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NOTES
INTRODUCTION:-
Non-traditional manufacturing processes is defined as a group of processes that remove excess
material by various techniques involving mechanical, thermal, electrical or chemical energy or
combinations of these energies but do not use a sharp cutting tools as it needs to be used for traditional
manufacturing processes.
Extremely hard and brittle materials are difficult to machine by traditional machining processes such
as turning, drilling, shaping and milling. Non traditional machining processes, also called advanced
manufacturing processes, are employed where traditional machining processes are not feasible,
satisfactory or economical due to special reasons as outlined below.
 Very hard fragile materials difficult to clamp for traditional machining
 When the workpiece is too flexible or slender
 When the shape of the part is too complex
Several types of non-traditional machining processes have been developed to meet extra required
machining conditions. When these processes are employed properly, they offer many advantages over
non-traditional machining processes.

DEFINITION:
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 workpiece into smaller parts.

Non Traditional Machining (NTM) Processes on the other hand are characterised as follows:
• 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
• In NTM, 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
• In NTM, the tool need not be harder than the work piece material. For example, in EDM, copper is
used as the tool material to machine hardened steels.
• 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.

Need for development of Non Conventional Processes

The strength of steel alloys has increased five folds due to continuous R and D effort.
In
aero-space requirement of High strength at elevated temperature with light weight led
to development and use of hard titanium alloys, nimonic alloys, and other HSTR
alloys. The ultimate tensile strength has been improved by as much as 20 times.

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Development of cutting tools which has hardness of 80 to 85 HRC which cannot be

machined economically in
conventional methods led to development of non –traditional machining methods.
1. Technologically advanced industries like aerospace, nuclear power, ,wafer
fabrication, automobiles has ever increasing use of High –strength temperature
resistant (HSTR) alloys (having high strength to weight ratio) and other difficult to
machine materials like titanium, SST,nimonics, ceramics and semiconductors. It is no
longer possible to use conventional process to machine these alloys.
2. Production and processing parts of complicated shapes (in HSTR and other
hard to machine alloys) is difficult , time consuming an uneconomical by
conventional methods of machining
3. Innovative geometric design of products and components made of new
exotic materials with desired tolerance , surface finish cannot be produced
economically by conventional machining.
4. 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 with a tolerance of 100 microns
♦ Difficult to machine material – e.g. Inconel, Ti-alloys or carbides, Ceramics,
composites , HSTR alloys, satellites etc.,
♦ Low Stress Grinding – Electrochemical Grinding is preferred as compared to
conventional grinding
♦ Deep hole with small hole diameter – e.g. φ 1.5 mm hole with l/d = 20
♦ Machining of composites

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Differences between Conventional and Non conventional machining

processes.
Sl.no Conventional Process Non Conventional Process

1 The cutting tool and work piece There is no physical contact between the
are always in physical contact tool and work piece, In some non
with relative motion with each traditional process tool wear exists.
other, which results in friction
and tool wear.
2 Material removal rate is limited NTM can machine difficult to cut and
by mechanical properties of hard to cut materials like
work material.
titanium,ceramics,nimonics,
SST,composites,semiconducting
materials
3 Relative motion between the Many NTM are capable of producing
tool and work is typically complex 3D shapes and cavities

rotary or reciprocating. Thus

the shape of work is limited
to circular or flat shapes. In
spite of CNC systems,
production of 3D surfaces is
still a difficult task.
4 Machining of small cavities , Machining of small cavities, slits
slits , blind holes or through and Production of non-circular,
holes are difficult micro sized, large aspect ratio,
shall entry angle holes are easy
using NTM
5 Use relative simple and Non traditional processes
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inexpensive machinery and requires expensive tools and

readily available cutting tools equipment as well as skilled
labour, which increase the
production cost significantly
6 Capital cost and maintenance Capital cost and maintenance
cost is low cost is high
7 Traditional processes are Mechanics of Material removal
well established and physics of Some of NTM process are still
of process is well understood under research
8 Conventional process Most NTM uses energy in direct
mostly uses mechanical form For example : laser,
energy Electron beam in its direct forms
are used in LBM and EBM
respectively
9 Surface finish and High surface finish(up to 0.1
tolerances are limited by micron) and tolerances (25
machining inaccuracies Microns)can be achieved
10 High metal removal rate. Low material removal rate.

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Classification of Advanced Manufacturing Techniques

Mechanical Electrochemical Electrothermal Chemical

Process Process Process Process

Abrasive Jet Electrochemical Electro-

Machining (AJM) Machining (ECM) Discharge Chemical
Ultrasonic Electrochemical Machining (EDM) Machining
Machining Grinding (ECG) Laser Jet (CHM)
(USM) Electrojet Drilling Machining (LJM) Photochemical
Water Jet (EJD) Electron Beam Machining
Machining Machining (EBM) (PCM)
(WJM) Plasma Arc
Abrasive Water Machining (PAM)
Jet Machining
(AWJM)
Abrasive Flow
Machining
(AFM)
Magnetic
SELECTION OF PROCESS:
Abrasive
The correct selection of the non-traditional machining methods must be based on the
Finishing (MAF)
following aspects.
Physical parameters of the process
Shape to be machined
Process capability
Economics of the processes

Physical parameter of the process:

The physical parameters of the different NTM are given in the Table 1.0 which indicates
that PAM and ECM require high power for fast machining. EBM and LBM require high

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voltages and require careful handling of equipment. EDM and USM require medium
power . EBM can be used in vacuum and PAM uses oxygen and hydrogen gas.

