MONOCRISTALLINE TYPE MINERAL STONE EQUIPPED WITH A CONE FOR CENTRING A PIVOT, AND MANUFACTURING METHOD THEREOF

Abstract

A method for manufacturing a stone for a timepiece from a mineral body of a monocrystalline type, the stone including a hole, includes ablating the body by scanning at least one face of the body with ultra-short pulse laser radiation from a laser for a duration less than one hundred picoseconds, and guiding a beam of the laser radiation using a precession system of at least three axes configured to at least partially cancel a conical focusing angle of the laser. The ablating includes digging of a cone of entrance to the hole. A mineral stone of monocrystalline type for a timepiece includes a face provided with a hole formed in a body of the stone, and a functional element at an entrance to the hole. The functional element has a shape of a cone.

Claims

1-13. (canceled)

14. A method for manufacturing a stone for a timepiece from a mineral body of a monocrystalline type, the stone comprising a hole, the method comprising: ablating the body by scanning at least one face of the body with ultra-short pulse laser radiation from a laser for a duration less than one hundred picoseconds; and guiding a beam of the laser radiation using a precession system of at least three axes configured to at least partially cancel a conical focusing angle of the laser, wherein the ablating includes digging of a cone of entrance to the hole, and the ablating is carried out layer by layer, each layer having a thickness comprised within an interval ranging from 1 to 10 μm.

15. The method according to claim 14, wherein the thickness is within an interval ranging from 2 to 4 μm.

16. The method according to claim 14, wherein the cone obtained during the ablating has an angle comprised within an interval ranging from 30° to 120°.

17. The method according to claim 16, wherein the angle is within an interval ranging from 45° to 90°.

18. The method according to claim 14, wherein the laser irradiation comprises pulses having a duration comprised within an interval ranging from 50 to 400 fs.

19. The method according to claim 18, wherein the duration is within an interval ranging from 250 to 300 fs.

20. The method according to claim 18, wherein the duration is within an interval ranging from 80 to 100 fs.

21. The method according to claim 14, wherein the laser has a wavelength comprised within an interval ranging from 400 to 600 nm.

22. The method according to claim 21, wherein the wavelength is within an interval ranging between 450 and 550 nm.

23. The method according to claim 14, wherein the mineral body comprises Al.sub.2O.sub.3.

24. The method according to claim 14, further comprising manufacturing the body by a Verneuil-type method before the ablating.

25. The method according to claim 14, further comprising finishing at least areas of the mineral body which have been ablated.

26. The method according to claim 25, wherein the finishing comprises at least one of lapping, brushing, and polishing of the mineral body.

27. The method according to claim 14, wherein the ablating further comprises digging the hole.

28. The method according to claim 27, wherein the hole is a through-hole between a lower face and an upper face of the stone.

29. A mineral stone of a monocrystalline type for a timepiece, comprising: a face provided with a hole formed in a body of the stone; and a functional element at an entrance to the hole, wherein the functional element has a shape of a cone.

30. The mineral stone according to claim 29, further comprising an upper face and a lower face, the lower face including the cone.

31. The mineral stone according to claim 29, wherein the hole is a through-hole connecting said cone to an upper face of said stone.

32. The mineral stone according to claim 29, wherein the stone comprises Al.sub.2O.sub.3.

33. A timepiece, comprising the mineral stone according to claim 29, for a damper bearing-block.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Other features and advantages will emerge clearly from the description which is given below, in an indicative and non-limiting manner, with reference to the appended drawings, wherein:

[0032] FIG. 1 is a block diagram of the production of a stone according to the method of the invention;

[0033] FIG. 2 is a schematic representation of a stone obtained after the laser ablation step using the method according to the invention;

[0034] FIG. 3 is a schematic representation of an assembly comprising a stone of FIG. 2 and an axis provided with a pivot.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] 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 contact a pivot in order to make the latter movable in rotation with minimal friction. It is therefore understood that the present invention allows in particular to produce a stone which can form all or part of a bearing-block of an axis mounted in rotation.

[0036] The stone is formed from a mineral body of monocrystalline type. The body comprises, for example, AL.sub.2O.sub.3.

[0037] The method 1, shown in FIG. 1, comprises a first step 2 of manufacturing the crystalline mineral body by a Verneuil-type method, 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 crystallises 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.

[0038] According to the invention, the method comprises a second laser ablation step 3 in order to form a cone of entrance to a hole in the stone. During the laser ablation step 3, the body is subjected to ablation of material by scanning on at least one side of the body with ultra-short pulse laser radiation the duration of which is less than one hundred picoseconds, and the beam of which 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 document WO 2017029210. There are different types of devices allowing to cancel at least in part the conical angle of the laser. Some devices use a five or six axis precession system.

