limits of lubrication in backward can extrusion: analysis by the finite-element method and physical...

Jo~nal of

Materials Processing Techuology

E L S E V I E R Journal of Malerials Processing Technology 61 (i 996) 275-286

Limits of lubrication in backward can extrusion: analysis by the finite-element method and physical modelling experiments

B. BennanP,*, N. Bay b,2

abMustrial and Human Automatic Control and Mechtmical Eng#te~'rfllg Laboratory, URA CNRS D! 775, Universitk dc Valem'iemws et du Hainaut Cambrbsis, BP 311, 59304 Valenciemws Cedex, France

bb~stitute of Manufactur#tg Eng#wer#tg, Technical University of Denmark, Building 425, 2800 Lynghy, Denmark

Received 28 February 1995

Industrial summary

The increasing demand in industry to produce cans at low reduction by the backward extrusion process involves better understanding of this process. To analyse the process, numerical simulations by the finite-element method and experimental simulations by physical modelling using wax a: a model material have been performed. These simulations gave good results concerning the prediction of the flow modes and the corresponding surface expansions of the workpiece material occurring at the contact surface between the can and the punch. These predictions set the limits of the can height, depending on the reduction, the punch geometry, the workpiece material and the friction factor, in order to avoid the risk of damage caused by stiction of the workpiece material to the punch face. The influence of these different parameters on the distribution of the surface expansion along the inner can wall and bottom is determined. The numerical and experimental simulations showed good accordance.

Keywords: Backward extrusion; Lubrication; Sliding prediction; Stiction prediction; Finite-element method analysis; Physical modelling experiment; Finite-elenlent method--experiment correlation

1. Introduction

Backward can extrusion is a commonly applied cold- forging process used for the production of tubes, cans for packaging, transmision units as homokinetic joints for automobile front wheel drives, etc. These cans are typically produced at reductions of greater than 50%. An increasing demand, however, is noticed in industry to produce cans also at lower reductions.

Backward can extrusion of steel is nevertheless one of the most critical cold-forging processes due to very high surface expansion and extremely severe tribological conditions at the contact between the punch land and the inner can wall. These severe tribological conditions may cause lubricant film breakdown, pick-up of the

* Corresponding author. Tel.: 33 27 14 13 83; fax: 33 27 14 12 78; e-mail: [email protected]

The present work was carried out at the institute of Manufactur- ing Engineering, Technical University of Denmark.

2 Tel.: 45 45 93 12 22 ext: 4764; fax: 45 45 93 01 90.

0924-0136/96/$15.00 © 1996 Elsevier Science S.A. All rights reserved

SSD! 0924-0136(95)02181-1

workpiece material on the tool and thereby damage of the specimen surfaces. This is especially so tbr can extrusion with low reduction, where the local surl~lce expansion reaches very high values even at moderate can height.

Recent experimental analysis of backward can extrusion with a model material as well as steel has shown the influence of punch geometry, and of material parameters such as strain-hardening and friction factor, and reduction on the resulting local surface expansion of the workpiece material under the punch [1]. Depend- ing of the value of these parameters, sliding or stiction of the workpiece material may appear at the contact surface of the punch nose.

Large surface expansion of the inner can wall and stiction of the workpiece material to the punch face, which cause insufficient lubricant supply to the land of the punch and thereby film breakdown, pick-up and cold welding to the land either during the cold-forging process or during ejection, have to be avoided.

276 B, Bennani, N. Bay~Journal of Materials Processing Technology 61 (1996)275-286

Dc

I

stm I

(a) (b)

Fig. I. Backward can extrusion: (a) process geometry, aL~ (b) notation of the punch geometry [3]. Dp: punch nose diameter; Dr: diameter of the fiat portion of the nose; 2~t: face angle of the punch nose; R: radius of curvature on the punch nose; h: punch land; 13: relief angle, and Ds: diameter of the punch stem.

To predict these risks, numerical simulations by the finite-element method (FEM) are performed with the DEFORM TM finite-element program [2]. The numerical simulations are carried out for different punch geometries and varying values of reduction, strain-hard. ening and friction factor. The numerical flow-mode predictions are compared with the experimental modes obtained by physical modelling experiments using wax as a model material [1]. The local surface expansion of the workpiece material under the punch and along the can wall are also computed to analyse the influence of each of the parameter previously mentioned.

Parallel to these computations, experimental analysis by physical modelling experiments using wax as a model material is performed to check the ability of the FEM program to simulate in detail the change in the local surface expansion when varying the geometry of the punch nose, the reduction, strain-hardening and friction factor.

r = Dp'-~2 (1) Dc 2

where Dp is the punch nose diameter and Dc is the container diameter (Fig. l(a)).

