Method of producing friction by indenting

Abstract

To provide a simple, reliable and reproducible friction device and a method of manufacturing the same.SOLUTION: A method of producing a tube (1) for a friction system comprising the tube (1) and an arbor (2), in particular a tube provided to rub around a pinion arbor, the method comprising: a first step of plastic deformation of the tube, in particular, a first step of plastic deformation of the tube that is controlled in deformation; and a second step of hardening of the tube, in particular, hardening by heat treatment.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The invention relates to a method for manufacturing a tube for a friction system. The invention also relates to a method for generating friction between a mandrel and said tube. The invention further relates to a tube for generating said friction. The invention further relates to an assembly for generating said friction. The invention further relates to a movement comprising said tube or said assembly. The invention finally relates to a timepiece, in particular a wristwatch, comprising said tube or said assembly or said movement. [Background technology]

[0002] The drive of the hands or discs for showing the time on a small watch is generally achieved by means of a cannon pinion which is clamped and then driven into the pivot of the center wheel. The clamping creates two ridges in the tube or on the inside diameter of the cannon pinion, which come into contact with the pivot and ensure, in the normal operating mode of the time display, the transmission of the rotation of the center wheel to the cannon pinion by friction of the ridges against the pivot.

[0003] Adjustment of the pivot diameter and the distance between the ridges ensures the transmission of torque that facilitates the rotation of the minute hand. The higher this torque, the better the hand will work in the event of a shock. In time-setting mode, the rotation of the winding stem results in the rotation of the cannon pinion with the corrector mechanism, which slides on the center wheel to position the hand in the correct position relative to the dial.

[0004] Such a cannon pinion / center wheel structure constitutes, for example, an indentation process.

[0005] The result of too high a sliding or friction torque is a difficult to set impression and also causes wear of the indentation.

[0006] For this reason, the torque transmitted by the cannon pinion must be high enough to prevent untimely slippage of the hands, but not too high in order to obtain a qualitative impression when setting the time.

[0007] For reasons related to the material and dimensions of the parts, it is difficult to obtain a high friction torque for pinions manufactured in a conventional manner with an inner diameter of about 0.3 to 1 mm. While this torque is sufficient for conventional needles, the use of needles made of precious metals or needles of large sizes requires a higher tightening torque, in particular to ensure retention when exposed to impacts.

[0008] If one attempts to produce a larger ridge in order to increase the torque, the material will crack and the results will be irregular. For this reason, it is not possible to guarantee the resistance of a needle with high inertia, especially to impacts, without cracking the cylindrical pin at the time of the indentation operation.

[0009] Traditionally, the indentation operation was performed by clamping, with the purpose of reducing the tube of the cannon pinion against the step or recess of the pivot. This clamping is a manual operation, the result of which depends on the dexterity and delicacy of the watchmaker and is therefore uneven. This is disadvantageous, since, as mentioned above, the purpose of the indentation is to ensure a certain level of friction between the cannon pinion and the cannon pinion during normal operation of the watch intended to show the time, while a torque higher than friction is applied during the manual operation of setting the time by the wearer. For this reason, the friction torque must not be too high.

[0010] For this reason, precise adjustment of the friction torque is difficult. The pinion is a fragile part, and reworking the indentation after removal often leads to deterioration that requires replacement of the pinion.

[0011] This makes accurate monitoring of the applied clamping force critical; traditional manual indentation processes cannot achieve this precision, nor the required repeatability.

[0012] In EP 1 369 636 the cannon pinion is adjusted by frictional engagement on the stem of the minute pinion, which usually contains a groove (indentation notch) for receiving two ridges formed in the wall of the cannon pinion. A sufficient quality of the assembly can only be guaranteed by matching the cannon pinion and the center wheel in such a way that the indentation is perfectly adjusted, at the risk of the cannon pinion wobbling and the hand moving at the wrong moment. EP 1 369 636 proposes a traditional solution involving the use of a pinion with a support cone, which ensures the centering of the cannon pinion on the center wheel before indentation.

[0013] For this reason, indenting the cannon pinions is a traditional method that requires dexterity on the part of the watchmaker, who must sometimes rework the cannon pinions to adapt them to the pinion, and who must have a thorough understanding of the resulting shape or torque, in the case of more industrial production.

[0014] The functional tolerances of the parts are small, the nominal dimensions of the parts are small, modifying the dimensions would potentially result in system malfunction, and in industrial production it would be necessary to match batches of dimensionally compatible pinions and cannons before proceeding to assembly, which would lead to significant logistical limitations.

