4/14/2021
Extensions and International Programs (EIP)
PRESENTATION TITLE
Advanced Manufacturing Engineering Certificate Program
Advanced Materials and Manufacturing Processes
Module 3: Advanced Machining Processes
Instructor: Sagil James, Ph.D.
Email: sagiljames@fullerton.edu
Contents
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Abrasive‐based Machining Processes
Advanced Mechanical Machining Processes
Thermal and Electrical Machining Processes
Electrochemical and Chemical Machining Processes
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Abrasive Jet Machining (AJM)
• Jet of inert gas consisting of very fine abrasive
particles strikes the workpiece at high velocity
– Usually between 200‐400 m/s
• Material removal through chipping/erosion action
• Used for cutting, cleaning, etching, polishing and
deburring
• Effective on hard and brittle materials such as glass,
silicon, ceramics
• Not effective on soft materials such as Aluminum,
Rubber
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AJM Machine Setup
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AJM Machine Setup
• Gas propulsion system supplies clean and dry gas to
propel the abrasive particles
– Air, Nitrogen or CO2
• Gas should be non‐toxic, cheap and easily available
• Spread of gas should be limited
• Compressor with air filter used for gas supply
5
Abrasive Feeder
• Required quantity of abrasive particles supplied by
abrasive feeder
• Abrasive quantity is controlled by vibration (electro‐
magnetic shaker)
• Particles propelled by carrier gas to a mixing
chamber
• Air‐abrasive mixture moves further to the nozzle
• Nozzle imparts high velocity to the mixture which is
directed at the workpiece surface
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Material Removal
• Material removal occurs due to the erosive action
of the jet of air‐abrasive mixture impinging on the
workpiece surface
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Machining Chamber
• Mixing chamber is well‐insulated from outside
environment
• Chamber is equipped with a vacuum dust collector
• Special consideration should be given if toxic
material is used
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AJM Nozzle
• Usually made of tungsten carbide or sapphire (usual
life = 300 hr)
• Nozzle material should have high wear resistance
• Nozzle is either made of circular or rectangular
cross‐section
• Nozzle design should minimize loss of pressure due
to bends and friction
• Nozzle pressure usually maintained between 2.8‐5
kgf/cm2 depending on material characteristics
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AJM Nozzle Contd..
• Wear of Nozzle causes divergence of jet steam
resulting in Stray Cutting and high inaccuracy
• Stray cutting can be controlled by using masks
made of soft material
• Masks should cover part of the workpiece where
machining is not desirable
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Abrasive Water Jet Machining (AWJM)
• Using abrasive water jets have
shown to improve the cutting
technology
• Compared to AJM, Water is used
as carrier fluid in place of gas
• Can be used for cutting, drilling,
cleaning of hard materials –
ceramics, composites, rocks,
metals
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AWJM Working Principle
• Water jet and abrasives are mixed and passed
through the nozzle
• Water jet momentum is transferred to abrasives
• High velocity mixture of abrasives and water
impinges on the workpiece
• Material removal occurs due to erosion, shear or
failure under rapidly changing localized stress fields
• Pressure of water jet is about 400 MPa
• Jet velocity is about 900 m/s
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Advantage of AWJM
• Can machine electrically non‐conductive as well as
difficult‐to‐machine materials
• Rapid and efficient machining compared to AJM
and WJM processes
• Dust‐free machining
• High cutting speed, multi‐directional cutting
capacity
• No fire hazard
• No thermal stresses
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Advantage of AWJM Contd..
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High quality of machined edge
Recycling of abrasive particles
Can be easily automated
Low power requirements
Almost no delamination
Reduced striations
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AWJM Machine
• AWJM Machine Setup consists of
– Pumping system
– Abrasive feed system
– Abrasive water jet nozzle
– Abrasive collector/recycling unit
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AWJM Setup
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Pumping System
• Pressurizes water to a pressure of more than 400 MPa
by means of an intensifier
• Use a high power motor (75 HP or more)
• Water flow rate up to 3 gpm
www.performancewat
erjet.com.au
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Abrasive Feed System
• Must deliver a controlled flow
of abrasive particles to jet
nozzle
• Delivers a stream of dry
abrasives
• Flow of water jet create
enough suction for flow of
abrasives
• Newer designs use liquid‐
mixed abrasives delivery
www.graco.com/
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Abrasive Water Jet Nozzle
• Mixes abrasive jet
and water
• Forms high velocity
water abrasive jet
• Made of sapphire,
tungsten carbine
(WC) or boron
carbide
multicam.ca
Nozzle Assembly for AWJM Process
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Abrasive Collector/Recycling Unit
• For capturing used
abrasive water jet
• Uses a water‐filled
settling tank
• Jet dies out in this
tank
• Abrasive particles are
filtered and
water/abrasive is
recycled
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Abrasives
• Selection of abrasives depends on the type of work
material, material removal rate and machining
accuracy desired
• Potential abrasive materials include
– Aluminum Oxide (Al2O3) ‐ for cleaning, cutting, deburring
– Silicon Carbide (SiC) – for harder work materials
– Glass Beads – for matte finishing
– Crushed Glass – for obtaining sharp edges
– Sodium Bicarbonate ‐ for soft work materials
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Abrasive Size
• Size of abrasives range from 10 to 50 μm
• Abrasives should have sharp and irregular shape
• Abrasives should be small enough to be suspended
in the carrier gas
• Small abrasives used for cleaning and polishing
– Small grains are less irregular
– Cutting ability is poor
• Large abrasives used for cutting
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Re‐use of Abrasives
• Re‐use of abrasives is not recommended
• Abrasives get contaminated with metallic chips
which may block the nozzle passage
• Cutting ability of the used abrasive particles
decreases
• Cost of abrasives is low
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Abrasive Machining ‐ Environmental
Concerns
• Issues include:
– Water pollution
– Spent water disposal
– Health hazards
– Soil Contamination
– Noise pollution
http://dotherightmix.eu/
• Loud operation can cause partial hearing loss
• Abrasive dust can cause irritation to the eyes, skin,
and respiratory tract
– Inhalation of abrasive dust can result in lung diseases
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Environmental Concerns Contd..
