STONE FOR A CLOCK MOVEMENT, AND ITS MANUFACTURING METHOD

Description

Field of invention

[0001] The invention relates to a method of manufacturing a stone for a watch movement.

[0002] The invention also relates to a stone, in particular a bearing, provided with a rim.

[0003] The invention also relates to a timepiece comprising such a stone. Background of the invention

[0004] In the state of the art of watchmaking, ruby ​​or sapphire stones are used in particular to form counter-pivots or guide elements, called bearings, in timepieces. These counter-pivots and guide elements are intended to come into contact with 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 a rotating shaft. The guide elements generally include a through hole for inserting the pivot shaft.

[0005] Synthetic stones are generally used in watch movements. The Verneuil process is particularly well known for manufacturing monocrystalline stones. There are also polycrystalline stones, which are manufactured by pressing a precursor to obtain a green body of the future stone using a pressing tool. The stones are then machined to obtain a finished shape with the desired dimensions.

[0006] In particular, for polycrystalline stone guide elements, the pressing tool is, for example, equipped with a wire that helps to create a hole blank. Monocrystalline stones are first laser-drilled to obtain the hole blank. The final hole size is then obtained through machining.

[0007] However, the machining techniques for these stones, whether monocrystalline or polycrystalline, do not allow for all the desired shapes to be obtained. Indeed, conventional machining is not precise enough for certain shapes. In particular, it is not possible to functionalize the surfaces of the stone beyond simple holes or rough recesses that must be finalized later.

[0008] Document EP 3367182 A1 describes a bearing with oiler and reduced contact surface with the shaft bearing surface.

[0009] US 2013 / 0175243 A1 discloses laser ablation machining of a gemstone using a laser beam manipulation system in which a mirror can be moved along the direction of the incoming laser beam, a laser beam rotation system, and a compensation system comprising laser beam displacement optical elements that can be fixedly rotated relative to each other. Summary of the invention

[0010] The aim of the present invention is to overcome all or part of the drawbacks mentioned above, by proposing a method of manufacturing a stone allowing the creation of particular shapes and the functionalization of surfaces with precision.

[0011] For this purpose, the invention relates to a method according to the appended claim 1.

[0012] Thus, it is possible to remove material from the stone extremely precisely, and thus to obtain shapes and surfaces that are impossible to form with known state-of-the-art laser methods. Such a device makes it possible to focus the laser beam with great precision, while at least partially canceling the conical angle of the laser, which is due to the focusing of the laser. Indeed, the focusing generates a cone-shaped laser, which does not allow for an identical beam diameter over the entire height at the laser location point, so that the ablation of material is not. The device makes it possible to cancel the cone angle on at least one side of the beam, which in particular makes it possible to obtain straight cuts. These straight cuts cannot be obtained with conventional cutting lasers.

[0013] In addition, the ultra-short pulses of the laser prevent thermal heating of the stone, which is detrimental to the quality of the stone.

[0014] Furthermore, the surface condition Ra of the stone obtained with the method according to the invention is of the order of 0.1µm, which then makes it possible to polish the stone with conventional polishing means, for example to obtain a Ra of the order of 0.025µm. Thus, this method provides significant advantages while maintaining an implementation without great complexity.

[0015] According to a particular embodiment of the invention, the ablation is carried out layer by layer, each layer having a thickness in a range from 1 to 10µm, preferably from 2 to 4µm.

[0016] According to a particular embodiment of the invention, the pulses have a duration in an interval ranging from 200 to 400 fs, preferably in an interval ranging from 250 to 350 fs, or even from 280 to 300 fs.

[0017] According to a particular embodiment of the invention, the laser has a wavelength in an interval ranging from 400 to 600nm, preferably between 450 and 550nm, or even 500nm.

[0018] According to a particular embodiment of the invention, the mineral body being of polycrystalline type, and comprising for example polyrubis of type al2O3Cr or Zirconia of type ZrO2, the method comprises the following preliminary steps: production of a precursor from a mixture of at least one powdered material with a binder; pressing of the precursor in order to form a green body, the pressing being carried out using an upper die and a lower die, and sintering of said green body in order to form the mineral body of the future stone in said at least one material.

[0019] 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 zones.

[0020] According to a particular embodiment of the invention, the laser ablation step comprises digging a hole through the body.

[0021] According to a particular embodiment of the invention, the laser ablation step comprises the digging of an entry cone of the through hole.