Shapes cutting capability:-

The different shapes can be machined by NTM. EBM and LBM are used for micro
drilling and cutting. USM and EDM are useful for cavity sinking and standard hole
drilling. ECM is useful for fine hole drilling and contour machining. PAM can be
used for cutting and AJM is useful for shallowpocketing

Process capability:
The process capability of NTM is given in Table 2.0 EDM which achieves higher
accuracy has the lowest specific power requirement. ECM can machine faster and has
a low thermal surface damage depth. USM and AJM have very material removal
rates combined with high tool wear and are used non metal cutting. LBM and EBM
are, due to their high penetration depth can be used for micro drilling, sheet cutting
and welding. CHM is used for manufacture of PCM and other shallow components

Table:-1.0

Table:-2.0

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ULTRASONIC MACHINING (USM)

INTRODUCTION

USM is mechanical material removal process or an abrasive process used to erode

holes or cavities on hard or brittle workpiece by using shaped tools, high frequency
mechanical motion and an abrasive slurry. USM offers a solution to the expanding
need for machining brittle materials such as single crystals, glasses and
polycrystalline ceramics, and increasing complex operations to provide intricate
shapes and workpiece profiles. It is therefore used extensively in machining hard and
brittle materials that are difficult to machine by traditional manufacturing processes.
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):
The process was first developed in 1950s and was originally used for finishing
EDM surfaces.
The basic process is that a ductile and tough tool is pushed against the work with a
constant force. A constant stream of abrasive slurry passes between the tool and the
work (gap is 25-40 μm) to provide abrasives and carry away chips. The majority of
the cutting action comes from an ultrasonic (cyclic) force applied.

The basic components to the cutting action are believed to be,

 brittle fracture caused by impact of abrasive grains due to the tool vibration;
 cavitation induced erosion;
 chemical erosion caused by slurry.

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USM working principle

• Material removal primarily occurs due to the indentation of the hard abrasive
grits on the brittle work material.
• Other than this brittle failure of the work material due to indentation some
material removal may occur due to free flowing impact of the abrasives
against the work material and related solid-solid impact erosion,
• Tool’s vibration – indentation by the abrasive grits.
• During indentation, due to Hertzian contact stresses, cracks would develop just
below the contact site, then as indentation progresses the cracks would propagate
due to increase in stress and ultimately lead to brittle fracture of the work material
under each individual interaction site between the abrasive grits and the workpiece.
• The tool material should be such that indentation by the abrasive grits does not
lead to brittle failure.
• Thus the tools are made of tough, strong and ductile materials like steel,
stainless steel and other ductile metallic alloys.

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USM Machine

USM Equipment

The basic mechanical structure of an USM is very similar to a drill press.

However, it has additional features to carry out USM of brittle work material. The
work piece is mounted on a vice, which can be located at the desired position under
the tool using a 2 axis table. The table can further be lowered or raised to
accommodate work of different thickness.
The typical elements of an USM are
 Slurry delivery and return system
 Feed mechanism to provide a downward feed force on the tool during machining
 The transducer, which generates the ultrasonic vibration
 The horn or concentrator, which mechanically amplifies the vibration to the
required amplitude of 15 – 50 μm and accommodates the tool at its tip.

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Working of horn as mechanical amplifier of amplitude of vibration:-

The ultrasonic vibrations are produced by the transducer. The transducer is driven by
suitable signal generator followed by power amplifier.
The transducer for USM works on the following principle
• Piezoelectric effect
• Magnetostrictive effect
• Electrostrictive effect

Magnetostrictive transducers are most popular and robust amongst all. Figure shows a
typical magnetostrictive transducer along with horn. The horn or concentrator is a
wave guide, which amplifies and concentrates the vibration to the tool from the
transducer.

The horn or concentrator can be of different shape like

• Tapered or conical
• Exponential
• Stepped

Machining of tapered or stepped horn is much easier as compared to the exponential

one. Figure shows different horns used in USM

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PROCESS VARIABLES:-
• 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
- Boronsilicarbide
- 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

Applications of USM
• 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.

Advantage of USM
USM process is a non-thermal, non-chemical, creates no changes in the
microstructures, chemical or physical properties of the workpiece and offers virtually
stress free machined surfaces.
The main advantages are;
· 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

Some 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

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ABRASIVE JET MACHINING (AJM)

INTRODUCTION

Abrasive water jet cutting is an extended version of water jet cutting; in which the
water jet contains abrasive particles such as silicon carbide or aluminium oxide in
order to increase the material removal rate above that of water jet machining. Almost
any type of material ranging from hard brittle materials such as ceramics, metals and
glass to extremely soft materials such as foam and rubbers can be cut by abrasive
water jet cutting. The narrow cutting stream and computer controlled movement
enables this process to produce parts accurately and efficiently. This machining
process is especially ideal for cutting materials that cannot be cut by laser or thermal
cut. Metallic, non- metallic and advanced composite materials of various thicknesses
can be cut by this process. This process is particularly suitable for heat sensitive
materials that cannot be machined by processes that produce heat while machining.

Working principle

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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.

AJM Equipment

In AJM, air is compressed in an air compressor and compressed air at a pressure of

around 5 bar is used as the carrier gas. Figure also shows the other major parts of the
AJM system. Gases like CO2, N2 can also be used as carrier gas which may directly be

issued from a gas cylinder. Generally oxygen is not used as a carrier gas. The carrier
gas

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is first passed through a pressure regulator to obtain the desired working pressure. To
remove any oil vapour or particulate contaminant the same is passed through a series of
filters. Then the carrier gas enters a closed chamber known as the mixing chamber. The
abrasive particles enter the chamber from a hopper through a metallic sieve. The sieve is
constantly vibrated by an electromagnetic shaker. The mass flow rate of abrasive (15
gm/min) entering the chamber depends on the amplitude of vibration of the sieve and its
frequency. The abrasive particles are then carried by the carrier gas to the machining
chamber via an electro-magnetic on-off valve. The machining enclosure is essential to
contain the abrasive and machined particles in a safe and eco-friendly manner. The
machining is carried out as high velocity (200 m/s) abrasive particles are issued from the
nozzle onto a work piece traversing under the jet.