• Chip recovery
• Abrasive recovery and reuse
• Need for liquid medium and abrasive that do not
require disposal or recycling
– High pressure cryogenic jet machining
• Liquid water replaced by Liquid nitrogen
• Abrasives replaced by Dry‐ice (Solid CO2) crystals
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Mechanical Machining Processes
• In mechanical machining
processes, stresses induced by a
tool overcome the strength of the
workpiece material
• The process produces complex 3D
shapes, with very good
dimensional control, and good
surface finish
• The method is wasteful of material,
and expensive in terms of labor
and capital
Fig Source: www.krenterprise.co.in , www.youtube.com
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Challenges in Mechanical Machining
• Involves applied and
residual stress
• Residual stresses are
stresses that remain in a
solid material after the
original cause of the
stresses has been
removed
• May lead to lower fatigue
life
Fig Source: www.stresstech.com/
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Challenges in Mechanical Machining
Contd..
• Increased heat at the workpiece
causes uneven dimensional
changes in the part being
machined which is difficult to
control
• Thermal errors are often the dominant type of error
in a precision machine, and thermal characteristics
such as thermal expansion coefficient and thermal
conductivity deserve special attention removed
Fig Source: www.shapecut.com.au/
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Mechanical Machining Categories
• In mechanical subtractive machining, physical
removal of unwanted material is achieved by
mechanical energy applied at the work piece
– Mechanical energy‐based material removal
• Mechanical material removing can be categorized
as
– Single point machining
– Multi‐point machining (Abrasive machining)
• Mechanical removal processes can be broken down
into four commonly recognized categories: turning,
milling, drilling and grinding
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Advanced Mechanical Machining
• Processing overcoming the limitations of
conventional mechanical machining process
• Addresses the economy of mechanical machining
• Higher machining productivity
• Achieves higher surface finish
• Address the issue of environment effects of
mechanical machining process
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Advanced Mechanical Machining Contd..
• Numerous attempts done in the past to address the
issues of conventional mechanical machining
processes
• Several technologies still under development stage
• Some of the key focus areas include
– High‐speed Machining, High‐power machining
– Hard Machining
– Dry and Near‐Dry Machining
– Cryogenic Machining
– Precision Mechanical Machining
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High‐speed Machining (HSM)
• High speed machining typically refers to making
light passes at high spindle speeds and feed rates to
achieve a high metal removal rate
• In comparison with conventional machining, HSM
enables to increase efficiency, accuracy and quality
of workpieces and at the some time to decrease
costs and machining time
• Can be effective for machining intricate core and
cavity geometries in mold machining, and for
quickly machining large, complex aircraft structural
components out of solid blocks of aluminum.
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HSM Contd..
• Even though High Speed Machining is known for a
long time (first tries were made in early twenties of
the past century) there are still a lot of questions
and less or more complicated definitions of HSM
• The first definition of HSM was proposed by Carl
Salomon in 1931.
• He has assumed that at a certain cutting speed
which is 5 –10 times higher then in conventional
machining, the chip tool interface temperature will
start to decrease
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Hard Machining
• Hard machining is defined as the process of removing
material from workpieces that have hardness values
over 45 Rc
– Hard Turning
– Hard Milling
• Hard machining is best accomplished with tool inserts
made from either CBN (Cubic Boron Nitride), Cermet or
Ceramic
• The process is capable of producing contours and
generate complex forms with the inherent motion
capability of modern machine tools
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Hard Machining Contd..
• High quality hard machining applications do require
a properly configured machine tool and the
appropriate tooling
• Hard machining can certainly be considered for
most pre‐machining applications, which are
followed by an abbreviated machining cycle
• In some cases, the hard turned surface may
complete the operation and will completely
eliminate the conventional machining altogether.
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Hard Machining Capabilities
• A properly configured hard turning cell would
typically demonstrate the following:
– Surface finishes of 0.00011” (.003 mm)
– Roundness values of .000009” (.00025 mm)
– Size control ranges of .00020” (.005mm)
– Production rates of 4‐ 6 over comparable grinding
operations
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Materials for Hard Machining
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Steel alloys,
Bearing steels
Hot and cold work tool steels
High speed steels
Die Steels
Case hardened steels
Waspoloy, Stellite and other aerospace alloys
Nitrited irons and hard chrome coatings
Heat treatable powered metallurgy
Unique hard materials and aircraft types that fall within
the hardness range
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Benefits of Hard Machining
• Price
– Conventional machine tools can be adapted for hard
machining
• Versatility
– Multiple operations can be machined with one set‐up
• Metal Removal
– Achieve higher metal removal rates and surface finish
• Flexibility
– Changes are easier if the part configuration changes
• Environmental Benefits
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Dry and Near‐Dry Machining
• Environmentally‐friendly machining is the need of
hour for sustainable manufacturing
• Cutting fluids are employed in machining to reduce
friction, cool the tool and work piece and to wash
away the chips from cutting area
• Dry Machining concept is to eliminate or minimize
the cutting fluid consumption, use of cutting tools,
and power requirements
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Role of Cutting Fluid
• Cutting fluids minimizes the tool wear and improves
the surface integrity of machined surface
• Minimize the cutting forces thus decrease power
consumptions thereby saving precious energy
• Cutting fluids remove the extra heat from cutting
area generated in machining operation resulting in
only longer tool life along with achieving close
dimensional control
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Drawbacks of Cutting Fluids
• A large quantity of the cutting fluid is required
involving higher manufacturing cost that in some
cases is more than twice the tool‐related costs
• The cutting fluid/lubricant is not able find its way to
cutting area owing to obstruction from chips
• Cutting fluids pose serious health hazard to the
machine operator, and long time exposure of
operator to toxic coolants in machining sometimes
may result in serious ailments: asthma, skin
problems, respiratory irritation, pneumonia, skin
cancer, etc.
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Drawbacks of Cutting Fluids Contd..