[0022] According to a particular embodiment of the invention, the laser ablation step comprises hollowing out a face to form a peripheral rim on the face.

[0023] According to a particular embodiment of the invention, the laser ablation step comprises hollowing out the face to form a convex zone.

[0024] According to a particular embodiment of the invention, the laser ablation step comprises hollowing out a peripheral face of the body to form a flared peripheral face of the body.

[0025] According to a particular embodiment of the invention, the laser ablation step comprises digging an oil retention recess around the through hole on one face of the body.

[0026] According to a particular embodiment of the invention, the laser ablation step comprises the ablation of at least part of a face of the stone to make it flat.

[0027] The invention also relates to a mineral stone according to the appended claim 14.

[0028] According to a particular embodiment of the invention, the stone comprises AL2O3 if it is of monocrystalline type, and it comprises polyrubis of al2O3Cr type or Zirconia of ZrO2 type if it is of polycrystalline type.

[0029] According to a particular embodiment of the invention, the face comprises a bearing face for the counter-pivot, the bearing face being arranged at the foot of the internal rim, the bearing face describing a circle.

[0030] According to a particular embodiment of the invention, the stone comprising a centered through hole, the face comprises a convex zone delimited between the bearing face and the hole, the zone being concentrically convex from the bearing face to the hole.

[0031] The invention also relates to a timepiece comprising such a stone, in particular for a bearing. Summary description of the drawings

[0032] Other features and advantages will become clear from the description given below, for information purposes only and in no way limiting, with reference to the attached drawings, in which: there figure 1is a block diagram of a first embodiment of a stone according to the method of the invention; the figure 2 is a block diagram of a second embodiment of a stone according to the method of the invention; figure 3 is a schematic representation of a polycrystalline mineral body obtained after the sintering step of the second embodiment of the method of the invention; figure 4 is a schematic representation of a polycrystalline mineral body obtained after a machining step of the second embodiment of the method of the invention; Figure 5 is a schematic representation of a stone obtained using the method after the laser ablation step for the two embodiments of the invention, the figure 6 is a larger scale view of part of a stone from the Figure 5 ; there figure 7is a schematic representation of a stone comprising a rim according to the invention, which is associated with a counter-pivot. Detailed Description of Preferred Embodiments

[0033] As explained above, the invention relates to a method for manufacturing a stone capable of forming a guide element of a timepiece. The stone is for example intended to come into contact with a pivot in order to make the latter mobile in rotation with minimal friction. It is therefore understood that the present invention makes it possible in particular to produce a stone capable of forming all or part of a bearing of an axis mounted in rotation.

[0034] The stone is formed from a mineral body, which may be of the monocrystalline type in a first embodiment, or of the polycrystalline type in a second embodiment. For the monocrystalline, the body comprises for example AL2O3, while for the polycrystalline, the body comprises for example polyruby of the al2O3Cr type or zirconia of the ZrO2 type. Depending on the embodiment, the method for obtaining the mineral body is different.

[0035] In the first embodiment of method 1, shown in the figure 1, process 1 comprises a first step 2 of manufacturing the crystalline mineral body by a Verneuil-type process, which is well known in the field of watchmaking. The material is formed from a powder melted by an oxyhydrogen torch at more than 2000°C. The body crystallizes after cooling below the melting point. The body is sized so as to obtain dimensions close to those desired, in particular to facilitate its future machining.

[0036] According to the invention, the first embodiment comprises a second laser ablation step 3 to give a definitive shape to the stone. The laser ablation step is described later in the description. Finally, a third finishing step 4 makes it possible to give the stone a surface condition compatible with its use. For example, the aim is to obtain a surface condition Ra=0.025µm. Such a finishing step may 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.

[0037] In the second embodiment 5 of the method, shown in the figure 2, such a method comprises a first step 6 of producing a precursor from a mixture of at least one powdered material with a binder. This material may be, in a non-limiting and non-exhaustive manner, ceramic. This step is intended to form a precursor from a ceramic-based powder taken in the binder.

[0038] In this context, the ceramic-based powder may comprise at least one metal oxide, a metal nitride or a metal carbide. For example, the ceramic-based powder may comprise aluminum oxide to form synthetic sapphire or a mixture of aluminum oxide and chromium oxide to form synthetic ruby, or zirconium oxide. In addition, the binder may be of various types, such as, for example, polymer types or organic types.

