GB2339551A

GB2339551A - Adjustable mould

Info

Publication number: GB2339551A
Application number: GB9815139A
Authority: GB
Inventors: Jason Rowe; Gordon Frederick Smith; Paul Kalvei Clarkson Wood
Original assignee: MG Rover Group Ltd
Current assignee: MG Rover Group Ltd
Priority date: 1998-07-14
Filing date: 1998-07-14
Publication date: 2000-02-02
Also published as: GB9815139D0

Description

2339551 ADAPTABLE TOOL The present invention relates to a moulding

assembly for defining a casting cavity, the shape of which can be varied to attain different configurations. Such a mould has particular, but not exclusive, application in plastics moulding processes.

A tool for use as a mould is known comprising a plurality of thin elongate wires bound together in a retainer by externally applied lateral pressure, the ends of the wires defining a surface of the tooling. The externally applied lateral pressure can be released to allow the wires to be moved so that the ends define a new surface, and the external pressure reapplied to maintain the new surface.

However, it is difficult to control the lateral pressure to keep the wires in place.

In addition, positioning errors can occur when the movement of one wire induces movement of neighbouring wires during positioning. Further, it is normally necessary to introduce a sheet material between the tool and a mould blank to prevent the ends of the wires either damaging the mould blank or leaving a stippled effect on the resultant moulded object.

It is an advantage of the present invention that it reduces or substantially eliminates these problems.

According to a first aspect of the present invention a variable mould assembly comprises an enclosure having an elastically deformable surface and shaping means to generate a desired configuration of the surface characterised in that releasable holding 1.

means are provided within the enclosure to maintain the surface in the desired configuration.

Preferably the surface comprises an elastic skin.

Preferably the shaping means comprises an array of elongate members passing into the enclosure to generate the desired configuration. More preferably at least some of the elongate members are connected to the surface.

Preferably the holding means may comprise liquid under pressure.

Alternatively, the holding means may comprise a material that may be allowed to maintain a liquid state to allow the desired configuration to be generated, and to maintain a solid state to maintain the desired configuration. Preferably, the material comprises a polymer or wax which is heated to the liquid state and allowed to cool to the solid state. Alternatively, the material comprises a electrorheological material which is normally in the liquid state, and on application of an electric charge takes on the solid state.

According to a second aspect of the invention a variable mould assembly comprises an enclosure having an elastically deformable surface and shaping means to generate a desired configuration of the surface characterised in that releasable holding means are provided within the enclosure to maintain the surface in the desired configuration and in that carrier means are provided to move at least that portion of the surface not lying on a predetermined datum to a position further away from the datum.

According to a third aspect of the invention a method of casting an article about a body or bodies comprises the steps of; providing a variable mould assembly comprising an enclosure having an elastically deformable surface, shaping means to generate a desired configuration of the surface, releasable holding means provided within the enclosure to maintain the surface in the desired configuration and carrier means to move at least that portion of the surface, generating a desired surface configuration by taking an impression of the body or bodies, causing the at least that portion of the surface not lying on a predetermined datum to move to a position further away from the datum, injecting a molten material into the mould between the body or bodies and the surface, allowing the material to solidify and removing the mould assembly.

Preferably the carrier means moves the at least that portion of the surface not lying on a predetermined datum a fixed distance away from the predetermined datum, such that the article is of even thickness. Alternatively, the carrier means moves different areas of the at least that portion of the surface not lying on a predetermined datum a different distance away from the predetermined datum, such that the article is of varying thickness.

Preferably the material from which the article is formed is a polymerisable material, such as a thermoplastic.

The invention will now be described, by way of example only, with reference io the accompanying drawings, in which:

Figure 1 shows a sectional side view of a mould assembly according to a first embodiment of the first aspect of the present invention in a first position; Figure 2 shows a sectional side view of the mould assembly of Figure 1 in a second position; Figure 3 shows a sectional side view of the mould assembly of Figure 1 in a third position; and Figure 4 shows a sectional side view of a mould assembly according to a second embodiment of the first aspect of the present invention. - Referring first to Figure 1, there is shown a side sectional view of a mould assembly according to a first aspect of the invention in a first position. The mould assembly comprises an enclosure 6 defined by a frame 2 and an elastically deformable surface 3. Side members 4,5 of the frame 2 are connected across an upper surface of 5 the enclosure 6 by an upper member 7, and across a lower surface by the elastically deformable surface 3. The upper member 7 comprises top and bottom plates 8,9. Each of the plates is provided with a matrix of holes 10. The holes 10 are aligned with those of the plate above or below respectively. Elongate members in the form of pins 12 pass through the holes 10 into the enclosure. The pins form a fluid seal at each of the holes. The ends of the pins 12 within the enclosure may be attached to the deformable surface 3. A cavity 14 is defined between the plates 8,9. A moulding material, preferably a liquid polymer, may be injected into the cavity 14 by way of an inlet (not shown). The inlet may take the form of a hollow pin in this assembly.

To generate a desired mould surface, the pins are moved into a position such that the ends of the pins within the enclosure define the desired surface. This may be done, for example, by driving each of the pins into an individual desired position. Alternatively, the mould assembly may be lowered onto a prototype or relief 16 to leave an impression of the desired shape in the mould. Once the pins are in the desired position, the pressure of the fluid in the cavity 14 is increased to hold the pins in position (Figure 2). The mould assembly may now be used. The mould assembly is used to form a mould cavity 18. The mould assembly may be used together with a fixed mould 19 (Figure 3) or another variable mould assembly to form the mould cavity.

