5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT
Guwahati, Assam, India
615-1
Comparative Evaluation of Mechanically Alloyed and Sintered
Magnetic Abrasives for Fine Finishing
Sehijpal Singh1*, Parmjit Singh2, H.S Shan3
1G. N.D. Engineering College Ludhiana-141006,[email protected] 2Dr.B.R.Ambedkar NIT, Jallandhar-144001,[email protected]
3Punjab Technical University, Kapurthala-144601,[email protected]
Abstract
The magnetic abrasives play a vital role as cutting tool in the performance of magnetic abrasive finishing (MAF)
process. In this paper, a comparison has been made between the performance and characteristics of magnetic
abrasives prepared by a newly developed technique (Mechanical alloying) and a common technique (Sintering).
Mechanical alloying and sintering process have been used to prepare magnetic abrasives having 15% SiC and 85%
Fe as constituent powders. An experimental set up was developed for the conduct of experimental work. The
experiments were conducted to examine the effect of mesh size of magnetic abrasives and machining time on the
performance when MAF is done on Stainless Steel 304 with sintered magnetic (SM) abrasives and mechanically
alloyed magnetic (MAM). The amount of lubricant, rotational speed of work piece, magnetic flux density and
quantity of magnetic abrasives and initial surface roughness of the tube surface were taken as constant parameters.
The performance parameter was taken as percentage improvement in surface finish (PISF).The best surface finish in
the range 0.01-0.04 µm was achieved on internal surface of SS 304 tube. The MAM abrasives with mesh size 52
gave best finishing results along with a good life. The SM abrasives with mesh size 130 and 180 also gave
comparable results but the life of these abrasives was not as good as that of MAM abrasives. Keywords: Magnetic Abrasive Machining, Mechanical alloying, Sintering, Surface finishing
1 Introduction
The final finishing operations play vital role in the
overall manufacturing cycle. Magnetic Abrasive
Finishing (MAF) is one of the promising processes for
obtaining high level of finish on metallic and non-
metallic surfaces. In MAF process, the magnetic
abrasives act as fine cutting tools and remove the
material at micro level by providing low mechanical
forces. Presently, it is required that the parts used in
manufacturing of semiconductors, atomic energy
equipment, medical instruments and aerospace
applications, should have very fine surface finish.
Magnetic Abrasive Finishing (MAF) has been explored
in numerous applications for fine finish of a wide range
of metallic and non metallic materials and various
components like solid rods, hollow pipes, plain surfaces
(Shinmura et al. 1987). MAF is widely used due to its
capability to produce good surface finish, to machine
hard materials and complex shapes and less cost as
compared to other finishing/machining processes by
which same surface finish and machining capability of
intricate parts can be achieved. MAF involves the use of
low cutting forces therefore the process causes
minimum thermal and mechanical damage during
finishing operation. In MAF process, cutting force is
controlled by magnetic field so the finishing process is
essentially accomplished without the need for designing
expensive rigid and vibration free machine tools.
During the implementation of MAF, one can simply
incorporate the required machining elements into the
existing conventional machine tools which help to
minimize the cost of new equipment. Some advantages
of MAF over other processes like super finishing,
lapping are mentioned below:
• Surfaces produced by MAF are free from burns and
thermal effects.
• The workpiece is subjected to lower stresses as
MAF process requires no rigid tools unlike
traditional grinding, lapping and honing process.
• Cutting forces are less so the energy consumption is
less.
• MAF is Ecologically safe.
Comparative Evaluation of Mechanically Alloyed and Sintered Magnetic Abrasives for Fine Finishing
• Easy implementation of process.
• Non-ferrous materials like aluminum, brass and
their alloys can be finished with equal case as
ferrous materials.
MAF has enormous applications in manufacturing a list
of various applications is given as follows:
1. Finishing of plane surfaces and surfaces of silicon
wafers
2. Sharpening and removal of burrs from partially
finished blades manufactured by vibro
3. Machining and finishing parts having close
tolerances with very small chip size and self
sharpening of tool.
4. Internal finishing of bottom of a clean gas bomb
with a narrow opening and clean gas piping which
are hard to finish by conventional finishing
processes.
5. Internal finishing of stainless steel sanitary tubes,
cold drawn elbows, SUS304 stainless steel bent
tubes and non-ferromagnetic complex shaped tubes.