[0039] The second embodiment then comprises a second step 7 of pressing the precursor from an upper die and a lower die of a pressing device, not shown in the figures, in order to form the green body of the future stone.

[0040] The second embodiment comprises a third step 8 of sintering the green body in order to form a body 10 visible on the figure 3 in the material which can be, as we mentioned previously, ceramic. In other words, this step 8 is intended to sinter the green body in order to form a ceramic body 10 of the future pierced stone. Preferably according to the invention, the sintering step 8 can include pyrolysis.

[0041] On the figure 3, the body 10 comprises a through-hole blank 14 provided with upper and lower parts 15a, 15b which are of different shapes. Indeed, the lower part 15b which constitutes the blank of the functional element has a conical shape and the upper part 15a which comprises the blank of the through-hole 14 has a cylindrical shape. Such a through-hole 14 also comprises a first opening 17a defined in the green body 10 and opening into the lower face 19 of this green body 10. The through-hole 14 also comprises a second opening 17b defined in the green body 10 and opening into the upper face 16 of this green body 10.

[0042] The body 10 further comprises a groove 18 on its lower face 19. The groove 18 describes a spherical path centered around the through hole 14 and has a triangular-shaped section. This groove 18 is formed by the lower die of the pressing device, the lower die having a negative shape of the groove 18, such as an annular rib.

[0043] It will be noted that such a blank makes it possible in particular to form the engagement cone of the pierced stone for easier mounting of the pivot, in particular when it is a question of mounting it blindly in the pierced stone forming in this example a guide element. It is therefore understood that the shape of the through hole 14 is provided by the shape of a punch of the lower die of the pressing device. Thus, such a pressing step 7 is intended to compress, using the upper die and the lower die, the precursor in order to form said green body of the future pierced stone with the body 10 which notably comprises the blank of the through hole 14.

[0044] The second embodiment comprises a fourth machining step 9 of the body 10 of the future stone of the figure 4The fourth step comprises a first turning sub-step for shaping the peripheral wall of the stone. Material is removed up to the top of the groove so as to obtain a peripheral wall 22 that is at least partly flared. The machining step also comprises a sub-step for shaping the upper face 24 and the lower face 26 to obtain a predefined stone thickness.

[0045] Furthermore, this step also includes the dimensioning of the through hole making it possible to connect the cone of the functional element 15a to said upper face 24.

[0046] The second embodiment comprises a fifth step 11 of laser ablation to give a definitive shape to the stone.

[0047] Finally, a sixth finishing step 12 allows the stone to be given a surface condition compatible with its use. Such a finishing step may thus include 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.

[0048] Both embodiments provide a monocrystalline or polycrystalline one-piece body depending on the embodiment.

[0049] According to the invention, during the laser ablation step 3, 11, the body is subjected to ablation of material by scanning on at least one face of the body an ultra-short pulse laser radiation whose duration is less than one hundred picoseconds, and whose beam is guided by a precession system of at least three axes configured to cancel at least in part the angle of the cone due to the focusing of the laser. Such a device is for example described in the document WO 2017029210. There are different types of devices making it possible to cancel at least in part the conical angle of the laser. Some devices use a five or six axis precession system.

[0050] Thus, the laser beam has at least one substantially straight edge, so that the surface of the stone can be hollowed out and given a specific shape. The ablation is carried out layer by layer, with the laser scanning an area of ​​the body to hollow it out. Each layer has, for example, a thickness in the range of 1 to 10 µm, preferably 2 to 4 µm. Material is removed layer by layer until the desired shape is achieved.

[0051] The laser has, for example, a wavelength between 400 and 600nm, preferably between 450 and 550nm, or even around 500nm. The pulse duration is less than a picosecond, for example in the range 200 to 400 fs, preferably in the range 250 to 350 fs, or even 280 to 300 fs. Such characteristics make it possible to hollow out the body without harming the properties of the material forming the stone.

[0052] As shown by the stone obtained on the Figures 5 and 6, the method makes it possible in particular to hollow out the body 20 to obtain a peripheral rim 27 on the upper face 25 of the stone 30. The face 25 of the body 20 is hollowed out layer by layer over a central area 29, leaving the edge of the upper face 25 intact. After several passes of the laser and a certain number of layers removed, the rim 27 is formed. Thanks to this method and the laser device, a rim 27 is obtained whose internal side 31 is straight with dimensions of great precision. The height of the rim 27 depends on the number of layers that have been removed and their thickness. A stone having, for example, a thickness of 0.18 mm and a diameter of 0.8 mm, has a rim of between 0.02 and 0.08 mm.

