CH716431A2 - Stone, in particular for a clock movement, and its manufacturing process. - Google Patents

Abstract

The invention relates to a method for manufacturing a stone (30), in particular for a timepiece, from a mineral body of the monocrystalline or polycrystalline type. 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 precession system of at least three axes configured to at least partially cancel the angle of the cone of the laser, which is due to the focusing of said laser. The invention also relates to a mineral stone (30) of the monocrystalline or polycrystalline type, in particular for a clock movement, the stone (30) being capable of being obtained by the method. The stone comprises in particular a face (25) provided with a peripheral rim (27), in particular to enclose laterally a counter-pivot (35) in a bearing.

Description

Description

Field of the invention

The invention relates to a process for manufacturing a stone, in particular for a clock movement.

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

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

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, in timepieces. 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 this, with minimal friction. Thus, they form, for example, all or part of a bearing of an axis mounted in rotation. Guide elements generally include a through hole for inserting the pivot pin.

[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] In particular, concerning polycrystalline stone guide elements, the pressing tool is for example provided with a wire participating in the construction of a hole blank. Monocrystalline type stones are first drilled with a laser to obtain the rough hole. The final dimension of the hole is subsequently obtained by machining.

[0007] However, the techniques for machining these stones, whether monocrystalline or polycrystalline, do not make it possible to obtain all the desired shapes. 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 preliminary recesses which must be finalized subsequently.

Summary of the invention

The object of the present invention is to overcome all or part of the disadvantages mentioned above, by proposing a method of manufacturing a stone allowing the realization of particular shapes and functionalization of surfaces with precision.

[0009] To this end, the invention relates to a process for manufacturing a stone, in particular for a timepiece, from a mineral body of the monocrystalline or polycrystalline type, characterized in that it comprises an ablation step in which the body is subjected to material ablation by scanning over at least one face of the body with ultra-short pulse laser radiation whose duration is less than one hundred picoseconds, and whose radius is guided by a precession system of at least three axes configured to at least partially cancel the angle of the cone of the laser, which is due to the focusing of said laser.

[0010] Thus, it is possible to remove material from the stone in an extremely precise manner, and thus to obtain shapes and surfaces which are impossible to form with laser methods known from the state of the art. Such a device makes it possible to focus the laser beam with great precision, while canceling at least in part 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 to have an identical ray diameter over the entire height at the point of location of the laser, so that the ablation of matter is not. The device makes it possible to cancel the angle of the cone on at least one side of the radius, which in particular makes it possible to obtain straight cuts. These straight cuts cannot be obtained with conventional cutting lasers.

[0011] 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.

[0012] In addition, the surface condition Ra of the stone obtained with the process according to the invention is of the order of 0.1 μm, which then makes it possible to polish the stone with conventional polishing means, for example for obtain a Ra of around 0.025pm. Thus, this method provides significant advantages while maintaining an implementation without great complexity.

[0013] 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.

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 250 to 350 fs, or even from 280 to 300 fs.

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 being of monocrystalline type, and comprising for example AL2O3, the process comprises a prior step of manufacturing the body by a Verneuil type process.

According to a particular embodiment of the invention, the mineral body being of the polycrystalline type, and comprising for example polyruby of the al2O3Cr type or Zirconia of the ZrO2 type, the process 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 state pressing operates 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.

[0018] 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 the digging of a hole passing through the body.

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

[0021] 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.

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

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.

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

[0025] 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.

The invention also relates to a mineral stone of the monocrystalline or polycrystalline type, in particular for a clock movement, the stone being capable of being obtained by the method according to the invention. The stone is remarkable in that it comprises a face provided with a peripheral rim, in particular to enclose laterally a counter-pivot in a bearing.

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

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.

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

[0030] The invention also relates to a timepiece comprising a teile stone, in particular for a bearing.

Brief description of the drawings

[0031] Other features and advantages will emerge clearly from the description which is given below, by way of indication and in no way limiting, with reference to the appended drawings, in which:

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

- 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 mineral body of the polycrystalline type obtained after the step of sintering the second embodiment of the method of the invention;

- Figure 4 is a schematic representation of a mineral body of polycrystalline type 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 by the process after the laser ablation step for the two embodiments of the invention,

- Figure 6 is a view on a larger scale of part of a stone of Figure 5;

- Figure 7 is 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

[0032] 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

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 which can form all or part of a bearing of an axis mounted in rotation.

[0033] The stone is formed from a mineral body, which can be of the monocrystalline type in a first embodiment, or of the polycrystalline type in a second embodiment. For monocrystalline, the body comprises, for example, Al2O3, while for polycrystalline, the body comprises, for example, polyruby of the α1203Cr type or Zirconia of the ZrO2 type. Depending on the embodiment, the process for obtaining the mineral body is different.

In the first embodiment of process 1, shown in Figure 1, process 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.