6. Internal finishing of capillary tubes using diamond
particle based spherical magnetic abrasives.
7. Outside finishing of shafts, rollers, pins & axles etc.
8. Fine finishing of strip materials (sheets and plates),
translucent aluminum discharge lamps etc.
9. Removal of oxide layers, protective coating and
burrs from bore edges in complicated bulk pieces.
10. Internal finishing of round surfaces (bomb shells,
roller bearing, thimbles, elbows) as well as
complicated parts (rubber rings, synthetic and
moulded parts)
1.1 Principle of magnetic abrasive finishing
The process principle of internal MAF using a work
piece rotation system is shown in Fig.1. When current is
passed through the coils of the electromagnet, the poles
of DC electromagnet generate the magnetic field. The
magnetic field attracts the magnetic abrasives to the
finishing area in the tube and presses the magnetic
abrasive particles against the inner surface of the tube.
The magnetic abrasives get conglomerated and form a
flexible brush at the finishing area under the influence
of magnetic force. When rotary motion is given
thework piece, the material is removed from the inne
surface of the tube by the magnetic abrasives due to the
relative motion. The finishing
magneticabrasive brush is controlled by the magnetic
force acting on the magnetic abrasives which in turn is
controlled by the current supplied to the el
1.2 Review of literature
The existing literature on MAF has been largely
focused on three major areas:
Comparative Evaluation of Mechanically Alloyed and Sintered Magnetic Abrasives for Fine Finishing
ferrous materials like aluminum, brass and
their alloys can be finished with equal case as
applications in manufacturing a list
is given as follows:
inishing of plane surfaces and surfaces of silicon
Sharpening and removal of burrs from partially
finished blades manufactured by vibro-forging.
hing parts having close
tolerances with very small chip size and self
Internal finishing of bottom of a clean gas bomb
with a narrow opening and clean gas piping which
are hard to finish by conventional finishing
ishing of stainless steel sanitary tubes,
cold drawn elbows, SUS304 stainless steel bent
ferromagnetic complex shaped tubes.
Internal finishing of capillary tubes using diamond
particle based spherical magnetic abrasives.
shafts, rollers, pins & axles etc.
Fine finishing of strip materials (sheets and plates),
translucent aluminum discharge lamps etc.
emoval of oxide layers, protective coating and
burrs from bore edges in complicated bulk pieces.
nd surfaces (bomb shells,
roller bearing, thimbles, elbows) as well as
complicated parts (rubber rings, synthetic and
Principle of magnetic abrasive finishing
The process principle of internal MAF using a work
in Fig.1. When current is
passed through the coils of the electromagnet, the poles
of DC electromagnet generate the magnetic field. The
magnetic field attracts the magnetic abrasives to the
finishing area in the tube and presses the magnetic
icles against the inner surface of the tube.
The magnetic abrasives get conglomerated and form a
flexible brush at the finishing area under the influence
of magnetic force. When rotary motion is given to
work piece, the material is removed from the inner
surface of the tube by the magnetic abrasives due to the
force of the
abrasive brush is controlled by the magnetic
force acting on the magnetic abrasives which in turn is
controlled by the current supplied to the electromagnet.
The existing literature on MAF has been largely
Fig.1 Schematic of internal magnetic abrasive
finishing(Shinmura, 1987)
1. Development of machines/setups for
external/internal/plain finishing with AC and DC
electromagnets
2. Process parametric optimization for obtaining best
surface finish for metallic and non
materials.
3. Application of magnetic abrasives for developing
new hybrid machining/finishing processes.
It has been recognized that very few research studies
are available in the direction of development and
characteristics of magnetic abrasives. A representative
brief literature review has been presented here for
highlighting major types of magnetic abrasives
employed by various researchers. The sintered magnetic
abrasives have been used by some researchers (Kim
2003, Wang and Dejin 2005, Ching et al. 2007
Kremen et al. (1996) prepared magnetic abrasives by
mixing ferromagnetic powder and abrasive power and
adhesive. A special type of glue and mixture of
ferromagnetic and abrasive particles were mixed in a
required proportion. In several studies (Singh et al.
2010, Khairy 2001, Mullik and Pandey 2011), the
simple mixture of ferromagnetic and abrasive powder
(commonly known as unbounded magnetic abrasive
particles) has been used. An exhaustive review of
various available methods of preparing magnetic
abrasives has been presented by Singh et al. (2005).
