Upload
others
View
6
Download
1
Embed Size (px)
Citation preview
Journal of the Faculty of Englneerlng, Shinshu University, Ne. 67, 1990
tstixl・IJit*XefKSfEes ng67e1
Forming Limit and Its Improvement in Thin-
Walled Tube-End Flaring Using Orbital
Rotary Forming with Cylindrical Tools
Kimiyoshi KITAZAWA* and Jiro SEINO** (Received October 30, 1989)
The possibility of the tube-end fiaring using orbltal rotary forming with a
cylindrical tool has been experimentally investigated from the viewpoint of form-
ing limit by using thin-walled copper tubes. The forming limit is determined by
occurrence of rupture and various kinds of bucklings. The diameter of a cylin-
drlcal tool has a major influence on the forming limit in orbital rotary flaring. The
flaring 11mit of tube in orbital rotary forming with a cyHndrical tool is greater than
that with a conical tooL Furthermore, to prevent buckling a pass schedule of a
cylindrical tool is proposed and experimeRtally examined. The buckling mode is
prevented under the proposed preventing condition so that the forming limit is
dramatically improved. Therefore, the proposed orbital rotary fiaring with a cylin-
drical tool is likely to be a hopefully practical working process from the viewpQint
of forming limlt.
I. INTRODUCTION
The conventional press forming is a process in which a sheet metal is
formed to fit on a die surface, Due to this fitting necessity, the conven-
tional press forming is not so flexible for production of small lots. In consid-
eration of this problem of manufacture fiexibility, the,concept of orbital
rotary forming was first introduced in l986 by Kitazawa et al. i) and shortly
afterwards was applied to tube-end forming and sheet metal forming by
Kitazawa et al. 2)A"6). Orbital rotary forming is a process in which a tube end
or sheet metal is formed to fit on a tool-envelope-surface made by a relative
motion of a tool around the sheee metal or tube, In orbital rotary fiaring and
nosing of a tube end, the tube end fits well on the tool-envelope-surface. 2)
Therefore, orbltal rotary forming seems to be a hopeful process for fiexible
manufacture from the viewpoint of die-less or too!-less operation. It has also
* Asslstant, Department of
Shinshu University.** Professor, Department of lng, Shinshu Universlty.
Mechanical Systems Englneering, Faculty of Engineering,
Mechanical Systems Engineering, Faculty ef Engineer-
2 K. KITAzAwA and J. SEINobeen clarified that the forming limit of a tube end in erbital rotary forming
is greater than that in press forming.3) Recently, a computer-controlled
orbital rotary forming machine has been developed which has a mechanism
capable of forming continuously an appropriate tool-envelope-surface corre-
sponding to a product shape during a stroke of forming6). Also, an orbitai
rotary flanging of tube ends has been carried out by using this machine,
and it is found that the metal-fiow behavior is dependent on the pass sched-
ule of the tool during the forming stroke. 6) There exist such a large num-
ber of degrees of freedom of this pass schedule that the method for optimiz-
ing the pass schedule of the tool has not yet been found,
The orbital rotary forming process and the so-called "potter's wheel"
process are alike in the relative motion of tool or finger around a thin-walled
material such as a cup. It may be possible that the sight of the motion of
fingers in the potter's wheei process, when observed carefully, wil! lead to
a new idea for optimizing the pass schedttle of a tool in the orbital rotary
forming process. One of the more interesting problems in the application
of the motion of fingers to orbitai rotary forming is the to devise a method
for preventing the buckling in orbital rotary flaring of thin-walled tubes.
In the present work, thin-walled copper tubes are subjected to an orbital
rotary flaring using a cylindrical tool, designed to imkate the finger, ln an
attempt to study on the fiaring limit in pursuit of its improvement method.
