Now, we move onto another part of this particular
course that is called Advanced Abrasive Machining
Process. We have completed already, the conventional
abrasive machining and finishing processes.
Some of them are applicable for machining;
some of them are applicable for finishing.
Now, exclusively what we see is advanced abrasive
machining processes, then once we complete
this then we move on to advanced abrasive
finishing processes ok.
So, that this is a particular segment, where
we come across some of the advanced abrasive
machining process, as I said machining process
will deal with how much material removal that
you have taken out from the work piece ok.
In a finishing processes normally you use
what is the final surface roughness that you
have achieved ok. From that point of you we
will going to see here the machining processes
using abrasives which are considered to be
advanced.
Some of the people call it as nontraditional
machining also ok. So, there is no much difference
between nontraditional machining, unconventional
machining and advanced machining ok. So, since
this particular course deal with abrasive
based processes that is why we are only talking
about some of the advanced machining processes
where abrasives are commonly used.
We will see the overview of the today’s
lecture. Normally we start up with what are
the advanced abrasive machining processes
that we are going to study in this particular
segment. Introduction to abrasive jet machining
so, we move on to one of the process called
abrasive jet machining. And we will see jet
machining process parameters and we move onto
the input parameters on output responses,
the effect how each input parameter plays
a vital role on the output responses. And
the material removal models for brittle and
ductile materials.
Applications of abrasive jet machining and
at last, we just see a glimpse of abrasive
jet polishing also. This particular process
also can be used for polishing applications
so, but the application wise for polishing
very less. So, just we see a glimpse that
is all.
So, advanced abrasive machining processes,
what are the processes that we are going to
study in this particular section of this course
is abrasive jet machining, abrasive water
jet machining, ultrasonic machining and elastic
emission machining. These are the mechanical
processes where abrasives are used and there
are few process, but these are predominantly
used abrasive processes in the spectrum of
advanced machining processes. We move onto
the abrasive jet machining.
We will see if you see this particular slide
most of the slides which we are borrowed from
Professor Vijay Kumar Jain, who is a professor
emeritus in IIT Kanpur. So, some of the slides
are courtesy to him because, he has shared
the slides to with me and I am very thankful
to Professor V K Jain for sharing his slides.
So, when a person hits a ball twice on a wall
with F1 and F2 ok; that means, that a person
is there he is person, this person is hitting
the wall with F1 and F2, whenever if you are
force is F1 and F2 the crater size or cavity
size that is formed is approximately assume
to be D1 and D2.
If the force F2 is greater than F1, then D2
will be; obviously, greater than D2, this
is basic physics, abrasive jet machining follows
like this. And D2 and D1 size is the thing
is a function of kinetic energy of the ball
when hitting the wall. That means, that the
particularly this particular abrasive jet
machining works on the various input parameters
such as how velocity of the abrasive particle
is travelling towards the work piece and how
it is hitting, whether the material work piece
material is a ductile material or a brittle
material so, on many parameters are there.
What one thing is that if you just hit with
a stone to a particular material assume that
you are hitting a stone to a dry mud. So,
what will happen? There will be a crater there
will be a cavity formation on the mud dry
mud ok.
So, that is the basic concept of a abrasive
jet machining. Now, we move on you can this
basic concept we can pile up or compile towards
using their abrasive jet machining. So, abrasive
jet machining works on the, this particular
principal whatever I explain where the stone
is hit a dry soil or a mud which is soil I
mean to say it is not a loose soil. It is
a lump of a solid where you have a clay just
hit with this particular stone which is slightly
harder than this one and this clay which is
a solid clay. So, it is less harder with respect
to the stone.
So, and it is a brittle material so, there
will be a crater formation that basic principle
which we will see in particularly in abrasive
jet machining. And if you are going to hit
this particular clay with force F1 and F2,
what will happen? The crater size or a cavity
size that is formed on that particular solid
clay will be more and more. If you are hitting
with low force small crater, if you are hitting
with high force crater will be very big.
So, now based on this particular principle
the people came up with a technology called
abrasive jet machining. You can see the abrasive
jet machining normally these are the highly
compressed air along with the abrasive particles
which impinge or which pass through a fine
nozzle. And you can achieve or you can cut
the intricate shapes like completes surfaces
you can do and you can do a glass cutting
or another cutting processes.
If you can clearly see here how a particular
shape of a glass is cutting using the air
and at the same time abrasive particles; the
air is considered to be the carrier medium.
As you have seen in the previous slide there
is abrasive jet machining, abrasive water
jet machining. So, in the abrasive jet machining
you are going to use air or some gas as the
carrier medium. In abrasive water jet you
are going to use water which is a liquid as
a carrier. In this particular AJM what you
have to note here is carrier medium is air.
Media or medium is one of the things is air,
then gas, you can use inert gases or some
other gases also you can use to carry the
abrasive particles along the direction of
the velocity of the air.
The principle, the fine particles normally
0.025mm are accelerated in a gas stream commonly
used is air at a few times atmospheric pressure;
that means, that you can use 10 bar, 20 bar,
30 bar, 50 bar like that if we can use in
terms of bar, people will understand that
is why I am saying a bar. But, internationally
if somebody is watching assume that if I am
going to use 10 bar; that means that 1 mega
Pascal ok.
So, you can use 1 mega Pascal, 2 mega Pascal,
3 mega Pascal of the pressure of the air which
is a carrier medium and you just mix the abrasive
particles and you just inject on a surface
to be impinged ok. So, that you can cut the
intricate shapes or you can generate the craters
as per your requirement. The particles are
directed towards the focus of the machining
less than 1mm or the tip that mean. Normally,
it is called the nozzle tip distance normally
you will come across all these words in the
upcoming slides. Just you just focus on the
work piece so that you can cut the work piece.
As the particle impacts on the surface, if
the particle impacts on the surface with high
velocity, this causes a small fracture and
the gas stream carries both abrasive particle
and the fractured particles away. So, this
what it will do is this gas stream which is
considered to be the air will carry both abrasive
particle and the fractured wear surface away
from the is; that means, that whenever you
impinge if it is a through cut. So, it will
carry the debris as well as abrasive particles
also.