There is a need to evaluate comparative performance of
various types of magnetic abrasives. This will help the
users to select suitable magnetic abrasive for an
application.
615-2
Fig.1 Schematic of internal magnetic abrasive
(Shinmura, 1987)
Development of machines/setups for
external/internal/plain finishing with AC and DC
Process parametric optimization for obtaining best
surface finish for metallic and non –metallic
pplication of magnetic abrasives for developing
new hybrid machining/finishing processes.
It has been recognized that very few research studies
are available in the direction of development and
characteristics of magnetic abrasives. A representative
brief literature review has been presented here for
highlighting major types of magnetic abrasives
employed by various researchers. The sintered magnetic
abrasives have been used by some researchers (Kim
Ching et al. 2007).
Kremen et al. (1996) prepared magnetic abrasives by
mixing ferromagnetic powder and abrasive power and
adhesive. A special type of glue and mixture of
ferromagnetic and abrasive particles were mixed in a
required proportion. In several studies (Singh et al.
2010, Khairy 2001, Mullik and Pandey 2011), the
simple mixture of ferromagnetic and abrasive powder
(commonly known as unbounded magnetic abrasive
particles) has been used. An exhaustive review of
various available methods of preparing magnetic
abrasives has been presented by Singh et al. (2005).
is a need to evaluate comparative performance of
various types of magnetic abrasives. This will help the
users to select suitable magnetic abrasive for an
5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT
Guwahati, Assam, India
615/3
2. Preparation of Magnetic Abrasives
In the present work, the magnetic abrasives have been
prepared by two techniques. The sintering process is
one of the common techniques where as mechanical
alloying has been explored as an alternative technique
for preparation of magnetic abrasives. The stepwise
procedure for preparing magnetic abrasive is given as
follows:
1. Mixing/blending of abrasive (SiC)
Ferromagnetic powder (Fe).
2. Compacting of mixture.
3. Annealing of the compacts.
4. Crushing/Turning of compacts.
2.1 Mechanically alloyed magnetic abrasives
In the present work, the mechanical alloying of
abrasive (15% by weight) and ferromagnetic powders
(85% by weight) is done in a high energy ball mill
(Attritor). The other details of the process parameters
are available literature (Singh et al., 2012). The
annealing of the mechanically alloyed powder is
necessary to remove any possibility of the oxidation of
the alloyed powder. For annealing of the mechanically
alloyed powder the cylindrical compacts were prepared
in a die using a hydraulic press. A layer of paste (Zinc
Stearate in Methanol) was applied to inner surface of
bore of die and end surface of the plunger for
lubrication purpose. Then, the bore of the die (2.3 cm in
diameter) was filled with mechanically alloyed powder
up to 4.6 cm in height (height of powder was kept
double than diameter of the die). A load of 2Ton/cm2
was applied for 20 seconds (generally used for iron
powders to prepare compacts) for compaction of
mechanically alloyed powder. The annealing of these
compacts was done in hydrogen gas environment at
1050°C for 3 hours in a stainless steel tube furnace. The
annealed compacts were mechanically crushed into
powder of different sizes using turning operation on a
lathe using tungsten carbide tool. The powder was
separated into different sizes using sieves. The average
mesh sizes of the Mechanically Alloyed Magnetic
(MAM ) abrasives obtained were 52, 80, 130, 180 and
200.
2.2 Sintered magnetic abrasives
For preparing Sintered Magnetic (SM) abrasives, the
same composition as taken in mechanical alloying was
used but both powders were mixed in a box and shaked
this box for 20 min so that the powder is properly
mixed. The preparation of compact of for sintering was
prepared by the same procedure and as mentioned for
mechanical alloying. The compact was placed inside the
tube furnace for 2.30 hour at 1150°c for sintering in
inert environment. After sintering the SM abrasive
compact were crushed and sorted in various mesh sizes.
