Effect of the process parameters on the surface roughness during magnetic

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 2, March - April (2013) © IAEME
310
EFFECT OF THE PROCESS PARAMETERS ON THE SURFACE
ROUGHNESS DURING MAGNETIC ABRASIVE FINISHING
PROCESS ON FERROMAGNETIC STAINLESS STEEL WORK-
PIECES
Shrikant Thote1
, Diwesh Meshram2
, Kapil Pakhare3
, Swapnil Gawande4
1
(Mechanical Department, G.H.Raisoni Academy of Engineering & Technology, Nagpur
Maharashtra, India)
2
Maharashtra, India)
3
Maharashtra, India)
4
Maharashtra, India)
ABSTRACT
Study of new and cost effective finishing processes has always been an area of keen
interest to overcome the difficulties of existing finishing process. Magnetic Abrasive
Finishing (MAF) is a process in which a mixture of non-ferromagnetic abrasives and
ferromagnetic iron particles is used to do finishing operation with the aid of magnetic force.
The iron particles in the mixture are magnetically energized using a magnetic field. The iron
particles form a lightly rigid matrix in which the abrasives are trapped. This is called Flexible
Magnetic Abrasive Brush (FMAB), which when given relative motion against a metal
surface, polishes that surface. The major studies concerning MAF have been done regarding
the behaviors of the process under the effect of various parameters like working gap, mesh
number of abrasive, speed of relative motion on cylindrical and flat work-pieces taking one
type of material, non-ferromagnetic or ferromagnetic only. But limited comparative study by
taking stainless steel with ferromagnetic behavior has been done to analyze the surface
roughness that is generated during the process. This paper has aim of development of
Magnetic Abrasive Finishing Process & studying the effect of the process parameters
(percent composition of iron powder, mesh number of abrasive and current) on the surface
roughness during MAF of ferromagnetic S.S. work-piece material for flat work-pieces. The
INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING
AND TECHNOLOGY (IJMET)
ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 4, Issue 2, March - April (2013), pp. 310-319
© IAEME: www.iaeme.com/ijmet.asp
Journal Impact Factor (2013): 5.7731 (Calculated by GISI)
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IJMET
© I A E M E

311
results of the experiments are statistically analyzed using design expert v.7 software for the
responses generated during the process. In case of ferromagnetic work-piece, percent
composition of iron powder has more effect than the other parameters. With increase in mesh
size of abrasive, percent improvement in surface roughness increases. With increase in
current the percent improvement in surface roughness value increases much more than the
other parameters, therefore effect of applied current is seen to the most significant amongst
all the parameters.
Keywords: Magnetic abrasive finishing, Surface Roughness, Mesh number, Stainless steel.
1. INTRODUCTION
A magnetic abrasive finishing process is defined as a process by which
material is removed, in such a way that the surface finishing and deburring is
performed with the presence of a magnetic field in the machining zone. Magnetic
abrasive finishing (MAF) has a magnetic field which assisted finishing process. The work
piece is kept between the two poles of a magnet. The method was originally introduced in the
Soviet Union, with further fundamental research in various countries including Japan.
Nowadays, the study of the magnetic field assisting finishing processes is being conducted at
industrial levels around the world.
1.1 Working Principle
The working gap between the work piece and the magnet is filled with magnetic
Abrasive particles (MAP), composed of ferromagnetic particles and abrasive powder. MAP is
prepared by sintering of ferromagnetic particles and abrasive particles. The magnetic abrasive
particles join each other along the lines of magnetic force and form a flexible magnetic
abrasive brush (FMAB) between the work piece and the magnetic pole .This brush behaves
like a multi-point cutting tool for finishing operation. When the magnetic N-pole is rotating,
the Magnetic Abrasive Finishing Brush (MAFB) also rotates like a flexible grinding wheel
and finishing is done according to the forces acting on the abrasive particles. In external
finishing of cylindrical surface, the cylindrical work piece rotates between the magnetic
poles, with the MAP filled in both the gaps on either side, whereas in internal finishing of
cylindrical surface, the work piece rotates between the magnetic poles and the MAP as shown
in (Fig 1). The magnetic field generator can be either electromagnetic coils or permanent
magnets. The relative motion between the induced abrasive particles of the FMAB and work
piece generates the necessary shearing action at the abrasive–work-piece interface to remove
material from the work-piece in the form of miniature chips.
Fig. 1 External cylindrical finishing & Internal cylindrical finishing.

