CA2191010A1

CA2191010A1 - Method of high pressure molding and apparatus therefor

Info

Publication number: CA2191010A1
Application number: CA002191010A
Authority: CA
Inventors: Junya Nakayama
Original assignee: Nakayama Engineering Co Ltd
Current assignee: Nakayama Engineering Co Ltd
Priority date: 1996-11-22
Filing date: 1996-11-22
Publication date: 1998-05-22

Abstract

A method of pressure molding a material into a desired shape 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 comprising 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.

Description

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 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.

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 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 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 - S -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 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 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 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.

Claims

1. A method of pressure molding a material into a desired shape which comprises:
placing the material in a hollow mold form, said mold form having a mouth for receiving a pressurizing unit, said unit comprising an inflatable resilient pouch;
inserting and securing the pressurizing unit in the mouth;
inflating the pouch under pressure 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.

2. The method of claim 1 wherein the pouch is inflated with pressurized liquid media.

3. The method of claim 1 wherein the pouch is inflated with pressurized gaseous media.

4. The method of claim 1 wherein the pouch is made of a synthetic rubber selected from the group comprising chloroprene, nitryl, silicone and fluorine and wherein the rubber is sufficiently heat-resistant to withstand the temperature at which the material is made pliable.

5. The method of claim 1 wherein the pouch is covered with a substantially heat-resistant coating.

6. The method of claim 1 wherein the hollow mold form comprises two or more interconnectable pieces.

7. The method of claim 1 wherein the pressurizing unit is secured to the mold form by way of an annular ring.

8. The method of claim 1 wherein the pressurizing unit additionally comprises a rigid base engaging the pouch.

9. The method of claim 1 wherein the material is held within the mouth of the mold form by way of a retaining means.

10. The method of claim 1 wherein the material is selected from the group comprising metals, synthetic resins and polymers.

11. A pressure molding apparatus suitable for molding a material into a desired shape 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; said pouch engaging the base and being capable, in an inflated condition, of pressing the material against the interior of the mold thereby transferring the shape of the mold form to the material; said securing means enabling removable attachment of the pressurizing unit to the mold form.

12. The apparatus of claim 11 wherein the pouch is made of a synthetic rubber selected from the group comprising chloroprene, nitryl, silicone and fluorine and wherein the rubber is sufficiently heat-resistant to withstand the temperature at which the material is made pliable.

13. The apparatus of claim 11 wherein the pouch is covered with a substantially heat-resistant coating.

14. The apparatus of claim 11 wherein the hollow mold form comprises two or more interconnectable pieces.

15. The apparatus of claim 11 wherein the securing means is an annular ring.

16. The apparatus of claim 11 wherein the material is held within the mouth of the mold form by way of a retaining means.

17. The apparatus of claim 11 wherein the material is selected from the group comprising metals, synthetic resins and polymers.

18. The apparatus of claim 11 wherein the pressurizing agent is liquid media.

19. The apparatus of claim 11 wherein the pressurizing agent is supplied to the pouch via a supply line traversing the base plate.

20. The apparatus of claim 11 wherein the mold is metal.