• The disposal of the used cutting fluids also poses a
major challenge
• The waste cutting fluids pollute surface and
groundwater, can cause soil contamination, affect
agriculture produce, and lead to food contamination, if
not recycled properly
• The waste disposal of cutting fluid is required to be
treated
• Biocides and antimicrobials are utilized in cutting fluids
to keep their efficiency intact rather than protecting the
operators
• Elimination of cutting fluids in metal cutting practice
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Dry Machining
• Dry machining is always preferred in the era of
environment friendly machining, which involves higher
cutting forces, higher power
• Requires special cutting tools like PCBN, PCD and
ceramic, etc. along with prudent design of tool
geometry (generally negative rake tools, honed and
chamfered edges are used
• But Dry machining is not always feasible as there are
materials, which are sticky in nature like nickel‐
chromium and titanium base alloys and stainless steel,
etc., these materials when machined dry tend to stick
to tool surface leading to tool failure and poor surface
finish on machined surface
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Near‐Dry Machining (NDM)
• When a minimal amount of cutting fluid is used
during machining, it is referred as near dry
machining (NDM) with minimum quantity
lubrication (MQL)
• Also known as micro lubrication machining, or
‘micro‐lubrication’, and ‘micro‐dosing
• In MQL machining, a small amount of cutting fluid
(10–100 ml/h, compared to 30,000–60,000 ml/hour
in flooded machining) is directed onto the tool‐
workpiece interface with proper ratio of
compressed air
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Minimum Quantity Lubrication (MQL)
• MQL is a total‐loss lubrication method rather than
the circulated lubrication method used with
emulsions
• The extreme reduction of lubrication quantities
results in nearly dry work pieces and chips; hence,
the name ‘NDM’
• Metalworking fluids do not spread throughout the
area around the machine, thus also making for a
cleaner workplace
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MQL Contd..
• MQL today uses such precise metering that the
lubricant is nearly completely used up
• The reduction in use of lubricants greatly reduces
health hazards caused by emissions of
metalworking fluids in breathed‐in air and on the
skin of employees at their workplaces
• The key factor here is the percentage of
metalworking fluid on the chips (less than 2%
adhering to the chip means that it is ‘dry’)
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MQL Working
• In NDM, the cooling/lubricating medium is supplied as
a mixture of air and an oil in the form of an aerosol
(often referred to as a mist)
• An aerosol is a gaseous suspension (hanging) in air of
solid or liquid particles
• Aerosols are generated using a process called
atomization
• An atomizer is an ejector in which the energy of
compressed gas, usually air is used to atomize the oil
• Oil is then conveyed by the air in a low‐pressure
distribution system to the machining zone
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MQL Working Contd..
• As the compressed air flows through the venturi
path, the narrow throat around the discharge
nozzle creates a low pressure in the mixing chamber
• This partial vacuum draws the oil up from the oil
reservoir where it is maintained under a constant
hydraulic head
• The air rushing through the mixing chamber
atomizes the oil stream into an aerosol of
micrometer‐sized particles
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MQL Atomizer
Fig Source: Astakhov, 2012
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Cutting Fluids for NDM/MQL
• The cutting fluids are basically of two types
– Oil‐based cutting fluids
– Chemical cutting fluids
• Oil‐based cutting fluids comprise of: straight oil, soluble
oil, whereas chemical cutting fluids can be further
categorized as synthetic and semi‐synthetic cutting
fluids
• Straight oils are non‐emulsifiable and are used in an
undiluted form
– These comprise of a base mineral or petroleum oil and
additives such as fats, vegetable oils and esters
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Cutting Fluids for NDM/MQL Contd..
• Straight oils provide the best lubrication and the
poorest cooling characteristics among cutting fluids
• Synthetic fluids contain no petroleum or mineral oil
base and instead are formulated from alkaline inorganic
and organic compounds along with additives
• For best cooling under extreme cutting conditions,
synthetic fluids preferred as these provide best cooling
among all cutting fluids
• The selection of cutting fluid depends on parameters
such as work piece material and nature of machining
process
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Cryogenic Machining
• Machining system delivers liquid nitrogen (at ‐321°
F) as coolant directly to the cutting edge enabling
substantially faster processing speeds and increased
tool life compared to conventional cooling methods
• It is more environmentally sound than other
coolants
• When it evaporates, Liquid Nitrogen is just
Nitrogen, which is the major constituent of air
• No harmful chemicals are involved
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Precision Mechanical Machining
• Precision machining is defined as machining in
which the relative accuracy (tolerance/object size) is
10–4 or less of a feature/part size
• Advanced machine tools equipped with precision
metrology and control tools
• Precision mechanical machining methods widely
extended for industrial use
• Ultra‐precision Machining ‐ The process by which
the highest possible dimensional accuracy is
achieved at a given point in time
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Ultrasonic Machining
• USM is a mechanical type non‐traditional machining
process
• Employed to machine hard and/or brittle materials
(both electrically conductive and non‐conductive)
– Hardness usually greater than 40 RC
• Uses a shaped tool, high frequency mechanical
motion and abrasive slurry
• Material is removed by the abrasive grains which
are driven into the workpiece by a tool oscillating
normal to the workpiece surface
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Ultrasonic Waves
• Ultrasonic waves ‐ sound waves of frequency higher
than 20 KHz
Frequency Spectrum
• High velocity longitudinal waves can easily
propagate in solids, liquids and gases
• A device that converts any form of energy into
ultrasonic waves is called ultrasonic transducer
• Ultrasonic waves can be generated using
mechanical, electromagnetic and thermal energy
sources
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Ultrasonic Waves Contd..
• Ultrasonic transducer converts high frequency electrical
signal in to high frequency linear mechanical motion (or
vibration)
• These high frequency vibrations are transmitted to the
tool via tool holder
• For achieving optimum material removal rate (MRR),
tool and tool holder are designed so that resonance can
be achieved
• Resonance (or maximum amplitude of vibration) is
achieved when the frequency of vibration matches with
the natural frequency of tool and tool holder assembly
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Principle of USM
• Tool of desired shape oscillates at ultrasonic
frequency over the workpiece
• Tool shape corresponds to shape to be produced in
the workpiece
• Tool is pressed downward with static load ‘F’
• Machining zone is flooded with slurry of abrasive
grits + water flowing continuously
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Principle of USM Contd..
• The tool shape is made converse to the desired
cavity
• The tool is placed very near to the work surface,
and the gap between the vibrating tool and the
workpiece is flooded with abrasive slurry made up
of fine abrasive particles and suspension medium
(usually water)
• As the tool vibrates in its downward stroke, it strikes
the abrasive particles
• This impact from the tool propels the grains across
the gap between the tool and the workpiece
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Principle of USM Contd..
• These particles attain kinetic energy and strike the
work surface with a force much higher than their
own weight
• This force is sufficient to remove material from the
brittle workpiece surface and results in a crater on it
• Each down stroke of the tool accelerates numerous
abrasive particles resulting in the formation of
thousands of tiny chips per second
• To maintain a very low constant gap between the
tool and the work, feed is usually given to the tool
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Mechanism of Material Removal
• Material is removed primarily due to
brittle fracture and chip formation
• Successive impacts and indentations of
abrasive particle causes machining and
material removal
• Possible Mechanism Include
– Hammering Action
– Throwing Action
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Mechanism of Material Removal Contd..