The International Cold Forging Group (ICFG) has recommended a punch geometry [3] as shown in Fig. l(b). It has been established that the face angle of the punch nose, 2~, and the diameter of the flat portion of the punch nose, Dr, together with the reduction have the most dominant influence on the workpiece flow [1]. The other parameters are therefore chosen to be constant and selected according to the ICFG recommenda- tions as follows:

h = 0.5x/~-p (D p in mm)

R = 0.075 Dp

fl = 4 ° (2)

2.2. Flow modes in backward can extrusion

2. Backward can extrusion process

2. I. Tool and workpiece geometry

The degree of deformation in backward can extrusion is specified by the reduction r, defined by:

The experiments [1], mentioned previously, have shown that the workpiece material can either slide over or stick onto the punch during the backward can extrusion process, Fig. 2(a) and (b) showing these two types of flow mode. The possible sliding or stiction is observed by studying the flow of the workpiece material. In the case of full stiction the radial distance from

B. Bemumi, N. Bay ,; Journal o.f Moterials Processing Teclmology 61 (1996) 2 75- 286 277

the center axis to the longitudinal lines would be the same at punch face as at the bottom of the specimen (see Fig. 2(a)). Full stiction to the punch face implies no lubricant transport to the punch land, which is fatal causing direct metal-to-metal contact between the inner can wall and the punch. Too large a degree of sliding may cause lubricant film breakdown under the punch nose and thereby damage the surface specimen.

In the numerical analysis, the flow mode is observed in the post-processor of the finite-element programs by studying the deformed grid mark being defined by square or circle grids. In the physical modelling experiments using wax material, the flow mode is observed by studying the deformation of the grid, which latter is applied to the meridian plane of the specimen by seri- graphic technique.

i I I., J

Silding R'>R Stiction R'=R

Fig. 2. Flow mode of backward can extrusion: (a) sliding over the ptmch face, and (b) stiction at the punch surface.

0 20 0 20 (a) ~ (b) L w I

Fig. 3. Estimation of the surface expansion in backward can extrusion by FEM simulation: (a) initial, and (b) final positions of the nodes located at the workpiece/punch contact surface.

0 20

(a) (b)

Fig. 4. Estimation of the surface expansion in backward can extrusion by physical modelling experiments: (a) concentric semi-circles on the e - ~ , . I c d " * ~ C . ~ , . . . : . . . . . ~ . . . . . . . i , , . , ~ . r . . . . . . . . ~ . . . . . . . . . . - . . _ . ~ _ _ , _ _

on the inner can wall. The surface expansion is expressed as a function of the folded-out inner-surface distance - from the can top divided by the punch diameter Dp (see Fig. 5).

2.3. Determ#zation of the suiface expansion

In the backward can extrusion, the tribological conditions are investigated by determining the surface expansion of the workpiece material under the punch and along the can wall during the process. In the finite-element analysis, the estimation of the surface expansion is obtained by following the disp!-'_~cement of the nodes located longitudinally under the punch (scc Fig. 3). In the case of the physical modelling experiments with wax material, the surlace expansion is estimated by painting concentric semi-circles on the end surface of the workpiece and measuring the distance between neighbou::ng circles after deformation (see Fig. 4).

The expression of the surface expansion is given by:

Table i Backward can extrusion, flow mode, data of the FEM simulations (varying parameters are set in bold)

a) Punch geometry 2a Dp Df R It ~ D b (o) (mm) (inn1) (mm) (ram) (o) (ram)

120 55.6 0.1Dp 4.245 3.76 135 0.6Do 150 165 180

b) Material properties Young Poisson Strain-hardening modulus ratio exponent, n (MPa)

55.6 0.1 0.2 0.3 0.4 0.5

Coulomb friction factor, la

210000 0.3 0 0.2

0.04 0.066

278 B. BemumL N. Bay Journal of Materials Processing 7"eclmolo~o' 61 (1996)275-286

I !

I !

I !

m

9 top

(b)

8

0 1 2 3 (c) folded out inner can surface distance from can top z/Dp

Fig. 5. Estimation of the surfi~ce expansion in backward can extrusion: (a) initial specimen; (b) deformed specimen, and (c) surface expansion curve as a function of the folded-out inner can surlhce distance from the can top.

X = A~ - A. (3) / lo

where Ao and At are the surface areas betbre and after deformation between the concentric circles through

two neighbouring nodes in case of the finite-element analysis and between neighbouring circles in case of the physical modelling experiments, respectively.