[0035] According to the invention, the first embodiment comprises a second stage of laser ablation 3 to give a final shape to the stone. The laser ablation steps are 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, it is sought to obtain a surface state Ra=0.025 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.

[0036] In the second embodiment 5 of the process, represented in FIG. 2, such a process 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, ceramics. This step is intended to form a precursor from a ceramic-based powder taken in the binder.

[0037] In this context, the ceramic-based powder may include at least one metal oxide, metal nitride or 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 more zirconium oxide. In addition, the binder can be of various natures such as, for example, polymeric types or organic types.

[0038] 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 future stone.

The second embodiment includes a third step 8 of sintering the green body to form a body 10 visible in Figure 3 in the material which can be as we mentioned earlier, 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 drilled stone. Preferably according to the invention, the sintering step 8 may include pyrolysis.

In Figure 3, the body 10 includes a through-hole blank 14 provided with upper and lower portions 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.

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 cross 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.

[0042] It will be noted that such a blank makes it possible in particular to form the engagement edge of the pierced stone for easier assembly of the pivot, in particular when it is a question of blind monier 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, with the aid of the upper matrix and the lower matrix, the precursor in order to form said green body of the future pierced stone with the body 10 which comprises in particular the outline of the through hole 14.

The second embodiment includes a fourth machining step 9 of the body 10 of the future stone of Figure 4. The fourth step includes a first turning substep to shape 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 partially flared. The machining step also includes a sub-step of shaping the upper face 24 and the lower face 26 to obtain a predefined stone thickness.

[0044] In addition, this step also includes the dimensioning of the through hole making it possible to connect the ebne of the functional element 15a to said upper face 24.

[0045] The second embodiment comprises a fifth stage 11 of laser ablation to give a final shape to the stone.

[0046] Finally, a sixth finishing step 12 makes it possible to give the stone a surface condition compatible with its use. 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.

[0047] Both embodiments provide a one-piece monocrystalline or polycrystalline body depending on the embodiment.

[0048] According to the invention, during the laser ablation step 3, 11, the body is subjected to material ablation by scanning on at least one face of the body with ultra-short pulse laser radiation, the the duration is less than one hundred picoseconds, and whose beam is guided by a precession system of at least three axes configured to at least partially cancel 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 at least partially cancel the conical angle of the laser. Some devices use a five or six axis precession system.

[0049] 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 performed layer by layer, with the laser scanning an area of the body to hollow it out. Each layer has for example a thickness comprised in an interval going 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 within an interval ranging from 200 to 400 fs, preferably within an interval ranging from 250 to 350 fs, or even from 280 to 300 fs. Such characteristics make it possible to hollow out the body without harming the properties of the material forming the stone.

As shown by the stone obtained in 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 layer by layer on a central area 29 leaving the edge of the upper face 25 intact. After several passes of the laser and a number of layers removed, the rim 27 is formed. Thanks to this process and to the laser device, a rim 27 is obtained, the inner side 31 of which 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 0.18mm and a diameter of 0.8mm, has a rim between 0.02 and 0.08mm.

The process can also be used to form an upper face 25 in the convex part 21 and/or have several levels. In Figure 5 or 6, the zone 29 which has been hollowed out to form the flange 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 surface 28 is higher than the convex zone 21 so that the counter-pivot rests only on this part and not on the convex remainder of the convex zone 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.

[0053] An upper face with such a rim 27 makes it possible, for example, to bioquer laterally an element arranged on the upper face of the stone, as shown in Figure 7. In the case of a bearing for a pendulum axis, in which the stone 30 serves as a guiding element, a counter-pivot stone 35 can be arranged so that it is blocked laterally by the internal side 31 of the rim 27 while resting on the bearing surface 28. The counter-pivot stone is dimensioned to correspond to the zone 29 of the stone having undergone the laser ablation. The element forms axial and radial support for the counter-pivot in the housing. Counter-pivot 35 is fitted into guide element 30 to support it axially and maintain it laterally.

[0054] Thus, we obtain an assembly comprising a guide element and a counter-pivot. Both can be used in a particular damping bearing. Such a guide element makes it possible to dispense with a kitten which maintains the guide element in the bearing.

According to other embodiments, the laser ablation step allows the hollowing out 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 to an upper face of larger surface. A teile peripheral face allows the stone to slide on an oblique face of the shock-absorbing block in the event of an impact, in particular to transform a radial movement into an axial movement. Thus, the peripheral face 22 of FIGS. 4 to 6 can be obtained for a monocrystalline or polycrystalline body. Thus, for the polycrystalline body, this is avoided during the machining step of the second embodiment.

[0056] Finally, the lower surface of the stone can be functionalized by hollowing out a cone at the entrance to the through-hole. 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. In the figures of the stones, the cone is roughed out in a preliminary phase, in particular in the example of the polycrystalline body. However, the cone can be drilled by the method according to the invention without the need for a blank cone, whether with a monocrystalline or polycrystalline mineral body.

