METHOD OF MUTUALLY POSITIONING A PAIR OF SHAPING-TOOL HALVES FACING EACH OTHER, AND SHAPING TOOL FOR THE MANUFACTURE OF PRECISION-MADE ARTICLES, IN PARTICULAR CONTACT LENSES

PROCEDE POUR LE POSITIONNEMENT MUTUEL DE PAIRES D'ELEMENTS DE MOULE OPPOSES, ET MOULE POUR LA FABRICATION DE PIECES DE PRECISION, NOTAMMENT DE LENTILLES DE CONTACT

English Abstract

Proposed is a shaping tool for manufacturing precision-made articles, in
particular contact lenses, said shaping tool comprising two halves fitted with
inserts (18, 38) and with a cavity (50) between them. The tool is made of
ceramic glass with negligible thermal expansion in a given work range. On each
side of the cavity (50) is a ceramic-glass insert which defines the shape of
the part being manufactured and which is positively held round its
circumference in a positioning plate (16, 36) also made of ceramic glass. The
positioning plates (16, 36) are each mounted on a ceramic-glass mounting plate
(14, 34).

French Abstract

L'invention concerne un moule pour la fabrication de pièces de précision, notamment de lentilles de contact, ledit moule comprenant deux parties formant une cavité (50), et deux inserts (18, 38). Ce moule est réalisé dans un matériau vitrocéramique présentant un allongement thermique négligeable dans une plage de travail donnée. Sur chaque côté de la cavité (50) est prévu un insert (18, 38) en vitrocéramique qui détermine la forme de la pièce de précision à fabriquer et est maintenu par liaison de forme au niveau périphérique, dans une plaque de positionnement (16, 36), également en vitrocéramique. Les plaques de positionnement (16, 36) sont placées chacune sur une plaque de support (14, 34) en vitrocéramique.

Claims

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claims:

1. A method for the reciprocal positioning of pairs of opposed shape-determiningmoulding tool portions that co-operate to form a mould cavity, for the manufacture of
precision articles, especially contact lenses,

in which method

(a) the position of each of the tool portions is determined by an associated
element made of a material that exhibits negligible thermal expansion in a
working temperature range, and

(b) the relative position of the two elements associated with the tool portions is
determined precisely by positioning means.

2. A method according to claim 1, in which

(a) the tool portions are each fixed, in the resulting positions, to a support made of
a material that exhibits negligible thermal expansion in a working temperature
range, and

(b) the positioning element is subsequently removed.

3. A method according to claim 1 or claim 2, in which
(a) the tool portions and, where appropriate, the supports are provided with
polished flat surfaces, and

(b) the fixing of the tool portions is effected by optical wringing.

4. A method according to any one of claims 1 to 3, in which a glass ceramics material
is used as material that exhibits negligible thermal expansion in a working temperature
range.


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5. A method according to any one of claims 1 to 3, in which a metal alloy having low
thermal expansion, for example Invar, is used as material that exhibits negligible
thermal expansion in a working temperature range.

6. A method according to any one of claims 1 to 5, in which a quartz glass is used as
material for the tool portion.

7. A moulding tool for the manufacture of precision articles, especially contact lenses,
that consists of two tool halves (10,12; 90, 92) having shape-determining tool
portions (18, 38; 96, 100), which tool halves form a mould cavity (32; 106),

in which moulding tool

(a) the position of the shape-determining tool portions (18, 38; 96, 100) in each of
the tool halves (10,12; 90, 92) is determined by supports (16, 36; 94, 98)
made of a material that exhibits negligible thermal expansion in a working
temperature range, and

(b) the reciprocal position of the supports (16, 36; 94, 98) is determined by
high-precision positioning means (54, 58; 114, 116) that act directly between the
two supports (16, 36; 94, 98).

8. A moulding tool according to claim 7, in which the tool inserts (18, 38; 96, 100) are
each mounted on a support plate (14, 34; 94, 98) made of a material that exhibits
negligible thermal expansion in a working temperature range.

9. A moulding tool according to either claim 7 or claim 8, in which there is provided on
each side of the mould cavity (32) a tool insert (18, 38; 96, 98) that determines the
shape of the precision article to be manufactured, which tool insert is held around its
circumference in a form fit in a positioning plate (16, 36; 110,112) made of a material
that exhibits negligible thermal expansion in a working temperature range.





