WO2010108628A1

WO2010108628A1 - Fixture and method for producing at least one workpiece

Info

Publication number: WO2010108628A1
Application number: PCT/EP2010/001734
Authority: WO
Inventors: Dirk Prust; Karl Deufel
Original assignee: Chiron-Werke Gmbh & Co. Kg
Priority date: 2009-03-25
Filing date: 2010-03-19
Publication date: 2010-09-30
Also published as: DE102009015919A1; EP2411876A1

Abstract

A fixture (23) for producing at least one workpiece (35) from a planar blank (34) of small wall thickness has a bottom part (26) which has a first plane bearing surface (38) for the blank (34) and a first outer side (39) pointing away from the first bearing surface (38). Furthermore, a top part (27) is provided which can be mounted on the bottom part (26) and can be secured to the latter and which has a second plane bearing surface (41) for the blank (34) and a second outer side (42) pointing away from the second bearing surface (41). In this case, the top part (27) and the bottom part (26) accommodate the blank (34) in a sandwich-like manner between the first and the second bearing surfaces (38, 41). There is provided in the top part (27) or the bottom part (26) a working opening (45, 43) which extends from the outer side (42, 39) thereof to the bearing surface (41, 38) thereof, wherein the working opening (45, 43) exposes a planar region of an accommodated blank (34) for machining, said region corresponding in its planar dimensions (46, 47) at least to those (48) of the workpiece to be produced.

Description

Fixture and method for producing at least one workpiece

The present invention relates to a fixture and a method for producing at least one workpiece, preferably a mounting plate for a watch, from a planar blank of small wall thickness.

Such methods and fixtures in which a workpiece is produced from a planar, thin blank are known. In connection with the present invention, planar, thin blanks refer to those workpieces whose transverse directions are at least ten times as large as their thickness or wall thickness. The production of such workpieces presents particular problems because the blanks have to be extremely flat or have to be clamped in place in an extremely flat manner so that they do not become distorted or bent during the production by machining.

This problem occurs in particular in the production of mounting plates for the watch industry, for these plates, at a diameter of, for example, 30 or 40 mm, have an end thickness of about 1 to 2 mm and are produced from round blanks having a wall thickness of about 3 mm.

This blank is clamped in place in a fixture in a conventional manner, the pockets, recesses, holes, etc., then being milled, or made in some other way, in order to accommodate the individual parts of the watch. In the process, the plate must be machined from both sides and also at least partly on its encircling face, which has a thickness of 1.5 mm for example.

An example for the machining of such plates is described in US 4,696,577, wherein a plurality of mounting plates are bolted one above the other with a base plate and a cover plate to form a stack and are then machined.

In other fixtures known to the applicant from his customers' applications, individual round discs, that is to say the circular blanks, or rectangles are clamped in place, are machined on the top side, are turned around and clamped anew, and are then machined on the underside.

So that the blank can be clamped in the correct position again in the known fixture after the turning, aligning pins are provided in the fixture and reference holes are provided in the blank. This is intended to ensure that the pockets and recesses to be produced on the front side and the top side of the plate are aligned with one another in an accurately fitting manner. However, it has been found that, due to this resetting of the blanks, certain accuracy problems occur if the aligning pins and holes are not arranged exactly symmetrically to one another and fit one another upon turning. In this case, the round disc has a larger diameter than the final plate, which is still connected, after completion of the machining process, via a few webs to the round disc left behind on the outside.

Once this round disc together with the plate still held on the inside has been finish- machined and removed from the fixture, the plates still have to be broken out of the annular border left behind, the break sites then having to be re-worked.

Document DE 44 07 800 Al discloses a comparable fixture. The known fixture comprises a base plate provided with several workpiece carriers each having a plane contiguous bearing surface for receiving one blank. Further provided are clamping rings, each one for each workpiece carrier, each said clamping ring having three small and short clamping fingers that clamp the blank at its outer area onto the respective bearing surface. The clamping rings are being hold between the base plate and a pressure plate in a floating manner so as to compensate for different thicknesses of the various blanks.

By this, nearly the entire upper surface of the blanks can be machined through the circular openings in the clamping rings. However, there is only a very small area where the blanks are clamped by the fingers, so that flat clamping cannot be assured. Further, the blanks have to be re-clamped in order to be able to machine their bottom sides. Still further, the blanks cannot be machined at their circumferential sides.

All this taken together leads to the fact that with the known fixture, the blanks cannot be machined neither in an accurate and reliable nor in a quick and efficient manner. Further, from each blank only one plate can be used. To produce several plates with the known fixture, as many blanks have to be individually clamped on a respective number of carriers, this being cumbersome and time consuming. The machining of such planar blanks having a small wall thickness to form work- pieces is carried out in machine tools of a conventional type of construction, that is to say, for example, in travelling column machines, as adequately known from the prior art. It is known that so-called fixtures are mounted on the work tables in such machine tools, these fixtures then serving to clamp in place the blanks to be machined to form the workpieces.