• Hammering Action
– Vibrating tool hammers the
abrasive grits onto the workpiece
surface
– Happens if particle is large and
machining gap is small
• Throwing Action
– Particle will be thrown by the
tool to hit the workpiece surface
– Happens if size of particle is small
and machining gap is large
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Other Possible Mechanisms
• Cavitation induced erosion
– A very small percentage (about 5 %) of material is also
believed to be removed by a phenomenon known as
cavitation erosion
– Collapse of the cavitation bubbles in the abrasive
suspension results in very high local pressures and
associated shock waves
– Micro‐cracks are generated at the interface of the
workpiece leading to chipping
• Chemical reaction
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USM Capabilities
• USM gives low MRR but it is
capable to machine intricate
cavities in single pass in fragile or
/and hard materials
• In USM, there is no direct contact
between the tool and workpiece
hence it is a good process for
machining very thin and fragile
components which otherwise
have high scrap rate
Figure Source: www.dreamstime.com, www.agstech.net
63
USM Capabilities Contd..
• A brittle material can be machined more easily than
a ductile one
• It is considered as a very safe process because it
does not involve high voltage, chemicals,
mechanical forces and heat
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Ultrasonic Machining System Contd..
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Transducers
• In USM, either of the two types of transducers are
used, i.e. piezoelectric or magnetostrictive type
• Piezoelectric crystals (say, quartz) generate
• a small electric current when they are compressed
• Also, when an electric current is passed through the
crystal, it expands; when the current is removed the
crystal attains its original size
• This effect is know as piezoelectric effect.
• Such transducers are available up to a power
capacity of 900 W
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Transducers Contd..
• Magnetostrictive transducer also changes its length
when subjected to a strong magnetic field
• These transducers are made of nickel, or nickel alloy
• Their conversion efficiency (20‐35%) is much lower
than the piezoelectric transducers’ efficiency (up to
95%) hence their cooling is essential to remove
waste heat
• These magnetostrictive type transducers are
available with power capacity as high as 2.4 kW
providing a maximum amplitude of vibration of 25
μm
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USM Tools
• Tool material should be tough
and ductile
– Low carbon steels and stainless
steels give good performance
– Aluminum and Brass wear faster
• Harder the tool material, the
faster its wear rate will be
• Mirror image of shaped tool
reproduced on the workpiece
Figure Source: edmtechman.com
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USM Tools Contd..
• Tools are usually made of relatively ductile
materials (brass, stainless steel, mild steel, etc) so
that the tool wear rate (TWR) can be minimized
• Value of the ratio of TWR and MRR depends upon
the kind of abrasives, workpiece material, and tool
material
• Surface finish of the tool is important because it will
affect the surface finish obtained on the workpiece
69
USM Tools Contd..
• To safeguard tool and tool holder against their early
fatigue failure, they should not have scratches or
machining marks
• Tools should be properly designed to account for
overcut
• Silver brazing of the tool with tool holder minimizes
the fatigue problem associated with screw
attachment method
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Advantages of USM
• It can be used machine hard,
brittle, fragile and non‐conductive
materials
• No heat is generated in work
• Less stress translates to high
reliability for critical applications
• USM apply to machining semi‐
conductor such as silicon,
germanium etc.
Figure Source: www.cimindustry.com/

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Applications of USM
• USM can be used to machine
– Hard, brittle metallic alloys,
semiconductors, glass, ceramics etc.
– Electrically non‐conductive ceramics
– Round, square, irregular shaped holes
Dies for wire drawing, punching and
blanking operations
– Precision mineral stones, jewelry, watch
bearing and industrial diamonds
• USM enables a dentist to drill a hole
on teeth without any pain
Figure Source: www.rigbyadvanceddental.com/
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Limitations
• USM has low material removal rate (MRR)
– Usually less than 50 mm3/min
• Machining area and depth is restraint in USM
• It is difficult to drill deep holes, as slurry movement
is restricted
• High Tool Wear rate
• High power consumption
Tool Wear in USM
Process
Figure Source: Yu et al., 2004
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Laser Beam Machining
• “Laser” is an acronym for Light Amplification by
Stimulated Emission of Radiation
• It was invented by amplifying ordinary light waves
based on similar principle
• Laser transmit light waves with constant frequency
and wavelength without interference
Fig Source: hyperphysics.phy‐astr.gsu.edu/, www.bronchotraining.org/ 74
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Laser Beam as an Energy Source
• Laser light is monochromatic, i.e. its wavelength
occupies a very narrow, portion of the spectrum
• Hence, a simple lens is
able to focus and
concentrate laser light to
a spot of much smaller
diameter and much
higher intensity than that
obtained by other types
of light
Fig Source: www.cityu.edu.hk/
75
Laser Beam as a Energy Source Contd..
• Laser light is coherent in nature (it travels in phase)
• Hence, it gives higher focused intensities than
normal light which is incoherent in nature
• The low divergence rate of lasers is also responsible
for high intensity of light
• Thus, laser beam is a light source having unique
properties like high monochromaticity, high degree
of coherence, high brightness, high peak power,
high energy per pulse, and very small size of the
focused spot
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Laser Beam Wavelengths
• Wavelength of commonly used lasers lies between
0.21 μm ‐ 11 μm
• Ruby = 0.7 μm
• Nd : YAG ≈ 1.0 μm
• CO ≈ 2.7 μm
• CO2 ≈ 10.6 μm
Fig Source: adarecosmetics.ie/
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Laser Device
• Three important elements of any laser device
– Laser medium (a collection of atoms, molecules, or ions)
– Pumping energy source required to excite these atoms to
higher energy level
– Optical feedback system
• Consider a gas laser consisting of a thin tube filled with
gas at low pressure
• There are electrodes placed at both ends of the tube
• Electric current when passed through provides
sufficient energy to stimulate the atoms/molecules of
the gas in the tube
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Laser Device Contd..
• The feedback mechanism for laser resonator
consists of parallel mirrors kept at the ends of the
tube
• One of these mirrors is fully reflective while the
other one is partially transparent to provide the
laser output (output mirror)
• It allows a beam of radiation to either pass through,
or bounce back and forth repeatedly through the
laser medium
79
Laser for Machining
• To make the laser beam
useful for processing of
materials, its power density
should be increased by
focusing
• The power density of laser
beam and its interaction with
the workpiece will determine
whether the beam will be
able to perform the function
of welding, cutting, heat
treatment or marking
Fig Source: www.bystronicusa.com/, www.sme.org/
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Laser for Machining Contd..
