Introduction to Non-Traditional

OR
Unconventional Machining Processes

CHANDRARAO.CHANDU

Department of Mechanical Engineering

SIR CRR COLLEGE OF ENGINEERING,
ELURU
So
Far
Limitations of Conventional Machining
Methods
► Increased workpiece hardness : decreased economic
cutting speed. Hence, lower productivity.
► Rapid improvements in the properties of materials
(hardness, strength, etc)
► Requires much superior quality of tool materials.
► Tool material hardness should be greater than
workpiece hardness.
Evolution of Advanced Machining
Processes(AMPs)
► Many Engineering materials are having much superior
properties such as ultra high strength , hardness, very
high temperature resistance difficult to machine by
convenventional machining methods.
Ex :Tungsten Carbide, Stainless Steel, Titanium and
its alloys etc
► If work piece material hardness is greater than the
tool material hardness. How are we going to
machine such a work piece material ?
Product
Requirement
► Complex shapes
► Machining in inaccessible areas
► Low tolerances (say, 0.01 mm)
► Better surface integrity (no surface defects, etc.)
► High surface finish (Nano-level Ra value)
► Miniaturization of products (examples: landline
phone & mobile, old computers & laptop, etc.)
► High MRR
► High production rate while processing difficult to
machine.
► Low cost of production .
► Precision and ultraprecision machining
► Requires material removal in the form of atoms
and / or molecules
Machining of Complex Shaped
Workpieces
Important characteristics of Advance Machining
Processes
► Process performance is independent of
workpiece :Strength & Hardness are not a barrier.
► Performance depends on thermal, electrical and
chemical properties of workpiece materials.
► Uses different kinds of energy in direct form.
► In general, low MRR but better quality products .
► Comparatively high initial investment cost of
machine tools and high operating cost
Classification of AMPs,Based on the Kind of
Energy used
Classification of AMPs, Based on Properties of
work material

► Applicable only for Electrically Conducting Materials :

ECM, EDM, EBM.
► Applicable for both electrically conducting & non -
conducting materials: USM , AJM, LBM, etc.
► Applicable for Non Magnetic materials : MAF, MRF,
etc.
► Thermal conductivity, Reflectivity, etc. also play an
important role in some processes: LBM
Classification of AMPs, Based on Electrical
Conductivity
Classification of µ-
Machining
 Mechanical
Machining
CHANDRARAO.CHANDU

Department of Mechanical Engineering

SIR CRR COLLEGE OF ENGINEERING, ELURU

Outlin
e
Abrasive Jet Machining

Water Jet Machining

Abrasive Water Jet

Machining Ice Jet

Machining

Ultrasonic Machining
Mechanical
Machining
► Jet Machining and Ultrasonic Machining (USM) are
typical examples of single action, mechanical non
traditional machining processes.
► The machining medium is solid grains
suspended in an abrasive slurry.
Abrasive Jet Machining: Machined
products
Abrasive Jet Machining: Machined
products
Abrasive Jet Machining
(AJM)

► In AJM, the material removal takes place due to

impingement of the fine abrasive particles.
► The abrasive particles are typically of 0.025mm
diameter and the air discharges at a pressure of
several atmosphere.
Mechanics of
AJM
► Abrasive particle impinges on the work surface at a
high velocity and this impact causes a tiny brittle
fracture and the following air or gas carries away the
dislodged small work piece particle.
Mechanics of
AJM
► Flaring of the Jet:- Cavity dimension changes with a
change in NTD.
► Abrasive particles repeatedly hit on the work surface.
► Brittle fracture separates out tiny particles (wear
particles) to produce a cavity. Cavity width greater than
or equal to Nozzle inner diam. (Depends on NTD).
► Cavity depth depends on work piece feed rate,
abrasive particle mass (or density) and pressure (or
velocity of the jet).
► Stray Cutting: Due to increase in NTD the jet
diameter goes on increasing.
AJM
System
AJM Process
Parameters
► For successful utilization of AJM process, it is
necessary to analyse the following process criteria.
1. Material removal rate.
2. Geometry and surface finish of the workpiece.
3. Wear rate of the nozzle.
► AJM processes are generally influenced by the
following process parameters.
► Abrasives:
Material shape size(µm) m˙ (g /min)
Abrasive Al O
2 3 , SiC Irregular 10 − 50 2 − 20
s
AJM Process Parameters
contd.
► Carrier Gas:

Composition ρ(kg/m3 ) V (m/s) P(bars)

Carrier Air,CO2,N2 1.3 500 − 2 − 10
► Gas
Abrasive Jet: 700

SOD(mm) Impinge V (m/s) Mixing ratio

Abrasive Jet 0.5-15 60 − 90◦ 100 − V˙ abr /V˙ gas
► Nozzle: 300

Material Diameter(mm) Life(hrs) NTD(mm)

Nozzle WC,Sapphire 0.2-0.8 12-300 0.25-75
► Note: SOD-Stand of Distance, NTD: Nozzle to Tip
Distance
Mathematical Modelling of
AJM
► Assumptions:
1. Abrasives are rigid and spherical in shape having
diameter
dg (grit diameter).
2. Kinetic energy of particle is used to cut the material.
3. for brittle materials, volume of material removal is
considered to be hemispherical in shape having
diameter equal to the chord length of the indentation
(2r).
4. For ductile materials, volume of material removal
is assumed to be equal to the indentation
Mathematical Modelling of
AJM

Case-1: Brittle Materials

► Indentation depth(δ) estimation:

AB 2 − AC 2 = (1
Mathematical Modelling of AJM
contd.
!2 !2
dg dg 2
(2
2 — −δ =
2 )
!2 r !2
dg dg 2 dg 2
− (3
2 2 — (δ) + 2δ
2 )
= r
r 2 = −δ2 + (4
)
dg δ As δ is small, we can neglect
δ2 r 2 = dg (5
δ )
(6
√ )
r= dg
δ
Mathematical Modelling of AJM
contd.
► For Brittle material:
Volume of material removal in brittle material is the
volume of the hemispherical impact crater and is
given by:
1 1 3 1 3 2 3
ΓB = πr 32 = π(r )2 = π(dg δ)2 = π(d 2
4
2 3 4
2 3 42 3 g
δ)
3 (7
)
Assume the grits Velocity(V). So the Kinetic Energy is
1
KE = MV 2 (8
2
)
where M is expressed by this
expression
M = mass of single abrasive grit=volume of grit *
Density of abrasive material(ρa)
Mathematical Modelling of AJM
contd.

► For Brittle material contd.:

where Volume of
3
grit is dg
Volume of grit= 3 = 6π dg
4
π
Then
2 3
the KE for single grit is
!
1 2 1 π
3
KE = 2
MV =
dg ρ a V
(9) 2
On impact, work material should 2 6
be subjected to
maximum force F, which would lead to indentation
of δ.
Mathematical Modelling of AJM
contd.
► For Brittle material contd.:

Here, you can see that the force is linearly varies

with δ
∫δ
(F = aδ)
Work done =0 aδdδ = 2a
δ
As F = aδ, so a δ 2

= Fthe work done is

So, 2
So,
Fδ Work done by the single grit during
such indentation is
Fδ
W= (10
2
)
Mathematical Modelling of AJM
contd.
► For Brittle material contd.:
Also we know the flow stress/Brinell
hardness of material(σw ). So,
2
F = stress ∗ area = σ w (11
πr = σ w πdg δ )
Using Eq. 10 and Eq. 11, we get
Fδ σ w πdg
W = 2 (12
= δ2 )
2 energy of the abrasives is
It is assumed that kinetic
fully used for material removal.
Kinetic energy of the particle = Work done by the
particle Using Eq. 9 and Eq. 12, we get
!
1 2 1 π 3 σ w πdg
MV 2 = (13
δ2 2 )
dg ρ a V
= 2 2
Mathematical Modelling of AJM
contd.
► For Brittle material contd.:
Simplify the equation 13. we
get δ as r
ρa
δ= g (14
Vd 6σw )
► MRR in AJM: MRR=(Volume of material removed
per grit)*(Number of abrasive particle impacting
per unit
Z(Z = 6m˙ time).a
) is the number of abrasive particle impacting
πd g3 ρa
per
unit time.(where m˙ a is the abrasive mass flow
rate)
2 3
MRR = π(dg δ)2 ∗ (15
3
Z )
using δ from Eq. 14, we
get
MRR = 2πZ dg3 V 32 ρ a 4
3

(16
3 6 w
)
σ
Mathematical Modelling of AJM
contd.

