Research into mirror surface finishing by the ironing process

Research into mirror surface finishing by the ironing process

Journal of Materials Processing Technology, 22 (1990) 123-136 123 Elsevier RESEARCH INTO MIRROR SURFACE FINISHING BY THE IRONING PROCESS NOZOMU KA...

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Journal of Materials Processing Technology, 22 (1990) 123-136

123

Elsevier

RESEARCH INTO MIRROR SURFACE FINISHING BY THE IRONING PROCESS

NOZOMU KAWAI

Professor, Department of Mechanical Engineering, Faculty of Engineering, Nagoya University, Nagoya, Japan KUNIAKI DOHDA

Associate Professor, Department of Mechanical Engineering, Faculty of Engineering, Gifu University, Gifu, Japan ZHRGANG WANG

Graduate Student, Department o/Mechanical Engineering, Faculty of Engineering, Nagoya University, Nagoya, Japan KAZUHIRO AKIYAMA

Engineer, Toyota Motor Corporation, Toyota, Aichi, Japan (Received May 6, 1989; accepted in revised form November 4, 1989)

Industrial Summary The object of this paper is to clarify the mechanism of mirror surface finishing by the ironing process. The mirror surface is in demand for electro-optical parts such as optical drums and magnetic discs, which hitherto have been finished by diamond bite cutting, lapping, etc. In the ironing process, the metal surface on the die side becomes a rubbed surface (Ra=0.05 pm for high-viscosity oil ) which is markedly inferior to the die surface (Ra = 0.006-0.011 pm); when oils of lower viscosity are used galling often occurs. The metal surface on the punch side becomes a near replica of the punch surface, the degree of replication increasing with larger reductions and lower viscosity oils or when the ironing is carried out dry. In these experiments, the metal surface was finished to Ra = 0.004 ~m under the following conditions: dry on the punch side; high-viscosity oil on the die side; and 50% reduction.

1. Introduction R e c e n t l y , m i r r o r s u r f a c e s h a v e b e e n in d e m a n d f o r e l e c t r o - o p t i c a l p a r t s s u c h as o p t i c a l d r u m s a n d m a g n e t i c discs, w h i c h h i t h e r t o h a v e b e e n f i n i s h e d b y d i a m o n d b i t e c u t t i n g , l a p p i n g , etc. H o w e v e r , if m i r r o r s u r f a c e s c a n be f i n i s h e d b y p l a s t i c d e f o r m a t i o n , a m a r k e d i m p r o v e m e n t in p r o d u c t i v i t y a n d c o s t c a n be expected. I n p l a s t i c d e f o r m a t i o n , t h e m e t a l s u r f a c e - t e x t u r e t h a t is c r e a t e d - a c c o m panied by bulk plastic deformation - results from frictional phenomena at the

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interface between the tool and the workpiece. Very many factors influence the metal surface-flattening process, amongst which are the contact pressure, the frictional shear stress, the relative slip between the tool and the workpiece, the presence of lubricants trapped at the interface between the tool and the workpiece, the surface textures of the tool and the workpiece and the compatibility between the tool and the workpiece. Although there have been many reports published to date on tribology in metal forming [ 1 ] in which surface texture has often been discussed in connection with lubricating mechanisms (such as the surface finishing of aluminium sheets in the cold-rolling process [2,3] or the surface problem of aluminium tubes in the drawing-ironing process [4,5 ] ) research on surface finishing remains inadequate. In the plastic-deformation process, the mirror surface-finishing of sheetand tube-parts may be realized, in principle, in drawing, extrusion and like operations. Initially, in this investigation, the ironing process is discussed. The aim of the present work is to determine the optimum conditions under which products with a mirror surface can be produced. To this end, ironing experiments have been carried out on soft commercially pure aluminium sheets (All00-0 by JIS) using a band sheet-ironing test apparatus. 2. Experimental conditions