Process Parameters and Machining Characteristics:-

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
• Carrier gas
o Composition – Air, CO2, N2
3
o Density – Air ~ 1.3 kg/m
o Velocity – 500 ~ 700 m/s
o Pressure – 2 ~ 10 bar
o Flow rate – 5 ~ 30 lpm
 Abrasive Jet
⎯ Velocity – 100 ~ 300 m/s
⎯ Mixing ratio – mass flow ratio of abrasive to gas
⎯ Stand-off distance – 0.5 ~ 5 mm
0 0
⎯ Impingement Angle – 60 ~ 90

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• Nozzle
⎯ Material – WC / sapphire
⎯ Diameter – (Internal) 0.2 ~ 0.8 mm
⎯ Life – 10 ~ 300 hours
The important machining characteristics in AJM are
3
• The material removal rate (MRR) mm /min or gm/min
• The machining accuracy
• The life of the nozzle

Effect of process parameters MRR

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Parameters of Abrasive Jet Machining (AJM) are factors that influence its Metal
Removal Rate (MRR). In a machining process, Metal Removal Rate (MRR) is the
volume of metal removed from a given work piece in unit time. The following are
some of the important process parameters of abrasive jet machining:
1. Abrasive mass flow rate
2. Nozzle tip distance
3. Gas Pressure
4. Velocity of abrasive particles
5. Mixing ratio
6. Abrasive grain size

Abrasive mass flow rate:

Mass flow rate of the abrasive particles is a major process parameter that influences
the metal removal rate in abrasive jet machining.

In AJM, mass flow rate of the gas (or air) in abrasive jet is inversely proportional to
the mass flow rate of the abrasive particles.
Due to this fact, when continuously increasing the abrasive mass flow rate, Metal
Removal Rate (MRR) first increases to an optimum value (because of increase in
number of abrasive particles hitting the work piece) and then decreases.
However, if the mixing ratio is kept constant, Metal Removal Rate (MRR) uniformly
increases with increase in abrasive mass flow rate.

Nozzle tip distance:

Nozzle Tip Distance (NTD) is the gap provided between the nozzle tip and the work
piece.
Up to a certain limit, Metal Removal Rate (MRR) increases with increase in nozzle
tip distance. After that limit, MRR remains constant to some extent and then
decreases.
In addition to metal removal rate, nozzle tip distance influences the shape and
diameter of cut.
For optimal performance, a nozzle tip distance of 0.25 to 0.75 mm is provided.

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Gas pressure:-
Air or gas pressure has a direct impact on metal removal rate.
In abrasive jet machining, metal removal rate is directly proportional to air or gas
pressure.

Velocity of abrasive particles:-

Whenever the velocity of abrasive particles is increased, the speed at which the
abrasive particles hit the work piece is increased. Because of this reason, in abrasive
jet machining, metal removal rate increases with increase in velocity of abrasive
particles.

Mixing ratio:-
Mixing ratio is a ratio that determines the quality of the air-abrasive mixture in
Abrasive Jet Machining (AJM).
It is the ratio between the mass flow rate of abrasive particles and the mass flow rate
of air (or gas).
When mixing ratio is increased continuously, metal removal rate first increases to
some extent and then decreases.

Abrasive grain size:-

Size of the abrasive particle determines the speed at which metal is removed.
If smooth and fine surface finish is to be obtained, abrasive particle with small grain
size is used.
If metal has to be removed rapidly, abrasive particle with large grain size is used.

Applications
 Abrasive water jet cutting is highly used in aerospace, automotive and
electronics industries.
 In aerospace industries, parts such as titanium bodies for military aircrafts, engine
 components (aluminium, titanium, heat resistant alloys), aluminium body parts
and interior cabin parts are made using abrasive water jet cutting.
 In automotive industries, parts like interior trim (head liners, trunk liners, door
panels) and fibre glass body components and bumpers are made by this
process. Similarly, in electronics industries, circuit boards and cable stripping
are made by abrasive water jet cutting.

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Advantages of abrasive water jet cutting:-

 In most of the cases, no secondary finishing required
 No cutter induced distortion
 Low cutting forces on workpieces
 Limited tooling requirements
 Little to no cutting burr
 Typical finish 125-250 microns
 Smaller kerf size reduces material wastages
 No heat affected zone
 Localises structural changes
 No cutter induced metal contamination
 Eliminates thermal distortion
 No slag or cutting dross
 Precise, multi plane cutting of contours, shapes, and bevels of any angle.

Limitations of abrasive water jet cutting:-

 Cannot drill flat bottom
 Cannot cut materials that degrades quickly with moisture
 Surface finish degrades at higher cut speeds which are frequently used for
rough cutting.
 The major disadvantages of abrasive water jet cutting are high capital cost and
high
 noise levels during operation.

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WATER JET MACHINING (WJM)

INTRODUCTION
Abrasive water jet cutting is an extended version of water jet cutting; in which the
water jet contains abrasive particles such as silicon carbide or aluminium oxide in
order to increase the material removal rate above that of water jet machining. Almost
any type of material ranging from hard brittle materials such as ceramics, metals and
glass to extremely soft materials such as foam and rubbers can be cut by abrasive
water jet cutting. The narrow cutting stream and computer controlled movement
enables this process to produce parts accurately and efficiently. This machining
process is especially ideal for cutting materials that cannot be cut by laser or thermal
cut. Metallic, non- metallic and advanced composite materials of various thicknesses
can be cut by this process. This process is particularly suitable for heat sensitive
materials that cannot be machined by processes that produce heat while machining.
The schematic of abrasive water jet cutting is shown in Figure which is similar to
water jet cutting apart from some more features underneath the jewel; namely
abrasive, guard and mixing tube. In this process, high velocity water exiting the jewel
creates a vacuum which sucks abrasive from the abrasive line, which mixes with the
water in the mixing tube to form a high velocity beam of abrasives.

