Thermal Removal Processes (Overview)

Non Conventional Machining
Thermal Metal Removal Processes

Contents
 Introduction
 Overview
 Basic description
 EDM
 EBM
 IBM
 PAM
 LBM

What is thermal process ?
 Thermal energy usually
applied to small portion
of work surface, causing
that portion to be
removed by fusion
and/or vaporization.

Thermal Energy Processes - Overview
 Very high local temperatures
 Material is removed by fusion or vaporization
 Physical and metallurgical damage to the
new work surface
 In some cases, resulting finish is so poor that
subsequent processing is required

Thermal Energy Processes
•Electric discharge machining (EDM)
•Electron beam machining(EBM)
•Laser beam machining(LBM)
•Plasma arc machining(PAM)
•Ion beam machining (IBM)

Electrical Discharge Machining (EDM)
 Required electrically conductive materials.
 Work piece – anode and tool cathode. Independent of material
hardness.
 Removal of material through melting or vaporisation caused by a
high frequency spark discharge.
 EDM machined surface may be deleterious to fatigue properties
due to the recast layer.
 good selection of the proper electrode material for the work
piece Produce deep holes, slots cavities in hard materials
without drifting or can do irregular contour.

Electric Discharge Processes
 Metal removal by a series of discrete electrical discharges
(sparks) causing localized temperatures high enough to melt
or vaporize the metal
 Can be used only on electrically conducting work materials
 Two main processes:
 1. Electric discharge machining
 2. Wire electric discharge machining
 Since spark discharges occur in EDM, it is also
called as "spark machining".

EDM Operation
 One of the most widely used non traditional
processes
 Shape of finished work surface produced by a formed
electrode tool
 Sparks occur across a small gap between tool and
work
 Requires dielectric fluid, which creates a path for
Each discharge as fluid becomes ionized in the gap

Work Materials in EDM
 Only electrically conducting work materials
 Hardness and strength of the work material
are not factors in EDM
 Material removal rate is related to melting
point of work material

Advantages of EDM
The major advantages of the process are:
 Any materials that are electrically conductive can be
machined by EDM.
 Materials, regardless of their hardness, strength,
toughness and microstructure can be easily machined /
cut by EDM process
 The tool (electrode) and workpiece are free from cutting
forces
 Edge machining and sharp corners are possible in EDM
process

 The process produces good surface finish, accuracy
and repeatability.
Hardened work-pieces can also be machined since
the deformation caused by it does not affect the final
dimensions.
EDM is a burr free process.
Hard die materials with complicated shapes can be
easily finished with good surface finish and accuracy
through EDM process.
Due to the presence of dielectric fluid, there is very
little heating of the bulk material.

Limitations of EDM
 Material removal rates are low, making the process
economical only for very hard and difficult to machine
materials.
 Re-cast layers and micro cracks are inherent features of
the EDM process, thereby making the surface quality
poor.
 The EDM process is not suitable for non-conductors.
 Rapid electrode wear makes the process more costly.
 The surfaces produced by EDM generally have a matt
type appearance, requiring further polishing to attain a

EDM Applications
 Tooling for many mechanical processes:
 Molds for plastic injection moulding, extrusion dies,
wire drawing dies, forging and heading dies, and
sheet metal stamping dies
 Production parts: delicate parts not rigid enough to
withstand conventional cutting forces, hole drilling
where hole axis is at an acute angle to surface, and
 Machining of hard and exotic metals

Applications of EDM
 The process is widely used for machining of exotic
materials that are used in aerospace and automatic
industries.
 EDM being a non-contact type of machining process, it is
very well suited for making fragile parts which cannot take
the stress of machining. The parts that fit such profiles
include washing machine agitators; electronic components,
printer parts and difficult to machine features such as the
honeycomb shapes.
 Deep cavities, slots and ribs can be easily made by EDM
as the cutting forces are less and longer electrodes can be
used to make such collets, jet engine blade slots, mould
cooling slots etc.