2.1 Test apparatus Since the presently used test apparatus is merely an improved version of an ironing-type friction testing machine reported elsewhere [6], only the principle of the test is shown in Fig. 1. A band sheet workpiece (~) is drawn up along with the punch (~), in the process of which it is ironed by the die (~). The metal surface on the die side is finished as a result of frictional sliding between the workpiece and the die accompanied by a comparatively large relative slip, and on the punch side as a result of very small relative slip under the high contact pressure acting at the workpiece/punch interface. In the present investigation, as will be illustrated below, the metal surface on the punch side can be finished with a mirror surface more easily, but the metal surface on the die side is discussed also, for comparison. The degree of ironing (i.e. the reduction in thickness) can be varied by transverse adjustment of the guide bearing (~). Both the normal force and the friction force acting on the die during the process can be measured by the measuring device ( ~ and entered into an X-Y recorder. 2.2 Experimental conditions In this investigation, the reduction in thickness, the punch surface roughness and the lubricants employed are taken to be the main factors influencing the surface finish. The main experimental conditions are shown in Tables 13. As illustrated in Table 1, ironing reductions in thickness were varied from 5% to 50%, ironing travel h was increased to 100 mm to enable the friction

125

k Ironingdirection

6uldebe~,./~ ~asurlng Punchholder

Puncl~

device Workplece

Fig. 1. Principle of the ironing test on band sheet metal. TABLE 1 Ironing conditions Die semi-angle, (x Ironing velocity Ironing travel, h Ironing reduction, Re Tool materials (Surface roughness )

Die Punch

10 o 1 mm/s 100 mm 5-50% SKD11 (Ra=0.011 p.m) Si3N4 (Ra=0.006 ~m) SKD11 Ra=(~) 0.004

0020 ® 0.057 Room temperature Room humidity

0.354 (pm) 20 _ 1 °C 45_+5%

coefficient to r e a c h a s t e a d y value a n d t h e ironing velocity was held at 1 m m / s so t h a t t e m p e r a t u r e effects f r o m frictional h e a t g e n e r a t i o n a n d h y d r o d y n a m i c effects w i t h i n t h e oils would be r e d u c e d as m u c h as possible. F o r m o d i f y i n g t h e frictional c o n d i t i o n s o n t h e die side, t h e dies were m a d e of alloy tool steel S K D l l a n d Si3N4, a n d t h e i r surface r o u g h n e s s e s were finished to R a = 0 . 0 1 1 ~tm a n d 0.006 p m r e s p e c t i v e l y b y lapping. T h e die exits were r o u n d e d a little (to R - 20 p m ) b u t n o b e a r i n g l a n d was provided. T h e die

126

surface was re-finished after each test to maintain the same test conditions. Punches having different surface roughnesses, made of SKD11 only, were prepared by grinding (Ra=0.354 pm) and lapping (Ra--0.057-0.004 pm), and are referred to hereafter as punches (~)-(~), as indicated in Table 1. The workpiece material used in the present experiments was commercially pure aluminium (A1100 by JIS ), the mechanical properties and chemical composition of which are presented in Table 2. A 20 mm width by 200 mm length workpiece was cut from a rolled sheet (thickness: 0.39 mm), the longitudinal direction of the workpiece coinciding with the rolling direction. Three paraffinic mineral oils (St, P4, P3 ) and one fluid paraffinic oil (L2) were used, their properties being given in Table 3. The lubrication conditions are expressed by symbols e.g. the symbol ( D ) S t - ( P ) L 2 is used when St is used on the die side and L2 on the punch side. After degreasing the tools and the workpiece with acetone, drying them with a cooler and then applying lubricant, the ironing test was carried out. Experiments were repeated at least four times for each set of conditions and all results are discussed. TABLE 2

Mechanical properties and chemical composition of the workpiece material used (Al100-0) Thickness

Tensile

Elongation

(ram)

strength (MPa)

(%)

0.39

98.0

40.3

nvalue 0.24

Surface roughness Ra (~m)

Rmax (pm)

0.21

1.55

Chemical composition (wt%) Si 0.15

Fe 0.59

Cu 0.07

Mn <0.01

Mg <0.01

Cr 0.00

Zn <0.01

Ti 0.01

AI 99.15

TABLE 3

Lubricants Lubricant

L2

P3

P4

St

Viscosity (10 6 m2/s, 20oC) Sulphur (wt.%) Ring analysis CA ( % )

19.8 0.00 0.0 28.5 71.5 305

70,9 0.15 5.5 26.8 67.6 393

321 0.25 7.0 24.5 68.5 519

5119 0.95 7.7 26.7 65.6 771

(n-d-m method) CN (%)

Cp (%) Mean molecular weight

CA ( % ), CN (%) and Cp (%) are respectively the percentages of aromaticity carbon, naphthene carbon and paraffin carbon in the total carbon.