Figure: Abrasive water jet machining

Applications:-
Abrasive water jet cutting is highly used in aerospace, automotive and electronics

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AMP NOTES By:-DJ

industries. In aerospace industries, parts such as titanium bodies for military aircrafts,
engine components (aluminium, titanium, heat resistant alloys), aluminium body parts
and interior cabin parts are made using abrasive water jet cutting.
In automotive industries, parts like interior trim (head liners, trunk liners, door panels)
and fibre glass body components and bumpers are made by this process. Similarly, in
electronics industries, circuit boards and cable stripping are made by abrasive water
jet cutting.
Advantages of abrasive water jet cutting
 In most of the cases, no secondary finishing required
 No cutter induced distortion
 Low cutting forces on workpieces
 Limited tooling requirements
 Little to no cutting burr
 Typical finish 125-250 microns
 Smaller kerf size reduces material wastages
 No heat affected zone
 Localizes structural changes
 No cutter induced metal contamination
 Eliminates thermal distortion
 No slag or cutting dross
 Precise, multi plane cutting of contours, shapes, and bevels of any angle.

Limitations of abrasive water jet cutting

 Cannot drill flat bottom
 Cannot cut materials that degrades quickly with moisture
 Surface finish degrades at higher cut speeds which are frequently used for
rough cutting.
 The major disadvantages of abrasive water jet cutting are high capital cost
and high noise levels during operation.

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Abrasive Water Jet Machining (AWJM)

Introduction
Abrasive water jet machining (AWJM) is a mechanical material removal process used to
erode holes and cavities by the impact of abrasive particles of the slurry on hard and
brittle materials. Since the process is non- thermal, non-chemical and non-electrical it
creates no change in the metallurgical and physical properties of the work piece.
Abrasive Water Jet Machining is a non-traditional machining process, which makes use of
the principles of Abrasive Jet Machining (AJM) and Water Jet Machining (WJM).
The Abrasive Jet Machining process involves the application of a high-speed stream of
abrasive particles assisted by the pressurized air on to the work surface through a nozzle
of small diameter. Material removal takes place by abrading action of abrasive particles.
Water jet machining is an erosion process technique in which water under high pressure
and velocity precisely cuts through and grinds away minuscule amounts of material. The
addition of an abrasive substance greatly increases the ability to cut through harder
materials such as steel and titanium. Water jet Machining is a cold cutting process that
involves the removal of material without heat. This revolutionary technology is an
addition to non- traditional cutting processes like laser and plasma, and is able to cut
through virtually any material. The water jet process is combined with CNC to precisely
cut machine parts and etch designs.
Since water jet machining is done with abrasives, it is often synonymous with abrasive jet
cutting. The combination of compressor, plumbing and cutting heads accomplishes the
pressure and velocity to attain the cutting ability. High-pressure compressors create a jet
of water under extreme pressure that exceeds the speed of sound. This slim jet of water
produced from a small nozzle creates a clean cut. Before cutting, the materials are
carefully laid on top of slates over or submerged in the catch tank.
Abrasive water jet uses the technology of high-pressure water typically between 2069
and 4137 bar, to create extremely concentrated force to cut stuff. A water cutter
pressurizes a stream of pure water flow (without abrasive) to cut materials such as foam,
rubber, plastic, cloth, carpet and wood. Abrasive jet cutters mix abrasive garnet to a
pressurized water stream to cut harder materials. Examples are stainless steel, titanium,
glass, ceramic tile, marble and granite. Water jet metal cutting machine yields very little

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heat and therefore there is no Heat Affected Zone (HAZ). Water jet machining is also
considered as "cold cut" process and therefore is safe for cutting flammable materials
such as plastic and polymers. With a reasonable cutting speed setting, the edges resulting
are often satisfactory.
In Abrasive Water Jet Machining, the abrasive particles are mixed with water and forced
through the small nozzle at high pressure so that the abrasive slurry impinges on the
work surface at high velocity. Each of the two components of the jet, i.e., the water and
the abrasive materials have both separate purpose and a supportive purpose. The
primary purpose of the abrasive material in the jet stream is to provide the erosive
forces. The water in the jet acts as the coolant and carries both the abrasive materic' and
eroded material to clear of the work.

Working Principle of AWJM:-

• The cutter is commonly connected to a high pressure water pump where the water is then
ejected from the nozzle, cutting through the material by spraying it with the jet of high
speed water.
• Additives in the form of suspended grit or other abrasives, such as garnet and aluminum
oxide can assist in this process.

Elements of AWJM:-

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Setup of AWJM:-

Schematic Setup of AWJM:-

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ESSENTIALS OF THE PROCESS:-

A schematic diagram of abrasive water jet machining is shown in Figure It consists of:
• Compressor
• Air filter cum drier
• Relief valve
• Pressure gauge
• Opening valve
• Mixing chamber
• Nozzle holder
• Nozzle
• Work piece

The compressed air from the compressor enters the mixing chamber partly prefilled
with fine grain abrasive particles and chemical. The vortex motion of the air created in
the mixing chamber carnes the abrasive slurry to the nozzle through which it is
directed on to the work piece.

Basic Methodology:-
• Water is pumped at a sufficiently high pressure, 200-400 MPa
• “Intensifier” works on the principle of pressure amplification using hydraulic
cylinders of two different cross-sections.
• When water at such a pressure is passed through a suitable orifice (nozzle having  =
0.2 – 0.4 mm), the potential energy of water is converted into kinetic energy.
• This yields high velocity (~ 1000 m/s) jet of water.
• Such a high velocity water jet can machine thin sheets/foils of aluminium, leather,
textile, frozen foods, etc.
• commercially pure water (tap water) is used for machining.