If you see here how the abrasive jet machining
works, this is the nozzle ok. So, this is
the nozzle tip distance, this is my work piece
which is nothing, but the distance between
work piece top surface to the nozzle exit
is nothing, but nozzle tip distance. And fine
abrasive particles plus air is coming here
and this is the crater depth that normally
this is a crater depth that is formed on a
surface.
So, how you can measure the crater diameter
as well as a crater depth, if you see this
is my crater, crater 
have it is own crater depth at the same time
crater diameter also you can measure. So,
depend on your input parameters like air pressure,
abrasive particle size, type of abrasive,
type of work piece material these are all
which will decide the crater depth as well
as crater diameter this it will decide.
If you see the schematic diagram of AJM system,
I mean to say previously whatever you have
seen is a machining region where nozzle is
there and work piece is in back, but how to
generate this much pressure? How to generate
the velocity of into abrasive particle and
other things? Will come under the complete
system, ok. So, first what you have to required,
what first what you need is air compressor,
so compressor with a relief valve, air filter,
drier and other things. Drier is required
because you do not want any wet condition
in the air force with pressure.
So, the compressed air now will be generated,
will be opened and the opening wall will be
there, pressure regulator. This pressure regulator
will tell what is the pressure, what is the
pressure? That means, that output pressure
what at what pressure it is the air that is
passing here is 1 mega Pascal or 10 mega Pascal
or 20 mega Pascal or something whatever the
Pascal that will show.
Now, it will go into a mixing chamber, this
is a mixing chamber where you are feeding
the abrasive particles and your gas is compressed
gas is coming ok, both will mix and it will
come like this. In this area what is compressed
air is there plus abrasives are there ok.
So, this abrasives and compressed air plus
abrasive particles will be there and this
will come and hit on the surface. So, that
you can generate a crater which have a crated
depth as well as crater diameter. Now, once
you the crater is generated or a cavity is
generated you can measure the crater and the
other things, crater diameter as well as.
If you see this particular diagram just whatever
you have seen in the previous one is just
shown in a schematic way.
So, the abrasives are falling on this one
and it will generate the crater which is having
2 parameters, one is crater diameter and crater
depth ok. The crater will be generated like
this which will have assume that if it is
like this, this is the diameter D and this
is the depth small d, this will be a crater
diameter and this will be crater depth. So,
like that you can generate the cavity or crater
on a particular material.
If you see the schematic diagram and the picture
normally you can compress the gas supply normally
air will be supplied. At the main motto to
show you is how the system look like and you
can also see the practical setups that are
developed by some of the IIT’s also. So,
the gas supply filters are required to filter
out the moisture or filter out the other things
and which is unwanted and the pressure regulator
just you mix the powders here and you can
even give the vibrations to it.
So, that you can get more and more mixing
at the same time once you done then you just
impinge. Now, if you can impinge what will
happen? The machining will takes place properly
and you can orient your nozzle as per your
requirement ok. So, practically you can see
how the cutting action is taking place by
the abrasive jet machining. So, the same thing
you can see here ok. So, this is a nozzle
and this is a machining ok. The box which
is shown in a schematic is clearly shown in
the experimental way.
So, this is the one of the experimental setup,
practically that is developed at IIT Kanpur.
So, again I am very thankful for the professor
who developed at IIT Kanpur this. The normally
1, 2, 3, 4, 5, 6, 7, 8, 9, 10 it shows hopper
for the abrasive pressure regulator flow meter
mixing and other things whatever if you see
here. So, this is a work piece and abrasive
jet machining region where the high pressure
abrasive mixing is coming and impinging on
your work piece surface; so, that the machining
takes place, the crater takes place and the
material removal takes place.
So, what are all the systems that you require?
What are the components that are that play?
What are the component that play a major role
in abrasive jet machining is one is the gas
propulsion system. That is nothing, but the
supplying of clean and dry air which propels
abrasive particles. Compressor are normally
required now when if you want to compress
the air for higher and higher you require
a compressor. And the gases which are non
toxic cheap available, easily available the
one of the best example is air.
Air is considered to be the cheapest and economic
one which is easily available in the atmosphere.
Then the abrasive feeder, normally the abrasive
feeder will have the quantity controlled by
the vibration you can control the vibration
and you can control the amount of the abrasive
particles that are falling and you can control
these particles how much particles you require.
You come up across one word called mixing
ratio in the upcoming slides.
So, there you will see how much abrasive particles
that are coming with respect to the carrier
medium that is nothing, but the air. Machining
chamber, well closed abrasive particles content
should be below harmful limit and the vacuum
dust collector should be attached; that means,
that as I said this particular things should
be carried out at the closed environment.
So, that the dust particles are because a
ceramic assume that you are going to machine
a ceramic material or a brittle material and
your abrasive particles is a brittle. What
will happen? There will be a brittle fracture
fragments will come up because, the fragments
will be a nano particles and the surface area
is so, high that this may come out and causes
lot of problems to the operator. So, it should
be done in a closed environment. The abrasive
jet nozzle so, normally sapphire nozzle will
be used whose life will be approximately 300
hours and circular or rectangular cross section
depends on your requirement.
Assume that if I want to make a whole, I can
go for circular. If I want to go for a pocket
some of the applications required pockets
and, in a ceramics, or something; in that
circumstances you can go for rectangular cross
section or a square cross section and this
type of cross sections. Nozzle pressure, normally
normal pressure which varies from 2 to 8.5
kgf per centimeter square when the work piece
material and MRR requirements are very high,
then you have to go for very high pressures.
Increased wear stray cutting and high inaccuracy,
if you are going for very high pressures and
high standoff distance or something then what
will happen? Stray cutting, normally stray
cutting does mean that assume that my assume
that this is the work piece and my requirement
is cutting in this section.
Assume that I want in this particular section
only, as if my nozzle is here the diversions
goes like this. Stray cutting means the extra
portions this is which is unwanted which is
called as a stray. So, here also you can see
here, see unwanted is nothing, but the stray.
So, it is going beyond what I require as a
customer or as a manufacturer if I want 5
centimeters a hole if I am generating 5.2
or 5.3 that extra portion is nothing, but
the stray.
So, the abrasives controlled by masking the
work piece you can control the whole size
and other things by masking the work piece.
