Balance for a clock movement and method for manufacturing such a balance

Abstract

The invention relates to a balance wheel comprising a shaft (10) and, arranged on the shaft, an inertial element (12), a plate (14) and a plate pin (16), characterized in that the shaft and at least two components among the inertial element, the plate and the plate pin, are manufactured in one piece from one piece. The invention also relates to a method of manufacturing such a balance wheel.

Description

Technical field

[0001] The present invention relates to the field of watchmaking. It relates more particularly to a mechanical watch movement balance and its manufacturing method. State of the art

[0002] In a watch movement, the balance wheel is a very important element for achieving good running, i.e. good precision of the movement. For the purposes of this application, the term balance wheel corresponds to the assembly of several components: a shaft which includes at its ends, pivots which will work with bearings mounted in the frame of the movement; the shaft also includes a certain number of bearings and shoulders to receive and position the other components below; an inertial element formed by a felloe mounted on the shaft by a hub, connected to the felloe by arms; a plate pin receiving and transmitting the impulses supplied by or to the escapement, a single or double plate, which carries the pin, the double plate including an additional level with a notch to limit the movements of the anchor by cooperating with the dart.

[0003] In watchmaking jargon, this assembly is commonly called a mounted balance wheel, because the different elements are made separately and assembled.

[0004] To achieve the most regular oscillations possible, and optimal interactions with the escapement, each component must be as perfect as possible, in its dimensions, balancing and centering. The geometries, materials and manufacturing processes currently used industrially are the result of experience accumulated throughout the history of watchmaking.

[0005] For reasons of precision and efficiency, bar turning is widely used. Thus, the shafts are bar turned, then rolled to make the pivots, the inertial elements and the plates are also bar turned. The pins are made separately, in ruby, and are planted in the plate. The various assembly stages are delicate and the final precision depends in particular on respecting the dimensions of the bearings on which the elements are arranged, the adjustment of the openings for mounting on the shaft. In the end, it is difficult to have a perfect and guaranteed geometric positioning of the different elements arranged on the shaft or of the pin on the plate, which can lead to variability in the interaction between the mounted balance wheel and the escapement and in any case, requires particularly precise controls.

[0006] The separate manufacturing of the different elements also allows for the use of differentiated materials, depending on the specificities required for each component: hard or hardenable for the shaft and pivots, heavier for the inertial element, etc.

[0007] It has already been proposed to produce assemblies of certain balance components in a single piece. For example, document FR2050375B1 proposes to produce the plate and the inertial element in a single piece, molded in plastic. This part is then assembled on the shaft. The use of plastic, however, is not compatible with current standards of mechanical watchmaking.

[0008] Document EP2791737 proposes to overmold the various components, to have an outer skin, in this case made of plastic. However, the constituent components are always manufactured separately, in different materials.

[0009] The aim of the present invention is to propose a new balance wheel, which makes it possible to at least partially overcome the assembly constraints linked to the manufacturing methods of the prior art. Disclosure of the invention

[0010] More specifically, the invention relates to a balance wheel, comprising a shaft and, secured to the shaft, an inertial element, a plate and a plate pin. According to the invention, the shaft and at least two components among the inertial element, the plate and the plate pin, are manufactured in a single piece. In other words, the shaft and at least two components among the inertial element, the plate and the plate pin, are manufactured in a single piece from the same material or are manufactured in a single piece. In other words, the shaft is manufactured in a single piece with at least two components among the inertial element, the plate and the plate pin.

[0011] The invention also relates to a set of elements intended to form a part of a balance wheel and their method of manufacturing, as defined in the claims. Brief description of the drawings

[0012] Other details of the invention will appear more clearly on reading the following description, made with reference to the appended drawing in which: THE figures 1 to 4 illustrate machining operations, tangential ( Figures 1 and 2 ) or at the end ( Figures 3 and 4 ), there Figure 5 is an isometric view of a first embodiment in which the shaft, the plate and the pin are made in a single piece, the figure 6 is an isometric view with another angle of view, of the embodiment of the Figure 5 , and the figure 7 is an isometric view of a second embodiment in which the shaft, the plate and the inertial element are made in a single piece. Method of carrying out the invention

[0013] Traditionally, a mounted clockwork balance wheel comprises a shaft, and arranged on the shaft, an inertial element (also called a rim), a single or double roller and a roller pin (fixed in the roller and therefore indirectly arranged on the shaft). The invention proposes to produce in a single piece, that is to say in a single piece, the shaft 10 and at least two components among the inertial element 12, the single or double roller 14 preferably, and the roller pin 16. In the present application, the terminology of balance wheel is adopted to designate the functional member corresponding to the mounted balance wheel, that is to say comprising the shaft, the inertial element, the roller and the pin. The hairspring must be added to obtain the complete resonator.

