4 Sheet metal forming and blanking
4.7 Fine blanking
In p ractice, fin e blan kin g is also kn own by th e term s p recision blan kin g or fin e stam p in g. Th e p rodu ction p rocess in volves sh ear blan kin g for th e
m an u factu re of p arts with a sm ooth cu t su rface. Like stan dard sh ear blan kin g, accordin g to DIN 8580 fin e blan kin g falls u n der th e m ain cate-
gory of m aterial sep aration or p artin g p rocesses, an d is defin ed accordin g to DIN 8588 u n der th e su b-category dividin g cf.
Fig. 2.1.2 . Com p ared to
stan dard sh ear blan kin g, also kn own as n orm al blan kin g cf. Fig. 4.5.1
, h owever, differen t p rocess p aram eters ap p ly, resu ltin g in a h igh er work-
p iece q u ality. Th e basic co n cep t o f fin e blan kin g is t h at , in co n t rast t o st an d ard
blan kin g, t h e m at erial is sep arat ed aft er bein g clam p ed o n all sid es o n ly as a resu lt o f m at erial flo w, i. e. wit h o u t a fract u red su rface cf.
Fig. 2.1.30 .
4.7.1 Fine blanking process
Advantages of fine blanking Ap art fro m t h e q u alit y-relat ed ad van t ages o f fin e blan kin g, co st -effec-
t iven ess is also a d ecisive fact o r in favo r o f t h e ap p licat io n o f t h is p ro cess. Sp ecific blan k-relat ed ad van t ages co m p ared t o n o rm al sh ear
blan kin g in clu d e: – sm o o t h blan ked su rfaces free fro m fract u re an d t earin g wh ich are
able t o fu lfil fu n ct io n s wit h o u t t h e n eed fo r rewo rkin g, – ext en d ed field o f ap p licat io n fo r sh ear blan kin g,
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
– sm aller d im en sio n al t o leran ces, – co n sist en t d im en sio n s t h ro u gh o u t a co m p let e series ru n , d u e t o
breakt h ro u gh s in t h e cylin d rical blan kin g p lat e. Process-related advantages are:
– n o blan kin g sh o ck an d t h e co n seq u en t red u ct io n o f n o ise levels an d vibrat io n s,
– fewer p ro d u ct io n st ep s in t h e p ro cessin g o f blan ked an d co m bin ed blan ked fo rm ed p art s.
As an exam p le, Fig. 4.7.1
illu st rat es t h e p ro d u ct io n o f a ch ain wh eel fo r a m o t o r cycle u sin g t h e co n ven t io n al an d fin e blan kin g m et h o d s. Th e
n in e wo rk o p erat io n s req u ired d u rin g co n ven t io n al p ro d u ct io n , in - clu d in g blan kin g o n in d ivid u al p resses an d m ach in in g t h ro u gh d ebu r-
rin g an d grin d in g, can be red u ced by u sin g t h e fin e blan kin g t ech n iq u e in a co m p let e blan kin g d ie t o t h ree o p erat io n s. Fin e blan kin g is also
m o re ad van t ageo u s h ere if we co n sid er t h e n eed fo r t im e-co n su m in g an d co st -in t en sive m ach in e ch an geo ver u sin g co n ven t io n al m et h o d s.
331
Fine blanking
Fig. 4.7.1
Conventional chain w heel production for a motor cycle top row : 1. blanking the outside contour; 2. piercing the inside hole; 3. piercing four w indow s;
4. levelling; 5. turning the inside hole and chamfering on both sides; 6. milling the teeth in the stack; 7. bevel turning of tooth tips on both sides;
8. boring holes and deburring; 9. grinding Production using fine blanking bottom row :
1. fine blanking; 2. bevel turning of tooth tips on one side, the second side already has the die-roll by the fine blanking process; 3. deburring
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
Th e fin e blan kin g p ro cess u sin g co m p o u n d p ro gressive d ies cf. Sect . 4.1.1
co m p rises o n ly t h ree st ages Fig. 4.7.2
: – free blan kin g wit h p ilo t p in s,
– em bo ssin g t h e ad d en d u m flan ks an d p iercin g t h e cen t er h o le, – cu t t in g o u t t h e t o o t h ed area an d ch am ferin g t h e cen t er h o le.