[0015] The pinion is traditionally machined from free-cutting steel (20AP or Finemac) and then hardened by heat treatment according to the supplier's instructions to achieve a hardness of 550±50HV. This hardness corresponds to a compromise to allow both the pinion to deform without cracking during the indentation stage and to maintain the torque over time. The material is brought to a metallurgical stage that allows the indentation to be corrected by the watchmaker until the correct torque is obtained.

[0016] The result of this hardening heat treatment is that in addition to increasing the hardness of the pinion to improve its resistance to wear, it also improves the springback and reduces the elongation at break, while on the other hand it modifies the dimensions of the pinion, albeit to a negligible extent, even at the scale of the watch.

[0017] Due to industrial manufacturing tolerances of the cannon pinion and center wheel, the batch of cannon pinions must be matched to the batch of center wheels to ensure dimensional consistency between the two.

[0018] The indentation step produces a contraction of the inside diameter of the axial pinion located in a plane perpendicular to the axis of the pinion such that the distance between the ridges achieves a selected theoretical value.

[0019] The parts are then assembled into the movement: the cannon pinion is driven onto the center wheel and the two ridges formed during the previous step are slightly elastically stretched during insertion into the pinion and then received into grooves or cones formed in the pinion, ensuring the positioning of the two parts on the axis of the cannon pinion and ensuring their relative rotational retention until a frictional torque is reached, also defined by the shape and stiffness of the parts.

[0020] The torque is controlled or measured and if the torque is not sufficient, the pinion is removed and replaced or retightened.

[0021] The material characteristics of the two parts are hardness 550±50HV for the cannon and 650±50HV for the pinion, both made from 20AP steel.

[0022] No. 5,399,633 is a recent alternative to indentation, achieved by means of a ring made of a shape memory alloy, intended to clamp the pinion around the pivot. The ring is expanded at low temperature (martensitic state), positioned against an area of ​​the pinion and then heated to obtain an austenitic structure, which allows the formation and controlled retention of the pinion on the pivot.

[0023] Patent Document 3 proposes a cannon pinion with a vertically divided canon that facilitates the insertion of the cannon pinion into the center wheel. The circular end formed at the bottom of the cannon pinion is inserted into a groove located between the steps of the center wheel.

[0024] The solutions known from the prior art are associated with several problems: Firstly, the typical torque values ​​measured on the cylindrical pinions obtained in the conventional manner are limited and higher torques can only be obtained by dimensional modifications, which is not always possible due to the respective dimensions of the parts and due to the mechanical properties of the materials.

[0025] For this reason, control of the indentation torque cannot be industrialized without matching using known methods, since the torque is very precisely determined by the inside diameter of the pinion and the outside diameter of the center wheel. Machining tolerances and additional variances caused by heat treatment and subsequent tightening require batch matching to ensure that the friction torque is within the specified tolerance. Even with such matching, the standard deviation of the torque measured on a set of 500 tubes assembled on at least 500 mandrels is on the order of 0.3 to 0.35 mNm. [Prior art documents] [Patent documents]

[0026] [Patent Document 1] Swiss Patent Application Publication No. 129931 [Patent Document 2] European Patent Application Publication No. 2881803 [Patent Document 3] Swiss Patent Application Publication No. 41140 Summary of the Invention [Problem to be solved by the invention]

[0027] The goal of the present invention is to make available an indented friction device and to improve upon the measures known from the prior art, in order to address the above-mentioned drawbacks. In particular, the present invention proposes a simple, reliable and reproducible friction device, as well as a method for manufacturing said device. [Means for solving the problem]

[0028] The method according to the invention is defined in claim 1.

[0029] Different embodiments of the method are defined in claims 2 to 8.

[0030] A tube according to the invention is defined in claim 9.

[0031] A tube set according to the invention is defined in claim 10.

[0032] The assembly according to the invention is defined in claim 11.

[0033] Various embodiments of the assembly are defined in claims 12 and 13.

[0034] A miniature clock movement according to the invention is defined in claim 14.

[0035] The watch according to the invention is defined in claim 15.

[0036] The accompanying drawings illustrate an embodiment of the watch. [Brief description of the drawings]

[0037] [Figure 1] FIG. 1 is a diagram of an embodiment of a watch. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] An embodiment of a watch 200 according to the invention is described below with reference to Fig. 1. The watch is for example a watch or a wristwatch. It comprises a watch movement 100, in particular a mechanical watch movement, in particular an automatic or electronic mechanical watch movement. The watch may further comprise a watch assembly, in particular a watch case intended to house the movement.

