CH716430A2 - Mineral stone of the monocrystalline type provided with a centering cone of a pivot, and its method of manufacture. - Google Patents

Abstract

The invention relates to a method for manufacturing a stone (10), in particular for a timepiece, from a mineral body of the monocrystalline type, the stone (10) comprising a hole (8). The method comprises an ablation step in which the body is subjected to material ablation by scanning over at least one face of the body with laser radiation with ultra-short pulses whose duration is less than one hundred picoseconds, and whose beam is guided by a precessing system of at least three axes configured to at least partially cancel the conical angle of focus of said laser, the laser ablation step comprising hollowing out an entry cone (12) of the hole (8). The invention also relates to a mineral stone of the monocrystalline type, in particular for a timepiece, said stone comprising a face (6) provided with a hole (8) formed in the body of the stone (10) and with a functional element at the entrance to the hole (10). The functional element has a cone shape (12).

Description

Description

Field of the invention

The invention relates to a drilled stone provided with a cone for refocusing a pivot, in particular for a clock movement

The invention also relates to a method of manufacturing a pierced stone teile.

The invention also relates to a clockwork comprising a pierced stone teile.

Background of the invention

[0004] In the state of watchmaking technology, ruby or sapphire type stones are used in particular to form counter-pivots or guide elements, called bearings. These counter-pivots and guide elements are intended to come into contact with the pivots in order to make the latter mobile in rotation and to do so with minimal friction. Thus, they form, for example, all or part of a bearing of an axis mounted in rotation.

[0005] In principle, synthetic stones are used in watch movements. In particular, the Verneuil-type process is known for manufacturing stones of the monocrystalline type. There are also stones of the polycrystalline type, which are manufactured by pressing a precursor with a view to obtaining a green body of the future stone from a pressing tool. The stones are then machined to obtain a finished shape with the desired dimensions.

[0006] The stones serving as a rotation guide element for a pivot generally have a through hole in which the pivot is inserted to rest on a counter-pivot. It is known to form a substantially hemispherical hollow around the hole on the insertion face of the pivot to facilitate insertion of the pivot. In addition, it allows the pivot to be put back in place in the event that it comes out due to a shock. The hollow is, for example, obtained by turning with a diamond chisel.

[0007] However, the hollow, obtained with such a process, has a protruding edge at the edge of the hole, so that the pivot can be damaged by said edge, and vice versa, for example under the effect of a shock, if the pivot comes out of the hole and re-enters.

To avoid this, it is known to replace the recess with a cone whose angle is smaller, so that the edge is less prominent. Thus, wear of the pivot in particular is avoided.

[0009] As regards polycrystalline stone guide elements, the pressing tool is for example provided with a cone shape and with a wire participating in the construction of a hole blank provided with a cone with its entrance.

[0010] The monocrystalline type stones are first drilled with a laser to obtain the rough hole. The final size of the hole is then obtained by machining with a diamond chisel. However, it is not known how to make a cone in a stone of the monocrystalline type, because conventional machining does not make it possible to obtain such a shape.

Summary of the invention

[0011] The purpose of the present invention is to overcome all or part of the drawbacks mentioned above, by proposing a manufacturing method for manufacturing a stone, in particular for a timepiece, from a mineral body of the type monocrystalline, the stone comprising a hole.

[0012] To this end, the method is remarkable in that it comprises an ablation step in which the body is subjected to an ablation of matter by scanning over at least one face of the body with ultra-pulse laser radiation. -short, whose duration is within one hundred picoseconds, and whose beam is guided by a precession system of at least three axes configured to at least partially cancel the conical angle of focusing of said laser, the laser ablation step comprising the digging of an entrance cone of the through hole.

[0013] Thanks to this process, it is possible to remove material from the stone in an extremely precise way, and thus to obtain shapes and surfaces that are impossible to form with laser methods known to the state of the art. art. Such a device makes it possible to focus the laser beam with great precision, while at least partially canceling out the conical angle formed by the laser beam, and which is due to the focusing of said laser. Indeed, the focusing generates a cone-shaped laser, which does not allow to have an identical ray diameter over the entire height at the point of localization of the laser, so that the ablation of matter is not. The System makes it possible to cancel the angle of the cone on at least one side of the radius, which notably makes it possible to obtain straight cuts. These straight cuts cannot be obtained with conventional cutting lasers.

