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

IIT Guwahati, Assam, India

823-1

CHEMO-ULTRASONIC ASSISTED MAGNETIC ABRASIVE

FINISHING: EXPERIMENTAL INVESTIGATIONS

NITESH SIHAG1, PRATEEK KALA2, PULAK M PANDEY3*

1M.Tech Student, IIT Delhi, 110016, E-Mail:nitusihag@gmail.com 2Research scholar, IIT Delhi, 110016,E-mail:kala.prateek@gmail.com

3*Associate Professor, IIT Delhi, 110016, E-mail:pmpandey@mech.iitd.ac.in

Abstract

Chemo-Ultrasonic Assisted Magnetic Abrasive Finishing (CUMAF) is a compound finishing process, which

integrates the use of CMP(Chemo-Mechanical Polishing), ultrasonic vibrations and MAF(Magnetic Abrasive

Finishing), to finish surfaces up to nanometer order within a short span of time.The present work is focused on

designing and fabrication of experimental set up to perform CUMAF. Using this set up experiments have been

conducted on copper alloy work piece and the effects of various process parameters like percentage weight of

abrasive, oxidizing agent concentration, rotational speed of magnet, working gap and pulse on time of ultrasonic

vibration on process response namely percentage change in average surface roughness value (%∆Ra) was

recorded. The experiments were planned using response surface methodology. Experimental data was analyzed

using analysis of variance to understand contribution of various process factors and interactions on process

response. Regression model was developed to predict the percentage change in surface roughness in terms of

significant process factors and interactions. Further the developed model was validated and was optimized

using genetic algorithm to maximize the performance of the developed process.

1 Introduction

Surface finish of a product is an important

parameter as it directly influences the product life and

enhances its functionality. In the present scenario with

advancement of technology there is need of various

advanced engineering materials like tungsten,

titanium alloys, ceramics, composites etc. These

materials possess some special characteristics such as

high hardness, high wear resistance, high toughness,

high strength etc. which make these preferred over

conventional materials in modern industries. Due to

the stringent properties these materials are difficult to

process. Different conventional finishing processes

like grinding, lapping, honing, buffing etc. are

generally inefficient in finishing these materials.

Although processes like abrasive flow machining,

magnetic field assisted finishing processes and

chemo-mechanical finishing may be used but these

may be less productive. Therefore a new process

which uses combination of chemical oxidation and

magnetic field assisted abrasion (magnetic abrasive

finishing) has been conceived in the present work for

faster processing.

MAF is a process in which material from work

piece surface is removed in form of microchips by

mixture of ferromagnetic and abrasive particles in the

presence of magnetic field (Jain, 2009). The gap

between upper magnet and work piece is filled with

ferromagnetic and abrasive particles. These particles

are attracted towards each other along magnetic lines

of force and form a flexible magnetic abrasive brush

(FMAB) which acts as a multi-point cutting tool. As

the brush rotates the abrasive particles remove

microchips from the workpiece surface resulting in

finishing of work piece. MAF has a high potential to

be used widely by the industries as it can produce a

mirror like finished surface of high quality for various

simple and complex surface forms. Also dressing of

tool is not required in MAF. However, it is less

efficient on hard materials. Many researchers worked

to improve the conventional MAF process and

attempted to combine other conventional processes to

overcome the limitation. Some of the important

literature in the area is discussed below.

Yin and Shinmura (2004) applied three modes of

vibration during MAF on a stainless steel (SS 304)

sample. By experimental results they reported that

providing vibration along the direction of feed and

perpendicular to the feed together resulted in

improved surface finish with reduced finishing time.

Mulik and Pandey (2010) applied ultrasonic

vibration during MAF on a high carbon anti friction

bearing steel (AISI 52100) sample. With the help of

experimental results they reported that with

application of ultrasonic vibration during MAF

tangential cutting force increased, which helpedin

obtaining better surface finish.

Kala et al. (2013) performed experiments with

ultrasonic assisted magnetic abrasive polishing to

polish Copper alloy and analysed the results. They

reported that addition of ultrasonic vibrations with

MAF resulted in significant increase in surface finish

of paramagnetic work piece.