3. Analysis of the backward can extrusion process

3.1. Prediction of the flow mode

To predict the flow mode occurring during the backward can extrusion process, FEM simulations were performed for a range of small reductions (0.1 ~<r~<0.5) and face angles of the punch nose. Other parameters investigated are the diameter of the flat portion of the punch nose, the friction factor and strain-hardening.

The finite-element simulations were carried out with a workpiece specimen (diameter: 80 ram, height: 148 mm) anO the ~cometry of the ounches and the material parmaters as defined in Table 1. The computations were achieved for a 40 mm punch displacement.

The results are expressed in graphical form using bar graphs where the sliding zone, the transition zone between sliding and stiction, and the full stiction zone, are represented by different hatched areas.

Figs. 6 -9 show the flow modes with respect to varying diameter of the flat portion of the punch nose, varying friction coefficient and varying strain- hardening exponent.

The bat" graphs indicate that the risks of lull stiction increase with: (i) decreasing reduction; (ii) increasing diameter of the flat portion of the punch nose; (iii) increasing face angle of the punch nose; (iv) increasing friction coefficient, and (v) increasing strain-hardening exponent.

I "~ " : ' ::: " i: ::' :':::::::": " : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 05 [~;ll;l.::ii~.i ~:::~ :~ ................. i . i . . . . i ~ L: : : : ~ : "i:i: : : ' : ~ : : : : :~' : :i: :~:' 'i: :i'" ':" !' ':'~+ ' ' ':":~:':':':':':':~>:':'--

li " 0.4 ~i~ ~ ~!~!~.~'.~!~!~i:i~:,::iiiiiii~:i:~:i~!~ii~ili!~i~i:i~ !iiii~:i~ i~i:i~!i!i!~!:!,!ii'.:~:~ t

IE~; ~.i~!:i~:iiii:!;iliiii:~!iiii:iii~:~:~i~i!i!:: :'. :'..i!!:~i::!i!::i::i::i!!:!:!i :?. i~i~i!i!:!::i?.!:!:~:i:!:::::~ 1 ~ 8 ~ 1 ]

ir:~:!:~i~i!:!!!i!i!i!!! :!!!i:!i!!ii!!:~:i!:-:i:!:i!:!i:i!i!i!i!!~!!-~i~!~i~i~i~i:~:i: ~ ' ~ t ~ ' ~ ~

~ii!i~ii~i~iii~i~i!i!i!~!~i~iii~!i~iii!~iiiiiiii:~i~!~iiii!i!i!i~!i~!!i~i~!i~ii~i~:~

0.1 ~*i:~:!:`;i : i~i:!:i :!:i : i : i~i:i:!:!:i~::~i~!:~:!:: . : i :~::i: i :~;~i:i~:i;i~i;i: i~i:~8~~

I

• o 3 ~J

~ 0 . 2

I I I I | 120 ~ 135 ~ 150 ° 165 ° 180 °

Face angle of the punch

• r

0 . 5 ~.~:~*~:~:.!~.::.:~.~*~:~.::?~:~:.:.*~:~.~*~:~!~:~:~:~!~:~.*~*~.:~:~:~..~:!~:~;~:~..:.::~:~l

i . . . . . . . . . . . . . . . . . . . . . . . . . .

0.2 iiiii !i!ii i:::i ':iiii!ii

0.1

1 ! I i !

120 ° 135 ° 150 ° 165 ° 180 °

Face angle of the punch E~periment [!ll

Fig. 6. Backward can extrusion, flow mode with n = 0.2 and la = 0.04: (a) D r = 0.1Dp, and D r = 0.6Dp.

B. Bemumi, N. Bay, Jourmd oJ MateriaL~" Processing Teclmoh~gy 61 (1996)275-286 279

0.5

0.4 m

O "~ 0 . 3 1 r j

~ 0.2,,,,

O A m

0 . S E

?ii:!:i?!ii:!?i?!?i~?:i?i???!ii:i!?~!?/!~!i!!i!iiii:i:!~!:!;i!i!!!?:!?i:!!!i?:!:!i 0.4

~0.3w ¢J

0.1

120 ° 135 ° 150 ° 165 ° 180 ° 120 ° 135 ° 150 ° 165 ° 180 °

Face ang le of the punch Face ang le of the punch ~ E x p e r i ~ [ l i 1

[:: sli, i.g ]

Fig. 7. Backward can extrusion, flow mode with n = 0.2 and Dr= 0.6Dr,: (a) t.t = 0.04, and (b) la = 0.066.

o

o

0.5

120 ° 135 ° 150 ° 165 ° 180 °

Face angle of the punch

0.5

0.4

• ~ 0.3 r j

~ 0 . 2

0.1

120 ° 135 ° 150 ° 165 ° 180 °

Face angle of the punch ]Experiment 11

Fig. 8. Backward can extrusion, Ilow mode with n = 0.2 and D r = 0.1Dp: (a) la =-0.04, and (b) la : : 0.066.

