Method for manufacturing the rotating surface of a clock or small clock part

Abstract

To provide a method for producing a surface of revolution of a clock or watch component made of ceramic, notably a balance staff or an arbor of an escapement wheel or an arbor of a seconds wheel.SOLUTION: A method for producing a surface of revolution 20 of a clock or watch component 1 comprises a step of machining, with a femtosecond laser beam, a first surface of the clock or watch component so as to obtain a second surface, in particular to obtain a second surface whose roughness Ra is less than 100 nm, or less than 70 nm, and then a tribofinishing step applied to the second surface so as to obtain the surface of revolution.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a rotating surface of a clock or small clock part, more particularly of a ceramic clock or small clock part. The invention also relates to a clock or small clock part obtained by said manufacturing method. The invention also relates to a clock or small clock movement comprising said clock or small clock part. The invention finally relates to a clock comprising said clock or small clock part or said clock or small clock movement. [Background technology]

[0002] The machining of clocks or small watch parts made of engineering ceramics, as described for example in US Pat. No. 5,399,633, is a delicate operation that requires mastery of the interaction between tool and material so as not to induce stresses in the ceramic that would act as initiating agents for cracks that are detrimental to the impact strength of the part, or to induce new defects, especially surface defects.

[0003] The manufacture of clock axles with a diameter smaller than 2 mm is particularly difficult, especially due to the presence of tenons with very small diameters (<200 microns, or even <100 microns) at the ends of the axles. These tenons must have a perfectly circular shape and dimensions that are faithfully respected. The tenons are provided to interact with the bearings, and any geometrical defects, such as out-of-roundness or incorrect diameter, will lead to a loss of the chronometric performance of the movement in which they are provided. This is particularly valid for the balance. This also applies if the surface of the tenons is not perfectly polished.

[0004] Therefore, prior art mandrels are machined from steel on a bar lathe and then the tenons are ground on a form grinding wheel to obtain the final surface finish and shape.

[0005] However, bar turning with cutting tools or grinding wheels takes a very long time and the tools wear out quickly, making this technique difficult to apply to ceramic parts.

[0006] An alternative to machining ceramics by grinding consists of machining ceramics by femtosecond laser ablation. The lasers used have extremely short pulses (femtosecond lasers) so as not to cause any thermal effects on the material being machined.

[0007] The currently available tools used by those skilled in the art to form electrodes in hard metals, or other elements of small dimensions (such as microforceps), in general, use lasers emitting in the infrared (frequency 1030 nm). So far, it has not been possible to obtain satisfactory results with this type of tool. The surface roughness obtained at the end of the machining is considerable, requiring special friction finishing processes that require very long times to achieve the required surface roughness, and, despite the geometrical conformity of the parts, the performance in terms of bending strength does not meet expectations.

[0008] The bending strength of tenons of identical mandrels, produced by conventional grinding or femtosecond laser machining, was measured by applying a force with a blade at a given distance from the end of the tenon, a part supported at the height of the bearing surface forming the contact area between the tenon and the body of the mandrel.

[0009] The bending strength of the tenons of the various mandrels is shown in Figure 9, which shows the final bending stress level of each tenon of these mandrels. The measured stress correlates with the cross-sectional area of ​​each tenon at the point of application of the maximum force that causes rupture.

[0010] As shown in FIG. 9, parts ground from 3% yttria-doped zirconia (3%ZrO2Y2O3) are stronger than parts of 3% yttria-doped zirconia (3%ZrO2Y2O3) laser machined according to femtosecond laser machining processes known from the prior art, even if they are subsequently polished or polished and then rubbed.

[0011] For this reason, it appears that femtosecond laser machined ceramic clock stems, even if dimensionally correct, may perform poorly in use. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] European Patent Application Publication No. 3258325 Summary of the Invention [Problem to be solved by the invention]

[0013] The object of the present invention is to provide a method for the manufacture of rotating surfaces of ceramic clock or small clock parts, which improves the methods known from the prior art. In particular, the invention proposes a method for the manufacture in a reproducible manner of reliable parts, in particular the axles of the balance or escape wheel or the axles of the seconds wheel or other axles forming part of the moving part of the final chain of a clock or small clock movement. The invention also aims to facilitate and make more reliable ceramic machining to obtain axle-type parts of the required dimensions (diameter <2 mm, with micron tolerances) while guaranteeing adequate impact strength. [Means for solving the problem]

[0014] According to the invention, the manufacturing method is defined in claim 1.