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Injection & SuspensionHeads:-

Cutting Heads:-

Catcher:-

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Typical Parameters in Entrained AWJM:-

• Orifice – Sapphires – 0.1 to 0.3 mm
• Focussing Tube – WC – 0.8 to 2.4 mm
• Pressure – 2500 to 4000 bar
• Abrasive – garnet and olivine - 125 to 60 micron
• Abrasive flow rate - 0.1 to 1.0 kg/min
• Stand off distance – 1 to 2 mm
• Machine Impact Angle – 60o to 900
• Traverse Speed – 100 mm/min to 5 m/min
• Depth of Cut – 1 mm to 250 mm

Material Removal in AWJM:-

• Mechanism of material removal in WJM or AWJM is rather complex.
• In AWJ machining of ductile materials, material is mainly removed by low
angle impact of abrasive particles.
• Further at higher angle of impact, the material removal involves plastic
failure of the material at the sight of impact.
• In AWJ Machining of brittle materials, material would be removed due to
crack initiation and propagation because of brittle failure of the material.
• In water jet machining, the material removal rate may be assumed to be
proportional to the power of the water jet.

Advantages of AWJM:-
• Cut virtually any material. (pre hardened steel, mild steel, copper, brass, aluminum;
brittle materials like glass, ceramic, quartz, stone)
• Cut thin stuff, or thick stuff.
• Make all sorts of shapes with only one tool.
• No heat generated.
• Leaves a smooth finish, thus reducing secondary operations.
• Modern systems are now very easy to learn and safe.
• Unlike machining or grinding, waterjet cutting does not produce any dust or particles
that are harmful if inhaled.
• Waterjet cutting can be easily used to produce prototype parts very efficiently

Disadvantages of AWJM:-
• One of the main disadvantages of abrasive waterjet cutting is that a limited number of
materials can be cut economically. While it is possible to cut tool steels, and other hard
materials, the cutting rate has to be greatly reduced, and the time to cut a part can be very
long. Because of this, waterjet cutting can be very costly.
• Another disadvantage is that very thick parts can not be cut with waterjet cutting and still
hold dimensional accuracy. If the part is too thick, the jet may dissipate.
Practical Applications:-
• Edge finishing
• Radiusing
• De-burring
• Polishing
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Applications of AWJM:-
• Paint removal
• Cleaning
• Cutting soft materials
• Cutting frozen meat
• Textile, Leather industry
• Peening
• Pocket Milling
• Drilling & Turning
• Nuclear Plant Dismantling

Summary:-
• Only abrasives and water is used in AWJM
• In AWJM no heat generate during machining
• It has faster cutting rates, longer component life and tighter tolerances will be
achievable
• AWJM that embrace simplicity and have a small environmental impact
• AWJM is have more advantage than other modern machining process

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ELECTROCHEMICAL MACHINING (ECM)

INTRODUCTION
Electrochemical machining (ECM) is a metal-removal process based on the principle
of reverse electroplating. In this process, particles travel from the anodic material
(workpiece) toward the cathodic material (machining tool). A current of electrolyte
fluid carries away the deplated material before it has a chance to reach the machining
tool. The cavity produced is the female mating image of the tool shape.

ECM process

Similar to EDM, the workpiece hardness is not a factor, making ECM suitable for
machining difficult-to –machine materials. Difficult shapes can be made by this
process on materials regardless of their hardness. A schematic representation of ECM
process is shown in Figure 8. The ECM tool is positioned very close to the workpiece
and a low voltage, high amperage DC current is passed between the workpiece and
electrode. Some of the shapes made by ECM process is shown in Figure.
Material removal rate, MRR, in electrochemical

machining

MRR = C .I. h (cm3/min)

C: specific (material) removal rate (e.g., 0.2052 cm3/amp-min for

nickel); I: current (amp);

h: current efficiency (90–100%).

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The rates at which metal can electrochemically remove are in proportion to the current
passed through the electrolyte and the elapsed time for that operation. Many factors
other than current influence the rate of machining. These involve electrolyte type, rate
of electrolyte flow, and some other process conditions.

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.

Material removal rate, MRR, in electrochemical

machining: MRR = C .I. h (cm3/min)

C: specific (material) removal rate (e.g., 0.2052 cm3/amp-min for

nickel); I: current (amp);

h: current efficiency (90–100%).

The rates at which metal can electrochemically remove are in proportion to the current
passed through the electrolyte and the elapsed time for that operation. Many factors
other than current influence the rate of machining. These involve electrolyte type, rate
of electrolyte flow, and some other process conditions.

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voltage, high amperage DC current is passed between the workpiece and electrode.
Some of the shapes made by ECM process is shown in Figure.
Material removal rate, MRR, in electrochemical

machining: MRR = C .I. h (cm3/min)

C: specific (material) removal rate (e.g., 0.2052 cm3/amp-min for

nickel); I: current (amp);

h: current efficiency (90–100%).

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ELECTRICAL DISCHARGE MACHINING (EDM)

INTRODUCTION

Electrical discharge machining (EDM) is one of the most widely used non-traditional
machining processes. The main attraction of EDM over traditional machining
processes such as metal cutting using different tools and grinding is that this technique
utilises thermoelectric process to erode undesired materials from the workpiece by a
series of discrete electrical sparks between the workpiece and the electrode.
The traditional machining processes rely on harder tool or abrasive material to remove
the softer material whereas non-traditional machining processes such as EDM uses
electrical spark or thermal energy to erode unwanted material in order to create
desired shape. So, the hardness of the material is no longer a dominating factor for
EDM process. A schematic of an EDM process is shown in Figure 2, where the tool
and the workpiece are immersed in a dielectric fluid.