► For Brittle material contd.:

3/2
MRR∝m˙1/4
aV
3/4
(17
ρa σ )
w
Mathematical Modelling of AJM
contd.
► For Ductile material:
For ductile material, volume of material removal in
single impact is equal to the volume of the
indentation and is expressed as:

dg πd δ2
ΓD = 2 δ = g (18
−
πδ 2 3 )
Home Work: Derive the 2 MRR for ductile material
in AJM Process?
Given: ΓD , Eq. 19
Hint: Similar to Brittle material

m˙
MRRD = (19
V 2w
a2
)
σ
Parametric Analysis in AJM

► Effect of Nozzle Tip Distance (NTD) on cavity

diameter
Parametric Analysis in
AJM ► Effect of Nozzle Tip Distance (NTD) on
MRR

► The NTD not only affects the MRR from the work
surface but also the shape and size of the cavity
produced.
► when the NTD increases, the velocity of the abrasive
particles impinging on the work surface increases due
to their acceleration after they leave the nozzle. This
increases the MRR. With a further increase in the
NTD, the velocity reduces due to the drag of the
Parametric Analysis in
AJM
► Effect of Abrasive flow rate on
MRR

► As the flow rate increases upto maxima, More

number of abrasive particles hit the surface. this
increases the MRR.
► If flow rate is greater than the optimum, velocity of
the jet decreases hence MRR also decreases.
Parametric Analysis in
AJM
► Effect of Nozzle Pressure on
MRR

► Little effect on MRR

► Kinetic Energy removes material: Due to erosive
action
► Certain minimum velocity for the given material of
workpiece.
Parametric Analysis in
AJM ► Effect of Mixing Ratio on
MRR

► Note: Mixing Ratio(m) is the ratio of volume flow rate of

abrasive to the volume flow rate of carrier gas.(α =mass
ratio)α is the ratio of mass flow rate of abrasive to the
mass flow rate of abrasive and gas carrier

m = V˙ α = m˙ (20
V˙ m˙
a a+
a
g )
g
Process Capabilities of
AJM
► Low MRR
► Intricate Details Can be Produced
► Narrow Slots (0.12 to 0.25 mm) can be made
► Low Tolerances (−0.12 to +0.12mm) can be
obtained
► Minimization of Taper Angle of Nozzle wrt Work
Piece
► Thin Sectioned, Brittle Material, Inaccessible areas
can be easily machined
► Almost no surface damage
Applications of
AJM
► Manufacture of Electronic Devices including
Fragile components
► Deburring of Plastics, Nylon, Teflon Parts
► Deflashing of Small Casting
► Drilling Glass Wafers, etc.
► Cutting, marking, engraving, cutting thin
sectioned.
► Glass frosting
Water Jet
Machining

► It has multidirectional cutting capacity with no heat

produced.
► Cuts can be started at any location without the
need for predrilled holes.
► The burr produced is minimal.
► Grinding and polishing are eliminated, reducing
secondary operation costs.
Water Jet Machining-
Products
Abrasive Water Jet
Machining

► Cut virtually any material.

► Cut thin or thick stuff and No heat generated.
► Abrasive Water jet cutting can be easily used to
produce prototype parts very efficiently.
Abrasive Water Jet Machining-
Products
Ice Jet
Machining

► In AWJ, waste of water is very high as waterjet

contains abrasive particles. To reuse the water very
complicated water cleaning system has to be
employed While in IJ, ice is used instead of Abrasives.
So as ice melts into the water, water treatment gets
eliminated and we can reuse the water
► solid waste is produced in the AWJ technology and it
pollutes the environment while IJ technology is
Ultrasonic Machining (USM)
Process
► The basic USM process involves a tool vibrating with
a low amplitude and very high frequency and a
continuous flow of an abrasive slurry in the small gap
between tool & work piece.
► The tool is gradually fed with a uniform force.
► The impact of the hard abrasive grains fractures the
hard and brittle work surface, resulting in the removal
of the work material in the form of small wear
particles.
► The tool material being tough and ductile wears out
at a

much slower
USM:Produc
ts
USM:Produc
ts
Ultrasonic Machining (USM) Process
contd.
► Mechanics of USM:
1. The hammering of the abrasive particles on
the work surface by the tool.
2. The impact of free abrasive particles on the
work surface.
3. The erosion due to cavitation.
4. The chemical action associated with the fluid
used.
Ultrasonic Machining (USM) Process
contd.
► Mechanics of USM contd.:

