- Email: [email protected]
Increasing the wear-resistance of steel components by ball burnishing
Wear, 34 (1975) 183 - 188 0 Elsevier Sequoia S. A., Lausanne - Printed in the Netherlands
INCREASING THE WEAR-RESISTANCE BALL BURNISHING
R. RAJASEKARIAH
OF STEEL COMPONENTS
183
BY
and S. VAIDYANATHAN
Indian Institute of Technology,
Madras (India)
(Received September 24,1974;
in final form January 28,1975)
Summary
The influence of several parameters of ball burnishing such as the diameter of the ball, feed, burnishing load and initial surface finish on the surface finish, surface hardness and wear-resistance were investigated. The experiments were conducted with a ball burnishing tool used on a lathe. The burnishing load is the major factor affecting wear-resistance of the surface layer of burnished components. There is an optimum burnishing load which gives the best results.
Introduction
The technique of applying a roller or a ball under pressure to a machined surface to harden the metal and improve surface finish has been used in engineering for at least 50 years. The results were often unpredictable, and adverse effects such as surface flaking occurred. Lack of understanding of the controlling factors meant that remedial measures comprised full scale trials which involved the scrapping of many components and in general, little useful information was gained for the treatment of other workpieces. Recently, however, an appreciation of the wider commercial possibilities, based on results obtained in the relatively few really successful applications [ 1 - 41 has led to a revival of interest. This paper reports an experimental study on the effect of ball burnishing on surface finish, surface hardness and wear-resistance. Burnishing is essentially a cold forming process, in which the metal of a machined surface is displaced from peaks to fill the valleys. In a typical set-up, a ball or a roller is pressed against a rotating cylindrical workpiece and fed parallel to the axis of the workpiece. The ball or roller rotates by frictional engagement. The principal burnishing action takes place in the central plastically deformed zone. The surface finish obtained by burnishing is better than the ground surface. Burnishing can have other advantages over grinding, such as, improved surface hardness, wear resistance, fatigue resistance, tensile strength and corrosion resistance. A surface burnished under carefully controlled conditions
Fig. 1. Cross-section of the ball burnishing tool. 0.50
\
A\
0.25 i
h
6mm
dia.
ball
+ 15mm
dia
ball
0 Zmm
dia. ball
l
0
I
20
LO
\I
60 Burnlshmg
60 load,
100 kgf
120
140
160
__c
Fig. 2. Relationship between burnishing load and surface finish.
can be similar to a superfinished surface regarding surface finish, but is poor regarding waviness. Burnishing is cheap and quick compared to superfinishing. Investigation The present investigation studied the effect of some burnishing para-
185
c?T
flf CT
12mm dia. bail 15mm dio boll ) 25mm dio ball 0.10
Fig. 3. Relationship
0.: 10
a30
between
>
OR0
Of!0
feed rate and surface finish.
meters (b~ishing load, feed, diameter of the ball and initial surface finish) on surface finish, surface hardness and wear-resistance of burnished components. A simple ball b~ishing tool of the elastic type was used, Fig. 1. The force is applied through a spring and for rolling contact the burnishing ball is made to bear against the outer race of a ball bearing. The burnishing tool was designed to use balls ranging from 10 mm to 25 mm diam. Effect of burnishing parameters on surface finish The burnished surface finish depends on burnishing load, feed rate, diameter of balls and also on the initial finish. It was found that, as bumishing had increased, the surface roughness first decreased (Fig. 2). Further increased load caused increased roughness, which can be related to partial damage to the surface layer. With a comp~tively low bum~hing load (approx. 50 kgf), ball burnishing gives a surface finish of about 0.16 cc (c.1.a. value). Varying the feed rate from 0.05 to 0.20 mm/rev. does not affect surface roughness (Fig. 3); the optimum feed rate is 0.20 to 0.40 mm/rev.,
186 0.50
! I
O&C
/
t e 0.3c g E a d B t 5 0.20
I
z 8 0 z 1
010
-
0 ”
I
2
3 lmtiol
Fig. 4. Relationship
roughness
between
L
5
KLAI
rmcrons
initial surface
6
7
__c
roughness
and surface
finish.
