NCM.pdf .

Department of Mechanical & Manufacturing Engineering, MIT, Manipal 1 of 196
MANUFACTURING TECHNOLOGY
CHAPTER 8
NON-CONVENTIONAL MACHINING

CONTENTS:
INTRODUCTION TO NCM
CLASSIFICATION
ADVANTAGES
DISADVANTAGES

Introduction:
A group of processes that remove excess
material by various techniques involving
mechanical, thermal, electrical, or chemical
energy (or combinations of these energies)
They do not use a sharp cutting tool in the
conventional sense.

Importance:
Need to machine newly developed metals and
non‑metals with special properties that make
them difficult or impossible to machine by
conventional methods
Need for unusual and/or complex part
geometries that cannot readily be accomplished
by conventional machining
Need to avoid surface damage that often
accompanies conventional machining

Need of Non traditional Machining:
Intricate shaped blind hole – e.g. square hole of
15 mm x 15 mm with a depth of 30 mm
Difficult to machine material – e.g. same example
as above in Inconel, Ti-alloys or carbides.
Low Stress Grinding – Electrochemical Grinding
is preferred as compared to conventional grinding
Deep hole with small hole diameter – e.g. φ1.5
mm hole with l/d = 20
Machining of composites.
Requirement of high order of surface finish

Traditional Machining Non Traditional Machining
1.Contact process i.e. Material
removed by interference
between tool and work
2. Machinability and MRR
depends on hardness.
3. Further deburring operation
is needed.
4. Relatively simple shapes.
Complex shapes are either not
possible or difficult to produce.
Non contact Process.
Not dependent on hardness.
Burr free operation.
Extremely complex shapes can
be produced with relative ease.

Traditional Machining Non Traditional Machining
5. Tool wear is considerable.
6. Tool should be harder than
work piece.
7. MRR is high.
8. Cutting force is large.
9. Stress can be induced in
the work piece.
No tool wear or negligible tool
wear.
Soft tool can be used.
MRR is low.
Practically no cutting force.
No stress is induced in the
work piece

Classification of Non Traditional Machining Processes :
Mechanical Processes
Abrasive Jet Machining (AJM)
Ultrasonic Machining (USM)
Water Jet Machining (WJM)
Electrochemical Processes
Electrochemical Machining (ECM)
Electro Chemical Grinding (ECG)
Chemical Processes
Chemical Milling (CHM)
Photochemical Milling (PCM) etc.
Electro-Thermal Processes
Electro-discharge machining (EDM)
Laser Beam Machining (LJM)
Electron Beam Machining (EBM)
Plasma Arc Machinig (PAM)

Classification:
Mechanical – typical form of mechanical action is
erosion of work material by a high velocity stream
of abrasives or fluid (or both)
Electrical – electrochemical energy to remove
material
Thermal – thermal energy usually applied to small
portion of work surface, causing that portion to be
fused and/or vaporized
Chemical – chemical etchants selectively remove
material from portions of work-part, while other
portions are protected by a mask

Abrasive Jet Machining (AJM)-Principle:
In AJM, the material removal takes place due to
the impingement of focused stream of abrasive
particles, carried away by compressed gas. The
material removal takes place due to the chipping
action.
AJM removes material by brittle fracture.
Fine abrasive particles are accelerated in a gas
stream.
The particles are directed towards the focus of
machining
As the particles impact the surface, they fracture
off the work material.

Construction:
Abrasive Jet Machines
consist of the following
basic elements:-
Air Compressor
Variable Control
Systems
Mixing Chamber
Nozzle
AIR
COMPRESSOR
ABRASIVES
CONTROL
VALVES
AND
VARIABLE MIXER
NOZZLE
WORK

Compressor:
For the machining process, compressors of the
following specifications are used:-
Power : 30-40 hp (20-40 kW).
Pressure Developed:1300-10000 kg/cm2
Type: Multistage ( Generally 2 stages).
Cylinder Specifications: Depending upon
Process Parameters.

Mixing Chamber:
It is the apparatus where the homogeneous
mixing of the abrasive and the compressed air
takes place.
Air/gas is mixed with predefined amount of
abrasive particles in the chamber.
This apparatus controls the flow of air as well as
the movement of abrasives into the machine tool.

Nozzle:
Nozzles are required to convert the large pressure head developed by the
compressor to high velocity required to cut the work piece.
Cross sectional area of orifice is 0.05-0.2 mm2
Orifice can be round or rectangular
Head can be straight, or at a right angle
Generally the nozzles are made of:-
1) Tungsten Carbide (L.s. up to 12-30 hr.)
2) Sapphire (L.s. up to 300 hr.)
3) Diamond (L.s. up to 500-1000 hr.)
4) Aluminum (L.s. up to 10-20 min. Depending upon
process parameters)

Abrasives:
They are the main cutting agents which cause the brittle fracture of the
work material.
They should on an average be as hard or harder than the work.
The grains should have sharp edges
Material diameters of 10-50 micron whereas dia of 15-20 micron is
optimal
Should not be reused as the sharp edges are worn down and smaller
particles can clog nozzle.
Some of the commonly used abrasive particles are:-
1) Aluminum Dioxide
2) Silicon Carbide
3) Diamond

Carrier Gas:
The carrier gas should be cheap and easily available
and not cause oxidation of the work piece.
It should also not react with the work, nozzle or the
abrasives materials.
Some of the common carrier gases used in AJM are:-
1) Air
2) Carbon Dioxide
Any other noble gas can also be used.

Process Parameters:
Factors that effect the process are:-
MRR
Geometry of Cut
Required Surface Finish
Rate of Nozzle Wear

Process Parameters:
Particle Size 10-50 microns
Nozzle Area 0.05-0.2 mm2
Nozzle Pressure 0.2-0.8 N/mm2
Velocity Of Jet 300 m/sec
Nozzle Tip Distance 12 mm

Working:
Air/gas is compressed up to a pressure
10000kg/cm2
in the compressor.
Optimum amount of abrasive particles are added
and homogeneously mixed in the mixing chamber.
This charge is made to pass through a nozzle where
the high pressure of the mixture is converted to
increased velocity.

When this mixture is made to focus on the work,
the abrasive particles cause chipping action on the
workpiece material due to brittle fracture.
The chips are removed by the high velocity gas
which also acts as a coolant.