Electron Beam Machining (EBM)
 Electron beam machining (EBM) has been used in
industry since the 1960s, initially in nuclear and aerospace
welding applications.
 Uses high velocity stream of electrons focused on
workpiece surface to remove material by melting and
vaporization
 Drilling small holes, cutting, engraving, and heat
treatment are a set of modern applications used in
semiconductor manufacturing as well as micromachining

EBM Operation
1.EB gun accelerates a continuous stream of electrons
to about 75% of light speed
2.Beam is focused through electromagnetic lens,
reducing diameter to as small as 0.025 mm (0.001 in)
3.On impinging work surface, kinetic energy of electrons
is converted to thermal energy of extremely
4. high density which melts or vaporizes material in a
very localized area

Parameters affecting EBM performance

EBM Applications:
1.Works on any known material
2. Ideal for micromachining Drilling small diameter holes - down to
0.05 mm(0.002 in)
3. Cutting slots only about 0.025 mm (0.001 in.)
4. Wide Drilling holes with very high depth-to-diameter ratios
greater than 100:1
5. EBM perforation can be applied to the production of filters and
masks of color television tubes. Other applications for perforation
lie in sieve manufacture, for sound insulation and in glass fiber
production.

Advantages :
1. Drilling is possible at high rates (up to 4000 holes per second).
2. No difficulty is encountered with acute angles.
3. Drilling parameters can easily be changed during machining.
4. No limitation is imposed by workpiece hardness, ductility, and
surface reflectivity.
5. No mechanical distortion occurs to the workpiece since there is no
contact
6. The process is capable of achieving high accuracy and repeatability
of 0.1 mm for position of holes and 5 percent for the hole diameter.
7. The process produces the best surface finish compared to other
processes.

Disadvantages:
1. High capital equipment cost
2. Long production time due to the time needed to
generate a vacuum
3. The presence of a thin recast layer
4. Need for auxiliary backing material

Ion Beam machining (IBM)
Definition =ion beam machining is an important
nonconventional manufacturing technology used in
Micro/Nanofabrication, using a stream of accelerated ions to
remove the atoms on the surface of the object.Ion beam
machining (IBM) takes place in a vacuum chamber using charged
ions fired from an ion source toward the work piece by means of
an accelerating voltage. The mechanism of material removal in
IBM differs from that of EBM. It is closely related to the ejection of
atoms, from the surface, by other ionized atoms (ions) that
bombard the work material. The process is, therefore, called ion
etching, ion milling, or ion polishing.

Working and Principle :
2.The machining system has an ion source that produces a
sufficiently intense beam, with an acceptable spread in its energy for
the removal of atoms from the workpiece surface by impingement of
ions. 3. A
heated tungsten filament acts as the cathode, from which electrons
are accelerated by means of high voltage (1 kV) toward the anode.
1.The beam removes atoms from the workpiece by transferring
energy and momentum to atoms on the surface of the object. When
an atom strikes a cluster of atoms on the workpiece, it dislodges
between 0.1 and 10 atoms from the workpiece material.

6.A magnetic field is produced between the cathode and anode that
makes the electrons spiral.
7.The path length of the electrons is, therefore, increased through
the argon gas, which, in turn, increases the ionization process.
8. The produced ions are then extracted from the plasma toward the
workpiece, which is mounted on a water-cooled table having a tilting
angle of 0° to 80°.
9. Machining variables such as acceleration voltage, flux, and angle
of incidence are independently controlled.
4. During the passage of these electrons from the cathode towards
the anode, they interact with argon atoms in the plasma source, to
produce argon ions.
5.Reaction takes place is Ar + e− →Ar+ + 2e

