W h en p ro d u cin g sm all sh eet m et al co m p o n en t s su ch as d rawer slid es, d isc carriers fo r au t o m at ic t ran sm issio n s, wish bo n es, bicycle
brake levers et c., t h e co il st o ck can be fed d irect ly t o t h e p ress by a co il lin e cf.
Fig. 4.3.1 . Th e sh eet m etal form in g p rocess takes p lace in a com -
p act p iece of eq u ip m en t, gen erally a h igh -sp eed p ress cf. Fig. 4.6.6
, a u n iversal cf.
Fig. 4.4.1 or tran sfer p ress cf.
Fig. 4.4.23 .
Th e fin ish ed p art s are p allet ized eit h er m an u ally o r by u sin g a st ack- in g d evice cf.
Fig. 4.4.41 an d m ad e read y fo r d o wn st ream p ro cessin g,
fo r exam p le weld in g, p ain t in g o r h em m in g. At t h e sam e t im e, scrap d is- p o sal t akes p lace.
For th e in trod u ction of n ew d ies for large p arts an d tran sfer p resses, try-ou t p resses cf.
Fig. 4.1.19 an d
4.1.20 an d sim u lators cf.
Fig. 4.1.24 are em p loyed . Th ese are u sed by th e d ie sh op to p rep are toolin g as well
as t ry-o u t o f t h e d ies befo re t h e fin al t ry-o u t o n t h e act u al p ro d u ct io n p ress.
Th is sh o rt en s t h e d ie t ry-o u t t im e o n t h e p ro d u ct io n p resses su b- st an t ially fo r o bt ain in g t h e first O K p art s. Co n seq u en t ly, t h is p ro ced u re
sh o rt en s t h e t im e n ecessary t o p ro d u ce t h e first O K p art s an d in creases t h e m ach in e u t ilizat io n rat e.
4.9.2 Layout
Th e followin g p rovid es a d etailed d escrip tion of a typ ical exam p le stam p - in g p lan t layou t. To sim p lify m atters som ewh at, ou r exp lan ation is based
on th e assu m p tion of id eal con d ition s an d n ew in stallation of th e com - p lete eq u ip m en t Green field p lan t. Th is is a typ ical task to establish
m an u factu rin g facilities for th e p rod u ction of m ed iu m -sized an d large car bod y p an els su ch as d oors, roofs, h ood s, floor p an els, sid e p an els,
fen d ers etc. for a p articu lar car typ e. Th ere are th ree p ress system s avail- able: tri-axis tran sfer p resses cf.
Fig. 4.4.27 , crossbar tran sfer p resses cf.
Fig. 4.4.38 an d p ress lin es cf.
Fig. 4.4.19 of variou s bed sizes.
Befo re p rep arin g t h e p lan t layo u t , it is first n ecessary t o d et erm in e wh ich p art s are t o be o u t so u rced an d wh ich are p ro d u ced in -h o u se. Th e
fo llo win g p art s are gen erally p ro d u ced in -h o u se: – o u t er p an els wh o se su rface co u ld be d am aged d u rin g t ran sp o rt ,
– jo in in g p art s wit h n arro w gap t o leran ces fo r p recise m at ch in g, – p arts of large volu m e resp . size wh ich are d ifficu lt to stack or tran sp ort.
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Sheet metal forming and blanking
Th ese so-called A-p arts – th ere are gen erally between 30 an d 40 of th em p er veh icle typ e – m u st be grou p ed togeth er to fam ilies of p arts.
Th ese are th en allocated to th e d ifferen t p ress system s on wh ich th ey can be econ om ically m an u factu red .
Figure 4.9.2 an d
Table 4.9.1 illu strate th e correlation between part size
an d press system . W h en processin g m ediu m -sized pan els, a press lin e with a m ediu m bed size or a tri-axis tran sfer press will be em ployed. Press lin es
with large bed sizes or crossbar tran sfer presses offer th e ideal con dition s for processin g large pan els with low in h eren t stiffn ess or dou ble pan els.
