Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02307045 2000-04-03
Differentiated press-molding process
The invention concerns a discontinuous forming~process
(press-molding process) for plastics based on the
working principle of volume displacement in the cavity
of a mold by means of a differentiated press-molding
process and concerns devices for carrying out the
process and components produced by the process or in
the device. The press-molding process according to the
invention allows a considerable reduction in the
necessary high pressing forces occurring in prior-art
press-molding processes, in each case in particular at
the end of the press-molding process, and consequently
a corresponding reduction in the structural expenditure
for the presses.
In the description of both the prior art and the
invention, use is made of some terms defined as
follows:
The term "cavity" used is defined as the space that is
variable in its surface and its volume during the
molding process, bounded by mold surfaces and by
surface areas along which the mold is closed. At the
end of the molding process, the cavity formed by the
mold is identical to the geometry of the product
(component) to be produced. The cavity is usually
bounded by surfaces of two mold halves. Additional
cavities (for example flow channels) which are
important for the molding process but do not belong to
the component geometry are not covered by the term
"cavity".
"Cavity subjected to.product" is understood as meaning
the part or the partial volume of the cavity which is
filled with material to be formed at the respective
point in time of the molding process.
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The term "surface subjected to product" refers to that
surface of the cavity which is in contact with the
material to be formed at the respective pointi.in time
of the molding process.
The working principle of a forming process (or molding
process) by volume displacement comprises exerting
pressure on a deformable mass in order to force the
latter into a specific shape. The term "introduction
of energy into the material to be formed" is understood
as meaning the introduction of mechanical energy into
the material to be formed in external items of
equipment or by corresponding movement of the cavity
surfaces subjected to product.
The discontinuous forming of plastics in a cavity
starts with the reduction of the cavity and ends at the
point in time when the cavity is completely filled with
the material to be farmed (filling phase). The
holding-pressure phase of the molding process, to
compensate for shrinkage, is not covered by the term
"discontinuous forming of plastics by volume
displacement in a cavity".
Prior-art processes to which the present invention can
be applied are:
Prior-art press-molding processes refer to those
molding processes in which the working principle of
volume displacement proceeds directly in the cavity.
During closing of the intrinsically rigid mold halves
during the molding process, the distance between the
two mold halves is reduced, whereby the volume of the
cavity is reduced-.- Wivh the reduction of the mold
opening, forming energy is introduced via the surfaces
of the cavity subjected to product into the material to
be formed.
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In prior-art press-molding processes, the entire
material mass is introduced into the opened cavity
directly before the beginning of the press-.molding
process. The press-molding process itself begins with
the movement of one or both mold halves, the
introduction of energy to the material to be formed
that is decisive for the molding process taking place
via the cavity surface subjected to product. With
increasing reduction of the mold opening during the
molding process, the cavity surface subjected to
product increases in size. The press-molding process
is considered to have been completed when the movements
of the mold halves come to a standstill, and
consequently forming energy is no longer being
introduced. During the closing movement of the mold
halves, intrinsically movable mold parts of the mold
halves which belong to the surface of the cavity, such
as ejectors or slides, stay in their basic position,
corresponding to the contour, so that the surface
contours of the cavity of the two mold halves can be
regarded as rigid during the entire press-molding
process.
The working principle of volume displacement requires
that "material flows" occur during the molding process.
The order of magnitude of the material movement or else
material stressing during the molding process in press
molding processes likewise allows a differentiation of
press-molding processes into a compression-molding
process and a flow-molding process.
The compression-molding process is understood as
meaning forming into a press-molded part in which the
press-molding mass--introduced into the opened cavity
corresponds in its shape to the greatest extent to the
projected surface area of the component contour, as a
result of which no great flow paths of the material to
be press-molded are necessary during the compression-
molding process. In the compression-molding process,
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the pressing energies introduced by the closing
movement of the mold halves are dissipated
predominantly in locally restricted plastic material-
forming processes and in compression work.
In the prior-art flow-molding process, the entire
press-molding mass is introduced into the cavity before
the beginning of the press-molding process, the mass of
the press-molding material introduced corresponding to
the mass of the component. The press-molding process
utilizes the flowability of the press-molding material
to be press-molded, with the chosen processing
parameters (pressure, temperatures, time), in order to
fill the cavity. Since, in the flow-molding process,
the press-molding mass introduced into the opened
cavity is significantly smaller in its shape than the
projected surface areas of the component contour, the
forming of the material introduced into the mold to
produce the component takes place by covering great
flow paths.
