A study on the surface characteristics of burnished components

Journal of MechanicalWorking Technology, 20 (1989)

129-138 Elsevier Science Publishers B.V., A m s t e r d a m - Printed i n T h e N e t h e r l a n d s

129

A STUDY ON THE SURFACECHARACTERISTICSOF BURNISHEDCOMPONENTS

S. Rajesham I

and

Jem Cheong Tak 2

1

Faculty of Mechanical Engineering U n i v e r s i t i Teknologi Malaysia Jalan Semarak, 54100 Kuala Lumpur (Malaysia). 2 Mechanical Engineering Department Technical I n s t i t u t e of Alor Setar 05400 Alor Setar, Kedah, (Malaysia).

SUMMARY Burnishing is a p l a s t i c deformation process in which the asperities of a machined surface are depressed to give a smooth and workhardened surface. In t h i s paper, the development of a r o l l e r type burnishing tool is reported together with some experimental results concerning roughness and microhardness of surfaces of alloyed aluminium components.

INTRODUCTION

Machining processes such as t u r n i n g , are

alone sometimes not s u f f i c i e n t .

However, though

boring, shaping, reaming and m i l l i n g

They are usually followed

by

grinding.

grinding without heat treatment does not improve the surface hardness it

gives a good surface f i n i s h .

asperities

of

Burnishing

is a process

where

a machined surface are depressed by r o l l e r or b a l l s to

the

give

a

smooth surface and at the same time the surface is workhardened due to p l a s t i c deformation. D i f f e r e n t machine components require d i f f e r e n t q u a l i t y of hardness, hness

and

capacity

other c h a r a c t e r i s t i c s on the surface.

Where l u b r i c a t i o n

combined with a high bearing contact area is desirable,

valleys should not close up completely by the burnishing force. hand,

resistance to wear,

the

rougholding surface

On the

other

fatigue, scratch or corrosion demand d i f f e r e n t kind

of surface c h a r a c t e r i s t i c s . Several

researchers have contributed to the development of the burnishing

process and i t s i n d u s t r i a l applications.

Downes ( r e f . l )

of burnishing process on some automobile components, cam shaft

has shown applications

for example,

a burnished

could reduce wear on a soft bearing compared to the one which

f i n i s h e d by grinding.

was

Shneider et al ( r e f . 2 ) observed considerable changes in

microhardness of the surface even with low burnishing pressures.

Anantha

Ram

and Krishnamurthy ( r e f . 3 ) discussed the influence of burnishing speed, feed and 0378-3804/89/$03.50

© 1989

EIsevierScience Publishers B.V.

130

force on surface f i n i s h .

Kotiveerachari and Murty ( r e f . 4 ) have derived mathe-

matical expressions to calculate optimum burnishing force and size changes burnishing for specific surface a s p e r i t i e s . In

the

burnishing

present work,

a study has been made involving the

influence

in of

force and work rotational speed on surface roughness and microhard-

ness of alloyed aluminium components. on a lathe in the experiments.

A r o l l e r type burnishing tool was

used

EXPERIMENTAL BURNISHING TOOL

An experimental r o l l e r type burnishing tool has been developed for use on a lathe machine.

A deep groove ball bearing having an outside diameter of

mm and a width of 8 mm was f i t t e d to the t o o l . was

used to a function as a r o l l e r due to i t s high q u a l i t y of

and

hardness.

A serrated

coupling

35

The outer race of the bearing

enables the axis of the

inclined at certain desired angles to the workpiece axis.

surface

finish

roller

to

be

A s p e c i a l l y designed

dynamometer with strain gauges applied on octogonal half rings and f i t t e d the tool responds to the radial and axial forces during burnishing,

with

the sensi-

t i v i t y of the measurements being ~ l N when connected to the s t r a i n indicators. Fig.l

shows the r o l l e r type burnishing tool with the dynamometer and

serrated

coupling.

Roller

P, n

Ser m ted

\

Coupling

-

L

~V,

~

~

Bynomometer

-I{------ ! ~ J -

Stem

Frome

~ -

#

H,'l ton

, L

;

~

-

~

J

~ I

~

Ii

_

/ ; I~,,--L._LI__~.Jz__I] --r--'l -TI

,

~

rtn~-,

I ~ - ~ , '~ '~' ,~-TIi Ii

J

i l .

~ I Jh

-L_

_

_LI

All dimensions in miliimetres

Figure I.

Experimental burnishing tool assembly

131

EXPERIMENTAL SET UP AND PROCEDURE i A 25

mm round bar of aluminium a l l o y was held with chuck a Harrison M400 lathe machine and was f i r s t

and

tailstock

centre

of

H.S.S.

tool with a recommended tool geometry, c u t t i n g speed of about 60 m/min,

feed of 0.2 mm/rev and a depth of cut of 0.2 mm. of

the

f i n i s h turned using

an

The length to diameter r a t i o

workpiece was maintained to be w i t h i n 5.