Setup:

Advantages of abrasive jet machining:
Extremely fast setup and programming
Very little fixture for most parts
Machines virtually any 2D shape
Very low side forces during the machining
Almost No heat generated on part
Limitations of abrasive jet machining:
Air pollution near the equipment due to flying
abrasive powder and dust
Difficult to control the kerf width
Limited to thin material

Applications:

Water Jet Machining

Definition:
A water jet cutter is a tool capable of slicing into
metal or other materials using a jet of water at
high velocity and pressure, or a mixture of water
and an abrasive substance.
The process is essentially the same as water
erosion found in nature but greatly accelerated
and concentrated.
It is the preferred method when the materials
being cut are sensitive to the high temperatures
generated by other methods.

“Green technology”
Water jet machining is also called as “Green
technology” this is because:-
Water jets produce no hazardous waste, reducing
waste disposal costs.
Water jets use very little water and the water that
is used can be recycled using a closed-looped
system.
Water jets also eliminate airborne dust particles,
smoke, fumes, and contaminates from cutting
materials such as asbestos and fiberglass.
This greatly improves the work environment and
reduces problems arising from operator exposure.

Operation:

Water jet cutting:
The cutter is 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.
Very high pressure jet of water up
to 55,000 psi (3930 bar) can be
obtained at faster rate.
At these pressures a slight leak
can cause permanent erosion
damage to components if not
properly designed.

Pump:
The pump is the heart of the water jet system. The
pump pressurizes the water and delivers it
continuously so that a cutting head can then turn
that pressurized water into a supersonic water jet
stream. Two types of pump can be used for water
jet applications — an intensifier based pump and
a direct drive based pump.

Direct drive based pump:
The direct drive pump operates in the same
manner as a low-pressure “pressure washer”
that you may have used to pressure wash a
house or deck prior to repainting.
It is a triplex pump that gets the movement of
the three plungers directly from the electric
motor.
This is also used for cleaning the surface of
the material.

Intensifier based pump:
Two fluid circuits exist in a typical intensifier pump, the
water circuit and the hydraulic circuit.
The water circuit consists of the inlet water filters,
booster pump, intensifier, and shock attenuator. The
filtered water is then sent to the intensifier pump and
pressurized to up to 60,000 psi.
The electric motor powers the hydraulic pump. The
hydraulic pump pulls oil from the reservoir and
pressurizes it to 3,000 psi. This pressurized oil is sent
to the manifold where manifold’s valves create the
stroking action of the intensifier by sending hydraulic oil
to one side of the plunger assembly, or the other.

Cont…
The intensifier is a reciprocating pump, in that
the plunger assembly reciprocates back and
forth, delivering high-pressure water out one
side of the intensifier while low-pressure water
fills the other side. The hydraulic oil is then
cooled during the return back to the reservoir.

Pumping system

Typical intensifier pumping unit

Nozzle:
When a high pressure water is
passed through the nozzle,
pressure is changed to velocity
and the cutting of work piece
takes place .
Diameter ranges from 0.004 to
0.010 inch for typical cutting.
Commonly used nozzle are
sapphire, ruby, diamond.
Sapphire is the most common
orifice material used today

Nozzle Material:
Material Life Use Comments
Sapphire 50 to 100 hours
Pure
Waterjet
General purpose,
though life reduces by
½ for abrasive waterjet
applications
Ruby 50 to 100 hours
Abrasive
Waterjet
Stream not suitable for
pure waterjet
applications
Diamond
800 to 2,000
hours
Pure &
Abrasive
10 to 20 times more
expensive than Ruby or
Sapphire

When to choose Water Jet Cutting?
When materials are non-ferrous.
When materials are unsuitable for lasers.
When accuracy is key.
When materials are thick.
When a small hole diameter to thickness
ratio is required.
When a heat affected zone is best
avoided.

Process parameters:
For successful utilization of WJM process, it is
necessary to analyse the following process criteria:
Material removal rate
Geometry and finish of work piece
Wear rate of nozzle.
MRR is directly proportional to nozzle diameter and
fluid pressure.
MRR is also greatly influenced by stand off distance
of nozzle tip from the surface of the material being
cut.

Process characteristics:
Uses a high velocity stream of abrasive
particles suspended in a stream of Ultra High
Pressure Water (30,000 - 90,000 psi) which is
produced by a Water-jet Intensifier Pump.
Is used for machining a large array of
materials, including heat-sensitive, delicate or
very hard materials.
Produces no heat damage to work piece
surface or edges.

Cont…
Nozzles are typically made of sintered boride.
Produces a taper of less than 1 degree on
most cuts, which can be reduced or eliminated
entirely by slowing down the cut process.
Distance of nozzle from work piece affects the
size of the kerf and the removal rate of
material. Typical distance is 0.125".

Effect of feed rate:
The removal rate increases with feed rate and
reaches a peak value and the tendency is to fall.
This may be because of the erosion and removal
process lagging behind the impacting
phenomenon.

Benefits:
No costly fixtures or tooling
No HAZ (Heat Affected Zone)
No Material Warping
No Burrs or Sharp Edges
Minimal material wasted
Tolerances Within ± .015"
No Work Hardening
Work area remains clean and dust free

Applications:
WJM is used to cut many nonmetallic
materials like Kevlar, glass epoxy, graphite,
boron, leather and many other brittle materials.
It is used mostly in shoe making industry and
now has entered into steel plant to descale the
chilled layer of steel ingots, in aircraft
industries to profile cutting of FRP aircraft
structures even glass windows.

Abrasive Water Jet Machining (AWJM):
When WJM is used on metallic workparts,
abrasive particles must usually be added to
the jet stream to facilitate cutting.
This process is therefore called abrasive water
jet machining (AWJM).
Introduction of abrasive particles in to the
stream complicates the process by adding to
the number of parameters that must be
controlled.
Among the additional parameters are abrasive
type, grit size and flow rate.

Aluminium oxide, silicon dioxide and garnet (a
silicate material) are typical abrasive materials
used, at grit sizes ranging between 60 and 120.
The abrasive particles are added to the water
stream at approximately 0.25 kg/min after it has
exited the WJC nozzle.
The remaining process parameters include those
that are common to WJM: nozzle opening
diameter, water pressure and stand of distance.
Nozzle orifice diameters are 0.25-0.63mm,
somewhat larger than in WJC to permit higher
flow rates and more energy to be contained in the
stream prior to injection of abrasives

Water pressures are about the same as in
WJC, stand off distances are somewhat less to
minimize the effect of dispersion of the cutting
fluid that now contains abrasive particles.
Typical standoff distances are between ¼ and
½ of those in WJC.