[0014] It should be noted that to simplify the text and given the simplicity of the elements previously identified, the numbering will not be systematic.

[0015] By monobloc manufacturing, we mean that the components come from one material or, in other words, that they have a continuity of material. We therefore move from one component to another while maintaining homogeneity of the material. There is therefore no assembly, welding or other operation of connecting dissociated parts, but directly a one-piece manufacturing, from a machined block of material. Thus, the very notion of component or element of the mounted balance wheel, loses its structural interpretation, to retain only its functional interpretation. Indeed, according to the invention, those which, among the shaft, the inertial element, the plate and the plate pin, are made in a single monobloc part, no longer structurally form only a single component. For reasons of clarity, we will refer in this document to a monobloc part.For the purposes of the present invention, the functional meaning of the various functional elements, corresponding to the traditional components, will be retained for the shaft, the inertial element, the single or double plate and the plate pin, even when they are structurally a single piece with other components.

[0016] Thus, as we will detail later, we can produce in a single piece: the shaft 10, the inertial element 12, the plate 14 and the plate pin 16, or the shaft 10, the inertial element 12 and the plate 14, or the shaft 10, the plate 14 and the plate pin 16.

[0017] Currently available machining methods make it possible to produce the shapes required to manufacture single-piece parts, as mentioned above, typically from a bar, which can be rotated as for bar turning. Depending on the portions to be machined, machining phases with the bar rotating and machining phases of the bar without rotation can be combined. Alternatively, a rough machining of the single-piece part can be carried out, followed by a finishing step. A rough machining is a rough preform of the part to be manufactured, from which the finished part can be obtained by a succession of material removal operations.

[0018] Non-exhaustively, the machining methods that can be used are the following, alone or in combination: laser (particularly ultrashort pulses, such as femto laser or pico laser), milling, turning, bar turning, wire EDM.

[0019] Depending on the machining techniques used, ablation can be tangential (internal or external), such as for bar turning, turning or laser or EDM machining. As can be seen in the figure 1 , tangential machining with the bar or blank rotating, allows the creation of revolution shapes, particularly circular shapes of the shaft, with its supports to receive the spiral, or the inertial element if it is added.

[0020] As can be seen on the figure 2 , tangential machining with the bar or blank fixed, allows transverse material removals to be carried out.

[0021] THE Figures 3 and 4represent axial ablation operations, i.e. parallel to the balance shaft or the future balance shaft, in other words parallel to the bar or the axis of the gripping member of the machine tool. This operation can be carried out, for example, with milling or laser machining, with dimensional control of the machining depth ( figure 3 ) or with through machining ( figure 4 ). In the latter case, successive passes can be made to obtain a clear result. A variation in the pulse duration, the number of pulses, the repetition rate can be considered depending on the desired effect (higher or lower ablation rate, more or less rough / smooth surface condition, etc.).

[0022] It will be possible to choose, for example, from the following materials, to produce the single-piece assembly of components forming the balance (the shaft 10, the inertial element 12, the plate 14 and the plate pin 16), or a part of the balance (the shaft 10, the inertial element 12 and the plate 14, or the shaft 10, the plate 14 and the plate pin 16): Ceramics comprising or consisting of oxides (e.g., zirconium oxide, aluminum oxide), non-oxide or oxide-free ceramics (e.g., tungsten carbide, silicon nitride), hardened austenitic stainless steel, CuBe (Cuproberyllium), carbon steels, BMG (metallic glasses), synthetic diamond, SiO x glasses, metal alloys based on gold, platinum, palladium or silver, ternary alloys composed mainly of precious metals (gold, silver, platinum and / or palladium), such as isoplus and the alloys disclosed in patent EP3743538 (e.g., 41% Pd, 38% Ag, 20% Cu, 0.5% Pt, 0.5% Zn), titanium alloys, of type Grade 2 or 5.

[0023] A metal alloy based on a metal X means that the metal X constitutes more than 50% by mass of the alloy.

[0024] If necessary, a coating can be applied to all or part of the single-piece part, after a finishing step or directly after the machining step. For example, a diamond or DLC (diamond-like carbon) coating can be applied to the dowel. The presence of a coating does not affect the single-piece character of the part, which is determined by the fact that there is continuity of material between the different functional elements. By finishing step or operation, we can mention surface treatments, polishing, rolling, tribofinishing and also decorative operations, such as sandblasting or microblasting...

[0025] Another option is to produce a portion of the one-piece part to size or in a final state, and to apply a finish or coating to only a portion of the one-piece part. A portion may or may not correspond to a functional element of the balance wheel. For example, a finish may be applied to only certain sides of the rim, and not to the arms, or the shaft pivots may be polished but not the entire shaft surface.