Figure 4.9.3 o ffers a m o re p recise allo cat io n o f p art s t o bo t h available
t ran sfer p ress syst em s. So m e p art s can be h an d led by cro ssbars wit h su ct io n cu p s as well as by grip p er rail syst em s. Th ey rep resen t t h e
o verlap bet ween t wo fam ilies o f p art s. So m e o f t h ese p art s, su ch as d o o rs, are p ro d u ced as sin gle p art s u sin g grip p er rail t ran sfer syst em s
cf. Fig. 4.4.29
o r as d o u ble p art s u sin g a cro ssbar t ran sfer syst em cf.
Fig. 4.4.34 .
Fig. 4.9.2
Press systems for the manufacture of car body parts medium dimension:
tri-axis transfer press crossbar transfer press
press line press line
typical family of parts
large dimension:
typical family of parts
up to
3 ,0
00 m
m
up to
5 ,0
00 m
m
tim e
up to
5 ,0
00 m
m up
to 3
,0 00
m m
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Organization of stamping plants
Th e select io n an d lo ad in g o f p resses d ep en d p rim arily o n t h e n u m - ber o f veh icles t o be p ro d u ced . Th e n u m ber o f veh icles d et erm in es t h e
p ro d u ct io n req u irem en t o f all p art s p er d ay. If t h e A-p art s o f a veh icle t yp e are m an u fact u red o n large-p an el t ran sfer p resses, t h e st am p in g
p lan t m u st h ave a cap acit y o f bet ween 3 an d 4 m illio n p art s p er year basis o f p lan n in g: 1 veh icle t yp e = 100,000 veh icles p er year.
Th e p ro d u ct io n sco p e p er year, i. e. t h e n u m ber o f p art s wh ich can be p ro d u ced o n t h e p ress syst em p er year, m u st be co -o rd in at ed wit h t h e
p ro d u ct io n req u irem en t . Th is calls fo r an o u t p u t an alysis o f t h e in d i- vid u al p ress syst em . Th e basis fo r calcu lat io n is t h e p ro d u ct io n st ro kin g
rat e. In t ran sfer p resses, t h is is eq u ivalen t t o t h e st ro kin g rat e set at t h e p ress. In t h e case o f p ress lin es, t h e p ro d u ct io n st ro kin g rat e is red u ced
t o so m e 50 t o 60 o f t h e set p ress st ro kin g rat e d u e t o st an d st ill p eri- o d s cau sed by t h e sin gle st ro ke o p erat io n . Th e n u m ber o f p art s wh ich
can be p ro d u ced d u rin g p ress o p erat io n also d ep en d s o n t h e fo rm in g req u irem en t s o f t h e in d ivid u al p art s. A co m p lex p art req u ires a lo n ger
p ro cessin g t im e. In ad d it io n , t h e t im e n ecessary fo r t ran sp o rt at io n o f
Table 4.9.1: Criteria for press selection large-panel transfer presses
press lines w ith differing
bed sizes part spectrum
medium-sized parts all parts
++ +
+ ++
+ ++
10 10
30 crossbar
transfer tri-axis
transfer large, unstable parts
and double parts complete part
production low
investment low space
requirement die change
time [min.]