AWJM

Cheaper than other processes.
• 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.
Clean cutting process without gasses or oils.
Advantages

• One of the main disadvantages of waterjet cutting is that
a limited number of materials can be cut economically.
• Another disadvantage is that very thick parts can not be
cut with waterjet cutting and still hold dimensional
accuracy.
Disadvantages

Ultrasonic machining (USM) -Definition:
Material Removing Process:
USM is used to erode holes and cavities in hard or brittle
work pieces by using shaped tools high-frequency
mechanical motion and an abrasive slurry.
USM is able to effectively machine all hard materials
whether they are electrically conductive or not.

The process and cutting tool:
The process is performed by a cutting tool, which
oscillates at high frequency, typically 20-40 kHz, in
abrasive slurry.
The shape of the tool corresponds to the shape to
be produced in the workpiece.
The high-speed reciprocations of the tool drives
the abrasive grains across a small gap against the
workpiece.

Cont…
The tool is gradually fed with a uniform force.
The impact of the abrasive is the energy
principally responsible for material removal in the
form of small wear particles that are carried away
by the abrasive slurry.
The tool material, being tough and ductile, wears
out at a much slower rate.

Elements of
Ultrasonic Machining:
The tool is oscillated
by a longitudinal
magnetostriction
A magnetic field
variation at ultrasonic
frequencies
The length of a
ferromagnetic object
changes

Material removal:
Occurs when the abrasive particles, suspended
in the slurry between the tool and work piece, are
struck by the down stroke of the vibration tool.
The impact propels the particles across the
cutting gap, hammering them into the surface of
both tool and work piece. Collapse of the
cavitation bubbles in the abrasive suspension
results in very high local pressures.

Cont…
Under the action of the associated shock waves
on the abrasive particles, micro cracks are
generated at the interface of the work piece.
The effects of successive shock waves lead to
chipping of particles from the work piece.

Material removal:

The basic components of the cutting
action are believed to be:
The direct hammering of the abrasive in to the
work by the tool
The impact of the abrasive on the work
Cavitation induced erosion

Power supply:
The power supply is a sine-wave generator
The user can control over both the frequency
and power of the generated signal.
It converts low-frequency (50/60 Hz) power to
high-frequency (10-15 kHz) power
Power Supply to the transducer for conversion
into mechanical motion.

Transducer:
Two types of transducers are used in USM to
convert the supplied energy to mechanical
motion.
They are based on two different principles of
operation
- Magnetostriction
- Piezoelectricity

Magnetostriction:
When the material is placed in a sufficiently
strong magnetic field, the magnetic moments of
the domains rotate into the direction of the
applied magnetic field and become parallel to it.
During this process the material expands or
contracts, until all the domains have become
parallel to one another.
As the temperature is raised, the amount of
magnetostrictive strain diminishes, so they
require cooling by fans or water.

Piezoelectric Transducers:
Such as quartz or lead, zirconate, titanate,
generate a small electric current when
compressed.
Conversely, when an electric current is
applied, the material increases minutely in
size.
When the current is removed, the material
instantly returns to its original shape.
The material undergoes polarization by
heating it above the Curie point.

Tool Holder:
Its function is to increase the tool vibration
amplitude and to match the vibrator to the
acoustic load.
It must be constructed of a material with
good acoustic properties and be highly
resistant to fatigue cracking.
Monel and titanium have good acoustic
properties and are often used together
with stainless steel, which is cheaper.
However, stainless steel has acoustical and fatigue
properties that are inferior to those of Monel and
titanium, limiting it to low -amplitude applications.

Tool Holder:
Nonamplifying holders are cylindrical and result in the
same stroke amplitude at the output end as at the input
end.
Amplifying tool holders have a cross section that
diminishes toward the tool, often following an
exponential function.
An amplifying tool holder is also called a concentrator.
Amplifying holders remove material up to 10 times
faster than the nonamplifying type.
The disadvantages of amplifying tool holders include
increased cost to fabricate, a reduction in surface finish
quality, and the requirement of much more frequent
running to maintain resonance.

The Geometry of the
Tool
The geometry of the tool
generally corresponds to the
geometry of the cut to be
made,
Tools:
Tools should be constructed from relatively ductile materials.
The harder the tool material, the faster its wear rate will be.
It is important to realize that finishing or polishing operations
on the tools are sometimes necessary because their surface
finish will be reproduced in the workpiece.
Because of the overcut, tools are slightly smaller than the
desired hole or cavity
Tool and tool holder are often attached by silver brazing

Abrasive Concentration:
With an abrasive concentration of about 50% by
weight in water, but thinner mixtures are used to
promote efficient flow when drilling deep holes or
when forming complex cavities.

Basic Machine Layout:
The acoustic head is the most complicated part of
the machine.
It must provide a static force, as well as the high
frequency vibration.

The vibrating head is supplied with a constant force
using Counter Weights, Springs, Pneumatic and
Hydraulics, Motors

Tools:
Hard but ductile metal
Stainless steel and low carbon
Aluminum and brass tools wear near 5 to 10
times faster

ABRASIVE SLURRY:
Common types of abrasive
Boron carbide (B4
C) good in general, but
expensive
Silicon carbide (SiC) glass, germanium, ceramics
Corundum (Al2
O3
)
Diamond (used for rubies, etc)
Boron silicarbide (10% more abrasive power than
B4
C)
Liquid:
• Water most common , benzene, glycerol, oils,
• High viscosity decreases MRR.

Advantages:
UM effectively machines precise features in hard,
brittle materials such as glass, engineered
ceramics, CVD SiC (Chemical Vapor Deposition
Silicon Carbide), quartz, single crystal materials,
PCD(Polycrystalline diamond), ferrite, graphite,
glassy carbon, composites, piezoceramics.
A nearly limitless number of feature shapes
including round, square and odd-shaped
thru-holes and cavities of varying depths, be
machined with high quality and consistency.