0.5 ~ ......... ii ;ii: ...... :~ii,, ' ..... :i I~:: i~

0.4 ransi o. J

o.3

~0.2 ~ ~ ~ ............. ~

0.1 ~

I | | | | 120 ° 135 ° 150 ° 165 ° 180 ° 120 ° 135 ° 150 ° 165 ° 180 °

Face angle of the punch Face angle of the punch ~Experiment l l ![

Fig. 9. Backward can extrusion, flow mode with ~ = 0.04 and Dr = 0.6Do: (a) n = 0, and (b) n = 0.2.

280 B. Bennani, N. Bay/Jourmd of Materials Processing Technology 61 (1996)275-286

Table 2 Backward can extrusion, influence of 2~, data of the FEM simulations (varying parameters are set in bold)

a) Punch geometry 2a Dr, D r R h 13 Db (°) (mm) (mm) (mm) (mm) (°) (mm)

120 56.6 0 135 150 165 180

4.245 3.76 4 55.6 0.5

b) Material properties Young Poisson Strain-hardening Friction modulus ratio exponent, factor, (MPa) n m

o

8

o~ X

140

120

100

80

60

40

20

0

m

1 2 3

~ E - - 120 °

• - - - t l - - . - 135 °

~ , _ _ 150 °

0 1650

~ L . . 180.

Fig. 11. Backward can extrusion, surface expansion as a function of folded-out inner can distance from the can top for varying face angle, r =0.5, n = 0 and m = 0 .

210000 0.3 0 0 3.2. Prediction of the surfilce expansion

The FEM-predictions of the flow mode were compared to the results of the physical modelling experiments and steel experiments given in Ref. [1], the correlation being noted to be good.

The reduction, the face angle of the punch nose, the diameter of the flat portion of the punch nose, the friction factor and the strain-hardening exponent, are all principle parameters influencing the flow of the workpiece material at the contact surface of the punch nose.

(a) (b)

(d) (e)

I

(c)

(0

/

t a ~

1

k

Fig. 10. Backward can extrusion, surface expansion for varying face angle, r = 0.5, n = 0 and m = 0: (a) initial; (b) 20t = 120°; (c) 20t = 135°; (d) 2at = 150"; (e) 2ct = 165", and (f) 2a = 180".

B. Bennani, N. Bay/Journal of Materials Processing Technology 61 (1996)275-286 281

Sets of FEM simulations were performed in which each parameter was studied separately. The local surface expansion of the workpiece material under the punch nose and along the can wall was analysed to determine the influence of the face angle of the punch nose, the diameter of the flat portion of the punch nose, the friction factor and the reduction.

The FEM predictions of the local surface expansion were finally compared with those determined by physical modelling to check the ability of the FEM program to simulate the change in local surface expansion with varying parameters.

3.2.1. Influence of the face angle of the punch nose To estimate the influence of the face angle of the

punch nose, 2~ (see Fig. 1), a set of FEM simulations was performed with the value of the face angle successively equal to 120 °, 135 °, 150 °, 165 ° and 180 °. The punch geometries and the material parameters are defined in Table 2.

The local surface expansion of the workpiece material under the punch and along the can wall is expressed by the displacement of ten nodes located at the punch face, as explained in Fig. 5. The final positions of these nodes for varying face angle of the punch nose are given in Fig. 10, whilst Fig. 11 shows the surface expansion distribution for varying face angle, from which latter figure it is seen that the surface expansion decreases with increasing face angle of the punch nose. A sudden shift from very small surface expansion to steadily increasing expansion with greater distance from can top ;,s noted in all curves, this shift occurring later with increasing face angle.

3.2.2. hlfluence of the flat portion of ,he punch nose The fiat portion of the punch nose is also an im-

portant geometrical parameter influencing the flow mode of the workpiece material at the contact surface of the punch nose and causing the appear- ance of the stiction phenomena. To confirm this, FEM simulations were performed with six sets of punch dimensions. The diameter of the flat portion is equal to respectively 0.1Dp, 0.2Dp, 0.3Dp, 0.4Dp, 0.5Op and 0.6Dp where Dp is the punch nose diameter (see Fig. 1). The previous computation without a flat portion of the punch nose were used as comparison to clarify the influence of the flat portion on the surface expansion. The punch geometries and the material parameters are defined in Table 3.