[0039] The movement comprises an assembly 3 or friction system 3, which comprises a stem 2 and a tube 1, in particular a tube provided for rubbing around a pinion stem or a tube provided for rubbing around the stem of an axially mounted pinion. The stem is housed within the tube 1. For example, the tube 1 is a cannon-pinion or a cannon-pinion cylinder, and the stem 2 is a center wheel, in particular a center wheel provided with an axially mounted pinion.

[0040] The mandrel 2 and the tube 1 each have a diameter D equal to a final operating clearance that allows the tube 1 to slide along the axis A relative to the mandrel 2 and allows the tube 1 to rotate about the axis A relative to the mandrel 2. The diameter D is, for example, comprised between 0.3 mm and 2 mm, or comprised between 0.6 mm and 1 mm. Preferably, the diameter D is equal to or less than 2 mm, or equal to or less than 1 mm.

[0041] The assembly includes an indentation, i.e. the mandrel 2 and / or the tube further includes specific structures 11 , 21 to create friction between the tube and the mandrel 2 .

[0042] The mandrel 2 includes a groove or conical recess 21 .

[0043] The tube includes at least one ridge 11 or at least one boss, preferably two, three or four ridges manufactured in the same plane P perpendicular to the axis A or at least substantially in the same plane P perpendicular to the axis A. Preferably, the one or more ridges are manufactured in the reduced wall portion 12 of the pinion.

[0044] Advantageously, the groove or conical depression, on the one hand, and the one or more ridges, on the other hand, are arranged to interact with each other by contact when the mandrel 2 is positioned in the tube 1, in particular when the tube is driven onto the mandrel 2 until a shoulder 22 formed on the mandrel 2 comes into contact with the abutment surface 13 of the tube.

[0045] In the structure shown in FIG. 1, one or more ridges contact a circle or portion of a groove or depression having a diameter d1.

[0046] Before positioning the mandrel 2 into the tube 1, the distance d2 (not shown) between the ridges, or the diameter d2 of a circle inscribed in a horizontal cross section of the tube at or near the height of the apex of the ridges, is smaller than diameter d1.

[0047] For example, 1.01 <d1 / d2<1.1、または1.02<d1 / d2<1.09、または1.03<d1 / d2<1.08である。

[0048] When the tube 1 is inserted on the mandrel 2, it is elastically deformed at the height of the ridges such that the distance between the ridges or the diameter of a circle inscribed in a horizontal cross section of the tube at or near the height of the ridge apex has a value d1. As a result, the tube 1 exerts radial or substantially radial forces on the mandrel 2. Combined with the sliding between the mandrel and the tube, these forces define a friction torque between the mandrel and the tube. Said torque depends primarily on the hardness of the ridges and / or their elastic deformation and / or the coefficient of friction at the contact surface between the mandrel and the tube.

[0049] Preferably, the friction torque between the mandrel 2 and the tube 1 is 1.8 mNm or more, or 2.0 mNm or more.

[0050] As mentioned above, the tube 1 may be a pinion tube. Preferably, a hand may be fixed to said tube. Alternatively, the hand may be kinematically connected to said tube. Thus, the assembly can be used for the correction of one or more hands for the display of small time information. Alternatively, the assembly may be used for the correction of any kind of device for the display of small time information or information derived from the time, in particular for correcting discs. Still alternatively, the assembly may be a clutch or a torque limiter. In the case of a vertical clutch, the axle 2 may be axially movable relative to the tube 1 between a position as shown in FIG. 1 (engaged position) and a position facing a deeper groove in the axle 2 where the ridges do not rub against each other (released position in which the tube 1 rotates freely around the axle).

[0051] Preferably, the tube 1 is made of 20AP alloy or Finemac alloy. Alternatively, the tube 1 may be made of stainless steel. Still alternatively, the tube 1 may be made of a copper-beryllium alloy such as CuBe2.

[0052] For example, the mandrel 2 is made of 20AP alloy or Finemac alloy.

[0053] An embodiment of a method for manufacturing a tube 1 for a friction system comprising a tube 1 and a mandrel 2 is described below.

[0054] According to a first embodiment, the method for manufacturing the tube 1 comprises the steps of: - the first stage of plastic deformation of tube 1, then a second stage of hardening of the tube 1, in particular by heat treatment; Includes.