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Sheet metal forming and blanking
large, u n st able p art s in creases. Becau se o f it s ran ge o f p art s an d lo n ger feed p it ch , a cro ssbar t ran sfer p ress is n o t able t o ru n at t h e sam e h igh
st ro kin g rat es as a t ri-axis t ran sfer p ress. In gen eral, it is t ru e t o say t h at t h e o u t p u t o f a p ress syst em m u st always be co n sid ered in t h e ligh t o f
t h e p art fam ily p lan n ed fo r p ro d u ct io n o n t h e p ress. In case o f d o u ble p art p ro d u ct io n in a cro ssbar p ress t h e p ro cessin g
t im e p er p art is red u ced . W h en d o u ble d ies are u sed , t h e average o u t p u t o f a cro ssbar t ran sfer p ress is larger t h an t h e o u t p u t o f a t ri-axis t ran sfer
p ress u sin g sin gle d ies, d esp it e o f t h e fact t h at t h e average p ro d u ct io n st ro kin g rat e is lo wer. Do u ble d ies are p referred fo r t h e m an u fact u re o f
o u t er an d in n er d o o rs, fro n t an d rear, left an d righ t . W h ere 10 d o o rs p er m in u t e can be p ro d u ced o n a t ri-axis t ran sfer p ress, fo r in st an ce, t h e
o u t p u t o f a cro ssbar t ran sfer p ress can be in creased by 50 t o 15 p art s p er m in u t e.
Th e n u m ber of h ou rs worked also plays an im portan t role in calcu latin g th e produ ction level, based for exam ple on th e n u m ber of days worked per
week, th e len gth of th e season al sh u t down s an d sh u t down s du e to pu b-
Fig. 4.9.3
Families of parts for large-panel transfer presses w ith different transfer systems
tri-axis transfer crossbar transfer
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
lic h olidays wh ich vary from cou n try to cou n try. Let u s assu m e between 200 an d 300 effective days’ work per year an d daily workin g periods of
between 840 an d 1,260 m in depen din g on two or th ree-sh ift operation . Th en th e an n u al produ ction capacity flu ctu ates between 100 at th e low-
er en d an d 225 at th e h igh er en d. Major in flu en cin g factors wh ich can - n ot be freely selected by th e m an u factu rer, su ch as statu tory labor legisla-
tion , collective agreem en ts etc. m ay determ in e th e possible fram ework. Th is m ean s th at produ ction capacity m u st always be calcu lated relative to
person n el requ irem en ts. O t h er in flu en cin g fact o rs in clu d e fo r exam p le n ecessary p ro d u ct io n
syst em m ain t en an ce in t ervals. If t h e st am p in g p lan t o p erat es at fu ll cap acit y, t h ese p erio d s m ay h ave t o be d ed u ct ed fro m t h e p ro d u ct io n
cap acit y. In case a five d ay week is wo rked , m ain t en an ce can be d o n e o n Sat u rd ays an d Su n d ays wit h o u t lo ss o f p ro d u ct io n .
If we redu ce th e workin g tim e by th e periods in wh ich n o produ ction takes place, we arrive at th e press availability or u ptim e. Particu lar factors
wh ich m u st be plan n ed for du rin g workin g h ou rs in clu de for exam ple die ch an ge, die settin g or die clean in g tim es. In addition to sch edu led press
stops, u n sch edu led down tim e m u st also be allowed for. Th is can be cau sed, for exam ple, by failu re of th e blan k su pply, press or dies. Overall, th e
u ptim e of m odern large-pan el tran sfer presses is gen erally in th e ran ge of 70 of th e total available work tim e
Fig. 4.9.4 . Th e actu al average lin e
ou tpu t is th u s calcu lated from th e produ ction strokin g rate, th e press oper- ation tim e an d th e proportion of press ru n n in g tim e du rin g wh ich dou ble
parts are produ ced. Extrapolated over a wh ole year, valu es of u p to 4.3 m il- lion parts m ay resu lt, depen din g on th e press system an d workin g h ou rs.
