Method for manufacturing a pivot stone for a timepiece movement

Abstract

The invention relates to a method for manufacturing a pivot stone, characterised in that the method comprises the following steps: - providing a ceramic or ceramic-based block to be machined; - machining the block using a machining device comprising a mechanical cutting tool that acts on the block through direct contact so as to remove chips from the block, and in that the step of machining the block is carried out using a spindle to which the block is attached and on which it is rotated at a speed greater than or equal to 30,000 rpm, or even greater than or equal to 32,000 rpm, or even greater than or equal to 35,000 rpm, or even greater than or equal to 38,000 rpm, or even greater than or equal to 40,000 rpm, while the mechanical cutting tool comes into contact with the block to remove material in successive passes, in order to form a timepiece component having rotational symmetry.

Description

[0001] Process for manufacturing a pivot stone for a watch movement

[0002] The present invention relates to a method of manufacturing a pivot stone for a watch movement. It also relates to a machining device which implements such a manufacturing method.

[0003] Generally speaking, the production of a watch component requires finding a good compromise between the following requirements:

[0004] - A high-performance material, which meets at least the high mechanical requirements imposed by the watchmaking application;

[0005] - A manufacturing process simple enough to consider large-scale implementation, in a reliable and robust manner.

[0006] A first existing solution consists of manufacturing a metal watch component by a bar turning process, involving a mechanical cutting tool that acts directly in contact with an initial block, to shape it by removing material. This cutting tool comes into direct contact with the block, unlike laser machining in which a laser beam can act remotely on such a block. Such a process makes it possible to achieve high precision in a rapid and well-controlled manner. However, depending on the alloy used, the metal has the disadvantage of being sensitive to magnetic fields, which can lead to problems with the reliability of the running of a watch in certain circumstances of use. On the other hand, the metal is not always sufficiently hard and requires additional operations to increase its hardness, and sometimes improve its surface condition, which ultimately complicates the manufacturing process.Finally, some non-magnetic and hard alloys prove to be too difficult to machine, as they cause excessive wear, or even breakage, of the cutting tools. A second existing solution is based on the choice of a very rigid non-magnetic material, such as ceramic, which does not have some of the defects of the metal in the first solution. However, the manufacture of a ceramic watch component requires a more complex process, generally involving laser machining, which is more difficult to master and slower than traditional machining.

[0007] In the case of pivot stones for watchmaking, these stones are determining elements for the proper functioning of a watch movement. Almost all rotational movements are ensured by axes pivoted in bearings, which are made in drilled ruby ​​elements, also called functional stones or pivot stones.

[0008] In a known manner, to produce a pivot stone, a ball of material, in particular a synthetic ruby ​​ball, more particularly a single-crystal synthetic ruby ​​ball, is cut by sawing or wire cutting or laser cutting into plates of a given thickness. These plates are then cut to form blanks (preparations) of the pivot stones which are brought to a cylindrical external shape, for example by a turning operation.

[0009] The pivot stones are then drilled, for example by laser or by a spindle, so as to obtain the rough shape of a pivot hole. The stones are then subjected to a magnifying step which allows to arrive at the final diameter and the desired surface finish of the pivot hole. A turning step then allows to bring the stone to its nominal external diameter. A possible hollowing operation allows to form a hollow on one or two faces of the stone to serve as an oiler for lubrication. Finally, a polishing allows to bring the thickness of the pivot stone to its final dimension and the desired surface finish. A possible final polishing allows to obtain a desired external surface finish. This polishing does not modify the surface finish of the pivot hole. Such a manufacturing process is complex, and there is a need to improve the manufacturing of a pivot stone for a watch movement.

[0010] Thus, the object of the present invention is to propose a solution for manufacturing a pivot stone for a watch movement which best meets the above-mentioned requirements and improves existing solutions.

[0011] More specifically, the invention aims to define a solution for manufacturing a pivot stone for a watch movement making it possible to simply, reliably and robustly manufacture a pivot stone with optimized mechanical properties.

[0012] To this end, the invention is based on a method of manufacturing a watch component, which is advantageously a pivot stone, characterized in that it comprises the following steps:

[0013] - Obtain a ceramic or ceramic-based machining block;

[0014] - Machining the block using a machining device comprising a mechanical cutting tool acting in direct contact with the block so as to remove chips from the block, and in that the step of machining the block uses a spindle on which the block is fixed and driven in rotation, at a speed greater than or equal to 30,000 rpm, or even greater than or equal to 32,000 rpm, or even greater than or equal to 35,000 rpm, or even greater than or equal to 38,000 rpm, or even greater than or equal to 40,000 rpm, while the mechanical cutting tool comes into contact with it to remove material in successive passes, to form a watch component having a symmetry of revolution.

