool with abrasive particles (60–320 grit number) on its periphery.
 Electrolyte flow, usually NaNO3, is provided for ECD.The wheel rotates at a
surface speed of 20 to 35 m/s, while current ratings are from 50 to 300 A.
ECG SYSTEM:
Material removal rate:
 When a gap voltage of 4 to 40 V is applied between the cathodic grinding
wheel and the anodic workpiece, a current density of about 120 to 240
A/cm2 is created. The current density depends on the material being, the
gap width, and the applied voltage.
 Material is mainly removed by ECD, while the MA of the abrasive grits
accounts for an additional 5 to 10 percent of the total material removal.
 Removal rates by ECG are 4 times faster than by conventional grinding,
and ECG always produces burr-free parts that are unstressed. The
volumetric removal rate (VRR) is typically 1600 mm3/min.
 McGeough (1988) and Brown (1998) claimed that to obtain the maximum
removal rate, the grinding area should be as large as possible to draw
greater machining current, which affects the ECD phase.

55
 The volumetric removal rate (mm3/min) in ECG can be calculated using
the following equation:
where e = equivalent weight, g
I = machining current, A
r = density of work piece material, g/mm3
F = Faraday‟s constant, C
Process characteristics
 The wheels and work piece are electrically conductive.
 Wheels used last for many grindings - typically 90% of the metal are by
electrolysis and 10% from the abrasive grinding wheel. Capable of producing
smooth edges without the burrs caused by mechanical grinding.
 Does not produce appreciable heat that would distort work piece.
 Decomposes the work
 piece and deposits them into the electrolyte solution. The most common
electrolytes are sodium chloride and sodium nitrate at concentrations of 2 lbs per
gallon.
 It uses a rotating cathode embedded with abrasive particles for applications
comparable to milling, grinding and sawing.
 Most of the metal removal is done by the electrolyte, resulting in very low tool
wear.
ECG PROCESS COMPONENTS:
 ECG is a hybrid machining process that combines MA(Mechanical Abrasion)
and ECD(Electro Chemical Deposition). The machining rate, therefore,
increases many times; surface layer properties are improved, while tool wear
and energy consumption are reduced.

56
 While Faraday‟s laws govern the ECD phase, the action of the abrasive
grains depends on conditions existing in the gap, such as the electric field,
transport of electrolyte, and hydrodynamic effects on layers near the anode.
 The contribution of either of these two machining phases in the material
removal process and in surface layer formation depends on the process
parameters. Figure shows the basic components of the ECG process.
 The contribution of each machining phase to the material removal from the
workpiece has resulted in a considerable increase in the total removal rate
QECG, in relation to the sum of the removal rate of the electrochemical
process and the grinding processes QECD and QMA, when keeping the
same values of respective parameters as during the ECG process.
APPLICATIONS:
The ECG process is particularly effective for
1. Machining parts made from difficult-to-cut materials, such as sintered carbides,
creep-resisting (Inconel, Nimonic) alloys, titanium alloys, and metallic composites.
2. Applications similar to milling, grinding, cutting off, sawing, and tool and cutter
sharpening.
3. Production of tungsten carbide cutting tools, fragile parts, and thin walled tubes.
4. Removal of fatigue cracks from steel structures under seawater. In such an
application holes about 25 mm in diameter, in steel 12 to 25 mm thick, have been
produced by ECG at the ends of fatigue cracks to stop further development of the
cracks and to enable the
removal of specimens for metallurgical inspection.
5. Producing specimens for metal fatigue and tensile tests.
6. Machining of carbides and a variety of high-strength alloys.
ADVANTAGES
 Absence of work hardening
 Elimination of grinding burrs
 Absence of distortion of thin fragile or thermo sensitive parts
 Good surface quality
 Production of narrow tolerances
 Longer grinding wheel life
DISADVANTAGES
 Higher capital cost than conventional machines
 Process limited to electrically conductive materials

57
5. Discuss about the electrochemical honing process and application in detail.
(NOV/DEC 2014, NOV/DEC 2007, APR/MAY2004, 2009)
 Electrochemical honing (ECH) combines the high removal characteristics of
ECD and MA of conventional honing. The process has much higher removal
rates than either conventional honing or internal cylindrical grinding.
 In ECH the cathodic tool is similar to the conventional honing tool, with
several rows of small holes to enable the electrolyte to be introduced directly
to the inter electrode gap. The electrolyte provides electrons through the
ionization process, acts as a coolant, and flushes away chips that are
sheared off by MA and metal sludge that results from ECD action.
 The majority of material is removed by the ECD phase, while the abrading
stones remove enough metal to generate a round, straight, geometrically true
cylinder. During machining, the MA removes the surface oxides that are
formed on the work surface by the dissolution process.
 The removal of such oxides enhances further the ECD phase as it presents a
fresh surface for further electrolytic dissolution. Sodium nitrate solution (240
g/L) is used instead of the more corrosive sodium chloride (120g/L) or acid
electrolytes.
 An electrolyte temperature of 38°C, pressure of 1000 kPa, and flow rate of 95
L/min can be used. ECH employs dc current at a gap voltage of 6 to 30 V,
which ensures a current density of 465 A/cm2. Improper electrolyte
distribution in the machining gap may lead to geometrical errors in the
produced bore.
Process characteristics
 The machining system shown in Fig. employs a reciprocating abrasive stone
(with metallic bond) carried on a spindle, which is made cathodic and
separated from the work piece by a rapidly flowing electrolyte.
 In such an arrangement, the abrasive stones are used to maintain the gap
size of 0.076 to 0.250 mm and, moreover, depassivate the machining surface
due to the ECD phase occurring through the bond. A different tooling system
(Fig.) can be used where the cathodic tool carries nonconductive honing
sticks that are responsible for the MA.
 The machine spindle that rotates and reciprocates is responsible for the ECD
process. The material removal rate for ECH is 3 to 5 times faster than that of
conventional honing and 4 times faster than that of internal cylindrical
grinding. Tolerances in the range of ±0.003 mm are achievable, while surface
roughnesses in the range of 0.2 to 0.8 μm Ra are possible.
 To control the surface roughness, MA is allowed to continue for a few
seconds after the current has been turned off. Such a method leaves a light
compressive residual stress in the surface.
 The surface finish generated by the ECH process is the conventional cross-
hatched cut surface that is accepted and used for sealing and load-bearing
surfaces. However, for stress-free surfaces and geometrically accurate
bores, the last few seconds of MA action should be allowed for the pure ECD
process.

ME8073 Unconventional Machining Processes - By www.LearnEngineering.in.pdf

ME8073 Unconventional Machining Processes - By www.LearnEngineering.in.pdf

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