[0014] Thus, one can obtain an entry cone for the hole in a body of the monocrystalline type, which was not possible with other systems. In particular, such a cone is useful for a pivot of an amagnetic axis, which is softer. Indeed, the combination of such an axis with a stone of the monocrystalline type is deformable under the effect of a shock, so that it is absorbed by fax.

[0015] In addition, the ultra-short pulses of the laser make it possible to avoid thermal heating of the stone, which is detrimental to the quality of the stone.

[0016] In addition, the surface condition Ra of the stone obtained with the process according to the invention is of the order of 0.1, which then makes it possible to polish the stone with conventional polishing means. Thus, this method provides significant advantages while maintaining an implementation without great complexity.

[0017] According to a particular embodiment of the invention, the cone obtained during the ablation step has an angle included in a range ranging from 30° to 120°, preferably from 45° to 90°.

According to a particular embodiment of the invention, the ablation is carried out layer by layer, each layer having a thickness comprised in an interval ranging from 1 to 10 μm, preferably from 2 to 4 μm.

[0019] According to a particular embodiment of the invention, the pulses have a duration comprised in an interval

ranging from 200 to 400 fs, preferably in an interval ranging from 50 to 350 fs, or even from 80 to 100 fs.

[0020] According to a particular embodiment of the invention, the laser has a wavelength comprised in an interval

ranging from 400 to 600 nm, preferably between 450 and 550 nm, or even 500 nm.

According to a particular embodiment of the invention, the mineral body comprises AL2O3.

[0022] According to a particular embodiment of the invention, the process comprises a prior step of manufacturing the body by a Verneuil-type process.

[0023] According to a particular embodiment of the invention, the method comprises an additional finishing step, for example lapping and/or brushing and/or polishing of the mineral body after the laser step, in particular on the ablation areas.

According to a particular embodiment of the invention, the laser ablation step comprises digging the hole, the hole preferably passing through between a lower face and an upper face of the stone.

[0025] The invention also relates to a mineral stone of the monocrystalline type, in particular for a timepiece, said stone comprising a face provided with a hole formed in the body of the stone and with a functional element at the hole entrance. The stone is remarkable in that the functional element has a cone shape.

According to a particular embodiment of the invention, the stone comprises an upper face and a lower face, the lower face comprising the cone

[0027] According to a particular embodiment of the invention, the hole passes through so as to connect said cone to the upper face of said stone.

According to a particular embodiment of the invention, said stone comprises AL2O3.

Finally, the invention also relates to a timepiece comprising a teile stone, in particular for a damping bearing.

Brief description of the drawings

[0030] Other features and advantages will emerge clearly from the description which is given hereafter, by way of indication and in no way limiting, with reference to the appended drawings, in which:

- Figure 1 is a block diagram of the production of a stone according to the method of the invention;

- Figure 2 is a schematic representation of a stone obtained after the laser ablation step using the process according to the invention;

- Figure 3 is a schematic representation of an assembly comprising a stone of Figure 2 and an axis provided with a pivot.

Detailed description of preferred embodiments

[0031] As explained above, the invention relates to a process for manufacturing a stone capable of forming a guide element for a timepiece. The stone is for example intended to come into contact with a pivot in order to make the latter rotatable with minimal friction. It is therefore understood that the present invention makes it possible in particular to produce a stone which can form all or part of a bearing of an axis mounted in rotation.

[0032] The stone is formed from a mineral body of the monocrystalline type. The body comprises for example AL2O3.

The process 1, shown in Figure 1, comprises a first step 2 of manufacturing the crystalline mineral body by a process of the Verneuil type, which is well known in the field of watchmaking. The material is formed from a powder melted by an oxyhydrogen torch at over 2000°C. The body crystallizes after cooling below the melting point. The body is dimensioned so as to obtain dimensions close to those desired, in particular to facilitate its future machining. This step provides a monocrystalline one-piece body.