Fig. 12 shows the estimation of the surface expansion by FEM simulations for the different values of the diameter of the flat portion. The comparison of these estimated surface expansions with the surface expansion obtained without a flat portion illustrates perfectly the influence of this geometrical parameter. A decrease in the surface expansion with increasing fiat portion of the punch nose is observed, this decrease being significant for values of the flat portion above 0.3Dp.

3.2.3. Influence of the strain-hardening exponent The influence of the strain-hardening exponent on

the flow mode was analysed by performing FEM simulations with two different values of the strain- hardening exponent, n, in the Holloman stress-strain curves a = C~:". The values chosen being n = 0 and , =0.2. The computations were carried out for the different face angles used previously. The punch

Table 3 Backward can extrusion, influence of Dr, data of the FEM simulations (varying parameters are set in bold)

a) Punch geometry 2~ D 0 Df R h 13 D b (o) (mm) (mm) (mm) (mm) (o) (mm)

120 56.6 0.1Do 4.245 3.76 0.2Dp 0.3Dp 0.4Do 0.SDp 0.6Dp


4 55.6 0.5

Friction factor, m

210000 0.3 0 0

Table 4 Backward can extrusion, influence of n, data of the FEM simulations (varying parameters are set in bold)

a) Punch geometry 2a Dp D r R h 13 Db (°) (mm) (mm) (mm) (mm) (°) (mm)

120 56.6 0 135 150 165 180

b) Material properties Young Poisson modulus ratio (MPa)

4.245 3.76 4 55.6 0.5

Strain-hardening exponent, n

Friction factor, m

210000 0.3 0 0.2

282 8. Bemumi, N. Bay/Jourmd t!/' Materials Processing Technology 61 (1996)275-286

i ,.o1 I

X

o.o

= 150.0 - - = - , = 120', Df=0.xDp .~

' " ° - 7 ~ ~ lOO.O ,50.0

' l ~ " " - ...... " - mJ~,,,- l ! I 0.0

2.0 3.0

--u,-.. 1200, Df--O.xDp

0.0 2.0 3.0

(a)

Folded out inner can surface distance from can top z/Dp

(b)


.[ 5o.o T 'oo.o T

0.0

--n-- 120% Dr=0.xDp ..~ 150.0,1,, -----. 120", Dl=0.xDp

2.0 3.0 0.0 2.0 3.0


(c) (d)


!ooT .o=oxv 5oo., .V xO 100.0 - X - 1 2 0 " , 1 3 f ~ ~ 100.0 ~ - + - - 120% D f . - ~ . 6 ~ = . / .

t o.o+ / / I ./"+...+.*" *

O.Ox.=,= ~ l l l i l ~ ; ~ = . ~ ~ i = o.0 ~ = ~ . . = d ~ , ~ = ~ ~ 0,0 2.0 3,0 0.0 2.0 3.0

Folded out inner can surface Folded out inner can surface distance from can top z/Dp distance from can top z/Dp

(e) (f)

Fig, 12, Backward can extrusion, surface expansion as a function of folded-out inner can surface distance from can top with the diameter of the fiat portion as a parameter, and surface expansion without a fiat portion for the comparison, r= 0.5, n = 0 and m = 0.

geometries and the material parameters are defined in Table 4,

The estimated surface-expansion distributions for n = 0 and n = 0.2 with varying face angle are given in Fig. 13, from which it is noted that the surface expansion decreases with increasing value of the strain-hardening exponent and that the modification of the surface expansion is important for values of the face angle greater than 150". A complete change of the flow mode is noted for the punch with 180 °C face angle, where sliding is observed when the strain-hardening exponent is equal to zero whereas full stiction is observed when the strain-hardening exponent is equal to 0.2 (Fig. 14).

3.2.4. Influence of the ]~iction factor Due to the severe tribological conditions occurring in

the backward can extrusion process, the friction condi- tion between the punch and the workpiece is obviously

an essential parameter influencing the surface expansion of the workpiece material. To study this parameter, FEM simulations were performed with the friction factor m = 0.2 for varying face angle of the punch nose. The corresponding estimated surface-expansion distributions are compared with those obtained with frictionless workpiece/punch contact conditions. The punch geometries and the material parameters are defined in Table 5.

