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1. Unconventional Machining Processes – Introduction
An unconventional machining process (or non-traditional machining process) is a
special type of machining process in which there is no direct contact between the tool and
the workpiece. In unconventional machining, a form of energy is used to remove unwanted
material from a given workpiece.
Definition
Unconventional Machining Process is defined as a group of processes that remove
excess (stock) material from work piece by various techniques involving Mechanical,
Thermal, Electrical and chemical energy or combination of these energies but do not use a
sharp cutting tools as it needs to be used for traditional machining processes.
Why unconventional machining processes are used?
 In several engineering industries have a rapid growth in the development of harder
and difficult to machine materials such as ceramics, carbides, stainless steels, High
Speed Steels, Heat Resisting Steels, and many other High-Strength-Temperature-
Resistant (HSTR) alloys. These hard-to-machine materials are found wide
applications in aircraft industry, research equipments, missile technology, nuclear
engineering, and other industries owing to their high strength-to-weight ratio,
hardness, and heat-resisting qualities.
 If such materials are machined with the help of conventional machining processes,
either the tool undergoes extreme wear (while machining hard workpiece) or the
workpiece material is damaged (while machining brittle workpiece).
 This is because, in conventional machining, there is a direct contact between the tool
and the workpiece. Large cutting forces are involved and material is removed in the
form of chips. A huge amount of heat is produced in the workpiece. This induces
residual stresses, which degrades the life and quality of the workpiece material.
 Hence, conventional machining produces poor quality workpiece with poor surface
finish (if the workpiece is made of hard and brittle material).
 For such materials the conventional edged tool machining, in spite of recent
technological advancement, is highly uneconomical and degree of accuracy and
surface finish attainable are poor. Besides, machining of these materials into
complex shapes is difficult, time-consuming and sometimes impossible.

2.  To overcome all these drawbacks, we use unconventional machining processes to
machine hard and brittle materials.
 We also use unconventional machining processes to machine soft materials, in order
to get better dimensional accuracy.
Classification of unconventional machining processes:
Unconventional machining processes can be broadly classified into several types
based on four main criteria. The classification of unconventional machining processes is
given below:
1. Based on the type of energy used
1. Mechanical Energy based Unconventional Machining Processes
2. Electrical Energy based Unconventional Machining Processes
3. Electrochemical Energy based Unconventional Machining Processes
4. Chemical Energy based Unconventional Machining Processes (e.g. Chemical
Machining)
5. Thermo-electrical (or Electro-thermal) Energy based Unconventional
Machining Processes
2. Based on the source of energy
1. High Current density
2. High Voltage
3. Hydraulic Pressure
4. Pneumatic Pressure
5. Ionised Particles
6. Light energy
3. Based on the mechanism of material removal
1. Erosion
2. Ion Displacement
3. Melting and Vapourisation
4. Chemical Etching
5. Blasting
4. Based on the medium of energy transfer
1. Electrons
2. Atmosphere
3. Ions
4. Electrolyte
5. Pressurized gas
6. Water
7. Ultrasonic waves
8. Plasma
9. Laser
10. Chemical reagent
11. Radiation

4. Classification of Unconventional Machining Processes based on Energy Used
Based on energy used, unconventional machining processes can be broadly classified
into five main types. They are:
1. Mechanical Energy based Unconventional Machining Processes
2. Electrical Energy based Unconventional Machining Processes
3. Electrochemical Energy based Unconventional Machining Processes
4. Chemical Energy based Unconventional Machining Processes
5. Thermo-electrical (or Electro-thermal) Energy based Unconventional Machining
Processes
1. Mechanical Energy based Unconventional Machining Processes:
In these processes, unwanted material in the workpiece is removed by mechanical
erosion. The mechanical erosion can be facilitated by using any medium. For example, in
abrasive jet machining, high velocity abrasive jet is used for eroding material from the
workpiece. In water jet machining, high velocity water jet is used for cutting the workpiece
material.
The four main mechanical energy based unconventional machining processes are:
1. Abrasive Jet Machining
2. Water Jet Machining or Water Jet Cutting
3. Abrasive Water Jet Machining
4. Ultrasonic Machining
2. Electrical Energy based Unconventional Machining Processes:
 Here, electric spark discharge is used to cut and machine the workpiece.
 In electrical energy based processes, no arc is produced (as in arc welding). Instead,
thousands of sparks are produced every second.
 These sparks increase the temperature of the workpiece, melt the unwanted portions
and vaporized those portions.
 A dielectric fluid is used for cleaning the workpiece and facilitating a smooth spark
discharge.
Processes that come under this category are:
1. Electrical Discharge Machining
2. Wire Cut Electrical Discharge Machining