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3. D i s c u s s i o n o f t h e s u r f a c e - f l a t t e n i n g p r o c e s s

The effects on surface flattening of ironing reduction in thickness, lubrication conditions and punch surface roughness, are discussed below.

3.1 Effects of ironing reduction in thickness Figure 2 shows the variation in metal surface roughness with increase in ironing reduction in thickness for various lubrication conditions, using punch (~) (surface roughness Ra = 0.020 ~tm). The metal surface roughness was measured transversely to the ironing direction using a stylus instrument. The metal surface on the die side becomes a rubbed surface (Ra--0.05 pm) for high-viscosity oil when the reduction in thickness is greater than 10%, irrespective of the die material and the lubrication conditions on the punch side. This was the best finished surface obtained in this investigation, even though it is inferior to the surface of the die (Ra--0.006 or 0.011 pm). Referring to results reported previously [7], it may be difficult to obtain better surfaces without employing a special method, because some scratching due to frictional slip on the die surface cannot be avoided. When lower-viscosity oils - such as P3, L2 - are applied, galling occurs with Si~ N,-SKDll SKDII-SKDll (D)St-(P)Dry E] (D)St-(P)Dry O O6

(D)St-(P)St •

(D)St-(P)St •

(D)L2-(P)Dry [] (D)P3-(P)P3 (D)L2-(P)St I..11

o4

.j----%,

/ /

/

/

(]) /

/

/

-~

A\/' / / /

/'

\

/

~ 02

r~

0

I

I

I

I

~ 15

I 20

~o2 N~, ~" Of

°! r~

of Punch (~) R a = 0 . O 2 0 P l ~ - : - ~

I 5

I IO

Ironing reduction Fig. 2. Surface roughness value Ra on the p u n c h and the die sides in relation to ironing reduction Re for various lubricating conditions a n d p u n c h C ) , where h = 100 mm.

128

increase in the reduction in thickness, but the galling for the Si3N4 die was very small compared with that for the S K D l l die. In particular, when L2 was applied on the die side using the S K D l l die, severe galling occurred and ironing deformation was impossible, but for the Si3N4 die, galling was partially confined. Once galling occurs, as shown in the figure, surface roughnesses vary widely because the scratched and rubbed portions are mixed over the surface. On the punch side, the metal surface roughness decreases with an increase in the reduction in thickness, for all lubrication conditions. When applying lower-viscosity oil (P3) or even no oil (dry), no galling could be observed on the metal surface and the metal surface-roughnesses approximated the punchsurface roughness, for reductions in thickness greater than 20%, but for higher viscosity oil (St), the value of Ra showed little increase. As is shown in Fig. 11 below, with an increase in the reduction in the thickness, Re, the contact pressure at the tool/workpiece interface decreases, but the relative slip increases at this interface. At present, although understanding of the flattening mechanism on the punch side is inadequate, the view expressed [8] that the bulk plastic deformation of a workpiece promotes the surface-flattening process may be well founded. Figures 3 and 4 show variations of metal surface texture on the punch side, for greater reductions in thickness: for comparison, the punch surface is shown also. As shown in Fig. 3, for ( D ) S t - ( P ) S t , when the reduction in thickness increases from 0% (b) to 20%(e), flattening of the metal surface develops steadily. It is noted that even when the reduction is 20%, the rolling texture is retained and micro-pools (black points) exist on the metal surface, presumably because of the thick lubricant film and the poor flow ability of high-viscosity lubricant. However, in the case of ( D ) S t - ( P ) d r y , as shown in Fig. 4, Ra=O.020 um

-]~

Ra=O.157 #m

...............

0.i~

(a) Punch surface (P~nch ~))

i

(c) Re=5%

Ra=0.21 .un

Ra=O. 045 ~ m

Ra=O.13?~m

Die: SKDI1;

0.1 n

(e) Re~20~:

(d) Re=10% Lubricant:

(D)St-(P)St;

(b) Re=0% (Before ironing)

Fig. 3. Surface appearance of the ironed workpiece on the punch side.

]-

h=lO0 m~

129 Ra=O. 065 p m

Ra=O. 096/= "

Ra=O. 025/z = !