312
2. LITERATURE REVIEW
Change in the strength of magnetic field in the direction of the line of magnetic force
near the work-piece surface will actuate the magnetic abrasive particle. The effective way of
changing the force/finishing pressure and rigidity of MAFB is through the change in diameter
“D” of magnetic abrasive particle. Hence, ferromagnetic particles of several times the
diameter of diamond abrasive “d” are mixed to form the magnetic abrasive brush. MAF is
affected by the material, shape and size of the work-piece, and shape and size of the magnetic
pole. Pressure increases with increase in flux density and decreases as the clearance gap
between tool & work-piece increases. Larger the particle size, poorer the finishing (except for
50µm particles) but higher is the stock removal which increases linearly with finishing time
[1].
The surface roughness is predicted as a function of finishing time by a model that has
been derived from the removed volume of material. Thus, it is possible, from the surface-
roughness model, to predict the time when existing scratches are completely removed [2].
The magnetic force acting on the magnetic abrasive, controlled by the field at the finishing
area, is considered the primary influence on the abrasive behavior against the inner surface of
the work-piece. [3].
With increase in working gap, the percentage improvement in surface roughness
increases initially, reaches a maximum value and then it starts decreasing [4]. Removal of
burrs in large surfaces with drilled holes using MAF shown that this method can be applied
both for ferromagnetic and non-magnetic parts. This method can be improved as applied to
new tasks of deburring [5].
The finishing characteristics of unbonded magnetic abrasive within cylindrical
magnetic abrasive finishing. The unbonded magnetic abrasive is a mechanical mixture of Sic
-abrasive and ferromagnetic particles with a SAE30 lubricant. Iron grit and steel grit, three
particle sizes were prepared for both and were used as ferromagnetic particles, each of them
being mixed with 1.2 and 5.5 µm Sic abrasive, respectively. Results indicate that steel grit is
more suitable for magnetic abrasive finishing because of its superior hardness and the
polyhedron shape. However its corrosion resistibility decreased on a surface that was finished
via steel grit mixed with SiC abrasive [6].Important parameters influencing the surface
quality generated during the MAF were identified as: (i) voltage (DC) applied to the
electromagnet, (ii) working gap, (iii) rotational speed of the magnet, and (iv) abrasive size
(mesh number). [7].
Efficient finishing of magnesium alloy is possible by the process. The volume
removed per unit time of magnesium alloy is larger than that of other materials such as brass
and stainless, that is, high-efficiency finishing could be achieved. Micro-burr of magnesium
alloy could be removed easily in a short time by the use of MAF [8].
MAF process creates micro scratches having width less than 0.5 µm on the finished surface.
Moreover, the surfaces have finished by the shearing of the peaks resulting in circular lays
formed by the rotation of the FMAB. It shows that the finished surface has fine
scratches/micro-cuts which are farther distant apart resulting in smoothened surface. But
these fine scratches would also disappear by using higher mesh number (finer abrasive
particles) [9].
A new technique was developed to compare the performance of the magnetic
abrasive powders and to find the powder that is appropriate for finishing and deburring of
drilled holes placed on a plane steel surface [10]