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10. A moulding tool according to any one of claims 7 to 9, in which the positioning
means comprise index pins (54; 114).

11. A moulding tool according to claim 9, in which the positioning plates (16, 36) are
held in a precisely defined position relative to one another by the positioning means
(54, 58).

12. A moulding tool according to claim 10, in which

(a) index pins (54) are mounted on one of the positioning plates (36), and

(b) the other positioning plate (16) has, in alignment with each index pin (54), an
opening (56) having an index bush (58), the tool inserts (18, 38) opposed to
one another being in correct alignment with one another when the index pins
(54) engage in the index bushes (58).

13. A moulding tool according to claim 10, in which

(a) index pins (114) are mounted on one of the support plates (98), and
(b) the other support plate (94) has, in alignment with each index pin (114), anopening (124) having an index bush (116), the tool inserts (96, 100) opposed
to one another being in correct alignment with one another when the index
pins (114) engage in the index bushes (116).

14. A moulding tool according to claim 13, in which

(a) the tool inserts (96, 100) are held in openings in positioning plates (110, 112),

(b) the positioning plates (110, 112) are guided with index bushes (118, 120) on
the index pins (114) that position the support plates (94, 98) relative to one
another and are thus positioned relative to one another and to the support
plates (94, 98), and


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(c) the positioning plates (110, 112) are joined to the support plates (94, 98) by
optical wringing.

15. A moulding tool according to any one of claims 8 to 14, in which each support
plate (14, 34; 94, 98) forms a stop (24, 44) against which the tool insert (18, 38; 96,
100) rests in the direction perpendicular to the support plate (14, 34; 94, 98).
16. A moulding tool according to claim 15, in which the tool insert (18, 38; 96, 100) is
joined to the support plate (14, 34; 94, 98) by optical wringing.

17. A moulding tool according to any one of claims 7 to 16, in which guide means for
guiding the mould halves to the closed position allow a small amount of lateral
movement of the mould halves so that alignment can be effected solely in accordance
with the positioning means (54, 58) of the supports (16, 36).

18. A moulding tool according to claim 8, in which each of the tool inserts (62) has a
plurality of mould-cavity-defining surfaces for the simultaneous manufacture of a
number of precision articles to be moulded.

19. A moulding tool according to claim 7, in which in each mould half

(a) there is mounted on a support plate (66) a plurality of tool inserts (68, 70) that
are made of a material that exhibits negligible thermal expansion in a working
temperature range, and

(b) each of the tool inserts (68, 70) is positioned individually relative to itscounterpart on the other mould half by positioning means (74, 76; 78, 80).

20. A moulding tool according to claim 19, in which each of the tool inserts (68, 70)
has a plurality of mould-cavity-defining surfaces for the simultaneous manufacture of
a number of precision articles to be moulded.


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21. A moulding tool according to claim 7, in which

(a) each of the mould halves has a single plate (82) made of a material that
exhibits negligible thermal expansion in a working temperature range, in which
plate there are formed a plurality of mould-cavity-defining surfaces (84) for
the simultaneous manufacture of a number of precision articles to be moulded,
and

(b) that plate (82) is positioned relative to its counterpart in the other mould half by
centring means (86, 88).

22. A moulding tool according to any one of claims 7 to 20, in which a glass ceramics
material is provided as material that exhibits negligible thermal expansion in a working
temperature range.

23. A moulding tool according to any one of claims 7 to 20, in which a quartz glass is
provided as material that exhibits negligible thermal expansion in a working temperature
range.

24. A moulding tool according to claim 23, in which mould inserts provided as shape-
determining tool portions consist of quartz glass.

25. A moulding tool according to any one of claims 7 to 20, in which a metal alloy
having low thermal expansion, for example Invar, is provided as material that exhibits
negligible thermal expansion in a working temperature range.

Description

CA 02249279 1998-09-17

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Method for the reciprocal positioning of pairs of oPposed shape-determining moulding
tool portions and a moulding tool for the manufacture of precision articles, esPeciallv
contact lenses

The invention relates to a method for the reciprocal positioning of pairs of opposed
shape-determining moulding tool portions that co-operate to form a mould cavity, for
the manufacture of precision articles, especially contact lenses.

The invention relates also to a moulding tool for the manufacture of precision articles,
especially contact lenses, that consists of two mould halves having shape-determining
tool portions, which mould halves form a mould cavity.