In a variant of the press-molding process, the
transfer-molding process, part of the transfer cylinder
surface reaches around part of one mold half. In the
transfer-molding process, the volume of material
corresponding to the completely closed cavity is placed
directly when the mold halves are opened into the
cavity additionally formed by the transfer cylinder.
Then, the mold halves are closed to the desired extent
without introducing forming energy. The decisive
introduction of energy into the material to be formed
takes place exclusively via the surface subjected to
product of the transfer cylinder, which moves as an
intrinsically rigid body. The molding process ends
with the movement of the transfer cylinder at the point
in time at which the geometry of the entire cavity
surface is identical to the desired component geometry.
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In the injection-stamping process, a special process of
the transfer-molding process, firstly the press-molding
material corresponding to the component mass is
introduced from outside via flow channels into a not
yet entirely closed mold. This takes place by
introducing forming energy into the material to be
formed in external items of equipment, such as for
example by injection-molding machines (injection
process). The further forming of the material
introduced into the cavity until the final component
geometry is obtained takes place according to the prior
art with the closing movement of one or both mold
halves (stamping operation). The introduction of
energy to the material introduced, decisive in the
stamping operation, takes place exclusively through the
closing movement of the rigid mold halves. During the
closing movement of the mold halves, intrinsically
movable mold parts of the mold halves which belong to
the surface contour of the cavity stay in their basic
position corresponding to the contour. The closing
operation of the cavities during the stamping operation
is a flow-molding process.
In virtually all the processes mentioned above, optimum
rheological design of the forming process presents a
great difficulty. An optimum rheological design of the
forming process is understood as meaning the
realization of optimum flow front profiles, flow path
lengths and pressure conditions during the filling
phase. Defined orientations are often also desired, in
particular in the case of fiber-reinforced materials,
but can scarcely be achieved with the prior-art press-
molding processes. For reasons of manipulation, only a
few inserts, usually only one is desired, can be placed
into the opened mold cavity and not by any means always
at the optimum locations for the flow-molding
operation. On account of the preparation of the press-
molding material, existing insertion geometries usually
.~w.
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constitute a constraint, which makes optimization of
the insertion situation even more difficult.
In a press-molding process, complete filling of the
cavity with material to be press-molded while
maintaining still permissible processing parameters and
fixed pressing forces as well as mechanical or
hydraulic press capacities of existing machines is
often of primary significance. The pressing forces
required for closing the mold halves are extremely high
toward the end of the flow-molding process, so that
very high pressing energies and, in particular,
pressing capacities are necessary for complete mold
filling. Therefore, presses which are used for the
flow-molding process must be dimensioned for their
pressing capacity, which is achieved inter alia by the
high kinetic energy of the moved mold half being used
for increasing the maximum pressing capacity, although
this in turn necessitates considerable expenditure on
controlling and regulating this energy. Moreover, in
the flow-molding process there is the great tendency
toward an impending risk of the mold tipping during
closing of the mold halves, which can be suppressed
only by considerable technical expenditure.
The prior-art discontinuous press-molding process
causes an enormous waste of pressing energies and
pressing capacities. This is reflected in considerable
technical expenditure, in high investment costs for
correspondingly large, precision-operating presses and
in high energy costs of a press-molding process.
Moreover, according to the current state of the art in
pressing control, the molding process is to a great
extent indifferent-in flow-molding processes.
The object of the present invention was to reduce the
pressing forces, pressing energies and pressing
capacities required during the forming of plastics in
the press-molding process, whereby considerable savings
CA 02307045 2000-04-03
in energy and equipment expenditure are made possible.
According to the present invention, this is achieved by
temporal and locational differentiation of the,. press
molding process into a number of partial press-molding
processes.
The subject matter of the present invention is
accordingly a process for the .discontinuous forming of
plastics by volume displacement in a cavity, in which
process the introduction of forming energy into the
material to be formed takes place through at least two
moved parts of the cavity surface, at least one mold
half containing one or more parts moved in relation to
it, at least part of the forming energy being
introduced through the relative movement of these parts
and the introduction of the forming energy taking place
in a temporally and locationally differentiated
controlled manner, seen over the entire forming
process, wherein only .part of the cavity surface of at
least one mold half, not lying parallel to the
direction of movement, is involved in the introduction
of the forming energy, seen over the entire forming
process.
The movements of the cavity surfaces are preferably
controlled in such a way that a standstill of flow
fronts is avoided or specifically selected rheological
flows and pressure conditions are realized during the
molding, which has positive consequences in the
achievable component qualities, the possible component
designs and the overall process stability of a flow-
molding process.