It is also known to use, instead of a work table, a so-called cradle device which has, for example, a cradle plate onto which different fixtures can be screwed. This cradle device constitutes a further machining axis; it enables the fixture and therefore the held blank to be pivoted about a longitudinal axis, which is normally oriented parallel to the x or y axis of the machine tool.

In view of the above, it is an object of the present invention to provide a fixture of the type mentioned at the outset with which planar blanks of small wall thickness can be processed into workpieces in a rapid and highly accurate manner.

According to the invention, this object is achieved by a fixture of the type mentioned at the outset which comprises a bottom part, which has a first plane bearing surface for the blank and a first outer side pointing away from the first bearing surface, and a top part which can be mounted on the bottom part and can be secured to the latter and which has a second plane bearing surface for the blank and a second outer side pointing away from the second bearing surface, wherein the top part and the bottom part accommodate the blank in a sandwich-like manner between the first and the second bearing surfaces, there is provided in the top part and/or the bottom part a working opening which extends from the outer side thereof to the bearing surface thereof, and the working opening exposes a planar region of an accommodated blank for machining, said region corresponding in its planar dimensions at least to those of the workpiece to be produced.

The object underlying the invention is completely achieved in this way. This is because, due to the sandwich-like clamping of the blank in place between top part and bottom part, provision is made also for a blank that is not quite flat to be "pulled straight", such that, when the blank is thinned out to form the workpiece, a flat workpiece can be produced.

Through the working opening, the workpiece can then be machined either through the top part or through the bottom part. Since the working opening corresponds approximately to the size of the workpiece to be produced, the blank is clamped in place wherever it does not have to be machined. This ensures highly accurate machining due to a large clamping area.

The working opening will normally be slightly larger than the workpiece to be produced in its planar dimension so that the workpiece can also already be separated from the blank, except for a few webs, that is to say machined also circumferentially in the same set-up.

In this case, the top part can be secured to the bottom part either directly via, for example, projections or edges or else indirectly via, for example, reference or aligning pins.

If the workpiece has to be machined on both the underside and the top side, it is preferred if a first working opening is provided in the bottom part and a second working opening is provided in the top part.

It is advantageous here that the blank does not have to be removed from the fixture, turned around and clamped anew, but rather the fixture only needs to be turned, which can be effected, for example, via a cradle device.

The sandwich-like interconnection between blank, top part and bottom part results in a robust interconnection which protects the blank from deflection and displacement. In this way, highly accurate and rapid machining of planar, thin blanks to produce even thinner workpieces is possible, which was not known previously from the prior art.

In this case, it is possible according to the findings of the inventors of the present invention, to produce a plurality of workpieces, preferably mounting plates, from such a planar, thin-walled blank in one set-up. Due to this "multiple clamping", tool change times are saved, since a plurality of workpieces can be machined one after the other using one tool before the tool has to be changed.

In one embodiment, four plates are produced from one blank in this case, and these plates can be machined on their top side and on their underside and also for the most part on their circumferential face in one set-up in the fixture.

Since the blank itself is not machined on its outer side, fully automatic production of the mounting plates is possible using the novel fixture, for the blank can first of all be put onto the bottom part by means of a conventional gripper device, whereupon the top part is then mounted on the bottom part carrying the blank and is secured to said bottom part. The described machining of the blank to produce a plurality of mounting plates is then carried out.

After completion of this machining, first of all the top part is removed from the bottom part and then the blank is gripped again by means of the work-changing device (that is to say the gripper) in the same way as during the insertion of the blank.

The blank can then be put down, for example, on a pallet.

In a development, it is preferred if first retaining means are provided on the bottom part or the top part in order to secure the blank to the bottom part on the first plane bearing surface, wherein additionally or alternatively second retaining means can be provided on the top part or on the bottom part in order to secure the blank to the top part on the second plane bearing surface.

In one embodiment, the retaining means are provided on the same part they are securing the blank on. This may be effected by magnetic means or by adhesion.

The machining speed and the machining accuracy are again increased by this measure, for the blank is already secured, after being put onto the bottom part, in such a way that it cannot slip. After the top part is mounted, a sandwich-like interconnection is then formed in which a retaining connection is produced in each case between top part and blank and between blank and bottom part.

In addition to the orientation and alignment via the first and second retaining means, aligning pins can also be provided on the top part and/or the bottom part, said aligning pins providing for an accurately fitting position of the blank and of top part and bottom part relative to one another.

However, since the blank now no longer has to be re-clamped, the problems normally associated with aligning pins and re-clamping are removed.

In another embodiment, the retaining means are provided on the respective other part. They may be arranged on the top part and press the blank against the top part, and/or vice versa.