Li et al. (2012) incorporated ultrasonic vibrations

into fixed abrasive pellets to enhance MRR and to

improve surface finish for fused silica polishing. He

CHEMO-ULTRASONIC ASSISTED MAGNETIC ABRASIVE FINISHING: EXPERIMENTAL INVESTIGATIONS

823-2

designed a prototype ultrasonic vibrator for his

experiments.

Yan et al. (2003)incorporated electrolytic process

with MAF to produce a passive oxide film on the

work piece surface which is easier to remove as

compared to parent metal. They observed that at

higher electrolytic current the finishing characteristics

were improved as compared to MAF.Increasing both

the electrolytic current and work piece RPM increased

finishing efficiency, and the surface roughness

improved rapidly.

El-Taweel(2008) integrated electro-chemical

turning (ECT) process with MAF to finish 6061

Al/Al2O3 (10% wt) composite. It was reported that

addition of ECT with MAF resulted in 33%

improvement in surface quality and machining

efficiency is increased by 147.6% as compared to that

was achieved with traditional MAF.Kim and Choi

(1997) analysed the finishing characteristic of a Cr-

coated roller with newly developed magnetic

electrolytic abrasive polishing (MEAP) system. They

showed that the finishing efficiency was increased by

addition of magnetic field.

Nanz and Camilletti(1995) compared different

CMP models to understand and investigate

assumptions of the models. They reported that both

primary removal mechanisms(mechanical and

chemical) will depend on the passive removable layer

and hence accurate modeling of the process is very

crucial to understand the process. Wrschka et al.

(2000) evaluated performance of two alumina based

slurries and two silica based slurries during CMP of

copper sample. Finished copper samples were

analysed using scanning electron microscopy. They

concluded that low etch rates of the slurry chemistry

is favourable for better removal rates.

Literature review discussed above showedthat

previous attempts were made to improve the

performance of MAF by incorporating ultrasonic

vibrations into it. Also some researchers have applied

electrolyte to the machining zone. But while using

electrolyte work piece must be electrically conducting

for electrolysis. UAMAF process may also be less

productive for non ferromagnetic hard materials due

to its low magnetic flux density. Also in the literature

discussed above, researchers have used ferromagnetic

work piece which produced high finishing forces for

effective finishing due to its high permeability. But

finishing non ferromagnetic material using MAF or

UAMAF may take long time to obtain the desired

results. Therefore it was planned to combine Chemo

mechanical polishing (CMP), ultrasonic vibration and

MAF. The new hybrid process is named as Chemo-

Ultrasonic Assisted Magnetic Abrasive Finishing

(CUAMAF).

The objective of the present study is to design and

fabricate a set up to conduct experiments on Cu-alloy

work piece using CUMAF process. Five parameters

namely percentage weight of abrasive, oxidizing

agent concentration, rotational speed of magnet,

working gap and pulse on time for ultrasonic

vibration, were selected as process parameters to

evaluate the performance of CUMAF process and

their effect on response variable namely percentage

change in surface roughness was recorded.

Furthermore, the overall change in work piece

morphology after finishing was observed with SEM

images.

2 Experimental set up

The developed experimental set up consisted of

two permanent magnetic tools, specially designed and

fabricated fixtures to hold the workpiece and an

ultrasonic generator unit. A permanent magnetic tool

was made of aluminium disk having four magnetic

poles. Each magnetic pole consists of set of ten

NdBFe magnetic disks(Φ25mm X 3 mm thick). The

magnetic poles have arrangement of alternative South

and North Pole. Magnetic flux density varies with

working gap and radial distance from cent of magnet.

The upper magnet was attached to spindle of CNC

Bevermill machine to provide required rotation to

magnet. Lower magnet was held above the machine

table with the help of specially designed fixture so

that the magnet was unaffected by machine table

movement.

Before starting the experiments, workpiece was

exposed to oxidizing agent for 30 minutes. Then

workpiece was held with help of specially designed

fixture. The gap between workpiece and upper magnet

was filled with ferromagnetic abrasive particles.

These particles formed a flexible magnetic abrasive

brush at four magnetic poles. The FMAB formed on

four magnetic poles of upper magnet has been shown

in top left of figure 1.

While performing experiments the workpiece held

in designed fixture was excited by ultrasonic

vibrations produced by ultrasonic generator through

horn. Figure 1 shows actual photograph of fabricated

experimental set up with various components.

