GB2260933A

GB2260933A - Manufacture of plastics articles

Info

Publication number: GB2260933A
Application number: GB9222177A
Authority: GB
Inventors: Stephen Paul Green
Original assignee: Dunlop Automotive Composites UK Ltd
Current assignee: Continental Automotive Telford UK Ltd
Priority date: 1991-10-31
Filing date: 1992-10-22
Publication date: 1993-05-05
Anticipated expiration: 2012-10-22
Also published as: GB9222177D0; JPH05237845A; FR2684916B1; GB9123154D0; FR2684916A1; GB2260933B; DE4236558A1; BE1006261A5

Abstract

In the manufacture of an article in a multi-segment mould of fusible material any spurious formation arising during manufacture is minimised by positioning the mould segments in a desired configuration and exposing adjacent edge regions to laser beam irradiation to unite the segments at said edge regions. One mould segment edge may be provided with a spurious rib formation 14 of fusible material, the adjacent segment edge being provided with a channel 15 to receive material flowing from said ribs on irradiation. Alternatively one segment edge may be provided with a deformable abutment 25 which is deformed in contact with a plain segment edge 22 prior to moulding. <IMAGE>

Description

12 15 '? -3 3 MANUFACTURE OF PLASTICS ARTICLES This invention relates to

the manufacture of articles of plastics material and in particular, though not exclusively, to the manufacture of articles by a "lost core" type of process in which plastics material is moulded with the aid of the fusible melt out mould core member which may be of a multi-segment type and which, subsequent to moulding, is removed by heating the mould core member to a molten state in which it can flow out from a cavity thereby defined by the moulded plastics material.

A problem which often arises in the manufacture of plastics articles by a moulding technique is that spurious formations, e g so-called flash lines of surplus material are formed near the point of injection of material into the mould. These spurious formations also arise elsewhere on the article if moulded with the use of a multi-segment type mould.

In the manufacture of precision type engineering products the removal of flash lines and other spurious formations needs to be undertaken carefully and therefore leads to additional manufacturing time and expense. Removal is particularly difficult if the formations are at relatively inaccessible surfaces of the moulded article, such as arises when an article of complex shape is moulded by a lost core technique with the aid of a multi-segment mould.

The difficulty of removing spurious protruberances is not so great if plastics materials of a particular type, such as thermosetting plastics are chosen. However, for many products the relatively brittle characteristics and high cost of thermosetting type plastics as compared with, for example, thermoplastic type plastics render thermosetting plastics unsuitable.

The present invention seeks to provide a method for the avoidance or mitigation of the aforementioned problem of spurious formations conventionally associated with the manufacture of products of plastics and 2. especially of thermoplastic type plastics materials.

In accordance with one of its aspects the present invention provides a method for the manufacture of a moulded plastics article comprising the use of a multi-segment mould of fusible material which defines at least in part a cavity f or the moulding of plastics material wherein prior to moulding of the plastics material the mould segments are positioned in a preselected orientation relative to one another and edge regions of confronting surfaces of the segments are subject to laser beam energy to unite the mould segments at least at said edge region and remove any spurious formations at said edge regions.

The invention f urther provides a method in which at least one of said edge regions is provided with a spurious rib formation which acts as a source of f iller material when heated by the laser beam to f ill small spaces between the confronting surfaces of the mould segments and facilitate a smooth surfaced joint.

One of said confronting surfaces may be provided with a deformable abutment formation which preferentially deforms when the confronting surfaces are urged towards one another so as substantially to effect a seal therebetween. The abutment formation may be longitudinally extensive, preferably longitudinally continuous, and preferably is disposed proximate one of said edge regions which is to be subject to said laser beam energy. The longitudinally extensive formation may extend rectilinearly and/or be curved.

In accordance with another of its aspects the present invention provides a method for the manufacture of a moulded plastics article in which a moulded plastics article is formed by a technique known per se and which results in a spurious formation on the article, said article then being subjected to energy from a laser beam directed to the spurious formation. The laser beam may be employed to remove the spurious 3.

formation by a cutting action or to melt it to blend with the neighbouring material forming the body of the plastics article.

The invention particularly envisages that the plastics material shall be a thermoplastic type plastics material. However, thermoset materials may also be used.