According to the prior art, the moulding tool consists of support plates in each mould
half, in each of which support plates a tool insert or a number of tool inserts is/are
mounted. The tool inserts of the two mould halves are in alignment with one another
and, when the mould is closed, form between them a mould cavity. In known moulding
tools for the manufacture of contact lenses, the support plates are made of
aluminium. A thin-walled cylindrical clamping bush is installed in a bore in the support
plate and is fastened to the support plate by a flange. A sleeve-shaped holder for the
tool insert is seated in the clamping bush. The clamping bush forms a pocket into
which pressure medium (clamping oil) can be introduced. The wall of the clampingbush is, as a result, deformed and the holder is clamped in place. A centring pin
serves to position the clamping bush initially. A number of tool inserts, or tool inserts
that have a number of mould cavities for the simultaneous manufacture of a number
of contact lenses or the like, can be held in the support plates in the manner
described.

The known moulding tools each require a large number of high-precision components.
All the components require complicated surface treatment. The registration of the tool
inserts opposed to one another in the two mould halves is difficult and time-
consuming, and hence expensive. Component tolerances are cumulative, with the
result that precision in the known moulding tools is limited. For that reason, handling
of the moulding tools requires great care.

CA 02249279 1998-09-17




A further important factor is that method steps involving the use of heat are not
permitted in the known moulding tools. The linear expansion of the components
varies. As a result, changes in temperature will seriously prejudice the alignment. The
oil pressure in the hydraulic clamping system also alters under the action of heat.

A problem arises when the mould is opened. The moulded precision articles may beretained by one or other of the mould halves. That depends on random influences that
are difficult to control. That uncertainty makes removal of the precision articles
difficult, especially when this is to be carried out automatically by a mechanism.

The problem underlying the invention is to construct a moulding tool of the typementioned at the beginning more simply, to simplify alignment and to counteract
misalignment.

According to the invention, the problem is solved by a method for the reciprocalpositioning of pairs of opposed shape-determining moulding tool portions that co-
operate to form a mould cavity, in which method

(a) the position of each of the tool portions is determined by an associated
element made of a material that exhibits negligible thermal expansion in a
working temperature range, and

(b) the relative position of the two elements associated with the tool portions is
determined precisely by positioning means.

Such materials are known perse. The material may be a glass ceramics material or a
specific metal alloy, such as Invar. Quartz glass also exhibits low thermal expansion.
The use of such a material for positioning the shaping tool portions in moulding tools
means that the geometry does not change in dependence on the temperature. A toolinsert does not need to be clamped in place hydraulically. The shaping tool portion
retains its position relative to the support also in the event of changes in temperature.
The relative position of the supports is again determined directly by high-precision

CA 02249279 1998-09-17




positioning means. It is then possible to use method steps involving the use of heat.
For example, by heating one of the mould halves it is possible to provide distinctly
varying adhesion of the moulded precision articles in the mould halves so that the
mouldings are all in one mould half after the mould has been opened.

Accordingly, in a moulding tool for the manufacture of precision articles, especially
contact lenses, that consists of two mould halves having shape-determining tool
portions, which mould halves form a mould cavity,
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(a) the position of the shape-determining tool portions in each of the tool halves is
determined by supports made of a material that exhibits negligible thermal
expansion in a working temperature range, and

(b) the reciprocal position of the supports is determined by high-precision
positioning means that act directly between the two supports.

The dependent claims relate to developments of the invention.

An embodiment of the invention is described in greater detail below with reference to
the associated drawings.

Fig. 1 is a diagrammatic representation of two mould halves having tool inserts
mounted inside.

Fig. 2 shows diagrammatically the reciprocal positioning of the mould halves.

Fig. 3 is a diagrammatic representation showing a positioning plate in which there
are mounted individual tool inserts, each for the manufacture of one contact
lens, the positioning plate being positioned relative to the opposed positioningplate in the manner shown in Fig. 2.

Fig. 4 is a diagrammatic representation showing a positioning plate in which there are
mounted a plurality of tool inserts, each of which tool inserts is configured for

CA 02249279 1998-09-17




the manufacture of a number of contact lenses or the like, but the positioning
plates are positioned relative to one another in the manner shown in Fig.2.

Fig. 5 is a diagrammatic representation showing two tool inserts made of glassceramics, each of which is configured for the manufacture of a plurality of
contact lenses and which are mounted without a positioning plate directly on a
glass ceramics support plate, the tool inserts themselves being provided
with positioning means for positioning relative to their counterpart (not shown).