• To perform a machining operation, laser beam
power density should lie between 1.5 x 106 to 1.5 x
108 W/cm2, and the workpiece should be kept very
close to prime focus
• However, for welding, lower power densities of the
order of 1.5 x 104 to 1.5 x 105 W/cm2 are adequate
81
Laser Beam Machining
• As the laser beam falls on the workpiece surface,
reflection and transmission of electromagnetic
waves at the interface of air‐workpiece material
takes place
• Reflection and transmission of electromagnetic
waves of given wavelength depend on its reflectivity
and absorption coefficient
82
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Laser Beam Machining Contd..
Fig Source: i0.wp.com/
83
Laser Beam Machining Contd..
• Depending upon the intensity of the beam, one of
the following events may take place:
– In case of low intensity beam, there may be no phase
change of the irradiated work material
– In case of high intensity beam, the work surface
temperature would rise up to or above its boiling point
and vaporization would lake place
84
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Types of Lasers
• There are two types of lasers ‐ solid state laser and
gas laser
Ruby Solid State Laser
Helium Neon Gas Laser
Fig Source: www.mechanicalengineeringblog.com/
85
Solid State Lasers
• Because of poor thermal properties of solid state
lasers (ruby and Nd:glass), they can’t be used for
heavy duty work
• Such lasers do not operate faster than 1 or 2 Hz
• They are used only for low pulse applications like
spot welding, drilling, etc.
• However, Nd: YAG laser, most powerful in solid state
lasers, is also used for operations like cutting
• It is usually employed for light works
86
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Solid State Lasers Contd..
• Many materials with laser action have been
developed ‐ calcium fluoride crystals doped with
neodymium
• The round crystal rods with reflective ends are used
• Crystalline ruby is another material used for laser
action
• It is aluminum oxide with chromium ion impurities
distributed through the aluminum lattice sites
• Flash lamp surrounding the ruby rod produces light
87
Solid State Lasers Contd..
• Flash lamp and ruby rod are enclosed in the cylinder
• This cylinder has highly reflective internal surfaces
• These surfaces direct light from the flash lamp into the
rod
• This light excites the chromium ions of ruby crystal to
high energy levels
• While on return journey to the normal state, these
excited ions at high energy levels release the photons
(or energy).
• Thus, desired energy is obtained in the form of short
duration pulses
88
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Gas Lasers
• In this type of laser, CO2, He, or N2 act as a lasing
medium
• These gases are recirculated and replenished to
reduce the operating cost
• Direct electrical energy is used to provide energy for
stimulating lasing medium
Fig Source: www.physics‐and‐radio‐electronics.com/
89
Gas Lasers Contd..
• Axial flow CO2 laser has a power giving capacity of
usually 100 W each meter length of the tube
• For higher powers up to 1500 W and reduced floor
space, folded resonator axial flow CO2 lasers are
used
• For very high power (several thousand watts) and
still very compact CO2 laser is known as transverse
flow, or gas transport laser
90
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Gas Lasers Contd..
• Large amount of gas volume is used
• The resonator mirrors are positioned to reflect the
beam several times before it escapes through the
output mirror
• Most of the lasers are computer controlled to take
advantage of their high speed processing
• During the processing of materials, motion can be
given to either workpiece or the beam or both
depending upon the design
91
LBM Process Characteristics
• The relative magnitudes of heat consumption as
losses and absorption by workpiece depend upon
thermal and optical properties of the work material,
and intensity and pulse duration of the laser beam
• A part of the material being expelled from the work
surface stays in the path of the beam in the form of
small droplets and continues to absorb energy
92
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LBM Process Characteristics Contd..
• High capital and operating cost, and low machining
efficiency (usually less than 1%) prevent LBM from
being competitive with conventional machining
techniques
• Machining by LBM technique also reduces fatigue
strength of the machined component as compared
to the fatigue strength of the component when
machined by conventional processes
93
LBM Modes of Machining
• Industrial lasers operate either in continuous wave
mode (CW) or pulsed mode
• CW lasers are used for processes like welding, laser
chemical vapor deposition (LCVD), surface
hardening which require uninterrupted supply of
energy for melting and phase transformation
• Controlled pulse energy is desirable for the
processes like cutting, drilling, marking so that HAZ
is minimum possible
94
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LBM Modes of Machining Contd..
Continuous Wave Mode
Pulsed Mode
Fig Source: www.sme.org/
95
Heat Affected Zone (HAZ) in LBM
• LBM results in a heat affected
zone (HAZ)
• It has also been found that as the
feed rate in LBM increases, the
thickness of the HAZ goes down
• The thickness of the HAZ is also
governed by the type of assisting
gas and its pressure (in case of
gas assisted laser cutting), gas
nozzle diameter, and the distance
between the nozzle tip and the
workpiece
Fig Source: www.cmxr.com/ , www.gasparini.it/
96
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LBM Process Capabilities
• In LBM, there are no mechanical forces exerted on
the workpiece
• LBM process is capable of easily machining
refractory, brittle, hard, metallic, and nonmetallic
materials such as cast‐alloy, tungsten, titanium,
alumina, and diamond
• It can machine through any optically transparent
material (say, glass)
• As long as the beam path is not obstructed, it can
be used to machine in otherwise inaccessible areas
97
LBM Process Capabilities
• The laser beam can operate through transparent
environment like air, gas, vacuum, and in some
cases even liquids
• However, LBM cannot be applied to highly
conductive and reflective materials which have high
heat conductivity or high reflectivity (aluminum,
copper, and their alloys)
• Because of this property, table made of aluminum is
used to hold the workpiece while machining it by
LBM process
98
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LBM Process Capabilities Contd..
