Altan T. Metal Forming Handbook
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Fig. 3.7.1 Eccentric wheel of a large-panel transfer press
both of metallurgical and casting technology. Maximum care in the
production process is an underlying requirement. According to the cur-
rent state of the art in the field of foundry practice, the following strin-
gent requirement criteria can be covered with GGG-70:
– high resistance to wear, i. e. the microstructure must be purely per-
litic even with wall thicknesses of up to 200 mm,
– guaranteed hardness of 240 to 300 HB in all wall thicknesses – also at
the tooth root,
– elongation over 2 % in order to avert fractures and to increase resis-
tance to overloading.
In its raw cast state, i.e. without transformation annealing, these
mechanical requirements are achieved using a selective alloying tech-
nique. The application of cooling elements made of iron, steel and sili-
con carbide, either cooled or uncooled, also serves to enhance hardness.
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Casting components for presses
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
However, the casting technician can only alloy and cool within restrict-
ed limits, as elongation drops with increasing hardness. Due to this type
of metallurgical-technological operation, and because of their geometri-
cal shape, castings such as eccentric wheels are inevitably exposed to
high degrees of residual stress. As a result, stress relief annealing at 560 to
580 °C is an absolute necessity.
In the foundry, quality standards must be assured in order to avert the
risk of cracks and fractures in the castings. The marked tendency of the
material to form scale substantially impedes the production of compo-
nents made of GGG-70. The porosity risk therefore is addressed by feed-
ing and selective solidification. All components, naturally including also
large parts for press drive systems, are subject to highly stringent quality
controls, including ultrasound, X-ray, crack detection and hardness test-
ing, as well as testing of mechanical values using test-bar specimen, cast
together with produced component.
122
Fundamentals of press design
Bibliography
Anselmann, N. (editor): Europäisches Recht der Technik, Beuth Verlag, Berlin, Vienna, Zurich (1993).
ANSI B11.1-1971: Safety requirements for the construction, care, and use of mechanical power
presses, American National Standards Institute Inc., New York (1971).
Becker, U., Ostermann, H.-J.: Wegweiser Maschinenrichtlinie, Bundesanzeiger-Verlag, Cologne (1995).
Bodenschatz, W., Fichna, G., Voth, D.: Produkthaftung, Maschinenbau-Verlag, Frankfurt/Main,
4th edition. (1990).
DIN EN 692 (Draft): Mechanische Pressen – Sicherheit, Beuth Verlag, Berlin (1992).
DIN EN 693 (Draft): Hydraulische Pressen – Sicherheit, Beuth Verlag, Berlin (1992).
DIN EN 1037 (Draft): Sicherheit von Maschinen, Trennung von der Energiezufuhr und Energieabbau,
Vermeidung von unerwartetem Anlauf, Beuth-Verlag, Berlin (1993).
Hoffmann, H., Schneider, F.: Schwingen verhindert-Hydraulische Zieheinrichtung für die Fertigung mit
hoher Qualität in einfachwirkenden Pressen, Maschinenmarkt 95 (1989) 51/52.
Hoffmann, H.: Vergleichende Untersuchung von Zieheinrichtungen, Bänder Bleche Rohre (1991) 12
and (1992) 1.
Kürzinger, F.-X.: Kraftneutrale Parallelregelung über gesamten Hub, Bänder Bleche Rohre (1995) 9.
Occupational Safety and Health Administration: OSHA Regulations 29 CFR Ch XVII, Part 1910, Office of
the Federal Register, Washington D.C., 7-1-92 Edition (1992).
Schmidt, K.: Die neue Druckbehälterverordnung, WEKA Fachverlag, Augsburg (1995).
Schwebel, R.: Geringe Parallelitätsabweichungen - Anwendungsspektrum hydraulischer Pressen,
Industriebedarf (1994) 9.
Süddeutsche Metall-Berufsgenossenschaft: Unfallverhütungsvorschriften, Carl Heymanns Verlag KG,
Luxemburg (1994).
TÜV Hannover-Sachsen-Anhalt: Kurzinformation EG-Maschinen-Richtlinie, Eigenverlag (1995).