Preferably the beam of laser energy is directed to the surface of the plastics article or multi-segment mould in a direction substantially perpendicular either to the surface of the plastics article in the vicinity of the spurious formation or substantially perpendicular to the surface of the mould in the vicinity of a localised edge region.

The beam of laser energy may be provided in known manner and may be suitably - de-tuned where, as will usually be the case, only a low level of energy input is required. In order to achieve a smooth joint between two segments of a multi-segment mould and thereby avoid any surface irregularities in confronting regions of the moulded article it is particularly preferred that use be made of a shaped laser pulse adapted to avoid an initial surge of energy during each pulse.

The present invention further provides that in a pair of mould segments of fusible material having respective surfaces for confronting one another when assembled to define at least in part a mould one of the surfaces is provided with a receptor zone (such as a groove or rebate) at an edge which is exposed when the confronting surfaces are in contact and the other surface is provided at a similarly exposed edge with a filler rib whereby laser energy applied to and in the vicinity of the filler rib causes spurious material of the f iller rib to f low into and f ill the receptor zone. The two mould segments may be united by said material which flows into the receptor zone.

The present invention also provides that in a pair of mould segments of fusible material having 4. respective surfaces for confronting one another when assembled to def ine at least in part a mould at least one of those surfaces is provided with a deformable abutment formation adapted to deform when said surfaces are urged towards one another. Preferably the abutment formation is substantially longitudinally continuous thereby to be able to provide a substantially continuous seal between the confronting surfaces when urged one towards the other. Preferably the abutment formation is provided on said confronting surface at a position proximate an edge of that surface which is to be subjected to laser beam energy.

It is not essential that the two mould segments be united at or only be united at an exposed edge region. The mould segments may be subjected to a deep welding technique in which confronting surfaces are 7elded together at a position lying within the body of the mould material, beneath the exposed edge region.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:- Figure 1 is a perspective view of a pair of mould segments in accordance with the present invention, and Figure 2 is a perspective view of a pair of mould segments in accordance with another embodiment of the present invention.

Figure 1 illustrates two identical mould segments (10,11) for uniting together by a method in accordance with the present invention. Each mould segment (10,11) is of a substantially semi-cylindrical tubular form and comprises a pair of faces (12,13) for confronting faces of the other segment. One segment (10) is formed with face regions (12) the radially inner edges of which are each provided with a spurious rib formation (14) of the material of the mould segment. The faces (13) of the other mould segment (11) are provided with longitudinally extending rebates (15), also at their 5. radially inner edges.

When the two mould segments are assembled together in the configuration shown in the accompanying drawings a beam of laser energy is directed to each f iller rib (14), typically by means of an of optical fibre assembly which can extend through the bore (16) def ined by the pair of segments. The fibre assembly is bent such that the beam of laser energy is directed radially outwards in a direction substantially perpendicular to the localised surf ace region of a pair of exposed edges of the confronting faces. The level of energy is controlled to result in filler rib material (14) flowing into the neighbouring rebate (15) which acts as a receptor zone for that material. The level of heat applied is sufficient to soften the moulded material which defines a longitudinally extending rebate (15) and thus result in the filler rib material forming a bond between the mould segments.

The aforedescribed process is conducted on a filler rib and rebate arranged to face vertically upwards so that the filler rib material is disposed naturally to tend to flow into the rebate. Subsequently with the two mould segments held by external means (not shown) in the required relative position the segments are turned through 180' about the longitudinal axis of the bore (16) and the aforementioned process is applied to the other filler rib and groove.

There thereby results a mould having a substantially seamless bore and in which an article may be moulded without the creation of flash lines or other spurious formations which normally would arise if use were made of a simple mould comprising two semicylindrical segments directly held in abutment.

It is not essential that the filler ribs (14) face radially inwards. In an alternative method to that described above the filler ribs (14) may be provided at radially outer edges of the face regions to face radially outwards, the rebates (15) then being 6. positioned at radially outer edges of the faces (13).

Figure 2 shows two mould segments (20,21) each of a substantially semicylindrical tubular form and comprising a pair of faces (22,23) for confronting faces of the other segment. One segment 21 has two faces 23 each provided near to their radially inner edge 24, with a small deformable abutment formation 25 which is integral with the material of the segment and extends continuously over that face parallel with the longitudinal axis of the segment. The faces 22 of the other segment 20 are planar.