Advantages:
The machining of parts with preexisting
machined features or metallization is possible
without affecting the integrity of the preexisting
features or surface finish of the workpiece.
USM machined surfaces exhibit a good surface
integrity and the compressive stress induced in
the top layer enhances the fatigue strength of the
workpiece.
The quality of an ultrasonic cut provides reduced
stress and a lower likelihood of fractures that
might lead to device or application failure over the
life of the product.

Disadvantages:
Ultrasonic machines have a relatively low MRR.
Material removal rates are quite low, usually less
than 50 mm3
/min.
The abrasive slurry also "machines" the tool itself,
thus causing high rate of tool wear, which in turn
makes it very difficult to hold close tolerances.
The slurry may wear the wall of the machined hole
as it passes back towards the surface, which limits
the accuracy, particularly for small holes.
The machining area and the depth of cut are quite
restricted

Electro-Chemical Machining (ECM):
Electrochemical machining (ECM) is a method of
removing metal by an electrochemical process.
ECM is opposite of electrochemical or galvanic
coating or deposition process

Theoretical
Background:
Electrolysis is the
name given to the
chemical process
which occurs, for
example, when an
electric current is
passed between two
conductors dipped
into a liquid solution.
Electrolysis of copper sulphate solution.

Ions which carry
positive charges
move through the
electrolyte in the
direction of the
positive current,
that is, toward the
cathode, and are
called cations.

Similarly, the negatively charged ions travel
toward the anode and are called anions.
The movement of the ions is accompanied by
the flow of electrons, in the opposite sense to
the positive current in the electrolyte, outside the
cell, as shown also in Figure and both reactions
are a consequence of the applied potential
difference, that is, voltage, from the electric
source.

Faraday’s Laws:
These results are embodied in Faraday’s two laws of
electrolysis:
The amount of any substance dissolved or
deposited is directly proportional to the amount of
electricity which has flowed.
The amounts of different substances deposited or
dissolved by the same quantity of electricity are
proportional to their chemical equivalent weights.

Dissolution Pattern:

General Description of ECM :
Electrochemical machining (ECM) is based on a
controlled anodic electrochemical dissolution
process of the workpiece (anode) with the tool
(cathode) in an electrolytic cell, during an electrolysis
process
Principal scheme
of
electrochemical
machining (ECM)

General Description of ECM :
Electrolysis is the name given to the chemical
process which occurs, for example, when an electric
current is passed between two electrodes dipped
into a liquid solution.
Electrochemical cell
A typical example is that
of two copper wires
connected to a source
of direct current and
immersed in a solution
of copper sulfate in
water as shown

Electrochemical Machining:
Uses an electrolyte and electrical current to
ionize and remove metal atoms
Can machine complex cavities in high-strength
materials
Leaves a burr-free surface
Not affected by the strength, hardness or
toughness of the material

Operating Principle:
As the tool approaches
the work piece it erodes
the negative shape of it.
Thus complex shapes
are made from soft
copper metal and used
to produce negative
duplicates of it. This
process is called
electrochemical sinking

Main Subsystems:
The power supply.
The electrolyte circulation system.
The control system.
The machine.

Power Supply:
The power needed to operate the ECM is
obviously electrical. There are many specifications
to this power.
The current density must be high.
The gap between the tool and the work piece must
be low for higher accuracy, thus the voltage must
be low to avoid a short circuit.
The control system uses some of this electrical
power.

Electrolyte Circulation System:
The electrolyte must be injected in the gap at high
speed (between 1500 to 3000 m/min).
The inlet pressure must be between 0.15-3 MPa.
The electrolyte system must include a fairly strong
pump.
System also includes a filter, sludge removal
system, and treatment units.
The electrolyte is stored in a tank.

Control System:
Control parameters include:
Voltage
Inlet and outlet pressure of electrolyte
Temperature of electrolyte.
The current is dependent on the above
parameters and the feed rate.

Machine:
The machine is a major subsystem of the ECM.
It includes the table, the frame, work enclosure
(prevents the electrolyte from spilling), the work
head (where the tool is mounted)
The tools (electrodes) are also part of the
machine system

Process Parameters:
Power supply
Type: Direct Current
Voltage: 5 to 30 V (continue or pulse)
Current: 50 to 40,000 A
Current Density: 10 to 500 A/cm2

Electrolyte
Most used: NaCl at 60 to 240 g/l
Frequently used: NaNO3 at 120 to 480 g/l
Temperature : 20 to 50°C
Flow rate: 1 l/min/100A
Velocity : 1500 to 3000 m/min
Inlet Pressure: 0.15 to 3 MPa
Outlet Pressure: 0.1 to 0.3 MPa
Frontal Working Gap :0.05 to 0.3mm
Feed rate: 0.1 to 20mm/min
Electrode material: Brass, copper, bronze

Advantages:
There is no cutting forces therefore clamping is
not required except for controlled motion of the
work piece.
There is no heat affected zone.
Very accurate.
Relatively fast
Can machine harder metals than the tool.

Advantages over EDM:
Faster than EDM
No tool wear at all.
No heat affected zone.
Better finish and accuracy.
Disadvantages
More expensive than conventional machining.
Need more area for installation.
Electrolytes may destroy the equipment.
Not environmentally friendly (sludge and other
waste)
High energy consumption.
Material has to be electrically conductive.

Applications:
The most common application of ECM is high
accuracy duplication. Because there is no tool wear,
it can be used repeatedly with a high degree of
accuracy.
It is also used to make cavities and holes in various
products.
It is commonly used on thin walled, easily
deformable and brittle material because they would
probably develop cracks with conventional
machining.

Department of Mechanical & Manufacturing Engineering, MIT, Manipal 100 of

Electrochemical Grinding(ECG)
It is a modern way of effective and speedy way of
abrasion and material removal. Burr free grinding
is possible.
The process involves when low-voltage,
high-current dc power is applied between the
grinding wheel and the workpiece in the presence
of the electrolytic solution to complete the
electrochemical cell.

In this process the material oxidizes and the wheel
can cut with the minimum stress thus eliminating
any burrs. The process basically combines
electrical and chemical energy for metal removal. It
being a non-abrasive process produces precise
cuts .
The best aspect of this kind is that the hardness
and machinability have a lesser impact on the
cutting tool. The process can be used for any
conductive material.

