ABRASIVE JET MACHINING, ULTRASONIC MACHINING, ELECTRON BEAM MACHINING, ELECTRO CHEMICAL MACHINING & ELECTRICAL DISCHARGE MACHINING

1. UNCONVENTIONAL MACHINING
PROCESS
P.HARIPRASAD
ASSISTANT PROFESSOR,
DEPARTMENT OF MECHANICAL ENGINEERING,
KIT-KALAIGNAR KARUNANIDHI INSTITUTE OF
TECHNOLOGY,
COIMABATORE - 641402

2. Non Traditional Machining (NTM)
• Material removal may occur with chip formation or even no chip
formation may take place. For example in AJM, chips are of
microscopic size and in case of Electrochemical machining
material removal occurs due to electrochemical dissolution at
atomic level
• In NTM, there may not be a physical tool present. For example in
laser jet machining, machining is carried out by laser beam.
However in Electrochemical Machining there is a physical tool
that is very much required for machining
• In NTM, the tool need not be harder than the work piece
material. For example, in EDM, copper is used as the tool
material to machine hardened steels.
• Mostly NTM processes do not necessarily use mechanical
energy to provide material removal. They use different energy
domains to provide machining. For example, in USM, AJM, WJM
mechanical energy is used to machine material, whereas in ECM
electrochemical dissolution constitutes material removal.

4. ABRASIVE JET MACHINING
PRINCIPLE
• In Abrasive Jet Machining (AJM), abrasive particles are
made to impinge on the work material at a high velocity.
• The jet of abrasive particles is carried by carrier gas or air.
The high velocity stream of abrasive is generated by
converting the pressure energy of the carrier gas or air to
its kinetic energy and hence high velocity jet.
• The nozzle directs the abrasive jet in a controlled manner
onto the work material, so that the distance between the
nozzle and the work piece and the impingement angle
can be set desirably.
• The high velocity abrasive particles remove the material
by micro-cutting action as well as brittle fracture of the
work material.

7. • Gas Propulsion System: The main purpose of gas
propulsion system is to provide clean and dry, high
velocity air or gas for machining. Mostly air, carbon
dioxide, Nitrogen etc. are used as gas in gas
propulsion system. This system consists,
compressor, air filter and drier. The gas used in this
system should easily available. First gas is
compressed into a compressor. This compressed gas
sends to filler and drier where all dust and
unwanted particle along with moisture remove
from it. Now these clean air send to mixing
chamber.
• Abrasive feeder: As the name implies, abrasive
feeder is used to provide abrasive particles in
mixing chamber. It is fed through a sieve which
vibrates at 50-60 Hz and mixing ratio is control by
the vibration of the sieve and its amplitude.

8. • Abrasive: These are the main particles which take part in
machining process. These particles should have high
metal removal rate and accuracy. The most common
abrasive particles used are aluminum oxide, silicon
carbide, boron carbide etc. The selection of abrasive
particle is depends upon material of work piece, speed of
machining, and machining environment.
• Cutting Nozzle: To direct the abrasive particle on work
piece cutting nozzles are used. They are usually made by
tungsten carbide. They are available in both circular and
square cross section. Its life is usually low about 30 hours
for tungsten carbide.
• Machining Chamber: It is fully closed air tight chamber
witch control the concentration of abrasive particle
around work piece. This is equipped with a vacuum dust
collector which collect used abrasive particle and
removed material from mixing chamber.

9. WORKING:
• First gas or air is compressed into gas compressor.
There the density and pressure of gas increases.
• Now this compressed gas send to filtration unit,
where dust and other suspended particle removed
from it.
• This clean gas sends to drier, which absorb moisture
from it. It is used to avoid water or oil
contamination of abrasive power.
• Now this clean and dry gas sends to mixing
chamber where abrasive feeder feed abrasive
particle in it. The abrasive particle is about 50 micro
meter grit size.

10. • This high pressuring abrasive carried gas send to
nozzle where its pressure energy converted into
kinetic energy. The velocity of abrasive particle
leaving the nozzle is about 200m/s.
• The standoff distance between work piece and
nozzle is about 2mm.
• Now these high velocity abrasive particles
impinge on work piece. These high velocity
abrasive particles remove the material by micro
cutting action as well as brittle fracture of the
work material.