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
4Sheet metal forming and blanking
4.1Principles of die manufacture
4.1.1Classification of dies
In metalforming, the geometry of the workpiece is established entirely or
partially by the geometry of the die. In contrast to machining processes,
significantly greater forces are necessary in forming. Due to the com-
plexity of the parts, forming is often not carried out in a single operation.
Depending on the geometry of the part, production is carried out in sev-
eral operational steps via one or several production processes such as
forming or blanking. One operation can also include several processes
simultaneously (cf. Sect. 2.1.4).
During the design phase, the necessary manufacturing methods as
well as the sequence and number of production steps are established in
a processing plan(Fig. 4.1.1). In this plan, the availability of machines,
the planned production volumes of the part and other boundary con-
ditions are taken into account.
The aim is to minimize the number of dies to be usedwhile keeping up
a high level of operational reliability. The parts are greatly simplified
right from their design stage by close collaboration between the Part
Design and Production Departments in order to enable several forming
and related blanking processes to be carried out in one forming station.
Obviously, the more operations which are integrated into a single
die, the more complex the structure of the die becomes. The conse-
quences are higher costs, a decrease in output and a lower reliability.
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
Types of dies
The type of die and the closely related transportation of the part between
diesis determined in accordance with the forming procedure, the size of
the part in question and the production volume of parts to be pro-
duced.
The production of large sheet metal parts is carried out almost exclu-
sively using single sets of dies. Typical parts can be found in automotive
manufacture, the domestic appliance industry and radiator production.
Suitable transfer systems, for example vacuum suction systems, allow
the installation of double-action dies in a sufficiently large mounting
area. In this way, for example, the right and left doors of a car can be
formed jointly in one working stroke (cf. Fig.4.4.34).
Large size single dies are installed in large presses. The transportation
of the parts from one forming station to another is carried out mechan-
124
Sheet metal forming and blanking
Fig. 4.1.1 Production steps for the manufacture of an oil sump
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
ically. In a press line with single presses installed one behind the other,
feeders or robots can be used (cf.Fig. 4.4.20 to 4.4.22), whilst in large-
panel transfer presses, systems equipped with gripper rails (cf. Fig. 4.4.29)
or crossbar suction systems (cf. Fig. 4.4.34)are used to transfer the parts.
Transfer diesare used for the production of high volumes of smaller
and medium size parts (Fig.4.1.2). They consist of several single dies,
which are mounted on a common base plate. The sheet metal is fed
through mostly in blank form and also transported individually from
die to die. If this part transportation is automated, the press is called a
transfer press. The largest transfer dies are used together with single dies
in large-panel transfer presses (cf. Fig. 4.4.32).
In progressive dies, also known as progressive blanking dies,sheet metal
parts are blanked in several stages; generally speaking no actual forming
operation takes place. The sheet metal is fed from a coil or in the form
of metal strips. Using an appropriate arrangement of the blanks within
the available width of the sheet metal, an optimal material usage is
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Principles of die manufacture
Fig. 4.1.2 Transfer die set for the production of an automatic transmission for an automotive
application
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
ensured (cf. Fig. 4.5.2to 4.5.5). The workpiece remains fixed to the strip
skeleton up until the last operation. The parts are transferred when the
entire strip is shifted further in the work flow direction after the blank-
ing operation. The length of the shift is equal to the center line spacing
of the dies and it is also called the step width. Side shears, very precise
feeding devices or pilot pins ensure feed-related part accuracy. In the
final production operation, the finished part, i. e. the last part in the
sequence, is disconnected from the skeleton. A field of application for
progressive blanking tools is, for example, in the production of metal
rotors or stator blanks for electric motors (cf. Fig. 4.6.11and 4.6.20).
In progressive compound diessmaller formed parts are produced in
several sequential operations. In contrast to progressive dies, not
only blanking but also forming operations are performed. However,
the workpiece also remains in the skeleton up to the last operation
(Fig.4.1.3and cf. Fig.4.7.2). Due to the height of the parts, the metal
strip must be raised up, generally using lifting edges or similar lifting
devices in order to allow the strip metal to be transported mechanical-
ly. Pressed metal parts which cannot be produced within a metal strip
126
Sheet metal forming and blanking
Fig. 4.1.3 Reinforcing part of a car produced in a strip by a compound die set
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
because of their geometrical dimensions are alternatively produced on
transfer sets.