Fig. 6 shows a moulding tool in which a single glass ceramics plate has recessesor projections for the manufacture of a plurality of contact lenses and has
positioning means for positioning the plate relative to the correspondingly
constructed counterpart, that plate simultaneously fulfilling the function of
support plate, positioning plate and tool insert.

Fig. 7 shows a further embodiment of a moulding tool in which, when the mouldingtool is closed, the support plates are in position relative to one another.

Fig.1 shows an "upper" mould half denoted by the reference numeral 10 and a
"lower" mould half denoted by the reference numeral 12. The upper mould half 10
consists of a support plate 14, a positioning plate 16 and a tool insert 18. The tool
insert 18 is positioned in an opening 20 of the positioning plate by optical wringing. In
the region of the tool insert 18, the support plate 14 has a bore 22. An annularprojection 24 having a polished end face 26 is formed around the bore on the surface
of the support plate that faces the tool insert 18. The likewise polished rear face 28 of
the tool insert 18 rests against the end face 26. The rear face 28 is joined to the end
face 26 by optical wringing. The front face 30 of the tool insert 18 is provided with a
recess and defines a mould cavity 32. The positioning plate 16 is joined to the support
plate 14.

The tool insert in this case forms a "shape-determining tool portion".

CA 02249279 1998-09-17




The "lower" mould half 12 is of similar construction to the mould half 10. The lower
mould half 12 consists of a support plate 34, a positioning plate 36 and a tool insert
38. The tool insert 38 is positioned in an opening 40 in the positioning plate 36 by
wringing. In the region of the tool insert 38, the support plate 34 has a bore 42. An
annular projection 44 having a polished end face 46 is formed around the bore 42 on
the surface of the support plate that faces the tool insert 38. The likewise polished
rear face 48 of the tool insert 38 rests against the end face 46. The rear face 48 is
joined to the end face 46 also by optical wringing. The front face 50 of the tool insert
38 is provided with a convexity and defines the mould cavity 32 on the side which, in
Fig.1, is the lower side. The positioning plate 36 is joined to the support plate 34.

The support plates 14 and 34, the positioning plates 16 and 36 and the tool inserts 18
and 38 are all made of a material having negligible thermal expansion in the working
range of the moulding tool.

That material is preferably a non-transparent glass ceramics material. It is also
possible, however, to use a metal alloy, such as Invar. The tool inserts are preferably
made of a transparent material (or one of the tool inserts is made of a transparent
material and the other is made of an absorbent, and hence non-transparent, material),
with the result that the moulded product, for example a contact lens, can be treated
with light inside the mould. Quartz glass, which also exhibits very low thermal
expansion, has proved suitable for that purpose. The light beam is delimited sharply
by the wall of the bores 22 and 42 since the material of the support plates 14 and 34
and that of the positioning plates 16 and 36 is non-transparent. Consequently, the
contact lenses can be manufactured with very precise edges.

The support plates 14 and 34 are joined to the associated positioning plates 16 and
36 also by optical wringing. Alternatively, however, a different method of fastening can
be used.

Fig. 2 shows positioning means that provide precise alignment of the positioningplates 16 and 36 relative to one another. A bore 52 is provided in the positioning
plate 36. An index pin 54 is seated snugly in that bore 52. A bore 56 is provided in the

CA 02249279 1998-09-17




positioning piate 16. An index bush 58 is also seated snugly in the bore 56. When the
mould is closed, the index pin 54 is guided with low tolerances in the index bush 58.
The index pin 54 tapers at one end 60 so that it can be inserted easily into the index
bush 58. In the region of the index pin 58, the support plate 14 has a bore 61 into
which the end of the index pin 54 projects in the closed state.

Opening and closing of the moulding tool is performed using a known mechanism not
shown. It is important that the mechanism allows a small amount of lateral play of the
support plates 14 and 34 and the positioning plates 16 and 36 relative to one another,
.
so that the position relative to one another of the positioning plates and thus of the
tool inserts 18 and 38 can be determined exclusively by the positioning means (Fig. 2)
mounted on the positioning plates 16 and 36.