Here, the first and/or second retaining means may comprise spring means arranged at said top part and/or at said bottom part for pressing said blank against the bearing surface of the other of said top part and bottom part, whereby preferably the spring means comprise at least one spring loaded bolt captivated within a through hole of said top part or said bottom part. The advantage here is that by simply putting the top part onto the bottom part with the blank interposed, and then securing the top part to the bottom part, e.g. by clamping means, the blank is flattened and comes to lie plane between the two bearing surfaces of top and bottom part. The more spring loaded bolts are provide, the better the flatness of the blank. Now, several mounting plates can be produced from this one-piece blank that only needs to be clamped once.

In this connection, it is preferred, if clamp means are provided for clamping said bottom part and said top part together, so that top and bottom part with interposed blank form a stable sandwich-like structure that allows the machining of as many mounting plates as working openings are provided within top part and/or bottom part.

It is also preferred in this case if the first and/or the second retaining means are partial vacuum- or negative pressure-generating suction means which suck the blank against the first or the second bearing surface, respectively.

With this measure, it is advantageous that the blank is secured to the two bearing surfaces via the suction means over a surface area, which ensures that the blank is oriented in a very flat manner, and therefore highly accurate machining of the top side and the underside thereof is ensured.

In a development, it is preferred if the first suction means have a first partial vacuum passage which is open towards the first bearing surface and which encloses the first working opening at least partly, preferably completely, and/or if the second suction means have a second partial vacuum passage which is open towards the second bearing surface and which encloses the second working opening at least partly, preferably completely.

The or each partial vacuum passage ensures in a simple manner that the blank is sucked against the first and the second bearing surfaces over the full surface area, thereby providing in a technically simple manner for effective and reliable securing of the blank between top part and bottom part.

The partial vacuum passages can at the same time be designed completely or partly as pockets, which ensure that the blank is sucked onto the bearing surfaces over a large surface area.

In general, it is preferred in this case if the first and the second partial vacuum passages are approximately opposite one another when the blank is accommodated.

With this measure, it is advantageous that a closed flux of force, as it were, is obtained, and the blank is sucked in the same regions against both the first and the second bearing surfaces, and therefore the blank is not distorted but rather oriented in an extremely flat manner by the application of the partial vacuum.

Furthermore, it is preferred if the first and/or the second partial vacuum passage is sealed off at least relative to the corresponding working opening by sealing means, wherein the sealing means preferably comprise sealing rings or sealing tapes, wherein furthermore the first and/or the second partial vacuum passage is preferably bordered by two sealing rings or sealing tapes.

With these measures, it is advantageous that the blank can be sucked against the bearing surfaces even more efficiently because the sealing rings or the sealing tapes prevent air from subsequently flowing through the working opening or from outside, a factor which could impair the tight contact. In this case, the sealing tapes can be adapted to partial vacuum pockets having various contours.

In general, it is also preferred if the first and/or the second working opening widens conically towards the respective outer side starting from the respective bearing surface. This measure is advantageous with regard to highly accurate and rapid machining, for it permits the use of tools that are very short when clamped in place. As already stated, during the machining of mounting plates for watch manufacture, the finish- machined workpieces are only about 1 to 2 mm thick and have a diameter of, for example, about 30 or 40 mm, and therefore the cutting tools themselves must have diameters within the region of 1 mm.

In order to be able to work with these tools in a highly accurate and rapid manner, they must be very short when clamped in place, and therefore there is the risk of the face of the tool holder, in which the tools are clamped in place, colliding with the top part or the bottom part. According to the invention, the conically opening working opening provides space for the tool holder to plunge into the working opening, although the working opening in the region of the blank has a smaller diameter, and therefore the blank can be clamped in place there with the maximum surface cover between the top part and the bottom part.

In general, it is also preferred if the bottom part is fastened to a cradle device, wherein the bottom part is preferably fastened on a cradle plate of the cradle device, and wherein at least one passage is provided in the cradle plate, said passage having larger transverse dimensions than the first working opening in the first outer side.

Due to this measure, that is to say the receiving of the blank in a fourth axis, the machining speed and the machining accuracy are again increased, for the fixture itself does not need to be re-clamped, but rather the one side is pivoted merely by 180° via the cradle device after the machining, such that the other side of the blank or of the workpiece, that is to say the mounting plate, can then be machined. This measure therefore enables the blank to be machined on four sides in one set-up.

When a machine tool is set up for machining planar blanks by means of the novel fixture, it is therefore necessary only once to orient the axes relative to one another in a highly accurate manner. The pivoting of the fixture then does not cause any additional inaccuracies, as inevitably occur when re-clamping the fixture, and even more so when re-clamping the blank.

