GB2266262A

GB2266262A - Removal of spurious formations formed during moulding of plastics articles

Info

Publication number: GB2266262A
Application number: GB9309677A
Authority: GB
Inventors: Stephen Paul Green
Original assignee: Dunlop Automotive Composites UK Ltd
Current assignee: Vitesco Technologies UK Ltd
Priority date: 1991-10-31
Filing date: 1992-10-22
Publication date: 1993-10-27
Anticipated expiration: 2012-10-22
Also published as: GB2266262B; GB9309677D0

Abstract

In the manufacture of an article by a moulding process any spurious formation arising during manufacture is removed by being subject to laser beam energy; where the process involves use of mould segments of fusible material the laser beam energy may be used to unite the segments.

Description

S UFACU 07 ICE ARTiCL#S This invention relates to the manufacture of articles c plastics material and in particular, touch not exclusively, to the manufacture of articles bv 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 ana 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 a 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 or spurious formations conventionally associated it h the manufacture of products of plastics and especially cf thermoplasti type mastics materials.

accordance witfl one of its aspects the invention provides a method far the manufacture cf a moulcec plastics article comprising the use of multi-segment mould cf fusible material which defines at least in part a cavity 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 further provides a method in which at least one of said edge regions is provided witn a spurious rib formation which acts as a source of filler material when heated by the laser beam to fill small spaces between the confronting surfaces a the mould segments and facilitate a smooth surfaced point.

One at 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 erect 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 cur-sed.

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 farmed by a technique known per se and which results in a spurious formation an the article, said article then being subjected to energy ram a laser beam directed to the spurious oration.

The laser ea may Se employed to remove the spurious formation bv a cutting action or to melt it to blend with the neighbouring material forming the bodv of he plastics article.

The invention particularly envisages that t plastics material shall be a thermoplastic type plastics material. However, thermoset materials mav 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 law 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 filler rib to flaw into and fill 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 respective surfaces far confronting one another when assembled to define at least in part a mould at least one of those surfaces is provided with a deformable abutment tarmatian adapted to deform wnen 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 welded 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 reverence to the accompanying drawings in which: Figure 1 is a perspective view of a pair at mould segments in accordance with the present invention, and Figure 2 is a perspective view of a pair at 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-cylinarical tubular farm and comprises a pair of faces (12,13) for cantranting faces of the other segment.One segment (10) is farmed xith 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 taces (13) of the other mould segment (11) are provided with longitudinally extendIng rebates (15), also at their radially inne edges.

When tne two mould segments are assembled together in the configuration snow in the accompanvino drawincs a beam of laser energy is directed to each filler rib (14), typIcally by means at an or optical fibre assembìy which can extend through the bore (16) defined 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 surface 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 flaw 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 1800 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 positioned at radially outer edges of the faces (13).

Figure 2 snows two mould segments (20,21) each of a substantially semi-cylindrical tubular form anc comprising a pair o aces (22,23) for con-rontino 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 at confronting surfaces.

The mould segments may be of a law melting temperature metal alloy such as lead-tin- ntimony or #in-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 to segments.

Where the invention is applied to removal of spurious formations from a plastics article, that article may be pre-for.,.ec with a depression proximate a region of the article at whIch a flash lie or similar spurious formation tends to occur whereby ere bean of laser energy may #e employed to cause tre spurious formation to flow into and be received by the depression. Alternatively the beam of laser ere may be utilised to remove tne flash line bv a cutting operation.

Claims

CLAIMS:

1. 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 subjected to energy from a laser beam directed to the spurious formation.

2. A method according to claim 1 wherein the laser beam energy is employed to remove the spurious formation by a cutting action.

3. A method according to claim 1 or claim 2 wherein the laser beam energy is employed to melt the spurious formation to blend with neighbouring material forming the body of the article.

4. A method according to any one of claims 1 to 3 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.

5. 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.

6. A method according to claim 1 or claim 5 and substantially as hereinbefore described.

7. 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 said surfaces are urged towards one another.

8. A pair of mould segments according to claim 7 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.

9. A pair of mould segments according to claim 7 or claim 8 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.

10. A pair of mould segments according to any one of claims 7 to 9 and substantially as hereinbefore described with reference to the accompanying drawings.

11. A method according to any one of claims 1 to 6 wherein the article is moulded by use of a pair of mould segments according to any one of claims 7 to 10.