[0015] Various embodiments of the method are defined in claims 2 to 12.

[0016] According to the invention, a clock or small clock part is defined in claim 13 or 14.

[0017] According to the invention, a clock or clock movement is defined in claim 15.

[0018] According to the invention, the watch is defined in claim 16.

[0019] The accompanying drawings illustrate, by way of example, embodiments of a watch according to the invention. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a schematic diagram of a timepiece embodiment, including a clock or small timepiece embodiment. [Diagram 2] FIG. 2 is a graph showing the surface roughness Ra values ​​of surfaces obtained by different laser machining processes of different ceramics. [Diagram 3] FIG. 3 is a graph showing the variation in surface roughness Ra values ​​for surfaces obtained by different laser machining processes of 3% yttria-doped zirconia. [Figure 4] FIG. 4a is a photograph of a 3% yttria zirconia tenon after infrared laser machining (reference 1030), FIG. 4b is a photograph of the same after 10 hours of friction finish machining following the same machining, and FIG. 4c is a photograph of the same after 20 hours of friction finish machining following the same machining. [Diagram 5] FIG. 5 is a graph showing the ultimate flexural strength values ​​of various 3% yttria-zirconia barbs obtained by various types of laser machining. [Figure 6] FIG. 6a is a photograph of a 3% yttria zirconia tenon after green laser machining (reference 515), and FIG. 6b is a photograph of a 3% yttria zirconia tenon after machining followed by 10 hours of rub finish processing. [Figure 7] FIG. 7a is a photograph of a 3% yttria-zirconia tenon after ultraviolet laser machining (reference 434), and FIG. 7b is a photograph of a 3% yttria-zirconia tenon after the machining followed by 10 hours of rub-finishing. [Figure 8] FIG. 8a is a photograph of a 3% yttria-zirconia tenon after machining by grinding, and FIG. 8b is a photograph of a 3% yttria-zirconia tenon after machining followed by 10 hours of friction finishing. [Figure 9] FIG. 9 is a graph showing the final bending stress values ​​of various 3% yttria-zirconia barbs obtained by various manufacturing methods. [Figure 10] FIG. 10 shows another embodiment of a clock or small watch part. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] An embodiment of a watch 200 according to the present invention will now be described with reference to FIG.

[0022] The watch 200 is, for example, a wristwatch. The watch preferably includes a miniature watch case and a miniature watch movement 100.

[0023] The miniature timepiece movement may be a mechanical movement, in particular an automatic movement.

[0024] The miniature clock movement comprises an embodiment of the miniature clock part 1.

[0025] A miniature clock part is, for example, a pinion, in particular a balance or escape wheel pinion or a seconds pinion of a miniature clock oscillator of the balance / spiral spring type. The diameter of the part, in particular the maximum diameter of the part, is, for example, less than or equal to 2 mm.

[0026] The small watch part preferably comprises a tenon 10. By "tenon" is meant a part of a part, in particular of a stem, which is provided for interacting, in particular by contact, with a bearing, in particular with a jewel bearing. The tenon may have at least one part of cylindrical or conical or truncated shape. The tenon is preferably arranged at one end of the stem. The tenon may be formed in the extension of a stem part, which includes, for example, a surface with a curved generatrice.

[0027] The miniature clock movement also includes a bearing 12, or several bearings mounted on elements of the movement, in particular on the frame of the movement.

[0028] The small watch part is intended, for example, to interact with the bearing 12, in particular by contact. In particular, the small watch part interacts with the bearing 12 at the height of the tenon 10. More specifically, the small watch part interacts with the bearing 12 at the height of a turning face 20 located at the height of the tenon 10. The diameter of the cross section of the turning face 20 is, for example, less than or equal to 200 μm, or even less than or equal to 100 μm. Optionally, the tenon may be delimited axially at one end 10a of the tenon 10 by a jewel 13. The elements 12 and 13 may be arranged in the same element having the shape of the shock absorber body. In this particular case, the axle is preferably the axle of a balance or escape wheel.

[0029] The bearing includes a bore, and the bore and rolling surface are sized and / or configured to have a limited functional clearance, for example on the order of 7 to 17 μm.