[0015] The invention also relates to a machining device comprising at least one spindle configured to hold a block to be machined and a mechanical cutting tool configured to act in direct contact with the block to be machined so as to remove chips from the block to be machined, characterized in that the machining device comprises a motor connected to the at least one spindle and / or to the mechanical tool so as to drive it in rotation, to implement the method for manufacturing a watch component described above, the motor being configured to drive the at least one spindle in rotation at a speed greater than or equal to 30,000 rpm, or even greater than or equal to 32,000 rpm, or even greater than or equal to 35,000 rpm, or even greater than or equal to 38,000 rpm, or even greater than or equal to 40,000 rpm, while the mechanical cutting tool comes into contact with it to remove material in successive passes.

[0016] The invention is more particularly defined by the claims.

[0017] These objects, characteristics and advantages of the present invention will be explained in detail in the following description of a particular embodiment given without limitation.

[0018] To simplify the description, we will conventionally use the longitudinal direction for the main direction along which the axis of a watch component in question extends, intended to pivot around this axis against the pivoting stone. This axis can also be, for example, an axis of revolution of a pivoting stone, or more generally a main axis, for example considered according to the direction of greatest dimension of the watch component. The adjective "transverse" will be used to designate a direction perpendicular to the longitudinal direction.

[0019] The concept of the invention consists in using a manufacturing method based on unconventional machining, in particular on unconventional bar turning, involving a very high relative speed between a block to be machined, in particular a bar to be machined, and a mechanical cutting tool, which comes into contact with the block to be machined. Traditional bar turning machines, as used in the state of the art to manufacture metal watch components, are totally unsuitable for the use of very rigid, fragile and hard materials such as ceramics, in particular zirconia-based. Indeed, such use would lead to catastrophic wear of the mechanical cutting tools, or even the breakage of these mechanical cutting tools and / or the block to be machined, explaining why such a solution does not exist.For example, machining tests of a very hard metal alloy known by its name P2000 during conventional machining in which a P2000 block is driven at a rotational speed of 12,000 rpm made it possible to manufacture only 150 parts before requiring the cutting tool to be changed. According to the invention, it was discovered against all expectations that a very high rotational speed implemented in a bar turning machine makes it possible to significantly reduce the wear and breakage of mechanical cutting tools, even when using a very hard base material such as a ceramic.

[0020] An embodiment of the invention will now be detailed for the manufacture of a pivot stone having a symmetry of revolution, at least over part of its length, around a longitudinal axis.

[0021] In this embodiment, a machine tool, also called a turning machine, is used, comprising at least one spindle intended for mounting a block, in particular a bar or a bar, to be machined, from which the pivoting stone will be formed by machining, by removing material. This spindle is associated with a motor intended to drive the spindle in rotation around an axis of rotation. The spindle further comprises a housing for fixing a block to be machined. This spindle is therefore a workpiece holder. According to this embodiment, the motor of the turning machine is adapted to drive the block to be machined at a very high rotation speed on itself, around an axis which corresponds to the longitudinal axis of the future watch component. This speed is greater than 30,000 rpm, or greater than or equal to 32,000 rpm, or greater than or equal to 35,000 rpm, or greater than or equal to 38,000 rpm, or greater than or equal to 40,000 rpm.The machining machine or device, also called a turning machine, also includes a mechanical cutting tool, which comes into direct contact with the block to be machined during its rotation, thus removing chips of material symmetrically around the axis of rotation of the block to be machined, which will form the axis of symmetry of the future pivot stone, which will have a symmetry of revolution. The cutting tool thus makes it possible to gradually remove material around the block to be machined, thus cutting its circumference and gradually sculpting the block to be machined until reaching the final pivot stone. Advantageously, the cutting tool passes several times over the same location, to remove chips of very low thickness, for example less than 5 μm thick, or even less than 2 μm, or even less than 1 μm, with each pass. Thus, the result obtained is of very high precision.Surprisingly, the higher the rotation speed of the block to be machined, according to the above-mentioned values, the less wear there is on the mechanical cutting tool, which thus makes it compatible with such a manufacturing solution.

[0022] This cutting tool may retain usual geometries and materials, in particular having a cutting surface in a rigid and / or hard material, for example cutting inserts made of natural or synthetic diamond, such as a polycrystalline synthetic diamond like PCD.