Fig. 3 is a diagrammatic representation of a moulding portion of a moulding tool of the
kind shown in Figs.1 and 2 having a plurality of tool inserts 38. Each of the tool
inserts 38 is configured for the manufacture of a single contact lens (or some other
precision article). Those tool inserts 38 are then mounted in rows and columns of
openings 40 (Fig.1) in the positioning plate 36. Two index pins 54 of the kind shown
in Fig. 2 are located in the corners of the positioning plate 36.

Fig. 4 is a modified development of a mould half. The positioning plate 36 in this case
has a number of, for example rectangular, openings 62. Seated in the openings 62are corresponding tool inserts 64, each of which has a plurality of recesses or
convexities for the manufacture of a plurality of contact lenses. Here too the
positioning plate 36 is centred relative to its counterpart by index pins 54.

In this case also, all the parts are made of a material such as a glass ceramicsmaterial having thermal expansion that is negligible in a working range.

Fig. 5 shows an arrangement in which two tool inserts 68 and 70 of glass ceramics
are mounted directly on a support plate 66. Each of those tool inserts 68 and 70 is
configured for the manufacture of a plurality of precision articles, such as contact
lenses, and has corresponding recesses or convexities 72. Each of the tool inserts 68

CA 02249279 l998-09-l7



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and 70 can be centred relative to its counterpart by pairs of index pins or index
bushes 74,76 and 78,80, respectively, in a manner similar to that described in the
context of Fig. 2. There are no positioning plates in this solution.

In the development according to Fig. 6, only a plate 82 of glass ceramics or the like is
provided as tool half. The plate 82 has rows and columns of recesses or convexities
84 for the simultaneous moulding of a plurality of contact lenses. The plate 82 can be
centred precisely relative to a corresponding counterpart by positioning means 86,88.
In this case there is neither a separate support plate nor a positioning plate. Instead,
the shape of the contact lenses is determined by the recesses or convexities 84 on
the plate 82 that forms the tool half.

Fig. 7 shows a further development of a moulding tool. The upper portion of the
moulding tool is denoted by the reference numeral 90. The lower portion of the
moulding tool is denoted by the reference numeral 92. The upper portion 90
comprises a support plate 94 and a tool insert 96. Fig. 7iS a fragmentary
representation. Generally, a plurality of tool inserts 96 will be mounted on a support
plate 94. The lower portion 92 comprises a support plate 98 and a tool insert 100. The
two tool inserts 96 and 100 form the "shape-determining tool portions" and define a
mould cavity 106 by means of a convex surface 102 and a recess 104. The support
plates 94 and 98 are made of glass ceramics having negligible thermal expansion.The surfaces of the support plates 94 and 98 that face one another are polished.
The tool inserts 96 and 100 are each seated in bores in the positioning plates 110 and
112, respectively. The positioning plates are also made of glass ceramics or some
other material having negligible thermal expansion.

Positioning means in the form of an index pin 114 and index bushes 116,118 and
120 provide for precise positioning relative to one another not only of the positioning
plates 110 and 112 but also of the support plates 94 and 98. For that purpose, the
index pin 1 14is seated in a bore 122 in the support plate 98. The index bush 116is
seated in a bore 124 in the other support plate 94. The other index bushes 118 and
120 are seated in bores 126 and 128, respectively, of the positioning plates 110 and

CA 02249279 1998-09-17




112, respectiveiy. All the index bushes 116,118 and 120 are guided on the index pin
114

Bores 130 and 132, which are in alignment with the tool inserts 96 and 100, are
provided in the support plates 94 and 98, respectively.

The support plates 94 and 98 and the positioning plates 110 and 112 are aligned
precisely with one another by the index pins 114 and index bushes 116,118 and 120.
That also ensures precise alignment of the tool inserts 96 and 100 that are held in the
positioning plates 110 and 112, both with one another and with the support plates 94
and 98. Those positions are to a very great extent independent of the temperature. In
those positions, the tool inserts 96 and 100, which have polished rear faces 134 and
136, respectively, are attached to the polished surfaces of the support plates 94 and
98, respectively, by optical wringing.

After being attached by wringing, it is possible for the positioning plates 110 and 112
to be removed again so that the mould halves 90 and 92 are formed only by the
support plates 94 and 98 and the tool inserts 96 and 100 that have been attachedthereto by optical wringing. For that reason, in Fig. 7 the positioning plates 110 and
112 are indicated by broken lines.

,_
It is, of course, also possible to leave the positioning plates 110 and 112 in the
moulding tool and to join them to the support plates 94 and 98, for example also by
optical wringing.

Representative Drawing