The embodiments mentioned relate exclusively to the
operating principle-~of volume displacement within the
cavity, independently of whether the entire material to
be formed corresponding to the component is in the
opened mold cavity before the beginning of the forming
process, or else the operating principle of volume
displacement within the cavity takes place
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simultaneously with an external introduction of
material to be formed in the cavity. Accordingly, the
entire material to be formed may already be,. in the
cavity at the beginning of the forming process. It is
S also possible, however, that material to be formed is
introduced into the cavity from outside during the
forming process.
The embodiments mentioned relate both to forming
processes in which the material to be formed that is
introduced into the cavity has to cover great material
movements in the form of flow paths, and to processes
in which even small material movements in the form of
locally plastic flowing or locally plastic deformations
are adequate to fill exactly the geometry of the cavity
closed to the desired extent, ensuring molding to
produce the desired component.
A further preferred embodiment of the present invention
consists in that material to be formed that is in the
cavity is firstly conveyed by the movement of one mold
half partly into a reservoir, which is formed by
yielding of a moved part of this cavity surface into a
negative relative position, and is subsequently
conveyed out of the reservoir into other regions of the
cavity by positive relative movement of this moved part
of the cavity surface. In this case, during the
closing movement of the mold, material to be formed is
firstly conveyed into the reservoir which, as mentioned
above, is formed by part of the cavity surface
yielding, i.e. performing a negative relative movement
and thereby reaching a negative relative position, and
subsequently moving back in the direction of the
cavity, i.a. performing -a positive relative movement.
This positive relative movement has the effect of
conveying the material out of the reservoir into other
regions of the cavity. By corresponding positioning
and shaping of one or more such reservoirs, it is
possible to avoid entirely the high pressing forces
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toward the end of the pressing operation that are
required in prior-art press-molding processes.
The positive relative movement of the moved part of the
cavity surface for emptying the reservoir is preferably
begun only when all the remaining mold surfaces have at
this point in time reached their end position and are
not performing any further movements.
With the present invention, the pressing energies,
pressing capacities and maximum allowed closing forces
required for the. forming in the press-molding process
can be optimally adapted individually to existing
machine sizes, so that mechanical closing and locking
systems can also be used, allowing a wide variety of
sizes of components to be produced extremely cost-
effectively.
The present invention also allows minimizing o~f the
technical expenditure for controlling. and regulating
devices required by the kinetics of the energies
occurring and necessary f.or suppressing the great
tendency of an impending risk of the mold tipping
during the press-molding process, which ultimately will
drastically reduce the costs of a press-molding device
corresponding to the invention.
Further subject matter of the invention are a device
for the discontinuous press-molding of plastics in a
cavity by the forming process according to the
invention, as well as a device for the injection-
stamping of plastics in a cavity by the forming process
according to the invention, in which devices at least
two parts of the cavityw surface are movably designed,
with at least one mold half containing one or more
parts moved in relation to it, in such a way that at
least part of the forming energy is introduced into the
plastic by the relative movement of these parts. The
movable parts of the cavity surfaces are in this case
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preferably additional presses. Preferred additional
presses are, for example, mechanical or hydraulic
presses, or ejectors or slides.
A mold which works on the principle of the
discontinuous ~ differentiated flow-molding process
usually comprises two mold halves. The mold half of
the mold on the male-die side is preferably connected
either to a hydraulic plunger or' to a mechanical
. 10 locking system and performs the closing movement or
opening movement of the press-molding mold. The mold
half on the female-die side is in this case fixedly
mounted on the press.
One or both. mold halves has or have one or more movable
parts, which belong to the mold contour and can perform
relative movements with respect to their mold halves,
it not being stipulated which part of a mold half
performs the movement.. All the movable parts which
belong to the mold contour are referred to as
additional presses if they carry out relative movements
with respect to their associated mold halves during the
forming process, and moreover, by their movement,
introduce forming energy into the press-molding
material, irrespective of the size of the contour
described.
The positive relative position of one additional press
with respect to further additional presses of its mold
half may exist already at the beginning of the press-
molding operation, or else be reached by relative
movements during the differentiated flow-molding
process. The positive relative position between an
additional press anzl its- mold half is used during the
cavity filling in the differentiated flow-molding
process to the extent that a smaller cavity wall
thickness is initially simulated in the contour region
of~ the additional press, which .is beneficial for the
development of specifically selected flow operations at
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the beginning of or during the differentiated flow-
molding process.