[0026] It is also possible to produce a rough part using conventional machining techniques, such as milling, bar turning, turning, pulsed laser machining, for example nano laser type, plastic deformation, cutting / stamping, and have final shaping by femto or pico laser or by EDM.

[0027] The blanks can also be made using MIM (metal injection molding) or additive manufacturing, or thermoforming, for example in the case of a BMG.

[0028] Thus, in a first variant illustrated on the Figure 5 , the shaft 10, the plate 14 and the plate pin 16 are manufactured in a single piece. The inertial element is added 12. In this example, one can start from a bar of the chosen material or directly from a blank.

[0029] Of course, the manufacture of the shaft involves the manufacture of bearing surfaces which remain necessary, in this embodiment, for the positioning of the inertial element and for the positioning of the spiral spring. This can be achieved by tangential machining with the bar or blank rotating. The single or double plate is also produced by machining the bar or blank.

[0030] End machining can be combined to produce a shape that is not of revolution, which allows an angularly indexed and / or rotationally fixed assembly of the inertial element or the balance spring for example, if the latter have a corresponding counterform.

[0031] Among the advantageous materials for producing a balance wheel in which the shaft 10, the plate 14 and the plate pin 16 are manufactured in a single piece, we can mention: ceramics of the Si 3 N 4 , SiC, ZrO 2 , BN, WC type advantageously with a nickel-based binder, metallic glasses (BMG). The material chosen can advantageously be adapted to the chosen machining technique. Indeed, a WC with a nickel-based binder is particularly suitable for wire electro-erosion machining (EDM).

[0032] The interactions between the plate pin and the escapement require particular attention to the machining of the plate pin 16. The latter can be produced by laser machining, at the end of the bar or blank, by precessions. The plate will of course have been machined with a sufficient thickness, that is to say greater than its final thickness, to allow the plate pin to be machined in the thickness of the plate in its intermediate state, the plate being brought back to its final dimension on the side of the pin 16, by machining the latter. Advantageously, the functional surfaces of the pin, that is to say intended to cooperate with the escapement, can be shaped by providing a through groove 18 in the plate 14 ( Figure 5). Thus, it is possible to overcome the power limitations that would be encountered with laser machining if the pin were to be machined while leaving the plate intact. The working surfaces 20 thus obtained are of better quality. The non-functional surfaces 22 can be machined in a non-through manner to maintain a rigid connection between the plate and the pin. Advantageously, the direct machining of the pin in a single piece with the shaft makes it possible to perfectly define the working surfaces 20 of the pin and to ensure their parallelism with the shaft, which is optimal for their work with the escapement.

[0033] In the case of a double chainring, the notch 24 can be produced by laser machining at the end, parallel to the balance shaft, with depth control so as not to cross the pin chainring. The removal of residual material on the pin side is done by end machining, particularly by laser.

[0034] In a preferred embodiment, the functional surfaces of the pivots and the bearing surfaces are produced by tangential precession machining, with the bar or blank rotating. This machining can be carried out by laser or EDM.

[0035] Optionally, a system for riveting the inertial element can then be produced, for example advantageously by creating crimping structures, on the bearing surface 26, in particular on the top of the bearing surface 26, intended to receive the inertial element. The crimping structures can be grains 28 advantageously obtained by producing grooves on the top of the bearing surface 26. Between the intersections of the grooves, plastically deformable grains 28 are left. Tabs can also be formed to form the crimping structures. The grooves can be produced by tangential laser machining, the bar or the balance blank not being driven in rotation. A conventional geometry, by a concave pit produced by end machining, is also conceivable for crimping the inertial element.

[0036] In this variant, the separately manufactured inertial element is attached to the assembly formed by the shaft 10, the plate 14 and the pin 16. Advantageously, the inertial element is assembled by riveting the grains formed as described above. Other techniques for assembling the inertial element may be used, such as brazing, driving and / or gluing for example.

[0037] In a second variant illustrated on the figure 7 , the shaft 10, the inertial element 12 and the plate 14 are manufactured in a single piece, while the pin is added.

[0038] If it is possible to start from a bar also for this variant, it will be preferable to start from a blank, in order to limit the quantity of material to be removed, particularly for the production of the inertial element 12. The blank can thus be advantageously obtained by ceramic or BMG molding, by additive manufacturing for steel or ceramic. The blank can still be obtained by traditional machining or by rough laser machining (nanosecond laser for example), even if the quantity of material to be ablated is not optimal.

[0039] Among the materials that can be used, we can mention the materials already mentioned, with the advantage of using low-density materials, so as not to make the balance too heavy. Thus, the aforementioned ceramics are advantageous, as well as titanium alloys, preferably Grade 2 or Grade 5.