Assume that this stray cutting if I want to
control in the circumstances, what you can
mask it assume that I want in this portion.
So, you can mask the other portions with other
material, sacrificial material so, that what
will happen? The required portion is exposed
and abrasives will take away the material
in the form of craters or cavities.
Mechanism of material removal if you seen
the abrasives and nozzle tip distance and
other things when the abrasive particle heat
what will happen? It will fracture the material
and the fracture mechanism and other things
you will see in the upcoming slides.
Whenever this particular abrasive comes and
hit so, it will generate the similar convex
shape of particular portion of hitting. And
it if it is a brittle material it goes out
as a brittle chip like this. If it is a ductile
material the material mechanism will be goes
by deformation, continuous deformation, then
the shearing, chipping and other things will
takes place in ductile work.
The fishbone diagram shows what are all the
parameters that are affected by abrasive flow,
what are the parameter that will affect the
output responses in abrasive jet machining.
So, one first one is a nozzle, nozzle will
play a major role. So, nozzle diameter, nozzle
type and cross section of nozzle as a we have
seen 2 cross sections will be there. One is
circular cross section one, another one is
rectangular cross section. The mixing chamber
the length of the chamber length of the chamber
is increases what will happen? What the mixing
will be better at the same time it may decrease
the velocity.
So, the bore diameter, type of chamber and
other things, work piece parameters normally,
hardness of the work piece, geometry details
and the other things will play a major role.
And the abrasives flowability of abrasives,
type of abrasives like SiC that is silicon
carbide or alumina or boron carbide or cerium
oxide. And what is the volume fraction that
you are going to mix; that means, whether
you are going to mix 1 is to 1 or 1 is to
10 or something. At the same time abrasive
particle size whether, it is fine size or
a core size or a medium size like that and
the carrier medium.
Career medium also play a major role which
type of carrier medium whether you are going
to use the air or whether you are going to
use argon or which is inert gas you are going
to use and pressure how much pressure, if
your pressure is very high what will happen?
The indentation will be very high.
So, the process parameters such as mixing
ratio, how much abrasive particles to the
carrier medium that you are going to mix and
the standoff distance, how far your nozzle
is from the work piece surface and the traverse
speed and the pressure. So, these are the
input conditions which determines the output
responses such as machining rate, how fast
you can do the machining, depth of cut and
the kerf quality; that means, that whether
you have achieved a good quality or a bad
quality which is a qualitative one.
So, the abrasive jet machining process parameters,
the main 3 parameters among all the spectrum
we have 3 or few more some people will follow.
So, the mostly important one is abrasive particle
which is nothing, but a composition, strength,
size and mass flow rate of abrasive particles.
At the same time carrier gas composition like
air whether you are going to use or argon
you are going to use or any other inert gas.
At what pressure and at what velocity it is
helping the abrasive particles to hit the
work piece and the nozzle, nozzle geometry,
nozzle material.
Because, nozzle material as we have seen in
the previous slide that the sapphire is one
of the best material; so, that the life will
be approximately 300 hours for one nozzle.
So, if you are going to use very low quality
materials for the nozzle what will happen?
Your nozzle goes out your nozzle on out and
you have to go for a new nozzle.
So, the non productive time increases. So,
the product cost will go off because, your
production time will increase for a particular
component. The standoff distance is one of
the thing that is nothing, but nozzle tip
distance. Some people, some of the books follow
nozzle tip distance, some of the books follow
the standoff distance. Standoff distance and
nozzle tip distance is both are same which
is nothing; but the starting of the nozzle
to the surface of the work piece. This is
nothing, but the standoff distance or nozzle
tip distance.
And the feed rate at the same time inclination
to the work. So, whether you want to go for
certain inclination to the work piece or whether
you want to put it perpendicular or that is
all the parameters that play a major role
among the fishbone diagram. You have a set
a complete set, but some of them have huge
influence or the major influence, some of
them have less influence. So, these are all
whatever you are seeing in this particular
slide are having a major influence on the
material removal rate, crater depth and crater
diameter.
So, the first one is abrasive particles that
play a major role. The abrasive should have
the sharp and irregular shape. Normally, all
the abrasive particles are randomly oriented
at the same shape is random. One abrasive
particle may like this; one abrasive particle
may like this, one abrasive like this. So,
shape normally will not be a constant in this
one. The fine enough to remain the suspended
in the carrier gas, if we you can go for particle
size, lower particle size, the suspension
or the suspending in the gas is very good
because of the high surface area. It should
have excellent flow characteristics because
it should follow the path of carrier gas.
So, that it will do the required purpose.
Al2O3 normally uses for the cleaning purpose,
cutting purpose and deburring purpose. The
silicon carbide normally uses for similar
applications of Al2O3. But for harder material;
that means, that if you are going to use Al2O3
for a softer materials slightly harder material
if you were customer comes with a slightly
harder material then you can go for silicon
carbide. And glass beads, you can go for Matter
finish or mat finish. Sodium bicarbonate,
normally you can use for the cleaning applications,
cutting, deburring of soft materials and other
things you can use.
So, abrasive sizes and functions, if the size
is small, large and other things, normally
if you see here the size the abrasive particle
size is 10 to 15 microns is a commonly used.
Because, if you are going to use very very
small then there will be a problem of agglomeration;
that means, that multiple particles will come
as agglomerate. But, normally in this particular
gas assisted process you may not get, but
in the water jet machining or some all people
will use some of the other liquids also there
the agglomerations will be a problem.
So, you should go for a specified particle
sizes. Normally, small sizes you will use
for cleaning and polishing and larger size
will be used for the cutting process. As I
said we see abrasive jet polishing at the
last of this particular class, where you will
use the fine abrasive particles; so, that
you can get the polishing operation.
Reuse basically it is not recommended because,
it will be contaminated with the chips and
may block the nozzle passage and lower cutting
ability and low cost; that means, that whenever
assume that I have a abrasive particle like
this, this is very sharp edge is there ok.
So, whenever you are using a first time the
sharp edge may remove the material, but whenever
you use the second time what will happen,
this will become blunt and its efficiency
goes down.