Figure 1 Experimental set up

Fixture to hold lower magnet

Ultrasonic horn

Upper magnet

Lower magnet Work piece holding fixture

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

IIT Guwahati, Assam, India

823-3

3 Selection of process parameters

In the first step of work some preliminary

experiments were conducted to get the idea about the

range of different process variables. Based on these

experiments the finishing time was fixed at 20

minutes for all the experiments. In the present work

five process variables were selected. Details and

levels of process factors are given in table 1.

Percentage change in surface roughness was

selected as process response, which was calculated by

the formula shown below:

%∆Ra� ������� ���� ��� �� ����� ��� ���� ����� ������� ���� ��� x100

Details of the parameters which were kept

constant aregiven in table 2.

4 Experimental procedures

After selection of levels of process factors design

of experiments is second most crucial step. Here

central composite design methodology was used as it

needs smaller number of experiments with reliable

predictions. A second order model was involved with

central composite design technique, also known as

response surface methodology.

Response equation of following form is yielded by

central composite design methodology.

� � �� � ����

����� � ������

�

���� ����!���! � "

!#�

Where, Y represents the response variable, k is

number of factors, ��,��,���,��! are constants, �� , �� , ���! are linear, square and interaction terms of

process factors respectively, and " is the random

error.

Initially, Ra was measured at three random points

and then average of these values was calculated. After

finishing the work piece again,Ra values were

measured at the same three points and average was

calculated. Based on inputs mentioned in table

1,experiments were carried out and the surface

roughness values and percentage change in Ra were

recorded.

5 Statistical model to predict change in

surface roughness

A statistical model for %∆Ra is obtained by

performing regression analysis. The results were

analysed with help of analysis of variance (ANOVA).

Initially model contained some insignificant terms

also. In second step the insignificant terms were

dropped and ANOVA was performed again with

significant terms. The final ANOVA table has been

shown in Table 3.The obtained model to predict

%∆Ra is given below.

%∆Ra = - 74.6 + 0.361 X1 + 45.1 X2 + 6.64 X3 +

3.97 X4 + 14.3 X5 - 0.000840 X12 - 11.7 X2

2 - 0.862

X32 - 1.70 X4

2 - 0.122 X5

2 (1)

Table 1: Process factors and levels

Description Level

-2 -1 0 1 2

Rotational speed

(RPM) (X1)

50 100 150 200 250

Working gap

(mm) (X2)

1 1.5 2 2.5 3

Conc. of NaOH

(X3) (gm/l)

1 3 5 7 9

Pulse on time for

ultrasonic

vibration, ton (s)

(X4)

1 2 3 4 5

%Weight of

abrasive(X5)

10 15 20 25 30

6 Effect of process parameters on %∆Ra

The main effect plot of different factors

considered in present study has been shown in figure

2. The main effect plot demonstrates the effect of

various process parameters on %∆Ra. It can be seen

from figure 3 that the rotational speed (22.89%) has

the highest impact on %∆Rafollowed by %weight of

abrasive (16.11%), ton (12.71%), concentration of

NaOH (12.06%) and working gap (0.72%).

Figure 4 shows the effect of various process

parameters on the response variable. It can be seen

from figure 4 that %∆Raincreases with increase in

rotational speed.Itmay be because athigher RPM the

striking rate of MAP’s increases which helps in fast

shearing of surface peaks resulting in increase in

%∆Ra. From figure 4 it can be seen that %∆Rais

maximum at some intermediate value of working gap.

Lower gap may cause excessive indentation resulting

in deterioration of work piece surface. At higher gaps

finishing forces may be insufficient to shear the peaks

of work piece surface which may lead to decrease in

%∆Ra. Some intermediate value of NaOH

concentration is favourable for optimum surface

finish. This may be due to the fact that very low

concentration of NaOH may not be able to oxidize the

required amount of copper atoms to form a uniform

oxide film, which may lead to surface deterioration.

At very high concentration of NaOH, copper atoms

start dissolving in NaOH solution, which deteriorates

the surface finish. Increasing ton causes long lasting

impact of abrasive particles and hence %∆Raincreases

with increase in ton. Increase in percentage weight of

abrasive results in increase in %∆Rainitially and after

sometime%∆Ra decreases.