Working principle of EDM:-

As shown in Figure 1, at the beginning of EDM operation, a high voltage is applied
across the narrow gap between the electrode and the workpiece. This high voltage
induces an electric field in the insulating dielectric that is present in narrow gap
between electrode and workpiece. This cause conducting particles suspended in the
dielectric to concentrate at the points of strongest electrical field. When the potential
difference between the electrode and the workpiece is sufficiently high, the dielectric
breaks down and a transient spark discharges through the dielectric fluid, removing
small amount of material from the workpiece surface. The volume of the material
removed per spark discharge is typically in the range of 10-6 to 10-6 mm3.
The material removal rate, MRR, in EDM is calculated by the following foumula:

MRR = 40 I / Tm 1.23 (cm3/min)

Where, I is the current amp,

Tm is the melting temperature of workpiece in 0C

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Figure: Schematic of EDM process

EDM removes material by discharging an electrical current, normally stored in a capacitor

bank, across a small gap between the tool (cathode) and the workpiece (anode) typically in
the order of 50 volts/10amps.

Dielectric fluids

Dielectric fluids used in EDM process are hydrocarbon oils, kerosene and deionised
water. The functions of the dielectric fluid are to:
 Act as an insulator between the tool and the workpiece.
 Act as coolant.
 Act as a flushing medium for the removal of the chips.

The electrodes for EDM process usually are made of graphite, brass, copper and
copper- tungsten alloys.
Design considerations for EDM process are as follows:
 Deep slots and narrow openings should be avoided.
 The surface smoothness value should not be specified too fine.
 Rough cut should be done by other machining process. Only finishing
operation should be done in this process as MRR for this process is low.

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Wire EDM

EDM, primarily, exists commercially in the form of die-sinking machines and wire-
cutting machines (Wire EDM). The concept of wire EDM is shown in Figure 4. In
this process, a slowly moving wire travels along a prescribed path and removes
material from the workpiece. Wire EDM uses electro-thermal mechanisms to cut
electrically conductive materials. The material is removed by a series of discrete
discharges between the wire electrode and the workpiece in the presence of dielectric
fluid, which creates a path for each discharge as the fluid becomes ionized in the gap.
The area where discharge takes place is heated to extremely high temperature, so that
the surface is melted and removed. The removed particles are flushed away by the
flowing dielectric fluids.
The wire EDM process can cut intricate components for the electric and aerospace
industries. This non-traditional machining process is widely used to pattern tool steel
for die manufacturing.
The wires for wire EDM is made of brass, copper, tungsten, molybdenum. Zinc or
brass coated wires are also used extensively in this process. The wire used in this
process should posses high tensile strength and good electrical conductivity. Wire
EDM can also employ to cut cylindrical objects with high precision. The sparked
eroded extrusion dies are presented in Figure.

This process is usually used in conjunction with CNC and will only work when a part
is to be cut completely through. The melting temperature of the parts to be machined
is an important parameter for this process rather than strength or hardness. The
surface quality and MRR of the machined surface by wire EDM will depend on
different machining parameters such as applied peak current, and wire materials.

Application of EDM:-
The EDM process has the ability to machine hard, difficult-to-machine materials.
Parts with complex, precise and irregular shapes for forging, press tools, extrusion
dies, difficult internal shapes for aerospace and medical applications can be made by
EDM process

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Advantages of EDM

The main advantages of EDM are:-

 By this process, materials of any hardness can be machined;
 No burrs are left in machined surface;
 One of the main advantages of this process is that thin and fragile/brittle
components can be machined without distortion;
 Complex internal shapes can be machined

Limitations of EDM

The main limitations of this process are:-

 This process can only be employed in electrically conductive materials;
 Material removal rate is low and the process overall is slow compared to
conventional machining processes;
 Unwanted erosion and over cutting of material can occur;
 Rough surface finish when at high rates of material removal.

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Laser Beam Machining

Introduction
Laser Beam Machining is a thermal machining process which uses laser beam to produce heat
and remove material from workpiece.
In this machining, metal is removed from workpiece by melting and vapourizing of metal
particles in a controlled from its surface using heat from laser. Laser Beam machining is
widely used in cutting sheet and drilling holes. It is a non-conventional machining process in
which tools are used. Laser machining is mostly used in cutting and drilling operations. Both
metallic and non-metallic workpiece can be machined using this machining process.

Principle Working:-
The full form of LASER is Light Amplification by Stimulated Emission of Radiation.
When electrons of an atom are provided an external energy source, they absorbs energy from
the external source. By absorbing the energy these electrons jump from their original energy
level to higher energy level.
But this is not stable condition of atoms, so this electron emits absorbed energy in the form of
photons of light and come back to its original state. This emission of photons by electrons is
called spontaneous emission.
The atom will emit double energy if it is already at higher energy level and it again absorbs
energy. The energy emitted by atom will have same frequency and wavelengths as that of
stimulating source. This is the fundamental principle on which laser works.
When a laser material is placed under some energy source, it absrobs energy to some extent
and release it when it reaches its absorbing limit. Thus the highly amplified light produced is
called laser.
Laser machining process works on the basic principle of laser. In this machining process, a
laser beam is used which is a monochromatic high intense light which can cut any metal and
non-metal.
Laser machining can be used to cut and remove material from even the hardest material
present which is diamond.

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Equipments and Main Parts :-

These are the main equipments that used in laser beam machining:-
1) Power Supply :-
The power supply is used in laser beam machining to provide energy for the excitation of
electron from lower energy level to higher energy level.
2) Laser Discharge Tube :-
Laser material is filled in laser discharge tube. The excitation of electron and coming
back to its original state takes place inside this laser discharge tube. One side of discharge
tube is partially transparent and other side is 100% reflected. It is situated between the
xenon lamps.