2. EXPERIMENTALPROCEDURE
To clarify the forming limit, orbital rotary flarillg tests were carried
out on a modified lathe. As shewn in Fig.1, the proposed orbital rotary
forming is a process in which the tool-envelope-surface made by the rela-
tive motion of a cylindriacl tool around the tube moves in the axial dlrection
while the tube rotates, and thus, the tube-end is flared to fiow along the
tool-envelope-surface. The tube held by a chuck rotates ae a constant speed
of 315 rpm, and the cylindrical tool and its holder mounted on a tool rest
which is swiveled to a required angle r equal to the half apex angle of the
tool-envelope-surface, traveis in the axial direction at a constant feed of f
mm/rev. The materials used are two kiRds of seamless copper tubes (outer
diameters 35 mm; lengths 70 mm; wall thicknesses l,O and 1.5 mm). The
length of fiaring zone is equal to the outer diameter of the tube so that
Euler buckling should not occur. The mechcanical properties of the tube
are given in Table 1. Pasty molybdenum disulphide (MoS2) and machine oii
are used as lubrlcant and are ceated on both the tool and the tube. The tube
is fiared with the cylidrical tool until a failure such as buckling or rupturing
Forming Llmit and Its Imprevement in Thin-Walled Tube-End Flarlng 3
¢d
L/2
L/2
s£
rr --II
--p-
Ii
-1}t
,
,
v/
'
tro
¢do
Fig.
( ldler rotated )
/ / CyliRdrical/ ip D
Tu.bular specidieR
:::;::.:i'i:{:::: Chuck
flaring
N
with
L=N=do=
7S
315
35
mm
rpm
mm
a cylindrical
tool
1 Orbital rotary tool.
Table 1 Mechanical properties of the materials used.
Material
(JIS)6uterDia.do/mm 'ro/mm
ThicknessIWorkhardeniRgexponeRtn P}asticcoeff2cientF/MPa
Hardcopper(C1220-H)
e.6 o.e2 450'l3sl e.s e.o2 460
Softcopper(cm2e-e)
35 O.6 9.46 6eo
takes place. Then, the magnitude of the limiting flaring ratio 2c7) defined by
Eq. 1 at buckllng or rupturing can be obtained by measurlng the final outer
diameter, d, of the tube end and comparing k with the initial outer diameter,
do, of the tube end:
2c=(d-do>/d6- (1)Effects on Iimiting flaring ratio 2c were investigated of the diameter, D, of
the cylindrical tool, the half apex angle, r, of the tool-envelope-surface,
the feed displacement, L of the tool per revolution, the lubrication, the
wall thlckness, To, of the tube, and the work-hardening exponent, n, of the
tube material over the range shown in Table 2, To confirm the advantage
of using a cylindrical tool over using a con!cal tool, 2e for a cylindrical tool
have been compared wlth that for a conical tooL Furthermore, a comparison
4 K. KITAzAwA and J. SEiNO
Table 2 Experimental conditions.
Factors Conditions
Halfapexangletool-envelope-surfaee
o£
7/o15,20,3e,45
'6e,75
Feeddisplacementperrevoltitlon
oftoolf/MM・rev-t
o.el2s,o.os, o .1,O.7
Lubrication PastymolybdenumMachineoil
disulph!de,
Tubewallthickness To/mm O.6,O.8 (do=35 pata)
Diaraeterofcylindricaltool D/mm
15,2e,25,30
has also been made between Rc for the proposed rotary forming and that
for the conventional press forming.
3. EXPERIMENTALRESULTS
3. 1 Bnfavorable deformatieit modes
For the orbital rotary fiaring with a cylindrical tool, forming limits were
determined by the occurrence of severai unfavorable deformation modes such
as various kinds of bucklings and rupturings, as shown iR Fig. 2. The photo
in Fig.3 shows the defects formed on thin-walled hard copper tubes when
fiared to rupture or buckle with a cyliRdrical tooL
When r{iS200, necks occurred and propagated in the direction parallei
to the axis of tube as shown in Fig.3 (a), and finally, a rupturing occurred
along the necked regions. It should be stressed that this necking mode is
a characteristic mode in orbital rotary fiaring. In press flaring, it is well
(a)
Flg.