According to the invention, the process comprises a second step of laser ablation 3 in order to form an entry cone for a hole in the stone. During the laser ablation step 3, the body is subjected to material ablation by scanning over at least one face of the body with laser radiation with ultra-short pulses whose duration is less than one hundred picoseconds, and whose the ray is guided by a precession system of at least three axes configured to cancel the conical angle of the

laser due to the focusing of said laser. Such a device is for example described in the document WO 2017029210. There are different types of devices making it possible to at least partially cancel out the conical angle of the laser. Some devices use a five or six axis precession system.

[0035] Thus, the laser beam has at least a substantially straight edge, so that these devices make it possible to hollow out the surface of the stone and give it a specific cone shape at the entrance to the hole of a monocrystalline mineral body. Thanks to this cone, if the pivot comes out of the hole due to a shock, the pivot returns to the hole without being damaged by the edge of the edge of the hole. Such a cone facilitates the insertion of a pivot into the hole, and avoids the risk of wear of the pivot in the event of an impact. The edge of a cone being less prominent, the risk of wear is greatly reduced. For example, an angle of between 30° and 120°, preferably between 45° and 90°, is chosen.

[0036] The ablation is carried out layer by layer, the laser scanning an area of the body to hollow it out. Each layer has, for example, a thickness ranging from 1 to 10 μm, preferably from 2 to 4 μm. Material is removed layer by layer until the desired shape is obtained.

The laser has for example a wavelength of between 400 and 600 nm, preferably between 450 and 550 nm, or even of the order of 500 nm. The duration of the pulse is less than a picosecond, for example comprised in an interval ranging from 200 to 400 fs, preferably in an interval ranging from 50 to 350 fs, or even from 80 to 100 fs. Such characteristics make it possible to hollow out the body without harming the properties of the material forming the stone.

[0038] It is also possible to dig the hole in the stone. This process step makes it possible to drill the hole directly to the right size, without having to go through a roughing, or a machining step so that the hole has exact and homogeneous dimensions over the entire height of the hole.

[0039] Finally, a third finishing step 4 makes it possible to give the stone a surface condition compatible with its use. For example, it is sought to obtain a surface state Ra=0.05 μm. Such a finishing step can thus comprise lapping and/or brushing and/or polishing allowing the adjustment of the final dimensions and/or the removal of edges and/or the local modification of the roughness.

[0040] As shown in Figures 2 and 3, the invention also relates to a stone 10, capable of being obtained by the method described above, the stone forming for example a guide element intended to be mounted in a bearing damper of a timepiece. However, such a stone cannot be limited to the watchmaking field and can apply to any mounted element that is mobile relative to a bearing. Stone 10 includes the features described in the process above. In particular, it is formed from a monocrystalline mineral material, comprising for example ALO3.

[0041] Advantageously, the stone 10 is traversed by a hole 8 intended to receive a pivot 17, also called a trunnion. The stone comprises an upper face 5 and an inner face 6, one of which comprises a cone 12 communicating with the through hole 8. In other words, the hole 8 communicates with the upper face 5 and also with a substantially conical recess defined in the lower face. 6. This recess then forms a cone for engaging the pierced stone 2. The cone 12 is preferably cylindrical. Cone 12 has a first opening 19 at its base and a second opening 21 at its top. The first opening 19 is larger than the second 21, and is formed in the lower face 6 of the stone 10. The connection of the cone 12 and the hole 8 is carried out by the second opening 21 to form an edge 15.

Thus, the flare of the cone 12 makes it easy to insert the pivot 17 of Tax 16 of a rotating part, especially in the event of an impact. The angle of the cone is chosen to prevent the edge 15 formed by the top of the cone and the hole 8 from protruding too much. For example, an angle of between 30° and 120°, preferably between 45° and 90°, is chosen.

[0043] It is also noted that an internal wall of the body of this stone 10 defined at the level of the hole 8 comprises a rounded zone intended to minimize contact with the pivot but also to facilitate possible lubrication. It will be noted that the minimization of the contact with the pivot makes it possible in particular to reduce the friction with the pivot.