The passage provided in the cradle plate and having larger transverse dimensions than the working opening in the outer side of the bottom part prevents the collision of the tool holder with the cradle plate, and therefore here, too, work can be carried out with tools that are short when clamped in place.

In general, it is then also preferred if the top part has an encircling rim which overlaps the bottom part.

This measure, too, increases the reliable clamping of the blank in place between the top part and the bottom part, for the encircling rim additionally orients the top part relative to the bottom part. In this way, provision is made, for example, for the first and the second working openings to be directly opposite one another, wherein provision is additionally made for the partial vacuum passages to also be opposite one another, such that force is exerted upwards and downwards on a clamped blank in the same surface regions. The force flow is therefore closed, which prevents bending of the blank.

In this case, the encircling rim increases the bending resistance of the top part, which likewise helps to ensure that the blank does not become bent or distorted during the clamping.

If a top part having an encircling rim overlapping the bottom part is used, it is not absolutely necessary to use additional aligning pins in order to orient top part, bottom part and blank relative to one another during the initial set-up, in which case this can further increase the accuracy. In a development, it then also preferred if at least one through-opening is provided in the rim, said through-opening exposing a marginal region of an accommodated blank for machining.

With this measure, it is advantageous that the margin of the workpiece, that is to say of the mounting plate, can not only be milled out but can also be machined on the face in large circumferential regions, whereby two or more opposite through- openings can also be provided.

If the machine tool has a pivoting head, oblique bores and pockets can also be made in this face of the circumferential margin of the mounting plate.

In general, it is preferred if the fixture is used for producing four mounting plates from a blank, wherein four working openings lying next to one another are provided for this purpose in the top part and/or the bottom part.

In view of the above explanations, the present invention likewise relates to a method for producing at least one workpiece, preferably a mounting plate for a watch, from a planar blank of small wall thickness by means of the novel fixture, comprising the steps:

putting the blank onto the bottom part,

securing the blank on the bottom part,

- mounting the top part on the bottom part carrying the blank,

securing the blank to the top part,

machining a first side of the blank through the at least one working opening, the fixture being in the basic position, re-clamping the blank or the fixture or pivoting the fixture from the basic position, preferably by 180°,

machining a second side of the blank through the at least one or the other working opening,

releasing the blank from the top part and/or the bottom part, disassembling the top part and the bottom part, removing the blank, together with the workpiece still held therein via webs, from the bottom part or the top part.

The advantages already discussed above are realized in this production method. The blank is clamped in place between top part and bottom part, whereupon the first side of the blank is machined through a working opening in the top part or bottom part. After that, either the blank or the fixture is reset, in which case, when a cradle device is used, the fixture is merely to be pivoted from the basic position by 180° before the second side of the blank can be machined through a working opening.

After that, the blank is released from the top part or the bottom part before the top part and the bottom part are separated from one another. In the process, the blank is held either on the top part or on the bottom part and can then be removed.

In this method, it is preferred if the blank is secured to the bottom part and/or the top part by applying a partial vacuum.

As already mentioned, this measure has the advantage that the blank can be applied in an extremely flat manner, and therefore highly accurate machining is possible.

During the removal of the blank, a positive pressure can be applied to the partial vacuum passages, such that the blank is easily lifted from the bearing surfaces, which facilitates the removal and prevents bending of the finish-machined workpiece, which otherwise could possibly "stick" to the bearing surfaces. In connection with the release of the blank, a positive pressure is therefore preferably used; the blank is thus released from the bottom part and/or top part by applying a positive pressure.

Furthermore, it is preferred if the fixture is pivoted by approx. 90° relative to the basic position and the workpiece is machined on the circumferential face thereof connecting the first and the second sides thereof.

With this measure, it is advantageous that the blank can be machined not only on its planar top side and underside but also on the circumferential face, such that reworking of the workpiece after it has been broken out of the blank can be virtually completely avoided; only the break sites of the webs have to be re-ground.

Further advantages follow from the description and the attached drawing.

It goes without saying that the abovementioned features and the features still to be explained below can be used not only in the respectively specified combination but rather also in other combinations or on their own without departing from the scope of the present invention.

An embodiment of the invention is shown in the drawing and is described in more detail below. In the drawing:

Fig. 1 shows, in a schematic front view, a diagrammatic sketch of a machine tool having a cradle device on which the novel fixture is mounted;

Fig. 2 shows, in a schematic exploded drawing, the novel fixture from Fig. 1 with a blank lying between top part and bottom part, in a section along line H-II in Fig. 3;

Fig. 3 shows a plan view of the top part in Fig. 2, as viewed in the direction of arrows HI-III in Fig. 2; Fig. 4 shows a plan view of a top part for producing four mounting plates from a blank, as viewed along arrows IV-IV in Fig. 2;

Fig. 5 shows a plan view of a blank with four machined plates which are still held on the blank via webs;

Fig. 6 shows, in a view as in Fig. 3, a cutaway illustration of a second embodiment of the top part;

Fig. 7 shows, in a view as in Fig. 3, a cutaway illustration of a third embodiment of the top part;

Fig. 8 shows a view as in Fig. 4, but with different retaining means; and

Fig. 9 shows a schematic partial side view of the retaining means as used in the embodiment of Fig. 8.