3. Experimentation for Performance
Testing
Fig. 2 shows schematic of the experimental setup
used for internal MAF. A known quantity of magnetic
abrasives mixed with required amount of lubricant was
packed inside the tube and magnetic field was applied
by the electromagnets. Due care was taken that the
abrasives should remain in a confined zone on the
internal surface of the tube. The magnetic field was
generated by two electromagnets, with their poles at
180°apart. The field strength in the working zone may
be controlled by the supply current to the
electromagnets. A set of samples was prepared for
carrying out MAF on inner surface of SS304 tubes for
various machining time and with different mesh sizes of
both types of magnetic abrasives. The inner surface of
samples was cleaned thoroughly with acetone before
and after polishing. The finishing capability of magnetic
abrasives was analyzed by measuring the surface
roughness (Ra) on the unfinished and finished inner
surface of the tube. The Ra value was measured at four
points along the length of tube. The percentage
improvement in surface finish over the initial finish of
the tube surface (PISF) is taken as performance
parameter. Surface roughness is measured using a
Mitutoyo surface roughness tester having a least count
of 0.01 µm.The values of constant and variables
parameters are given in Table 1.
Fig. 2 Schematic of the experimental setup used for
MAF
4. Results and Discussions
The experimental results obtained after MAF of SS
304 tubes have been presented and discussed in this
section.
Comparative Evaluation of Mechanically Alloyed and Sintered Magnetic Abrasives for Fine Finishing
615-4
Table 1 Experimental Conditions
Work piece: SS304 bored
tube
O.D. 37 mm
Thickness- 1mm
Composition of Magnetic
abrasive (M.A.)
Fe- 85%+ SiC- 15%
Poles and work piece gap 0.5mm
Quantity M.A. 10gms
Magnetic flux density 0.5T
Rotational speed of
workpiece
1000 RPM
Mesh size of M.A. 52, 80, 130, 180, 200
Fig. 3 shows the effect of machining time on
percentage improvement in surface finish (PISF) on
inner surface of the SS304 tube when MAF was done
with Mechanically Alloyed Magnetic (MAM)
abrasives. The trend of curves indicates that coarser
abrasives (mesh size 52 and 80) have shown better PISF
as compared to finer abrasives (mesh size 130, 180,
200). It is further observed that nearly 95%
improvement in surface finish over the initial surface
finish has been achieved after machining time of 10
minutes with these coarser MAM abrasives. Though
the PISF decreased when the sample was finished for
more time for mesh size 80 but it remains consistently
high for mesh size 52. For all sizes (except mesh size
52) the performance of MAM abrasives deteriorates
when used for more time.
Fig. 3 Effect of machining time and mesh size of
abrasives on the PISF using MAM abrasive
Fig. 4 Effect of machining time and mesh size of
abrasives on PISF using SM abrasives
Fig. 4 shows the effect of machining time on PISF
on inner surface of SS 304 tube when MAF was done
with Sintered Magnetic (SM) abrasives. The SM
abrasives of mesh size 130 and 180 gave the best
performance (nearly same as given by MAM abrasives),
However after 30 minutes of MAF the PISF drastically
reduced for both mesh sizes of SM abrasives. Further,
the SM abrasives with mesh size 80 performed well but
these need more time. After 50 minutes of MAF its
performance increases and after 90 minutes of MAF its
performance is best (nearly 90%).
On the basis of experimental results, it can be
hypothesised that the mesh size of abrasives play very
dominant role on the performance of MAM abrasives
and SM abrasives. As the process of manufacturing of
these abrasives is different, there is a need to understand
this observation in detail.
The magnified photos of polished samples of
magnetic abrasives prepared by both the methods have
been taken using an optical microscope. From
examination of these photomicrographs, it appears that
a layer of SiC is formed around Fe particles but the SiC
has not entered deep into the iron matrix (Fig. 5)
whereas the SiC particles seems to be embedded in iron
matrix in case of MAM abrasives (Fig. 6). The SEM
image of a single MAM abrasive particle (shown in Fig.
7) also supports the likelihood of
penetration/embedding of SiC (Black flakes) into the
iron matrix (Grey). This observation may be used to
understand the behaviour of magnetic abrasives in
MAF. The consistent finish for long machining time
given by MAM abrasives (of mesh size 52) as indicated
by Fig. 3 may be due to the reason that the
0
20
40
60
80
100
120
10 30 50 70 90
PIS
F
Machining Time(Minutes)
Mesh Size
52
Mesh size
80
Mesh Size
130
Mesh Size
180
Mesh Size
200
0
20
40
60
80
100
120
10 30 50 70 90
PIS
F
Machining Time(Minutes)
Mesh Size
52
Mesh size
80
Mesh Size
130
Mesh Size
180
Mesh Size
200
5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12
Guwahati, Assam, India
mechanically alloyed abrasives are able to work for
long time as the abrasive part is mixed with iron matrix
more effectively. However, this behaviour is not true
with fine mesh sizes. This observat
studied further. In case of SM abrasives, the bond
between SiC and Fe may not be as strong as that in
MAM abrasives. Therefore the performance of SM
abrasives (all sizes) does not remain consistent with
long use. Therefore, a significant statement may be
given as “the life of SM abrasives is not as good as that
of MAM abrasives”. Further investigations are needed
to verify the statement.