0.i mrm

:,7., =o

"7==

i

Punch (~);

(c) I~e=20%

(b) Re=lO%

(a) Re=5~o Die: $EDll;

Labricant:

(O)St-(P)Ory;

h=lO0 zm

Fig. 4. Surface appearance of the ironed workpiece on the punch side. when the reduction in thickness increases from 5% (a) to 20% (c), the rolling texture on the workpiece surface gradually disappears and the metal surfacetexture approximates the punch surface-texture. In any case, flattening due to replication of the punch surface develops with greater reduction in thickness.

3.2 Variation of surface roughness with ironing travel Figure 5 shows the variation with ironing travel of the metal surface-roughness on both the die and the punch side and also the friction coefficient on the die side, in the case of Re = 20%. As mentioned above, with the application of lower-viscosity oils on the die side, galling occurs, so that the surface roughness and the friction coefficient on the die side increase and fluctuate severely. However, the metal surface roughness on the punch side, which is virtually unaffected by the ironing conditions on the die side, becomes almost constant when the ironing travel is above 20 mm. Especially, when applying the lower viscosity oil P3 on the punch side and even for dry conditions, no galling occurs and the metal surface-roughness on the punch side converges to within 0.02 pm of the punch surface-roughness. However, a slight fluctuation of the metal surface-roughness on the punch side can be noted in the case of (D) L2- ( P ) Dry, in which the value of Ra on the die side fluctuates severely.

3.3 Effect of lubrication conditions Figure 6 shows the metal surface-roughness on both the die and the punch sides at h = 100 m m for Re = 20% under various lubrication conditions: qualitatively clear observations can be made. The best metal surface on the die side, i.e. a rubbed surface (Ra--0.05 pm), is obtained when high-viscosity oil St is applied to the die side. In comparison, the best metal surface on the punch side

130

E :I

m~

0,8

• co~ 0,20

(D ]:3

Friction

Surface roughness on punch side

....

Surface rou~hoess on die side _ _ / /

(]9 -~

~0,6

~_ 0,:15

(]9

u

coefficient

die surface . . . .

I

0,4~k-.

/

• 0 0 []

<9 or:

um

----- -

SKDII ( D ) S t - ( P ) S t $KDI1 (D)St-(P)Dry // SKDll (D)P3- (P)P3 / ./ SigN,* (D)L2-(P)Dry / ~ "

//

O~

~

.

-/"

~

(19

0,3

///" .1-'0% . /

_~-

=I tO

©

~0,4 (I0 C

Q k_.

~0,2 Lo %-L._

~0

---0

. . . . . . .

m

o,lo / - - / 'I);

~_c:o =°~

,

IW ; 1~ [

®~- 0.05

0,2 .~

I I

/

t ,

.~ ~

I I

I

l/

\

~

.

,\

/

/- - o , z

~----7~._

U

8

_,

4-k-. kL.

CO

o

20 4o do Ironing travel h Punch ~);

Die: SRDll;

do

soo

0

mm

Re=20%

Fig. 5. Variation of metal surface-roughness with ironing travel.

is obtained under the conditions (D) St- ( P ) dry and approximates to the punch surface. In these cases, the range of fluctuation of surface roughness is very small. It is recognized, however, that the metal surface-roughness Ra on the punch side reduces with a decrease in the viscosity of the lubricant applied on the die side, when St is applied on the punch side. This result suggests that flattening of the metal surface on the punch side can be promoted by a rise in the contact pressure originating from high-friction conditions on the die side. The relationship between the metal surface-texture on the die side and the punch side is shown in Fig. 7 for the lubricating conditions ( D ) P 3 - ( P )P3, in which band galling occurs on the die side. In these experiments, in the metal surface on the die side, gouged bands 3-5 mm wide (B') exist enmixed with the rubbed surface (A'). Under these conditions, the metal surface on the punch side becomes a virtual mirror surface B of the corresponding positions of the gouged bands B'. The roughness profiles of the rubbed surface and the gouged surface on the die side are shown at the top of the figure and the corresponding surfaces

131 1.5

-

{D

r'r"

1.2-

g-8 0 5 o g 02(]3 U

o lo -

b (j~

0.05- { 0 E

r-r" 0.06

-

~m o 5 004 -

~g 03 _U

0.02 Surface roughness of punch Ra=O.O20~m 0 Punch Dry JL2 JP3 [P4 JSt P5 DryJ st Dryj L2 J St -

-

P3

St

Die

Die Punch

St

SKD II

L2 Si3N4

SKD I I

Punch ~); h=lO0 ms; Re=2OZ; I : Fluctuation range; Niddle bar: Average value Fig. 6. Relationship between the lubricating conditions and the metal surface-roughness.