Designated by 10 in Fig. 1 is a machine tool, which is only shown schematically and not true to scale.

The machine tool 10 has a spindle head 11 in which a work spindle 12 is mounted, said work spindle 12 carrying a tool holder 14 in which a tool 15 is clamped in place in the conventional manner.

The machine tool 10 is a travelling column machine in which the spindle head 11 is traversable relative to a work table or base indicated at 16 in the three coordinates x, y and z, as indicated by a coordinate system 17. Here, therefore, all three axes are arranged in the tool. However, another distribution of the axes between workpiece and tool can also be selected, as is the case, for example, in a cross-piece table machine, where two axes are arranged in the workpiece and one in the tool.

In the present case, a cradle device 18 is arranged on the base 16 and comprises two blocks 19, to which a cradle plate 21 is fastened in a pivotable manner about the x axis. The pivotability is indicated by an arrow 22 in Fig. 1.

A fixture 23 which is designed for machining planar workpieces of small wall thickness is fastened to the cradle plate 21.

The spindle head 11 is configured as a pivoting head in a manner known per se; it can be pivoted about the y axis, which is indicated by an arrow 24.

Due to the construction selected, machining, for example milling or drilling, can be carried out with the tool 15 at various locations of a blank clamped in place in the fixture 23 in a manner still to be described, oblique bores also being possible on account of the pivoting head.

Since the fixture is fastened to the cradle device 18, machining of rear sides can also be carried out by pivoting the cradle plate 21, for which purpose a passage is provided in the cradle plate 21, which is indicated at 25 and through which the tool 15 can machine the blank 34, as will now be described in detail in connection with Fig. 2.

The fixture 23 is shown in an exploded illustration in Fig. 2, the fixture being shown sectioned along line II-II in Fig. 3.

The fixture 23 comprises a bottom part 26 fastened to the cradle plate 21 and a top part 27 which is shown above said bottom part 26 and which has an encircling rim 28 which stiffens the top part 27 and overlaps the bottom part 26 when the top part 27 is mounted on the latter. Provided on the top part 27 are two pivotable locks 29, which, after the top part 27 is mounted on the bottom part 26, engage in corresponding recesses 31 which are provided in the bottom part 26. By this, the top and bottom part are clamped together and already form a sandwich-like interconnection.

Two aligning pins 32 can also be seen on the bottom part 26, said aligning pins 32 engaging in corresponding holes 33 on the inside in the top part 27.

In this way, the bottom part 26 and the top part 27 can be arranged relative to one another and locked together in an accurately fitting manner.

A planar blank 34 of small thickness, from which a workpiece indicated at 35 has been produced, which is still connected to the blank 34 via webs 36, can be seen schematically between top part 27 and bottom part 26.

Two through-holes 37, via which the blank 34 is oriented on the bottom part 26 via the aligning pins 32, can be seen in the blank 34.

When being put onto the bottom part 26, the blank 34 comes to lie on a bearing surface 38 of the bottom part 26. With its outer side 39 which points away from the bearing surface 38, the bottom part 26 rests on the cradle plate 21 and is fastened there in a suitable manner.

When the blank 34 has been put onto the bottom part 26, the top part 27 is mounted, as a result of which the top part 27 comes to lie with its bearing surface 41 on the blank 34. The top part 27 then points upwards with its outer side 42, which points away from the bearing surface 41.

Provided in the bottom part 26 is a working opening 43, which first of all widens conically from the bearing surface 38 towards the outer side 39 and then merges into a cylindrical section 44, which in the plane of the outer side 39 has a smaller area than the passage 25 in the cradle plate 21.

In a corresponding manner, a working opening 45 is provided in the top part 27, said working opening 45 extending from the bearing surface 41 to the outer side 42 and widening conically towards the outer side 42.

In the bearing surfaces 38 and 41, the working openings 43 and 45, respectively, have respective diameters 46 and 47 which are greater than the diameter 48 of the workpiece 35.

In this way, the working openings 43 and 45 expose a planar region of the blank 34 from which the workpiece 35 can be machined.

On account of the conical configuration of the working openings 43 and 45, the tool holder 14 can penetrate partly into the working openings 43 and 45 so that the tool 15 can machine the blank 34 over the entire diameter 46 or 47, respectively, without there being the risk of collision between bottom part 26 or top part 27 and tool holder 14, even if the tool 15 is very short when clamped in place.