[0023] It appears that such a manufacturing method makes it possible to form components of very small dimensions, for example having cross sections with a diameter less than or equal to 350 μm, or even with a diameter less than or equal to 200 μm, or even less than or equal to 100 μm, or even less than or equal to 70 μm. Such a production of small dimensions is very important since it is obligatory for the precise manufacture of a pivot stone. More generally, the manufacturing method according to the invention makes it possible to form a pivot stone whose largest cross section is inscribed in a circle with a diameter less than or equal to 2 mm, or even less than or equal to 1 mm, or even less than or equal to 0.4 mm, the block to be machined thus being able, for example, to be a bar with a diameter equal to 2 mm, or 1 mm, or 0.4 mm. The block can thus, for example, be in the form of a cylindrical bar, such as a ruby ​​rod.

[0024] On the other hand, it appears that the method according to the invention makes it possible to manufacture a given geometry of a pivot stone with great precision and reliability, and great dimensional repeatability.

[0025] The spindle of the lathe is also designed to ensure the block to be machined is securely fixed, without it moving despite the significant forces it undergoes during the machining operation. In addition, the overall rigidity of the machining device ensures that neither the block to be machined nor the cutting tools vibrate or deform, which guarantees a controlled trajectory of the cutting tool. To optimize the stability of the machining device, a machining strategy that minimizes forces is preferred, in particular by multiplying the cutting passes that remove very small chips with each pass, as detailed previously.

[0026] On the other hand, advantageously, the machining device implements high and precise accelerations and decelerations.

[0027] According to an advantageous embodiment, the machining device comprises a multi-spindle lathe, i.e. comprises several spindles which operate at the same time, allowing for example parallel manufacturing of several pivot stones by breaking down the machining operations between the different spindles.

[0028] According to an advantageous embodiment, the machining device comprises a secondary workpiece holder, allowing the component to be reworked after it has been detached from the initial bar or rod.

[0029] The invention is not limited to the turning machine described above, the same principle being able to be implemented using any machining lathe. The invention thus makes it possible to advantageously machine a ceramic block, which was not possible in the prior art, and considered impossible by the person skilled in the art. The invention applies, for example, from a block to be machined entirely or based on ceramic. The ceramic is preferably a sintered and hardened ceramic. The block to be machined may be based on zirconia, in particular yttria-containing zirconia, the expression "based on" meaning that it comprises at least 50% by weight of zirconia. Alternatively, it may be entirely made of zirconia, in particular yttria-containing zirconia. Alternatively, it may be alumina-based or entirely alumina-based, entirely or based on a zirconia-alumina composite, entirely or based on silicon carbide, entirely or based on silicon nitride.

[0030] Preferably, the material chosen is a technical ceramic, in particular an alumina, more particularly monocrystalline or polycrystalline ruby ​​(Cr-doped alumina). The material may be a corundum or a spinel or a zirconia or SiC or a silica, or possibly other natural or synthetic stones such as diamond. The material may be polycrystalline or monocrystalline corundum, for example ruby, in particular Cr-doped alumina, for example synthetic Cr-doped alumina, or even polycrystalline Cr-doped alumina. The material may also be in an alumina-zirconia combination. The material may also be a nitride or a carbide or an oxide or a carbo-nitride or an oxy-nitride or an oxy-carbide or an oxy-carbon-nitride, such as for example SiC or TiSiC or Si3N4.

[0031] The invention is more generally suitable for machining by direct material removal, from a block of hardness greater than or equal to 800 HV, or even greater than or equal to 1000 HV, or even greater than or equal to 1200 HV.

[0032] The invention more advantageously makes it possible to manufacture a pivot stone by the single machining step described above, or at least one functional surface of such a pivot stone by this main step. In other words, advantageously, this main step makes it possible to manufacture an almost finished blank of a pivot stone, which comprises a periphery of the pivot stone having its final, or almost final, dimension.

[0033] However, this main step is supplemented by a second separate step of making a pivot hole and / or a central hollow within the pivot stone. This second separate step may be implemented by machining, according to the principle of the invention described above, and implemented to manufacture the pivot stone blank. Alternatively, this second step may comprise any known cutting method, using a cutting tool, such as a shaping tool, a drill, etc. Alternatively, it may comprise laser machining. Alternatively, it may comprise a traditional method of threading onto a wire with a diamond suspension, as described in document WO2024 / 105218.

[0034] According to an alternative embodiment, the second step described above can be implemented before the main step of producing the pivot stone blank. The block can, for example, be in the form of a tube, such as a ruby ​​tube, in which case the hole is already present before the implementation of the main step.