[0030] Advantageously, the miniature clock part includes two tenons 10 for interacting with two bearings 12 in order to guide the miniature clock part relative to the bearings, and more generally relative to the miniature clock movement elements to which the bearings are attached.

[0031] Advantageously, the miniature watch part or part of the miniature watch part is made of ceramic. The rotating surface 20 is made of ceramic, i.e. the rotating surface is formed or located on the ceramic part of the part. Preferably the ceramic is zirconia, in particular yttri-zirconium oxide, especially 3% (by weight) yttri-zirconium oxide, monocrystalline alumina or alumina-zirconia bond (ATZ).

[0032] For this reason, preferably, the small watch part is entirely or partly made of ceramic and comprises a turning face 20 with a roughness Ra of 15 nm or less. Even more preferably, the small watch part comprises a tenon comprising said turning face. Advantageously, the shear fracture stress of the tenon of the part is less than 200 N.mm -2 Over or 250N.mm -2 It's super.

[0033] An embodiment of a method for manufacturing the rotating surface 20 of the ceramic small watch part 1 will now be described.

[0034] The manufacturing method is - a step of machining a first surface of the small watch part with a femtosecond laser beam to obtain a second surface, in particular to obtain a second surface having a roughness Ra of less than 100 nm or less than 70 nm, and then - a friction finishing step applied to the second surface to obtain said surface of revolution; Includes.

[0035] The method makes it possible to obtain a clock or small watch part comprising a ceramic turning surface that is geometrically accurate and has an appropriate roughness after a reasonable time of rubbing, typically around 10 hours. The rubbing step must be parameterized so as not to modify the shape of the surface, in particular to avoid excessive rounding of the end of the tenon or tenons comprising the turning surface in order to maintain control of the contact area between the tenon and the bearing. For this reason, it is important that the initial roughness before the step is low enough to allow rubbing for a reasonable duration. For example, the roughness Ra of the final turning surface 20 is around 10 to 15 nm.

[0036] This type of method offers an alternative to machining ceramics by grinding and consists in machining ceramics by femtosecond laser ablation without reducing their mechanical durability. The laser used has an extremely short pulse (femtosecond laser) with a suitable wavelength so as not to affect the surface of the material and so as not to cause thermal effects on the material to be machined.

[0037] Advantageously, this method allows the production of not only the turning surface 20 of the small watch part 1, but also the entire surface of the tenon that includes said surface 20, or of the entire surface of the small watch part.

[0038] Various tests were performed on different materials for the zirconia, yttria-zirconate, monocrystalline alumina (sapphire) or alumina-zirconia bond (ATZ). More specifically, 3% yttria-zirconate was used.

[0039] Preferably, the laser beam is emitted in the infrared with a wavelength between 800 nm and 1100 nm, ideally 1030 nm±5 nm, or in the green with a wavelength between 500 nm and 540 nm, ideally 515 nm±2.55 nm, or in the blue with a wavelength between 400 nm and 480 nm, or in the ultraviolet with a wavelength below 400 nm, ideally 343 nm±25 nm.

[0040] Preferably, the machining step includes a pivoting phase, i.e. a machining step in which the miniature watch part is rotated about an axis of rotation and the laser beam is movable relative to said axis of rotation. From the moment the laser beam passes through the surface of the part, other kinematics are possible.

[0041] Preferably, for the materials and dimensions tested, the laser beam has an average energy per pulse (also called fluence) between 0.001 mJ and 2 mJ, preferably between 0.01 mJ and 0.5 mJ, or between 0.04 mJ and 0.05 mJ.

[0042] The lateral overlap, i.e. the overlap perpendicular to the direction of travel or perpendicular to the part spindle, is defined by the part rotation speed and the laser frequency and can be defined between 0% and 99.9%. The lateral overlap is preferably between 20% and 99.9%, and ideally between 99.6% and 99.8%.

[0043] The longitudinal overlap is defined by the scanning or moving speed of the beam and the frequency of the laser and can be defined between 0% and 99.9%. The longitudinal overlap is preferably between 20% and 99.9%, and ideally between 20% and 80.8%. Note that a longitudinal overlap of 100% corresponds to the execution of the cutting of the parts.