At the same time whenever you are going to
use it, what will happen? This may accompanied
by the chip material also this chip material
accompanying. So, the performance of this
particular abrasive particle goes down and
the performance goes down by lowering the
cutting ability, at the same time abrasive
particles are not that much costly.
So, it is economical to go for Al2O3 or SiC
normally these particles now a days or the
previously which we used in the 2015 and 16.
So, you can get in Indian market like a 1000
mess size or something approximately like
below 500 rupees. So, the 1000 mesh size up
to thousand mesh size you can get approximately
500 rupees per kg Al2O3 or SiC, both proximately
you can get this particular mesh size for
within India.
So, some of the companies placed in Agra and
this companies provides this type of abrasive
particles. If you are going for better abrasives
which placed in abroad nations like Germany
and other countries. So, import and export
charges maybe come into picture and the cost
of the abrasives may goes up. For the applications
of abrasive jet machining I guess you can
go ahead with this particular thing, I guess
you can go ahead with these available abrasive
particles in India.
So, the second thing which you have to note
down is normally the aluminium oxide that
Al2O3, silicon carbide, sodium bicarbonate,
dolomite and glass bead these are the commonly
used the particles different particle sizes
are also mentioned in this one. And this aluminium
oxide and silicon carbide are mostly used
in abrasive jet machining for the cutting
operation, grooving operation.
At the same time light finishing if at all
I want to go normally I go for sodium bicarbonate
and which can use for the finishing applications.
At the same time dolomite you can use for
etching and polishing applications and the
light polishing and fine deburring if at all
you want to go you can go for the glass beads
ok. So; that means, that in the abrasive jet
machining process if you can control the pressure,
if you can vary the abrasive particles, if
you can vary the pressure you can convert
this particular process into abrasive jet
polishing process also.
So, some of the people who are do doing masters
and wish to do PhD and other things. So, you
can work with this particular thing that how
to convert or how to change the setup or change
the parameters to change from abrasive jet
machining to abrasive jet polishing. So, there
may be a very less papers on abrasive jet
polishing. So, you can choose this particular
thing or abrasive polishing, abrasive jet
polishing as one of the topics by choosing
dolomite or a sodium bicarbonate as your abrasive
particles. You use appropriate pressures and
you can do all those workpiece materials,
you just do some literature and you can get
some information and you can move on to a
good topic.
So, the second one is a carrier gas, normally
carrier gas it should be non toxic, cheap,
easily available. I can say instead of cheap
you can say economic is a good word to use
rather than cheap. It must not flare excessively
when the discharge from the nozzle; that means,
that it should not diverge much. If it is
diverges then what is my requirement will
be gone.
And commonly used gases are CO2, nitrogen
air and other things, air is commonly available
one. So, the air is mostly preferred due to
universal availability and it is non toxic
nature because really we are breathing it.
So, air is non toxic at the same time it is
economic.
So, these are the nozzles, the third one is
a nozzles you can go for this type of nozzles
of various dimensions, you can see all here
multiple nozzles also available and single
big nozzles also here available. You can go
this type of nozzles to fit into the abrasive
jet machining and you can achieve your goals
ok.
The nozzle material is most important one.
So, it has to be it has to withstand the erosive
action of abrasive particles that are passing
by the nozzle. Because, the abrasive particles
are mixed with the highly pressurized gas
in the mixing chamber, then it is pushed;
that means, that this abrasive particles also
attack the walls of or the inner walls of
the nozzle.
So, the erosive wear of this particular nozzle
should be less. High resistance to wear; that
means, that it should be wear resistant material
that the nozzle is fabricated. And the circular
or rectangular cross section normally you
can use a tungsten carbide and sapphire is
basically used material; so, tungsten carbide
if you see and sapphire if you see normally
the nozzle life.
If you see here tungsten carbide is approximately
20 to 30 hours. But, here the problem is that
you have to replace the nozzle again and again.
Assume that average if it is like 20 hours
or something. So, every 20 hours you have
to replace the nozzle, because of this the
non productive work or the non productive
cost of your manufacturing will increase.
So, to avoid that you can go for the sapphire
whose life is 300 hours ok. So, the changing
of this nozzle will be reduced, at the same
time the time will be saved and the production
rate will be increased. So, you can sell the
product at the economic price subjected to
the cost of tungsten carbide and sapphire.
If the both cost are approximately same then
you can recommend to your shop floor people
that you can go for the sapphire.
So, the material removal mechanism, the ductile
materials, in case of ductile materials material
is removed by the plastic deformation and
cutting wear and plastic strain and the deformation
wear. During the impact, when the yield strength
of the material is locally exceeded, the plastic
deformation takes in the vicinity of the impact.
That means, that whenever the abrasive particle
goes and hit a ductile material there will
be a plastic deformation and nothing in this
world is perfectly flat. So, you have a peaks
on the surface. So, it also shear the peaks;
that means, that it will remove the material
by shearing action also.
So, after multiple impacts, plastically deformed
surface layer may form a near eroded surface,
and, therefore, the yield strength of the
material increases due to strain hardening.
And upon further deformation, the yield strength
at the surface of the material will eventually
become equal to the fracture strength. No
further plastic deformation will takes place
and the fracture will takes place. At this
point the material surface become brittle
and fragments may be removed in a subsequent
impact.
That mean that if you are going to impinge
because the millions and millions of abrasive
particles which are carried by the carrier
gas impinges on the work piece. So, plastic
deformation, plastic deformation, strain increase
and the plastic deformation still goes on
increase and fracture will takes place. At
certain position what will happen becomes
the eventually yield strength will become
the fracture strength and the fracture will
takes place in the material and it will goes
out as a chip ok. This particular point you
have to note that the yield strength increases
and it will reaches to the fracture strength
and the fractured material will goes off as
by leaving a cavity there.
So, material removal mechanism, normally whatever
you have seen in the previous slide that is
for ductile material. If you are going for
brittle material what will happen? During
the brittle material erosion process, at the
particle impact produces different types of
cracks and the chipping is due to brittle
fracture and negligible plastic deformation
ok.
So, whatever you are seeing here there is
a plastic deformation is taking place for
the ductile material. And whatever you are
going to see here is a for a brittle material.