1. The position JAJ indicates the instant the tool

face touches the abrasive grain.
2. The period of movement from JAJ to JBJ represents
the impact.
3. The indentations, caused by the grain on the tool and
the work surface at the extreme bottom position of
the tool from the position JAJ to position JBJ is JhJ (the
total indentation).
Ultrasonic
Machine
► It consists of the following machine components: The
acoustic head, feeding unit, tool, abrasive slurry and
pump unit, body with work table.
USM Acoustic
Head
► The Acoustic heads function is to produce a
vibration in the tool.
► It consists of a generator for supplying a high
frequency electric current, a transducer to convert this
into a mechanical motion (in form of a high frequency
vibration).
USM Acoustic
Head
► A concentrator to mechanically amplify the
vibration while transmitting it to the tool.
► The ultrasonic vibrations are produced by the
transducer. The transducer is driven by suitable signal
generator followed by power amplifier. The transducer
for USM works on the following principle:
Piezoelectric effect, Magnetostrictive
effect and Electrostrictive effect
USM Abrasive
Slurry
► The most common abrasives are Boron Carbide
(B4C ), Silicon Carbide (SiC), Corrundum (Al2O3),
Diamond and Boron silicarbide.
► B4C is the best and most efficient among the rest
but it is expensive.
► SiC is used on glass, germanium and most
ceramics.
► Diamond dust is used only for cutting Daimond
and Rubies.
► Water is the most commonly used fluid although
other liquids such as Benzene, Glycerol and oils are
also used
M.C. Shaw Model of USM
Contd.
► Assumptions:
1. The rate of work material removal is proportional to
the volume of the work material per impact.
2. The rate of work material removal is proportional to
the no. of particles making impact per cycle.
3. The rate of work material removal is proportional to
the frequency (no. of cycles per unit time).
4. All impacts are identical.
5. All abrasive grains are identical and spherical in
shape. Thus, volume of work material removal
rate (Q)

Q ∝ VZν

(21)

► Note:V = volume of the work material removal per impact,

M.C. Shaw Model of USM
Contd.

► Consider the impact of a rigid, spherical abrasive

grain diameter d on the work surface and D is
diameter of the indentation at any instant and hw
( = h in figure) is the corresponding depth of
penetration. D 22 d 2
= (22
2 d2 — −
2 )
M.C. Shaw Model of USM
Contd.
2 2
D 2 = d 2 − (d − 2hw )2 or D = 4dh w −w (23
4h )
Since hw is small, so 4h
w
2 is very small. so,

neglect it √
D≈2 w (24
dh )
Volume of material removal from the work piece in brittle
material is the volume of the hemispherical impact crater
and is given by:
2 D 3 2
Γw = π = (25
3 3 3/2
π(dhw ) )
2
So, from Eq. 21 and
25
2
MRRw (Q) = Γ Z ν = w ) 3/2 Zν (26
3
w )
π(dh
M.C. Shaw Model of USM
Contd.

Since the abrasive has irregular shape. So, the actual

indentation is occurs by the effect of spherical
projections(with diameter d1) as shown in the figure.(it is
observed that d1 = µd 2 )
So, the actual Volume2 of D
material
3
2 removal from the work
piece is: Γw = π = (27
3 3
π(d1 hw )3/2 )
So, Actual MRR from2 Eq. 2 3/2
27 (28
MRRw (Q) = Γw Zν = π(d1hw ) Zν
3 )
M.C. Shaw Model of USM
Contd.
► Since the mean speed of the tool is low, the mean
static feed force F applied to the tool must be equal
to the mean force of the tool on the grains.
► Duration of an impact is ∆ T and the maximum
value of the impact force F is Fmax .
M.C. Shaw Model of USM
Contd.

► The nature of variation of F with time is shown in fig.

6.10.(previous slide) So, It will not be very much
erroneous to assume the nature of variation of F to be
traingular. Now, ∫ T
F =1 F (t)dt ≈1 Fmax (29
∆ T0
T 2
T )
► where T is the time period of each
cycle.
M.C. Shaw Model of USM
Contd.

If the distance travelled by the tool from the position A

to the position B is h(the total indentation), then

h = hw + ht

(30)
If A is the amplitude of oscillation of the tool. then the
average velocity of the tool during the quarter cycle O
to B is given by A/(T/4)
M.C. Shaw Model of USM
Contd.

