Need for unconventional or non-traditional process: -

1. The hardness and strength of the material is very high or the material is too brittle.
2. The work piece is too flexible, slender or delicate to withstand the cutting or grinding forces,
or the parts are difficult to fixture.
3. The shape of the part is complex, including such features as internal and external profiles or
small diameter.
4. Surface finish and dimensional tolerance requirements are more rigorous than that obtained
by other process.
5. Temperature rise and residual stresses in the work piece are not desirable or acceptable.

• Selection of a Process is done based on the following factors

1. Physical parameters of the process
2. Shapes to be machined
3. Process capability
4. economics

Abrasive Jet Machining (AJM): -

A high velocity of jet of dry air, nitrogen or carbon dioxide, containing abrasive
particles, is aimed at the work piece surface under controlled conditions. The impact of
the particles develops a sufficiently concentrated force to perform operations such as
cutting small holes, slots, or intricate patterns in very hard or brittle metallic and non-
metallic materials, deburring or removing small flash from parts, trimming and
bevelling etc.
The gas supply pressure is of order 850 Kpa and the abrasive jet
velocity can be as high as 300m/s and is controlled by a valve. The hand-held nozzles
are usually made of tungsten carbide or sapphire. The abrasive size is in the range of
10 to 50micrometer. Because of the flow of the free abrasives tends to round off
corners, designs for abrasive-jet machining should avoid sharp corners.

Advantages:
  Can be used to machine brittle materials with thin sections
 Can be used in areas which are inaccessible by ordinary methods
 Leaves little or no heat generation. Hence, insignificant surface damage
 Low capital investment and low power consumption.
Limitations: -
• Not suitable in ductile materials
• Machinability accuracy is poor
• Lower metal removal rates
• Nozzle wear rate is high
• Tends to pollute the environment
• Tapering of drilled holes

ULTRA SONIC MACHINING(USM): -

In Usm, material is removed from the surface by microchipping and erosion with fine
abrasive grains in a slurry. The tip of the tool(sonotrode) vibrates at a frequency 20KHz and low
amplitude. This vibration in turn imparts a high velocity to abrasive grains between the tool and the
work piece.
The stress produced by the impact of abrasive particles on the work piece surface is
high because (a) the time contact between the particle and the surface is very short and, (b) the area
of contact is very small. In brittle materials, these impact stresses are sufficiently high to cause
microchipping and erosion of the work piece.

Water Jet Machining (WJM): -

In water jet machining, high velocity water jet is allowed to strike a given workpiece.
During this process, its kinetic energy is converted to pressure energy. This induces a
stress on the workpiece. When this induced stress is high enough , unwanted particles
of the work piece are automatically removed.
 • 1% long chain polymer is mixed with the water
• Water + polymer mixture is sent to the pump/intensifier to increase the pressure
of the fluid to the required level
• From pump/intensifier mixture goes to the accumulator.
• During the idle time, energy is stored in the accumulator and given out during
cutting
• Control unit takes care of maintenance of pressure and flow rate in the system
• Piping used may be fixed or flexible
• Jet of fluid comes out of the nozzle at pre-defined pressure and velocity
• When fluid strikes the work surface erosion takes place on work surface.
Applications: -
1. Hydraulic mining of coal
2. Cutting both coal and rock
3. Demolishing reinforced concrete structures
4. Cutting anti-skid groves in airfield runways and roads
5. Making trenches.

Advantages: -
1. Water is cheap, non-toxic, readily available and easily disposable
2. Operation is possible both in horizontal and vertical planes.
3. Any contour cut is possible
4. Gives clean and sharp cut
5. Heat generation is absent.

Electron Discharge Machining (EDM): -

The principle of EDM also called as electro discharge or spark erosion
machining, is based on the erosion of metals by spark discharges. We know that when
two current conducting wires are allowed to touch each other, an arc is produced. If we
look closely at the point of contact between the two wires, we note that a small portion
of the metal has been eroded away, leaving a small crater.
The basic EDM system consists of a shaped tool(electrode) and the workpiece,
connected to a dc power supply and placed in a dielectric (electrically conducting)
fluid. When the potential difference between the tool and the workpiece is sufficiently
high, a transient spark discharges through the fluid, removing a very small amount of
metal from the workpiece surface. The capacitor discharge is repeated at rates of
between 50KHz ad 500KHz with voltage usually ranging between 50V and 380V and
currents from 0.1A to 500A.

Applications:-
1. Tools, dies, fixtures, cutting tools, gauges etc
2. Press tools, extrusion dies, die rings and fixtures
3. Plastic dies, injection moulds, mould inserts, repair and modification of
mould inserts
4. Diecast moulds, mould inserts, re-machining of damaged moulds
5. Manufacturing of forging dies, repair of damaged dies for hot or cold forging
dies, trimming dies
6. Press roller dies, hammer moulds, forging
7. Sintering and press dies
8. Cutting and calibrating tools
9. Dies for vulcanizing moulds and automatic glass presser.

Limitations:-
11.Can be performed on electrically conductive materials, regardless of strength,
toughness and hardness
12. Process works without any cutting force, hence it allows machining of
thin, fragile, complicated jobs
13. The material does not get heat treated by the power to the core.
14. The surface damage is small and can be easily corrected
15. The process dimensional repeatability and the surface finish obtained is
finishing are extremely good.