The negative relative position of one additional press
with respect to further additional presses of its mold
half may exist already at the beginning of the press-
molding operation, or else be reached by relative
movements during the differentiated flow-molding
process. The purpose of a negative relative position
between an additional press and its mold half during
mold filling in the differentiated flow-molding process
is that of creating during the filling phase additional
volume in the mold cavity for temporary material
reservoirs, since a greater cavity wall thickness is
simulated in the contour region of the additional
press.
Additional cavities of a corresponding mold which are
not part of the mold cavity but are in connection with
the latter and via which neither press-molding mass nor
energy is introduced into the press-molding mass of the
mold cavity subjected to product during the mold-
filling operation, may serve to compensate for
fluctuations in the inserted press-molding mass.
The main task of an additional press is not to keep the
cavity contour rigid during the filling phase of the
differentiated flow-molding operation but to form by
the possible movements of the additional presses
specifically selected volume cavities in the mold
cavity, serving as temporary material reservoirs.
During the positive relative movement of an additional
press, press-molding material is press-molded, the
displaced press-moidir~g- material on the one hand
serving for shaping the corresponding mold cavity and
on the other hand, if necessary, for filling one or
more further material reservoirs which are formed by
the negative relative positions of the respective
additional presses. The closing movement of an
r~..
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additional press ends at the position corresponding to
the desired component thickness or just above it
(shrinkage). The further partial cavities are filled
in an analogous way by the positive relative movements
of the individual additional presses, it being possible
for the individual movements of the additional presses
to take place simultaneously, in an overlapping manner
or else sequentially. The entire molding of the
component in the differentiated flow-molding process is
completed when every desired location of the component
surface coincides with the surface contour of the mold,
and every partial press-molding operation has been
completed, which is the case at the beginning of the
differentiated flow-molding operation when there is
exact mass metering and introduction of the flowable
mass to be press-molded into the opened mold cavity.
At this point in time, the entire cavity surface is
subjected to product.
The force required for the movements and for preserving
the static equilibrium of the individual additional
presses during the differentiated flow-molding
operation may be applied both mechanically and
hydraulically. The mechanically performed movements of
the additional presses take place via corresponding
levers (toggle levers) or spring elements. For
instance, it is also quite conceivable for
corresponding lifting functions of ejectors or slides
integrated in the mold to assume the function of the
additional presses. The force required for the
individual additional presses may, however, also be
applied hydraulically.
The controlling -or -regwlating of the individual
movements of the additional presses may take place both
in dependence on the travel of the male die and in
dependence on the press-molding time. The controlling
or regulating of the movements of the additional
presses may, however, also take place on the basis of
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measured mechanical or hydraulic closing forces or else
on the basis of internal mold pressures measured at any
desired location in the mold cavity. 1.
Represented in Figures 1 to 4 is a preferred form of
the device, that is to say of the mold, used for
carrying out the process, in 4 typical positions
corresponding to the sequence of the process of the
discontinuous differentiated flow-molding process. The
mass of press-molding material introduced into the
cavity at the beginning of the differentiated press-
molding process corresponds to the mass of the
component, so that no additional press-molding mass is
introduced into the cavity during the differentiated
press-molding process. Since, at the beginning of the
press-molding process, the surface of the cavity
subjected to product is significantly smaller than the
overall surface of the cavity at the end of the forming
process, the forming takes place for the most part by
virtue of the flowability of the press-molding mass,
with relatively great flow paths occurring.
Figure 1 shows the technical mold-related components
required for the differentiated flow-molding process
and their position at the start of a differentiated
flow-molding process. The mold half (1) on the female-
die side is of an intrinsically rigid design and is
fixedly mounted, its mold surface contours being
identical to the corresponding component geometry. The
mold half on the male-die side comprises the mold parts
(3), (4) and (5), forming movable cavity surfaces. The
press-molding material to be press-molded which is
introduced into the opened mold cavity and the mass of
which corresponds t~ the-desired mass of the component
is denoted by (2). Under the chosen process
parameters, the press-molding material introduced is in
a flowable form.
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The force required for the movements and for preserving
the required closing forces of the individual moved
mold parts may in the embodiment mentioned be,.applied
both mechanically and hydraulically. The individual
movements of the mold parts (3), (4) and (5) may take
place simultaneously, in an overlapping manner or else
sequentially, in a controlled manner.
Figure 2 schematically shows the beginning of the
discontinuous differentiated press-molding process.