, ,
'f 11
Necking/ (b) Buckiing (c) Bulging (d) Buckling
Rupture at tool inle't near chuck2 Unfavorable deformation modes for tube-endrotary fiaring with a cylindrical tooL
(e) Week bulging in f!ared zone
fiaring by orbital
Forrning
Fig.
known that
meridlonal
Lirnit and Its Improvement iR Thin-Walled Tube-End Flaring
7=15e 7=20e 7=30e A.c=g.26 Ac=G.344 A.c=O.383 Buckling Bulging and Buckling with fiecking rupture at tool inlet
7=45e 7=6eO , 7=75e A.cmO.362 Ze=O.319 Ac=O.273 Buckling Blickling Buckling at tool inlet at too} iRlet at toel inlet
3 Unfavorable deformatioR modes in the process of orbitalrotary flarlng with a cylindrlcal tooL (Hard copper tube:
Outer diameter 35 mm; Wall thickness O. 6mm; D = 15mm;f=O.Imm/rev. Lubricant: Pasty rnolybdenum disulphide)
-!- tt -- -l.
tt :t
,
(a) Necking mode
Flg.4 Necking deve!oped press fiaring.
wall thickness disulphide)
necks started
direction as shown
ee,,ew=i'i"{''i"'afew/Li,k gee eqeegetw
a=300 a=45e Ac=e,325 Zc=O.351 (b) Necking and ruptupe
and rupture orlginated at the tube end and
at about 450 to the merldional direction iR (Hard copper tube: Outer diameter 35mm;
O.6mm. Lubricant: Pasty molybdenum
at the tube end aRd develQped at about
iR Fig. 4(a).
450 to
5
the
K. KITAzAwA and J. SEINo
On the other hand, in the range r}l:300, no necks occurred, and the form-
ing limit was determined by the onset of buckling at the tool iniet as shown
in Fig.2 (b). When r=30e, it is observed that the weak bulging mode shown
in Fig.2 (e) takes place after the above-mentioned buckling mode has taken
place. Furthermore, it is also found that the occurrence is restrained of
curling or waviness observed in the press flaring and orbital rotary flariRg
with a conical tool.
3.2 Forming limit
The relationship between the half apex angle of tool-envelope-surface r
and limiting flaring ratio 2c is shown in Fig.5 for two diameters of cylin-
drical tool D: 15 and 30 rnm. It is shown that 2c increases as r decreases,
O.6
o ct
o tsN o.4 tlt
.:
q O.2 ue ..H. 'G kH e.o o
Fig. 5 Influence between the ing falrlng thickness O.6 disulphide.
reaching a maximum
ases. As has been
occurrence ef neck
The shape of the 2c
case of D=15 mm,
Figure 6 shows the
2c. It is shown that
' -'-
/
OM :D :15 mm @tw:I)=3q mm
-. -ege --s.ee
"""-'Nhl op × NN
3o 6e gg Half apex angle of lt/e tool-envelope-surface
of the diameter of cylindrical tool D on the relationships
half apex angle of toel-envelpe-surface r and the limit- ratio 2c. (Hard copper tube: Outer diameter 35mm; wall
mm; f=O.1 mm/rev. Lubricant: Pasty rnolybdenum Otw: Buckling mode at tool inlet. []@: Other modes)
value at rr300, and then decreases as r further decre-
dlscussed above, in the range r)3eO, it is noted that the
and rupture observed in the range rl:i{200 is restrained.
curve in the case of D=:30 mm is similar to that in the
although 2c for D=:l5 mm !s grater than that for 30 mm.
dependence of tool diameter D on limiting fiarlng ratio
2c increases as D decreases and approaches a maximum
Forming Limit and Its Improvement in Thin・Walled Tube-End Flaring 7
O.5
x
.-O-jN
£ e.4
es:.
va
to O.3Tfi
".J
.E
A
--.e-NeNts
otw
r
:
ox
7=3oe7=45e
8x
Nx
7
×,.
