Stone material, especially for timepiece movements, and method for its manufacture

Abstract

The invention relates to a method for manufacturing a stone (30) from a mineral body of the monocrystalline or polycrystalline type, in particular for use in a timepiece. The method comprises an ablation step in which the body is subjected to material ablation by scanning on at least one face of the body using ultrashort pulse laser radiation, the duration of which is less than 100 picoseconds and whose beam is guided by a precession system having at least three axes, the precession system being configured to at least partially offset the laser cone angle caused by the focusing of the laser. The invention also relates to a mineral stone (30) of the monocrystalline or polycrystalline type, in particular for use in a timepiece movement, the stone (30) being obtainable by the method. The stone comprises in particular a face (25) provided with a peripheral edge (27) in particular for laterally clamping an end stone (35) in a bearing.

Description

Technical Field

[0001] The invention relates to a method for producing stone, in particular for a timepiece movement.

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

[0003] The invention also relates to a timepiece movement comprising such a stone. Background Art

[0004] In the prior art of horology, stones of the ruby ​​or sapphire type are used in particular to form end stones or guide elements called cousines in timepieces. These end stones and guide elements are intended to come into contact with a pivot in order to enable the pivot to move in rotation with a minimum of friction. They thus form, for example, all or part of a bearing of a rotationally mounted shaft. The guide element generally comprises a through hole in order to insert the pivot therein.

[0005] In principle, synthetic stones are used for timepiece movements. In particular, the Verneuil-type process for making stones of the monocrystalline type is known. There are also polycrystalline types of stones, which are made by pressing a precursor using a pressing tool to obtain the raw body (corps vert) of the future stone. The stone is then machined to obtain the final shape with the desired dimensions.

[0006] In particular, with regard to guide elements made of polycrystalline stone, the pressing tool is provided, for example, with a wire that helps to construct the hole blank. The stone of the monocrystalline type is first laser-drilled to obtain the hole blank. The final size of the hole is then obtained by machining.

[0007] However, the techniques for machining these stones, whether they are single crystal or polycrystalline, do not allow all the shapes desired to be obtained. In fact, conventional machining is not precise enough for certain shapes. In particular, it is not possible to functionalize the surface of the stone, except for simple blank holes or recesses, which should then be given the final shape. Summary of the invention

[0008] The object of the present invention is to completely or partially remedy the above drawbacks by proposing a method for manufacturing stone which allows precise realization of specific shapes and functionalization of the surface.

[0009] To this end, the invention relates to a method for manufacturing a stone from a mineral body of monocrystalline or polycrystalline type, in particular for use in a timepiece, characterized in that the method comprises an ablation step in which the body is subjected to material ablation by scanning it on at least one face of the body using ultrashort pulse laser radiation, the duration of which is less than 100 picoseconds and the beam of which is guided by a precession system having at least three axes, the precession system being configured to at least partially offset the laser cone angle caused by the focusing of the laser.

[0010] Thus, it is possible to remove material from the stone in an extremely precise manner and thereby obtain shapes and surfaces that cannot be formed with the laser methods known in the prior art. Such an apparatus allows focusing the laser beam with high precision while at least partially offsetting the laser cone angle caused by the focusing of the laser. In fact, said focusing produces a laser in the shape of a cone, which does not allow the same beam diameter over the entire height at the laser positioning point, so that material ablation would not be the case. The apparatus allows offsetting the cone angle on at least one side of the beam, which in particular allows obtaining straight cuts. These straight cuts cannot be obtained with conventional cutting lasers.

[0011] In addition, ultrashort laser pulses can avoid thermal heating of the stone, which would damage its quality.

[0012] Furthermore, the surface state Ra of the stone obtained with the method according to the invention is about 0.1 μm, which allows the stone to be subsequently polished with conventional polishing methods, for example to obtain a Ra of about 0.025 μm. The method thus offers significant advantages while remaining simple to implement.

[0013] According to a particular embodiment of the invention, the ablation is performed layer by layer, the thickness of each layer being in the range of 1 to 10 μm, preferably 2 to 4 μm.