11. • Abrasive
– Material – Al2O3 / SiC /
glass beads
– Shape – irregular /
spherical
– Size – 10 ~ 50 μm
– Mass flow rate – 2 ~ 20
gm/min
• Carrier gas
– Composition – Air, CO2, N2
– Density – Air ~ 1.3 kg/m3
– Velocity – 500 ~ 700 m/s
– Pressure – 2 ~ 10 bar
– Flow rate – 5 ~ 30 lpm
• Abrasive Jet
– Velocity – 100 ~ 300 m/s
– Mixing ratio – mass flow
ratio of abrasive to gas
– Stand-off distance – 0.5 ~ 5
mm
– Impingement Angle – 600 ~
900
• Nozzle
– Material – WC / sapphire
– Diameter – (Internal) 0.2 ~
0.8 mm
– Life – 10 ~ 300 hours

12. Applications
• For drilling holes of intricate shapes in hard and brittle
materials
• For machining fragile, brittle and heat sensitive
materials
• AJM can be used for drilling, cutting, deburring,
cleaning and etching.
• Micro-machining of brittle materials
Limitations
• MRR is rather low (around ~ 15 mm3/min for machining
glass)
• Abrasive particles tend to get embedded particularly if
the work material is ductile
• Tapering occurs due to flaring of the jet
• Environmental load is rather high.

13. ULTRASONIC MACHINING
PRINCIPLE
• It works on the same principle of ultrasonic
welding.
• This machining uses ultrasonic waves to produce
high frequency force of low amplitude, which act as
driving force of abrasive.
• Ultrasonic machine generates high frequency
vibrating wave of frequency about 20000 to 30000
Hz and amplitude about 25-50 micron.
• This high frequency vibration transfer to abrasive
particle contains in abrasive slurry.
• This leads indentation of abrasive particle to brittle
work piece and removes metal from the contact
surface.

16. • Power Source: As we know, this machining
process requires high frequency ultrasonic wave.
So a high frequency high voltage power supply
require for this process. This unit converts low
frequency electric voltage (60 Hz) into high
frequency electric voltage (20k Hz).
• Magnetostrictive transducer: As we know,
transducer is a device which converts electric
single into mechanical vibration. In ultrasonic
machining magnetostrictive type transducer is
used to generate mechanical vibration. This
transducer is made by nickel or nickel alloy.

17. • Booster: The mechanical vibration generated by
transducer is passes through booster which amplify it
and supply to the horn.
• Tool: The tool used in ultrasonic machining should be
such that indentation by abrasive particle, does not leads
to brittle fracture of it. Thus the tool is made by tough,
strong and ductile materials like steel, stainless steel etc.
• Tool holder or Horn: As the name implies this unit
connects the tool to the transducer. It transfers amplified
vibration from booster to the tool. It should have high
endurance limit.
• Abrasive Slurry: A water based slurry of abrasive particle
used as abrasive slurry in ultrasonic machining. Silicon
carbide, aluminum oxide, boron carbide are used as
abrasive particle in this slurry. A slurry delivery and return
mechanism is also used in USM.

19. WORKING
• First the low frequency electric current passes through
electric supply. This low frequency current converts into
high frequency current through some electrical
equipment.
• This high frequency current passes through transducer.
The transducer converts this high frequency electric
signal into high frequency mechanical vibration.
• This mechanical vibration passes through booster. The
booster amplify this high frequency vibration and send to
horn.
• Horn which is also known as tool holder, transfer this
amplified vibration to tool which makes tool vibrate at
ultrasonic frequency.
• As the tool vibrates, it makes abrasive particle to vibrate
at this high frequency. This abrasive particle strikes to the
work piece and remove metal form it.

20. Applications
• Used for machining hard and brittle metallic alloys,
semiconductors, glass, ceramics, carbides etc.
• Used for machining round, square, irregular shaped
holes and surface impressions.
• Machining, wire drawing, punching or small blanking
dies.
Limitations
• Low MRR
• Rather high tool wear
• Low depth of hole

21. ELECTRON BEAM MACHINING
Principle of EBM:
• The high velocity electron strikes the work piece.
• The kinetic energy of electrons converts into heat which
is responsible for melting and vaporization of work piece
material.
• The surface of thermo electronic cathode is heated to
such a high temperature that the electrons acquire
sufficient speed to escape out to the space around the
cathode.
• The stream of large number of electrons moves as a small
diameter beam of electrons towards the anode. As a
result, work piece is heated by the bombardment of
these electrons in a localized area, to such a high
temperature that is melted and vaporized at the point of
bombardment.

23. • Electron Gun: It is called heart of electron beam
machining. It is used to generate electron. It is
simply a cathode ray tube which generates electron,
accelerate them to sufficient velocity and focus
them at small spot size. In this gun cathode is made
by tungsten or tantalum. This cathode filament
heated upto 2500 degree centigrade which
accelerate to electron emission by thermionic
reaction. There is very low vacuum in the chamber
• Annular Bias Grid: It is next element of EBM. It is
just after the electron gun. It is a anode which is
connected by the negative bias so the electron
generated by the cathode do not diverge from its
path and approach to the next element. When the
electrons leave this section, the velocity of electron
is almost half the velocity of light.