[0044] The upper face 5 of the stone comprises a rim 7, in particular to grip laterally against a pivot in the case of a landing. The rim 7 is preferably peripheral, that is to say it delimits the edge of the upper face 5 of the stone 10. 11 and the outlet of the opening hole 8, and a concentrically convex zone 14 from the bearing face 11 to the hole 8.

[0045] An upper face 5 with such a rim 7 makes it possible, for example, to bioquer laterally an element arranged on the upper face of the stone 10. In the case of a bearing for a pendulum axis, in which the stone 10 serves as guide element, it is possible to arrange a counter-pivot stone such that it is blocked laterally by the internal side 18 of the edge 7 while resting on the bearing face 11. The counter-pivot stone is dimensioned to correspond to the zone 9 of the stone having undergone laser ablation. The stone thus forms an axial and radial support for a counter-pivot. The counter-pivot, not represented in the figures, can be fitted into stone 10 to support it axially and hold it laterally.

[0046] In addition, the stone 10 has a partially flared peripheral face 13 connecting the lower face 6 of smaller surface to the upper face 5 of larger surface.

[0047] Of course, the present invention is not limited to the illustrated example but is susceptible to various variants and modifications which will appear to those skilled in the art. In particular, other types of functional elements formed during the laser ablation step can advantageously be envisaged according to the invention.

Claims (14)

Claims 1. Process (1) for manufacturing a stone (10), in particular for a timepiece, from a mineral body of the monocrystalline type, the stone (10) comprising a treu (8), characterized in that in that it comprises an ablation step (3) in which the body is subjected to material ablation by scanning over at least one face of the body with laser radiation with ultra-short pulses whose duration is less than hundred picoseconds, and whose beam is guided by a precession system of at least three axes configured to at least partially cancel the conical angle of focus of said laser, the laser ablation step comprising the hollowing out of a cone ( 12) hole entry (8). 2. Method according to claim 1, characterized in that the cone (12) obtained during the ablation step (3) has an angle comprised in an interval ranging from 30° to 120°, preferably from 45° to 90°. 3. Method according to claim 1 or 2, characterized in that the ablation (3) is carried out layer by layer, each layer having a thickness comprised in an interval ranging from 1 to 10 μm, preferably from 2 to 4 μm. 4. Method according to any one of the preceding claims, characterized in that the pulses have a duration comprised in an interval ranging from 200 to 400 fs, preferably in an interval ranging from 50 to 350 fs, or even from 80 to 100 fs. 5. Process according to any one of the preceding claims, characterized in that the laser has a wavelength comprised in a range ranging from 400 to 600 nm, preferably between 450 and 550 nm, or even 500 nm. 6. Process according to any one of the preceding claims, characterized in that the mineral body comprises Al2O3. 7. Process according to any one of the preceding claims, characterized in that it comprises a prior stage of manufacture (2) of the body by a Verneuil type process. 8. Method according to any one of the preceding claims, characterized in that the method (1,5) comprises an additional finishing step (4, 12), for example lapping and/or brushing and/or polishing of the mineral body after the laser step, in particular on the ablation zones. 9. Method according to any one of the preceding claims, characterized in that the laser ablation step (3, 11) comprises the digging of the hole (8), the hole preferably passing through between an inner face ( 6) and an upper face (5) of the stone (10). 10. Mineral stone of monocrystalline type, in particular for a timepiece, lachte stone comprising a face (6) provided with a hole (8) formed in the body of the stone (10) and with a functional element at the entrance to the hole (10), characterized in that the functional element has a cone shape (12). 11. Mineral stone according to claim 10, characterized in that it comprises an upper face (5) and a lower face (6), the lower face (6) comprising the cone (12). 12. Mineral stone according to claim 10 or 11, characterized in that the hole (8) passes through so as to connect said cone (12) to the upper face (5) of said stone (10). 13. Stone according to any one of claims 10 to 12, characterized in that it comprises Al2O3. 14. Timepiece, comprising a stone (10) according to any one of claims 10 to 13, in particular for a damping bearing.