Work holders – Holder encloses work
Reexamination Certificate
1999-03-10
2001-11-06
Hail, III, Joseph J. (Department: 3723)
Work holders
Holder encloses work
C279S004090, C029S402070
Reexamination Certificate
active
06311967
ABSTRACT:
The invention relates to a process for the production of a clamping means for clamping a component having contact surfaces in a holder, especially for clamping moulding tool inserts in a support plate in order to produce a moulding tool for the manufacture of precision articles, for example contact lenses.
The invention further relates to a clamping means for clamping a component having contact surfaces in a holder, especially for clamping moulding tool inserts in a support plate in order to produce a moulding tool for the manufacture of precision articles, for example contact lenses.
With moulding tools used to manufacture precision articles, it is very important that the tool inserts are held in a releasable manner in the support plate in precisely defined and reproducible positions. Clamping means are used for this purpose. However, such clamping means may also be employed for example for the positioning and clamping of workpieces, for example during the clamping operation, in which high clamping precision of the workpiece is similarly required.
The invention further relates to a process for producing a moulding tool for the manufacture of precision articles, especially contact lenses, whereby the moulding tool has
two tool halves, each half containing a tool holder into each of which is clamped one tool insert of at least one pair of shape-determining tool fingers having contact surfaces, and
positioning means, by means of which the tool holders when the moulding tool is closed are positioned relative to one another in such a way that each of a pair of shape-determining tool inserts is opposite the other and interacts with the other to form a mould cavity.
The invention also relates to a moulding tool for the manufacture of precision articles, especially contact lenses, containing
(a) two tool halves, each half containing a tool holder into each of which is clamped one tool insert of at least one pair of shape-determining tool inserts having contact surfaces, and
(b) positioning means, by means of which the tool holders when the moulding tool is closed are positioned relative to one another in such a way that each of a pair of shape-determining tool inserts is opposite the other and interacts with the other to form a mould cavity
Moulding tools of this kind for the manufacture of contact lenses require very high precision of concentricity between two opposed tool inserts, whereby the eccentricity of the closed moulding tool may not be greater than ±5 &mgr;m. This in turn leads to very high precision requirements of the clamping means used. In addition, the clamping power of the clamping means must be sufficient for an axial force of >500 N to be capable of being exerted on the tool insert without any shift of the clamped tool insert in an axial direction.
Commercial clamping means for tool machines, in which a workpiece is positioned and clamped, only fulfill the precision requirement of <±5 &mgr;m to a limited extent in their standard programme.
Moulding tools for the manufacture of contact lenses are known. They consist of two halves of a mould, in which several pairs of opposed moulding tool inserts are arranged in two support plates. The tool inserts of the two mould halves are in alignment with one another and when the mould is closed they form a mould cavity between them. In known moulding tools for the manufacture of contact lenses, the support plates are made of aluminum. The moulding tool inserts are clamped in the support plates by clamping means. To serve this purpose, a thin-walled, cylindrical clamping bush is inserted in a bore of 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 means (clamping oil) can be introduced. As a result, the wall of the clamping bush is deformed and the holder is clamped in place. A centering pin serves to position the clamping bush initially. The support plates may hold several tool inserts, which form several mould cavities for simultaneous manufacture of several contact lenses or the like, in the manner described. With this known moulding tool, a centering precision and a concentricity of the clamped tool inserts of ±5 &mgr;m is achieved.
These 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 other in the two mould halves is difficult and time-consuming and hence expensive. Tolerances of the components are cumulative, so that precision in the known moulding tools is limited. For this reason, great care must be taken when handling the moulding tools. Furthermore, the hydraulic clamping means takes up a lot of room, so that only a relatively small number of tool inserts can be accommodated in a given support plate of the dimensions concerned.
Furthermore, with these known moulding tools, process steps involving the use of heat are not permitted. The linear expansion of the components is variable. As a result, when there are temperature changes, both the alignment and the clamping power are greatly affected. The oil pressure of the hydraulic clamping system also alters under the action of heat.
A problem arises when the mould is opened. Then, the moulded precision articles may be retained by either one or the other of the mould halves. This depends on random influences that are difficult to control. This uncertainty makes it difficult to remove the precision articles, especially if this is to be carried out automatically by a machine.
A moulding tool for the manufacture of precision articles, especially contact lenses, is known from DE 196 10 563 A1. This is intended to eliminate the above-described disadvantages. As with the above-described moulding tool, the moulding tool consists of two mould halves, in which several pairs of opposed shape-determining moulding tool inserts are arranged in bores in two support plates. No clamping means are used to clamp the tool inserts in the support plates, but the tool inserts are held in the bores of the support plates by optical wringing. The tool inserts of the two mould halves align with one another and when the mould is closed form a hollow cavity between them. Both the tool inserts and the support plates consist of a material which has negligible thermal expansion at the operational temperature range of the moulding tool. This material may be a glass ceramics material, or a specific metal alloy such as invar or quartz glass. In this way, the geometry of the bores of the support plates, which serve to receive the moulding tool inserts, does not change in dependence on temperature, so that the tool inserts maintain their positions relative to the support plates even during temperature changes.
A disadvantage of this moulding tool described in DE 196 10 563 A1 is the complex production process. The conventional tool inserts used in the above-described moulding tool cannot be used here. New tool inserts have to be produced, whereby the contact surfaces have to be worked very precisely, so that optical wringing is possible. Since the connection between the tool inserts and the support plates is effected by optical wringing, release of the tool inserts is complex.
The invention is based on the problem of providing a clamping means to clamp a component in a holder, which is of simple construction, and by means of which the component to be clamped can be clamped in the holder with high precision.
The invention is based especially on the problem of providing a moulding tool for the manufacture of precision articles, particularly contact lenses, in which tool inserts can be clamped in tool holders in a simple manner with high precision.
This problem is solved according to the invention by a process for the production of a clamping means according to claim
1
or a process for the production of a moulding tool according to claim
2
.
This problem is also solved according to the invention b
Gorman Jr. Robert J.
Hail III Joseph J.
Meece R. Scott
Novartis AG
Shanley Daniel
LandOfFree
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