The closing movement of the mold part (3) has the
effect that forming energy is introduced into the
press-molding material to be formed, resulting in a
forming of the press-molding material placed into the
press. The closing movement of the mold part (3) in
this case ends at the position corresponding to the
desired component thickness and stays in this position
during the remaining molding in the differentiated
press-molding process. The movable mold part (4)
fitted into the mold part (3) performs the same closing
movement as the moved mold part (3) in this phase of
the differentiated press-molding process. The negative
relative position of the mold part ( 4 ) with respect to
the mold part (3) at the beginning of the
differentiated press-molding process makes it possible
to set up a temporary material reservoir in the
corresponding cavity region of the mold part (4).
The movable mold part (5) performs no movement in the
first phase of the differentiated press-molding
process.
The next process phase of the discontinuous
differentiated press-molding process is shown in
Figure 3. The closing movement of the movable mold
part (5) produces a form fit between the mold half on
the male-die side and the mold half on the female-die
side, in order to ensure the tightness of the cavity,
which is necessary for the complete forming process.
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By achieving a correspondingly early tightness of the
cavity by the form fit of the movable mold part (5) on
the male-die side with the mold part (1) on the_female-
die side, a positive mold is not necessary. The
closing movement of the mold part (5) can, but does not
necessarily have to, introduce forming energy into the
press-molding material via any surfaces subjected to
product. The other movable mold parts (3) and (4) do
not perform any movements in this phase of the
described sequence of the differentiated press-molding
process and consequently do not introduce any forming
energy into the press-molding material.
The still remaining forming of the press-molding
material to produce the final component in the
differentiated press-molding process takes place
according to Figure 4 exclusively by the closing
movement of the movable mold part (4) on the male-die
side. Consequently, seen over the entire forming
process, only part of the cavity surface of at least
one mold half, not lying parallel to the direction of
movement, is involved in the introduction of the
forming energy.
A required holding pressure (shrinkage) is applied by
means of additional small closing movements of all the
movable mold parts on the male-die side which are not
in contact with the mold half on the female-die side
via a direct form fit.
Both the size and shape of the individual movable mold
parts on the male-die side can be individually adapted
for technical mold-related reasons and on account of
rheological condit-inns-. - The individual sequences of
movements of the moved mold parts on the male-die side
may be additionally controlled individually. This
situation opens up considerable scope for finding the
ideal molding process in a discontinuous differentiated
press-molding process. In this sense, the closing
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phases described here of the strictly sequential order
of the sequences of movements will take place in
practice in simultaneously proceeding closing movements
of the individual movable mold parts . In the sense of
the present invention, however, it corresponds to a
preferred embodiment of the discontinuous
differentiated press-molding process that the final
phases of the forming process, that is to say complete
mold filling, take place by introducing forming energy
via those cavity surfaces of the movable mold parts
which have the smallest cavity surfaces.
The process and the device according to the invention
are suitable for press-molding all plastics capable of
being press-molded, in particular those which are
plastic or flowable under press-molding conditions.
Preferred are thermosetting or thermoplastic materials,
such as for example urea, melamine or phenolic resins,
epoxies, polyolefins, such as for example polyethylene,
or polypropylene, polyamides, polyimides, polyesters,
polyether ketones, polyester ketones, polysulfides,
polysulfones or aramids. The plastics mentioned may be
both unfilled and filled or used with the addition of
customary additives. The process and the device
according to the invention are also suitable for the
press-molding of metals and ceramic materials.
Further subject matter of the invention are components
made of plastics which are produced by the process
according to the invention, or components which are
produced in the device according to the invention.
Such components are, for example:
machine parts and components of the automotive
industry: -- - -.
for example car bodies, doors, engine hoods, fenders,
tailgates, roofs, side sills, bumper brackets, engine
capsules, spare wheel recesses, front ends, battery
holders, underfloor panels, dashboards, seat shells,
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interior trim and exterior panels for automobiles,
motorcycle fairings, etc.;
machine parts and components in aerospace and shipping:
structural components, seat shells, baggage, racks,
panels, transport containers, etc.;
components of the electrical and electronic
industries:
housing parts, coverings, domestic appliances, switch
cabinets, lamp housings, housings and structural
components of the computer industry, support structures
for electronic components, etc.;
components of the construction industry, the furniture
industry and the household industry:
shower cubicles, swimming pools, bath tubs, wash
basins, chemical. containers and chemical equipment,
gullies, containers, trays, eating utensils, facade
structures, garden benches, roof domes, tool housings,
transport containers, semifinished product manufacture,
etc.