CHEMO-ULTRASONIC ASSISTED MAGNETIC ABRASIVE FINISHING: EXPERIMENTAL INVESTIGATIONS

823-4

Table 2: process parameters kept constant in

experiments

S.

No.

Process parameter Value

1 Pulse off time of ultrasonic

vibrations, Toff (s)

2.0

2 Mesh number of Al2O3

powder

1200

3 Ultrasonic power supply (W) 720

4 Time for each experiment

(min)

20

This may be due to the reason that at very low

percentage weight of abrasive, cutting edges required

for finishing are less, which results in poor cutting

action and hence low %∆Ra. As percentage weight of

abrasive increases, after a certain value ratio of

magnetic particles become low and hence overall

magnetic force required to form the chain reduces and

the chain starts disintegrating. Hence effectiveness of

the process reduces.

7 Process Optimization

The change in surface roughness obtained as

equation (1) is maximized to predict the best

performance level of CUAMAF. The function is

optimized using genetic algorithm toolbox in

MATLAB 12 software and the results are presented in

Table 4.

Figure 2 Main effect plot of process

parametersduring CUAMAF

Figure 3 Percentage contributions of significant

factors on %∆Ra

Figure 4 Effect of (a) Rotational speed, (b)

working gap, (c) conc. of NaOH, (d) pulse on time,

and (e) % weight of abrasive; on %∆Ra

The surface roughness profiles obtained at

optimum process conditions are shown in figure 5. It

can be observed that by CUMAF the maximum peak

to valley height is reduced to approximately 1/6th

after finishing.

Table 4: Optimization results

Sample Cu Alloy

RPM 215

Gap (mm) 1.9

Conc. of NaOH

(gm/l)

4

Pulse on time (s) 4.2

%weight of

abrasive

16

% ∆Ra 82.86

25020015010050

70

65

60

55

50

3.02.52.01.51.0 97531

54321

70

65

60

55

50

3025201510

RPM

Mean

Gap Conc. of NaOH

Pulse on time %wt. of abrasive

Main Effects Plot for %∆Ra

Data Means

RPM Working Gap (mm) Conc. of NaOH (gm/l)

Pulse on time (s) % wt of abrasive

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

IIT Guwahati, Assam, India

Table 3: Analysis of variance (ANOVA) after

Source DF Seq SS

Regression 10 2952.1

Linear 5 2018.47

Square 5 933.63

Interaction 0 0

Residual error 21 158.88

Lack-of-Fit 16 108.36

Pure error 5 50.52

Total 32 3129.86

Figure5Surface roughness plot of specimen

with (a) Ra =0.3571 µm (b) Ra =0.

The surface roughness profiles alone do not

explain the exact mechanism of material removal and

the quality of surface generated. Therefore, scanning

electron microscope (SEM) images of rough and

finished surfaces were taken. Figure 6(a) shows SEM

image of unfinished Cu sample. Figure 6(b

SEM images of the same sample when it is finished

using processing conditions given in table 5.

Table 5 Detail of each parameter selected for

SEM images shown in figure 6

It is observed that CUMAF has remarkably

finished the surface and very fine machining marks

are left after finishing as compared to initial rough

surface.

Fig

No. RPM

Gap

(mm)

Conc.

of

NaOH

(gm/l)

ton

(s)

%wt of

abrasive

6.b 150 2 5 3

6.c 200 2.5 3 4

6.d 150 2 5 3

6.e 200 1.5 3 2

6.f 200 1.5 7 4

(b) R(a) Ra = 0.3571µm

All India Manufacturing Technology, Design and Research Conference (AIMTDR 2014) December 12

Analysis of variance (ANOVA) after dropping insignificant terms

MS F P R2 Remark

295.21 39.02 0 94.92%

173.163 22.89 0

186.725 24.68 0

7.566

6.733 0.67 0.75

10.104

model is adequate and lack of fit

is insignificant

Surface roughness plot of specimen

0.0617µm

The surface roughness profiles alone do not

explain the exact mechanism of material removal and

generated. Therefore, scanning

electron microscope (SEM) images of rough and

. Figure 6(a) shows SEM

Cu sample. Figure 6(b-f) show

SEM images of the same sample when it is finished

given in table 5.

Detail of each parameter selected for

images shown in figure 6

t is observed that CUMAF has remarkably

finished the surface and very fine machining marks

ng as compared to initial rough

Figure 6SEM image (2000 X)

finishing; (b-f) after finishing with the

parameters given in table 5.