If there is an impact is coming and hit on
the surface there will be a cracks and this
will eroded material will remove the material
in the form of a fine chips. So; that means,
that for the abrasive jet machining the best
suitable material to remove material is the
brittle materials.
So, nozzle tip distance versus cavity, if
the tip distance increases what will happen?
The cavity diameter will increase and the
depth will decrease. If you see here this
is a schematic for your better understanding.
And if you see here so, your diameter G1 stands
for nozzle tip distance and G2 stands for
the increased nozzle tip distance goes on
increase. Then your diameter will increase,
but your depth will decrease that is what
we want to convey from this particular slide.
Effect of nozzle tip distance on the cavity
diameter, in the cutting nozzle position by
very closely to the work piece, normally the
distance is 0.8mm. At the close nozzle tip
distance cutting rates are compared for the
sake of increasing accuracy; that means, that
whenever the nozzle tip distance is low; that
means, that your interest is to get the perfect
cut or perfect dimensions that you want so,
the accurate dimensions that you want. If
the nozzle tip distance eliminates the taper
and minimize the kerfs whenever you are going
for smaller distances.
The typical divergence angle normally will
be 7 degrees for the air. The if you are going
to increase the nozzle tip distance to 5 to
12.5mm, abrasive jet stream become widened
and used for the cleaning and pinning application;
that means, that. So, at higher distances
what is happening here is it is not going
to do the machining operation. However, it
is going to do the cleaning operation or the
pinning operation. The light-duty operations
such as glass frosting are accomplished with
the normally the nozzle tip distance beyond
20.5mm.
So, whenever you want to do the glass frosting
and other things you just go for far away
distances like beyond 25mm. So, that it will
do some texturing on the surface of the glass.
So, some of the people who want to take up
the research areas for texturing of the brittle
materials then you can go for abrasive jet
texturing process also.
So, the parametric analysis if you see abrasive
flow rate, the maximum observed normally,
high abrasive flow rate will lead to high
material removal rate. The more cutting higher
MRR, if the abrasive particle size is very
big the cutting action will be very high and
material removal will be very high. And low
abrasive flow rate normally what will happen?
To lower MRR due to less cutting edges and
other things nozzle tip distance as I said.
If your nozzle tip distance is low, you can
use for cutting purpose, if the nozzle tip
distance is high, you can use for cleaning
purpose or pinning purpose and other things.
If the nozzle pressure is very high what will
happen? The material removal rate will be
very high. If the nozzle pressure is low what
will happen? You can use for cleaning or texturing
applications and other things.
Just the mixing ratio so, the other keyword
here is the mixing ratio that is nothing,
but the volume flow rate of the abrasive particles
to the volume flow rate of the carrier gas;
that means, that you have 2 things here, one
is a gas another one is a abrasive particles.
If the mixing ratio is very high; that means,
that your abrasives are higher in number compared
to your carrier gas ok.
So, an increase in the value of M that is
nothing, but the mixing ratio increases volumetric
material removal rate; normally, some people
may represent MRR that is nothing, but material
removal rate. And MRRV represent volumetric
material removal rate. See here it is shown
MRRV nothing, but it is volumetric material
removal rate.
But large value of M may decrease the jet
velocity and sometimes it may block the nozzle
also. If you everything has its own limitation,
if you are going to use more and more abrasive
particles what will happen? The abrasive particles
collide each other and they lose the original
velocity at which they have to travel and
it has to heat. At the same time there is
another problem that these abrasive particles
may block the nozzle.
So, if the more amount of abrasive particles
are there, it will be a disadvantage. So,
always as a manufacturing engineer you should
think about the optimum mixing ratio. So,
that you can get you required function that
is a whether it is a machining, whether it
is a cleaning or pinning or something.
So, volumetric flow rate of abrasive to volumetric
flow rates of carrier gas is nothing, but
the mixing ratio. Normally, mass ratio also
is there that is nothing, but mass of the
abrasive particles to combination of mass
of abrasive particle with carrier gas. So,
volumetric material removal rate if you see
here cf(ϴ)m Vn which is given by the Finnie
in 1960 where c and n are constant and the
flow stress of the work piece is also given
here.
So, the flow rate, if you see the output responses
that is how the abrasive jet machining works.
The MRR increases only up to certain value
then if the abrasive flow rate increases as
I said what will happen? In the phase one,
the as you increase till 12 to 16 what will
happen? The value of the material removal
rate will gradually increases. Because, if
the abrasives are more what will happen? The
number of times of abrasive particles will
hit will be very high. So, the craters formation
very high and material removal will takes
place.
If you beyond a certain values were going
to increase the abrasives what will happen?
The abrasives will hit one other and its velocity
will be reduced. The abrasive flow rate increases,
the number of abrasive particles cutting work
piece is also increases thereby material removal
increases. This refers to part 1 ok.
However, with further increase in abrasive
flow rate, the abrasive velocity goes down
because in the section 2 what will happen?
The abrasives try to collide each other and
there will be a loss in the velocity. At the
same time this may also clog the exit of the
nozzle. If it is partially clogged then; that
means, that completely the velocity at which
it has to come maybe completely disrupt.
So, you have that is the cost for the second
portion. So, the material removal rate will
be decreased if you are going beyond certain
values. So, from this particular graph what
is the inference is people should can go approximately
this is the values where one can use for optimum.
Like you can go for 10 grams per minute, maximum
216 grams; if your material removal rate is
good at 10 grams per minute; so, you can go
for 10 grams per minute; so, that you can
achieve the better material removal rate in
this particle context.
So, if you see the other parameters normally
nozzle tip distance, if the nozzle tip distance
is increases, what is happens here is the
crater diameters will. If the nozzle tip distance
is low what will happen? The material removal
will be good.
If you are going to increase beyond which
what will happen? The crater depth will reduce,
but crater diameter will increase. But, whatever
the problem here is if you are going to increase
the distances between the nozzle and the work
piece, what is going to happen here is the
velocity, it loses the velocity. As the distance
is D1, if you go for D2 what is going to happen
is it loses its velocity.
So, the losses will be there because it is
coming into the far fear, the pressure difference
is there because of the pressure difference
the velocity will lose. If your mixing ratio
is high; that means, that abrasive particles
are high. Normally, what you are going to
expect is the curve will move like this ok.
