Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2~91877
-- 1 --
59162.558
Apparatus and process for cold-forminq films
The invention relates to apparatus and a process
for cold-forming films such as plastics films or sheet
metal films, particularly but not exclusively
polypropylene films of various thicknesses.
Currently, polypropylene films are formed both
thermally and cold with the aid of compressed air or
vacuums. In particularly difficult fields of
application, so-called roughing punches are used.
All these practices cause the polypropylene film
which is to be deformed to shrink or expand as a result
of thermal action.
Punches which are heated and used to deform
polypropylene films cause the polypropylene blank to
wrinkle or crease, particularly when the blank is
removed from the die or forming punch whilst still warm.
DE-A-l 704 303 (corresponding to U.S. Patent No.
3,546,221) describes a process for produciny products of
thermoplastic material. The deformation is carried out
at working temperatures below the normal thermoforming
temperature. This process uses two forming dies, one
forming die containing a resilient element consisting of
rubber, for example, into which the piece of film which
is to be deformed is pressed by means of a mating die.
The forming die with the resilient element has a channel
passing through this element to prevent underpressure
after the product has been formed. The resilient
element of this die acts as a counter-mould to the
forming punch of the mating die. This forming punch is
, provided in the centre with a pneumatically controlled
ejector. After the tools have been opened the blank is
~, 35 removed by means of the ejector.
It has now been found that films of polypropylene
, or sheet metal can be formed even at ambient
A
,.,
X
~'
i'
.'
''
,
20~187 i
-- 2
temperature, i.e. w~thout any previous warming of the
material, in a versatile manner, without using a
counter-punch by pressure, by providing a punch with a
central bore or inner cavity connected to the exterior
by means of one or more transverse passages or bores,
the punch being engageable with a perforated die the
hole or bore diameter of which matches the external
diameter of the punch.
Viewed from one aspect the invention provides
apparatus for the cold-forming of films, without
preheating, comprising a forming punch engageable in the
hole of a perforated die, the forming punch having an
inner cavity which is connected to atmosphere by at
least one transverse passage.
Viewed from another aspect the invention provides a
process of cold-forming a film without preheating,
comprising introducing the film to be deformed between a
perforated die and a clamping member, bringing together
the perforated die and a forming punch with an inner
20 cavity and at least one transverse passage, so as to
carry out the forming operation, separating the
perforated die and the forming punch, and retracting the
clamping member so that the formed blank can be removed.
The invention is particularly advantageous for the
25 cold-forming of plastics films, such as polypropylene
films, or sheet metal foils.
The inner cavity in conjunction with the transverse
passage guarantees a constant exchange of pressure with
the environment throughout the entire pressing
30 operation. The presence of the vented inner cavity in
the punch and the use of a perforated die ensure that
there are no pressure differences on the pressed part
` during the pressing operation. When the formed blank is
h removed from the forming punch, there is no suction on
35 the formed blank which could have a deforming effect.
The invention therefore provides tools consisting
of a forming punch and an associated perforated die for
J'
, '
., ~
20~1877
-- 3
forming plastics films, particularly polypropylene
films, and sheet metal foil in the cold state without
causing any significant shrinkage of the deep-drawn
blank when the forming punch is removed.
During the forming operation it is sufficient for
one forming element (e.g. the perforated die) to move
towards the other (e.g. the forming punch). Thus either
forming element can be held stationary and the other
moved, or they can both be moved. However, it is
advantageous if the perforated die is moved towards the
forming punch, since it is easier to attach fixing
elements, such as one or more clamping members, to the
perforated die for fixing continuous films. Thus in a
preferred process, the forming punch is held stationary
and the perforated die and clamping member are moved
relative thereto.
Certain embodiments of the present invention will
now be described by way of example and with reference to
the accompanying drawings, in which:-
Figures I to III are cross-sectional views through
a first embodiment of the cold-forming apparatus,
respectively before, during and after a deformation
process for producing a round depression in a blank (as
shown in Figure IX);
` 25 Figure IV is a cross-sectional view of the punch of
` the first embodiment, supported on a mandrel;
Figure V is a longitudinal sectional view through a
; second embodiment of the cold-forming apparatus, before
a deformation process for producing an elongate or oval
: 30 depression in a blank (as shown in Figure X);
Figure VI is a cross-sectional view through the
second embodiment, before the deformation process;
Figure VII is a partial longitudinal sectional view
~, through the second embodiment, during the deformation
, 35 process;
Figure VIII is a partial cross-sectional view
through the second embodiment, after the deformation
:.~
~,.
,~
.,
, .
2091877
-- 4
process;
Figure IX shows a typical sectional view and a plan
view of a blank formed with a round depression by the
first embodiment of the cold-forming apparatus; and
Figure X shows a longitudinal sectional view, a
cross-sectional view and a plan view of a blank formed
with an elongate or oval depression by the second
embodiment of the cold-forming apparatus.
Referring to the first embodiment, Figure I shows
the initial situation when the apparatus is open, before
a polypropylene film 3 to be deformed is deep-drawn by
means of a forming punch 1. A clamping member 2 serves
to fix the film 3 which is to be deformed to a
perforated die 4 adapted to fit the punch 1. A
receiving mandrel 5 is provided for the forming punch 1.
Figure II shows the apparatus in the closed
condition, wherein the forming punch 1 is shown having
entered the perforated die 4, so deforming the film 3,
which is held securely on the perforated die 4 by the
clamping member 2.
Figure III shows the apparatus in the open
condition, with a formed blank 6 removed therefrom.
Figure IV shows a cross-section through the forming
punch 1 which has a central vent bore 8 and transverse
bores 9 which serve during the forming process to
equalise the atmospheric pressure.
; Figure IX shows a formed blank 6 having a round
depression made from the polypropylene film 3 using the
first embodiment of the apparatus shown in Figures I to
IV.
Referring now to the second embodiment, Figures V
and VI show in longitudinal and transverse section a
forming punch 1 of elongate construction such as is
required to produce a formed blank as shown in Figure X,
e.g. for reliably accommodating a capsule or the like in
an elongate depression. Figures V and VI additionally
show a space 10 for avoiding adhesions when shaping the
2091877
-- 5 --
elongate depression, thereby ensuring atmospheric
pressure equalisation. As in the first embodiment there
is a central vent bore 8 into which the transverse bore
9 opens for the free escape of air.
In the partial longitudinal sectional view shown in
Figure VII, the forming punch l has been inserted in the
perforated die 4. During the forming operation the
polypropylene film 3 is clamped between the perforated
die 4 and the clamping member 2. The forming punch 1 is
removably screwed into the receiving mandrel 5.
Figure VIII shows a partial cross-sectional view of
the apparatus in the open condition, with the cold-
formed blank 6 (e.g. a depression in a blister pack)
removed therefrom. The perforated die 4 has returned to
the starting position.
Figure X shows a formed blank 6 having an elongate
depression which has been cold-drawn from the flat film
3, as is clear from the plan view, using the second
embodiment of the apparatus shown in Figures V to VIII.
During cold-forming, first a film 3 is introduced
between the clamping member 2 and the perforated die 4.
The clamping member 2 is raised so that the film 3 lies
above the forming punch 1. The forming is produced by
the pressure of the perforated die 4 on the clamping
member 2, whilst the two elements with the stretched
; film 3 slide over the forming punch 1, preferably at a
reduced speed. The blank 6 thus formed is freed by the
perforated die 4 and clamping member 2 being pulled back
from the forming punch 1, the perforated die being
pulled back to a greater extent, so that the blank
resting on the clamping member is freed and can thus be
pulled sideways between the clamping member and the
perforated die.
