Th ese are sim p lified fo rm u lae wh ich , h o wever, are su fficien t in p rac- t ice fo r ap p ro xim at e calcu lat io n s. Th e ben d in g wo rk W
b
[Nm ] am o u n t s t o :
if t h e p at h o f t h e p u n ch fro m im p act wit h t h e sh eet m et al u n t il t h e en d o f t h e ben d in g p ro cess is d esign at ed as h [m ]. Th e co n st an t valu e x
t akes in t o acco u n t t h e u n even fo rce p ro gressio n alo n g t h e p at h o f t h e p u n ch an d gen erally lies bet ween x = 0.3 an d 0.6, d ep en d in g o n ben d -
in g req u irem en t s an d m ach in e set t in g.
Exa m ple:
If a 2 m m t h ick alu m in iu m sh eet AlMg5Mn m easu rin g 50 m m wid e wit h a m in - im u m t en sile st ren gt h o f R
m
=280 N m m
2
is ben t in a V-d ie wit h a wid t h o f w = 15 m m u sin g a p u n ch d isp lacem en t of h = 7 m m , th e resu ltin g ben d in g force
is:
W h en ben d in g u sin g a V-d ie, t h e p ro cess fact o r x = 1 3. Th e ben d in g wo rk t h u s am o u n t s t o :
4.8.2 Roll forming and variety of sections
Process Ro ll fo rm in g is cat ego rized acco rd in g t o DIN 8586 as a m et h o d o f fo rm -
in g by ben d in g u sin g a ro t ary d ie m o t io n cf. Fig. 2.1.3
. Du rin g ro ll fo rm in g, t h e sh eet co il o r blan k is fo rm ed in a st ep less an d co n t in u o u s
373
Bending
F b s
R w
N w s
F s
w b s
R w
N w s
b s
m
b s
m
= ⋅ ⋅
[ ]
≥
= + ⋅ ⋅ ⋅ ⋅
[ ]
2
2
10
1 4
10 fo r
o r fo r
W x F
h Nm
b b
= ⋅ ⋅
[ ]
,
F mm mm N mm
mm N
b
= ⋅
⋅ =
50 4 280 15
3 733
2 2
,
W N
m Nm
J
b
= ⋅ ⋅ = = 1
3 3 733 0 007 8 7 8 7
, .
. .
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
p rocess to create p rofiles with th e aid of rollers Fig. 4.8.6
. On e p air of rollers is req u ired p er form in g stage
Fig. 4.8.7 . Th e ad van tage of th e
sh ap in g p rocess, com p ared to oth er ben d in g m eth od s, is th at sh eet strip s of an y len gth can be form ed at a relatively h igh sp eed .
Basic section geom etries Sect io n s are m an u fact u red in st ep s u sin g a co m bin at io n o f sim p le basic
ro ll fo rm s: – Rolling: Th e ed ge o f a p ro file is sh ap ed by m o re t h an 180°. Th ree d if-
feren t co n figu rat io n s are m o st co m m o n ly u sed Fig. 4.8.8
.
374
Sheet metal forming and blanking
Fig. 4.8.5
Bending in the V-die h
die punch
w orkpiece
Fig. 4.8.6 Pair of forming rolls:
last forming stage
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
– Folding: st ep -by-st ep ben d in g o f st raigh t legs aro u n d a co m m o n p o in t Fig. 4.8.9
. – Beading: recesses in t h e p ro file, e. g. fo r rein fo rcem en t
Fig. 4.8.10 .
– Doubling: Th e m at erial is d o u bled back o n it self, fo r exam p le at t h e ed ges
Fig. 4.8.11 .
375
Bending
Fig. 4.8.8 Rolling: a eye: circular shape w ith only one radius; b oval: circular shape, made
up of several radii; c loop: material not entirely bent over
a b
c
Fig. 4.8.7
Roll forming: roll bending in several stages
Fig. 4.8.9
Folding
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
Application exam ples By com bin in g th e basic sh ap es, it is p ossible to m an u factu re an y op tion -
al section Fig. 4.8.12
to 4.8.17
. Figure 4.8.18
illu strates th e step -by-step m an u factu re of a sp ecial section geom etry.
Roll bending radius Du rin g t h e ro ll ben d in g p ro cess, t h e act u al ben d in g rad iu s m u st be
bet ween t h e m axim u m an d t h e m in im u m ad m issible ben d in g rad iu s:
wit h t h e m o d u lu s o f elast icit y E [N m m
2
], t h e yield st ren gt h R
eL
o r R
p 0,2
[N m m
2
] cf. Sect . 4.2.2
an d t h e m at erial co efficien t c [–] in acco rd an ce wit h
Table 4.8.3 .