Th is m et h o d can lead t o p ro d u ct io n co st savin gs o f aro u n d 80 co m p ared t o co n ven t io n al m et h o d s.
Die principle Th e ad van tages of fin e blan kin g are based u p on d ifferin g p rocess p ara-
m eters. Du rin g fin e blan kin g, th ree forces act via th e d ie on th e p u n ch ed m aterial
Fig. 4.7.3 left. Before th e start of blan kin g, a vee-rin g is p ressed
over th e p ressu re p late ou tsid e th e blan kin g lin e with th e vee-rin g force F
R
. In sid e th e blan kin g lin e, th e m aterial is p ressed by th e cou n terforce F
G
via th e ejector on to th e blan kin g p u n ch . In th e clam p ed statu s, th e blan kin g p rocess is carried ou t by th e blan kin g force F
S
.
332
Sheet metal forming and blanking
Fig. 4.7.2
Strip layout for a three-station compound progressive die w hen manufacturing a chain w heel
open blanking with pilot forms
embossing of tooth head be els and punching of
the central hole cutting out the teeth and
chamfering the central hole pilot pin
throughfeed direction
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
O n ce t h e blan kin g p ro cess is co m p let ed , t h e vee-rin g fo rce an d co u n - t erfo rce are bo t h d eact ivat ed , t h e d ie o p en s an d aft er a cert ain o p en in g
st ro ke t h e scrap web an d t h e in n er fo rm slu gs are st rip p ed o ff t h e p u n ch by t h e st rip p in g fo rce F
Ra
Fig. 4.7.3 right . Th e fin e blan ked wo rkp iece is
eject ed fro m t h e blan kin g p lat e by t h e eject io n fo rce F
Ga
. Supplem entary forces and functions
In fin e blan kin g p resses, th e slid e always works from th e bottom u p ward s. Th e slid e stroke is d ivid ed in to a rap id closin g, tou ch in g, blan k-
in g an d a rap id retu rn travel Fig. 4.7.4
. Du rin g th e blan kin g p rocess, th e vee-rin g p iston an d cou n terforce p is-
ton are d isp laced u n til th e com p letion of th e blan kin g p rocess. Du rin g th e retu rn m ovem en t of th e slid e, th e p art is ejected from ou t of th e
blan kin g p late by th e ejector p u n ch , th e in n er form slu g is strip p ed by th e ejector p in an d both are th en rem oved from th e d ie m ou n tin g area
by m ean s of an air jet or rem oval arm . Th e coil feed cycle also takes p lace d u rin g th e retu rn m ovem en t of th e slid e. Ju st before th e slid e reach es th e
bottom d ead cen ter, th e crop p in g sh ear sep arates th e scrap web.
333
Fine blanking
Fig. 4.7.3
left: Tooling principle of a fine blanking die during blanking right: Tooling principle of a fine blanking tool after ejection of the blank, stripping of
the inner form slug and the scrap w eb h
f i
blanking punch
blanking plate inner form punch
ejector inner form ejector
vee-ring plate pressure pin
scrap w eb fine blanked part
inner form slug vee-ring
blanking force F
S
vee-ring force F
R
stripping force F
Ra
ejection force F
Ga
counter- force F
G
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
Blanking force-stroke diagram Figure 4.7.5
co m p ares t h e variat io n o f t h e blan kin g fo rce o ver t h e slid e st ro ke o r t h e t im e req u ired fo r n o rm al blan kin g t o t h at req u ired fo r fin e
blan kin g. Du rin g n o rm al blan kin g, t h e sh eet m et al is in it ially elast ical- ly d efo rm ed o n im p act o f t h e blan kin g p u n ch I an d t h en cu t II. In
p h ase III, t h e p art t ears t h ro u gh , an d in p h ase IV t h e syst em vibrat io n s in t h e m ach in e an d d ie d ecay in all t h ree d irect io n s cf.
Fig. 4.5.1 . Th is
is t h e p h ase in wh ich t h e great est d ie wear t akes p lace. Du rin g fin e blan kin g, t h e t earin g an d t h e vibrat io n p h ases are elim in at ed . Th e sp e-
cial p ro cess p aram et ers in vo lved in fin e blan kin g p reven t t h e su d d en breakt h ro u gh o f t h e p art , en su rin g a sm o o t h cu t o ver t h e en t ire sh eet
m et al t h ickn ess. Blanking clearance
Th e blan kin g clearan ce is t h e d im en sio n al d ifferen ce o r gap bet ween t h e blan kin g p u n ch an d t h e blan kin g d ie m easu red o n a sin gle sid e.