[0035] Optionally, the main step, or more precisely the two steps described above, can be supplemented by an optional finishing step, particularly a step of tribofinishing the pivot stone. Such a step makes it possible, for example, to adapt the surface condition of one or more functional surfaces of the pivot stone, such as the roughness Ra. However, it has a negligible impact on the overall geometry of the pivot stone. In particular, such a finishing step modifies by a maximum of 1%, or even a maximum of 0.5%, or even a maximum of 0.1%, the dimension of a cross-section of the pivot stone resulting from the main machining step described above. At the end of the process, a functional surface of the pivot stone may have a roughness Ra less than or equal to 0.5 μm, or even less than or equal to 0.1 pm, or less than or equal to 50 nm, or less than or equal to 20 nm, or less than or equal to 15 nm.

[0036] In other words, the invention is particularly advantageous in that the machining step, also called the main step, makes it possible to form the complete and final, or quasi-final, geometry of the pivot stone, and not just a rough rough cut. Thus, the machining described above alone makes it possible to achieve the final dimension of the pivot stone, or the final dimension of at least one functional portion of the pivot stone, in particular outside a pivot hole or a hollow, or even a part of the final dimension of at least one functional portion of the watch component different by less than 1%, or even less than 0.5%, or even less than 0.1%, from the final dimension of the at least one functional portion of the pivot stone.A "functional portion" is a portion that interacts with another component, in particular the pivot portion that allows the component to rotate in a fixed part formed by the pivot stone that serves as its support. The second step remains a relatively simple step compared to the main step of manufacturing the pivot stone.

[0037] Naturally, the invention may be combined with any other existing manufacturing method, such as milling or grinding, which other method may be used to manufacture another portion of the pivot stone, such as a pivot hole as previously described, and / or the same portion, before or after implementing the invention.

[0038] In all cases, the invention makes it possible to form at least one functional portion of a pivot stone, at least one cross-section of which is inscribed in a circle with a diameter less than or equal to 2 mm, or 1.5 mm, or 1 mm, or 200 μm, or even less than or equal to 100 μm, or even less than or equal to 70 μm. It also makes it possible more generally to form a pivot stone, of small size, the largest cross-section of which is inscribed in a circle with a diameter less than or equal to 2 mm, or even less than or equal to 1 mm, or even less than or equal to 0.5 mm.

[0039] The invention also makes it possible to manufacture any watch component, and particularly all or part of a watch shaft, such as a balance shaft or an anchor stem or a barrel arbor, all or part of a pinion, such as an escapement pinion or a gear train pinion. In particular, it makes it possible to manufacture a pivoting jewel, intended to receive the pivoting of a watch shaft, such as a balance shaft.

[0040] The invention also relates to a machining device comprising at least one spindle configured to hold a block to be machined and a mechanical cutting tool configured to act in direct contact with the block to be machined so as to remove chips from the block to be machined, characterized in that the machining device comprises a motor connected to the at least one spindle and / or to the mechanical cutting tool so as to drive it in rotation, to implement the method for manufacturing a watch component as described above, in particular the main step of manufacturing a pivoting jewel, the motor being configured to drive the at least one spindle in rotation at a speed greater than or equal to 30,000 rpm, or even greater than or equal to 32,000 rpm, or even greater than or equal to 35,000 rpm, or even greater than or equal to 38,000 rpm, or even greater than or equal to 40,000 rpm,while the mechanical cutting tool comes into contact with it to remove material in successive passes.,

Claims

CLAIMS 1. Method for manufacturing a pivot stone for a watch movement, characterized in that it comprises the following steps: - Obtain a ceramic or ceramic-based machining block; - Machining the block using a machining device comprising a mechanical cutting tool acting in direct contact with the block so as to remove chips from the block, and in that the main step of machining the block uses a spindle on which the block is fixed and rotated, at a speed greater than or equal to 30,000 rpm, or even greater than or equal to 32,000 rpm, or even greater than or equal to 35,000 rpm, or even greater than or equal to 38,000 rpm, or even greater than or equal to 40,000 rpm, while the mechanical cutting tool comes into contact with it to remove material in successive passes, to form a pivot stone having a symmetry of revolution.

2. Method for manufacturing a pivot stone according to the preceding claim, characterized in that it comprises a second step distinct from the main step comprising the production of a pivot hole or a hollow or in that the block to be machined is in the form of a tube.

3. Method for manufacturing a pivot stone according to one of the preceding claims, characterized in that the block to be machined is entirely made of sintered and hardened ceramic.