× ±
gI
Fig.
/
e2 10 2e 30 4Q Diameter of cykndrical tool D/mm
6 Relationships between the diameter of cylindricalfiarlng ratlo 2c. (Hard copper
ness O.6 mm; f=O.1 mm/rev. Lubricant: Pastyphide. Otw: Buckling mode at tooKnlet)
ip D
tool and limitingtube: Outer diameter 35 mm; wall thick-
molybdenum disul-
value at about D= 20 mm. In the case of annealed copper tubes, the buckling
mode (Figs. 2 (c) and (d)) occurs in an early stage of fiaring. The effect of
tube wall thickness To on limiting flaring ratio Rc is shown in Fig. Z 2c in-
creases as To incerases. The effect of the feed displacement of tool per rev-
olution, f, on 2c is shown in Fig. 8. From thls figure, it is seen that 2c in-
creases as f increases.
4. DISCUSSION
From these experimental, results it is found that higher limiting fiaring
ratios are obtainable with cylindrical tools having smaller diameters, smaller
worltrhardening exponents of tube materials, smaller half apex angles of tool-
envelope-surfaces, Iarger wall thicknesses of tubes, and larger feed dis-
placements of tool per revolution as shown in Table 3. Considering production
cost, it is desirable that limiting flaring ratie increases as the feed displace-
ment of tool per revolution increases. It is recommended that the diame-
ter of the cylindrical tool is ha}f the outer diameter of the tube, considering
both the rigidity of cylindrical tool and the experimental results shown in
Fig. Z As shown in Fig. 8, it ls obvious that the limiting flaring ratio in
orbital rotary flaring increases as the feed displacement of tool per revolu-
tion increases, although the llmiting flaring ratio for the proposed rotary
forrning in Fig. 3 and those for the conventional press forming in Fig. 4
8
Table
K. KITAzAwA and J.
3 Method for improving
SEINO
flaring limit.
D/mpt f/mmrev To/mm 7/e n
X(--e.sdo) / / X(305) x/: High value, X :Low value
oKe--pptkua=.-fues
r--l
ig
bo=
'"'t
P.Hua
-"
e.6
O.4
O.2
o. o
g
"r'-gexastsz .-
l tw ee N N
N
OM : To= O.6 himtw pa : [I"o :O.8 mm
Fig.
o 3o 6o gg ' }lalf apex angle ef 7/e tool-envelope-surface '
7 Influence of tube wall thickness To on limiting flaring ratio 2c.(Hard copper tube: Outer diameter 35 mm; wall thicl<ness O.6 mm;
D=15 mm; f= O.1 mm/rev. Lubricant: Pasty molybdenum disulphide.O@: Buckling mode at tooHnlet. []tw: Other modes)
o K
o,r-
"ptkbo=J-suas
"--{
-tocr.etg-)lri
N.H"
O.5
O.4
e.3
O.2
-o
e/e7 -- 3oo
/x or×7=6oe
"t
Fig.
o.ol g.1 1.o Feed dispiacemeRt of the tool f/tum・rev'f
per revolution
8 Influence of the feed displacement of tool per reyolution f on !imiting
flaring ratio 2c. (Hard copper tube: Outer diameter 35 rnm; wall thick-
ness e,6 mm; D =15 mm. Lubricant: pasty molybdenum disulphide.O@: BuckHng mode at tool inlet)
Formlng Limit and Its Improvement in Thifi-Walled Tube-End Flaring 9
,.O, e.s O:Cylindrical teol : a=oo o tw:a=15e .H X @:ar3ee k O.4 to ¢ --.4 .r-l ts .・ ・-・a}-li・G g.:. o.3 N@k!iteta,.oge.N.ce-... '
IE S' O.2 o lg 2o 3e 4o (a) Eqtiivalent diameter Equivalent diameter of tool Deq/mm of tool Deq (b) 7=4se
Fig. 9 Infiuence of the equivalent diameter of tool Deq on limiting flaring ratio Rc. (Hard copper tube; Outer diameter 35 mm; Wall thickness O.6 mm. Lubricant: Pasty molybdenum disulphide)
are approximately the same. Thus, it is suggested that the forming limit
of orbital rotary forming is higher than that of press formlng.