Once the blank 34 has been machined, for example on its first side 49 through the working opening 45, the entire fixture 23 together with the blank 34 clamped in place in a sandwich-like manner is pivoted by 180° so that the blank 34 can now be machined on its second side 51 through the working opening 43. It can be seen in Fig. 2 that the passage 25 in the cradle plate 21 is larger than the working opening 43 in the outer side 39.

So that the blank 34 or the workpiece 35 can also be machined on its circumferential face 52 connecting the first and the second sides 49 and 51, a through-opening 53 is provided in the encircling rim 28 of the top part 27, through which through-opening 53 the tool 15 can machine the clamped blank 34 if the fixture 23 is pivoted by approx. 90° from the basic position shown in Fig. 2.

In order to secure the blank 34 to the bearing surfaces 38 and 41 in a plane-parallel and fixed manner, retaining means 54 and 55 are provided in the bottom part 26 and the top part 27, said retaining means 54 and 55 each applying a partial vacuum to the blank 34, that is to say they suck it against the respective bearing surface 38 or 41.

These retaining means or suction means 54, 55 each comprise a partial vacuum passage 56 or 57, respectively, which encloses the respective working opening 43 or 45. Connection passages 58 and 59 lead from the partial vacuum passages 56 and 57, respectively, to olives 61 and 62, respectively, which are arranged on the top part 27 and the bottom part 26, respectively, and serve to connect the partial vacuum passages 56 and 57, respectively, to a suitable partial vacuum source.

The partial vacuum passages 56 and 57 are each bordered by two encircling sealing rings 63 and 64, respectively, so that, when an appropriate partial vacuum is applied, the blank 34 is sucked onto both the bearing surface 38 and the bearing surface 41 and is held in place there.

This results in an accurately fitting arrangement of the blank 34 on the bottom part 26 and top part 27, provision likewise being made for plane-parallel contact of top part 27, blank 34 and bottom part 26 like a sandwich. This interconnection gives the blank 34 high stability and provides for flat plane-parallel contact, such that even thinner, extremely flat workpieces 35 can be produced from large-area but thin blanks 34.

The arrangement in this case is made in such a way that the two partial vacuum passages 56 and 57 are opposite one another, such that a type of closed flux of force is obtained when the blank 34 is accommodated in a sandwich-like manner between bottom part 26 and top part 27. This also ensures that the blank 34 is not bent but is kept flat.

A view of the top part 27 from the direction of arrows III-III in Fig. 2 is shown in Fig. 3.

It can be seen that the sealing rings 64 and the partial vacuum passage 57 completely surround the working opening 45, such that the partial vacuum passage 57 is sealed off both towards the working opening 45 and towards the bearing surface 41.

It can also be seen in Fig. 3 that two through-openings 53 are provided in the rim 28, such that a tool can machine a workpiece 35 at two faces through the through- opening 53.

The entire machining process now takes place in such a way that first of all a blank 34 is slipped onto the aligning pins 32 and is put onto the bearing surface 38 of the bottom part 26. The blank 34 is then sucked against the bearing surface 38 by applying a partial vacuum to the olive 61.

After that, the top part 27 is mounted and locked, whereupon partial vacuum is applied to the olive 62, such that the top part 27, workpiece 35 and bottom part 26 form a fixed interconnection which orients the workpiece 35 in a plane-parallel manner.

The blank 34 is then machined on its first side 49. The fixture 23 is thereupon pivoted by 180° and the blank 34 is machined on its second side 51. The blank is thereupon pivoted by 90° so that part of the face 52 of the blank 34 can be machined through the first through-opening 53. After renewed pivoting by 180°, a further marginal region of the blank 34 or of the workpiece 35 can be machined through the opposite through-opening 53. After that, the fixture 23 is again pivoted by 90°, whereupon first of all the top part 27 and then the blank 34 with machined workpiece 35 are removed. In order to be able to lift the blank 34, thus machined, together with the now highly filigree workpieces 35 from the bearing surfaces 38, 41 in a careful manner, that is to say without the risk of bending, air is blown in through the olives 61, 62 and as a result a small positive pressure is exerted, which lifts the blank 34.

Air blown into the olives 61, 62 also serves to clean the various passages.

A top part 27 for machining only one workpiece 35 from a blank 34 is shown in Figs 2 and 3, but it is also possible to machine a plurality of workpieces 35 from a blank 34 simultaneously, for which purpose four working openings 45, for example, are then arranged next to one another in the top part 27, as shown schematically in Fig. 4. Of course, four working openings 43 are then also provided in a corresponding bottom part 26, the cradle plate 21 then likewise requiring four passages 25. This is not shown for the sake of clarity.

A blank 34 machined with such a fixture 23 is schematically shown in Fig. 5. It can be seen that a total of four workpieces 35, which can be, for example, mounting plates for watches, have been machined from the blank 34. The workpieces 35 have also already been machined on their circumferential side; they are merely still connected to the blank 34 via some webs 36.