[0044] Preferably, the laser beam scans the first surface along a helical trajectory, ie a helical trajectory that can be traced on the machined rotating surface.

[0045] Preferably, the laser beam is applied in a direction tangential to the first surface or substantially tangential to the first surface, alternatively, the laser beam is applied in a direction normal to the first surface or substantially normal to the first surface.

[0046] Preferably the laser beam has a diameter for the material and dimensions being tested between 5 μm and 100 μm, preferably between 10 μm and 60 μm, ideally between 15 μm and 25 μm, the diameter being measured perpendicular to the beam axis at the position of impact of the beam on the first surface.

[0047] Preferably, the rub finishing step takes less than 20 hours, preferably less than 10 hours.

[0048] Preferably, the abrasive finishing step comprises a bulk polishing step. Preferably, the abrasive finishing step comprises the use of diamond abrasive particles having a size of the order of 1 μm. Preferably, the abrasive finishing step comprises the use of ceramic supports in the form of beads having a size between 125 and 250 μm, to which water and additives are added.

[0049] Various tests were carried out, varying the properties of the laser beam. In particular, several lasers operating in the infrared (IR, frequency 1030 nm), green (frequency 515 nm) or ultraviolet (UV, frequency 343 nm) were tested, using equipment allowing the parameterization of the relative speed of the scanning of the laser beam and the rotation of the small clockwork part. However, the parameterization, as well as the scanning speed of the beam and the rotation speed of the small clockwork part, were kept the same (denoted "E5") in all the tests presented below, in particular the level of the laser fluence, which was kept constant between the different laser beams.

[0050] As shown in the graph of figure 2, the green laser (reference 515) and the ultraviolet laser (reference 343) allow for a sufficient surface roughness of around 50 nm at the end of machining for various engineering ceramics. The infrared laser (reference 1030) allows for a surface roughness of around 50 nm to 100 nm at the end of machining for various engineering ceramics, provided that the structure of the equipment allows for the optimization of the parameters for the equipment and the parameters known from the prior art (reference 1030-C).

[0051] As shown in FIG. 3, small watch parts made of 3% yttria-doped zirconia machined with green (reference 515), ultraviolet (reference 343) and infrared (reference 1030) lasers and rubbed by mechanical load, vibrated in a bath using a polishing mixture with diamond abrasive particles of about 1 μm diameter mixed with a ceramic carrier in the form of beads with a diameter between 125 μm and 250 μm, with water and additives, all reach a suitable final roughness of 10 to 15 μm. This suitable final roughness is obtained after 10 hours of rub-finishing, starting from the small watch parts machined with green (reference 515) and ultraviolet (reference 343) lasers. To obtain a comparable roughness, starting from the small watch parts machined with infrared laser (reference 1030), 20 hours of polishing are required. This results in changes in the dimensions and shape of the part, especially in the height of the end tenons, as is evident from figures 4a, 4b and 4c (representing a 3% yttria-containing zirconia tenon after infrared laser machining (reference 1030), after 10 hours of rubbing finish machining following said machining and after 20 hours of rubbing finish machining following said machining, respectively), which affect the operation of the small watch part. Figures 6a and 7a show the appearance of a 3% yttria-containing zirconia tenon immediately after the machining steps with a green laser and an ultraviolet laser, respectively. Figures 6b and 7b show the appearance of a 3% yttria-containing zirconia tenon after the rubbing finish machining performed on the tenon shown in figures 6a and 7a, respectively. The final surface roughness of the part shown in figures 4c, 6b and 7b is sufficient, while the end of the tenon in figure 4c is rounded. This change in shape affects the chronometric performance of the small watch in which said tenon is provided.

[0052] The results of the observations and dimensional measurements were confirmed by bending strength measurements to ensure that the mandrel-type miniature watch components were capable of performing their functions.

[0053] As shown in the graph of Figure 5, the bending strength of the tenon, as measured by the force exerted by the blade at a given distance from the end of the tenon relative to the cross-sectional area of ​​the tenon at the location of application of the blade, is greater for clocks or small clock parts machined with a green laser (Reference 515) versus clocks or small clock parts machined with an infrared laser (Reference 1030) or an ultraviolet laser (Reference 343). The tests were performed on small clock parts of 3% yttria-zirconium oxide.