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

Claims (19)

Other shapes, not shown in the figures, can be obtained by this process. For example, the laser ablation step includes hollowing out an oil retention recess around the through hole on one side of the body. It is also possible to remove at least part of one face of the stone to make it flat, and/or to give it a determined thickness. It is also possible to hollow out a functional element of a different shape from the cone, such as a hollow whose bottom is spherical. [0059] As represented in FIGS. 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 apply to any mounted element that is mobile relative to a bearing. Stone 30 includes the features described in the process above. Advantageously, the stone 30 is traversed by a hole 14 intended to receive a pivot, also called pin. 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 an engagement cone of the pierced stone 2. [0060] It is also noted that an internal wall of the body of this stone defined at the level of the hole 14 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. According to the invention, the upper face 25 of the stone comprises a rim 27, in particular to enclose laterally a counter-pivot in the case of a landing. The rim 27 is preferably peripheral, that is to say it delimits the edge of the upper face 25 of the stone 30. 28 and the outlet of the through hole 14, and a concentrically convex zone 21 from the bearing face 28 to the hole 14. [0062] In addition, 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. [0063] It will be noted that in an alternative stone, not shown in the figures, the stone may comprise another functional element defined on the lower surface in place of the cone. The functional element has the shape of a hollow, the bottom of which is spherical. The hollow has the same function as the cone. The hollow can be obtained by laser ablation or by machining with a diamond chisel. [0064] 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 1. Process (1, 5) for manufacturing a stone (30), in particular for a timepiece, from a mineral body (10, 20) of the monocrystalline or polycrystalline type, characterized in that it comprises an ablation step (3, 11) in which the body (10, 20) is subjected to material ablation by scanning over at least one face of the body with 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 at least partially cancel the angle of the cone of the laser, which is due to the focusing of said laser. 2. Method according to claim 1, characterized in that the ablation (3, 11) 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. 3. Method according to claim 1 or 2, characterized in that the pulses have a duration comprised 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. 4. 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. 5. Method according to any one of the preceding claims, characterized in that, the mineral body (10, 20) being of the monocrystalline type, and comprising for example Al2O3, the method comprises a prior manufacturing step (2) of the body by a Verneuil-type process. 6. Process according to any one of claims 1 to 4, characterized in that the mineral body (10, 20) being of the polycrystalline type, and comprising for example polyruby of the al2O3Cr type or Zirconia of the ZrO2 type. , the process comprises the following preliminary steps: - production (6) of a precursor from a mixture of at least one powdered material with a binder; - pressing (7) of the precursor in order to form a green body, the state pressing operates 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 in said at least one material. 7. 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. 8. Method according to any one of the preceding claims, characterized in that the laser ablation step (3, 11) comprises the digging of a hole (14) passing through the body (10). 9. Method according to the preceding claim, characterized in that the laser ablation step (3, 11) comprises the digging of an inlet cone (15a) of the through hole (14). 10. Method according to any one of the preceding claims, characterized in that the laser ablation step (3, 11) comprises the hollowing out of a face (24) to form a peripheral rim on the face (27 ). 11. Method according to any one of the preceding claims, characterized in that the laser ablation step (3, 11) comprises the hollowing out of a face (24) to form a convex zone (21). 12. Method according to any one of the preceding claims, characterized in that the laser ablation step (3, 11) comprises the hollowing out of a peripheral face of the body to form a flared peripheral face (22) of the body (20). 13. Method according to any one of the preceding claims, characterized in that the laser ablation step (3, 11) comprises the digging of an oil retention recess around the through hole on one face of the body. 14. Method according to any one of the preceding claims, characterized in that the laser ablation step (3, 11) comprises the ablation of at least part of a face (24, 26) of the stone (20) to make it flat. 15. Mineral stone of the monocrystalline or polycrystalline type, in particular for a clock movement, the stone (30) being capable of being obtained by the method according to any one of the preceding claims, characterized in that the stone comprises a face (25) provided with a peripheral flange (27), in particular to grip laterally a counter-pivot (35) in a bearing. 16. Stone according to claim 15, characterized in that it comprises AI2O3 if it is of the monocrystalline type, and it comprises polyruby of the AI2O3Cr type or Zirconia of the ZrO2 type if it is of the polycrystalline type. 17. Stone according to claim 15 or 16, characterized in that the upper face (25) comprises a bearing face (28), in particular for the counter-pivot (35), the bearing face (28) being disposed at the foot of the peripheral rim (27). 18. Stone according to any one of claims 15 to 17, characterized in that, the stone (30) comprising a hole (14) passing through the center, the upper face (25) comprises a convex zone (21) delimited between the bearing face (28) and the hole (14), the zone being concentrically convex from the bearing face (28) to the hole (14). 19. Timepiece (27), comprising a stone (30) according to any one of claims 15 to 20, in particular for a bearing.