Although the workpieces 35 have now been machined in a filigree manner, which is merely indicated by the recesses, through-openings and incisions in Fig. 5, the blank 34 itself can be gripped on the outside via a gripper, indicated at 65, without there being the risk of the machined workpieces 35 becoming damaged.

In this way, it is possible to first of all place a blank 34 automatically on a bottom part 26 by means of the gripper 65 and also remove it again automatically after the machining. The area of the partial vacuum passage 57 shown in Fig. 3 is possibly too small in order to be able to hold the blank 34 on the bearing surface 41 with sufficient force, for which reason the partial vacuum passages 57 can also be designed with or as pockets, which provide a larger area over which the partial vacuum can be applied to the blank.

In Figs 6 and 7, two embodiments for top parts 27 are shown cutaway in the view according to fig. 3.

In the example according to Fig. 6, partial vacuum pockets 66 are provided which are surrounded on the outside by sealing tapes 67 and lie between the working openings 45, which they partly enclose. Here, the working openings 45 require no separate sealing rings. The partial vacuum pockets 66 have a small width between the rims 28; they are designed to be narrow in this direction.

In the example according to Fig. 7, a partial vacuum pocket 68 is provided which completely surrounds two or more working openings 45 and is surrounded on the outside by a sealing tape 69. The working openings 45 are here again surrounded by one sealing ring 64 in each case. The partial vacuum pocket 68 offers an even larger area for applying the partial vacuum, but requires more space between the rims 28, and is therefore wider.

Corresponding partial vacuum pockets 66, 68 can also be provided in the bottom part 26.

Fig. 8 shows a view as in Fig. 4, but with different retaining means 54. Each working opening 45 is surrounded by four through holes 71, wherein each one spring mechanism 72 is arranged. Such through holes 71 and spring mechanisms 72 may be arranged on the top part 27, as shown, but also or alternatively on the bottom part 26. Fig. 9 shows a schematic partial side view of the spring means 72 as used in the embodiment of Fig. 8. Each spring mechanism 72 comprises a captivated spring loaded bolt 73 retained by an upper and a lower retaining ring 74, 75 at a shoulder 76 within through hole 71. Arranged between lower retaining ring 75 and a lower shoulder 77 at bolt 73 is a disc spring 78 pressing bolt 73 downwardly in Fig. 9 such that its tip 79 contacts blank 34 and presses blank 34 onto bearing surface 38 of bottom part 26.

Thereby, the various bolts 73 press blank 34 flat onto bearing surface 38 and possibly also on bearing surface 41, if bolts 73 are provided on both, the top part 27 and the bottom part 26.

Due to the fact, that top part 27 and lower part 26 are clamped together by a clamping mechanism, as shown in Fig. 2 at 29, they form together with blank 34 again a sandwich-like structure. Depart from the different retaining means as used in the embodiment of Figs. 8 and 9, when compared to the embodiment of Figs. 2 to 7, top part 27 and bottom part 26 have the same constructional details with the same advantages and features as already described.

Claims

1. Fixture for producing at least one workpiece (35), preferably a mounting plate for a watch, from a planar blank (34) of small wall thickness, comprising

a bottom part (26) which has a first plane bearing surface (38) for the blank (34) and a first outer side (39) pointing away from the first bearing surface (38),

a top part (27) which can be mounted on the bottom part (26) and can be secured to the latter and which has a second plane bearing surface (41) for the blank (34) and a second outer side (42) pointing away from the second bearing surface (41), wherein

the top part (27) and the bottom part (26) accommodate the blank (34) in a sandwich-like manner between the first and the second bearing surfaces (38, 41),

there is provided in the top part (27) and/or the bottom part (26) a working opening (45, 43) which extends from the outer side (42, 39) thereof to the bearing surface (41, 38) thereof, and

the working opening (45, 43) exposes a planar region of an accommodated blank (34) for machining,

said the region corresponding in its planar dimensions (46, 47) at least to those (48) of the workpiece (35) to be produced.

2. Fixture according to Claim 1, characterized in that a first working opening (43) is provided in the bottom part (26) and a second working opening (45) is provided in the top part (27).

3. Fixture according to Claim 1 or 2, characterized in that first retaining means (54) are provided on the bottom part (26) or on the top part (27) in order to secure the blank (34) to the bottom part (26) on the first plane bearing surface (38).

4. Fixture according to anyone of Claims 1 to 3, characterized in that second retaining means (55) are provided on the top part (27) or on the bottom part (26) in order to secure the blank (34) to the top part (27) on the second plane bearing surface (41).

5. Fixture according to Claim 3 or 4, characterized in that the first retaining means (54) are partial vacuum-generating suction means which suck the blank (34) against the first bearing surface (38).