• The least, diameter to which a laser beam can be
focused depends upon the laser beam divergence,
which is a function of the quality of the laser
material and depth at which machining is being
done
• Using LBM, holes of large aspect ratio (= hole
depth/diameter of hole) and of a very small
diameter can be drilled
• The taper angle of a drilled hole reduces with an
increase in the depth of the hole
99
Recast Layer
• Recast layer (i.e.
any molten or
vaporized material
that re‐solidifies
• Deposits on the
machined surface
has microcracks
and is loose
enough to be
scraped off easily
Fig Source: image.thefabricator.com/
100
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Applications of LBM
• Laser beam energy has been favorably employed for
cutting difficult‐to‐machine materials such as
hardened steels, composites, ceramics
• However, the process is employed to those
materials which have favorable thermal and optical
properties
• Laser beam energy has been utilized for operations
like drilling, cutting
101
Applications of LBM Cond…
• Laser beam energy has been utilized for operations
like drilling, cutting, micromachining, trepanning,
trimming, marking, welding, soldering, brazing
Fig Source: www.vy‐tek.com/
102
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Laser Beam Drilling
• LBM process is extensively used for making small holes
(microhole dia. < 1 mm, small hole dia. 1.0‐3.2 mm
• Also known as laser percussion hole drilling
• The workpiece is placed at or near the focal point of
the laser beam
• The localized high intensity heat results in melting of a
part of the material and a small part may vaporize
• Escaping of vaporized material results in most of the
volume of molten material to be removed as a spray of
the droplets
103
Laser Beam Drilling Contd..
• Superalloys due to their properties like toughness,
creep strength, and hot corrosion resistance at high
temperatures, are commonly used materials for the
turbine components like blades, guide vanes,
afterburners and casings where temperatures as
high as 2000°C can reach
• A large number of cooling holes are required to be
drilled in some of these components
• LBM is commonly used for this purpose
104
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Laser Beam Cutting
• Larger sized holes (> 1.2 mm diameter) can’t be
drilled by this process because of low power density
of the focused beam
• Cutting is done at high speed and it is capable to
pierce the workpiece at any location and can cut
omni‐directionally
• The gas jet assists in clearing the material from the
cut, and also to keep debris away from
contaminating the focusing lens
• Laser cutting does not involve any mechanical type
of forces
105
Laser Beam Engraving
• LBM can be used to imprint letters, numerals and
symbols on metal and nonmetal workpieces
• The system is made up of pulsating laser system and
a computer‐controlled beam scanning system
Fig Source: bookwormlaser.com/, s‐media‐cache‐ak0.pinimg.com/
106
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LBM – Miscellaneous Applications
• LBM is being employed for both micromachining as
well as macro machining
• A three‐dimensional laser beam machining process
can be performed using two independent lasers
simultaneously to cut two grooves which are
moving closer to each other
• When these two grooves converge, a volume is cut
off without being melted/vaporized
107
Plasma Arc Machining
• Uses plasma
stream operating
at very high
temperatures to
cut metal by
melting
108
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Operation of PAC
• Plasma = superheated, electrically ionized gas
– PAC temperatures: 10,000C to 14,000C (18,000F to
25,000F)
• The plasma flows through water‐cooled nozzle that
constricts and directs stream to desired location
• The plasma arc is generated between electrode in
torch and anode workpiece
109
Applications of Plasma Arc Machining
• Most applications 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, aluminum
110
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Thermo‐Electric Machining Process
• Machining processes based on thermoelectric
energy between the workpiece and an electrode
• In this process, the material is removed electro‐
thermally by a series of successive discrete
discharges between tool and the workpiece
• Electrical Discharge Machining (EDM)
111
DEFINITION OF EDM
• Electrical Discharge Machining (EDM) is the process
of machining electrically conductive materials by
using precisely controlled sparks that occur
between an electrode and a workpiece in the
presence of a dielectric fluid
• Material removal is caused due to localized
temperatures high enough to melt or vaporize the
metal
• The electrode may be considered the cutting tool
• Can be used only on electrically conducting work
materials
112
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Schematic of EDM
(a) Setup of process and (b) close-up view of gap, showing discharge and
metal removal
113
EDM as a Non‐Traditional Machining
Process
• One of the most widely used non‐traditional
processes
• It is a thermoelectric process in which heat energy
of a spark is used to cause material removal
• EDM differs from most chip‐making machining
operations in that the electrode does not make
physical contact with the workpiece for material
removal
• Since the electrode does not contact the workpiece,
EDM has no tool force
114
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EDM as a Thermal Process
• Material is removed by heat
• Heat is introduced by the flow of electricity
between the electrode and workpiece in the form
of a spark
• Material at the closest points between the
electrode and workpiece, where the spark
originates and terminates, are heated to the point
where the material vaporizes
115
EDM as a Thermal Process Contd..
• While the electrode and workpiece should never
feel more than warm to the touch during EDM, the
area where each spark occurs is very hot
• The area heated by each spark is very small so the
dielectric fluid quickly cools the vaporized material
and the electrode and workpiece surfaces
• However, it is possible for metallurgical changes to
occur from the spark heating the workpiece surface
116
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Working Principle of EDM
• Workpiece and tool should be made of electrically
conductive materials
• Tool and Workpiece electrodes are immersed in
dielectric medium such as kerosene and are
connected to a capacitor
• Capacitor is charged from a direct current (DC)
source
• As the potential across the electrodes crosses the
breakdown voltage, the sparking takes place at a
point of least electrical resistance
117
Working Principle of EDM Contd..
• Sparking usually occurs at the smallest inter‐
electrode gap
• Spark energy is capable of partly melting and partly
vaporizing the materials from a localized area on
both electrodes (workpiece and tool)
• The material is removed in the form of craters
which spread over entire surface of the workpiece
• Cavity produced in the workpiece is approximately
replica of the tool
118
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Sparking Gap
• The electrode must always be spaced away from
the workpiece by the distance required for sparking,
known as the sparking gap
• Should the electrode contact the workpiece,
sparking will cease and no material will be removed
• Location of spark is determined by the narrowest
gap between the tool and workpiece
119
Sparking Process
•
•
•
•
Only one spark occurs at any instant
Duration of each spark is very short
Entire cycle time is usually few micro seconds
Sparking occurs in a frequency range from 2,000 to
500,000 sparks per second causing it to appear that
many sparks are occurring simultaneously
• In normal EDM, the sparks move from one point on
the electrode to another as sparking takes place
120
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Sparking Process Contd..
121
Sparking Process Contd..
• The spark removes
material from both the
electrode and workpiece,
which increases the
distance between the
electrode and the
workpiece at that point
• This causes the next spark
to occur at the next‐closest
points between the
electrode and workpiece
122
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Lightning Analogy
• Lightning is a discharge
phenomenon of nature
accompanied by a flash of light
and the crash of thunder
• Normally a gas, such as air, does
not conduct electricity
• However, when conditions are
right, a discharge of electrical
current can flow through air
• This phenomenon is
accompanied by a bolt of
lightning (light & heat) and a roll
of thunder (sound & pressure)
Figure Source: www.nssl.noaa.gov, www.ec.gc.ca
123
Lightning Analogy Contd..
