Note: Descriptions are shown in the official language in which they were submitted.
CA 02695585 2010-02-04
PCT/EP2008/060525
DESCRIPTION
METHOD AND MOULD CLOSURE FOR AN INJECTION MOULDING
MACHINE WITH A TOOL CLAMPING PLATE
TECHNICAL FIELD
The invention relates to a method for achieving as high
a plane parallelism as possible of the tool clamping
surface, in particular of the tool clamping plate on
the nozzle side of injection moulding machines, in the
operating state under the mould closure forces which
engage on the tool clamping plate via rails outside the
mould region. The invention further relates to a mould
closure of an injection moulding machine with tool
clamping plates which are deflected or deformed under
the mould closure forces.
PRIOR ART
The invention relates to the type of injection moulding
machines with rails. The great advantage of the rail
machine lies in that the forces are closed onto the two
tool clamping plates via at least four rails arranged
in the outermost corners of the four-cornered tool
clamping plate in longitudinal direction of the
injection moulding machine. In the past, the tool
clamping plates were produced as solid cast bodies
which weighed tons. The two mould halves were also
solid in construction. In the course of the ongoing
improvements to material usage, both the tool clamping
plates and also the moulding tools themselves were
constructed increasingly lighter. Independently
thereof, however, the requirements increased relating
to the closure forces, whether due to process or due to
ever larger moulds in multiple injection moulds. It is
interesting that the relatively small moulds, for
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example for the production of cans or buckets, produce
the greatest problems. If the force is introduced via
engagement points on the outer corners, the tool
clamping plate on the nozzl.e side easily deflects in
the case of tools in which the principal forces occur
in the centre. This is very harmful for the tools and
is disadvantageous for the i_njection moulding process.
The entire development led in a sense to a conflict of
aims:
= Independently of the mould size, in every case the
best qualities are required of the injection
moulded articles.
= Regardless of aiming for a lighter construction of
the entire injection moulding machine, the mould
manufacturer, precisely under the highest required
injection moulding pressures or closing forces for
the moulds, expects that the clamping plates do
not deflect or that these remain as far as
possible absolutely plane-parallel. In particular,
the forces from the rails lying on the outside
should not stand out on the flat tool clamping
surface of the tools or moulds.
= As in several cases of application, not only a
quite specific mould size but also the most varied
mould dimensions are used in the same machine, it
is required that the forces onto the mould halves
are transmitted uniformly for the smallest and
largest moulds or tools in the central region.
This is in the case of small injection moulding
machines of for example 50 t up to large injection
moulding machines of 1000 t and more closure
force.
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On the part of the driven or movable tool clamping
plate, the machine manufacturer generally has
sufficient design freedom, in order to introduce the
driving forces optimally in the region of the tools. On
the basis of the above-mentioned requirements, in rail
machines with a rail guide on the outer four corners, a
problem has been observed with regard to possible
deformations of the tool clamping plate on the nozzle
side. Specific structural measures must be taken in
order to ensure a maximum plane parallelism of the tool
clamping surfaces in operation even under the highest
loads.
The US patent document 4 615 857 (Motorola) suggests
solving the problem of deflection of the support
surface in that the deflection of the tool clamping
plate on the nozzle side is detected by measurement
technology and is compensated over the region of the
tool bearing surface by a plurality of locally engaging
support bodies.
EP 747 196 (Husky) suggests a design with two plates or
walls or respectively a double wall design. The double
wall is formed as a mould counter-pressure plate with
two walls spaced apart from each other, with an
intermediate support structure. The actual mould
clamping plate or wall is designated as the first wall
and the spaced plate is designated as the second wall.
The rails engage directly on the corners of the second
wall, which transfer the holding forces into the centre
region of the second plate. The intermediate structure
is designed to the corresponding force transmission and
has a wide end on the dosing side. The intermediate
structure is embodied so as to be bent, conical, V-
shaped or C-shaped, so that the forces are transmitted
over the bulge-shaped elements to the centre region of
the first wall. Because the second wall is constructed
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as a solid wall, all transverse forces are absorbed in
the second wall, so that only longitudinal forces or
compressive forces are introduced onto the central zone
directly in the region of the mould support. In this
way, with regard to the tool support, any deflection is
to be avoided. A disadvantage is the relatively complex
box structure without appreciable saving on weight, at
least compared with DE 40 04 026.