On the

same machine,

the

c u t t i n g tool was then replaced by the burnishing tool and the s t r a i n indicators were connected to the dynamometer.

Spindle speeds of 45, 58 and 80 rpm equiva-

lent to burnishing speeds of 3.14, 4.56 and 6.28 m/min r e s p e c t i v e l y and feed of 0.02 mm/rev were used. N,

The magnitudes of r a d i a l forces applied were 350 N, 420

490 N and 560 N giving respectively

Nmm-I with

the

bearing

50 Nmm-l,

outer race e f f e c t i v e width

Corresponding to every r a d i a l force applied, also taken during burnishing. nished

for

60 Nmm-l,

70 Nmm-I and 80

of 7 mm.

the a x i a l force reading

was

Both the ends of the workpiece were l e f t unbur-

comparison with the burnished surfaces in between.

used as lubricant during burnishing.

In the experiments,

Kerosene

was

the r o l l e r axis was

held p a r a l l e l to the workpiece. Fig.2 shows the schematic diagram of the experimental set up. hing

tool

and

the workpiece mounting arrangement on the lathe

The burnisis

shown in

Fig.3.

r Strain indicator I 1. Head-stock 2. Tail-stock Z,. Burnishing tool Figure 2.

J

i Strain I indicator [I

3.Workpiece

Schematic diagram of experimental setup for burnishing

After burnishing in one pass, workpieces were tested for surface roughness and microhardness.

A Taylor Hobson surface measuring machine gave the surface

roughness in Ra values while displaying the surface roughness p r o f i l e s together with bearing r a t i o and amplitude d i s t r i b u t i o n curves.

132

Figure 3. Photograph showing the burnishing tool and workpiece set up on ~ lathe machine. The burnishing r o l l e r axis is held p a r a l l e l with workpiece ,~xi~

A Vicker's hardness testing machine was used to measure the below

the

surface

of the f i n i s h turned workpiece and those

microhardnes~.

burnished

under

varying burnishing forces and speeds. RESULTS AND DISCUSSION

Surface p r o f i l e s , bearin 9 r a t i o and amplitude d i s t r i b u t i o n I t is seen from Fig.4 that the turned surface p r o f i l e peaks are to

a

depressed

depth of 8.8~m and i t s valleys are raised to a height of 8.7 p m ~ f t e r

burnishing.

Burnished

Turned

8.8~ ll,0rnm Assessed Measured at x2000

-B,7 ~.uo mm

Figure 4.

Roughness p r o f i l e s of turned and burnished surfaces

133

From Figs.5 and 6, the f o l l o w i n g observations could be made: The depth

burnished surface has a bearing r a t i o (tp) of 46.7% even at a p r o f i l e

of 3.6~m whereas the turned surface has a tp value of 44.8% at a

depth

of 16.2 ~ m.

I U/"NORMAL I0.0mm ASSESSED I 16.3

~ED

~m

@xlO00

AMPLITUDE

BEARING R~TIO

DISTRIBIJTIO#~

Figure 5. Surface texture of the turned surface. Work material: Alloyed Aluminium; Cutting speed: 62 m/min; Feed: 0.2 mm/rev; Depth of cut: 0.2 mm; H.S.S. Tool G e o m e t r y : ~ 20",~s = 20",e e= lO°,es = lO°, Ce = 5", Cs = lO°, = O.

The High Spot count (HSC) and Peak Count (PC) values reduced to a mere and 48

14

2 cm-I respectively f o r the burnished surface from corresponding values of and

16 cm-lfor the turned surface before burnishing.

representative

of

The

HSC value

is

h a l f the number of times the p r o f i l e crosses the mean l i n e

whereas the PC is the number of peak/valley pairs which project above and below two

reference

profile.

levels,

positioned

equidistant about the

mean l i n e

of

the

134

3,7jJ®l

LO.O mm ASSESSEP I'IEI:W:~,.IRED e xlO00

- 6 . 7 IJ

BE~I~ RATIO

~pLITUDE pISTRIBUTI.OH

Figure 6. Surface texture of the burnished surface. Work material: Alloyed Aluminium, Burnishing force: 50 N mm"I Burnishing speed: 3.14 m/min, Tool feed: 0.02 mm/rev.

The

ordinates

of

amplitude d i s t r i b u t i o n curve along the

depth

of

the

p r o f i l e increased towards the top while those at the lower end decreased s i g n i ficantly.