• In Electrical Discharge Machining (EDM) a very
small “lightning bolt” or spark is created between
the electrode and the workpiece many hundreds to
thousands of times per second
• A hole is made by repeatedly melting the work
piece at this point of electric discharge and blowing
away the molten material by pressure
124
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Lightning Analogy Contd..
• In nature, lighting usually strikes a
place that is closest to the storm
cloud – a tall tree, the peak of a
mountain or the lightning rod on a
roof for example
• Just as in nature, the spark in EDM
occurs at the closest point between
the electrode and the work piece.
However, the big difference between
Nature and EDM is that the spark
occurs in a gap the thickness of a
human hair
Lightning
EDM
Figure Source: www.atlantaedm.com/, www.tomstockton.us/
125
Dielectric Fluid
• A dielectric material is required to maintain the
sparking gap between the electrode and workpiece
• This dielectric material is normally a fluid
• Die‐sinker type EDM machines usually use
hydrocarbon oil, while wire‐cut EDM machines
normally use deionized water
• The main characteristic of dielectric fluid is that it is
an electrical insulator until enough electrical voltage
is applied to cause it to change into an electrical
conductor
126
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Dielectric Fluid Contd..
• The dielectric fluids used for EDM machining are
able to remain electrical insulators except at the
closest points between the electrode and the
workpiece
• At these points, sparking voltage causes the
dielectric fluid to change from an insulator to a
conductor and the spark occurs
• It should take minimum possible time to breakdown
once the breakdown voltage is reached
127
Ionization Point of Dielectric
• The time at which the dielectric fluid changes into
an electrical conductor is known as the ionization
point
• When the spark is turned off, the dielectric fluid
deionizes and the fluid returns to being an electrical
insulator
• This change of the dielectric fluid from an insulator
to a conductor, and then back to an insulator,
happens for each spark
128
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Ionization Point Contd..
129
Functions of Dielectric Fluid
• Dielectric fluid used in EDM machines provides
important functions in the EDM process
• These are:
– Controlling the sparking‐gap spacing between the
electrode and workpiece
– Cooling the heated material to form the EDM chip
– Removing EDM chips from the sparking area and
cleaning the sparking gap
• Gap cleaning is one of the crucial factors for good
EDM
130
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Common Dielectric Fluids
• The fluids commonly used as dielectric are
transformer oil, paraffin oil, kerosene, lubricating
oils, and deionized water
• Deionized water gives high MRR and functions as
more effective cooling medium but also causes high
electrode wear rates and cause corrosion
• Filtration of dielectric fluid before recirculation is
highly essential so that a change in its insulation
qualities during the process is minimal
131
EDM Chip Formation
• As each spark occurs, a small amount of the
electrode and workpiece material is vaporized
• The vaporized material is positioned in the sparking
gap between the electrode and workpiece in what
can be described as a cloud
• When the spark is turned off, the vaporized cloud
solidifies
• Each spark then produces an EDM chip or a very
tiny hollow sphere of material made up of the
electrode and workpiece material
132
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EDM Chip Formation Contd..
• Spark ON: electrode and workpiece material
vaporized
133
EDM Chip Formation Contd..
• Spark OFF: vaporized cloud suspended in dielectric
fluid
134
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EDM Chip Formation Contd..
• Spark‐OFF: vaporized cloud solidifies to form EDM
chip
• For efficient
machining, the EDM
chip must be removed
from the sparking area
• Removal of this chip is
accomplished by
flowing dielectric fluid
through the sparking
gap
135
Work Materials in EDM
• Work materials must be electrically conducting
• Hardness and strength of work material are not
factors in EDM
• Material removal rate depends on melting point of
work material
136
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Tool Materials in EDM
• The material to be used as tool electrode should
possess desirable properties like easily machinable,
low wear rate, good conductor of electricity and
heat, cheap, and readily available
• Tool materials include:
– Graphite (easily machinable, low wear rate, and high
conductivity)
– Copper, brass (highly stable and relatively low wear rate)
– Cast aluminum, copper boron, and silver tungsten
• Copper and graphite are more commonly used
137
Types of EDM
• Die‐sinking EDM (also known as ram type)
– Requires the electrode to be machined in the exact
opposite shape as the one in the workpiece
• Wire‐cut EDM
– Uses a continuous wire as the electrode
– Sparking takes place from the electrode wire‐side
surface to the workpiece
• Small hole EDM
– Similar to die‐sinking but is used to merely burn a hole
through a usually hardened workpiece
138
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Electrolysis of NaCl
• Consider an electrolytic cell
in which DC battery sends
electric current through the
molten sodium chloride salt
• Electrons from the battery enter the melt at the
cathode, and when the circuit is complete, they
leave the melt at the anode returning to the battery
Fig Source: www.gcsescience.com/
139
Electrolysis of NaCl Contd..
• Sodium ions (Na+) from the
medium combine with the
electrons available at the
cathode, and produce sodium
metal which accumulates at
the cathode region
• Thus, sodium ions are
reduced (reduction process
involves the addition of
electrons) at the cathode
140
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Electrolysis of NaCl Contd..
• At the same time, chloride
ions migrate towards the
anode and are oxidized (in
oxidation process electrons
are released) to chlorine
• In order to get a sustained
flow of current, and to avoid
accumulation of ions at the
electrode, reactions must keep
occurring at the electrode, to
maintain electrical neutrality
141
Electrochemical Machining (ECM)
• Electrolysis has been successfully put to work in the
areas like electroplating, electroforming and
electropolishing
• Electrochemical Machining (ECM) is the process of
controlled metal removal by electrochemical
dissolution
• Technology known as long back as 1780 AD but it is
only over the last couple of decades that this
method has been used to advantage
142
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ECM as a Non‐traditional Machining
Process
• Uses electrical energy is used in combination with
chemical reactions to remove material
• Tool does not contact the workpiece directly
– Also known as contactless electrochemical forming
143
ECM Contd..
• During electrolysis, the
electrical energy is used to
produce a chemical
reaction, therefore, the
machining process based
on this principle is known
as electrochemical
machining (ECM)
• This process works on the
principle of Faraday’s laws
of electrolysis
144
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Faraday’s Laws of Electrolysis
• In an electrolytic cell (or ECM cell), material removal
is governed by Faraday’s laws of electrolysis
– Law 1: The amount of chemical change produced by an
electric current (or the amount of substance deposited
or dissolved) is proportional to the quantity of electricity
passed.