Next to the dies already mentioned, a series of special diesare avail-
able for special individual applications. These dies are, as a rule, used
separately. Special operations make it possible, however, for special dies
to be integrated into an operational sequence. Thus, for example, in
flanging diesseveral metal parts can be joined together positively
through the bending of certain metal sections (Fig.4.1.4andcf.
Fig. 2.1.34). During this operation reinforcing parts, glue or other com-
ponents can be introduced.
Other special dies locate special connecting elements directly into
the press.Sorting and positioning elements,for example, bring stamping
nuts synchronised with the press cycles into the correct position so that
the punch headscan join them with the sheet metal part (Fig.4.1.5). If
there is sufficient space available, forming and blanking operations can
be carried out on the same die.
Further examples include bending, collar-forming, stamping, fine
blanking, wobble blanking and welding operations (cf. Fig. 4.7.14and
4.7.15).
127
Principles of die manufacture
Fig. 4.1.4A hemming die
123
blank holder
inner door
outer door
seaming bed
pressure block
tilting block
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
4.1.2Die development
Traditionally the business of die engineering has been influenced by
the automotive industry. The following observations about the die
development are mostly related to body panel die construction. Es-
sential statements are, however, made in a fundamental context, so
that they are applicable to all areas involved with the production of
sheet-metal forming and blanking dies.
Timing cycle for a mass produced car body panel
Until the end of the 1980s some car models were still being produced for
six to eight years more or less unchanged or in slightly modified form.
Today, however, production time cycles are set for only five years or less
(Fig. 4.1.6). Following the new different model policy, the demands on
die makers have also changed fundamentally. Comprehensive contracts
of much greater scope such as Simultaneous Engineering (SE) contracts
are becoming increasingly common. As a result, the die maker is often
involved at the initial development phase of the metal part as well as
in the planning phase for the production process. Therefore, a much
broader involvement is established well before the actual die develop-
ment is initiated.
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Sheet metal forming and blanking
Fig. 4.1.5A pressed part
with an integrated
punched nut
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
129
Principles of die manufacture
Fig. 4.1.6 Time schedule for a mass produced car body panel
2-3 year period
go-ahead for
a new model
trend and market
research
concept phase
participation of the toolmaker in the development and production process
styling phase
design of the
outer car
bodywork
design of the bodywork
reinforcement
prototype parts pilot series parts
various try-out
phases with prototype
parts
various try-out phases
with pilot series parts
start of
series production
period up to production stop
start on development of follow-up model
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998
The timetable of an SE project
Within the context of the production process for car body panels, only
a minimal amount of time is allocated to allow for the manufacture of
the dies. With large scale dies there is a run-up period of about 10
months in which design and die try-out are included. In complex SE
projects, which have to be completed in 1.5 to 2 years, parallel tasks
must be carried out. Furthermore, additional resources must be provid-
ed before and after delivery of the dies. These short periods call for pre-
cise planning, specific know-how, available capacity and the use of the
latest technological and communications systems. The timetable shows
the individual activities during the manufacturing of the dies for the
production of the sheet metal parts (Fig.4.1.7). The time phases for
large scale dies are more or less similar so that this timetable can be con-
sidered to be valid in general.
Data record and part drawing
The data record and the part drawing serve as the basis for all subse-
quent processing steps. They describe all the details of the parts to be
130
Sheet metal forming and blanking
Fig. 4.1.7 Timetable for an SE project
production releasespecifications
start of SE project
milestones:
purchasing release
pre-production
series
pilot seriesseries
pre-planning
process planning
CAD data
prototype parts
draw development
project planning
die design
casting models
machining
casting
bench work
home try-out
series try-out
design die production die
development
Metal Forming Handbook / Schuler (c) Springer-Verlag Berlin Heidelberg 1998