So, the time required to travel from A

to B is
h T hw + th T
∆T ≈ . (31
A 4 A
= )
Subsitute equation 31 in 29, we 4
obtain
1 hw + h t T
F ≈ ma (32
1
2 x A 4
F )
o T
r
8F
(33
Fmax ≈ wA+ t
h )
h
M.C. Shaw Model of USM
Contd.
► Z is the number of abrasive grains are
simultaneously in contact during a period ∆ T . So,
Force per grain is Fmax /Z
► grain is4π D 2 = area of contact on the work
The approximate
► surface
πd 1 hw . perthe maximum stress developed in the work
Therefore,
piece is given as
Fmax
σw =
(34) πZd1hw
Using the Equation 33 in 34,
we get
8F
σw (35
πZd1 hwA(hw + h
= )
) t
M.C. Shaw Model of USM
Contd.
► It is quite reasonable to assume that the depth of
penetration is inversely proportional to the flow stress
of the material as long as other parameters are
constant. So, h ∝ 1/σ .
► If σt and σw are the stresses developed in the tool
and work, the ratio of the corresponding indentation
is given as ht σw (36
= = λ
)
hw σt
Since the flow stress σ and the brinell Hradness
H(σ w = Hw , σ t = Ht ) are the same, equation 35
and 36 yield
8F
2
hw = (37
πZd1 HAw (1 + )
λ)
M.C. Shaw Model of USM
Contd.
► Again, it may be assumed that the number of grains
acting is inversely proportional to the square of the
diameter of each grain for a given area of the tool
face. Therefore,
C
(38
Z∝ C 2
or Z = χ 2
)
d d

where C is the concentration of the abrasive

grains in the slurry and χ is a constant of
proportionality. s
8F
► A d1 = µd 2 . sohthe
w hw becomes (39
πχ CµHAw (1 +
= )
λ)
MRR in USM
process
So, From Equation 28 and 39,
we get
1/2 3/2
2 8FA C
MRR(Q) = π µd χ ν (40
3 πχ CµHw (1 + d2
2 )
λ)
3 3
2 1 3 1 dF 14 A 4 C
MRR(Q) 4 π 4 µ 4 χ 3 3
ν (41
= 34
4
Hw (1 + )
3 λ )3 4
dF 14 A 4 C
MRR(Q) ∝ 4 3 ν
Hw4 (1 + 3 (42)
λ) 4
d is the nominal diameter, d1 is the average diameter of
projection(diameter of the indenting projections), C:
concentration of the abrasive grains in the slurry. F: mean
static feed of
amplitude force, A:
oscillation of tool, Hw : work piece hardness, Ht
χλ =
is aH wconstant,
, Z: number of grains are simultaneously
in contact
USM Process
Parameters
► Frequency
► Amplitude
► Static loading (feed force),
► Hardness ratio of the tool and the workpiece,
► Grain size,
► Concentration of the abrasive in the slurry.
USM MRR vs Frequency and
Amplitude

► With an increase in frequency of the tool head the

MRR should increase proportionally. However,
there is a slight variation in the MRR with
frequency.
► When the amplitude of the vibration increases the
MRR is expected to increase.
► The actual nature of the variation is shown in
Figure
USM MRR vs abrasive diamter and
concentration

► MRR should also rise proportionately with the

mean grain diameter JdJ.
► When JdJ becomes too large, the crushing
tendency increases.
► Concentration of the abrasives directly controls the
number of grains producing impact per cycle. MRR
1/4
USM MRR vs Feed
Force

► MRR increases with increasing feed force but after a

certain critical feed force it decreases because the
abrasive grains get crushed under heavy load
USM, Dependence of Surface Finish on
Grain Size

► The figure shows that the surface finish is more

sensitive to grain size in case of glass which is softer
than tungsten carbide. This is because in case of a
harder material the size of the fragments dislodged
through a brittle fracture does not depend much on
the size of the impacting particles
Summary of
USM
 Electric Discharge
Machining
CHANDRARAO.CHANDU