Fig. 15 shows the estimated surface expansion for m = 0 and m--0.2 with varying face angle. It is noted that the surface expansion decreases with increasing friction factor. The decrease of the surface expansion due to increased friction is not significant for the face angles 2~--120 °, 135 ° and 150 °, whereas risk of full stiction exists for 180 ° face angle when the value of the friction factor is greater than 0.1.

£aeanaae oql ~Iaoqa ol pomaojaod o.~om l~!.ml~m iopom ~ s~ x~,a ~tnsn sluam!aodxo ~UlllOpom lea!s,(qd

suoll~!pa.td gU!llapotu lnO!S£tl d pun IlgWu4 atll fo uos!.ooduto D "9"g'f

"uo!lanpoa ~u!se~aaop ql!* soseoaaop uolsuedxo oaejans oql leql polou s! 1! '£lluonbosuoD "VO ~ .t ql!m ooej qaund oa!luo oql aoao tlOll3!lS IlnJ ol g'O = .~ ql!~a Ie!aoletu o:~o!d~IaOm oql jo ~tqp!!s moaj so~ue, qa opotu ~aOlJ oq.l. "uo!lanpoa ~m£aea aoj sopotu mOlj poletu!lso oql smoqs 9I "~!d "9 olq~£ u! pouuo p oae, saolouleaed lelaOle, m oql pu~, so!.~lotuoo~ qound o q l "osou qaund oql jo Oli~Ue oaej o0g| aoj g'0 = .t ol I'0 = .t moo uo!lonpoa oql i~Ut£aeA potuaojaod 0aoA~ suo!lelntu!s IAI~ld "g'0 ~ a 'sonleA mo I osoql le opotu A~O[I oql UO uo!lanpoa oql jo oouonitu ! oql £pms ol £1!sso:~ou oql So!ldtu ! uo!lanpoa A~O I le SUUO oonpoad ol £alsnpu! u! pup.mop ~u!snoaou! o q l

uo!l.)np<zt aql fo a.~um[fftq "~'F'F

"Z'O = u (q) pue '0 = u (e) :0 "= u~ pue o081 = zZ 'luouodxo ~u!uapJuq-m.e~ls oql jo onlea ~m£a~,A aoj apotu mOlJ 'uo[snalxo uva paea~lae8 "~l "~!d

(q) (e)

oooooo~i iO~OOOOOl ~O000OOl ~O00OOOOl IOOOOOOOl )OO IOOOO~ )OO )OOOOl )OO iOOOOl ~00 )OOOOl )oo IOOOOl ~OO ~OOOl )OO )OOOOl )00 IOOOO~ )Oo iOoool

booooooo* )OOOOOOOt )OOOOOOOl )OOOOOOO¢ )OOOOOOOl )OOOOOOOl ~OOOOOOOl ,OOOOOOOl ~OOOOOOO( ~OOOOOOO( ~O000OOO¢ ~OOOOOOOl ~OOOOOOO( iOOOOOOO( ,OOOOOOO( IQOOOQOQ( ~OOOOOOOt

"0 = tu pup 0 = "0 'g'O = .~ '.lolotu~a~d s~, luouodxo ~uluop.l~,q-u!~als otll tll!~a dol tn,3 Otll tuo.u o3uP, ls!p aa~;j.ms tn, a .lauu} lno-poplo j Otll .Io uo{lounj 1; sP uotstn,,dxa aa~,jans 'uo!snalxa tlea p.m~a~lal:[! "~1 '~}d

d o / z dol uea moaj aau~ls!p aaejans uea ~ouu! lno paplo d

( o j

0"~, O'Z 0"0

0"0t ~

/ o,o 0"0~

O=u',O~t - - ' - - J. 0"0~ ~"

d o / z dol uea moaj o~u~s!p oaejans ue3 Jauu.~ lno paplod

(p) (a) d o / z dol uea moaj a~uels!p oaej~ns ue3 ~auu! lno pap|o:I

00"~ 00"~ 00"0 0"~ 0"~ 0"0

" 00"0 x ~ + ~ + n 0"0 X

~ + ~ , t 0"0~ ~ ~ " + ' ~ ' - " - " 0"09

oo'o o'o~ 8

oo'o~, ~ o

00.09 / : ÷ - + 00, 00"08 ~'= * O=U'oO~i ~ * - - , ~ 0"~{. ~'=

dcl/z do~ uea tuo.~j a a u ~ s ! p

oaejans uea aauu! lno poPlO d

(q) (e) dQ/z dol ue:~ moJj aauels!p a:mj-ms uea -~auu! 1no pap[o,.q

o'~ o'z o'~ o'o o'f, o'z o'~ 0"0 * ~ ~ x ~ x ~ x ~ × o'o x x

o'o9 ~ ~ o'o9 ~ o'ooz o'oo .. o i 'oO L !.