334
Sheet metal forming and blanking
Fig. 4.7.4
Supplementary forces and functions during the slide stroke rapid closing stroke
tracing stroke blanking stroke
rapid return travel stroke
movement sequence vee-ring piston
movement sequence counterforce piston
cycle for removalair jet ejection of parts and scrap
feed cycle of the punched material
scrap seperator cycle slide
stroke [mm]
BDC BDC TDC
time [s]
time [s] supple-
mentary functions
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
Th e sm o o t h sect io n o f t h e cu t su rface an d t h e blan kin g clearan ce are clo sely relat ed : t h e great er t h e blan kin g clearan ce, t h e lo wer t h e
sm o o t h cu t p ro p o rt io n . In ad d it io n t o it s size, t h e u n ifo rm it y o f t h e gap alo n g t h e p art co n t o u r is also im p o rt an t . Th e gap sh o u ld rem ain co n -
st an t wh en su bject ed t o lo ad d u rin g t h e blan kin g o p erat io n . Th e size o f t h e blan kin g clearan ce is p rim arily d et erm in ed by t h e
sh eet m et al t h ickn ess t o be cu t , bu t also by t h e n at u re an d st ren gt h o f t h e wo rkp iece m at erial. In co n t rast t o t h e blan kin g clearan ce o ccu rrin g
d u rin g st an d ard blan kin g o f aro u n d 5 t o 10 o f t h e sh eet m et al t h ick- n ess, t h e co rresp o n d in g valu e fo r fin e blan kin g lies at aro u n d 0.5
Fig. 4.7.6 . In cert ain cases, t h e blan kin g clearan ce can also vary o ver
t h e p art co n t o u r. Part s wit h t o o t h in g, fo r exam p le, are m an u fact u red wit h a blan kin g clearan ce wh ich is great er in t h e area o f t h e t o o t h ro o t
t h an it is at t h e t o o t h t ip . Vee-ring
Th e vee-rin g is a ch aract erist ic feat u re o f fin e blan kin g d ies. It ru n s in t h e fo rm o f a raised serrat ed jag at a d efin ed d ist an ce fro m t h e blan kin g
lin e an d is p ressed in t o t h e scrap web. It s fu n ct io n is t o h o ld t h e p u n ch ed m at erial o u t sid e t h e blan kin g lin e an d so p reven t lat eral flo w
o f t h e m at erial d u rin g t h e blan kin g p ro cess. In ad d it io n , it serves t o ap p ly co m p ressive st ress t o t h e sh eet m et al, so im p ro vin g t h e flo w
p ro cess. To sim p lify m ain t en an ce, wh ere sh eet m et al t h ickn esses o f u p t o
4.5 m m are bein g p ro cessed , t h e vee-rin g is m o u n t ed o n t h e p ressu re
335
Fine blanking
Fig. 4.7.5
Press force-stroke curves for standard and fine blanking I II
III IV
blanking force
F
s
time [s], stroke [mm] F
F
s max Abriß
standard blanking
fine blanking
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
336
Sheet metal forming and blanking
2 4 6 8 10 12 14 16
0.2 0.4
0.6 0.8
1.0 1.2
1.4 1.6
sheet metal thickness s [mm] standard
blanking
fine blanking bl
an k
cl ea
ra nc
e u
[m m
]
Fig. 4.7.6 Guideline values for the blank-
ing clearances for standard and fine blanking in function
of sheet metal thickness s
Fig. 4.7.7
Guideline values for vee-ring dimensions 45
° 45
°
R R
H
R
A
blanking plate A
H
R
R 2.8 - 3.2
2.5 0.6
0.6 3.3 - 3.7
2.5 0.7
0.7 3.8 - 4.5
2.8 0.8
0.8
[mm ] [mm]
[mm] [mm]
A
r R
r R
H
R
h
R
45 °
45 °
45 °
45 °
0.1mm 4.5 - 5.5
2.5 0.8
0.8 0.5
0.2 5.6 - 7.0
3.0 1.0
1.0 0.7
0.2 7.1 - 9.0
3.5 1.2
1.2 0.8
0.2 9.1 - 11
4.5 1.5
1.5 1.0
0.5 1 1.1 - 13
5.5 1.8
2.0 1.2
0.5 13.1 - 15
7.0 2.2
3.0 1.6
0.5 A
H
R
R h
R
r
sheet metal thickness
sheet metal thickness
.