DE 40 04 026 (Toshiba) suggests composing the
stationary or fixed tool clamping plate from two
plates. The actual tool clamping late is guided
loosely, independently of the rails. An end plate is
arranged on the rear side of the tool clamping plate.
The rails rest on the outer end plate. The outer end
plate is placed with a projecting intermediate ring in
a force-fitting manner onto the tool clamping plate on
the nozzle side. The advantage of this solution lies in
that any deformations on the end plate from the holding
forces have no direct influence on the flatness of the
tool support surface of the tool clamping plate on the
nozzle side. By means of the ring-shaped transmission
surface, the holding forces are applied in a defined
manner in the central region onto the tool support
surface. The disadvantage of this solution lies in that
on the dosing side, two relatively heavy plates are
required, so that the aim of a weight reduction is not
solved. With regard to the problem description,
reference is made to DE 40 04 026 with Figures 1, 2 and
3 as prior art. In this device, a stationary moulding
tool is fastened to a stationary mould plate 3, which
is clamped on the ends of several rails 4 (usually
four) by means of nuts S. The other ends of the rails 4
are connected by means of nuts 5 with a device
producing a clamping force, which is formed by a large-
capacity oil pressure cylinder 6. The movable moulding
tool 2 is fastened to a movable mould plate 9, which is
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moved through the action of the oil pressure cylinder 6
along the rails 4 onto the stationary mould plate 3 to
and away from the latter. The clamping force which
clamps the stationary moulding tool 1 and the movable
moulding tool 2 together is produced by the device
producing a clamping force, which contains a large-
capacity oil pressure cylinder 6. The clamping force is
applied via the movable mould plate 9 onto the
stationary moulding tool 1 and the movable moulding
tool 2. The reaction force produced by the application
of the clamping force is applied via the tool clamping
plate 3, 12 on the nozzle side and the rails 4 onto the
device producing a clamping force.
In the mould closure according to DE 40 04 026, the
tool clamping plate 3, 12 on the nozzle side is
connected with the rails 4 at the four corners of the
end plate 12 by nuts 5. The points A and B, at which
the clamping force is applied onto the moulding tools,
have a distance from each other which produces the
bending movement shown in Fig. 3. Thereby, the clamping
force is not applied uniformly onto a mould cavity 10,
which is delimited between the stationary tool 1 and
the movable tool 2. By the bending of the stationary
mould plate 3, the rails 4 also bend, as is shown in
Fig. 3. When, under this condition, hot melt 11 is
injected through an injection nozzle, which is not
shown, into the mould cavity 10, owing to the pressure
P of the melt 11 the dimension of the cavity 10 is
altered, so that no mould products with precise
dimensions can be obtained.
The mould closure, as is shown in Fig. 1 according to
DE 40 04 026, contains a stationary metal mould 1 which
is fastened to a stationary tool clamping plate 3 on
the nozzle side. On the rear face of the stationary
tool clamping plate 3 on the nozzle side, a projection
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13 is formed which has substantially the same size as
the metal mould 1. The end element, an end plate 12, is
fastened on the right-hand ends of the rails 4 by means
of nuts 5, so that the plate 12 lies against the end of
the projection 13. Openings 14 are formed at the four
corners of the plate 3, so that the rails 4 extend
loosely through the openings 14. The internal diameter
of each opening 14 is somewhat greater than the
external diameter of each rail 4. The rails 4 therefore
penetrate the openings 14 freely. According to DE 40 04
026, the tool clamping plate on the nozzle side and the
rails 4 no longer bend on application of the clamping
force. The openings 14 need to be only slightly greater
than the diameters of the rails 4. The left-hand ends
of the rails 4 are connected by nuts 8 with a flange 6A
of a device 7, producing a clamping force, in the form
of a large-capacity oil pressure cylinder 6.
All solutions of the prior art have in common the fact
that the initially described problems are solved by
relatively complex means. In addition, a heavy
construction of the tool clamping plate on the nozzle
side is the result.
REPRESENTATION OF THE INVENTION
The invention was now presented with the problem of
developing a design for a mould closure which allows a
noticeable weight reduction, at least of the tool
clamping plate on the nozzle side, in which even under
the greatest closure forces, no harmful effects of
deflections or deflection forces occur onto the tool
clamping surface.