The abrasives in the rotating grinding wheel continually
remove this film and expose a fresh surface for
oxidation. Metal deposition on the grinding wheel
(cathode) is avoided by proper choice of electrolyte.
Dissolution of the metal,
combined with the
mechanical removal of
the oxides, results in an
efficient low-stress cut.

Principle of ECG:
According to Faraday's Laws the quantity of
chemical change occurring at an electrode is
directly proportional to the amount of current
passing between the electrodes.
Low voltage, high current electrical energy
supplied by a properly designed DC power supply
is central to the Electrochemical Grinding process.
Since the voltages are low, spark discharge and
the associated heat are avoided.
In addition, the low voltages used prevent any
electrical shock hazard to the operator.

Features:
Uses a rotating cathode embedded with abrasive
particles for applications comparable to milling, grinding
and sawing
Most of the metal removal is done by the
electrolyte,(90%) and about 10% by conventional
grinding, resulting in very low tool wear.

Electrolytes:-Aqueous solution of sodium silicate,
borax, sodium nitrate.
Electrochemical grinding (ECG) is an electrolytic
material-removal process involving a negatively
charged abrasive grinding wheel, a conductive fluid
(electrolyte), and a positively charged workpiece.
Workpiece material depletes in to the electrolyte
solution.
ECG is similar to electrochemical machining except
that the cathode is a specially constructed grinding
wheel instead of a tool shaped like the contour to be
machined.

Process Characteristics
Utilizes electrically conductive grinding wheels
Removes material by electrochemical decomposition
and abrasive action
Depletes workpiece materials and deposits them in
electrolyte
Wheels wear extremely slowly
Workpieces are electrically conductive

Grinding Wheel:
Abrasives – Aluminium oxide, diamond.
Size: 60-80 mesh grid.
Bonding agents: copper, brass and nickel.
Functions of abrasives particles are:-
Act as insulator to maintain small gap between
wheel and work piece.
Removes electrolysis products from work area.
Cut chips

Advantages Over Other Machining Methods
Metal
Remo
val
Proce
ss
Milling,Turning,
Sawing,
Abrasive Grinding
EDM Laser Water-jet
Adva
ntage
s of
ECG
Equip
ment
Burr free
No metallurgical damage
from heat
No work hardening
Faster for tough materials
Stress free
Better finish
No cracking
Improved wheel life
Less frequent wheel
dressing
No wheel loading or glazing
No metallurgical
damage from
heat
No heat affected
zone
No recast layer
Faster cutting
No
metallurgic
al damage
from heat
No heat
affected
zone
No recast layer
Can cut thicker
materials
More precise
tolerances
Lower
consumable
costs
Faster
Quieter

Limitations:
Initial cost of ECG is high.
Non conducting materials can not be
machined.
Most electrolyte are corrosive in nature
Applications:
Grinding following materials:
• Carbide cutting tools.
• Refractory metals.
• High strength steels.
• Nickel and cobolt based alloys.

Grinding Vs ECG
Grinding ECG
Grinding is due to
mechanical abrasion
(contact process)
Grinding is due to
electrolytic action(90%)
and abrasion(10%).
Insulated bonding material
to manufacture grinding
wheel.
Metal bonded G W acts as
conductor of electricity
Considerable tool wear. Negligible tool wear
(1/10th
)
Reasonable surface finish. Excellent surface finish.

Cont…
Grinding is slow process ECG is more rapid.
Several passes are
required.
Single pass grinding.
Coolants are used. Electrolyte is used.
Can be used for conducting
and non conducting
materials.
Only for conducting
materials.
Work is subjected to
mechanical and thermal
stresses.
Free from any kind of
stresses.

Electric Discharge Machining (EDM)
It is also known as spark erosion or spark
machining.
It is a process of metal removal based on the
principle of erosion of metals by an interrupted
electric spark discharge between the electrode tool
(cathode) and the work (anode).
In EDM process electric energy is used to cut the
material to final shape and size. Efforts are made to
utilize all the energy by applying it at the exact spot
where the operation to be carried out.

No complicated fixtures are needed for holding the
job and even very thin jobs can be machined to the
desired dimensions and shape.
All the operating is carried out in a single setup.
This process may be applied to machine steels,
supper alloys, refractories etc.
Principle Of Operation:
The basic EDM system consists of a shaped tool
and the work piece, connected to a dc power supply
and placed in a dielectric fluid.

When the potential difference
between the tool and work piece
is sufficiently high, a transient
spark discharges through the
fluid, removing a very small
amount of metal from work piece.
Millions of sparks are targets on
to the small area over the work
piece causing pitting action.
Principle Of Operation:
The basic EDM system consists of a shaped tool and
the work piece, connected to a dc power supply and
placed in a dielectric fluid.

EDM Operations:
Charge up an electrode
Bring the electrode near a metal work piece
(oppositely charged)
As the two conductors get close enough a spark
will arc across a dielectric fluid.
The process is based on melting temperature, not
hardness, so some very hard materials can be
machined this way.

Basic Process:

Setup

Process Parameters:
Gap - 0.01 to 0.5 mm
Pressure - 2 kgf/ cm2
Current - 0.5 to 400 A
Voltage - 40 to 300 V
Pulse Duration - 2 to 2000 x10-6

Dielectric Fluid:
The most common dielectric fluid used are-
White spirit
Transformer oil & Mineral oil
Kerosene
Deionized water
Ethyl glycol
Recent trends involve use of clear low viscosity
fluids. Although more expensive, these fluids make
cleaning easier.

Function of Dielectric Fluid:
Act as an insulator until the potential is
sufficiently high
Act as a flushing medium and carry away the
debris in the gap
Rapid quenching
Break-down rapidly into ionized state
Provide a cooling medium

Electrodes:
Electrodes for EDM are usually metals having
good electrical properties.
These include:
Graphite
Brass
Copper
Zinc-tin alloy
Copper-tungsten alloy

Basic Requirements:
The basic requirements for the work pieces are -
Good electrical conductivity.
High machinability.
Low ionization rate.
Good resistance to corrosion
High melting point.