which gives the best surface quality and the greatest output rate. Increasing the feed rate from 0.40 to 0.80 mm/rev. leads to a sharp rise in surface roughness. An initial surface roughness, within the range 1 to 3 P (c.1.a.) does not have a significant effect on the burnished surface (Fig. 4); an increase in initial roughness leads to a sharp reduction in quality of the burnished surface. Effect
of burnishing
on wear-resistance
The accuracy, performance and life of a machine depends on the wearresistance of the rubbing surface of such components as spindles, stepped and plain shafts, leadscrews and bushes. Burnishing, by workhardening materials, improves wear-resistance. Figure 5 shows the variation of surface hardness of mild steel specimens burnished under different loads. The surface hardness increases rapidly with increase in burnishing force up to a certain value and then decreases. The optimum burnishing load varies with the burnishing ball diameter. A wear test rig was used to compare the wear-resistance of burnished
187 190
160
120 0
20
LO
60 Burnishmg
80
100
I20
load, kgf -
Fig. 5. Relationship between burnishing toad and surface hardness.
and unbumished specimens. It consists of a hardened steel disc mounted on a vertical shaft. The specimen is held in a holder perpendicular to the plane of the disc and is loaded via a loading platform directly above. The specimen holder can be fixed at any desired radial distance over the steel disc by a sliding attachment. Thus, different sliding velocities can be obtained even though the disc rotates at constant speed. Specimens were loaded with 50 kgf, giving a pressure of 10 kgf/cm2. Wear in terms of the weight lost by the specimen was measured for every one or two kilometers travel of the rubbing surface. Figure 6 shows that wear of the specimen decreases with increasing burnishing load. An increase in wear-resistance of 40% can be obtained by burnishing. Conclusions The burnished surface finish depends on the burnishing load, feed rate and initial surface roughness. There is an optimum burnishing load which gives the best results. Increasing the feed rate and an increase in the initial surface roughness leads to a reduction in the burnished surface quality. Burnishing of steel components produces a high degree of strain hardening in the surface layers; the burnishing load is the main factor affecting work-hardening and wear-resistance of the surface.
188 1.L
1.2
IO
0.0 I F 5 3
0.6
I
0.1
0.2
Distance
travelled.
km
-
Fig. 6. Wear curves for burnished and unburnished specimens.
References 1 2 3 4 5
J. J. Marklew, Machinery, 114 (2930) (1969) 42 and 114 (2933) (1969) 162. Yu. G. Shneider, Russ. Eng. J., 43 (7) (1963) 34. R. Legrand, Amer. Mach., 108 (9) (1964) 81. V. A. Belov, Mach. Tool., 37 (11) (1966) 21. Yu. G. Proskuryakov, Mach. Tool., 35 (7) (1964) 42.
INCREASING THE WEAR-RESISTANCE BALL BURNISHING
R. RAJASEKARIAH
OF STEEL COMPONENTS
183
BY
and S. VAIDYANATHAN
Indian Institute of Technology,
Madras (India)
(Received September 24,1974;
in final form January 28,1975)
Summary
The influence of several parameters of ball burnishing such as the diameter of the ball, feed, burnishing load and initial surface finish on the surface finish, surface hardness and wear-resistance were investigated. The experiments were conducted with a ball burnishing tool used on a lathe. The burnishing load is the major factor affecting wear-resistance of the surface layer of burnished components. There is an optimum burnishing load which gives the best results.
Introduction
The technique of applying a roller or a ball under pressure to a machined surface to harden the metal and improve surface finish has been used in engineering for at least 50 years. The results were often unpredictable, and adverse effects such as surface flaking occurred. Lack of understanding of the controlling factors meant that remedial measures comprised full scale trials which involved the scrapping of many components and in general, little useful information was gained for the treatment of other workpieces. Recently, however, an appreciation of the wider commercial possibilities, based on results obtained in the relatively few really successful applications [ 1 - 41 has led to a revival of interest. This paper reports an experimental study on the effect of ball burnishing on surface finish, surface hardness and wear-resistance. Burnishing is essentially a cold forming process, in which the metal of a machined surface is displaced from peaks to fill the valleys. In a typical set-up, a ball or a roller is pressed against a rotating cylindrical workpiece and fed parallel to the axis of the workpiece. The ball or roller rotates by frictional engagement. The principal burnishing action takes place in the central plastically deformed zone. The surface finish obtained by burnishing is better than the ground surface. Burnishing can have other advantages over grinding, such as, improved surface hardness, wear resistance, fatigue resistance, tensile strength and corrosion resistance. A surface burnished under carefully controlled conditions
Fig. 1. Cross-section of the ball burnishing tool. 0.50
\
A\
0.25 i
h
6mm
dia.
ball
+ 15mm
dia
ball
0 Zmm
dia. ball
l
0
I
20
LO
\I
60 Burnlshmg
60 load,
100 kgf
120
140
160
__c
Fig. 2. Relationship between burnishing load and surface finish.