The method according to the invention is characterized
in that the tool clamping plate which is on the nozzle
side and/or is movable is at least partially deflected
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or elastically deformed in terms of the mould closure
forces on a processing table, and a flat processing is
carried out in the region of the tool clamping surface
under the deformation force.
The device according to the invention is characterized
in that the tool clamping surface of the tool clamping
plate, which is on the nozzle side andlor is movable,
in the unstressed stated has at least partially a
convex shape which is able to be transferred under the
mould closure forces into an approximately flat or
slightly concave shape.
It has been found by the inventors that the problem of
changing the shape of the clamping plate is not only a
pure deflection problem but likewise a problem of the
mould itself. With regard to the moulds, three cases
occur:
= Moulds which have weak points in a central region,
for example through large cavities, e.g. for the
injection moulding of buckets. The disadvantage
lies in that the mould parts sustain damage in the
corresponding region.
= Moulds which are constructed so as to be very
light and do not tolerate any deflections
whatsoever of the tool clamping surface or in
which the quality of the injection moulded parts
is impaired with the deflection of the mould.
= Moulds having a large area, in which no deflection
in the plane parallelism is permissible on the
whole tool clamping surface under highest mould
closure forces.
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The new invention allows consideration to be given to
these particular cases, and is therefore able to be
used flexibly. Generally, the machine manufacturer has
knowledge of the specific mould problems and still in
the manufacturing plant can carry out a preventive
processing of the tool clamping surface in line with
specific objectives.
The invention permits a number of particularly
advantageous developments, for which reference is made
to Claims 2 to 7 and 9 to 12.
The deflection force for the flat processing is at
least 50% of the maximum mould closure forces which are
to be expected. This means that with a 50-ton machine
at least 25 tons and with a 100 ton machine at least
500 tons deflection force is applied during flat
processing. As a consequence, the result is that the
deflection force is selected so that the tool clamping
surface of the tool clamping plate assumes a flat shape
with at least 50% of the mould closure force. Quite
particularly preferably, the deflection force for the
flat processing is 60% to approximately 100% of the
mould closure forces. Here, the deflection which is to
be expected in the operating state is compensated with
respectively a maximum mould closure force at 60% to
1000. In practice, this tool clamping plate is placed
onto the processing table for processing in the region
of the rail engagement sites, a pressure force for the
deflection force is applied in the central region of
the tool clamping plate and thereby a three-dimensional
deflection form is produced which is as similar as
possible to the deflection in the mould closure state.
The aim is to apply the acting forces already in the
flat processing of the tool clamping plate on the
nozzle side in as similar a manner as possible to how
they occur in the actual case of the mould closure
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forces. This presupposes clamping arrangements by which
operations are carried out in an analogous manner to
the situation of the mould closure. The aim is that in
the mould closure phase, the tool clamping surface
assumes a flat state at the latest after the start of
the injection process under the mould closure forces.
When the deformation force engages, on flat processing,
approximately in the centre of the tool clamping plate,
an increasing thickness is removed from the central
region up to the outer edge of the tool clamping
surface. The removal amounts to a few tenths of a
millimetre towards the outside, at all events
approximately 0.5 millimetres.
According to a further development idea, the removed
material is transferred at least approximately from the
convex shape occurring under the actual closure forces
by corresponding processing into a flat surface. In
order to achieve this, the forces of the actual case of
mould closure are taken into consideration in the
processing with an approximately average mould
dimension.
According to a further particularly advantageous
development, the tool clamping plate on the nozzle side
is supported for processing in the region of the tool
support or only in an inner weak region of the tool,
and a pressing force is applied for the deflection
force in the central region of the tool support
surface.
BRIEF DESCRIPTION OF THE INVENTION
The invention is now illustrated my means of some
example embodiments with further details, in which:
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Figure 1 shows the prior art on the basis of DE 40 04
026 with a double wall of the tool clamping plate on
the nozzle side;
Figure 2 shows a still older prior art with a simple
tool clamping plate on the nozzle side;
Figure 3 shows the solution according to Figure 2 with
exaggeratedly illustrated deflection of the tool
clamping plate on the mould side, and of the rails;
Figure 4 shows the mould closure side of an injection
moulding machine;
Figures 5a, 5b, 5c show the case examples with load
regions of differing size for the tool clamping plate
on the nozzle side;
Figures 5d and 5e show diagrammatically the movable
tool clamping plate;
Figure 6 shows the tool clamping plate on the nozzle
side at the start and at the end of the flat
processing;
Figures 7a, 7b and 7c show three situations, without
load (Figure 7a), with full load (Figure 7b) and with
full load, but with approximately 50 - 60% compensation
in the flat processing (Figure 7c).