In Re£ 3, orbital rotary flaring and nosing with a conical tool are de-scribed and forming limlts are reported except for the range r<450. From the
results of Ref. 3, the effects of D, r, f, To, and n on 2c are similar to the
above experlmental results. One of the main differences between the orbital
rotary formlng with a cylindrical tool and that with a conical tooi is in the
tool shape. To compare forming limits of both cylindrical and conical tools,
we have introduced the concept of "equivalent diameter of tool Deq" defined
in Flg. 9 (a). Figure 9 (b) compares fiaring limits of cylindrical and conical
tools by transforming results for conical tools into those for cylindrical tools
using Deq. It is found that the iimiting fiaring ratio for a cylindrical tool
is greater than that for a conical tooL Furthermore, the Iimiting fiaring
ratio increases with decreasing equlvalent diameter of tool for both cylin-
drical and conical tools. It is suggested that the equivalent diameter of tool
Deq has a major effect on the forming limit in orbital rotary forming.
The fitting behavior of tube to tool-envelope-surface is controlied by
contact area ratio defined as the ratio of the contact area to the total de-
formed area of the tube. 2) As has been discussed above, 2c increases with in-
creasing f and with decreasing Deq. On the other hand, the contact area ratio
decreases as both f and Deq decrease. Thus, it is suggested that the contact
area ratio does not seem to be a factor affecting 2c: the onset of buckling
at the too! lnlet ls indepeRdent of the contact area ratio. This burkling which
ssa
.tr.7 c
r;
;
:r?.1
×'.
:Z Deq× +-t
.-
10 K. KiTAzAwA and J. SEINOeccurred at the tool inlet is a local buckling of the mode, and propagated
in the circumferential direction of tube. 3) It was observed by Kitazawa et
al. 3) that it ls diMcult to predict the occurrence of the above 'buckling mode
by means of buckling load, and that the onses of buckling is affected b'y
local meal fiow. Thus, it is suggested that the effect of Deq on 2c is connected
closely with this local metai-flow phenomenon.
As has been mentioned above, from the viewpoint of how to improve
the formlng limit in orbital rotary flaring of thin-walled tubes, the method
for preventing buckling is the most important problem. In a previous paper, 3)
Kitazawa et al. have proposed the continuous lnclination method of the pass
schedule of conical tool in tube end flanging but we point out a difficulty in
applying this method to pi"eventing buckling that occurs at the tool iniet.
The motion of fingers in the potter's wheel process suggests a new idea,
the mothod for preventing buckling shown in Fig, 10, for the pass schedule
of a cy!indrical tool in the orbital rotary forming process. Then, we intro-
duced the modified inclination method of the pass schedule of a cyiindrical
tool shown in Fig. 10 (b). Th!s method is a process in which the tube at the
tool inlet is repeatedly flared to prevent buckling by using a cylindrical tool
( Idlep rotated )
Cylindrical tool
Z' , i' , 2[l'
l ,
Tubular
}
'
speclmeB
tC/ii3 '
(a) IRclination method
iZ ! ii])/1[ii
-t , ,
(b) Proposed method ( Modified inclination method )
method for the preventing of the buckling
'
Fig. Ie Proposed at tool inlet.