can be similar to a superfinished surface regarding surface finish, but is poor regarding waviness. Burnishing is cheap and quick compared to superfinishing. Investigation The present investigation studied the effect of some burnishing para-
185
c?T
flf CT
12mm dia. bail 15mm dio boll ) 25mm dio ball 0.10
Fig. 3. Relationship
0.: 10
a30
between
>
OR0
Of!0
feed rate and surface finish.
meters (b~ishing load, feed, diameter of the ball and initial surface finish) on surface finish, surface hardness and wear-resistance of burnished components. A simple ball b~ishing tool of the elastic type was used, Fig. 1. The force is applied through a spring and for rolling contact the burnishing ball is made to bear against the outer race of a ball bearing. The burnishing tool was designed to use balls ranging from 10 mm to 25 mm diam. Effect of burnishing parameters on surface finish The burnished surface finish depends on burnishing load, feed rate, diameter of balls and also on the initial finish. It was found that, as bumishing had increased, the surface roughness first decreased (Fig. 2). Further increased load caused increased roughness, which can be related to partial damage to the surface layer. With a comp~tively low bum~hing load (approx. 50 kgf), ball burnishing gives a surface finish of about 0.16 cc (c.1.a. value). Varying the feed rate from 0.05 to 0.20 mm/rev. does not affect surface roughness (Fig. 3); the optimum feed rate is 0.20 to 0.40 mm/rev.,
186 0.50
! I
O&C
/
t e 0.3c g E a d B t 5 0.20
I
z 8 0 z 1
010
-
0 ”
I
2
3 lmtiol
Fig. 4. Relationship
roughness
between
L
5
KLAI
rmcrons
initial surface
6
7
__c
roughness
and surface
finish.
which gives the best surface quality and the greatest output rate. Increasing the feed rate from 0.40 to 0.80 mm/rev. leads to a sharp rise in surface roughness. An initial surface roughness, within the range 1 to 3 P (c.1.a.) does not have a significant effect on the burnished surface (Fig. 4); an increase in initial roughness leads to a sharp reduction in quality of the burnished surface. Effect
of burnishing
on wear-resistance
The accuracy, performance and life of a machine depends on the wearresistance of the rubbing surface of such components as spindles, stepped and plain shafts, leadscrews and bushes. Burnishing, by workhardening materials, improves wear-resistance. Figure 5 shows the variation of surface hardness of mild steel specimens burnished under different loads. The surface hardness increases rapidly with increase in burnishing force up to a certain value and then decreases. The optimum burnishing load varies with the burnishing ball diameter. A wear test rig was used to compare the wear-resistance of burnished
187 190
160
120 0
20
LO
60 Burnishmg
80
100
I20
load, kgf -
Fig. 5. Relationship between burnishing toad and surface hardness.
and unbumished specimens. It consists of a hardened steel disc mounted on a vertical shaft. The specimen is held in a holder perpendicular to the plane of the disc and is loaded via a loading platform directly above. The specimen holder can be fixed at any desired radial distance over the steel disc by a sliding attachment. Thus, different sliding velocities can be obtained even though the disc rotates at constant speed. Specimens were loaded with 50 kgf, giving a pressure of 10 kgf/cm2. Wear in terms of the weight lost by the specimen was measured for every one or two kilometers travel of the rubbing surface. Figure 6 shows that wear of the specimen decreases with increasing burnishing load. An increase in wear-resistance of 40% can be obtained by burnishing. Conclusions The burnished surface finish depends on the burnishing load, feed rate and initial surface roughness. There is an optimum burnishing load which gives the best results. Increasing the feed rate and an increase in the initial surface roughness leads to a reduction in the burnished surface quality. Burnishing of steel components produces a high degree of strain hardening in the surface layers; the burnishing load is the main factor affecting work-hardening and wear-resistance of the surface.
188 1.L
1.2
IO
0.0 I F 5 3
0.6
I
0.1
0.2
Distance
travelled.
km
-
Fig. 6. Wear curves for burnished and unburnished specimens.
References 1 2 3 4 5
J. J. Marklew, Machinery, 114 (2930) (1969) 42 and 114 (2933) (1969) 162. Yu. G. Shneider, Russ. Eng. J., 43 (7) (1963) 34. R. Legrand, Amer. Mach., 108 (9) (1964) 81. V. A. Belov, Mach. Tool., 37 (11) (1966) 21. Yu. G. Proskuryakov, Mach. Tool., 35 (7) (1964) 42.