Fig. 4 indicates that after some use, there is a trend
of improved PISF. This may be attributed to the
possibility of exposure of new/fresh cutting edges due
to fragmentation/breaking of abrasives. But in MAF the
chances of fragmentation of abrasives seems to be low
as very less mechanical forces are involved (as
compared to other processes like grinding). Th
of breaking of magnetic abrasives needs to be
investigated further
Fig. 5 Microphotograph of SM abrasives
(Magnification X 200)
Fig. 6 Microphotograph of MAM
(Magnification X 200)
All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12
mechanically alloyed abrasives are able to work for
long time as the abrasive part is mixed with iron matrix
more effectively. However, this behaviour is not true
with fine mesh sizes. This observation need to be
studied further. In case of SM abrasives, the bond
between SiC and Fe may not be as strong as that in
MAM abrasives. Therefore the performance of SM
abrasives (all sizes) does not remain consistent with
atement may be
given as “the life of SM abrasives is not as good as that
of MAM abrasives”. Further investigations are needed
Fig. 4 indicates that after some use, there is a trend
of improved PISF. This may be attributed to the
ssibility of exposure of new/fresh cutting edges due
to fragmentation/breaking of abrasives. But in MAF the
chances of fragmentation of abrasives seems to be low
as very less mechanical forces are involved (as
compared to other processes like grinding). The process
of breaking of magnetic abrasives needs to be
Fig. 5 Microphotograph of SM abrasives
(Magnification X 200)
Fig. 6 Microphotograph of MAM abrasives
(Magnification X 200)
Fig. 7 SEM photograph of a single MAM abrasive
particle (Magnification X1500)
5. Conclusions
On the basis of experimental results obtained in the
present study, following conclusions have been drawn:
• The magnetic abrasives prepared by mechanical
alloying and sintering process are able to fine finish
SS304 tubes when used in Magnetic Abrasive
Finishing. The best achieved range of surface
roughness value in both the cases is 0.01
• The manufacturing process for preparing the
magnetic abrasives and mesh size of the abrasives
has dominant effect on the performance of magnetic
abrasive finishing of a selected surface.
• The life of magnetic abrasive prepared by
mechanical alloying is better as compar
sintered magnetic abrasives.
• In mechanically alloyed magnetic abrasives, the SiC
particles were embedded into the Iron matrix while
a layer of SiC particles was observed around Fe
particles in case of sintered magnetic abrasives
• To achieve best finishing results when all other
parameters of MAF are kept same, the mesh size
130 and 180 is suitable for sintered magnetic
abrasives and mesh size of 52 is the best for
mechanically alloyed magnetic abrasives.
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Iron
SiC
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Backin
SiC
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Backing
All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT
615/5
Fig. 7 SEM photograph of a single MAM abrasive
particle (Magnification X1500)
On the basis of experimental results obtained in the
present study, following conclusions have been drawn:
The magnetic abrasives prepared by mechanical
alloying and sintering process are able to fine finish
SS304 tubes when used in Magnetic Abrasive
Finishing. The best achieved range of surface
roughness value in both the cases is 0.01-0.04 µm.
ring process for preparing the
magnetic abrasives and mesh size of the abrasives
has dominant effect on the performance of magnetic
abrasive finishing of a selected surface.
The life of magnetic abrasive prepared by
mechanical alloying is better as compared to that of
In mechanically alloyed magnetic abrasives, the SiC
particles were embedded into the Iron matrix while
a layer of SiC particles was observed around Fe
particles in case of sintered magnetic abrasives
best finishing results when all other
parameters of MAF are kept same, the mesh size
130 and 180 is suitable for sintered magnetic
abrasives and mesh size of 52 is the best for
mechanically alloyed magnetic abrasives.
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