If the deformable surface 3 is connected to the ends of the pins 12, the mould cavity will have the shape of the object to be moulded. If the deformable surface is 5 not so connected, the injected polymer will fill the mould cavity, pushing the deformable surface into contact with the ends of the pins, thereby to form the desired shape of the object to be moulded.

Once the moulding process has been completed the mould assembly may be used again either for the same mould configuration or a different mould configuration. If a different configuration is desired, the fluid pressure in the cavity is released allowing the pins to be moved to form the different mould configuration.

Instead of injecting fluid under pressure into the cavity 14 in the upper member 7 of the frame 2, an electrorheological fluid may be used. Such a fluid is normally in a liquid state, but on application of an electric charge becomes solid, thereby maintaining the pins in the required position.

As a further alternative, a polymer or wax material may be provided in the cavity 14 within the frame 2. The wax material may be heated to become molten to allow the pins to move and subsequently allowed to cool when the pins have achieved the desired configuration.

A second embodiment of the invention is shown in Figure 4. A mould assembly comprises an enclosure 26 defined by a frame 22 and an elastically deformable surface 23. Side members 24,25 of the frame are connected across an upper surface of the enclosure 26 by an upper member 27, and across a lower -surface by the 5 elastically deformable surface 23.

The upper member 27 is provided with a plurality of holes 30 through which elongate members in the form of pins 32 extend. Within the enclosure there is provided a electrorheological fluid. It is not necessary for this liquid to fill the enclosure. However if it does, means need to be provided to drain any excess fluid when certain mould assembly configurations are adopted.

As in the previous embodiment the pins are arranged in a desired configuration either by driving the individual pins or by placing the mould assembly onto a prototype or other relief having the desired shape and allowing an impression to be taken. Once the desired shape has been attained, an electric charge is applied to the fluid. The fluid then becomes solid and movement of the pins is prevented. The mould assembly can then be used as required. The mould assembly may be used together with a fixed mould 39 (Figure 4) or another variable mould assembly to form the mould cavity 38. When a new configuration is required, the charge is removed allowing the electrorheological fluid to become liquid once more. The mould assembly is now able to adopt the new configuration.

In a further embodiment (not shown), a mould assembly, such as that shown in Figures I to 3, or that shown in Figure 4, is fitted with carrier means which enables each of the pins to be moved individually. A datum position is defined as that position when all of the pins are aligned to form a planar surface at the deformable 5 surface.

When the mould assembly is placed over a body or bodies to form the desired shape, the deformable surface is moved away from the datum position over at least part of its area. Once the desired shape has been achieved, the carrier means are used to move those pins defining the shape of the deformable surface over the part of its area moved from the datum further away from the datum. This creates a cavity between the body or bodies and the deformable surface.

A molten material may now be injected into the cavity to form an article, the outer shape and size of which are defined by the deformable surface of the mould assembly. The material is allowed to solidify before the mould assembly is removed.

If each of the pins that are moved are moved an equal amount, the article will be of uniform thickness. It will be understood that a uniform thickness will not always be required. In such a case each of the pins may be moved an individual different amount to create an article having the desired thickness at various points.

Preferably, the material from which the article is formed is a polymerisable material, such as a thermoplastic.

Claims

-10CLAIMS

1. A variable mould assembly comprising an enclosure having an elastically deformable surface and shaping means to generate a desired configuration of the surface characterised in that releasable holding means are provided within the enclosure to maintain the surface in the desired configuration.

2. A mould assembly according to claim 1, characterised in that the surface comprises an elastic skin.

3. A mould assembly according to either claim I or claim 2, characterised in that the shaping means comprises an array of elongate members passing into the enclosure to generate the desired configuration.

4. A mould assembly according to claim 3, characterised in that at least some of the elongate members are connected to the surface.

5. A mould assembly according to any of claims I to 4, characterised in that the holding means comprises liquid under pressure.

6. A mould assembly according to any of claims 1 to 4, characterised in that the holding means comprises a material that may be allowed to maintain a liquid state to allow the desired configuration to be generated, and to maintain a solid state to maintain the desired configuration.

7. A mould assembly according to claim 6, characterised in that the material comprises a polymer or wax which is heated to the liquid state and allowed to cool to the solid state.

8. A mould assembly according to claim 6, characterised in that the material comprises a electrorheological material which is normally in the liquid state, and on application of an electric charge takes on the solid state.

9. A variable mould assembly substantially as described herein with reference to and as illustrated in Figures 1 to 3 of the accompanying drawings.

10. A variable mould assembly substantially as described herein with reference to and as illustrated in Figure 4 of the accompanying drawings.

11. A variable mould assembly according to any of claims I to 10, characterised in that carrier means are provided to move at least that portion of the surface not lying on a predetermined datum to a position further away from the datum.

12. A method of casting an article about a body or bodies comprises the steps of, providing a variable mould assembly according to claim 11, generating a desired surface configuration by taking an impression of the body or bodies, using the carrier means to cause the at least that portion of the surface not lying on a predetermined datum to move to a position further away from the datum, injecting a molten material into the mould between the body or bodies and the surface, allowing the material to solidify and removing the mould assembly.

13. A method according to claim 12, characterised in that the carrier means moves the at least that portion of the surface not lying on a predetermined datum a fixed distance away from the predetermined datum.

14. A method according to claim 12, characterised in that the carrier means moves different areas of the at least that portion of the surface not lying on a predetermined datum a different distance away from the predetermined datum, such that the article is of varying thickness.

15. A method according to any of claims 12 to 14, characterised in that the material from which the article is formed is a polymerisable material.

16. A method according to claim 15, characterised in that the polymerisable material is a thermoplastic.

17. A method of casting an article about a body or bodies substantially as described herein with reference to and as illustrated in the accompanying drawings.