Comparative Evaluation of Mechanically Alloyed and

5th International & 26th All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT

Guwahati, Assam, India

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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:


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.

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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


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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.


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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


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


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


Fig. 6 Microphotograph of MAM abrasives


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.

References

Kim Jeong-Du (2003), Polishing of Ultra

Surfaces Using Magnetic Force, International Journal

of Advanced Manufacturing Technology,

91–97.

Kremen G.Z., Elsayed E.A., Rafalovich V.I. (1996),

Mechanism of material removal in the magnetic

abrasive process and the accuracy of machining

Iron

SiC

Plastic

Backin

SiC

Iron

Plastic

Backing

All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12th–14th, 2014, IIT

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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.

hing of Ultra-clean Inner

International Journal

of Advanced Manufacturing Technology, vol. 21, pp.

d E.A., Rafalovich V.I. (1996),

Mechanism of material removal in the magnetic

the accuracy of machining,


615-6

International Journal of Production Research, vol. 34,

no.9, pp. 2629-2638.

Khairy Ahmed B. (2001), Aspects of Surface and edge

finish by Magnetoabrasive Particles, Journal of

Materials Processing Technology, vol. 116, pp. 77-83.

Lin Ching-Tien, Yang Lieh-Dai, Chow Han-Ming

(2007), Study of magnetic abrasive finishing in free-

form surface operations using the Taguchi method,

International Journal of Advance Manufacturing

Technology, vol.34, pp. 122–130.

Mulik R.S., Pandey P.M. (2011), Magnetic abrasive

polishing of hardened AISI 52100 steel, International

Journal of Advanced Manufacturing Technology, Vol.

55, pp. 501-515.

Shinmura Takeo,Takazawa Koya, Hatano Eiji (1987),

Study on magnetic abrasive finishing-effects of various

types of magnetic abrasives on finishing characteristics,

Bull Japan Society of Precision Engg., vol. 21, no.2, pp.

139-141.

Singh Lakhvir, Khangura Sehijpal Singh, Mishra PS

(2010), Performance of abrasives used in magnetically

assisted finishing: A state of the art review,

International Journal of Abrasive Technology, vol. 3,

no. 3, pp. 215-227.

Singh Dhirendra K. Jain V.K Raghuram V. (2005),

On the Performance Analysis of flexible magnetic

abrasive brush, Machining Science and

Technology, Vol. 9, pp. 601-619.

Singh L., Singh Sehijpal, Singh A. (2012), Nano

finishing of brass tubes with mechanically alloyed

magnetic abrasives, Proc. ASME International

manufacturing Science and Engineering Conference

(MSEC 2012), University of Notre Dame, Indiana

USA, June 4-8, 2012

Wang Yan, Hu Dejin (2005), Study on the inner surface

finishing of tubing by magnetic abrasive finishing,

International Journal of Machine Tools &

Manufacture, vol. 45, pp. 43–49

Documents

Comparative Evaluation of Mechanically Alloyed and