Auxiliary Set-Up:
Spark generator
Constant tool feed
Circulation system

Advantages:
Suitable for thin fragile sections
Suitable for mass production
Can be fully automated
No complicated fixtures required
Surface finish is very good
Can be used for any hard materials
Good tolerance can be achieved

Disadvantages:
Not economically viable for soft materials
High power consumption
Not suitable for large metal removal
Work piece must be electrically conductive
Excessive tool wear

Applications:
Used in the manufacture of
Press tools
Dies
Nozzles
Injectors
Engine Valves

Comparison with ECM
ECM EDM
Tool is the female mating
image of the cavity to be
produced
No specific tool shape
Continuous power supply Intermittent power supply
Electrolytes used Dielectric medium used
Complete submersion not
necessary
Work piece submerged in
the dielectric fluid
Absolutely free from
thermal stresses
Thermal stresses may be
developed

Laser Beam Machining (LBM)

Introduction:
The word laser is an acronym for Light
Amplification by the Stimulated Emission of
Radiation.
Lasers are used in a wide array of applications
from industrial manufacturing applications to
home entertainment, medicine security
systems and weaponry.
The three most important attributes of laser
light are: It is coherent i.e. all photons that
make up the beam are in phase with each
other.

Cont…
It is collimated, because photons that diverge
from the parallel are lost through the chamber
walls a very parallel beam is issued.
It is monochromatic, literally one colour, that is
of one wavelength. Different media used to
stimulate the photons generate different
wavelengths, but each type of laser has a
specific wavelength. The purity of the medium
used is of paramount importance

LASER CONCEPT:
Laser material processing utilizes the energy from
coherent beams of light to remove, melt or thermally
modify materials. Add energy to make electrons
jump to higher energy orbit.
Electron relaxes and moves to equilibrium at ground
state energy level.
Emits a Photon in this process (key laser
component).Two mirrors reflect the photons back
and forth and excites more electrons.
One mirror is partially reflective to allow photons of
suitable amplitude to pass through that is the Laser
beam.

Nucleus
Electron Ground
State
Excited
State
Orbits
Photon
Electron is energized
to the excited state
Electron relaxes to
ground state and
photon is produced

Pictorial Representation of Formation of Laser Beam
1. The laser in its non -
lasing state
2. The flash tube fires and
injects light into the ruby
rod. The light excites
atoms in the ruby.

3. Some of these atoms
emit photons.
4. Some of these photons
run in a direction parallel
to the ruby's axis, so they
bounce back and forth off
the mirrors. As they pass
through the crystal, they
stimulate emission in
other atoms.

5. Monochromatic, single-phase(single alternating
voltage), columnated(made accurately parallel)
light leaves the ruby through the half-silvered
mirror - laser light.

Representation
of how a CO2
laser beam is
generated.

LASER Materials:
There are basically two types of laser materials:
1. Solid state laser materials: This includes
a. “Ruby Crystals “ which is basically crystalline
Aluminum oxide or Sapphire , somewhat restricted in
application due to relatively short wavelength.
b. “YAG” which is basically ‘Yttrium Aluminum
Garnet’ with a wavelength 1.06 microns and
Neodymium in glass or Neodymium-YAG.
2. Gas laser materials: This includes Carbon Dioxide
with 10.6 microns wavelength. Carbon Dioxide lasers
is used to process metals and high strength non
metals.

Lasing Material Selection
Depending upon wavelength required, lasing material are
selected as follows:
Lasing Material Wavelength (nm)
Argon fluoride (UV) 193
Krypton fluoride (UV) 248
Xenon chloride (UV) 308
Nitrogen (UV) 337
Argon (blue) 488
Argon (green) 514
Helium neon (green) 543
Helium neon (red) 633
Rhodamine 6G dye (tunable) 570-650
Ruby (CrAlO3) (red) 694
Nd:Yag (NIR) 1064
Carbon dioxide (FIR) 10600

Process Of Laser Beam Machining:
An initial source of 250 to 1000 watts of electrical
power is used to activate Tungsten or Krypton arc
flash lamp located near gas medium (or solid
crystal).
Mirrors located inside the optical oscillator or
discharge tube are used to reflect and focus the
light on the laser medium or some laser equipment.

The light is focused onto the laser medium by
mirror finished, gold plated reflectors. The radiation
from the light source excites electrons in the
storage medium and raises them to higher energy
level.
When the atoms relax back to their normal energy
level the released energy emerges as a stream of
Photons flowing almost parallel to axis of medium.
The collimated laser beam is focused to provide the
beam spot of precise size needed to do the
machining.

The workpiece rests on a sacrificial table.
Workholding is minimal due to absence of cutting
forces and when used is mainly for location.
The focal point of the laser is focused onto the
surface of the workpiece. The follower takes into
account any variation in height of the workpiece.
The material vapourises instantly, producing a kerf
in the material
The machine axes move to generate the correct
profile. The speed of cutting is such that the Heat
Affected Zone (HAZ) is minimal - compared to flame
cutting.

A gas assist jet clears the molten metal that has not
vapourised (as in oxy-fuel cutting). Note: the gas
assist gas may be one of two types, inert and
exothermic.
Inert gasses commonly used are Nitrogen and
Argon. Exothermic gasses, Air or pure Oxygen. Inert
gasses help keep oxidisation to a minimum, cool the
cutting zone and prevent flammable materials
burning. Exothermic gasses cause a reaction that
improves cutting performance.

Schematic of Laser Beam Machining Device

Laser Beam Machining:
More Precise.
Useful with a variety of
materials
Metals, Plastics, Ceramics
and Composites.
Smooth clean cuts.
Faster Process.
Decreased heat affected
zone.

Internal Structure Of Finished Work Piece By Laser
Beam Machining :

Materials that may be cut:
A wide range of materials may be cut using a
laser beam, however care must be taken in
choosing the correct type of laser. Below is a
table outlining the suitability of both CO2 and
Nd:YAG lasers for materials likely to be
encountered in the course of an average
manufacturing business

0 = IMPOSSIBLE / DANGEROUS, 5 = EXCELLENT
Material CO2 Nd:YAG
MILD AND CARBON STEEL 5 5
STAINLESS STEEL 4/5 4/5
ALLOY STEEL 4/5 4/5
TOOL STEEL 5 5
ALUMINIUM ALLOYS 2/3 4/5
COPPER ALLOYS 1 3
TITANIUM 4 4
PLASTICS 5 0/1
RUBBER 4 1
PAPER (GASKETS ETC) 5 ¾
CERAMICS 3/4 3/4

