Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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FIELD OF THE INVENTION
This invention concerns a method of pressure molding a
material into a desired shape and an apparatus for use therefor.
BACKGROUND OF THE INVENTION
In the field of materials molding, one of the conventional
press working techniques involves using a uniform-pressure facing
mold (known as the "Uniform Pressure Facing Method") in which fluid
applies uniform pressure from all directions. Using this method,
it is possible to apply high pressure onto the entire surface of
the metallic material steadily for a long period of time. In
comparison with a mechanical working press, this method reduces
spring-back, providing the benefit of precision processing.
Moreover, the process is relatively inexpensive as the need to
produce a punch or mold is eliminated and the process has generally
been considered convenient for molding small quantities of a
product.
There are, however, difficulties in using the Uniform Pressure
Facing Method as the pressurized fluid does not ensure a secure
seal thereby allowing the fluid to spurt out during the draining
and/or injecting process. This not only adversely affects the
working conditions but also makes it difficult to ensure the safety
of the procedure.
Another known molding technique is a method of expansion
molding, in which a tubular material is placed over a
multiple-parts punch mold. The punch is then opened up and
enlarged by a wedge-shaped tool, resulting in the application of
tensile force to the material in a centrifugal direction. The
shape to be transferred to the material can be placed on the mold
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pressing into the material, or on the die located on the outside
into which the material is pressed into.
In expansion molding, the production of a tubular mold tends
to be complicated. Also, this method is more costly as it requires
a multiple-parts punch and wedge-shaped tools. This latter
requirement renders this method unsuitable as a molding process for
complicated shapes and profiles.
It is an object of the present invention to obviate or
mitigate the above disadvantages.
SUMMARY OF THE INVENTION
The present invention provides a method of pressure molding a
material into a desired shape which comprises placing the material
in a hollow mold form, wherein the mold form provides, at one end,
a mouth for receiving a pressurizing unit, said unit c~mprising a
resilient pouch capable of being inflated under pressure, inserting
and securing the pressurizing unit in the mouth, and inflating the
pouch using a pressurizing agent such that the pouch forces the
material against the interior of the mold form thereby transferring
the shape of the mold form to the material.
The significant advantages of this method include its
simplicity, its adaptability to mold shapes of any complexity and
its ability to reduce spring-back, a problem which plagues many
other molding techniques. This reduction in spring-back results in
improved and more uniform contact between the interior of the mold
and the material thereby eliminating irregularities in the final
molded product.
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As discussed above, contamination is a one of the problems
encountered with the Uniform Pressure Facing Method, particularly
as the pressurized fluid is not sealed and tends to leak out during
the injecting or draining process. In contrast, with the method of
the present invention, the pressurizing agent is sealed within a
pouch so no leakage or gushing of the agent occurs under pressure
or inflation of the pouch. The method of the present invention
does not require the insertion of rubber or fluid before molding,
as is the case with the bulge molding process, which eliminates
cleaning and draining the mold after use. This significantly
improves the efficiency and cost-effectiveness of the method of the
present invention.
In another aspect of the present invention, an apparatus
suitable for pressure molding a material into a desired shape is
provided which comprises a hollow mold form defining in its
interior a desired shape and having a mouth at one end thereof, a
pressurizing unit comprising a resilient pouch capable of being
inflated by a pressurizing agent, a base plate and a securing
means, wherein the pouch engages the base plate and is capable, in
an inflated form, of pressing the material against the interior of
the mold. The securing means enables removable attachment of the
pressurizing unit to the mold form.
The use of this apparatus enables the precise transfer of the
shape and profile of the mold to the material in an efficient and
economical way. Moreover, the problems associated with previous
apparatus have been overcome.
DESCRIPTION OF THE DRAWINGS
The present invention is described by way of the following
non-limiting drawings wherein:
Figure 1 represents a side view in cross-section of the
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apparatus of the present invention; and
Figure 2 represents a perspective view of one embodiment
of a pressurizing unit and mold form.
PREFERRED EMBODIMENTS OF THE INVENTION
With reference to the figures and particularly to Figure 1,
wherein like numerals depict the same feature as between the
drawings, there is provided generally at 1 a pressurizing unit
comprising a resilient pouch 2, a base plate 3 and securing means
7. A mold form 10 defines a shape, pattern or configuration in its
interior against which material M to be molded may be placed when
the apparatus is in use. Base plate 3 is traversed vertically by
supply line 4 through which a pressurizing agent F may pass from
supply connector 6 to the interior of pouch 2.