376
Sheet metal forming and blanking
Fig. 4.8.10
Beading
Fig. 4.8.11
Doubling
Fig. 4.8.12
UC and rail sections
r s E
R mm
r s c
i eL
i max
min
= ⋅
⋅
[ ]
= ⋅ 2
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
377
Bending
Fig. 4.8.13
Hat sections
Fig. 4.8.14
Angular, L and Z sections
Fig. 4.8.15 T and omega sections
Fig. 4.8.17 Wide strip sections
Fig. 4.8.16
Closed sections
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
Exa m ple:
W h en ro ll fo rm in g wit h 2 m m t h ick st rain h ard en ed sh eet st eel in St 37-2 m at erial n u m ber 1.0037 wit h t h e m o d u lu s o f elast icit y E = 2.1 · 10
5
N m m
2
fo r st eel an d yield st ren gt h R
eL
= 220… 240 N m m
2
t h e u sefu l rad iu s ran ge is calcu - lat ed as fo llo ws:
Th e act u al rad iu s wh en ben d in g at righ t an gles t o t h e ro llin g d irect io n sh o u ld t h u s be at least 1 m m in size.
378
Sheet metal forming and blanking
r mm
N mm N mm
mm mm
r mm
mm
i i
max min
. ,
. =
⋅ ⋅
⋅ =
= =
⋅ =
2 2 1 10
2 240 210 000
240 875
2 0 5
1
5 2
2
3 6
7 8
9 3
6 9
8 7
Fig. 4.8.18
Step-by-step manufacture of a section using 20 rolls
flow er diagram
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
Roll form ing lines Ro ll fo rm in g lin es are classified acco rd in g t o t wo d ifferen t o p erat in g
m o d es. Start-stop lin es co n sist in t h eir sim p lest fo rm o f a d eco iler, a co il lo o p , a ro ll fo rm in g m ach in e an d a p art in g d ie. Th e p ro d u ct len gt h is
d et erm in ed by t h e ro ll fo rm in g m ach in e Fig. 4.8.19
. Du e t o t h e u se o f t h e st art -st o p m et h o d , blan kin g an d em bo ssin g o p erat io n s are also p o s-
sible u sin g t h e ro ll fo rm in g m ach in es p o sit io n in g syst em . Continuous running roll form ing lines o p erat e at a co n st an t sp eed . Th is
t yp e o f lin e is u sed t o p ro cess sh eet m et al blan ks o r st rip s t o creat e lo n g sect io n s. W h ile o n blan k p ro cessin g lin es cu t -t o -len gt h blan k m et al
379
Bending Table 4.8.3: M aterial coefficient c for the calculation of r
i min
M aterial coefficient c M aterial
Bending direction compared to rolling
direction of sheet M aterial soft
annealed M aterial strain
hardened Al transverse 0.01 0.30
longitudinal 0.30 0.80 Cu transverse 0.01 1.00
longitudinal 0.30 2.00 M s 67, M s 72,
transverse 0.01 0.40 CuZn 37 longitudinal 0.30 0.80
St 13 transverse 0.01 0.40 longitudinal 0.40 0.80
C 15 – C 25 transverse 0.10 0.50
St 37 – St 42 longitudinal 0.50 1.00 C 35 – C 45
transverse 0.30 0.80 St 50 – St 70 longitudinal 0.80 1.50
Fig. 4.8.19
Start-stop roll forming line decoiler w ith coil
infeed unit coil loop roll forming machine
straightening machine outfeed roller conveyor
parting device
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
sh eet s are p ro cessed , wh en u sin g a sh eet st rip p ro cessin g lin e t h e p ro - d u ced p ro file is p art ed aft er ro ll fo rm in g u sin g au t o m at ic cu t -t o -len gt h
d evices. Th e ad van t age o f a blan k p ro cessin g lin e is t h at t h e co m p lex p ro -
file p art in g d ie can be su bst it u t ed by a sim p le cro ss-cu t t in g sh ear. Th is elim in at es t h e n eed fo r co st ly d ie in sert s, a p art icu larly im p o rt an t co n -
sid erat io n wh ere d ifferen t p ro file sh ap es o r wid t h s are bein g p ro cessed . Ho wever, a fu rt h er p o in t o f co n sid erat io n is t h at t h is m et h o d req u ires a
cert ain m in im u m sh eet len gt h , as t h e feed fo rce o f t h e ro llers m u st always be great er t h an t h e t o rq u e n ecessary fo r t h e fo rm in g p ro cess
wh ich h as t o be o verco m e. Fu rt h erm o re, ad eq u at e p ro visio n m u st be m ad e t o en su re efficien t blan k gu id an ce.
Th e ben efit o f a co n t in u o u sly o p erat in g lin e p ro d u cin g o ff t h e co il is it s h igh er o u t p u t wh en p ro cessin g great er p ro file len gt h s. Th is p ro d u c-
t io n m et h o d is essen t ial if co n t in u o u sly ru n n in g p ro cesses su ch as lo n - git u d in al seam weld in g, glu in g, fo am in g, et c. h ave t o be in t egrat ed d u r-
in g p ro filin g, o r wh ere wit h resp ect t o t h e m ach in e size excessive m ass- es wo u ld h ave t o be accelerat ed .