[0039] Thus, the laser beam has at least one substantially straight edge, so that these devices allow to dig 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 an impact, the pivot returns to the hole without being damaged by the rim 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. As the rim of a cone protrudes less, the risk of wear is greatly reduced. For example, an angle comprised between 30° and 120°, preferably between 45° and 90°, is selected.

[0040] The ablation is done layer by layer, the laser scanning an area of the body to dig it. Each layer has, for example, a thickness comprised within an interval ranging from 1 to 10 μm, preferably from 2 to 4 μm. Material is removed layer by layer until the desired shape is obtained.

[0041] The laser has, for example, a wavelength comprised between 400 and 600 nm, preferably between 450 and 550 nm, or even of the order of 500 nm. The duration of the pulsation is less than the picosecond, for example comprised within an interval ranging from 50 to 400 fs, preferably within an interval ranging from 250 to 300 fs or from 80 to 100 fs. Such features allow to dig the body without adversely affecting the properties of the material forming the stone.

[0042] It is also possible to dig the hole in the stone. This step of the method allows the hole to be drilled directly to the correct dimension, without having to go through a blank, then a machining step so that the hole has exact and homogeneous dimensions over the entire height of the hole.

[0043] Finally, a third finishing step 4 allows to give the stone a surface state compatible with its use. It is sought for example to obtain a surface state Ra=0.05 μm. Such a finishing step can thus include a lapping and/or a brushing and/or a polishing allowing the adjustment of the final dimensions and/or the removal of rims and/or the local modification of the roughness.

[0044] As shown in FIGS. 2 and 3, the invention also relates to a stone 10, obtainable by the method described above, the stone forming for example a guide element intended to be mounted in a damper bearing-block of a timepiece. However, such a stone cannot be limited to the watchmaking field and can be applied to any element that is movably mounted relative to a bearing-block. The stone 10 includes the features described in the method above. In particular, it is formed from a monocrystalline mineral material, comprising for example ALO.sub.3.

[0045] Advantageously, the stone 10 is traversed by a hole 8 intended to receive a pivot 17, also called a trunnion. The stone includes an upper face 5 and a lower 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 hollow defined in the lower face 6. This hollow then forms an engagement cone of the drilled stone 2. The cone 12 is preferably cylindrical. The 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 opening 21, and is formed in the lower face 6 of the stone 10. The connection of the cone 12 and the hole 8 takes place through the second opening 21 to form a rim 15.

[0046] Thus, the flaring of the cone 12 allows to easily insert the pivot 17 of the axis 16 of a part movable in rotation, in particular in the event of an impact. The angle of the cone is selected to prevent the rim 15 formed by the top of the cone and the hole 8 from protruding too much. For example, an angle comprised between 30° and 120°, preferably between 45° and 90°, is selected.

[0047] It is also noted that an internal wall of the body of this stone 10 defined at the hole 8 includes a rounded area intended to minimise contact with the pivot but also to facilitate possible lubrication. It will be noted that minimising contact with the pivot allows in particular to reduce friction with the pivot.

[0048] The upper face 5 of the stone comprises a flange 7, in particular for laterally enclosing a counter-pivot in the case of a bearing-block. The flange 7 is preferably peripheral, that is to say that it delimits the edge of the upper face 5 of the stone 10. In addition, it defines an internal area 9 of the upper face 5 including a bearing face 11 and the outlet of the through-hole 8, and a concentrically convex area 14 from the bearing face 11 to the hole 8.

[0049] An upper face 5 with such a flange 7 allows for example to laterally block an element arranged on the upper face of the stone 10. In the case of a bearing-block for a balance axis, wherein the stone 10 serves as a guide element, a counter-pivot stone can be disposed in such a way that it is laterally blocked by the internal side 18 of the flange 7 while resting on the bearing face 11. The counter-pivot stone is dimensioned to correspond to the area 9 of the stone that has undergone laser ablation. The stone thus forms an axial and radial support for a counter-pivot. The counter-pivot, not shown in the figures, can be fitted into the stone 10 to support it axially and hold it laterally.

[0050] Furthermore, the stone 10 has a peripheral face 13 which is partly flared connecting the lower face 6 of smaller surface to the upper face 5 of larger surface.

[0051] Of course, the present invention is not limited to the example illustrated but is liable to numerous variations and modifications which will be apparent to the person skilled in the art. In particular, other types of functional elements formed by the laser ablation step can be advantageously considered according to the invention.