UNIT-3

LASER Beam Machining (LBM): -

In LASER beam machining , the source of energy is LASER (Light
Amplification by Simulated Emission of Radiation), which focuses optical energy on
the surface of the workpiece. The highly focused, high density energy melts and
evaporates portions of the workpiece in a controlled manner. This process, which does
not require vacuum is used to machine a variety of metallic and non-metallic materials.

Steps in LASER production;

 A laser is created when the electrons in atoms in special glasses, crystals, or
gases absorb energy from an electrical current or another laser and become
excited.
 These excited electrons move from a lower-energy orbit to a higher-energy orbit
around the atom’s nucleus. When they return to their normal or “ground” state,
the electrons emit photons (particles of light).
 These photons are all at the same wavelength and are coherent. In contrast with
ordinary visible light which comprises of multiple wavelengths and is not
coherent.

Advantages of LASER Beam Machining

 It can melt and vaporise any known material
 Can weld or machine through glass or any optically transparent material
 No direct contact between tool and workpiece
 Can easily weld dissimilar metals
 Can weld or machine in otherwise inaccessible place unless its path is
obstructed.
Limitations of LASER beam Machining
  Cannot be used to cut materials that have high heat conductivity or high
reflectivity.
Eg: Alluminium, Copper and their Alloys
 Machined area can be irregular due to off-axis modes that may be generated
during laser action
 The least diameter to which the laser beam can be focussed depends on the laser
beam divergence
 Output energy from laser is difficult to control precisely
 The laser system is quite inefficient
 Pulse repetition rates are slow
 Limitations of Laser Beam Machining.

PLASMA ARC MACHINING: -

What is Plasma?
Solids, liquids, and gases are the three familiar states of matter. In general, when
solid is heated, it turns to liquids and the liquids eventually become gases. When a
gas is heated to sufficiently high temperature, the atoms molecules) are split into
free electrons and ions. The dynamical properties of this gas of free electrons and
ions are sufficiently different from the normal unionized gas.
So, it can be considered as a fourth state of matter, and is given a new name,
PLASMA.
when the following gas is heated to a sufficiently high temperature of the order
of 11,000°C to 28,000°C, it becomes partially ionized and it is known as
‘PLASMA’.

When a D.C power is given to the circuit, a strong arc is produced between
the electrode (cathode) and the nozzle (anode).
A gas usually hydrogen (H2) or Nitrogen (N2) is passed into the chamber.
This gas is heated to a sufficiently high temperature of the order of 11,000°C to
28,000°C by using an electric arc produced between the electrode and the nozzle. In
this high temperature, the gases are ionized and a large amount of thermal energy is
liberated.
This high velocity and high-temperature ionized gas (plasma) is
directed on the workpiece surface through the nozzle.
This plasma jet melts the metal of the workpiece and the high-velocity gas
stream effectively blows the molten metal away.
The heating of workpiece material is not due to any chemical reaction but due to
the continuous attack of plasma on the workpiece material So, it can be safely used
for machining of any metal including those which can be subjected to the chemical
reaction.
Applications: -
1. It is used for cutting alloy steels, stainless steel, cast iron, copper,
nickel, titanium, aluminium, and alloy
2. It is used for profile cutting.
3. It is successfully used for turning and milling of hard to machine
materials.
4. It can be used for stack cutting, shape cutting, piercing, and under
water cutting.
Advantages: -
1. It can be used to cut any metal.
2. The cutting rate is high.
3. As compared to the ordinary flame cutting process, it can cut plain
carbon steel four times faster.
4. It is used for rough turning of very difficult materials.
Limitations: -
1. Protection of eyes is necessary for the operator and persons
working in nearby areas.
2. Oxidation and scale formation takes place. So, it requires
shielding.
3. The work surface may undergo metallurgical changes.
4. Needs eye shielding noise protection for the operator.
5. It produces a tapered surface.

ELECTROM BEAM MACHINING: -

Material is removed with the help of a high velocity focussed stream of electrons
which heat, melt and vaporise the work material at the point of bombardment.
Electrons can be obtained in the free state. Thermo-electric cathodes are used where in
metals are heated to the temperature at which the electrons acquire sufficient speed for
escaping to the space around the cathode.
 The source of energy in electron-beam machining is high velocity electrons,
which strike the surface of the workpiece and generate heat. The machines utilize
voltages in the range of 50kV-200kV to accelerate the electrons to speeds of 50% to
80% of speed of light. Beam is generated in vacuum to avoid oxidation of emitter at
high temperature and reduce collisions of electrons with air molecules. Power density
of the order of a billion Watts/cm2 can fuse and vaporise any material on which it falls.
Its applications are similar to those of laser-beam machining, except that EBM requires
a vacuum.
Process Capabilities: -
i) Can provide holes of diameter in the range of 100µm to 2mm with a
depth up to 15mm (I/d ration around 10).
ii) Hole can be tapered along the depth or barrel shaped.
iii) By focussing the beam below the surface, a reverse taper can also be
obtained.
iv) Edge rounding at the entry point and presence of recast layer.
Advantages: -
i) Excellent strategy for micro machining. It can drill holes or cut
slots.
ii) Can cut any known material, metal or non-metal, irrespective of
their mechanical properties that would exist in vacuum.
iii) No cutting tool pressure or wear having distortion free machining
and resulting in precise dimensions. Work holding and fixture cost
is very less.
iv) Fragile and brittle materials can be machined.
v) No physical/metallurgical damage. HAZ is less. Can provide holes
of any shape.

Limitations: -
i) High initial equipment cost
ii) Regular maintenance for vacuum.
iii) Significant non-productive pump time for vacuum.
iv) Recast layer formation.
v) High operator skill required.