[0053] The method can also be used to form an upper face 25 which is partly convex 21 and / or has several levels. On the figure 5 or 6, the area 29 which has been hollowed out to form the rim 27, comprises a bearing face 28 for a counter-pivot, and has a convex shape from the bearing face 28 to the hole 14. The bearing face 28 is higher than the convex area 21 so that the counter-pivot rests only on this part and not on the convex remainder of the convex area 21. The convexity makes it possible to have the through hole as close as possible to the counter-pivot, and the same for the pivot.

[0054] An upper face with such a rim 27 makes it possible, for example, to laterally block an element arranged on the upper face of the stone, as shown in figure 7. In the case of a bearing for a balance shaft, in which the stone 30 serves as a guide element, a counter-pivot stone 35 can be arranged such that it is laterally blocked by the inner side 31 of the rim 27 while resting on the bearing face 28. The counter-pivot stone is sized to correspond to the area 29 of the stone having undergone laser ablation. The element forms an axial and radial support for the counter-pivot in the housing. The counter-pivot 35 is fitted into the guide element 30 to support it axially and hold it laterally.

[0055] This results in a unit comprising a guide element and a counter-pin. Both can be used in a particular shock absorber bearing. Such a guide element eliminates the need for a kitten that holds the guide element in the bearing.

[0056] According to other embodiments, the laser ablation step allows the hollowing of a peripheral face of the body to form a flared peripheral face of the body. The stone obtained has a beveled peripheral face connecting a lower face of smaller surface area to an upper face of larger surface area. Such a peripheral face allows the stone to slide on an oblique face of the shock absorber block in the event of an impact, in particular to transform a radial movement into an axial movement. Thus, the peripheral face 22 of the figures 4 to 6 for a monocrystalline or polycrystalline body. Thus, for the polycrystalline body, it is avoided to do this during the machining step of the second embodiment.

[0057] Finally, the lower surface of the stone can be functionalized by hollowing out a cone at the entrance of the through hole. Thanks to this cone, if the pivot comes out of the hole due to an impact, the pivot returns to the hole without being damaged by the edge of the hole. In the figures of the stones, the cone is roughed out in a preliminary phase, particularly in the example of the polycrystalline body. However, the cone can be drilled by the method according to the invention without needing a roughing cone, whether with a monocrystalline or polycrystalline mineral body.

[0058] It is still possible to drill the through hole in the stone. This process step allows the hole to be drilled directly to the correct size, without having to go through a roughing and then a machining step to ensure the hole has exact and consistent dimensions throughout the entire height of the hole.

[0059] Other shapes, not shown in the figures, can be obtained by this method. For example, the laser ablation step includes the hollowing of an oil retention recess around the through hole on one face of the body. At least part of one face of the stone can also be ablated to make it flat, and / or to give it a determined thickness. A functional element of a shape different from the cone can also be hollowed out, such as a hollow with a spherical bottom.

[0060] As shown on the figures 5 to 7, the invention also relates to a stone 30, capable of being obtained by the method 1, 5 described above, the stone forming for example a guide element intended to be mounted in a bearing of a timepiece. However, such a stone cannot be limited to the watchmaking field and can be applied to any element mounted movably relative to a bearing. The stone 30 comprises the characteristics described in the method above. Advantageously, the stone 30 is crossed by a hole 14 intended to receive a pivot, also called a journal. The stone comprises an upper surface 25 and a lower surface 26, one of which comprises a functional element 15a, here a cone, communicating with the through hole 14. In other words, the hole 14 communicates with the upper surface 26 and also with a substantially conical recess defined in the lower surface 24. This recess then forms a cone for engaging the pierced stone 2.

[0061] It is also noted that an internal wall of the body of this stone defined at the level of hole 14 has a rounded area intended to minimize contact with the pivot but also to facilitate possible lubrication. It will be noted that minimizing contact with the pivot makes it possible in particular to reduce friction with the pivot.

[0062] According to the invention, the upper face 25 of the stone comprises a rim 27, in particular for laterally gripping a counter-pivot in the case of a bearing. The rim 27 is preferably peripheral, that is to say that it delimits the edge of the upper face 25 of the stone 30. In addition, it defines an internal zone 29 of the upper face 25 comprising a bearing face 28 and the outlet of the through hole 14, and a zone 21 convex concentrically from the bearing face 28 to the hole 14.