Department of Mechanical Engineering

SIR CRR COLLEGE OF ENGINEERING, ELURU
Electric Discharge Machining
(EDM):Products
Electric Discharge Machining
(EDM)► Electro Discharge Machining (EDM) is an electro-
thermal non-traditional machining process, where
electrical energy is used to generate electrical spark
and material removal mainly occurs due to thermal
energy of the spark.
► EDM is mainly used to machine difficult-to-machine
materials and high strength temperature resistant
alloys. EDM can be used to machine difficult
geometries in small batches or even on job-shop
basis.
► Work material to be machined by EDM has to be
electrically conductive.
Electric Discharge Machining
(EDM)
► Plasma formation and Spark generation in
EDM:
1. Voltage across the electrodes reaches the
breakdown Voltage
2. Dielectric Breakdown: Formation of plasma
3. Spark Generation at the point of lowest IEG
4. Melting and Vaporization of Work Piece
Material
5. Bubble generation and their Expansion
6. Plasma Channel Explodes
Electric Discharge Machining
(EDM)► Plasma formation and Spark generation in EDM
contd.:

► EDM gap phenomenon and material removal

mechanism with positive polarity Stages 1 to 4:
normal discharges; Stage 5: repeated discharges
leading to debris accumulation; and Stage 6: excess
debris causing spurious discharges through clusters
Electric Discharge Machining
(EDM)
Elements of E D M
Process
► Tool Electrode: 1. Good Electric conductivity, High
thermal Diffusivity, High melting and boiling point,
good machinablity etc
2. Examples are graphite, brass, copper, tungsten
etc
► Work piece Material: Any material which is
electrically conductive can be machined through
EDM
► Power Supply: Resistance capacitance(RC) and
Transistor type circuits are used. Transistor
circuits(TC) are incapable to produce nano pulses.
TC is used where high MRR required.
► Servo System: To maintain a constant spark gap
between electrodes.
► Dielectric Fluid: It acts as the insulator medium
between tool and work piece. Examples are
Variants of E D M
process
Different power generators in
E D M► Resistance Capacitance based power supply
The RC circuit is basically a relaxation oscillator with
a resistor and a capacitor, as illustrated in Fig.. It is
a simple, reliable, robust, low-cost power source for
EDM. It can provide very small pulse energy and is
used extensively in micro EDM and finishing EDM to
achieve fine surface finish. The drawback of RC
generator is the lack of precision control, particularly
for timing and slow charging.
Different power generators in E D M
contd.
► Analysis of RC Circuit
contd.:
Loop-1(charging Loop-2(Discharging
crircuit)
uo −uc duc
Circuit)
duc
ic = =C uc
R ie = −C dt = Rs
dt
uc = uo (1 − e −t /RC ) uc = ue e −t /Rs C
duc uo
ic = C = e −t /RC ie = uc
= ue
e −t /Rs C
dt R Rs Rs
where, ic is the charging current in loop-1,ie is the current
in loop-2 uo is the supply voltage,ue is the break down
voltage and uc is the charged and discharged voltage of
the condenser at time t. R and R s is charging resistance
and sparking resistance and C is capacitance of the
condenser.
RC Circuit in E D M
contd.
► Power Delivered to the Discharging Circuit:
The energy delivered to the discharging circuit at any
time t is given by
dE = icucdt

(1)
uo2 −t/τ τ −2t/τ
Substituting
E the—values
τe of u+ c and
e ic and
+ integrate
k(constant)
both side R (2)
=
2
Note: τ = RC (time constant), k is a constant, and
can be evaluated by using the boundary condition
(E = 0 at t = 0), Substitute the value of k in (2) to
get
uo2 τ 1
E + e− 2t/τ − (3
1
= )
R 2
e− t/τ
2
Analysis of RC Circuit
contd.
► Suppose the energy E is delivered to the discharging
circuit for time t. then the average power delivered
(P avg ) is given by
E u2 1
= o e− 2x − (4
P avg = 1
+ )
t xR 2 − x
where, x = t/τ . The e
2 condition for the maximum
power to be delivered to the discharging circuit is
given by
dPavg (5
d =
)
x
After solving Eq 5, we 0get x = 1.26. Substitute this
value of x in uc (x = t/τ ) we get

uc = uo (1 − e−1.26) ≈ 0.72uo
(6)

Thus, the discharging voltage for the

Analysis of RC Circuit
contd.

► The energy Ed of each individual spark discharge is

given by
1 2
Ed = Cue
2
(7)
Analysis of RC Circuit
contd.