6. Fixture according to Claim 4 or 5, characterized in that the second retaining means (55) are partial vacuum-generating second suction means which suck the blank (34) against the second bearing surface (41).

7. Fixture according to Claim 5 or 6, characterized in that the first suction means (54) have a first partial vacuum passage (56) which is open towards the first bearing surface (38) and which encloses the first working opening (43) at least partly, preferably completely.

8. Fixture according to Claim 6 or 7, characterized in that the second suction means (55) have a second partial vacuum passage (57, 66; 68) which is open towards the second bearing surface (41) and which encloses the second working opening (45) at least partly, preferably completely.

9. Fixture according to Claim 7 or 8, characterized in that the first and the second partial vacuum passages (56, 57) are approximately opposite one another when the blank (34) is accommodated.

10. Fixture according to anyone of Claims 7 to 9, characterized in that the first and/or the second partial vacuum passage (56, 57) is sealed off at least relative to the corresponding working opening (43, 45) by sealing means.

11. Fixture according to Claim 10, characterized in that the sealing means comprise sealing rings (63, 64) or sealing tapes (67, 69).

12. Fixture according to Claim 11, characterized in that the first and/or the second partial vacuum passage (56, 57) is bordered by two sealing rings (63, 64).

13. Fixture according to Claim 3 or 4, characterized in that the first and/or second retaining means (54) comprise spring means (72) arranged at said top part (27) and/or at said bottom part (26) for pressing said blank against the bearing surface (38, 41) of the other of said top part (27) and bottom part (26).

14. Fixture according to Claim 13, characterized in that the spring means (72) comprise at least one spring loaded bolt (73) captivated within a through hole (71) of said top part (27) or said bottom part (26).

15. Fixture according to anyone of Claims 1 to 14, characterized that clamp means (29) are provided for clamping said bottom part (26) and said top part (27) together.

16. Fixture according to anyone of Claims 1 to 15, characterized in that the first and/or the second working opening (43, 45) widens conically towards the re- spective outer side (39, 42) starting from the respective bearing surface (38, 41).

17. Fixture according to anyone of Claims 1 to 16, characterized in that the bottom part (26) is fastened to a cradle device (18).

18. Fixture according to Claim 17, characterized in that the bottom part (26) is fastened on a cradle plate (21) of the cradle device (18), wherein at least one passage (25) is provided in the cradle plate (21), said passage (25) having larger transverse dimensions than the first working opening (43) in the first outer side (39).

19. Fixture according to anyone of Claims 1 to 18, characterized in that the top part (27) has an encircling rim (28) which overlaps the bottom part (26).

20. Fixture according to Claim 19, characterized in that at least one through- opening (53) is provided in the rim (28), said through-opening (53) exposing a respective marginal region of an accommodated blank (34) for machining.

21. Fixture according to anyone of Claims 1 to 20, characterized in that aligning pins (32) are provided which hold top part (27), bottom part (26) and blank (34) in alignment with one another.

22. Fixture according to anyone of Claims 1 to 21, characterized in that, to produce four plates (35) from a blank (34), four working openings (43, 45) lying next to one another are provided in the top part (27) and/or the bottom part (26).

23. Method for producing at least one workpiece (35), preferably a mounting plate for a watch, from a planar blank (34) of small wall thickness by means of a fixture according to anyone of Claims 1 to 19, comprising the steps: putting the blank (34) onto the bottom part (26),

securing the blank (34) on the bottom part (26),

mounting the top part (27) on the bottom part (26) carrying the blank (34),

securing the blank (34) to the top part (27),

machining a first side (49) of the blank (34) through the at least one working opening (43, 45), the fixture (23) being in the basic position,

re-clamping the blank (34) or the fixture (23) or pivoting the fixture (23) from the basic position, preferably by 180°,

machining a second side (51) of the blank (34) through the at least one or the other working opening (43, 45),

releasing the blank (34) from the top part (27) and/or the bottom part (26), disassembling the top part (27) and the bottom part (26), removing the blank (34), together with the workpiece (35) still held therein via webs (36), from the bottom part (26) or the top part (27).

24. Method according to Claim 23, characterized in that the blank (34) is secured to the bottom part (26) and/or the top part (27) by applying a partial vacuum.

25. Method according to Claim 23, characterized in that the blank (34) is secured to the bottom part (26) and/or the top part (27) by spring means (72).

26. Method according to anyone of Claims 23 to 25, characterized in that the fixture (23) is pivoted by approx. 90° relative to the basic position and the workpiece (35) is machined on the circumferential face (52) thereof connecting the first and the second sides (49, 51) thereof.

27. Method according to anyone of Claims 23 to 26, characterized in that the blank (34) is released from the bottom part (26) and/or the top part (27) by applying a positive pressure.