Various shapes and configurations of pouches may be suitable
for use within the present invention so long as the pouch has a
character of resiliency and is capable of inflation and deflation
under pressure. In one preferred form, the pouch is shaped liké
the bellows. Furthermore, the pouch must be of sufficient size and
shape such that when used in a desired mold, on inflation of the
pouch, material M is forced against the interior surface of the
mold, thereby transferring the shape, pattern or configuration of
the mold to the material. The pouch must also be sufficiently
heat-resistant to withstand the temperature of material M at its
most pliable stage (the temperature at which material M may be
molded). Alternatively, the pouch may be covered in a heat-
resistant material. Preferably, the pouch is made of a synthetic
rubber selected from the group comprising chloroprene, nitryl,
silicone and fluorine.
In order to provide support to the resilient pouch, base plate
3 is provided. Pouch 2 may be removably or permanently attached
the base plate. In a preferred form, attachment may be achieved by
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the use of an annular ring or flange (indicated at 7) which ensures
that the pouch does not become detached from the base plate during
inflation and deflation. Practically, when pouch 2 is inflated
under pressure, the base plate has sufficient rigidity to prevent
the pouch from floating up or moving out of place. Generally, base
plate 3 may be of any reasonable size and configuration to achieve
the objects described above.
In a preferred embodiment, retainer 5 is provided at the
periphery of the joint of mold 10 and pouch 2 (when pouch is
inflated) to assist in maintaining material M in place. For
example, retainer 5 may be an annular ring, flange or doughnut
shape. The retainer of the present invention must be made of a
sufficiently heat-resistant composition to withstand the
temperature at which the particular material to be molded becomes
pliable. Alternatively, the retainer may be covered with a
sufficiently heat-resistant material.
The pressure molding apparatus of the present invention, in
addition to comprising the pressurizing unit described above, also
comprises mold 10 defining, on its interior surface, the intended
shape, pattern or configuration to be molded. Generally, mold 10
comprises a hollow body and an aperture, opening or mouth at one
end thereof which is of an appropriate size and shape to receive at
least the deflated pouch. Alternatively, the mouth may be large
enough to receive the entire pressurizing unit. Mold 10 may be
divisible into a number of interconnectable sections for ease in
removal of the final molded product. These "sections" may be
connectable by hinge, by interlocking means or any other suitable
method.
In one embodiment of the present invention as depicted in
Figure 1, the mouth or aperture of mold 10 is as wide or wider in
diameter than the hollow body of the mold proper. In another
embodiment as depicted in Figure 2, the diameter of the mouth is
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smaller than that of the body proper. In each embodiment, the
preferred method of pressure molding, as described further
hereinbelow, is the same.
It is not necessary or desired within the scope of the present
invention that conventional "male/female~ type molds be used. All
that is required of the mold for use with the present invention is
that it define a desired shape within its hollow interior and that
it has means to allow the pouch, at least when deflated, to be
inserted within the body. Use of this simple type of mold lowers
production costs compared to conventional molds and thereby lowers
the cost of the finished molded product.
In operation, and with reference to both Figures 1 and 2, a
mold type is selected based on the desired internal shape,
configuration or pattern. The material M to be molded is made
pliable (for example, by subjecting to high temperatures) and is
then place as a lump, tubular mass or sheet in the hollow mold
form. Pressurizing unit 1 including pouch 2 and base plate 3 is
then used to transfer the shape of the interior of the mold to the
material. Pressurizing unit 1 is placed over the mouth of mold 10
such that deflated pouch 2 is disposed towards the interior of the
mold form. In one embodiment, the mouth may hold the entire
pressurizing unit. Securing means 7 ensures attachment of pouch 2
to base plate 3. Retainer 5 is secured in place to hold the
peripheral part of material M by sandwiching it against both the
underside of base plate 3 and the outside rim of the mouth of mold
10. A pressurizing agent F is then supplied from supply connector
6 to pouch 2 via supply line 4 until the pouch is sufficiently
inflated to press or force tightly the exterior of material M
against the interior of mold 10. The amount of pressure and exact
length of time for which pouch 2 must be inflated depends largely
on the type of material being molded. It is within the ability of
a skilled technician to make these determinations. Once the
molding of material M is completed, the pressure is released from
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pouch 2 via supply line 4 thereby deflating the pouch.