Table 4.9.2 illu strates an exam ple of ou tpu t for a produ ction system com -
prisin g a blan kin g lin e an d two large-pan el tran sfer presses. Providin g th at dou ble parts are produ ced for 50 of th e tim e on th e crossbar tran sfer
press, with a total of arou n d 3.9 m illion produ ction strokes of th e tran sfer presses per year, we arrive at an ou tpu t of 4.8 m illion sh eet m etal parts per
year. W h en gen erat in g a p ress lo ad sch ed u le, bat ch sizes an d t h e p ro d u c-
t io n seq u en ce are d efin ed . Th e seq u en ce is rep eat ed wit h in each co m - p let e cycle, wh ereby a p art can be p ro d u ced several t im es d u rin g an y
o n e cycle. Figure 4.9.5
illu st rat es an exam p le o f a p ress lo ad sch ed u le an d t h e relevan t in ven t o ry in t h e in t erm ed iat e st o rage o f fin ish ed p art s
fo r t h e p ro d u ct io n o f fo u r d ifferen t sh eet m et al p art s. Part s A an d B are
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Sheet metal forming and blanking
each m an u fact u red t wice in o n e cycle wit h bat ch sizes o f 5,000 an d 3,000, wh ile t yp e C an d D p art s are o n ly p ro d u ced o n ce in a cycle wit h
bat ch sizes o f 4,800 an d 3,300 resp ect ively. Du rin g p ro d u ct io n , t h e in ven t o ry o f t h e relevan t p art in creases in t h e in t erm ed iat e st o rage.
Ho wever, at t h e sam e t im e p art s are rem o ved illu st rat ed in Fig. 4.9.5
fo r p art A. Th e st eep er t h e p ro d u ct io n cu rve, t h e sh o rt er t h e p ro cessin g
Fig. 4.9.4
Availability and dow ntimes of large-panel transfer presses availability
70 organization
1 part-specific
tooling 2
blank logistics 3
die cleaning 5
dies 4 transfer
1 blankloader
3 press
3 die change
6 blanks
2
Table 4.9.2: Actual part output of a blanking line and tw o large-panel transfer presses
blanking line 20 ... 55 27 65 17.5 80 3,916,000 3,916,000 12 ... 16 14 70 9.8 80 2,193,000 2,193,000
10 ... 12 11 70 80 2,584,500 1,723,000 crossbar transfer press
50 single dies, 50 double dies
tri-axis transfer press set stroking
rate [1min]
average production
stroking rate
[1min] availability
[] net output
[partsmin] planned
utilization rate
[] output w ith
1,260 min w orking period
on 222 days year
strokesyear resp.
blanksyear
single dies 7.7 double dies 15.4
average 11.55
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Organization of stamping plants
t im e p er p art . Die ch an ges an d set t in g o f n ew d ies t akes p lace wit h in p ress st o p s bet ween p ro d u ct io n , wh ereby t h e d ie ch an gin g t im e p lays
an im p o rt an t ro le cf. Sect . 3.4
. Pro d u ct io n m u st be resu m ed o n ce t h e st o rage d ro p s t o t h e d efin ed
safet y in ven t o ry level, gen erally o n e d ay’s p ro d u ct io n . If we t ake t yp e A, fo r exam p le, t h is level wo u ld be reach ed at 6,200 p ieces, wh ile fo r t yp e
B t h e co rresp o n d in g figu re is 2,800 p ieces. Th e 5,000 o r 3,000 p art s p ro - d u ced , less t h e p art s u sed d u rin g m an u fact u re, m u st last u n t il t h e n ext
p lan n ed p rod u ction p eriod – arou n d 14 resp . 22 h ou rs later. W h en com - p ilin g th e load sch ed u le, a fin e balan ce m u st be d rawn : On th e on e h an d
th e p rod u ction p eriod for a batch size h as to gu aran tee su fficien t tim e for set-u p of th e d ie set for th e n ext p art. At th e sam e tim e, h owever,
excessively large batch sizes violate th e p rin cip le of ju st-in -tim e p rod u c- tion in term s of cap ital costs for work-in -p rocess an d costs for in term e-
d iate storage of fin ish ed p arts.