24. • Magnetic Lenses: After the anode, magnetic lenses
are provided which shape the beam and does not
allow to diverge electron or reduce the divergence
of beam. These lenses allow to pass only
convergent electron, thus a high focused beam is
obtained. They also capture low energy electron,
thus increase the quality of beam.
• Electromagnetic lens and deflection coil:
Electromagnetic lens is used to focus the electron
beam at a spot. They use to focus beam at a spot on
work piece so a high intense beam reaches at work
surface, which produces more heat and improve
machining. The defecting coil does not allow to
beam deflect and take care of all electrons moves in
series thus form a high intense beam.

25. • Work piece and work holding device:It can machine both
metallic and non-metallic material. The work piece is hold by
suitable fixture which is mounted on a CNC table. This table can
be move in all three direction which control the shape of
machining.
Working:
• The EBM works same as laser beam machining. its working can
be summarize into following points.
• First electron gun produces high velocity electron particles.
These electron particles move towards anode which is placed
after cathode tube.
• Now this high intense electron beam passes through magnetic
lenses. There are a series of lenses which take care of only
convergent electron passes through it. It absorb all divergent
electron and low energy electron. It provides a high quality
electron beam.
• This electron beam now passes through electromagnetic lens
and deflecting coil. It focus the electron beam at a spot.

26. • The high intense electron beam impinges on the work
piece where kinetic energy of electrons convert into
thermal energy.
• The material is removed from contact surface by melting
and vaporization due to this high heat generated by
conversion of kinetic energy into thermal energy. This
whole process take place in a vacuum chamber otherwise
these electron collide with air particle between path and
loses its kinetic energy.
Application:
• It is used to produce very small size hole about 100 micro
meters to 2 millimeter.
• It is used to produce holes in diesel injection nozzle.
• Used in aerospace industries for producing turbine blade
for supersonic engines and in nuclear reactors.

27. Advantages:
• It can be used for produce very small size hole in any shape.
• It can machining any material irrespective its hardness and
other mechanical properties.
• It provides good surface finish. No any surface finishing
process is require after EBM.
• Highly reacting material can be machine easily because
machining is done under vacuum.
Disadvantages:
• High capital cost.
• High skill operator required.
• Low material removal rate.
• Regular maintenance is required
• Material removal rate is very low compare to other
conventional process.
• It is difficult to produce perfect vacuum.

28. ELECTRO CHEMICAL MACHINING
Principle of Electrochemical Machining:
• Electrochemical machining works on the Faraday law of
electrolysis which state that if two electrode are placed in
a container which is filled with a conductive liquid or
electrolyte and high ampere DC voltage applied across
them, metal can be depleted form the anode (Positive
terminal) and plated on the cathode (Negative terminal).
• This is the basic principle of electrochemical machining.
In this machining process, tool is connected with the
negative terminal of battery (work as cathode) and work-
piece is connected with the positive terminal of battery
(work as anode).
• They both are placed in a electrolyte solution with a small
distance. When the DC current supplied to the electrode,
metal removed from work-piece. This is basic
fundamental of electrochemical machining.

30. • Power supply: In electrochemical machining process, a
high value of direct current around 40000A and low value
of potential difference around 10-25V is desirable. The
electrodes are place at a inter electro gap witch is
desirable for machining. If the inter electro gap not too
small witch can generate arc or not too high witch is not
suitable for machining. It is about 1mm. This high values
DC current is form by convert three phase AC current into
DC current by using Silicon Controlled Rectifier.
• Electrolyte supply and cleaning system: It consist piping
system, storage tank, pump, control valve, pressure
gauge, heating or cooling coil etc. in the electrochemical
process, the metal removed from work-piece form sludge
which should be remove form electrolyte. This system
control the flow and cleaning of electrolyte solution into
the container. Piping system is made of SS steel, Glass
fiber reinforced plastic, plastic lined MS or similar other
anti-corrosive material. The tank capacity is about 500
gallon for per 10000A of current.

31. • Tool and Tool feed system:Tool is made by an anti-
corrosive material because it has to withstand in
corrosive environment for long time. It should also
have high thermal conductivity and easily
machinable. The dimension accuracy and surface
finish of work piece is directly depends on tool
dimension. Those part of the tool, which is not
required for machining, should be properly
insulated because lack of insulation tends to
unwanted machining which give dimensional
inaccuracy.
• Work piece and work holding system: In this
process, work piece should be well electric
conductive. Only electric conductive material can
be machined by this method. Work piece take as
anode in this process. The work holding devices
should have non-conductive property.