Applications of IBM :
1.IBM is used in smoothing of laser mirrors as well as reducing
the thickness of thin films without affecting their surface finish.
2. Using two opposing beams, a thin circular region on a rotating
sample can produce samples for transmission electron microscopy.
3. Polishing and shaping of optical surfaces by direct sputtering of
pre- forms in glass, silica, and diamond is performed using
patterning masks.
4. The process can produce closely packed textured cones in
different materials including copper, nickel, stainless steel, silver.
5.Atomically clean surfaces can be produced by IBM that are used
in the adhesion of gold films to silicon and aluminum oxide

Advantages of IBM :
1.the ibm is used as a micro- and nano-machining tool, to modify
or machine materials at the micro- and nanoscale.
2.Ibm tools are designed to etch or machine surfaces, an ideal
FIB might machine away one atom layer without any disruption of
the atoms in the next layer, or any residual disruptions above the
surface.
3.The ibm is also commonly used to prepare samples for the
transmission electron microscope.
4. ibm is also used for maskless implantation
5.Other techniques, such as ion millingor electropolishing can be
used to prepare such thin samples.

Disadvantages of IBM :
1. High capital equipment cost
2. Long production time due to the time
needed to generate a vacuum
3. The presence of a thin recast layer
4. Need for auxiliary backing material

Laser Beam Machining (LBM)
 technology that uses a laser beam (narrow beam of
intense monochromatic light)
 to cut required shapes or profile or pattern in almost
all types of materials.
 The high amount of heat thus generated either melts,
burns, or vaporizes away the material at the focused
region.
 The process can be used to make precise holes in
thin sheets and materials.

Principle of Laser
The word laser is an acronym for Light
Amplification by the Stimulated Emission
of
Radiation. When an atom absorbs a
quantum of energy from a light source,
the orbital
electron of an atom jumps to a higher
energy level. The electron later drops to
its original
orbit and emits the absorbed energy. If
the electron, which is already at high
energy level,
absorbs the second quantum of energy, it

Mechanism of Material Removal / Cutting :
 Place the workpiece on the table. As there is absence of cutting forces, fewer
work holding devices are needed.
 The focal point of the laser is intentionally focused onto the surface of the
workpiece for providing the heat in a concentric manner.
 Due to the striking of laser beam, heat is generated at the work-piece surface
and as a result, the material vaporizes instantly, producing kerf in the material.
 The movement of machine-axis is through the computer control which helps
to achieve the required profiles on the workpiece. Heat Affected Zone (HAZ) is
minimal in laser as compared to flame cutting.
 To clear the molten metal that has yet not vaporized or clogged on the surface
of the workpiece, the assist gas, (inert gas or exothermic gas is used for this
propose) under pressure is passed on-to the workpiece. The use of different
assist gases with different work materials

Advantages:
 The ability to cut almost all materials
 No limit to cutting paths as the laser point can move in any paths.
 No cutting lubricants are required
 As there is an absence of direct contact between the tool and
workpiece; thus no
forces are induced and as a result it is not necessary to provide the
work holding system to hold the workpiece.
 The fragile materials are easy to cut on a laser without any support.
 Flexibility exists in precision cutting of simple or complex parts.
 There is no tooling cost or associated wear costs due to it.
 Laser produces high quality cuts without extra finishing requirements

Disadvantages:
 Laser processes involve high capital investments and high operating
costs.
 Laser holes are tapered to some extent (approximately 1% of the
drill depth)
 It cannot drill blind holes to precise depths. Hence there is limitation
on its thickness.
 Heat affected through the lasers may change the mechanical
properties of the metallic materials and alloys
 The processing time in larger holes is slower due to trepanning
action (process) involved in it.
 Reflected laser lights can lead to safety hazards.
 Assist or cover gases are required for safety purposes.