313
Proper deburring conditions are suggested to satisfy the productivity and the
accuracy. In addition to deburring, efficiency influence to surface roughness is analyzed. To
improve the surface roughness and purity, volume of powder, height of gap, inductor
rotational frequency, feed velocity and the method of coolant supply are analyzed and proved
that the continuous flow of coolant and the Fe powder without abrasive is effective for
deburring and surface quality. [11]
3 EXPERIMENTAL SET-UP
Fundamental requirements of the experimental set-up are:
3.1 Magnetization Unit
Basic purpose of magnetization unit is to generate the required magnetic field to assist
the finishing process. Main parts of magnetization unit are –
• D.C. Power supply
• Electromagnet
To energize the electromagnet a constant voltage/current D.C. regulated power supply of
output voltage from 0 to 30 V and output current from 0 to 5 A was used. By controlling the
induced current from D.C. power supply the generated magnetic field can be controlled.
3.2 Electromagnet
A round flat faced electromagnet with diameter of 100 mm and height 57 mm was
used for experimentation. Electromagnet has a centered N-Pole (diameter 42 mm), surrounded
with a coil (thickness = 24 mm), further surrounded by an outer S-Pole (Thickness=6mm).
Other dimensions of Electromagnet are given in Table 1.
Table 1 Dimensions of Electromagnet
Dimensions
External Diameter of magnet 110 mm
Height of magnet pole 55 mm
Permissible current value 0– 6 amp
Wire used for winding Copper
Permissible required voltage 0– 25 V
Magnetic field intensity 0– 1.2 T
Diameter of north – pole 42 mm
Thickness of south – pole 5 mm
Thickness covered by the coil 24 mm
Material used for outer body shell EN – 8
Carbon Bush dimension 31.5 × 20 × 7.5 mm3
3.3 Magnet Rotary Motion Unit
To get the finished surface, it was necessary to get relative motion between FMAB and
work piece. This unit was used to rotate the magnet and consequently to get the relative
motion between work piece and FMAB. This facility already exists in vertical milling
machine available in our machine tool lab.

314
3.4 Motion Control Unit
The machine is equipped with a precise motion control unit (MCU). The work piece
can be easily and accurately positioned to get the finished surface. There are three different
lead screw attachments to accurately position the work piece with respect to the electromagnet
in three mutually perpendicular directions viz. X, Y, and Z, respectively. The work piece can
be controlled in X, Y and Z direction. The X and Y directions are automatic controlled and Z
direction is manually controlled.
3.5 Fixture and Work Piece
Magnetic stainless steel was chosen as work piece material. The work piece was made
of rectangular shaped. The length of the work piece was 100.6 mm which is slightly greater
than the diameter of the electromagnet which was 100 mm. It was taken slightly more
deliberately because, in this case there was not chance of breaking of flexible brush
phenomenon during finishing. During experiments the work pieces were mounted on the table
with a base plate without the fixture.
4 EXPERIMENTAL PROCEDURE
The experiments were conducted according to following steps-
4.1 Work pieces were initially ground by surface grinder to give most same initial surface
roughness value.
4.2 After the grinding process, the work pieces were manually cleaned by acetone to remove
the foreign particles. Initial surface roughness values were measured by using Telesurf
analyzer’ with least count of 0.001µm.
4.3 To conduct the surface finish experiments, the work piece was mounted on the table of
MAF machine with a base plate. The work piece was made parallel to the electromagnet
using a dial indicator (least count-0.01mm) to maintain proper gap between them. The work
piece was made parallel in both X and Y direction. The position of work piece in XY plane
was kept in such a way that the center of the electromagnet coincide with the center of the
work piece.
4.4 Working gap between electromagnet and work piece was maintained by a filler gauge and
this gap was filled with the MAP. The amount of MAP depends on the working gap. Percent
by weight method was used to calculate the amount of MAP in the working gap.
4.5 The current to the electromagnet was supplied and got it energized and abrasive powder
fill between the electromagnet and work piece making FMAB. By giving rotation to the
magnet, this FMAB performs the actual finishing operation.
4.6 After completing the finishing operation, work piece was again cleaned manually using
acetone and final surface roughness value was measured.

315
4.7 Selection of parameters for experimentation
As per the data given by various researchers, various parameters such as Type and size
of abrasive particles, Percentage composition of iron particles and abrasive particles, Size of
iron particles , RPM of magnet, Finishing time etc. effect the surface roughness produced, but
all of the above cannot be taken for experimentation due to various practical difficulties .
Therefore only three parameters were chosen for present study are-
4.7.1 Mesh size of the abrasive particles,
4.7.2 Current supplied
Table 2 Variable parameters and their ranges
Parameter Values
Mesh size of the abrasive particle 30 # - 200 #
Current(Amp) 0.2 - 1.0
Percent composition of iron in MAPs 60 % - 90 %
Table 3 Fixed parameters and their values
Parameter Value
Gap 2.5 mm
Size of iron particles 80#
Abrasives used in MAP Al2O3
Percent of oil in MAP 2 %
Finishing time 12 min
Work-pieces Flat stainless steel
4.8 Response Characteristics
The effect of selected process parameters was studied on the response characteristic of
MAF process.
The surface roughness was measured at near centre of work-piece using Digital Surf Analyzer
CY510 having least count 0.001µm. The average of Surface finish (Ra) values was calculated
and the percentage improvement in roughness was estimated as:
■Ra = (Initial roughness – final roughness) × 100
Initial roughness
4. 9 Observations
Design data is obtained by using the DX 7 software. By putting the range values of the
process parameters we obtained the standard and the run denotes the run which we have to
perform i.e. for 1st experiment we have to perform the experiment using 12th row’s
parameters. Here the response value taken is (■Ra) in Table 3.