[0040] Regarding the machining techniques that can be used, it is advantageous to carry out laser machining of the bar or the rough part, with the following 3 modes of use: tangentially, with the bar or blank rotating, to generate the bearing surfaces, pivots and the exterior of the inertial element, tangentially, with the bar or blank stopped, to generate certain shapes, such as the notch of the plate, it will be noted that the latter can also be machined at the end, at the end, with the laser beam coaxial with the balance shaft (or the future shaft), the bar or blank being stopped, to generate the functional surface of an opening 26 in the plate for the insertion of the added pin ( figure 4 ), or for the finishing stages of the arms of the serge. In this embodiment, the tray pin is manufactured separately and inserted into the opening 26 in the tray. The pin may be made of ruby, chased and / or glued into the opening.

[0041] In a further variant, the shaft 10, the inertial element 12, the plate 14 and the plate pin 16 are manufactured in a single piece. To manufacture the four functional elements in a single piece, the tungsten carbide has a combination of interesting properties, with a density of 15.6, which makes it possible to produce an inertial element with sufficient mass and therefore a moment of inertia adapted to watchmaking needs, and also a hardness of 2600 HV, adequate to produce the pin. A coating, for example diamond or DLC type, can be applied to the pin. In this variant, the manufacturing steps mentioned for the two embodiments above will be combined, to machine the pin in a single piece with the plate, as in the first embodiment, as well as the inertial element, as in the second embodiment, with the plate and the shaft.

[0042] In a variant that can be combined with the second and third embodiments above, in which the inertial element is manufactured in a single piece with the shaft and the plate (or even with the pin in the third embodiment), the manufacturing step comprises a step of measuring the unbalance and / or the inertia of the balance, and a step of correcting or adjusting the dimensions of the inertial element. This can be carried out in a static or dynamic approach.

[0043] Thus the invention proposes to overcome at least partially the difficulties and errors of assembling the components which usually form a mounted balance wheel, by manufacturing in a single piece, at least three (including the shaft) or even four, of the functional elements, that is to say the shaft 10, the inertial element 12, the plate 14 and the plate pin 16.

Claims

1. Balance wheel comprising a shaft (10) and, arranged on the shaft, an inertial element (12), a plate (14) and a plate pin (16), characterized in that the shaft and at least two components among the inertial element, the plate and the plate pin, are manufactured in one piece from one material.

2. Balance wheel according to claim 1, characterized in that the shaft (10), the inertial element (12) and the plate (14) are manufactured in one piece from the same material.

3. Balance wheel according to claim 1, characterized in that the shaft (10), the plate (14) and the plate pin (16) are made from a single piece.

4. Balance wheel according to claim 1, characterized in that the shaft (10), the inertial element (12), the plate (14) and the plate pin (16) are manufactured in one piece from one material.

5. Balance wheel according to one of the preceding claims, characterized in thatsaid one-piece part is made from a material chosen from: - Oxide ceramics, - Non-oxide ceramics, - Hardened austenitic stainless steel, - Copper beryllium, - Carbon steels, - BMG (metallic glasses), - Synthetic diamond, - SiO glasses x , - Metal alloys based on gold, platinum, palladium or silver, - Ternary alloys composed mainly of metals from among gold, silver, platinum and / or palladium).

6. Balance wheel according to claim 2, characterized in that said one-piece material is made of tungsten carbide.

7. Assembly intended to form a balance wheel, comprising a shaft (10), a plate (14) and a plate pin (16), manufactured in one piece from one material.

8. Assembly according to claim 7, characterized in that It is made of Grade 2 or Grade 5 titanium alloy.

9. Assembly according to one of claims 7 or 8, characterized in thatit includes a system for riveting an inertial element formed of crimping structures, on a surface intended to receive the inertial element.

10. Assembly intended to form a balance wheel, comprising a shaft (10), a plate (14) and an inertial element (12) manufactured in one piece from material.

11. Method of manufacturing a balance wheel according to one of the preceding claims, characterized in that said part from material is manufactured using one or more of the following machining techniques: - ultrashort pulse laser, end or tangential, on a rotating or fixed part, - milling, - turning, - bar turning, - wire electro-erosion (EDM), on a rotating or fixed part.

12. Manufacturing method according to claim 11, characterized in that it is carried out on the basis of a draft.

13. Method according to claim 12, characterized in thatsaid blank is manufactured using one or more of the following techniques: - milling, - bar turning, - turning, - pulsed laser machining, - plastic deformation, - cutting / stamping, - MIM (metal injection molding) - additive manufacturing, - thermoforming.

14. Method of manufacturing an assembly according to claim 9, characterized in that said crimping structures are obtained by making grooves on the top of said bearing surface, to leave plastically deformable structures.

15. Watch movement comprising a balance wheel according to one of claims 1 to 6, or an assembly according to one of claims 7 to 10.

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