5. 3. Electrochemical Energy based Unconventional Machining Processes:
In these processes, unwanted portions of the workpiece are removed by
electrochemical effect. The workpiece (in contact with an electrolyte) is machined by ion
dissolution. Processes that come under this category are:
1. Electrochemical Machining
2. Electrochemical Grinding
3. Electrochemical Honing
4. Chemical Energy based Unconventional Machining Processes:
Here, chemical energy is used to remove material from the workpiece. We know that
metal can be easily converted to metallic salt, if suitable reagent is used. Chemical energy
based processes exploit this principle. Material is removed by controlled etching of the
workpiece in the presence of a reagent known as enchant.
Chemical machining, chemical milling and photochemical milling (PCM) are the
processes that come under this category.
5. Thermo-electrical (or Electro-thermal) Energy based UCM Processes:
Thermo-electrical energy based unconventional machining processes make use of
this principle. In these processes, electrical energy is converted to a huge amount of heat by
some means. This heat is applied on a small region of the workpiece. That particular region
is either melted or vaporized. By this way, material is removed. The following are some of
the important thermo-electrical energy based unconventional machining processes:
1. Plasma Arc Machining
2. Electron Beam Machining
3. LASER Beam Machining
4. Ion Beam Machining
Selection of machining methods:
Sl.No. Material Methods of Machining
1. Non Metals like ceramics,
Plastics and glass
USM, AJM, EBM, LBM
2. Refractories USM, AJM, EBM, EDM
3. Titanium EDM
4. Super alloys AJM, ECM, EDM, PAM
5. Steel ECM, CHM, EDM, PAM

6. Process Selection
In orderto make use of the non-traditional machining processes efficiently, it is necessary
that the exactnature of the machiningproblemmustbe known.The points which should be looked
into before the selection of these processes are;-
 Physical parameters
 Properties of the work material and the shape to be machined
 Process capability or machining characteristics
 Economic considerations
Physical parameters

7. Shapes to be machined
Process capability
Process economy

8. Conventional Manufacturing Processes Vs Unconventional Manufacturing Processes
Sl.No. Conventional Manufacturing Processes Unconventional Manufacturing Processes
1. Generally macroscopic chip formation by
shear deformation.
Material removal may occur with chip
formation or even no chip formation may
take place. For example in AJM, chips are of
microscopic size and in case of
Electrochemical machining material
removal occurs due to electrochemical
dissolution at atomic level
2. There may be a physical tool present. for
example a cutting tool in a Lathe
Machine,
There may not be a physical tool present.
For example in laser jet machining,
machining is carried out by laser beam.
However in Electrochemical Machining
there is a physical tool that is very much
required for machining.
3. Cutting tool is harder than work piece at
room temperature as well as under
machining conditions
There may not be a physical tool present.
For example in laser jet machining,
machining is carried out by laser beam.
However in Electrochemical Machining
there is a physical tool that is very much
required for machining.
4. Material removal takes place due to
application of cutting forces – energy
domain can be classified as mechanical
Mostly NTM processes do not necessarily
use mechanical energy to provide material
removal. They use different energy domains
to provide machining. For example, in USM,
AJM, WJM mechanical energy is used to
machine material, whereas in ECM
electrochemical dissolution constitutes
material removal.
5. Conventional machining involves the
direct contact of tool and work –piece
Whereas unconventional machining does
not require the direct contact of tool and
work piece.
6. Lower accuracy and surface finish. Higher accuracy and surface finish.
7. Suitable for every type of material
economically
Not Suitable for every type of material
economically
8. Tool life is lessdue to high surface contact
and wear.
Tool life is more
9. Higher waste of material due to high
wear.
Lower waste of material due to low or no
wear.
10. Noisy operation mostly cause sound
pollutions
Quieter operation mostly no sound
pollutions are produced.
11. Lower capital cost Higher capital cost

9. 12. Easy set-up of equipment. Complex set-up equipment.
13. Skilled or un-skilled operator may
required
Skilled operator required.
14. Generally they are manual to operate. Generally they are fully automated process.
15. They cannot be used to produce
prototype parts very efficiently and
economically.
Can be used to produce prototype parts
very efficientlyAnd economically.
Advantages of Non-conventional machining:
1. Increased productivity
2. High accuracy and surface finish
3. Close tolerance is possible
4. no direct contact of tool and workpiece, so there is less/no wear
5. Toll material need not be harder than workpiece
6. Machined surface does not have residual stress
7. Tool life is more
8. Quieter operation
Disadvantages of non-conventional machining:
1) High cost
2) Complex set-up
3) Skilled operator required