[0014] According to a particular embodiment of the invention, the duration of the pulses is in the range of 200 to 400 fs, preferably in the range of 250 to 350 fs, or even in the range of 280 to 300 fs.

[0015] According to a particular embodiment of the invention, the wavelength of the laser light is in the range of 400 to 600 nm, preferably between 450 and 550 nm, or even 500 nm.

[0016] According to a particular embodiment of the invention, the mineral body is of single-crystalline type and comprises, for example, Al2O3, the method comprising a preliminary step of manufacturing the body by a Verneuil type method.

[0017] According to a particular embodiment of the invention, the mineral body is of polycrystalline type and comprises, for example, polyrubis of the Al2O3Cr type or zirconium oxide of the ZrO2 type, the method comprises the following preliminary steps:

[0018] - producing a precursor from a mixture of at least one powder material and a binder;

[0019] - pressing the precursor to form a green body, the pressing being carried out with the aid of an upper die and a lower die, and

[0020] - Sintering said raw body in order to form the mineral body of the future stone from said at least one material.

[0021] According to a particular embodiment of the invention, the method comprises an additional finishing step, such as grinding and / or brushing and / or polishing of the mineral body after the laser step, in particular on the ablated areas.

[0022] According to a specific embodiment of the invention, the laser ablation step comprises: recessing a hole through the body.

[0023] According to a specific embodiment of the invention, the laser ablation step comprises: recessing an entrance cone of the through hole.

[0024] According to a particular embodiment of the invention, the laser ablation step includes creusement of the face to form a peripheral edge on the face.

[0025] According to a specific embodiment of the invention, the laser ablation step includes concavely ...

[0026] According to a specific embodiment of the invention, the laser ablation step includes concavely ...

[0027] According to a specific embodiment of the present invention, the laser ablation step includes: recessing an oil retaining recess around the through hole on the face of the body.

[0028] According to a particular embodiment of the invention, the laser ablation step comprises ablating at least a portion of the face of the stone material to make it flat.

[0029] The invention also relates to a mineral stone of monocrystalline or polycrystalline type, in particular for a timepiece movement, obtainable by the method according to the invention. This stone is characterized in that it comprises a face provided with a peripheral rim, in particular for laterally clamping an end stone in a bearing.

[0030] According to a particular embodiment of the invention, the stone comprises Al2O3 if it is of the monocrystalline type, and comprises polyruby of the Al2O3Cr type or zirconium oxide of the ZrO2 type if it is of the polycrystalline type.

[0031] According to a particular embodiment of the invention, the face comprises a bearing surface for the end stone, which bearing surface is arranged at the bottom of the inner rim, which bearing surface forms a circular shape.

[0032] According to a particular embodiment of the invention, the stone comprises a central through hole, the face comprising a raised area delimited between the support surface and the hole, the area projecting concentrically from the support surface to the hole.

[0033] The invention also relates to a timepiece comprising such a stone, in particular for use in a bearing. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Other characteristics and advantages will emerge clearly from the description which follows, given by way of indication and not limitation, with reference to the accompanying drawings, in which:

[0035] - Figure 1 is a block diagram of a first embodiment of a stone material according to the method of the present invention;

[0036] - Figure 2 is a block diagram of a second embodiment of a stone material according to the method of the present invention;

[0037] - Figure 3 is a schematic representation of a mineral body of polycrystalline type obtained after the sintering step of a second embodiment of the method of the invention;

[0038] - Figure 4 is a schematic representation of a mineral body of polycrystalline type obtained after the processing steps of the second embodiment of the method of the present invention;

[0039] - Figure 5 is a schematic diagram of the stone obtained by the method after the laser ablation step of two embodiments of the present invention,

[0040] - Figure 6 yes Figure 5 an enlarged view of a portion of the stone;

[0041] - Figure 7 is a schematic diagram of a stone comprising a border according to the invention, the border being associated with an end stone. DETAILED DESCRIPTION

[0042] As mentioned above, the invention relates to a method for manufacturing a stone capable of forming a guide element of a timepiece. The stone is intended, for example, to come into contact with a pivot in order to enable the latter to move in rotation with minimal friction. It will thus be understood that the invention in particular allows the production of a stone capable of forming all or part of a bearing of a shaft mounted in rotation.

