Method for manufacturing a timepiece component

Abstract

The invention relates to a method for manufacturing a timepiece component (10), 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] Manufacturing process of a watch component

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

[0003] 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] Thus, the object of the present invention is to propose a solution for manufacturing a watch component which best meets the above-mentioned requirements and improves existing solutions.

[0008] More specifically, the invention aims to define a solution for manufacturing a watch component making it possible to simply, reliably and robustly manufacture a watch component with optimized mechanical properties.

[0009] To this end, the invention is based on a method of manufacturing a watch component, characterized in that it comprises the following steps:

[0010] - Obtain a ceramic or ceramic-based machining block;

[0011] - 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.

[0012] 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 as 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.

[0013] The invention is more particularly defined by the claims.

[0014] These objects, characteristics and advantages of the present invention will be explained in detail in the following description of a particular embodiment made without limitation in relation to the attached figures among which:

[0015] Figure 1 represents a balance shaft obtained by a manufacturing method according to an embodiment of the invention.

[0016] Figure 2 shows an enlarged portion of the balance shaft pivot obtained by the manufacturing method according to one embodiment of the invention.

[0017] To simplify the description, we will conventionally use the longitudinal direction for the main direction along which a watch component in question extends, for example an axis of revolution of a watch component, or more generally a main axis, for example considered along the direction of greatest dimension of the watch component. The adjective "transverse" will be used to designate a direction perpendicular to the longitudinal direction. The concept of the invention consists in using a manufacturing method based on unconventional machining, in particular on unconventional 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 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, particularly those based on zirconia. 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 traditional machining in which a P2000 block is driven at a rotation speed of 12,000 rpm made it possible to manufacture only 150 pieces before requiring the cutting tool to be changed.According to the invention, it has been discovered against all expectations that a very high rotation speed implemented in a 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 ceramic.

[0018] An embodiment of the invention will now be detailed for the manufacture of a watch component having a symmetry of revolution, at least over part of its length, around a longitudinal axis.

[0019] 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 rod, to be machined, from which the watch component 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.

[0020] 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 watch component, 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 watch component. 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.

[0021] 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.

[0022] 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 manufacture of a watch component, in particular a balance staff or an anchor stem or a barrel arbor, all or part of a pinion, such as an escapement pinion or a gear train pinion. More generally, the manufacturing method according to the invention makes it possible to form a watch component 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.

[0023] On the other hand, it appears that the method according to the invention makes it possible to manufacture a given geometry of a watch component with great precision and reliability, and great dimensional repeatability.

[0024] 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.

[0025] On the other hand, advantageously, the machining device implements high and precise accelerations and decelerations.

[0026] According to an advantageous embodiment, the machining device comprises a multi-spindle lathe, i.e. it comprises several spindles which operate at the same time, allowing for example parallel manufacturing of several watch components by breaking down the machining operations between the different spindles. For example, an additional spindle can carry a cutting tool for producing a toothing, for example to produce a watch pinion. 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.

[0027] The invention is not limited to the turning machine described above, the same principle can be implemented using any machining lathe.

[0028] 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, to a block to be machined that is 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 based on alumina or entirely made of alumina, entirely or based on a zirconia-alumina composite, entirely or based on silicon carbide, entirely or based on silicon nitride.

[0029] 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.

[0030] The invention more advantageously makes it possible to manufacture a watch component by the single machining step described above. However, it can be supplemented by an optional finishing step, particularly a step of tribofinishing the watch component. Such a step makes it possible, for example, to adapt the surface condition of one or more functional surfaces of the watch component, such as the roughness Ra. However, it has a negligible impact on the overall geometry of the watch component. 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 watch component resulting from the machining step described above. At the end of the process, a functional surface of the watch component 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.

[0031] In other words, the invention is particularly advantageous in that the machining step makes it possible to form the complete and final, or quasi-final, geometry of the watch component, and not just a rough shape. Thus, the machining described above alone makes it possible to achieve the final dimension of the watch component, or the final dimension of at least one functional portion of the watch component, 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 watch component.The term "functional portion of the watch component" means a portion of the component which interacts with another component, in particular such as the driving portion to accommodate, for example, a mobile plate or a balance wheel or a hairspring, or such as the pivoting portion which allows the rotation of the component in a fixed part (such as a jewel) which serves as its support, or such as the transmission part formed, for example, by a toothing.

[0032] Naturally, the invention can be combined with any other existing manufacturing process, such as milling or grinding, this other process being able to be used to manufacture another portion of a watch component, or the same portion, before or after the implementation of the invention, such as for example a pinion.

[0033] In all cases, the invention makes it possible to form at least one functional portion of a watch component, at least one cross-section of which is inscribed in a circle 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. It also makes it possible, more generally, to form a watch component, 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.

[0034] The invention makes it possible to manufacture any watch component, and particularly all or part of a watch axis, 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.

[0035] Figures 1 and 2 represent by way of example a balance staff 1 manufactured by a manufacturing method according to an embodiment of the invention. In this example, the balance staff is fully machined from a ceramic block turned at a rotation speed of 38,000 rpm. Advantageously, the block is in the form of a bar. In addition, the ceramic may be yttria-treated zirconia. The method makes it possible to manufacture a pivot 2, on the right in Figure 1, more particularly illustrated by Figure 2, having a section 22 at its end with a diameter equal to 0.066 mm. This pivot is extended on the left of Figures 1, 2 by a first cylindrical portion 3 with a diameter 33 equal to 0.25 mm. As shown in Figure 1, the balance staff 1 then comprises a succession of cylindrical portions of different diameters, connected together by frustoconical portions. The maximum diameter of balance shaft 1 is 0.5 mm, and its length is 3 mm. The balance shaft 1 further comprises a geometry towards its second end, on the left in Figure 1, of similar dimensions to the first pivot on the right. More generally, the invention is particularly suitable for the manufacture of a watch shaft.

[0036] 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, 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 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.

2. Method of manufacturing a watch component according to the preceding claim, characterized in that the block to be machined is entirely made of sintered and hardened ceramic.

3. Method for manufacturing a watch component according to the preceding claim, characterized in that the ceramic is based on zirconia, in particular yttria-containing zirconia, or based on alumina, based on a zirconia-alumina composite, based on silicon carbide, or based on silicon nitride.

4. Method for manufacturing a watch component according to claim 1, 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.

5. Method of manufacturing a watch component 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.

6. Method for manufacturing a watch component 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.

7. Method for manufacturing a watch component 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.

8. Method for manufacturing a watch component according to one of the preceding claims, characterized in that it comprises a step of finishing the watch component, 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.

9. Method for manufacturing a watch component according to one of claims 1 to 7, characterized in that the step of machining the block forms the final geometry of the watch component, or the final dimension of at least one functional portion of the watch component, or 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%, of the final dimension of at least one functional portion of the watch component.

10. Method for manufacturing a watch component according to one of the preceding claims, characterized in that it manufactures at least one functional portion of the watch component 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.

11. Method for manufacturing a watch component according to one of the preceding claims, characterized in that it manufactures a watch component 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 watch component of which at least one cross-section is inscribed in a circle 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.

12. Method for manufacturing a watch component according to one of the preceding claims, characterized in that it manufactures all or part of a watch axis, 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.

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 watch component 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 revolutions / minute, or even greater than or equal to 32000 rpm, or even greater than or equal to 35000 rpm, or even greater than or equal to 38000 rpm, or even greater than or equal to 40000 rpm, while the mechanical cutting tool comes into contact with it to remove material in successive passes.

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