Basic Types of Laser Machining:
There are many types of laser machining that
are commonly used in Industry and technology
processing. Each type has its own applications
and uses that differ from other types. We will
identify five types of this machining process.
▪ Laser Cutting Process
▪ Laser Drilling Process
▪ Laser Heat-Treating Process
▪ Laser Scoring Process
▪ Laser Scribing Process

A. Laser Cutting Process
This process is defined as a machining
process in which a laser beam passes over the
material being cut. The beam vaporizes the
material and the path of the beam determines
the shape that is cut. There are two variables
that should be considered in this process
which are: the specification of the object that
will be cut and the speed of cutting

The Mechanics of Laser Cutting/Welding:

B. Laser Drilling Process
Laser drilling is the process of repeatedly
pulsing focused laser energy at a specific
material. The drill beam can drill in very difficult
locations or areas of materials and the holes
that are made by the laser drilling process can
be drilled with reliable and consistently good
quality or performance. The picture illustrates
the laser drill process:

C. Laser Heat-Treating Process
A surface alteration process created to change
the microstructure of metals by controlled
heating and cooling. The laser, because of its
ability to pinpoint focus its energy, can heat
treat small sections or strips of material without
affecting the metallurgical properties of the
surrounding area.

D. Laser Scoring Process
Laser scoring is a process of utilizing a
focused spot of laser energy to remove
material to specified depth. Laser scoring is
useful in designing a crease to be torn or bent
easily as with tear away checks, folders, cards,
etc. The following pictures illustrate the laser
scoring process:

E. Laser Scribing Process
Laser scribing is a process in which lines and
characters of different fonts can be produced on
materials. Unlike laser engraving, the line being
laser scribed is only as wide as a single laser
beam and is set to a specific tolerance depth. The
line consists of a series of small, closely spaced
holes in the substrate that is produced by laser
energy pulses. Ceramics, glass and wood are
common laser scribed products. Laser is focused to a small
spot and scanned over the surface.

Process Parameters:
Metal removal principle: Melting & Vaporization
Lasing Material: Ruby Crystal
Energy Density: 10 kW/mm2
Accuracy in cutting : +0.01 mm
Accuracy in Drilling: +0.02 mm
Cooling Agent: Liquid Nitrogen, Water, Air
Light Source: Flash Lamp, Argon, Krypton, Neon

Advantages: Machining of any metal and non-metal is possible
- drilling and cutting of areas not readily accessible are possible
- heat affected zone is small because of collimated beam
- extremely small holes can be machined
- there is no wear
- rubber and plastics can also be machined.
Limitations: Cannot be used to cut metals that have high heat conductivity
– Actual efficiency is extremely low
– process is limited to thin sheets
– low MRR
– machine holes are not round and strong
– cost is high
– life of flash lamp is short.
Application: Machining of small holes and complex profile of hard materials and
ceramics – partial cutting and engraving, steel metal trimming, blanking and resistor
trimming – in mass micro-machining production.

Advantages:
No physical contact between tool and work piece
and hence no tool wear.
Suitable for all types of metals and non metals.
Precision location is ensured by focusing the laser
beam.
Small holes can be drilled in very hard materials
like diamond in few seconds.
Very precise cutting process.
Heat affected zone is very less.

Limitations:
Very low metal removal rate.
Can’t be used for large scale metal removal.
Holes produced are not straight and round hence
depth of cut is very limited.
Very costly setup.
Not applicable to blind machining of metals.
Working on Laser machines may cause damages
in the eyes and burn hands

Limitations:
Since laser action is essentially an inefficient
process, will have significant electrical power
needs, often at high voltage and three phase.
Electrical safety, especially during maintenance
and repair, is therefore a significant risk that needs
to be adequately controlled by manufacturers and
employers that use laser products.

Applications:
Manufacturing of metal sheets for truck bed hitch
plates
Splicing of aluminum sheets in the aircraft industry
Cutting of Multi Layered Insulation for spacecraft
In aerospace where cooling holes needs to be formed,
nozzle guide vanes, combustion rings and engine
blades are common components drilled with lasers
Used to perform precision micromachining on all
microelectronic substrates such as ceramic, silicon,
diamond, and graphite
Patterning displays of glass or plastic
Trace cutting on semiconductor wafers and chips

Plasma Arc Cutting (PAC)

Principle of PAC:
In the principle of plasma arc
machining(PAM),a plasma
torch known as the gun or
plasmatron, a volume of gas
such as H2
, 02
, N2
etc. is
passed through a small
chamber in which a high
frequency spark (arc) is
maintained b/w tungsten
electrodes (cathode) and the
copper nozzle (anode), both of
which are water cooled

Plasma cutters work by sending a pressurized gas,
such as nitrogen, argon, or oxygen, through a small
channel. In the center of this channel, you'll find a
negatively charged electrode.
When you apply power to the negative electrode, and
you touch the tip of the nozzle to the metal, the
connection creates a circuit. A powerful spark is
generated between the electrode and the metal. As the
inert gas passes through the channel, the spark heats
the gas until it reaches the fourth state of matter.
This reaction creates a stream of directed plasma,
approximately 30,000 F (16,649o
C) and moving at
20,000 feet per second (6,096 m/sec), that reduces
metal to molten slag.

Inside the Torch:
Plasma cutters come in all shapes and sizes. There
are monstrous plasma cutters that use robotic arms.
There are also compact, handheld units. Regardless of
size, all plasma cutters function on the same principle
and are constructed around roughly the same design.
There are three major components inside the torch
body.
Electrode
Gas Baffle (Swirl Baffle)
Nozzle

Transferred & Non-transferred Modes:
Transferred :
Electric current flows between the plasma torch
electrode (cathode) and the work piece (anode).
This method is used in case of ferrous, conductive
metals for cutting.
Non-transferred :
Electric current flows between the electrode and the
torch nozzle. Allows plastics and other
nonconductive materials to be cut. This is method is
generally not preferred in industries because
transferred arc method is much efficient and
maximum amount of heat generated is used in case
of transferred arc

Types of Torch:
1.Dual Gas Plasma Torch
Equipment based on this technique has the same
general characteristics as the conventional plasma arc
devices. The main difference is the addition of an outer
shield of gas around the nozzle to reduce the shearing
effect of the atmosphere on
the cutting gas.