- 0 0"0~I ~ 0 =u'oOzz ~m~- ~ O'O~t

~8-~ 98F -ff / g (9661) 19 ,f~OlOml.~aJ ~u!s'sa.JO.td ,~lO!.l,~wl;V .1o IZm.mof / ,tT~/ "N '!uouua~ "~

284 B. Betmani, N. Bto'/'Journal of' Materials Processing Technology 61 (1996)275-286

Table 5 Backward can extrusion, influence of the friction factor, data of the FEM simulations (varying parameters are set in bold)

a) Punch geometry 2a Dp Df R h ~ D b C °) (ram) (ram) (ram) (turn) (°) (mm)

120 56.6 0 4.245 3.76 135 150 165 180

b) Material properties Young Poisson Strain-hardening modulus r a t i o exponent, n (MPa)

4 55.6 0.5

Friction factor, m

210000 0.3 0 0 0.2

of the FEM simulations in predicting the variation of the local surface expansion with varying geometry of the punch nose, strain-hardening, friction factor and reduction ratio.

The physical modelling experiments were performed in an electric driven press using semi-cylindrical specimens (diameter: 80 mm, height: 100 mm) deformed in a semi-cylindrical tool (diameter: 80 mm). An ortho- gonal grid with 5 mm mesh and circles, 2 mm in diameter, was applied to the semi-cylindrical specimens to study the deformation modes. To measure the local surface expansion at the contact surface of the workpiece-punch nose, 4 mm spacing concentric semi-circles were painted on the end surface of the specimens (see Fig. 4).

The experiments were carried out with a parafin wax with a strain-hardening exponent of n = 0.2, a friction factor of m = 0.2 determined using the ring test [4], and

-m- ~aionless 120 ° 150.00 I - X - 0.2 friction factor .

+ ++t< ~ 50.00

x 0.00 X,

0.0 1.0 2.0 3.0

(a)


I 120.00 ,if-i@ h'ictionless 135 °

~ 2o.oo |

o.o 1.o 2.0 3.0

(b)


.~ I00.0080.00 I '-0-"" O,2h'/ctl°nleSSlriction facto, p ¢I 50 °

40.OO

20.1111

0.1~

0 . ~ 2 .~ 4 . ~


(c)

80.00 ..o ~ 60.00

20.00

X 0.00

0.0

(a)

frictionless 165° - 'F- 0.2 friction factor ~

/

_g+.+t 2.0 4.0

Folded eai inner can surface distance from can top z/Dp

4o.o0 18o ° ~ . / ......... ~ ° $ ~ ~ " 0'2 fricti°n fact°r /

X .

0.0 2.0 4.0

(e)


Fig. 15. Backward can extrusion, surface expansion for zero and 0.2 friction factor with varying face angle, r = 0.5 and n = 0.

B. Bem~ani, N. Bay/Journal o f Materials Processing Technology 6l (1996)275-286 285

Table 6 Backward can extrusion, influence of the reduction, data of the FEM simulations (varying parameters are set in bold)

a) Punch geometry 2a D o Df R h [5 D b (o) (ram) (mm) (mm) (mm) (°) (mm)

180 56.6 0 4.245 3.76


4 55.6 0.1 0.2 0.3 0.4 0.5

Constant mean friction factor, m

210000 0.3 0.2 0.2

|0o.??o__o _o0ooo, 1~0oo_900oo_ o, i~0oo_o_oooooo! ll0~00e~eO~oo,

boo~oo~oo~oooooq b,56ooooooooo~ooq ~ o o o o o ~ o o o o o o ® ~ (a)

(c} (d)

bO®OOOO ~ O O )O®®®OOOOO®®®I

(b)

~OOOO~Oq

(el

Fig. 16. Backward can extrusion, flow mode with varying reduction, m = 0.2 and n = 0.2: (a) r = 0.1; (b) r = 0.2; (c) r = 0.3; (d) r = 0.4, and

(e) r = 0.5.

varying face angle of the punch. The measured surface- expansion distributions by physical modelling experiments are plotted in Fig. 17 and compared with those calculated by the FEM simulations. The correlation between the two types of simulation is noted to be good, Fig. 18 where the predicted flow modes obtained by FEM simulation and physical modelling experiments are compared, giving an illustration of the good correlation between the two types of simulation.