– Law 2: The amounts of different substances deposited or
dissolved by the same quantity of electricity are
proportional to their chemical equivalent weights
145
Faraday’s Laws of Electrolysis Contd..
• M ∝ I.t
• m = Z.I.t
– where, I is the current strength (amperes), t is the time
(seconds), Z is the electrochemical equivalent and m is
mass in grams
• Z = Atomic Mass/(n.F)
– where F is Faraday’s constant (96500 As) and n is valence
number of ions of the substance (electrons transferred
per ion)
146
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Working Principle of ECM
• In ECM, small electric DC potential (5‐25 V) is
applied across the two electrodes ‐ cathode and
anode (anode is work and cathode is tool)
immersed in electrolyte
• The transfer of
electrons between
the ions and the
electrodes completes
the electrical circuit
147
Working Principle of ECM Contd..
• The metal is detached, atom by atom, from the
anode surface and appears in the electrolyte as
positive ions
• In electrochemical machining, detached metal
appears as precipitated solid of metal hydroxides
• During the electrolysis of water, its molecules gain
electrons from cathode so that they separate into
free hydrogen gas and hydroxyl ions.
148
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Working Principle of ECM Contd..
• As the anode dissolves, negatively charged hydroxyl
ions are electrically balanced by positively charged
metal ions entering into the electrolyte
• Metal ions do not remain as ions in the solution when
neutral electrolytes are used, but combine with the
hydroxyl ions to form metal hydroxides
• These hydroxides are insoluble in water hence they
appear as solid precipitates and no longer affect the
electrochemical reaction
149
Derivatives of ECM Process
• Other machining processes which is based on
electrochemical dissolution of anode
– ECB (Electrochemical Boring)
– ECD (Electrochemical Drilling)
– ECDe (Electrochemical Deburring)
– ECDS (Electrochemical Die Sinking)
– ECG (Electrochemical Grinding)
– ECH (Electrochemical Honing)
– ECM (Electrochemical Milling)
150
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ECM vs. Electroplating
• ECM is reverse electroplating
• ECM removes metal while electroplating add metal
on substrate surface
ECM Process
Electroplating Process
Fig Source: www.selectiveplatinginc.com/
151
ECM vs. Electropolishing
• ECM involves removal of metal from targeted area
on workpiece
• It involves change in size and shape of the
workpiece in a controlled manner
• Electropolishing removes material from the entire
workpiece surface
• Magnitude of current density employed in ECM is
very high
152
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Interelectrode Gap (IEG)
• Smaller the interelectrode gap (the gap between
the two electrodes), greater will be the current flow
because resistance decreases and higher will be the
rate of metal removal from the anode
• High current density, in the small spacing (usually
about 0.5 mm or less), promotes rapid generation
of reaction products ‐ hydroxide solids and gas
bubbles
• These reaction products act as a barrier to the flow
of electrolyzing current
153
Interelectrode Gap Contd..
• The cathode is moved towards the anode at the
same rate at which the work is being dissolved so
that the gap between the two electrodes remains
constant
– It really does not matter even if work is fed towards the
tool
• This will help in maintaining a constant material
removal rate (MRR)
• Smaller gap at various points between confronting
surfaces of the electrodes‐tool and work‐will result
in higher current density (J) and hence higher MRR
154
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Electrolyte
• Electrolytes used in ECM consist of either acids or,
more generally, basic salts
• Electrolyte flowing at high velocity in the IEG serves
different functions,
– Dilutes the electrochemical reaction products and
removes them out from the gap
– Dissipates heat at a faster rate, and limits the
concentration of ions at the electrode surface to give
higher machining rates
155
Electrolyte Contd..
• Sodium chloride (NaCl) at the concentration of 20% ‐
for ferrous alloys (e.g. Steels and cast irons and cobalt
alloys
• Sodium nitrate (NaNO3) ‐ for ferrous alloys.
• Hydrochloric acid (HCl) ‐ for Nickel alloys.
• A mixture of sodium chloride (NaCl) and sulfuric acid
(H2SO4) ‐ for nickel alloys.
• A mixture of 10% hydrofluoric acid (HF), 10%
hydrochloric acid (HCl), 10% nitric acid (HNO3) ‐ for
Titanium alloys
• Sodium hydroxide (NaOH) ‐ for tungsten carbide (WC)
156
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Electrolyte properties
• Electrolyte variables which determine the geometry
of the machined component include
– Composition
– Concentration
– pH value
– Temperature
– Concentration of foreign elements
157
Electrolyte properties Contd..
• Amount of hydroxides in the electrolyte is confined by
continuous removal using large settling tanks, filters,
and centrifuging pumps
• Composition, concentration and pH value of electrolyte
solution are controlled by adding water and salt
solution
• Their quantity to be added depends upon the periodic
analysis of the check samples
• Temperature is another important factor which governs
the electrical properties of the electrolyte
– It is controlled (within ± 1° C) by heating or cooling the
electrolyte while in the tank
158
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Electrolyte properties Contd..
• Selection of electrolyte is quite important
• However, inexpensive, easily available and
commonly used electrolyte is sodium chloride
(common salt)
• It is also necessary to pump the electrolyte at very
high pressure through the IEG, so that the desired
MRR can be maintained
– Pressure of 2 to 35 kg cm‐2, leading to the electrolyte
flow velocity as high as 10‐50 m/s
159
Advantages of ECM
• No mechanical force
• It can machine highly complicated and curved
shapes in a single pass
• A single tool has been used to machine a large
number of pieces without any loss in its shape and
size
• Theoretically, tool life in ECM is very high
• The machinability of the work material is
independent of its physical and mechanical
properties
160
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Mechanical Properties of ECM’d Parts
• It has been reported that there is no effect of ECM
on ductility, yield strength, ultimate strength, and
micro‐hardness of the machined component
• Surface layers damaged during conventional
machining or by some other processes, may be
removed by ECM and this may result in
improvement in wear resistance
• However, such removal of layers from the work
surface reduces fatigue strength of a conventionally
machined component
161
Summary
• In this module, we have discussed:
– Abrasive‐based Machining Processes
– Advanced Mechanical Machining Processes
– Thermal and Electrical Machining Processes
– Electrochemical Machining Processes
162
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