Rubbed surface A'

6ouged surface ~-~

B'

0.5 ml

5

==

I

t~

0.5 me A

Non-bright surface

-

B

Bright surface

r,lnch @; Die: SKDII; Lubricant: (D)P3-(P)P3; Re=19.2%; h=lO0 mm Fig. 7. Surface profiles of the ironed metal.

132

k

0

20 8O 60 80

100%

Fig. 8. Relative bearing curves of a bright surface and a cloudy surface.

on the punch side at the bottom of the figure. It can be recognized clearly that the roughness of B (the surface corresponding to gouged surface (B') ) is noticeably smaller than A (the surface corresponding to rubbed surface (A') ). Further, by visual observation, A is noted to be a somewhat cloudy rubbed surface and B an entirely bright surface. Figure 8 shows the relative bearing curves of surfaces A and B, which suggest that the bright surface B is more uniform than the cloudy surface A. This result is very interesting, for it may provide one method of mirror surface finishing.

3.4 Effects of punch surface-roughness Four kinds of punches having different surface roughnesses were prepared for investigating the effects of punch surface roughness on the flattening process. Figure 9 shows the variation in metal surface-roughness on the punch side Ra with the ironing reduction Re used for these punches: the ordinate is drawn to a logarithmic scale. Punch (~), with a surface roughness of 0.354 I~m, is rougher than the workpiece and is employed only for reference in discussions of the replication mechanism. In the case of this punch, with greater ironing reduction the metal surface-roughness approximates the punch surface-roughness, irrespective of the lubrication conditions. It seems that oils flow more easily over a rough surface. Because the punch is rougher than the workpiece, the metal surface becomes rough by the replication process. When the punch surface-roughness becomes less coarse, in the order of punches (~, (~), C), the replicability of the punch surface onto the metal surface becomes worse than for dry conditions, when applying the high-viscosity oil St. Thus, the effects of lubricating conditions are reinforced. Moreover, for an extra-fine surface finish, punch C) (Ra--0.004 pm) was prepared, which is virtually the best surface finish attainable for SKD 11 tool steel: in the case of (D)St-( P )Dry, when the ironing reduction increases in the order of 41.3%, 49.1%, 52%, almost the same surface as that of the punch is obtained at Re ~ 50%. Figure 10 shows the relationship between the replicability and the punch surface-roughness. For a rough punch such as punch (~) or punch (~), metal

133

~,

Surface roughness of punch @ Ra=O.354pu

0.5

~ "~ ' ~

0.1

~ ( D ) S t - (P)Dry "1.(~ (D)St-(P)St |"~ /(D)St-(P)St ~.@

~

== o.os -~ Surface roughness of punch

g

~.. Surface roughness of punch _

0.01 ~

"~'~-"-~..~~" ®j (D)St-(P)St/~--.... t (D)St- ( P ) D r y /

@ ea=O.O57pn

¢p

®

Ra O.O...

{

of punch 1~) Ra=O.OO4pm 0.005 fSurface roughness I I I 5

o

/" ~-"0

t._ -

tO 15 Ironing reduction ReP~

I

20

Fig. 9. Variation of the metal surface-roughness with increase in ironing reduction. 0.5

Surface roughnessof

.e,:,±p.ci.e.

q

~/

RaooO 2 , . .

l

--

i

I

m

0.I o= 0.05

~,

o.ol

N 0.005

g Re=32%

~,Re--41~

l

I

I

[

I

i

|

I /

~ ® ® ® Ra=O.004 # n Ra=O.O2Opm iRa=O.?5?pa Ra=O.354p./ I 0.5 0.005 0.01 0.05 0. I Surface roughness of punch Rap pe

Fig. 10. Relationship between the punch surface-roughness and the metal surface-roughness on the punch side.

surface-finishes close to that of the punch used can be obtained at Re = 20%, irrespective of the lubricating conditions applied. For smoother punches, a higher ironing reduction is necessary to promote the replication process, but even when punch (~) is used, a surface-finish similar to that of the punch can be obtained at Re = 50%. It is clear, therefore, that a surface-finish similar to that of the punch can be obtained, principally by the replication process, during ironing.