32. Working of Electrochemical Machining:
Electrochemical machining works inverse as
electroplating process. Metal is removed form anode into
electrolyte and convert into slag form by reacting opposite
ions available in electrolyte. This process works as follow.
• In ECM, the electrolyte is so chosen that there is no
plating on tool and shape of tool remain unchanged.
Generally NaCl into water takes as electrolyte.
• The tool is connected to negative terminal and work is
connected to positive terminal.
• When the current passes through electrode, reaction
occur at anode or workpiece and at the cathode or tool.
To understand proper working let’s take an example or
machining low carbon steel.
• Due to potential difference ionic dissociation take place
in electrolyte.

33. NaCl ↔ Na+ + Cl-
H2O ↔ H+ + OH-
• When the potential difference applied between the
work piece and tool, positive ions move towards
the tool and negative ions towards the work piece.
• Thus the hydrogen ion moves towards tool. As the
hydrogen reaches to the tool, it takes some electron
from it and converts into gas form. This gas goes
into environment.
• When the hydrogen ions take electron from tool, it
creates lack of electron in mixture. To compensate
it, a ferrous ions created at the work piece (anode)
which gives equal amount of electron in mixture.

34. 2H+ + 2e- = H2 ↑ at Cathode
Fe = Fe+ + + 2e- at Anode
• These Ferrous ions react with opposite chlorine ions
or hydroxyl ions and get precipitate in form of
sludge.
Iron (Fe) ↔ Fe++ + 2e-
Fe++ + 2Cl- ↔ FeCl2
Fe++ + 2(OH)- ↔ Fe(OH)
Fecl2 + 2(OH)- ↔ Fe(OH)2 + 2Cl
• This will give ferrous or iron into electrolyte and
complete the machining process. This machining
process gives higher surface finish because
machining is done atom by atom.

35. Application:
• ECM is used to machining disk or turbine rotor blade.
• It can be used for slotting very thin walled collets.
• ECM can be used to generate internal profile of internal cam.
• Production of satellite rings and connecting rod, machining of gears
and long profile etc.
Advantages:
• It can machine very complicated surface.
• A single tool can be used to machining large number of work-piece.
Theoretically no tool wear occur.
• Machining of metal is independent on strength and hardness of tool.
• ECM gives very high surface finish.
Disadvantages:
• High initial cost of machine.
• Design and tooling system is complex.
• Fatigue property of machined surface may reduce.
• Nonconductive material cannot be machined.
• Blind hole cannot be machined form ECM.
• Space and floor area requirement is high compare to conventional
machining.

36. Electrical discharge Machining
• Electrical discharge machining process works on
the basic principle of spark generation and metal
removed by spark erosion.
• EDM spark erosion is same as electric spark
which burn a small hole in a piece of metal
through witch it contacts.
• The spark generated by this process produces
heat, which remove metal by erosion and
evaporation.
• In this machining process both the work piece
and tool must be made by conductive material.

38. • Power Supply: In a EDM process a high
frequency current used to generate spark
between electrode and work piece. This spark
generates heat and remove metal form work
piece.
• Dielectric fluid supply and flushing system: The
dielectric fluid acts as a vehicle to drive away the
chips and thus preventing them from sticking to
the surface. This fluid acts as flushing system for
chips.
• It also helps in increasing the metal removal rate
by promoting spark between tool and work. This
fluid also works as coolant medium.

39. • Tool and tool holding devices: In EDM process,
tool also erodes due to spark hence the
selection of tool depends on wear ratio, ease to
tool fabrication and cost of material. The most
commonly used electrode material are Cu,
Tungsten alloy, Cast Iron, Steel, Silver tungsten
alloy, graphite.
• Work piece and work holding devices: In this
process only good conductors of electricity can
be machined. So the work piece should have
good electric conductivity. This process does not
depend on hardness of work piece so there is no
criteria of hardness.

40. Working:
• First both work piece and tool are submerged into
dielectric fluid. The dielectric fluid help to control
the arc discharge. This also removes suspended
particles of work piece material and tool from the
work cavity.
• A servomechanism is used which maintains a very
small gap between the work piece and the tool. This
gap is desirable for proper arc formation. It is about
the thickness of human hair.
• The tool is made as the opposite shape of work
piece.
• A high frequency current supplied to electrode,
which produces a spark between the tool and work
piece. This spark generates high in work cavity.

41. • The metal removed from the work piece due to
erosion and evaporate ion.
• The chips or suspended particle between tool and
work piece should be removed to prevent them to
form bridge that causes short circuit. This is done by
continuous supply of dielectric fluid.
• The EDM produce a cavity slightly larger than the
electrode because of overcut.

42. Advantages:
• Every conductive material can be cut by this process.
• It is independent on hardness of workpiece so hardened
work piece can be machined easily.
• Complex die section and complex shapes can be produce
accurately.
• This process is burr free.
• Thin section can be easily machined without deforming
the part.
Disadvantages:
• In this machining process high tool wear occurs.
• Tool wears limits accuracy and surface finish of metal.
• Only good conductors of electricity can be machined by
EDM.