316
Table.3 Observations
Std Run
Factor 1 Factor 2 Factor 3 Reponce 1
A: B: C: D:
Size Current Iron Powder ■Ra
(mesh) (amp) (%age) (gm)
1 12 62.26 0.35 64.05 28.21
2 11 160.32 0.35 64.05 35.23
3 20 62.26 0.62 64.05 20.01
4 3 160.32 0.62 64.05 28.3
5 14 62.26 0.35 75.95 23.25
6 18 160.32 0.35 75.95 21.90
7 17 62.26 0.62 75.95 35.73
8 10 160.32 0.62 75.95 35.43
9 6 28.00 0.50 70.00 21.61
10 2 200 0.50 70.00 34.75
11 15 112.00 0.30 70.00 26.01
12 5 112.00 1.0 70.00 28.23
13 9 112.00 0.50 60.00 24.08
14 1 112.00 0.50 90.00 23.13
15 7 112.00 0.50 70.00 20.88
16 19 112.00 0.50 70.00 20.01
17 16 112.00 0.50 70.00 19.55
18 4 112.00 0.50 70.00 19.45
19 8 112.00 0.50 70.00 18.12
20 13 112.00 0.50 70.00 18.22
5 RESULTS & DISCUSSIONS
It is not always necessary that all the input process parameters have significant
contribution in surface response. Some of the parameters may be very much significant than
other parameters. In Central rotatable Composite Design, the combination of the input
parameters in actual experiments is such that only one experiment is conducted at extreme
value for each variable. Therefore it is not much worthy to do analysis at extreme values to
see the effectiveness of input variables. Moreover in central run experiments, same
experiments are repeated many times so they also cannot be taken to see the effect.
From the design data using Design expert v.7 software, response curves were drawn.
From Figure 2, (1) the %age of iron powder in the FMAB increases (from 64% to 76%)
resulting increase in the %age improvement in surface roughness (■Ra). (2) as the abrasive
size increases (from 63 to 166), the %age improvement in surface roughness (■Ra) increases.

317
Fig. 2 Effect of % of iron powder & Abrasive size on ■Ra
Fig.3 Effect of % of Current & Abrasive size on ■Ra
Figure 3 represent (1) as the value of Current in the FMAB increases (from 0.3 to 0.6 amp)
resulting increase in the %age improvement in surface roughness (■Ra). (2) as the abrasive
size increases (from 63 to 166), the %age improvement in surface roughness (■Ra) increases.
It can be seen in Figure 4, (1) as the value of iron %age in the FMAB increases (64 to 76)
resulting increase in the %age improvement in surface roughness (■Ra). (2) as the current
increases (0.38 to 0.62), the %age improvement in surface roughness (■Ra) increases.
Fig. 4 Effect of % of Iron powder & Current on ■Ra

318
5. CONCLUSIONS
All the three individual parameters, mesh size of abrasive, current and percent composition of
Fe powder in MAP have significant effect on the surface roughness in ferromagnetic work
piece Fe percent has higher contribution to ■Ra. In case of ferromagnetic work piece if the Fe
percent in MAP is high then,
The conclusions regarding %age Improvement in Surface finish are as follows
1. Due to this the rigidity of FMAB will be more in ferromagnetic case and it will make more
contribution to finishing process. Current has high contribution in ■Ra.
2. In surface finish experiments % of iron powder is the most significant factor for work-
piece material.
3.In case of ferromagnetic work-piece, percent composition of iron powder has more effect
than the mesh size of abrasives.
4. With increase in mesh size of abrasive, percent improvement in surface roughness value
also increases.
5. With increase in current of power supply the percent improvement in surface roughness
value increases.
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