134

4. Replicability

As mentioned above, replicability can be increased by increasing the ironing reduction Re for the reasons given below. Figure 11 shows the variation of relative-slip length on the punch side lp and the average contact pressure measured on the die surface, with ironing reduction. Here, Ip is the relative-slip length of the workpiece in relation to the punch and is calculated on the assumption that deformation is uniform from inlet to exit. As illustrated above, with increased Re, the contact pressure decreases and the relative-slip length increases: however, the relative-slip length is still small (0.055 mm) even when the ironing reduction is 20%. These three factors (relative-slip length, average contact pressure and ironing reduction) are regarded as influencing effectively the flattening process but, unfortunately, in these experiments it has not been possible to vary the factors independently: their separate effects will be discussed in the future. For the present, as influential factors on the metal surface-roughness on the punch side, the contact pressure P and ironing reduction Re are singled out, their effects being shown in Fig. 12. It thus becomes clear that the larger are the values of Re and P, the finer is the flattening of the surface.

Dlo

Lubricant Dis Punch



St

Dry'L2

(~D

P3

P3

0

L2

L2

3OO SKDII

o-

t

NI~ N.

P3

-~

Symbol

st

Dry

[] []

P3

~]

/

/ /

0,06

E E

,

200

0,04

i00

0,02

~

5

o)

c~

Relative sliding length of punch side

i0 Ironing reduction

15

20

Re %

Fig. 11. Variation of the relative-slip length on the punch side lp and the average contact pressure P with ironing reduction.

135

SKDI!

st

I

L2 Dry

i I



......... r 11

St ~

I

~D 0

0

4 p--

[]

P

0

¢ 0

I00

200

C o n t a c t pressure on t h e d i e s u r f a c e

300 p MPa

Fig. 12. Conditions for an extra-fine surface finish.

5. C o n c l u s i o n s

Flattening tests on band workpieces of commercially pure aluminium, using punches of different surface roughness and employing widely different lubricating conditions as well as ironing reductions, have shown that an extra-fine surface can be obtained by the ironing process. On the die side, galling often occurs when low-viscosity oils are used. When higher-viscosity oils are employed, the metal surface becomes a rubbed surface having a value of Ra=0.05 pm: this latter value is the best obtained in the present experiments but is somewhat inferior to that of the die surface. On the punch side, the metal surface becomes a near-replica of the punch surface, the degree or replication increasing for greater reductions, when using lower-viscosity oils or when dry. In employing the punch for which Ra--0.02 pm, the metal surface becomes a complete replica of the punch surface when the reduction is increased to 20%. In the case of employing the punch for which Ra-- 0.004 ~tm (which latter value is virtually the best surface finish attainable for S K D l l ) under ironing conditions of dry and Re--50%, a complete replica of the punch again can be obtained. In conclusion, it can be stated clearly that a metal surface approaching, in quality, that of the punch surface can be obtained by the replication mechanism in the ironing process.

136

References 1 N. Kawai and K. Dohda, Tribology in metal forming processes, Advanced Technology of Plasticity, Vol. 1, Proc. 1st Int. Conf. on Technology of Plasticity, Tokyo (1984) 145-156. 2 T. Mizuno, K. Matsubara and H. Kimura, Friction and lubrication in the cold rolling of thin sheet metals, Bull. JSME, 12 (50) (1969) 359-367. 3 A. Azushima, Oil film thickness in rolling and surface roughness of roll and materials, Trans. JSME (in Japanese), 44 (377) (1978) 332-339. 4 R. Kelly and J. Byers, Synthetic fluids for high-speed can drawing and ironing bodymakers, J. ASLE, 40 (1) (1984) 47-52. 5 J.E. Knepp and L.B. Sargent, Lubricants for drawing and ironing aluminum alloy beverage cans, J. ASLE, 34 (4) (1978) 198-201. 6 N. Kawai, T. Nakamura and K. Dohda, Development of anti-weldabilitytest in metal forming by means of strip-ironingtype friction testing machine, Trans. ASME, J. Eng. Ind., 104 ( 1982 ) 375-382. 7 N. Kawai and K. Dohda, Laboratory simulation for galling in metal forming, metal transfer and galling in metallic systems, Proc. Conf. Orlando, Florida, 1986, Metall. Soc. AIME, ( 1987 ) 63 86. 8 T. Nakamura, The frictional mechanism on surface of metals plastically defbrmed, Bull. JSME, Vol. 17 (108) (1974) 803-809.