Pressurizing unit 1 is then separated from mold 10 to allow
retrieval of the final molded product
Many materials may be molded in accordance with the apparatus
and method of the present invention. In a preferred form, the
material is a metal, synthetic resin or polymer.
The pressurizing agent may be any suitable liquid or gaseous
media including, but not limited to, water and other liquids such
as oils and compressed air and other gases. In a most preferred
form, the pouch is pressurized by hydraulic pressure via a
pressurizer (not shown in the figures). In this way, the
pressurizing agent is pressurized by a high-pressure pump and flows
through supply line 4 via supply connector 6. The high-pressure
pump also serves to deflate pouch 2 by ~draining" the pressurizing
agent from the pouch at the completion of the molding cycle.
In a preferred form, pressurizing unit 1 is maintained in an
air-tight condition during molding by a hydraulic operating device
so as to prevent the unit from lifting itself when pouch 2 is
inflated.
Supply line 4 is depicted in the figures as vertically
traversing the base plate. Although this is a preferred
configuration, it is by no means the only way in which pouch 2 may
be supplied with pressurizing agent.
In summary, a preferred operation of the invention using
hydraulic pressure is as follows: after placing almost
tubular-formed Material M in Mold 10 closely assembled and
positioned low, Pressurizer Unit 1 is lowered from the above. Then
pouch 2 of Pressurizer Unit 1 is inserted into Material M while in
a deflated state without the supply of pressurizing agent or fluid
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F. Then, highly pressurized agent or fluid F is supplied into
pouch 2 from fluid pressurizer through supply connector 6 and fluid
supply line 4. As a result, pouch 2 inflates and presses material
M against the interior surface of Mold 10, where it maintains the
pressure. Once the transfer of molding shape on the interior
surface of mold 10 is completed, fluid F is removed from pouch 2.
When pouch 2 is deflated, it is lifted out of material M. Mold 10
is separated and disassembled to allow for the retrieval of
material M.
The present invention can facilitate the transfer of the
molding pattern of mold 10 onto material M, using pouch 2 inflated
under the pressure supplied by agent such as fluid F to press
material M against the inside of mold 10. As the pressure is
maintained steadily when pouch 2 inflates, the problem of
spring-back is reduced, resulting in improved and closer contact of
material M against the shape of mold 10, which enables processing
of more complex patterns with greater accuracy. Furthermore, the
method of the present invention can be operated at a lower cost
since, unlike conventional expansion molding methods, it does not
require complicated structures or forms such as an enlargeable
punch.
As this is a pressing process that utilizes pressure from a
highly pressurized agent such as fluid , all-directional pressure
is maintained uniformly inside pouch 2, enabling an even transfer
of the surface shape of mold 10. In addition, high pressure is
applied for an extended period of time during the supply of
pressurizing agent F to pouch 2 inside pressurizing unit 1,
reducing spring-back to ensure a high degree of duplication
accuracy.
Furthermore, unlike conventional methods, the method of the
present invention does not use the male/female form of mold, but
requires only mold 10 as described herein into which pouch 2 is
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inserted. This helps to lower the cost of producing molds, which
in turn contributes to the provision of lower-priced molded
products
This method is particularly suited for the molding of, for
example, hollow helmet-shaped products with narrow openings and
flaring body cavities as it does not require complicated structures
or components, procedure or control of division, breaking and
removal direction in releasing the mold as is the case with
conventional methods.
In the use of a highly pressurized agent such as fluid, the
safety of operation within the present invention is ensured as the
pressurized agent is sealed in a pouch such that there is no
leakage or gushing of the agent under pressure. In contrast to the
expansion molding method which uses the enlarging of a punch
resulting in a restricted molding capability, this invention
suffers no restriction. It does not require insertion of rubber or
fluid before molding, as the bulge mold process requires, thus
resulting in the elimination of the need to clean and drain the
mold. This contributes significantly to labour savings.