WAYS AND EMBODIMENT OF THE INVENTION
Figure 4 shows the entire mould closure side or
respectively the mould closure of an injection moulding
machine, without the injection unit. On the left-hand
side, a drive support plate 20 is illustrated, in the
central region a movable tool clamping plate 9 and on
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the right the fixed tool clamping plate 3 on the nozzle
side. A toggle lever mechanism 21 and a toggle lever
drive 22 are arranged between the drive support plate
20 and the movable tool clamping plate 9. The drive
support plate 20 is only placed onto the lower part 23.
The movable tool clamping plate 9 is supported by means
of guide tracks 24 via guide bearings 25 which are
constructed so as to be free of play. The movable tool
clamping plate 9 can only be moved horizontally. In the
operating state, the tool clamping plate 3 on the
nozzle side is securely fixed on the lower part 23 by
screws 26. The longitudinal axis of the machine is
designated by 15. The tool clamping plate 3 on the
nozzle side is stationary with a moulding tool 1.
An injection cylinder 16 is brought up to the injection
opening of the moulding tool 1. A normal operating
situation is illustrated diagrammatically, during the
injection process with full action of the mould closure
forces "Z", which are closed over the rails 4 and the
tool clamping plate 3. The tool clamping surface 17 is
illustrated totally flat. This means that the
theoretical deflection of the tool clamping plate on
the nozzle side within the processing was compensated
100% at the machine manufacturer's works.
Figure 5a shows an example case in which not only the
entire support surface 17, i.e. the entire region of
the moulding tool, but also the remaining surface of
the tool clamping plate on the support side is
processed, which is emphasized diagrammatically by a
dot-and-dash circle 38 or respectively with spacer
sleeves 35 for the processing.
In Figure 5b the processing is carried out so that only
a corresponding surface according to the dot-and-dash
circle is taken into account.
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The solution according to Figure 5c is to be provided
in accordance with circle 39 or respectively in
accordance with the spacer sleeves 36 in cases in which
the tool has an inner weak region, for example in the
case of a large central cavity.
Figure 5d shows a view of the movable tool clamping
plate 9 with the engagement sites for the toggle levers
21.
Figure 5e shows a side view of Figure 5d with an
exaggeratedly illustrated barrel-shaped deflection of
the tool clamping plate (radius R).
Figure 6 shows diagrammatically the flat processing of
the tool clamping surface 17. The tool clamping plate 3
is fastened rigidly via guide rods 30 and spacer
sleeves 31 to a stand plate 32 of a flat processing
machine. The support surface is drawn to the right by a
tension screw 33 with tightening nut 34 of a force k of
50 - 100% of the mould closure forces, so that the
support surface deflects to a concave shape 17a.
Subsequently, the support surface is transferred
through a flat processing under the tensile force "K"
into a flat surface 17b. Here, an increasing thickness
"X" is removed from the inside outwards, which in
practice can amount for example to 0.1 to 0.5 mm.
After the flat processing and the loosening of the
tightening nut 34, the flat surface lb continues into a
convex surface 17c (Figure 7a). Accordingly, the
injection moulding machine is delivered to the
injection moulder with a convex support surface 17c of
the tool clamping plate. The customer mounts the tool 1
on the nozzle side in accordance with Figure 7a onto
the clamping plate 3. Figure 7b shows a situation with
the action of the full closure forces and with a 100%
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compensation of the deflection which is theoretically
to be expected. The support surface 17d is totally
flat. Thereby, a uniform bearing force is produced onto
the tool, with the advantages described in the
introduction.
In the case of more robust tools, the tensile stress
for the flat processing can be set for example to only
60 - 80% of the mould closure force which is
theoretically to be expected. The result is that in the
operating state with full mould closure force, in
accordance with Figure 7c, the support surface assumes
a slightly arched or concave shape 17e.