[0043] The stone is formed of a mineral body which may be of the monocrystalline type in a first embodiment or of the polycrystalline type in a second embodiment. For a monocrystalline, the body comprises, for example, Al2O3, while for a polycrystalline, the body comprises, for example, polyruby of the Al2O3Cr type or zirconium oxide of the ZrO2 type. Depending on the embodiment, the method of obtaining the mineral body is different.

[0044] exist Figure 1 In the first embodiment of the method 1 shown, the method 1 comprises a first step 2 of manufacturing a crystallized mineral body by a Verneuil type method well known in the field of timepiece manufacturing. The material is formed from a powder melted by an oxyhydrogen torch at a temperature above 2000° C. The body crystallizes after cooling below the melting point. The body is dimensioned so as to obtain dimensions close to those required, in particular to facilitate its future processing.

[0045] According to the invention, the first embodiment comprises a second laser ablation step 3 to give the stone its final shape. The laser ablation step will be described later in this specification. Finally, a third finishing step 4 allows the stone to be given a surface state adapted to its intended use. For example, it is sought to obtain a surface state Ra=0.025 μm. Thus, this finishing step may comprise grinding and / or brushing and / or polishing, allowing the final dimensions to be adjusted and / or edges to be removed and / or roughness to be locally modified.

[0046] In the second embodiment 5 of the method, if Figure 2 As shown, this method comprises a first step 6 of producing a precursor from a mixture of at least one powder material and a binder. This material can be a non-limiting and non-exhaustive ceramic. This step aims at forming a precursor from a ceramic-based powder solidified in a binder.

[0047] In this context, the ceramic-based powder may include at least a metal oxide, a metal nitride or a metal carbide. For example, the ceramic-based powder may include aluminum oxide to form synthetic sapphire, or a mixture of aluminum oxide and chromium oxide to form synthetic ruby, or even zirconium oxide. Furthermore, the binder may be of a more varied nature, such as polymeric or organic type.

[0048] Then, the second embodiment includes a second pressing step 7, that is, pressing the precursor using an upper mold and a lower mold of a pressing device not shown in the figure, so as to form an unprocessed body of the future stone.

[0049] The second embodiment comprises a third step 8, namely sintering the green body so as to form in the material which may be ceramic as described above. Figure 3In other words, this step 8 aims at sintering the raw body so as to form the ceramic body 10 of the future drilled stone. Preferably, according to the invention, the sintering step 8 may comprise pyrolysis.

[0050] exist Figure 3 In the embodiment, the body 10 comprises a through-hole blank 14 provided with an upper portion 15a and a lower portion 15b having different shapes. In practice, the lower portion 15b of the blank constituting the functional element has a conical shape, and the upper portion 15a of the blank comprising the through-hole 14 has a cylindrical shape. Such a through-hole 14 also comprises a first opening 17a defined in the unprocessed body 10 and leading to the bottom face 19 of the unprocessed body 10. The through-hole 14 also comprises a second opening 17b defined in the unprocessed body 10 and leading to the top face 16 of the unprocessed body 10.

[0051] The body 10 also includes a groove 18 on its bottom surface 19. The groove 18 is formed into a spherical path centered around the through hole 14 and has a triangular cross section. The groove 18 is formed by a lower mold of a pressing device, which has a negative mold shape of the groove 18, such as an annular rib.

[0052] It should be noted that such a blank in particular allows the formation of the engagement cone of the drilled stone in order to make it easier to mount the pivot, in particular when the pivot is blindly mounted in the drilled stone forming the guide element in this example. It is therefore understood that the shape of the through hole 14 is provided by the shape of the punch of the lower die of the pressing device. Thus, this pressing step 7 aims at pressing the precursor using the upper die and the lower die in order to form said raw body of the future drilled stone using the body 10 of the blank including in particular the through hole 14.

[0053] The second embodiment includes processing Figure 4 The fourth step 9 of forming the body 10 of the future stone in the present embodiment comprises a first sub-step of turning to shape the peripheral wall of the stone. Material is removed up to the apex of the groove in order to obtain an at least partially flared peripheral wall 22. The machining step also comprises a sub-step of shaping the top face 24 and the bottom face 26 to obtain a predetermined stone thickness.