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3) Laser Material:-
There are many kinds of laser materials available but in laser machining mostly CO2 and
nd:YAG is used. Carbon dioxide is a laser material which emits light in infrared region.
Carbon dioxide can provide power upto 25 KW power in continuous wave mode.
bd:YAG is a solid state laser which can deliver light through optical fiber. In pulse mode
it can produce upto 50 kW power and in continuous mode it can produce power upto 1
KW. Focusing lens :Focusing lens is used to focus the light at the workpiece. It is a
convex lens.

Working of laser beam machining:-

The steps involved in laser beam machining:-
At first laser material co2 or other laser material is filled into discharge tube. After that the
power supply is switched on which is used to light up the flash lamp. The light from flash
lamp is used to excite the electrons of atom.
Then the atoms of laser material absorbs energy from the light energy produced by flash lamp.
Due to absorption of energy, the electron of atom jump from lower energy level to higher
energy level. But this is unstable condition of atom.
When the atom reaches its absorption limit, it starts emitting energy continuously. This energy
is emitted in the form of highly amplified same frequency and same wavelength coherent
light.
This laser light released by atom is collected in the convex lens and is directed towards the
workpiece.
As the laser falls on workpiece, it starts the machining process by melting or vapourising
material from contact surface of workpiece.

Advantages:
1 It can be used to cut aby material.
2) No tool cost because no physicla tool is required and hence no cost for mantenance and
replacement of tools.
3) No delamination is caused as there is no physical contact with the workpiece.
4) It can be easily automated and is very flexible.
5) Complex shapes of different sizes can be machined as laser can be moved in any path.
6) It gives very good surface finish.
7) Micro holes can be drilled in workpiece with high accuracy.

Disadvantages:-
1. The initial cost of acquiring a laser beam is moderately high. There are many accessories
that aid in the machining process, and as most of these accessories are as important as the
laser beam itself the startup cost of machining is raised further.
2. Handling and maintaining the machining requires highly trained individuals. Operating the
laser beam is comparatively technical, and services from an expert may be required.
3. Laser beams are not designed to produce mass metal processes.
4. Laser beam machining consumes a lot of energy.
5. Deep cuts and blind hole are difficult with workpieces with high melting points and usually
cause a taper.

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Plasma Arc Machining (PAM)

Introduction
Plasma Arc Machining is used to remove material from the workpiece. In this process, a high
velocity jet of high-temperature gas is used to melt and remove material from the workpiece.
This high velocity of hot gas is also known as plasma jet.
When a gas or air is heated at a temperature of more than 5000 °C, then it will start getting
ionized into positive ions, negative ions and neutral ions. When the gas or air is ionized its
temperature reaches from 11000 °C to 28000 °C and this ionized gas is called plasma.
The gas or air is heated with arc and the plasma produced by heating gas is used to remove
material from the workpiece. So the whole process is called Plasma Arc Machining.
In this process, a high velocity of high temperature air is used to remove material from the
workpiece by melting it.
The gas used in plasma arc machining is chosen according to the metal which is used as the
workpiece.
The plasma arc machining is used for cutting alloys steels, stainless steel, aluminum, nickel,
copper and cast iron.

Plasma
When a gas or air heated at high temperatures, the number of collisions between atoms
increases. When you heat the gas above 5500ºC, it partially ionises into positive ions, negative
ions and neutral ions. When you further heat the gas above 11000ºC then, it completely
ionises. Such a completely ionised gas is called Plasma. Plasma State lies in between
temperatures 11,000ºC to 28,000ºC.

Working principle of Plasma Arc Machining

PAC system uses DC power source. PAC systems operate either on nontransferred arc mode
or transferred arc mode (Fig.(i) (ii) In the earlier case, the thermal efficiency is low (65-75%)
and power is transferred between the electrode and the nozzle. This non-transferred arc
ionizes a high velocity gas that is streaming towards the workpiece. The workpiece may be
electrically conductive or non-conductive.

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AMP NOTES By:-DJ

In case of a transferred arc mode, the arc is maintained between the electrode (negative
polarity) and the electrically conductive workpiece (positive polarity). Note that only
electrically conductive workpiece can be machined or cut by transferred arc system. The arc
heats a coaxial-flowing gas and maintains it in a plasma state. The electrothermal efficiency is
up to 85-90%. PAC system can deliver up to 1000 A at about 200 V (DC). The flowing gas
pressure may be up to 1.4 MPa resulting in a plasma velocity of several hundred
metres/second. Higher the gas flow rate, more will be momentum of the plasma jet. It will
ease out removal of the molten material from the machining zone. The plasma jet is
constricted by the flowing gas which acts as a cooling agent sandwiched between the nozzle
wall and the plasma jet.

Components of Plasma Arc Machining:

1 Plasma Gun:-
Different gases like nitrogen, hydrogen, argon or mixture of these gases are used to create
plasma. This plasma gun has a chamber which has a tungsten electrode. This tungsten
electrode is connected to the negative terminal and nozzle of the plasma gun is connected to
the positive terminal of the DC power supply. The required mixture of gas is supplied to the
gun. A strong arc is produced between the anode and the cathode.
After that, there is a collision between the electron of the arc and the molecules of the gas and
due to this collision, gas molecules get ionized and heat is generated.
2 Power Supply:-
DC Power Supply is used to develop two terminals in the plasma gun. Heavy potential
difference is applied across cathode and anode so that arc produced is strong and is able to
ionize the gas mixture and convert it into plasma.
3 Cooling Mechanism:-
A cooling mechanism is added to the plasma gun as heat is produced in it as hot gases
continuously pass out from the nozzle.
A water jacket is used to cool the nozzle. The nozzle is surrounded by water jet.
4 Workpiece:-
Different materials can be worked using this plasma arc machining. Different metals like
aluminum, magnesium, carbon, stainless steel and alloy steels can be worked using this
process.