This as compared to the turned surface indicates pushing of the bulk

of material towards top surface due to burnishing action. Burnishing force and speed The finish

burnishing force and speed has a s i g n i f i c a n t influence on the surface (Fig.7).

improves, surface

As

the

burnishing force is increased

the

surface

finish

A higher burnishing speed also has brought up an improvement in the f i n i s h w i t h i n the range of speed and force values used in the

ex p e r i-

ments.

Microhardness The results of the microhardness are shown in Fig.8.

I t is seen from i~he

f i g u r e that the microhardness increases with the increased values of

burnihinq

135 force and the same decreases as the depth increases from the surface. true

since

a

workhardened Fig.9

higher burnishing force causes a

depth

is

greater

seen to be about 0.45 mm f o r

all

This is

workhardening. burnishing

shows the diamond indentations and microhardness values f or

The

forces,

turned

and

burnished specimens. Relationship between a x i a l and r a d i a l forces A

linear

r e l a t i o n s h i p is seen to e x i s t between a x i a l and r a d i a l

while

burnishing.

cient

of

m/min.

f r i c t i o n which is found to be 0.084 at a burnishing As

forces

The r a t i o between these two forces represents the c o e f f i -

the burnishing speed increased to 4.56 m/min,

speed of

the c o e f f i c i e n t

3.14 of

f r i c t i o n increased to 0.14 (Fig.lO).

Work speed :

O 3.1(,m/min A /,.56 m/min

1.6

x 6.28m/rain

E1.2

6 rY (/t

==0.s t=

O

n~

0.4

m

0 /.0

Figure 7. finish.

I I I 50 60 70 Burnishing F o r c e , N m m -1

I 80

90

Diagram showing the e f f e c t of burnishing force and speed on surface

136

66 x

Turned

Burnished of force O 50 Nmm-*

6~

A

60 Nmm-I

® 70 Nmm-I Nmm-I 62 -r

'~ 60 C O r O

~,

58-

56

54 0

I

I

I

0.1

0.2

0.3 Depthfrom

I

I

0.4 0.5 surface, mm

I

0.6

0.7

Figure 8. Diagram showing the e f f e c t of burnishing force and speed on micro hardn~ - of burnished surfaces. Work material: Alloyed Aluminium, 3urnishin~ speed: 6.28 m/min, Feed:O.02 mm/rev.

Fig. ga MicrohardnessiHv) values below the surface of the turned workpiece

137

F i g . 9 b M i c r o h a r d n e s s ( H v } v o l u e s below the s u r f a c e of the burnished w o r k p i e c e u s i n g 80 N m m - l force.

z 100

Work speed: x 3.1/, m/min O ~.16 m/min Feed : 0.02 mm/rev. J

o

o

-~

50

O

"x <~

300

I 400 Radial

I 500 force, N

600

Figure I0. Diagram showing the r e l a t i o n s h i p between a x i a l and r a d i a l forces at d i f f e r e n t burnishing speeds.

CONCLUSION A deep groove ball bearing, in

the

the outer race of which was used as a r o l l e r

burnishing tool developed did perform well on

burnishing

of

alloyed

aluminium workpieces. The surface f i n i s h has improved and the bearing r a t i o has increased a f t e r burnishing in a single pass.

The burnished workpiece has i t s surface workhardened and the microhardness below the surface improved over a depth from the surface of 0.45 mm. The axial

force

induced while burnishing has a relationship

with

the

radial force applied. Thus, surface

burnishing as a process can be used to advantage for improvement in

finish

coupled with surface hardness of

components for

engineering

applications.

ACKNOWLEDGEMENT

Grateful Production neering,

thanks

are due to Mr.

Awaluddin bin Mohd Shaharoun,

and I n d u s t r i a l Engineering Department, Universiti

Teknologi

Malaysia,

Head of

Faculty of Mechanical Engi-

for the encouragement

and

support

extended to the authors in carrying out the work reported in this paper.

REFERENCES

I.

K.J. Downes, Finishing of automobile components by r o l l i n g , A paper presented

to the Coventry Science of the I n s t i t u t i o n of Production

Engineers,

1963, pp.376-382. 2.

Yu.

G. Shneider et a l . , Characteristics of burnished components, Machines

3.

B.L. Anantha Ram and R. Krishnamurthy, Surface i n t e g r i t y studies in bur~li-

and Tooling, Voi.38, No.l, pp.19-22. shing, Proc. 8th AIMTDR Conf. l I T , Bombay, 1978, pp.488-490. 4.

B.

Kotiveerachari and R.L.

Murty,

Study of optimum force in burnishing,

Proc. l l t h AIMTDR Conf,. l I T , Madras, 1984, pp.408-414.