► Material Removal Rate in RC Circuit: uc for loop-1

can be rewritten as
1
t= (8
1−
RCln )
Frequency of charging (f )uisc /uo
c
given by " #
1 = 1 1
fc = (9
tc l 1 )
1− ue
n
/uo
At t = tc , uc = ue
Note: tc is the charging
time
Analysis of RC Circuit
contd.
► Material Removal Rate in RC Circuit contd.:
Material removal rate should be proportional to
the total energy delivered in the sparking per
second.
1 2
MRR ∝ E d fc = Cue fc (10
2 )

Substitute the value of fc , and let K be a

constant of proportionality. "Then,
2 1 # 1
MRR = KCu e. (11
1 )
l
RC n 1− ue
/uo
Thus,MRR ∝ 1/R, i.e R should be decreased to
increase MRR, however, at very low value of R, it
will result
The in arcing.
minimum value of the resistance(R) that
q will
prevent
arcing is known as critical resistance. (R L
mi C
> 30 n )
Voltage and Current variation with time in RC
Circuit
► This is the actual variation of current and volatge
with time.
Transistor Based power based
EDM
► Pulse Chain of Voltage and
Current

Fig: Pulse chain and six key EDM process

parameters
Different power generators in E D M
contd.
► Transistor Based powered EDM process
parameters:
► Open voltage (uo ): The voltage when the EDM
circuit is in the open state and energy has been
built up for discharging.
► Discharge voltage (ue ): The voltage during
discharge.
► Discharge current (ie ): The current during
discharge.
► Discharge delay time (td ): The time duration when
the circuit is energized to open voltage and waiting
for discharge.
► Discharge time (te ): The time duration for discharge.
► Pulse interval (to ): The waiting time to be energized
to open voltage.
Servo Reference Voltage in
EDM
► Transistor-based EDM Generator:
► The motion control of an EDM machine electrode is
controlled by adjusting the average cycle voltage to
keep adequate gap distance. The average cycle
voltage u¯ is defined as:ue te +
uo td (13
u¯ =
te + td + )
► to
A shortcoming of the transistor-based EDM generator
is the limit to deliver very low discharge energy for
finishing EDM to generate fine surface finish or
micro features due to the cost and performance of
high frequency MOSFET transistor. RC generators
could be more cost-effective in finishing EDM
applications. Some EDM machines incorporate both
the transistor generator for roughing EDM and RC
generator for finishing EDM.
Volatge and current Pulses of RC and transisitor
Generator:

(a) is Isofrequency pulses by RC generator and (b) is

Transistor generator enabled Isopulse.
The machining mode schematically presented in figure (b)
is called Isopulse, because every discharge has the same
on-time, independently of the pre-breakdown duration
General Characteristics of MRR in
EDM
E D M Surface
Integrity
► Due to the high temperature, metallurgical changes
occur in the subsurface layers of the EDM
workpiece. Commonly there are three zones that can
be observed:
(1) Recast zone
(2) Heat-affected zone
(3) Conversion zone.
Applications of
EDM
Applications of
EDM
 Laser Beam
Machining
CHANDRARAO. CHANDU

Department of Mechanical Engineering

SIR CRR COLLEGE OF ENGINEERINHG, ELURU
Laser Beam
Machining
► A laser is a device that emits light through a process
of optical amplification based on the stimulated
emission of electromagnetic radiation. The term
”laser” originated as an acronym for:
Light Amplification by Stimulated Emission of
Radiation
► Lasing process describes the basic operation of laser,
i.e. generation of coherent (both temporal and
spatial) beam of light by ”light amplification” using
”stimulated emission”.
► The laser differs from other incoherent light because
it is:
1) Monochromatic
2) Coherent
3) Directional or collimated
4) Bright
Schematic Diagram of Laser Beam
Machine
-
Principle of
LASER
► The electrons at ground state can be excited to
higher state of energy by absorbing energy form
external sources like electronic vibration at elevated
temperature, through chemical reaction or by
absorbing photons.
► On reaching the higher energy level, the electron
reaches an unstable energy band. And it comes
back to its ground state within a very small time by
releasing a photon. This is called spontaneous
emission.
Spontaneous vs. Stimulated
Emission
Working of
LASER
LASER beam and depth of
focus
−8 2
I (r ) = (1
r
I0 exp w )
2
where I0 is the maximum intensity, r is defined as the
distance from the center of the beam in gaussian
distribution of laser beam, and w(minimum spot or
gaussian beam diameter) is the diameter at which the
Intensity is 1/e2 of its maximum value.
Types of
LASERS
Light
Spectrum
Machining with long pulse lasers and short
pulse laser
Machining with long pulse lasers and short
pulse laser
Laser Material
Interaction
Process
characteristics