Beyond certain value again it will goes down
because as you have seen the same reasons
in the previous slide that it decreases the
velocity and it may block the nozzle also.
If you see here mixing ratio with respect
to nozzle pressure that mean that how much
pressure you are increasing. If you are increasing
the pressure the jet will come and hit with
high velocity. For that purpose the material
removal completely increases. At the same
time if you are going to increase the mixing
ratio; obviously, the material removal increases.
If the nozzle pressure increases what will
happen? The velocity at which the abrasive
particle hits will be very high and the crater
size will be very high and the material removal
volume will be very high.
Mixing ratio as you have seen in the first
slide that mixing ratio, if your mixing ratio
is up to certain value like what the 10 is
a value if it is increases beyond which it
blocks and internal collection of the abrasive
particles will lead to the pressure, velocity
decrease and other things will takes place.
If you see the standoff distance, if the standoff
distance is increasing for the mixing ratios;
here you can see the mixing ratio 2 point,
previously whatever you have seen is a qualitative
things those are taken, but if at all correct
values are required quantitatively and other
things.
Better material removal is achieved if your
mixing ratio is very high. At the same time
for the standoff nozzle standoff distance
is approximately 16. For this particular thing
you can achieve better value. So, the mixing
ratios are ranged from 0.05 to 0.268. So,
the mixing ratio; that means, that abrasives
are increased, if the abrasives are increase
normally the number of craters generation
will be also increased ok.
So, the material removal; obviously, increase.
If the standoff distance is increased, if
the standoff distance is too less what will
happen? You do not have sufficient velocity
to carry. So, you also need the standoff distance
a optimum value so, that you can hit the work
piece.
If you see the standoff distance with respect
to volumetric material removal rate and the
penetration rate is the penetration rate.
If the standoff distance is too low, the normally
the penetration rate is also somewhat low.
But, if your penetration rate will be slightly
increased if you give sufficient space are
to the nozzle. If you give sufficient space
to the nozzle what will happen? It has certain
distance where it can carry the velocity and
hit the work piece.
For that purpose, normally the penetration
rate will increase and beyond which the penetration
rate will decrease. If the penetration rate
decreases what will happen? The volumetric
material removal also will go on decrease
that is what you can see in this particular
slide.
So, nozzle pressures, nozzle pressures with
the volumetric material removal rate here
you can see all the values. So, previous slide
similar slide we have seen, but the thing
is that there it is a qualitative one. As
you increase it will increase, but how much
increase of the input parameter will increase
the how much output response that we are going
to see here. Here 0.143 mixing ratio gives
the highest value; that means, that mixing
ratio is high.
So, the higher material removal rate is achieved
for the higher nozzle pressure. If the nozzle
pressure is 30 you are getting the higher
value. So, if your nozzle pressure is very
high. So, the impact will be very high; that
means, that the abrasive particles will be
hit with the high velocity.
So, the material removal will takes place;
that means, that the nozzle pressure that
is volumetric material removal is shown in
the one. What is the kinetic energy of abrasive
particle is responsible for material? So,
if your nozzle pressure is very high, the
kinetic energy of the abrasive particle will
be very high and the material removal rate
will be increased. Now, we see about the material
removal models for the brittle and ductile
materials using abrasive jet machining process.
Material removal model for the brittle materials
which is proposed by Neema and Pandey , Professor
Pandey; so, assumption material removal by
normal impact only; that means, that there
is no additional things involved. So, abrasive
particles hit the work piece and the work
piece material will be removed that is a simple
assumption.
So, MRR is taken in kgs per second. So, 0.1156
Pa Ma and Va square so, by upon 103 σfw.
Where Pa stands for abrasive particles density,
our Ma is stands for mass flow rate of the
abrasive particles, Va is a component of particle
velocity that is in and normal to the work
surface. That means, that assume that my work
piece is like this and my jet is like this
and abrasive particles are coming and hitting
perpendicular to this particular surface ok.
So, this is how it is and σfw is the flow
stress of the work piece material. The normally
what are the flow stress of this work piece
material these are the abrasive particles
and this is a nozzle from where the . So,
this is normally what Professor Pandey has
proposed for the brittle materials.
So, if you see the material removal model
for the ductile materials, as you have seen
this particular process is mainly suitable
for the brittle materials because abrasives
are coming and hitting. So, the fracture and
small-small fragments of the chips, then it
will goes off. That is the most major mechanism
or this is suitable for the brittle materials,
but people have used for the ductile materials
also. As I discussed in the previous, as I
discussed in the previous slides, that the
where the flow stress will be equivalent to
your fracture and then it will goes off as
a chip.
So, in the same way the ductile materials
also proposed here the material removal model.
Sheldon and Kanhere is proposed the model
for MRR for the ductile materials. If you
see MRR in the volumetric material removal
normally k1 d cube and Va cube and whereby
the various terms are given here. The ρa
and HVW this is the one equation.
So, where k1 is a constant of the proportionality
and dm is the mean diameter of the abrasive
particle or abrasive grain. Va is the volume
of importing particle; that means, that the
how much material is going away and ρa is
abrasive particles density that is kg per
mm cube. And HVW is the Vickers diamond pyramid
hardness number of the target material; that
means, that indirectly you are is saying about
the hardness of the work piece material.
And the amount of material removed is related
to the depth of penetration of the particle;
that means, that how much particles are hitting
it is generates the deformation, then act
and prolonged abrasive particles will hit,
hit, hit, then the fracture will be a removed.
So, that is what the amount of material is
removed related to the depth of penetration;
that means, that how much penetration is taking
place in the work piece material will be taken
into consideration for this particular model.
These are the 2 mathematical models that are
proposed by different different authors. So,
this may be useful for the people who want
to do some of the possible research or some
of the relative research. If at all you want
to move ahead with this particular model you
can move ahead also as considering these equations
of the base equations.
The process capabilities: if you see the low
MRR normally 0.015 centimeter cube per minute
is the material removal. So, intricate details
in hard and brittle materials can up to for
the lower material removal rate; that means,
that normally if at all you want to do the
abrasive jet machining for intricate shapes
and you do not bother about much MRR that
is material removal rate. Because, the intricate
shapes it has to go and it has to do. So,
for that purpose you do not look for the material
removal that is why the material removal is
very low for that one.