[0054] Furthermore, this step also comprises dimensioning the through hole to allow connecting the cone of the functional element 15 a to said top surface 24 .

[0055] The second embodiment comprises a fifth laser ablation step 11 to give the stone its final shape.

[0056] Finally, a sixth finishing step 12 allows giving the stone a surface condition adapted to its use. This finishing step may thus comprise grinding and / or brushing and / or polishing, allowing the final dimensions to be adjusted and / or edges to be removed and / or roughness to be modified locally.

[0057] According to an embodiment, two embodiments provide a monocrystalline or polycrystalline one-piece body.

[0058] According to the invention, during the laser ablation steps 3, 11, the body is subjected to material ablation by scanning at least one face of the body with ultrashort pulse laser radiation, the duration of which is less than 100 picoseconds and whose beam is guided by a precession system having at least three axes, which is configured to at least partially offset the laser cone angle caused by laser focusing. Such an apparatus is described, for example, in document WO 2017029210. There are different types of devices that allow at least partially offsetting the laser cone angle. Some devices use a five-axis or six-axis precession system.

[0059] The laser beam thus has at least one substantially straight edge, making it possible to indent the surface of the stone and give it a specific shape. The ablation is carried out layer by layer, the laser scanning an area of ​​the body to indent it. The thickness of each layer is, for example, in the range of 1 to 10 μm, preferably 2 to 4 μm. The material is removed layer by layer until the desired shape is obtained.

[0060] For example, the wavelength of the laser is between 400 and 600 nm, preferably between 450 and 550 nm, or even about 500 nm. The duration of the pulse is less than a picosecond, for example in the range of 200 to 400 fs, preferably in the range of 250 to 350 fs, or even in the range of 280 to 300 fs. Such characteristics allow the body to be concave without damaging the properties of the material forming the stone.

[0061] like Figure 5 and Figure 6 This method allows in particular to concave the body 20 so as to obtain a peripheral edge 27 on the top face 25 of the stone 30, as shown in the stone obtained in . The surface 25 of the body 20 is chiseled layer by layer on the central area 29, leaving the edge of the top face 25 intact. After several passes of the laser and a certain number of layers removed, the edge 27 is formed. Thanks to this method and the laser device, an edge 27 is obtained, the inner side 31 of which is straight and has high precision of dimensions. The height of the edge 27 depends on the number of layers that have been removed and the thickness of the layers that have been removed. For example, a stone with a thickness of 0.18 mm and a diameter of 0.8 mm has an edge between 0.02 and 0.08 mm.

[0062] This method can also be used to form the top surface 25 of a partial protrusion 21 and / or a top surface having several layers. Figure 5 or Figure 6In the embodiment of the invention, the area 29 (which has been chiseled to form the rim 27) comprises a bearing surface 28 for the end stone and has a convex shape from the bearing surface 28 up to the hole 14. The bearing surface 28 is higher than the raised area 21, so that the end stone rests only on this part and not on the rest of the projection of the raised area 21. This convexity allows the through hole to be as close as possible to the end stone, and also for the pivot.

[0063] like Figure 7 As shown, a top face with such a rim 27 allows, for example, to block laterally elements arranged on the top face of the stone. In the case of a bearing for a balance staff, in which the stone 30 is used as a guide element, an end stone 35 can be arranged so that it is blocked laterally by the inner side 31 of the rim 27 when it rests on the bearing surface 28. The end stone is dimensioned to correspond to the area 29 of the stone that has been laser ablated. This element forms an axial and radial support for the end stone in the housing. The end stone 35 is nested in a guide element, which serves to support the end stone axially and to retain it laterally.

[0064] Thus, an assembly is obtained comprising a guide element and an end stone. In particular, both can be used in a damping bearing. Such a guide element allows to dispense with a chassis (chaton) which holds the guide element in the bearing.