4. Conclusions

In backward can extrusion, the phenomenon of stiction of the punch face and very large surface expansion at the punch face have to be avoided in order for this forging operation to succeed. Stiction is fatal due to lack of lubricant supply at the punch land, and so is also excessive surface expansion, leading to thinning down of the lubricant film.

To predict these risks, numerical simulations of backward can extrusion have been performed with the finite- element method (FEM) for the critical range of reduction 0.1 ~< r <~ 0.5 and varying face angle of the punch nose. The diameter of the fiat portion of the punch nose, the friction factor and the strain-hardening exponent are used as parameters. The FEM simulations have been performed with the DEFORM TM FEM program.

The numerical analyses pointed out that the risk of stiction mcreases with: (i) increasing face angle of the punch; (ii) increashlg diameter of the fiat portion of the punch nose; (iii) increasing strain-hardening exponent; (iv) increasing fi'iction factor, and (v) decreashag reduction.

Good correlation between the FEM prediction of the flow mode and the experimental modes [1] is noted.

The influence of the face angle of the punch nose, the size of the fiat portion of the punch nose, the strain- hardening, the friction factor and the reduction ratio were analysed by performing systematic FEM simulations computing the distribution of the surface expansion of the workpiece material along the can wall and bottom. This analysis confirms previous conclusions.

The analyses have confirmed the good ability of the FEM simulations to estimate the local surface expansion when severe modifications of the tribological conditions occur. The correlation between the FEM silnulations and the physical modelling experiments was noted to be good.

Acknowledgements

This paper is the result of a project carried out in the Department for Mechanical Processing of Materials at

286 B. Bemtani, N. Bay : Joztrnal o/" Materkds Processing Technoh~gy 61 (1996)275-286

= 8O .o

~ 2o

× o

----- l~M-simulation 120 ° Physical modelling -I

,innn~un~ nnm''un' ~ : := ".

0.0 2.0 4.0

50 , p . - - - FEM-simulation 135 ° "~ 40 1 " " Physical model.n 5

2O

X

0.0 2.0 4.0

Folded out inner can surface distance from can top z / D p


(a) (b)

2O

i 15

I0

5

x 0

(c)

.... l~M-simulation 150° 1 Physical modelling

A

. v .

0.0 2.0 4.0

Folded out inner can surface distance from can top z /Dp

o~ 20,1, "---- FEM-simulation 165°

~ .

X 0 . . . . [ . . . . . . . . . . . . . . . . . . . m'~

0.0 2.0 4.0

Folded out inner can surface distance from can top z /Dp

(d)

= 20 .o E iS

X 0,

..--.-- l~M-simulation 180 ° - - Physical modelLiAng

0.0 2.0 4.0


(e)

Fig, 17, Backward can e×trusion, estimated distributions of surl:ace expansion by FEM simulations and physical modelling experiments with varying I;ace angle, n = 0.2, m = 0.2 and r = 0.5.

)O000®O0( )CO000000( )(2)O0O000( )0(2)00000( )O00000Q( )0000000( )(2)®00000( )OOO0000c

(

bOOOOQOO( PO000000C )O000000C ,O000000C pO00000~)C t , O Q O 0 0 0 ~ c

0 20 0 20 ! 0 I

(a) (b)

Fig. 18, Backward can extrusion, flow modes for 180 ° face angle, n = 0.2, m = 0,2 and r = 0.5: (a) FEM simulation, and (b) physical modelling experiment.

the Technical University of Denmark within the frame- work of the Human Capital and Mobility program financed by the Commission of the EU. Thanks are due to Professor Niels Bay, my supervisor during the project, Professor J6r6me Oudin for his support and special thanks to Rikke Hallstrom and Bente Post- Pedersen for performing the physical modelling experiments.

References

[I] N. Bay, S. Las,~en, K.B. Pedersen and V. Maegaard, /hm. CIRP, 40 (1991) 239.

[2] S.l. Oh, W.T. Wu, J.P. Tang and A. Vedhanayagam, J. Mater. Proc. Techol., 27 (1991) 25.

[3] General Recmnmendations Jbr Design, Manufacture and Opera- tional Aspects of Cold Extrusion Tools .for Steel Components, International Cold Forging Group, Portullis Press, Vol. 6, 1983.

[4] P.H. Hansen, N. Bay and P, Christensen. Prec. XVhh NAMRC, Urbana Champaign, III, USA, 1998, p. 41.

limits of lubrication in backward can extrusion: analysis by the finite-element method and physical...

Documents