Narrow slots, you can cut a narrow slots normally
0.12 to 0.25mm slots you can cut using abrasive
jet machining. You can achieve low tolerances
ranging from plus 0.12 to minus 0.12 microns
you can achieve. And the good surface finish
normally from the nano surface point of you
this is not a good value, but for the machining
purpose the surface finish that you are going
to get is minimum is 0.25, which is a good
surface finish from the finishing point of
view.
But, this particular process is dominated
by the material removal mechanism that is
nothing, but it is a machining process. That
is why we are considered this abrasive jet
machining as one of the advanced abrasive
machining processes. So, minimum radius that
can be produced is 0.2 micrometer. So, this
can produce a good amount of a good radius
ok.
So, process capabilities still there are some
more process capabilities, steels up to 1.5,
glass up to 6.3mm thickness you can cut; that
means, that if at all you have a steel plate
of very small thickness, you can cut or your
glass plates with big thickness you can cut
using the abrasive jet machining. Thin sectioned,
brittle materials, inaccessible areas can
be machined by this particular AJM process.
So, these are the capabilities of abrasive
jet machining process. Almost no surface damage
because there is a gap between abrasive particles.
At the same time heat generation in this particular
process is normally low because you have air
which is a lubricant or which act as a coolant
in this particular action of the abrasive
jet machining and there is no surface or subsurface
damage.
In the thinner materials taper is 0.005 inch
per in of the material thickness; that means,
that normally if you are going for 1 inch,
0.005 inch is the taper that normally observed.
So, this is if the requirement to the customer
is very minimal, then you have to think about
some other processes. If this is within the
limits of their requirements then you can
go for abrasive jet machining process.
Low taper can be tolerated in the cutting
edge. So, the nozzles or the work piece can
be sometimes tilted to the component compensate
this; that means, that. So, if at all you
do not want this type of tapers then you can
tilt it. Nowadays you can tilt the nozzle
assume that if this is your nozzle you can
tilt as per your requirement if at all you
do not want. Assume that some microns taper
is coming, just you move your nozzle or you
give some tilt to your nozzle in opposite
direction of that much micron; so, that you
can compensate it.
This effect of negative taper or the part
double the taper than scrap; that means, that
you can improve and if at all you want the
tapered holes are something then you can use;
obviously, this particular process with slight
experience and other things.
Advantages of abrasive jet machining, if you
see the ability to machine heat sensitive,
brittle fragile materials; that means, that
if it is heat sensitive material assume that
any materials are mostly subjected to heat
sensitive then those can be machined by abrasive
jet machining because, this particular process
do not develop any heat during the machining
process.
Very little or no heat generation due to non
contact cutting and microscopic material removal;
that means, that the material removal is very
very minute. At the same time non contact
cutting tool that is nothing, but you have
abrasive particle, abrasive particle in between
there is a air gap. So, air will act as a
lubricant or a coolant or something. So, it
is a sufficient time or a ample time is there
between one abrasive particle to another abrasive
particle if your mixing ratio is slightly
less.
So, there would not be any generation of heat
in this particular process. So, low capital
investment and low power consumption; that
means, that you can develop this abrasive
jet machining in your laboratory with a very
minimal cost. That mean that if you have a
if you do not have funding also you can develop,
you need a one compressor. So, normally compressors
are not that much costly. So, you can have
different different ratings of compressors
and you can get those compressors, then you
just put a feeder, abrasive feeder and you
can mix it in a mixing chamber and you just
impinge on the work piece.
So, you can start work basic research with
low investments which assume that if your
institute or university can give a minimum
amount of some amount. A minimum amount if
they can give then you can develop this abrasive
jet machining and power consumption also very
less.
So, I think the universities will, higher
authorities of universities will allow you
for going ahead of this particular process.
Low part chatter or vibration is observed
because there is no chance of vibration. So,
if at all what you have to do is you have
to firmly hold your work piece. So, that if
at all there is anything such small small
minute things are there from the point of
chatter or something then can be avoided.
So, machines are very hard, it can machine
very hard materials; that means, that hard
to brittle materials normally brittle materials
are hard materials also. So, you can do the
machining of these hard materials
Disadvantages of this particular process,
nozzle wear rate is very high as I said you
have to go for sapphire. If you go for sapphire
normally you go for 300 hours ok. If you are
going for the tungsten carbide or some other
things now you it will be reduced by 10 times,
that is maximum you were going to get is 20
hours or 30 hours. Abrasive particle cannot
reused that is the biggest problem because,
this abrasive particles once hits the work
piece it loses it is cutting edges. At the
same time assume that I have a short cutting
edge here. So, after uses what will happen?
This will goes off.
So, that mean that will become blunt, at the
same time this will catch up some of the chips
of the work piece material and these chips
are hardness compared to the tool material,
that is abrasive materials. For that purpose
what will happen? You cannot reuse in most
of the cases. It cannot use the machines for
soft and ductile materials because, whenever
you use a soft and ductile materials these
abrasive particles go and indent, sometimes
it will stay also.
So, assume that I have a soft material here
abrasive particle can come and hit to the
work piece and can stay like this only ok,
it will stay like this. So, in a soft material
this is a biggest problem ok. So, you may
not recommend this particular abrasive jet
machining to machine soft materials. Sometimes,
additional cleaning operation is required
on a machine part. Because, if assume that
some of the indentations are generated or
some of the abrasive particles are stayed
there. So, you need a post processing that
is nothing, but the cleaning.
Stray cutting and machine accuracy is poor;
that means, that because of the divergence
assume that my nozzle is here because of the
divergence what will happen? The stray cutting
also will takes. Assume that I required only
in this region so, I am getting a stray in
this region which I do not want because, the
air is a gas, gas try to expand because of
that problem the divergence will stay and
the stray cutting will takes place. Because
of that what will happen? Accuracy of that
particular hole or accuracy of that particular
part which has to be generated will go beyond
what was the customer require. So, the customer
has every chance to reject that particular
part.