Fig. 4.9.5
Load schedule and parts inventory for production on a large-panel transfer press
inventory of finished parts in the intermediate storage
for part A part A: 7 pmin
part B: 10 pmin part C: 8 pmin
part A: 11 pmin
daily w orking hours: 15 hours
time [hours] 10 min die change after each batch
ba tc
h si
ze [p
cs .]
production cycle: ABCABD 10,000
8,000 6,000
4,000 2,000
6 12 18 24 30 36
42 48 56
production cycle of 50 hours
A A B C A B D
6,400 9,000
6,200 8,800
6,400 4,800
3,300
part cycle A
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Sheet metal forming and blanking
Exa m ple:
A p ro d u ct io n u n it h as t o be co n figu red in wh ich 44 p ressed p art s – p rim arily A p art s – h ave t o be p ro d u ced every year fo r 100,000 veh icles. Th e u n it co m p rises
a blan kin g lin e, a cro ssbar t ran sfer p ress an d a t ri-axis t ran sfer p ress. A p o ssible co n figu rat io n o f t h is st am p in g p lan t wit h o p t im ized m at erial flo w an d p erip h -
eral d evices is illu st rat ed in
Fig. 4.9.6 . Th e m at erial is su p p lied in t h e fo rm o f co il
st o ck an d st o red in t h e co il st o rage, fro m wh ere it is fed t o t h e blan kin g lin e. Th is su p p lies t h ro u gh t h e blan k st o rage bo t h large-p an el t ran sfer p resses wit h a
t o t al o f 4 m illio n blan ks a year. Fo llo win g p ro d u ct io n o n t h e t ran sfer p resses, t h e p art s are t ran sp o rt ed in p art -sp ecific racks t o t h e in t erm ed iat e st o rage fo r
fin ish ed p art s.
Table 4.9.3 list s t h e p art sp ect ru m fo r bo t h fo rm in g p resses. Th e cro ssbar t ran s-
fer p ress is ru n u sin g eigh t in d ivid u al an d eigh t d o u ble d ie set s, wh ereby t h e d o u ble d ies in t h is exam p le always p ro d u ce t wo d ifferen t p art s. Th eir d ie
ch an ge t im e am o u n t s t o 10 m in . Th e t ri-axis t ran sfer p ress m an u fact u res 20 d if- feren t p art s u sin g 20 d ie set s. Th e d ie ch an ge t im e is also 10 m in . O verall, t h e 44
p art s are p ro d u ced u sin g 36 set s o f d ies – 20 o n t h e t ri-axis t ran sfer p ress, an d 24 o n t h e cro ssbar t ran sfer p ress.
If 222 wo rkin g d ays are available p er year, p art s fo r 450 veh icles m u st be p ro - d u ced every d ay. In t h ree-sh ift o p erat io n wit h wo rkin g p erio d s o f 1,260 m in p er
d ay, t h e t o t al o f ap p ro x. 4.8 m illio n p art s in d icat ed in Table 4.9.2
ach ieved wit h 3.9 m illio n st ro kes can be p ro d u ced every year o n t h e t ran sfer p resses.
Th is is based o n a p lan n ed cap acit y u t ilizat io n o f 80 . Th ree d ays are select ed as a p ro d u ct io n cycle. If we t ake t h e sim p lified assu m p t io n t h at every p art is
o n ly ru n o n ce p er cycle, t h ree t im es 450 p art s m u st be p ro d u ced p er cycle. Th e in t erm ed iat e st o rage fo r fin ish ed p art s h as a t h eo ret ical m axim u m in ven t o ry o f
1,800 p ressed p art s o f each p art t yp e: 1,350 p art s fro m ru n n in g p ro d u ct io n p lu s 450 p art s as a m in im u m safet y in ven t o ry. O n average, h o wever, as bo d y-in -
wh it e p ro d u ct io n ru n s o n a p arallel basis, o n ly aro u n d h alf o f t h e p art s are lo cat ed in t h e in t erm ed iat e st o rage. At an y p o in t in t im e, t h e in ven t o ry co m -
p rises 900 3 44, i. e. ap p ro x. 40,000 p art s. As a resu lt , t h e p art st o rage an d t h e cap it al in vest m en t t h is in vo lves are co n sid erably lo wer t h an wh en p ro d u cin g
o n co n ven t io n al p ress lin es.
4.9.3 Quality assurance through quality control