4. A method of manufacturing a pivot stone according to one of claims 1 or 2, characterized in that the ceramic is based on zirconia, in particular yttria-containing zirconia, or based on alumina, in particular an alumina, more particularly ruby ​​(Cr-doped alumina) monocrystalline or polycrystalline, based on a zirconia-alumina composite, based on silicon carbide, or based on silicon nitride, or based on silica, or other natural or synthetic stones such as diamond, or polycrystalline or monocrystalline corundum, or based on nitride or carbide or an oxide or a carbo-nitride or an oxy-nitride or an oxy-carbide or an oxy-carbo-nitride, such as for example SiC or TiSiC or Si3N4.

5. Method for manufacturing a pivot stone according to one of the preceding claims, characterized in that the block to be machined has a hardness greater than or equal to 800 HV, or even greater than or equal to 1000 HV, or even greater than or equal to 1200 HV.

6. Method of manufacturing a pivot stone according to one of the preceding claims, characterized in that the step of machining the block is a mechanical turning carried out by a turning machine in which the block to be machined is fixed on a spindle and driven in rotation, the turning machine being a single-spindle machine or a multi-spindle machine.

7. Method of manufacturing a pivot stone according to one of the preceding claims, characterized in that the mechanical cutting tool acts on the block to be machined in fine passes making it possible to remove chips less than 5 microns thick during one pass.

8. Method of manufacturing a pivot stone according to one of the preceding claims, characterized in that the mechanical cutting tool comprises a natural or synthetic diamond, in particular a polycrystalline synthetic diamond.

9. Method for manufacturing a pivot stone according to one of the preceding claims, characterized in that it comprises a step of finishing the pivot stone, particularly a tribofinishing step, which modifies by a maximum of 1%, or even a maximum of 0.5%, or even a maximum of 0.1%, the dimension of a cross-section of the watch component resulting from the step of machining the block.

10. A method of manufacturing a pivot stone according to one of claims 1 to 8, characterized in that the step of machining the block forms the final geometry of the pivot stone outside a pivot hole or a pivot recess, or the final dimension of at least one functional portion of the pivot stone, or a part of the final dimension of at least one functional portion of the pivot stone different by less than 1%, or even less than 0.5%, or even less than 0.1%, from the final dimension of the at least one functional portion of the pivot stone.

11. Method for manufacturing a pivot stone according to one of the preceding claims, characterized in that it manufactures at least one functional portion of the pivot stone with a roughness Ra less than or equal to 0.5 pm, or even less than or equal to 0.1 pm, or even less than or equal to 50 nm, or even less than or equal to 20 nm, or even less than or equal to 15 nm.

12. Method for manufacturing a pivot stone according to one of the preceding claims, characterized in that it manufactures a pivot stone whose largest cross-section is inscribed in a circle with a diameter less than or equal to 2 mm, or even less than or equal to 1 mm, or even less than or equal to 0.5 mm, and / or at least one functional portion of the pivot stone of which at least one cross-section is inscribed in a circle with a diameter less than or equal to 2 mm, or even less than or equal to 1 mm, or even less than or equal to 200 pm, or even less than or equal to 100 pm, or even less than or equal to 70 pm.

13. Machining device comprising at least one spindle configured to hold a block to be machined and a mechanical cutting tool configured to act in direct contact with the block to be machined so as to remove chips from the block to be machined, characterized in that the machining device comprises a motor connected to the at least one spindle and / or to the mechanical tool so as to drive it in rotation, to implement the method for manufacturing a pivot stone according to one of the preceding claims, the motor being configured to drive the at least one spindle in rotation at a speed greater than or equal to 30,000 rpm, or even greater than or equal to 32,000 rpm, or even greater than or equal to 35,000 rpm, or even greater than or equal to 38,000 rpm, or even greater than or equal to 40,000 rpm, while the mechanical cutting tool comes into contact with it to remove material in successive passes.

14. Method of manufacturing a watch component, characterized in that it comprises the following steps: - Obtain a ceramic or ceramic-based machining block; - Machining the block using a machining device comprising a mechanical cutting tool acting in direct contact with the block so as to remove chips from the block, and in that the step of machining the block uses a spindle on which the block is fixed and driven in rotation, at a speed greater than or equal to 30,000 rpm, or even greater than or equal to 32,000 rpm, or even greater than or equal to 35,000 rpm, or even greater than or equal to 38,000 rpm, or even greater than or equal to 40,000 rpm, while the mechanical cutting tool comes into contact with it to remove material in successive passes, to form a watch component having a symmetry of revolution.

15. Method of manufacturing a watch component according to the preceding claim, characterized in that it manufactures all or part of a watch axis, such as a balance shaft or an anchor rod or a barrel arbor, all or part of a pinion, such as an escapement pinion or a gear train pinion.