[mm] [mm]
[mm] [mm] [mm] [mm]
vee-ring plate
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
p late of th e d ie, wh ile for th icker m aterials a secon d vee-rin g is req u ired on th e blan kin g p late. W h ere th e in n er form s are p articu larly large, th e
ejector also featu res a vee-rin g, wh ich is p ressed in to th e in n er form slu gs in sid e th e blan kin g lin e. Dep en d in g on th e th ickn ess an d sh ap e of th e
p art, th e vee-rin g is bein g in creasin gly p laced on th e d ie p late. In in d i- vid u al cases, fin e blan kin g also takes p lace with ou t th e u se of a vee-rin g.
Th e d im en sio n s o f t h e vee-rin g an d t h e d ist an ce fro m t h e blan kin g ed ge d ep en d o n t h e t h ickn ess o f t h e sh eet m et al
Fig. 4.7.7 . In so m e
cases, vee-rin gs are m o u n t ed o n ly p art ly in t h e d ie area wh ere a sm o o t h cu t is req u ired fo r fu n ct io n al reaso n s.
W ork result Gen erally, n orm al blan ked p arts featu re a sm ooth an d a fractu red cu t su r-
face Fig. 4.7.8
. Th e p rop ortion of th e sm ooth p ortion relative to th e fractu red su rface d ep en d s on a wid e n u m ber of d ifferen t in flu en cin g vari-
ables, with for exam p le as little as
1 4
sm ooth to
3 4
fractu red su rface. Th e sm ooth area featu res th e d ie-roll, wh ile on th e op p osite sid e is th e blan k-
in g bu rr cf. Sect. 4.5
. Th e flatn ess an d d im en sion al toleran ces of th e stan d ard blan ked p art are in ferior. Th e fin e blan ked su rface, in con trast,
is tear an d fractu re-free over th e en tire th ickn ess of th e sh eet m etal an d
337
Fine blanking
Fig. 4.7.8
Work result for standard blanking left and fine blanking right
s s
burr fracture zone
blanking punch vee-ring plate
blanking plate ejector
smooth cut zone die-roll
u ~ 5 s u ~ 0,5 s
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
Steel group Group
Abbreviation M aterial no.
as per DIN as per EURO standard
soft, unalloyed steels hot strip
1614 StW22
1.0332 FeP11
EN111 metal sheet
1623 St14
1.0338 FeP04
EN10130 cold strip
1624 St4
1.0338 general structural steels
17 100 St37-3N
1.0116 Fe360D1
EN10025 St44-3N
1.0144 Fe430D1
EN10025 fine-grain structural steels 17 102
StE420 1.8902
S420N EN10113-2
StE460 1.8905
P460N EN10028-3
case hardening steels 17 210
Ck15 1.1141
16M nCr5 1.7131
heat-treatable steels 17 221
Ck45 1.1191
2C45 EN10083-1
17 222 41Cr4
1.7035 41Cr4
EN10083-1 17 200
42CrM o4 1.7223
42CrM o4 EN10083-1
tool steels 17 350
100Cr6 1.2067
C85W 1.1830
stainless steels 17 440
ferritic X6Cr13
1.4000 X30Cr13
1.4028 austenitic
X5CrNi18.10 1.4301
Aluminium and aluminium alloys Copper and copper alloys
Abbreviation M aterial no.
as per DIN Abbreviation
M aterial no. as per DIN AlM g3
3.3535 1745
CuZn37 2.0321
17670 AlM gSi1
3.2315 1745
CuSn8 2.1030
17670 CuNi25
2.0830 17670
ap p roxim ately vertical relative to th e su rface of th e sh eet m etal. Th e fin e blan ked p art is also flat t er t h an a st an d ard blan ked p art .
4.7.2 Fine blanking materials, forces, quality characteristics and part variety
Kategori