Forming Limit and Its Imprevement in Thin-Walled Tube-End Fiaring
tts,
wa
me
tttttt l
t"t
11
Single process IRciiRatioB method Proposed method (Ac=e.319) (Zc=O,455) (Ac=e.692)
Flg. 11 Effect of the proposed method on forming 11rnit. (r=60e. Hard copper tube: Outer diameter 35 mrn; Wal! thickness O.6 mm; D==15 mm; f=O.l rnm!rev. Lubricant: Pasty molybdenum disulphide)
with a small angle r uRder applicatioR of the above inclination method. Figure
11 shows that the buckling mode is prevented under the proposed prevent-
ing condition so that the forming Iimit is dramatically improved.
Therefore, the proposed orbital rotary flaring with a cylindrical tooi is
likely to be a hopefully practical working process from. the viewpoint of
formlng limit.
5. CONCLUSION
The possibility of the tube end flaring using orbital rotary £orming with
a cylindrical tool has been experimentally investigated from the viewpoint
of forming limit by using thin-walled copper tubes, The resuks are summa-
rized as follows:
1) Forming limits were determined by the occurrence of several unfavor-
ab!e deformation modes such as various kiRds of bucklings and rupturings.
In the range r:;E{200, a rupture mode occurred and propagated in the direc-
tion parallel to the axis of tube. On the other hand, ln the range rk300,
the forming limit was determined by the onset of buckling at the tool inlet.
2) It was found that higher limiting fiaring ratios are obtainab!e with
cylindrical tools having smaller diameters, smaller work-hardening exponents
of tube materials, smaller half apex angles of tool-envelope-surfaces, larger
wall thicknesses of £ubes, and larger feed displacements of tool per revoltt-
tion. The forming limit of orbital rotary forming is higher than that of
press forming.
3) It was found that the limiting fiaring ratio for a cylindrical tool is great-
er than that for a conical tooL The equivalent diameter of tool Deq has
12 K. KITAzAwA and J. SEINoa major infiuence on the forming limit in orbital rotary forming. It is recom-
mended that the diameter of cylindrical tool should be half the outer dia-
meter of tube.
4) A modified inclination method in which the tube at the tooi inlet is
repeatedly fiared by using a cylindricai tool with a small angle r during tube-
end fiaring, is introduced to prevent buckling. Then, lt was found that the
bucklng mode is prevented under the proposed preveRting condition so that
the forming limit is dramatically improved.
'
Ael{nowledgment
The authors would like to thank Dr. Matsuo Miyagawa, Dr. Hisashi
Nishimura and Dr. Ken-ichi Manabe for their advice. The authors are also
indebted to Mr. Akira Fujita and Mr. Nobukazu Tsutsumi for producing the
tooling.
REFERENCES
(1) K. Kitazawa, M. Kobayashi and H. Maruno: Proc. 1986 Japan Spring Conf. Tech-
nology of Plastlcity, 343-346 (1986).
(2) K. Kitazawa, M. Kobayashi and H. Maruno: Journal of the Japan Society for Tech-
nology of Plasticlty, Vol.29, No.330, 767-774 (1988).
(3) K. Kitazawa, M. Kobayashl and H. Maruno: Journal of the Japan Society for Tech-
nology of Plasticity, Vol.30, No.344, 1259-1266 (1989).
(4) K. Kitazawa and M. Kobayashi: Proc. 37th Japan Joint Con£ Technology of Pla- sticity, 349-352 (1986).
(5) K. Kitazawa, J. Seino and K. Fujita: Proc. 40th japan Joint Conf. Technology
of Plasticity, 37-4e (1989).
(6) K. Kitazawa, M. Iida and M. Kobayashl: Proc. 1989 Japan Spring Conf. Tech-
nology of Plasticity, 343-346 (1989).
(7) K. Manabe and H. Nishimura: Journal of the Japan Society for TechnQlogy of
Plasticity, Vol.24, No.266, 276-282 (1983).