[0054] For this reason, it seems advantageous to work in the green light (515 nm) or ultraviolet light (343 nm) range in order to obtain the minimum possible roughness and maximum bending strength at the end of the machining.

[0055] For simplicity and clarity, "small watch part" means a part produced using the method regardless of the stage of production, i.e., "small watch part" means the part before laser processing, after laser processing, or after the rub finish processing, even if the part is changed during the process.

[0056] The surface of revolution 20 is described here in particular at the height of the tenon of the balance, but the same method can be used for other surfaces of revolution of small watch axles for which a particular shape and / or roughness should be achieved. In particular, the method described above makes it possible to manufacture the axles of escape wheels or seconds wheels or other axles which form part of the moving parts of the final chain of a small watch movement.

[0057] Such a shaft may comprise a first toothed portion 30. This portion 30 may be integral with the shaft, which may thus be in the form of a pinion shaft. The pinion shaft may comprise a second portion 40 for receiving a gear plate. In particular, the pinion shaft may be entirely made of ceramic.

[0058] Alternatively, the first toothed portion 30 may be applied, for example by press fitting, to a third portion for receiving the mandrel. In this case, the first toothed portion 30 may be made of metal.

[0059] The maximum diameter of the first toothed portion 30 is, for example, 2 mm or less. The teeth of the first portion 30 may have a conventional profile, such as a trabecular profile.

[0060] Compared to conventional techniques using cutting tools, the use of femtosecond laser beams (green or ultraviolet) offers time savings and optimization of the properties of the final part, provided that certain machining conditions are observed. Moreover, femtosecond laser beams operating in the infrared make it possible to obtain satisfactory results in certain conditions.

[0061] As used herein, "ceramic" means a homogeneous or nearly homogeneous material, including on a microscopic level.

[0062] Preferably, the ceramic is homogeneous in at least one direction, or in all directions, over a distance greater than 6 μm, or greater than 10 μm, or greater than 20 μm.

[0063] More preferably, the ceramic is free of non-ceramic material in at least one direction, or over a distance greater than 6 μm, or greater than 10 μm, or greater than 20 μm in all directions.

[0064] Preferably, the fact that a part and / or a part of a part is made of ceramic means that said part or part consists entirely of ceramic, more preferably, the fact that a part and / or a part of a part is made of ceramic excludes that said part or part of a part is made of a material made of ceramic grains bound by a non-ceramic matrix, such as a metal matrix.

[0065] The described method is particularly suitable for the manufacture of ceramic components or parts of components, although of course metal components, such as tungsten or tantalum or other hard metals that are difficult to machine by conventional methods, can also benefit from such a method, especially mandrels. [Explanation of symbols]

[0066] 1. Small watch parts 10 Mortice 12 Bearings 20 Surface of Revolution 100 Small Clock Movements 200 Watches

Claims

1. A method for manufacturing a rotation surface (20) of a clock or small watch part (1), comprising the steps of: machining a first surface of said clock or small clock part with a femtosecond laser beam to obtain a second surface; and a finishing step applied to said second surface to obtain said surface of revolution; the rotating surface is made of a ceramic, the ceramic being zirconia, yttria-zirconia, single crystal alumina or an alumina-zirconia bond; The method, wherein the finishing step comprises a polishing step.

2. the clock or small watch part is a stem, and / or the diameter of the part is 2 mm or less; The method of claim 1.

3. the surface of rotation is the surface of a tenon of the clock or small clock part, and / or the diameter of the surface of rotation is less than or equal to 200 μm, or less than or equal to 100 μm; The method according to claim 1 or 2.

4. The step of performing machining includes a turning stage in which the clock or small clock part rotates about an axis of rotation.

4. The method according to any one of claims 1 to 3.

5. The laser beam is an infrared laser beam, or a green laser beam, or an ultraviolet laser beam, or a blue laser beam.

5. The method according to any one of claims 1 to 4.

6. The laser beam has an energy between 0.001 mJ and 2 mJ.

6. The method according to any one of claims 1 to 5.

7. the laser beam scans the first surface along a helical trajectory; 7. The method according to any one of claims 1 to 6.

8. The laser beam has a diameter between 5 μm and 100 μm.

8. The method according to any one of claims 1 to 7.

9. The finishing step requires less than 20 hours.

9. The method according to any one of claims 1 to 8.

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