In use the two segments are urged together to cause the abutment formations 25 to deform against and tend to embed into the confronting faces 23 of the other segment. Continuous contact therefore is ensured between the two pairs of confronting surfaces and this assists in ensuring that a subsequently applied beam of laser energy is able readily to form continuous welds between each pair of confronting surfaces.

The mould segments may be of a low melting temperature metal alloy such as lead-tin-antimony or tin-bismuth, and which are re-usable subsequent to melting to remove from a moulded plastics article. The method of the present invention does not rely on any other material other than that of the mould core segments to result in their unification for use as a mould and thus the mould core material is readily available for re-use without removal of contaminants such as might be necessary if, for example, an adhesive or soldering technique were utilised to join together the two segments.

Where the invention is applied. to removal of spurious formations from a plastics article, that article may be pre-formed with a depression proximate a region of the article at which a flash line or similar spurious formation tends to occur whereby the beam of laser energy may be employed to cause the spurious formation to flow into and be received by the depression. Alternatively the beam of laser energy may be utilised to remove the f lash line by a cutting operation.

8.

Claims

CLAIMS:

1. A method for the manufacture of a moulded plastics article comprising use of a multi-segment mould of fusible material which defines at least in part a cavity for the moulding of plastics material wherein prior to moulding of the plastics material the mould segments are positioned in a pre-selected orientation relative to one another and edge regions of confronting surfaces of the segments are subject to laser beam energy to unite the mould segments at least at said edge region and remove any spurious formations at said edge region.

2. A method according to claim 1 wherein at least one of said edge regions is provided with a spurious rib formation adapted to act as a source of filler material when heated.

3. A method according to claim 1 or claim 2 wherein at least one of said confronting surfaces is provided with a deformable abutment formation adapted preferentially to deform when said confronting surfaces are urged one towards the other.

4. A method according to claim 3 and comprising the use of an abutment formation which is longitudinally continuous.

5. A method according to claim 3 or claim 4 and comprising the use of a deformable abutment formation which is disposed on one of said confronting surfaces at or near to an edge region thereof which is to be subject to said laser beam energy.

6. A method according to any one of the preceding claims wherein the beam of laser energy is directed to the surface of the multi-segment mould in a direction substantially perpendicular to the surface of the mould in the vicinity of a localised edge region of a confronting surface.

7. A method for the manufacture of a moulded plastics article wherein a moulded plastics article is formed by a technique known per se to result in a spurious formation on the article, said article then being 9. subjected to energy from a laser beam directed to the spurious formation.

8. A method according to claim 7 wherein the laser beam energy is employed to remove the spurious formation by a cutting action.

9. A method according to claim 7 or claim 8 wherein the laser beam energy is employed to melt the spurious formation to blend with neighbouring material forming the body of the article.

10. A method according to any one of claims 7 to 9 wherein the beam of laser energy is directed to the surface of the plastics article in a direction substantially perpendicular to the surface of the article in the vicinity of the spurious formation.

11. A method for the manufacture of an article by a moulding process wherein any spurious formation arising during manufacture is removed by being subjected to laser beam energy.

12. A method according to claim 1, claim 7 or claim 11 and substantially as hereinbefore described.

13. A pair of mould segments of fusible material having respective surfaces for confronting one another when assembled to define at least in part a mould, one of said surfaces being provided with a receptor zone at which an edge is exposed when the confronting surfaces are in contact, the other surface being provided at a similarly exposed edge with a filler rib whereby laser energy applied to and in the vicinity of the filler rib causes spurious material of the filler rib to flow into and fill the receptor zone.

14. A pair of mould segments according to claim 13 wherein said receptor zone comprises a groove, rebate or like formation.

15. A pair of mould segments of fusible material having respective surfaces for confronting one another when assembled to define at least in part a mould, at least one of said surfaces being provided with a deformable abutment formation adapted to deform when 10.

said surfaces are urged towards one another.

16. A pair of mould segments according to claim 15 wherein said deformable abutment formation is substantially longitudinally continuous thereby to be able to provide a substantially continuous seal between said confronting surfaces when said surfaces are urged one towards the other.

17. A pair of mould segments according to claim 15 or claim 16 wherein the deformable abutment formation is provided on a confronting surface at a position thereof proximate an edge of that surface which is to be subject to laser beam energy.

18. A pair of mould segments according to any one of claims 13 to 17 and substantially as hereinbefore described with reference to the accompanying drawings.