[0065] According to other embodiments, the laser ablation step allows the outer peripheral surface of the body to be concave in order to form a flared outer peripheral surface of the body. The stone obtained has a chamfered outer peripheral surface connecting a bottom surface with a smaller surface area to a top surface with a larger surface area. Such an outer peripheral surface allows the stone to slide on the inclined surface of the damping block in the event of an impact, in particular to convert a radial movement into an axial movement. Thus, for single crystals or polycrystalline bodies, it is possible to obtain Figures 4 to 6 The outer peripheral surface 22. Therefore, for a polycrystalline body, this situation is avoided in the processing steps of the second embodiment.

[0066] Finally, the functionalization of the bottom surface of the stone can be achieved by recessing a cone at the entrance to the through hole. Thanks to this cone, if the pivot comes out of the hole due to an impact, it returns to the hole without being damaged by the ridges at the edge of the hole. In the figures of the stone, especially in the case of polycrystalline, the cone is roughed in the initial stage. However, the cone can be drilled out by the method according to the invention without the need to roughen it, whether with a single crystal or a polycrystalline mineral body.

[0067] A through hole can still be recessed in the stone. This method step allows the hole to be drilled directly to the correct size without the need for a blank and subsequent machining steps to make the hole have a precise and uniform size throughout the height of the hole.

[0068] Other shapes not shown in the figures can be obtained by this method. For example, the laser ablation step consists in making an oil retaining recess around the through hole on the face of the body. It is also possible to ablate at least a portion of the face of the stone material so as to make it flat and / or give it a determined thickness. It is also possible to make a functional element with a shape other than a cone, for example a spherical bottomed creux.

[0069] like Figures 5 to 7 As shown, the invention also relates to a stone 30 possibly obtained by the aforementioned methods 1, 5, forming a guide element for example for mounting in a bearing of a timepiece. However, this stone is not limited to the watchmaking field, it can be applied to any element movable relative to a bearing. The stone 30 comprises the features described in the above method. Advantageously, the stone 30 is traversed by a hole 14 intended to receive a pivot, also known as a trunnion. The stone comprises a top surface 25 and a bottom 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 top surface 26 and also with a substantially conical recess defined in the bottom surface 24. This recess then forms the engagement cone of the drilled stone 2.

[0070] It should also be noted that the inner wall of the stone body defined at the hole 14 comprises a rounded area intended to minimize contact with the pivot, but also to facilitate possible lubrication. It should be noted that minimizing contact with the pivot allows in particular to reduce friction with the pivot.

[0071] According to the invention, the top face 25 of the stone comprises a rim 27, which is used in particular for lateral clamping of the end stone in the case of a bearing. The rim 27 is preferably peripheral, that is, it delimits the edge of the top face 25 of the stone 30. Furthermore, it delimits an inner region 29 of the top face 25, which comprises the bearing face 28 and the outlet of the through hole 14, and a region 21 which protrudes concentrically from the bearing face 28 to the hole 14.

[0072] Furthermore, the stone material has an open peripheral surface 22 which connects a bottom surface 26 having a smaller surface area to a top surface 25 having a larger surface area.

[0073] It should be noted that in a variant of the stone material not shown in the figures, the stone material may include another functional element defined on the bottom surface instead of the cone. The functional element has the shape of a cavity with a spherical bottom. The function of the cavity is the same as that of the cone. The cavity may be obtained by laser ablation or by machining with a diamond chisel.

[0074] Obviously, the invention is not limited to the examples shown, but may have various variations and modifications that will be apparent to a person skilled in the art. In particular, other types of functional elements formed during the laser ablation step may advantageously be considered according to the invention.