[0063] Furthermore, the stone has a flared peripheral face 22 connecting the lower face 26 of smaller surface area to the upper face 25 of larger surface area.

[0064] It should be noted that in a stone variant, not shown in the figures, the stone may include another functional element defined on the lower surface in place of the cone. The functional element has a hollow shape with a spherical bottom. The hollow has the same function as the cone. The hollow can be obtained by laser ablation or by machining with a diamond chisel.

[0065] 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, while remaining defined by the appended claims. In particular, other types of functional elements formed during the laser ablation step can be advantageously envisaged according to the invention.

Claims

1. A method (1, 5) for manufacturing a synthetic stone (30), in particular for a timepiece, from a mineral body (10, 20) of polycrystalline type, characterised in that it comprises an ablation step (3, 11) in which the body (10, 20) is subjected to a material ablation by scanning on at least one face of the body using ultra-short pulse laser radiation whose duration is less than one hundred picoseconds, and whose beam is guided by a precession system having at least three axes configured to at least partially cancel the angle of the laser cone, which is due to the focusing of said laser.

2. The method according to claim 1, characterised in that the ablation (3, 11) is performed layer by layer, each layer having a thickness within a range of 1 to 10 µm, preferably of 2 to 4 µm.

3. The method according to claim 1 or 2, characterised in that the pulses have a duration within a range of 200 to 400 fs, preferably a range of 250 to 350 fs, or even of 280 to 300 fs.

4. The method according to any one of the preceding claims, characterised in that the laser has a wavelength within a range of 400 to 600nm, preferably between 450 and 550nm, or even of 500nm.

5. The method according to any one of claims 1 to 4, characterised in that, the mineral body (10, 20) being of polycrystalline type, and comprising for example al2O3Cr type polyruby or ZrO2 type Zirconia, the method includes the following preliminary steps: - producing (6) a precursor from a mixture of at least one powder material with a binder; - pressing (7) of the precursor in order to form a green body, the pressing being carried out using an upper die and a lower die, and - sintering (8) of said green body in order to form the mineral body (10), of the future stone, from said at least one material.

6. The method according to any one of the preceding claims, characterised in that the method (1, 5) comprises an additional finishing step (4, 12), for example a lapping and / or a brushing and / or a polishing of the mineral body after the laser step, in particular on the ablation areas.

7. The method according to any one of the preceding claims, characterised in that the laser ablation step (3, 11) comprises recessing a hole (14) passing through the body (10).

8. The method according to the preceding claim, characterised in that the laser ablation step (3, 11) comprises recessing an inlet cone (15a) of the through hole (14).

9. The method according to any one of the preceding claims, characterised in that the laser ablation step (3, 11) comprises recessing a face (24) to form a peripheral rim on the face (27).

10. The method according to any one of the preceding claims, characterised in that the laser ablation step (3, 11) comprises recessing a face (24) to form a convex area (21).

11. The method according to any one of the preceding claims, characterised in that the laser ablation step (3, 11) comprises recessing a peripheral face of the body to form a flared peripheral face (22) of the body (20).

12. The method according to any one of the preceding claims, characterised in that the laser ablation step (3, 11) comprises recessing an oil retention recess around the through hole on a face of the body.

13. The method according to any one of the preceding claims, characterised in that the laser ablation step (3, 11) comprises the ablation of at least one portion of a face (24, 26) of the stone (20) to make it planar.

14. A mineral stone of monocrystalline or polycrystalline type, for a horological movement, the stone (30) being likely to be obtained by the method according to any one of the preceding claims, characterised in that the stone comprises a face (25) provided with a peripheral rim (27), in particular for laterally clamping an endstone (35) in a bearing, said face (25) comprising a bearing face (28), in particular for the endstone (35), the bearing face (28) being disposed at the foot of the peripheral rim (27).

15. A stone according to claim 14, characterised in that it comprises Al2O3 if it is of monocrystalline type, and it comprises al2O3Cr type polyruby or ZrO2 type Zirconia if it is of polycrystalline type.

16. The stone according to claim 15, characterised in that the stone (30) comprising a centred through hole (14), said face (25) comprises a convex area (21) delimited between the bearing face (28) and the hole (14), the area being convex concentrically from the bearing face (28) to the hole (14).

17. A timepiece (27), comprising a stone (30) according to any one of claims 14 to 16, in particular for a bearing.