8 Conclusions

1) In the present work, paramagnetic

copper alloy is successfully finished using unbounded

magnetic abrasive particles. Ultrasonic vibration

caused enhanced interaction of abrasive grains with

the peaks on the work piece and NaOH formed a

softer oxide layer over the surface. Combination of

%wt of

abrasive

%

∆Ra

20 79.5

15 79.2

20 74.8

15 67.1

20 60.1

(b) Ra = 0.0617µm 10 µm

10 µm

10 µm

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

823-5

insignificant terms

Remark

model is adequate and lack of fit

is insignificant

(2000 X) (a) before

f) after finishing with the

parameters given in table 5.

1) In the present work, paramagnetic work piece i.e.,

copper alloy is successfully finished using unbounded

magnetic abrasive particles. Ultrasonic vibrations

caused enhanced interaction of abrasive grains with

and NaOH formed a

softer oxide layer over the surface. Combination of

=2.34

>

=2.156

<

10 µm

10 µm

10 µm

CHEMO-ULTRASONIC ASSISTED MAGNETIC ABRASIVE FINISHING: EXPERIMENTAL INVESTIGATIONS

823-6

these two resulted into better surface quality with

minimum surface defects.

2) It is observed that rotational speed of magnet has

maximum percentage contribution (22.89%) on

surface finish during CUMAF.

3) With optimum parameters, 82.86% improvement in

surface finish is observed during CUMAF. Surface

finish of a Cu alloy sample with initial surface

roughness 357 nm can be improved to final surface

roughness 61 nm using the developed process. It is

observed from surface roughness profiles obtained

using Talysurfthat the maximum peak to valley height

has been reduced to approximately 1/6th after

finishing.

9 References

El-Taweel, T.A. (2008), Modelling and analysis of

hybrid electrochemical turning magnetic abrasive

finishing of 6061 Al/Al2O3 composite, Int J

AdvManuf Technol., Vol. 37, pp. 705-714.

Jain, V.K.(2009), Magnetic field assisted abrasive

based micro-nano-finishing, Mater. Process. Technol.,

Vol.20, pp. 209.

Kala, P., Kumar, S. and Pandey, P.M. (2013),

Polishing of copper Alloy using double disk

ultrasonic assisted magnetic abrasive polishing,

Mater. Manuf. Process., Vol. 28, pp. 200–206.

Kim, J. and Choi, M. (1997), Development of the

magneto-electrolytic abrasive polishing systems

(MEAPS) and finishing characteristics of a Cr-coated

roller, Int. J. Mach. Tools Manufact., Vol. 37, pp.

997-1006.

Li, Y., Wu1, Y., Zhou, L., Fujimoto, M., Wang, J.,

Sasaki, S., and Kemmochi, M. (2012), Chemo-

mechanical manufacturing of fused silica by

Combining ultrasonic vibration with fixed-abrasive

pellets, International Journal of Precision Engineering

and Manufacturing., Vol. 13, pp. 2163-2172.

Mulik, R.S. and Pandey, P.M. (2010), Ultrasonic

assisted magnetic abrasive finishing of hardened AISI

52100 steel using unbondedSiC abrasives, Int. Journal

of Refractory Metals and Hard Materials, Vol. 29, pp.

68-77.

Nanz, G. and Camilletti L.E. (1995),Modeling of

Chemical-Mechanical Polishing: AReview, IEEE

transactions on semiconductor manufacturing, Vol. 8,

pp. 382-389.

Wrschka, P., Hernandez, J., Oehrlein, G.S. and King,

J. (2000), Chemical Mechanical Planarization of

Copper Damascene Structures, Journal of The

Electrochemical Society, Vol. 147, pp. 706-712.

Yan, B.H., Chang, G.W., Cheng, T.J., and Hsu, R.T.

(2003), Electrolytic magnetic abrasive finishing,

International Journal of Machine Tools &

Manufacture., Vol. 43, pp. 1355-1366.

Yin, S. and Shinmura, T. (2004), A comparative

study: polishing characteristics and its mechanisms of

three vibration modes in vibration-assisted magnetic

abrasive polishing, International Journal of Machine

Tools & Manufacture, Vol. 44, pp. 383–390.