Usually the main cutting gas is nitrogen. Choice of
the shield, or secondary gas depends on the metal
being cut. For example for the machining of
stainless steel, aluminium and other non-ferrous
metals, hydrogen is often employed as the shield
gas. Carbon dioxide gas is also popular with both
ferrous and non ferrous metals. The shield gas
may be air or oxygen for a mild steel workpiece.

2. Water Injected Plasma Torch
Although nitrogen is still employed as the main gas,
the shield gas is replaced by water. In order to give
maximum constriction of the arc, a radial
water-injecting jacket is fitted to the nozzle. This
cooling
effect of the water is found
to reduce the width of
cutting zone. The quality of
the cut is also found to be
improved because of the
cooling effect of the water.

3. Air Plasma Torch
Air cutting was introduced in the early 1960s for
cutting mild steel. The oxygen in the air provided
additional energy from the exothermic reaction with
molten steel. This additional energy increased
cutting speeds by about 25% over plasma cutting
with nitrogen.

Factors Affecting the Machining Process:
Gas Purity
The purity of gas is essential for good cut quality
and long electrode life. Minimum purity
requirements for nitrogen are 99.995%. If purity
levels are less than recommended minimum the
following could occur.
Inability of the arc to penetrate thin materials at
any current level.
Depending on the degree of contamination,
variation in cut quality.

Extremely short electrode life.
When using N2
, appearance of a black film
residue on the face of the electrode and in the
nozzle bore. More the contamination, more the
residue.

Gas Pressure/Flows
Each nozzle is designed to perform at an optimum
current based on a given gas pressure/flow.
Increasing this pressure can result in a decrease
in electrode life. This is evident by a drilled
appearance in the tungsten insert. With nitrogen
there will be a problem with torch starting.
If the torch fails to start at high pressure, a
sputtering pilot arc may be observed. Where high
gas pressure may create problems, low gas flow
will usually result in a double arc failure.

Kerf:
Kerf is the width of material
(perpendicular to the torch
and cut axis) removed
during the plasma cutting
process. Kerf is affected by
three major variables.
Cutting Speed
Cutting Amperage
Standoff Distance

Cutting Speed
Faster cutting speeds with other variables constant
will result in a narrower kerf. The kerf will continue
to narrow until loss of penetration occurs. Slower
travel speeds will result in a wider kerf until loss of
arc occurs.
Cutting Amperage
Increasing cutting amperage with the other two
variables constant will result in a wider kerf.
Lowering amperage will result in a narrower kerf,
until penetration is lost.

Standoff
Standoff is the distance maintained between torch
and work-piece after piercing (while cutting).
Increasing the standoff distance requires increase
in arc voltage resulting in widening of the kerf.
Lowering standoff will lead to a narrower kerf.

Arc Voltage:
Arc voltage is not a independent variable. It is
dependent on:
Current (amperage)
Nozzle orifice size
Standoff
Cut gas flow rate
Cut water flow rate (if applicable)
Cutting speed

Plasma Arc Cutting/Machining

Advantages:
It can be used on any metal(Alloy steel, cast
iron, refractory material).
High material removal rate.
A plasma arc is hot enough to burn through
most surface coatings such as paint and rust
and still provide excellent cutting results.
Very small Heat Affected Zone (HAZ).

Disadvantages:
Metallurgical alterations of the surface occurs.
Oxidation and scale formation takes place and
thus it requires shielding.
It produces tapered surfaces.
Protection from noise is necessary.
Protection of eyes is necessary for the
operator and persons working in nearby areas.
Cost of equipment is high.

Applications:
1. Profile Cutting of Flat Plates
The profile cutting of metals such as stainless
steel, aluminium and copper alloys, which are
difficult to machine by oxy-fuel gas techniques, is
now a widespread industrial use for plasma
machining, particularly when adapted for CNC.
Rates four times faster than oxy-fuel gas
methods have been reported for plasma cutting
of plates of thickness 6 to 25 mm.

Applications:
2. Grooves
Grooves about 1.5 mm deep and 12.5 mm wide
have been formed in stainless steel by plasma arc
machining at metal removal rates of up to 80
mm³/min with equipment operated at 50 KW.
These rates are about 10 to 30 times greater than
those of conventional chipping and grinding.
Plasma arc techniques can be used for similar
groove formation in non-conducting materials,
although the material removal rate is then reduced
to about 30 mm³/min.

Applications:
3. Turning
Since the tool and workpiece do not come in contact
in PAM, this method is particularly attractive for
turning, especially with materials that are difficult to
machine by conventional methods. The plasma
torch is held in a standard lathe in the same way as
a conventional tool. The torch is usually mounted
tangentially to the workpiece, at an angle of about
30°. The depth of cut can be controlled by either
power or surface speed

Electron Beam Machining (EBM)
In EBM electrons emitted by a hot surface and
accelerated by a voltage of 10-50kV are focused to
a very small area on the work piece.
This stream of high energy electron posses a very
high energy density of the order of 104
kW/mm2
and
when this narrow stream strikes the work piece the
KE of the electrons is converted to powerful heat
energy which is quite sufficient to melt and
vaporize any material.

Even though the electron can penetrate metals to a
depth only few atomic layers, the electron beams
can cut metal to a depth of 25mm or more.
These electron beams are focused on the work
piece by electrostatic or electromagnetic lens.
It is done in a high vacuum chamber to eliminate
the scattering of the electron beam as it contacts
the gas molecules on work piece.

EBM Equipment

Process parameters:
Material removal by - melting, vaporization
Medium – Vacuum
Tool - beam of electrons moving at very high
velocity
Maximum MRR = 10 mm3
/min
Specific Power Consumption = 450W/mm3
/min

Critical Parameters - accelerating voltage, beam
current, beam diameter, work speed, melting
temperature
Materials Application - all materials
Shape Application - drilling fine holes, cutting
contours in sheets, cutting narrow slots
Limitations - very high specific energy
consumption, necessity of vacuum, expensive
machine.

Advantages
High accuracy.
High rate of production.
Metals and non metals can be machined.
No chemical and thermal distinction.
Limitation
MRR is low.
Method is quite difficult.
Equipment is expensive.
Holes produced in materials of greater
thickness is tapered.

Applications:
Micro machining operations on thin metals
including drilling perforating and scribing the
engraving.
It is used to manufacture field emission cathodes,
integrated circuits and computer memories.
Useful for materials with high melting points and
low thermal conductivity.

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