The process tend to pollute the environment
because abrasive particles are brittle materials
whenever the abrasive particles are hitting
the hard materials of the work piece, hard
work piece material. So, it will generate
some dust like gas is there already you have
air plus abrasive dust this will lead to pollution
ok.
So, low material removal rate at the same
time the short nozzle standoff distance when
used for the cutting purpose; that means,
that if at all you want to go for cutting.
So, you have to use nozzle tip distance or
the standoff distance very low ok. This has
to be taken care if at all you are going for
a cutting operation. If you are going for
a pinning operation or surface cleaning operation
you have to go for high standoff distances.
Applications, if you see the applications
normally silicon or tungsten carbide configuration
requirement for AJM, for the trimming of electronic
components. At the same time you can use AJM
trimmed for the silicon you can use at different
angles ok. You can use at different angles
for trimming application this is one of the
technique that you can use. AJM is successfully
employed for manufacturing of small electronic
devices consisting of 0.38mm thickness.
Silicon wafer brazed to 0.75mm thickness tungsten
disk and other things you can use for the
brazing then you can do the trimming also.
After the 2 materials are brazed together
the silicon wafer must be trimmed and beveled
without harming the tungsten disk. And AJM
nozzle is mounted at desired angle and directed
slowly rotating part and unwanted silicon
is trimmed off for the part ok. That means,
that you can trim off as per your requirement,
this is the one of the special thing about
this particular process ok.
The applications, if you see the applications
as I said you can see the capability how beautiful
capability by drawing or by creating some
sculptures on egg shells. So, egg shell is
to brittle material on and it is a very thin
material also. So, if you can generate a beautiful
sculpture on top of it; that means, that it
has tendency to not break any type of physical
brittle material so; that means, that it is
very superior process to make in a brittle
and thin sections any type of sculptures.
That means that this particular AJM has ability
to machine intricate shapes into a brittle
work pieces with low thickness. At the same
time you can see some of the metals that are
being cut using this. So, thin sections also
you can go if you see this particular work
piece material, see how much thick it is.
So, you can cut the thick sections, you can
cut the thin sections, at the same time you
can cut multiple types of geometries ok. So,
some of the geometries are you can cut like
some of the complex geometries you can cut
on a some of the thick sheets also.
It is used to drill and cut the hardened metals
normally you can do the drilling or cutting
of the hardened metals also can be possible.
It is used for machining of brittle and heat
sensitive materials like glass, quartz, sapphire,
mica, and ceramic. These are the some of the
advanced materials where you can generate,
where you can make without any heat generation.
So, that if these are heat sensitive it may
change it is metrological structures morphological
structures or something. So, if at all you
do not want all this metallurgical changes,
which are changing with respect to temperature
you can use for this in this particular abrasive
jet machining. So, that this there is would
not be any heat generation because of which
there would not be any changes in a thermo
sensitive materials.
It uses the manufacturing of electronic devices
which we have seen in the advantages. It is
used for the deburring of micro holes also.
So, if there is a bur assume that this is
my hole on a surface there are there are burrs.
So, you can use by some tilting of your nozzle
you can remove the burse ok. This type of
applications also you can use for the, this
type of deburring applications also you can
use, this type of deburring applications also
can be done by the abrasive jet machining
process.
So, some of the applications as you can see
the butterflies, dendrites structures, cycle
structures and gears can be manufactured;
at the same time many complex shapes with
the thin structures and as well as thick structures
can be made ok. Thin as well as thick structures
one can cut using the abrasive jet machining
process.
Stainless steel work pieces, you can see the
good and complex structures are fabricated.
At the same time thin structures and mild
steel also can be cut. You see the thickness
of this particular material, it is too thick
material and you can cut using abrasive jet
machining for this particular material, if
some of the people might have used for by
abrasive water jet machining also.
These are the same applications.
And if you see the applications removing of
the flash, parting lines of the injection
moulded parts can be done. And deburring and
polishing plastic, nylon, Teflon components
can be done and the cleaning of metallic mould
cavities which otherwise may be inaccessible
by other processes can be done by this abrasive
jet machining process.
Cutting thin sectioned fragile component that
is brittle component made up of glass, ceramics
can be machined using abrasive jet machining.
Removing of the glue paint from the paintings
and other leather objects can be easily fabricated.
Posting interior surface of the glass tubes
normally if at all you want to generate some
textures can be done by using this particular
process.
Manufacturing of electronic devices as we
have seen the silicon and other things can
be done or trimmed by using this abrasive
jet machining by giving some tilt to the nozzle.
Permanent marking on rubber stencils can be
done by the abrasive jet machining. And drilling
of on glass wafers, titanium and other foils
can be done. Marking and engraving and glass
frosting is another application of this one.
So, other part I just want to touch here is
abrasive jet machining you can manipulate
or you can modify to abrasive jet polishing
also.
So, just I am going to give you 1 or 2 slides
of the glimpse. Abrasive jet polishing process
was the first introduced by Fahnle in the
Delft University. Their research showed that
this is feasible to utilize abrasive jet polishing
for the precision optical manufacturing and
abrasive jet process they polished BK7 optical
glasses and rms values are decreased from
350 nanometers to 25 nanometers.
That is the best value that they have achieved.
So, that mean that if you are looking for
the abrasive jet polishing techniques it will
be also can be done, but make sure that BK7
is one of the brittle and is brittle and material
ok.
So, Horiuchi O also made such research and
abrasive jet polishing process. And these
are the some literature that I am giving because
not much research work is done on abrasive
jet polishing. That is why you can go through
this particular thing and if at all some people
want to take up or modify the existing abrasive
jet machining process to abrasive jet polishing
that can be done. And if the roughness values
are 1.49 nanometers and pre machined can be
done from the surfaces also ok.
The summary of this abrasive jet machining
can be summarized like this, advanced abrasive
machining processes I just give you what are
the process that I am going to cover in this
particular section. Introduction to abrasive
jet machining, then abrasive jet machining
process parameters, what are the parameter,
input parameters and what is needs to influence
and output responses.
Effect of input, material removal models for
brittle and ductile materials, applications,
as well as at the same time I have just touched
the abrasive jet polishing ok. So, this is
about the abrasive jet machining process.
Thank you for your kind attention and we will
see the next process in the next class.
Thank you.