Claims

1. A single crystal type or polycrystalline type mineral synthetic stone for a timepiece movement, if the mineral synthetic stone is a single crystal type, the mineral synthetic stone comprises Al2O3, if the mineral synthetic stone is a polycrystalline type, the mineral synthetic stone comprises Al2O3Cr type polyruby or ZrO2 type zirconia, characterized in that: The mineral composite stone comprises a top face (25) provided with a peripheral rim (27) for laterally clamping an end stone (35) in a bearing, wherein the inner side (31) of the peripheral rim (27) is straight, and wherein the top surface (25) comprises a support surface (28) for the end stone (35), the support surface (28) being arranged at the bottom of the peripheral edge (27); wherein the mineral synthetic stone (30) comprises a central through hole (14), the top surface (25) comprises a raised area (21) defined between the support surface (28) and the hole (14), the area protruding concentrically from the support surface (28) to the hole (14); wherein the supporting surface (28) is higher than the raised area (21); The mineral synthetic stone (30) can be obtained by the following method: The method comprises a laser ablation step in which the mineral body is subjected to material ablation by scanning on at least one face of the mineral body using ultrashort pulse laser radiation having a duration of less than 100 picoseconds and whose beam is guided by a precession system having at least three axes, the precession system being configured to at least partially offset the laser cone angle caused by the focusing of the laser, wherein the laser ablation step comprises: concave a face (24) to form a peripheral edge on the face and a support surface (28) at the bottom of the peripheral edge (27), and wherein the inner side (31) of the peripheral edge (27) is straight.

2. A method for manufacturing a mineral synthetic stone (30) according to claim 1 from a single crystal type or a polycrystalline type mineral body, wherein the mineral synthetic stone is used for a timepiece, the single crystal type includes Al2O3, and the polycrystalline type includes Al2O3Cr type polyruby or ZrO2 type zirconia.

3. The method according to claim 2, characterized in that The laser ablation step is performed layer by layer, with the thickness of each layer ranging from 1 to 10 μm.

4. The method according to claim 2 or 3, characterized in that: The duration of the pulses is in the range of 200 to 400 fs.

5. The method according to claim 2 or 3, characterized in that: The wavelength of the laser light is in the range of 400 to 600 nm.

6. The method according to claim 2 or 3, characterized in that: The mineral body is of the single-crystalline type and the method comprises a preliminary step (2) of manufacturing the mineral body by a Verneuil type method.

7. The method according to claim 2 or 3, characterized in that: The mineral body is of polycrystalline type and the method comprises the following preliminary steps: - producing (6) a precursor from a mixture of at least one powder material and a binder; - pressing (7) the precursor to form a green body, the pressing being carried out with the aid of an upper mould and a lower mould, and - Sintering (8) the green body in order to form the mineral body (10) of the future stone from the at least one material.

8. The method according to claim 2 or 3, characterized in that: The method comprises an additional finishing step.

9. The method according to claim 2 or 3, characterized in that: The laser ablation step includes recessing a through hole (14) through the mineral body (10).

10. The method according to claim 9, characterized in that The laser ablation step includes: recessing an entrance cone (15a) of the through hole (14).

11. The method according to claim 2 or 3, characterized in that: The laser ablation step includes concavely indenting the face (24) to form a raised area (21).

12. The method according to claim 2 or 3, characterized in that: The laser ablation step includes: concavely indenting the outer peripheral surface of the mineral body to form an open outer peripheral surface (22) of the mineral body.

13. The method according to claim 2 or 3, characterized in that: The laser ablation step includes: forming an oil retaining recess on the face of the mineral body around the through hole.

14. The method according to claim 2 or 3, characterized in that: The laser ablation step includes ablating at least a portion of the surface of the mineral synthetic stone (30) to make it flat.

15. The method according to claim 8, characterized in that The method comprises grinding and / or brushing and / or polishing the mineral body after the laser ablation step.

16. The method according to claim 8, characterized in that The method comprises grinding and / or brushing and / or polishing the mineral body on the ablated areas after the laser ablation step.

17. The method according to claim 2, characterized in that The laser ablation step is performed layer by layer, with each layer having a thickness of 2 to 4 μm.

18. The method according to claim 2 or 3, characterized in that: The duration of the pulses is in the range of 250 to 350 fs.

19. The method according to claim 2 or 3, characterized in that: The duration of the pulses is in the range of 280 to 300 fs.

20. The method according to claim 2 or 3, characterized in that The wavelength of the laser is between 450 and 550 nm.

21. The method according to claim 2 or 3, characterized in that: The wavelength of the laser is 500 nm.

22. A timepiece comprising the mineral composite stone (30) according to claim 1.

23. The timepiece according to claim 22, characterized in that The mineral synthetic stone (30) is used for bearings.

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