Applications:
 One of the problems associated with the conventional approach
in cutting of tough materials such as titanium alloy is that, at
high cutting speeds the life of the cutting tool is very short. As
the titanium alloys are used extensively in the aerospace
industry, there is a tremendous interest and curiosity for
developing this technique especially for enabling higher cutting
rates.
 Laser machining is used for making very accurate sized holes as
small as 5 microns in metals, ceramics and composites without
warpages.
 It is widely used for fine and accurate drilling and cutting of
metallic and non-metallic materials.
 Electronic and automotive industries also find extensive
applications for laser beam machining.

LBM Applications
 Drilling, slitting, slotting, scribing, and
marking operations
 Drilling small diameter holes - down to 0.025
mm
(0.001 in)
 Generally used on thin stock
 Work materials: metals with high hardness
and
strength, soft metals, ceramics, glass and glass
epoxy, plastics, rubber, cloth, and wood

Plasma Arc Cutting (PAC)
 Uses a plasma stream operating at very
high temperatures to cut metal by melting
 It is an arc cutting process wherein the
severing of the metal is obtained by
melting a localized area with a constricted
arc and removing the molten material with
a high velocity jet of hot, ionized gas
issuing from the orifice.

GASES:
 The gases that are used in plasma-arc
cutting:
1. Nitrogen
2. Nitrogen + hydrogen
3. Nitrogen + argon
4. Compressed air

1.Working Principle of PAM
 In this process gases are
heated and charged to
plasma state. Plasma state
is the superheated and
electrically ionized gases at
approximately 5000C⁰
These gases are directed
on the work piece in the
form of high velocity stream.
Working principle and
process details are shown in
Figure 5.

Operation of PAC
 •Plasma = a superheated, electrically ionized
gas
 •PAC temperatures: 10,000 C to 14,000 C
(18,000 F to 25,000 F)
 •Plasma arc generated between electrode in
torch and anode workpiece
 •The plasma flows through water-cooled nozzle
that constricts and directs stream to desired

Advantages
(i) It cuts carbon steel up to 10 times faster than
oxy-fuel cutting, with equal quality more
economically.
(ii) It leaves a narrower kerf.
(iii) Plasma cutting being primarily a melting
process can cut any metal.
(iv)Arc plasma torches give the highest
temperature available from many practicable
sources. The energy seems to be unlimited in

Disadvantages
(a) Its initial cost is very high.
(b) The process requires over safety precautions which further
enhance the initial cost of the setup.
(c) Some of the workpiece materials are very much prone to
metallurgical changes on excessive heating so this fact imposes
limitations to this process.
(d) It is uneconomical for bigger cavities to be machined.

Applications of PAM
The chief application of
this process is profile
cutting as controlling
movement of spray
focus point is easy in
case of PAM process.
This is also
recommended for
smaller machining of
difficult to machining
materials.

Applications of PAC
 •Most applications of PAC involve cutting of
flat metal sheets and plates
 •Hole piercing and cutting along a defined
path
 •Can be operated by hand-held torch or
automated by CNC
 •Can cut any electrically conductive metal
 •Most frequently cut metals: carbon steel,
stainless steel, aluminium

APPLICATION OF PLASMA ARC
1. Plasma cutting is used to cut particularly those nonferrous and
stainless metals that cannot be cut by the usual rapid oxidation
induced by ordinary flame torches.
2. Plasma cutting can be used for stack cutting, plate bevelling, and
shape cutting and piercing.
3. With some modifications, plasma arc cutting can be used under
water.
4. Plasma arc cutting finds applications in many industries such as
shipyard, chemical, nuclear and pressure vessel.
5. It is used for removing gates and risers in foundry.
6. It cuts hot extrusions to desired length.
7. It is used to cut any desired pipe contour.
8. It is also employed for gouging applications.
9. It finds use in the manufacture of automotive and railroad

VARIOUS TYPE OF PLASMA ARC CUTTING
 Air Plasma Arc Cutting
 Dual-flow Plasma Arc Cutting
 Underwater Plasma Arc Cutting

Thermal Removal Processes (Overview)

Thermal Removal Processes (Overview)

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