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Construction of Plasma Arc Machining:-

The plasma arc cutting torch carries a tungsten electrode fitted in the chamber. This tungsten
electrode is connected to the negative terminal of the DC power supply. For plasma arc
machining, a plasma gun is required. This plasma gun has a chamber. This plasma gun has a
tungsten electrode fitted inside the chamber. This tungsten electrode is connected to the
negative terminal of DC Power Supply and acts as a cathode.
At the bottom of the chamber, there is a copper nozzle that is connected to a positive terminal
of the DC Power Supply and acts as an anode. The rest of the chamber is made of insulating
material and acts as an insulator. Gas enters the chamber through a small passage present at
the right side of the chamber. The cathode and the anode remain cool despite the hot gases
passing through them as they are water cooled. Water circulation is present around the torch.

Working:-
At first, when a D.C power is supplied to the circuit, a strong arc is produced between the
cathode ( electrode ) and the anode (nozzle). After that, gas is supplied to the chamber. This
gas can be hydrogen, nitrogen, argon or mixture of these gases chosen according to the metal
to be worked. The gas used in the process is heated using the arc produced between the
cathode and the anode. This gas is heated to very high temperatures from 11000 °C to 28000
°C.
As the arc comes into contact with the gas, there is a collision between the electron of the arc
and the molecules of the gas and the molecules of the gas will dissociate into separate atoms.
Due to the high high temperature generated from the arc, electrons from some atoms will be
displaced and atoms are ionized ( electrically charged ) and the gas turns into plasma. As the
gas is ionized, a large amount of thermal energy is liberated.
After the gas is ionized, this high temperature ionized gas is directed towards the workpiece
with high velocity. The electric arc has some other benefits like it increases the temperature of
ionized gas, makes the beam almost parallel, and increases the velocity of the gas. As the
plasma jet reaches the workpiece, the plasma melts the workpiece and the high-velocity gas
blows away the molten metal. In this way, plasm arc machining is used to remove material
from the workpiece.

Following are some of the parameters involved in PAM that you must consider
are:
• Current: Up to 1000A
• Voltage: 30-250V
• Cutting speed: 0.1-7.5 m/min.
• Plate thickness: Up to 200mm
• Power require: 2 to 200 KW
• Material removal rate: 150 cm3 /min
• Velocity of Plasma: 500m/sec
• Material of workpiece: As previously stated, you can use any metal as material of
workpiece. For instance, aluminium and stainless steel are highly recommended for
this process.

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Advantages:-
1) Hard as well as brittle metals can be easily machined with this process.
2) Plasma Arc Machining gives a faster production rate.
3) Small cavities can be machined using this process with good dimensional accuracy.
4) It can be used for rough turning of very hard materials.
5) It is also used in machines that are used to repair jet engine blades.
Disadvantages:-
1) The equipment used in Plasma Arc Machining are very costly.
2) Metallurgical changes take place on the surface of the workpiece.
3) The consumption of inert gas is high.
4) As oxidation and scale formation takes place, shielding is required
Applications of PAM:-
1) It is used in mill applications.
2) It is also used in the nuclear submarine pipe system.
3) Used in welding rocket motor case.
4) Used in welding of stainless steel tubes.
5) It is used for profile cutting.

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CHEMICAL MACHINING (CHM)

INTRODUCTION
Chemical machining (CM) is the controlled dissolution of workpiece material
(etching) by means of a strong chemical reagent (etchant). In CM material is removed
from selected areas of workpiece by immersing it in a chemical reagents or etchants;
such as acids and alkaline solutions. Material is removed by microscopic
electrochemical cell action, as occurs in corrosion or chemical dissolution of a metal.
This controlled chemical dissolution will simultaneously etch all exposed surfaces
even though the penetration rates of the material removal may be only 0.0025–0.1
mm/min. The basic process takes many forms: chemical milling of pockets, contours,
overall metal removal, chemical blanking for etching through thin sheets;
photochemical machining (pcm) for etching by using of photosensitive resists in
microelectronics; chemical or electrochemical polishing where weak chemical
reagents are used (sometimes with remote electric assist) for polishing or deburring
and chemical jet machining where a single chemically active jet is used. A schematic
of chemical machining process is shown in Figure.

(a)Schematic of chemical machining process

(b) Stages in producing a profiled cavity by chemical machining (Kalpakjain &
Schmid)

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CHEMICAL MILLING:-
In chemical milling, shallow cavities are produced on plates, sheets, forgings and
extrusions. The two key materials used in chemical milling process are etchant and
maskant. Etchants are acid or alkaline solutions maintained within controlled ranges
of chemical composition and temperature. Maskants are specially designed
elastomeric products that are hand strippable and chemically resistant to the harsh
etchants.

Steps in chemical milling:-

 Residual stress relieving: If the part to be machined has residual stresses from
the previous processing, these stresses first should be relieved in order to
prevent warping after chemical milling.
 Preparing: The surfaces are degreased and cleaned thoroughly to ensure both
good adhesion of the masking material and the uniform material removal.
 Masking: Masking material is applied (coating or protecting areas not to be
etched).
 Etching: The exposed surfaces are machined chemically with etchants.
 Demasking: After machining, the parts should be washed thoroughly to
prevent further reactions with or exposure to any etchant residues. Then the
rest of the masking material is removed and the part is cleaned and inspected.

Applications:
Chemical milling is used in the aerospace industry to remove shallow layers of
material from large aircraft components missile skin panels (Figure ), extruded parts
for airframes.

Figure : Missile skin-panel section contoured by chemical milling to improve

the stiffness- to- weight ratio of the part (Kalpakjain & Schmid)
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AMP NOTES By:-DJ

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