Geometry of a drilled hole using LBM

process
α (e −
ta c) (2
2 = 2
n )
d
Power Density and MRR in
LBM► The input and focus of LBM are converted to thermal
energy to vaporize the work piece material. The size
of the spot diameter ds is determined by

ds = F l θ (3
)
► where Fl is the focal length of lens and θ is the
beam divergence angle (rad).The area of the laser
beam at focal point, As , is
π
As = (F 2 (4
4
θ)l )
Power Density and MRR in
LBM
► The power of the laser beam, Lp , is given by

Lp = E s /∆t

(5)
► where E s is the laser energy (in the unit of J) and
∆t is the pulse duration of the laser.
► The power density of theLplaser beam,
4LpP d (in the
P =
unit of W/mm ), is given
2 d =
by π(F
(6) A s l
θ)2
Power Density and MRR in
LBM
► The drilling feed rate f (in the unit of mm/s) can be
described as follows:
Cl Lp Cl P d
f = =
(7) E v As
► Ev
where the conversion efficiency Cl is a constant
depending on the material and conversion efficiency
and E v is vaporization energy of the work piece
material (J/mm3).
► The MRR can be calculated as C
follows:
l Lp
MRR = fA s
= (8
Ev
)
Parametric Analysis:Cutting front vs cutting
speed
Parametric Analysis:Laser
Cutting
Parametric
Analysis
LASER
applications
LASER
applications
-
 Electrochemical
Machining

CHANDRARAO. CHANDU

Department of Mechanical Engineering

SIR CRR COLLEGE OF ENGINEERING, ELURU
Electrochemical Machining:
Products
Electrochemical
Machining
► Electrochemical machining is one of the most
unconventional machining processes.
► The process is actually the reverse of electroplating
with some modifications.
► It is based on the principle of electrolysis.
► In a metal, electricity is conducted by free electrons
but in a solution the conduction of electricity is
achieved through the movement of ions.
► Thus the flow of current through an electrolyte is
always accompanied by the movement of matter.
► In the ECM process the work-piece is connected to a
positive electrode and the tool to the negative
terminal for metal removal.
Electrochemical Machining
contd.
Electrochemical Machining
contd.
Electrochemical
Reactions
Polarization
Curve
Electrical Double
Layer
Over Potential in
ECM
Electrochemistry of ECM
process
► The electrolysis process is governed by the
following two laws proposed by Faraday
• The amount of chemical change produced by an
electric current, that is, the amount of any material
dissolved or deposited, is proportional to the quantity
of electricity passed.
• The amounts of different substances dissolved or
deposited by the same quantity of electricity are
proportional to their chemical equivalent weights.

m ∝ ItE

(1)

where m is the mass of dissolved metal, I is the

current, t is time and E is the gram chemical
equivalent (E = A/Z ), A is the atomic mass of
Material removal in
ECM

► Material removal (m) in ECM follows faradays

laws of electrolysis:
ItE
m (2
F
= )
where F is the Faraday constant.
► Material removal rate (MRR) can be
obtained as
m I
= m˙ (3
E
= )
t
F
Material removal in
ECM
► MRR can be
obtained as
ρava ρaAaya (4
= =
)
IE t t
F
ya
► MRR l (linear material
MRRlremoval
= rate) (5
IE
t
is obtained as = )
Fρ a A a
where, ρa is the density of anode, va = volume of
material removed from the anode in time t, Aa =
cross-sectional area on the anode from which material
is being removed in time t, ya is the thickness of
material removed in time t.
Linear material removal rate in
ECM
As J = I /A a (current
density),
ya JE
MRRl = (6
t
= )
Fρa
As (V − ∆ V ) is the voltage available for driving current
through the electrolyte. so, the current density can be
expressed as
I (V − ∆ V ) (V − ∆ V ) (V − ∆ V
J= ) (7
Aa = = kAy A a = k y )
a
RA a
So, the MRR l can be
written as
V − ∆V kAa E
MRRl (8
= Aa y )
Fρa
Where ∆ V is over potential, k = electrolyte’s
electrical conductivity
Applications of
ECM
► Die sinking
► Profiling and contouring
► Trepanning
► Grinding, Drilling and Micro-
machining
Applications of ECM
contd.
Thank
You