In p ract ice, t h e basic fo rm s o f t h is p ro cessin g t ech n iq u e are fre- q u en t ly u p grad ed , eit h er d u e t o in su fficien t o u t p u t o r becau se ad d i-
t io n al p u n ch ed p at t ern s h ave t o be t aken in t o co n sid erat io n . In t h is case, d o u ble lo o p lin es wit h a sep arat e p u n ch in g d evice are u sed .
To keep set-u p tim es to a m in im u m , roll form in g lin es are freq u en tly eq u ip p ed with d u al swivel-m ou n ted d ecoilers cap able of accom m od at-
in g two coils an d coil en d weld in g m ach in es. Th e coil en d weld in g m ach in es join th e en d of th e p reviou s coil to th e start of th e n ext on e,
savin g n ot on ly th e tim e req u ired for feed in g in a n ew coil bu t also red u cin g th e am ou n t of scrap gen erated at th e start an d en d of each coil.
Die changeover techniques with roll stand sets and rolling dies To allo w d ifferen t sect io n sh ap es t o be m an u fact u red o n a sin gle p ro -
d u ct io n lin e, vario u s ro ll ch an geo ver t ech n iq u es are available. Th e ro llin g d ies are m o u n t ed o n rigid st an d s o r o n st an d s wit h t elesco p ic
ro ll set o r d irect ly m o u n t ed o n t h e gear blo cks Fig. 4.8.20
. Th e st an d s are co n n ect ed t o t h e gear u n it s o f t h e ro ll fo rm in g m ach in e by m ean s
o f u n iversal jo in t d riven card an sh aft s. W idth adjustable roll sets p erm it th e m an u factu re of p rodu cts with dif-
feren t web width s an d leg h eigh ts u sin g a com m on roll set Fig. 4.8.21
.
380
Sheet metal forming and blanking
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
Th e ro ll st an d fo r profile roll changeover is u sed fo r t h e m an u fact u re o f co m p act sect io n s wit h fixed d im en sio n s. Ho wever, if sp acers are m an u -
ally in sert ed in t o each st an d , it is also p o ssible t o m an u fact u re sect io n s wit h d ifferen t wid t h s
Fig. 4.8.22 . Bo t h st an d t yp es – rigid an d wit h
t elesco p ic ro ll set – p erm it t h e ro llin g d ies t o be exch an ged by d et ach - in g t h e fro n t st an d u p righ t . Ho wever, t h is in vo lves lo n g set -u p t im es.
Drive shaft changeover o ffers a co m p ro m ise bet ween exch an gin g in d i- vid u al ro llers an d exch an ge o f a co m p let e st an d . At a sp ecial wo rk st a-
t io n eq u ip p ed wit h a su it able cran e h arn ess, t h e u p p er an d lo wer d rive sh aft s are exch an ged t o get h er
Fig. 4.8.23 . Th is h elp s t o avo id set -u p
erro rs an d saves t h e n eed fo r a seco n d st an d set . Th e t im e req u ired fo r t h is ch an geo ver p ro cess lies so m ewh ere bet ween t h at req u ired fo r
exch an gin g ro llers an d t h at req u ired wh en u sin g p allet s fo r t h e st an d s.
381
Bending
Fig. 4.8.20 Roll stands
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
It is also p ossible to u se a sep arate set of stan d s for each d ifferen t sec- tion . Th is p erm its n ot on ly fast resettin g bu t also a h igh d egree of p rocess
reliability an d rep eat accu racy Fig. 4.8.24
. For stand changeover th ere are two d ifferen t ch an geover tech n iq u es p ossible:
– Exch an ge o f in d ivid u al p allet s u sin g a cran e: Pallet ch an geo ver is ad visable wh ere sh o rt set -u p t im es are req u ired . Th e ro ll fo rm in g
382
Sheet metal forming and blanking
Fig. 4.8.21
Width adjustable telescopic roll set
gear box cardan shaft telescopic shaft
w idth adjustment forming roll
frame
Fig. 4.8.22
Roll stand for exchange of section rolls
gear box cardan shaft forming roll shaft
w idth adjustment frame
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
st an d s, fo r exam p le t h ree o r fo u r, are m o u n t ed in a fixed set t in g o n p allet s t o get h er wit h t h e ro lls. Th e p allet s are raised u sin g a cran e. Fo r
fast en in g an d cen t erin g, m ech an ical o r h yd rau lic syst em s are u sed d ep en d in g o n t h e level o f au t o m at io n .
– Exch an ge o f in d ivid u al p allet s o r co m p let e set s o f ro lls an d st an d bearin gs: Fo r fu lly au t o m at ic reset t in g, t h e t o o l p allet s are exch an ged
u sin g a rack h an d lin g syst em . Th is m et h o d is m o re eco n o m ical wh ere freq u en t reset t in gs are req u ired .
4.8.3 Roller straightening