[0055] According to a second embodiment, the method for manufacturing the tube 1 comprises a step of plastic deformation of the tube 1, in particular a step of plastic deformation of the tube 1 in which the deformation is controlled, the deformation step being carried out on a part of the tube in the annealed state and / or having an elastic limit smaller than 1000 MPa and / or a hardness smaller than 400 HV or smaller than 350 HV.

[0056] Research has revealed that controlling the clamping of the tube 1 in terms of dimensions (rather than in terms of force, as known from the prior art) makes it possible to better control the tool and to some extent to narrow the standard deviation of the final dimensions of the tube 1, in particular the distance D2 between the ridges (not shown).

[0057] Thus, according to a third embodiment, the method for manufacturing the tube 1 comprises: a first stage of plastic deformation of the tube 1, in particular of controlled deformation, which is carried out on a section of the tube in the annealed state and / or with an elastic limit smaller than 1000 MPa and / or with a hardness smaller than 400 HV or smaller than 350 HV, followed by - the second stage of hardening of the tube, specifically by heat treatment; Includes.

[0058] Surprisingly, the applied heat treatment has virtually no effect on the dimensions of the parts, but does result in a modification of the part's response to mechanical stress, such that the response to torque is more uniform for parts clamped in the annealed or delivery condition than for parts that are pre-hardened and then clamped.

[0059] Furthermore, the dimensionally controlled clamping performance improves the dimensional regularity of the inter-ridge spacing. Finally, the clamping induced variations of the non-hardened material are lower than those of the hardened material. As a result, the clamping has a more uniform and repeatable behavior compared to the thermosetting material, and the method-related variations of the final dimensions of the tube 1, in particular the inter-ridge dimension d2, are significantly lower.

[0060] For this reason, the processed material is more ductile and less variable than heat-hardened material. For example, the plastic deformation step can be carried out on the as-received material, on lightly cold-worked material or on the material in the annealed state. This allows for a larger plastic deformation and subsequently makes it possible to obtain a higher friction torque, for example more than 1.6 mNm. Combined with the control of the clamping in terms of size, not in terms of force, this solution makes it possible to further reduce the variability within a batch of tubular pinions and to avoid matching of the tube 1 and the mandrel 2.

[0061] In various embodiments, the step of plastically deforming the tube 1 comprises forming at least one bulge in the tube, said deformation being preferably formed by clamping.

[0062] In various embodiments, and depending on the type of alloy, the tube hardening step may include a quenching process followed by a stress relief anneal and, if necessary, a tempering or structural hardening anneal.

[0063] By proceeding according to the above-mentioned embodiment, a higher friction torque can be obtained for the tube / mandrel assembly. For this, the manufacturing range of the tube is modified and a ridge is formed on the tube before the hardening heat treatment. The higher the friction torque, the better the risk of slipping of the minute hand relative to the center wheel is prevented, in particular in the case of impact. If the hand (made of precious metal) is heavy or has large dimensions, for a given friction torque, the risk of slipping in the case of impact is high.

[0064] By proceeding according to the above described embodiment, it is possible to obtain different microstructures in the height of the protuberances compared to proceeding according to the prior art range, for example using slightly larger sized carbides for the Finemac alloy, without affecting the behavior of the assembly.

[0065] Preferably, the plastic deformation of the tube 1 to form the ridges is performed not by controlling the force of the clamping tool pressed against the tube, but by controlling and / or measuring the displacement of material inside the tube 1. Alternatively, it is also possible to measure and / or control the distance that exists between the ridges during their realization or formation.

[0066] When the ridges on the tube 1 are formed on a portion of material in the annealed state, or generally before hardening, less force is required, the springback of the material is lower and the material is more ductile, preventing cracks and allowing the formation of ridges of larger dimensions, i.e. ridges with a smaller dimension d2 between the ridges.

[0067] On the other hand, according to the prior art, the tube clamping operation is carried out on hardened material (e.g. Rp0.2[20AP]>1800MPa and Rp0.2[Finemac]>1600MPa after heat-hardening treatment), which demands high forces but limits the permissible deformation to about 3%. In this material state, larger deformations would cause cracks in the tube.

[0068] Thus, according to the prior art, if the machined and finished, heat-hardened pinion is tightened in a conventional manner, the deformation required to obtain a sufficiently high torque to prevent the large mass of the needle from slipping may not be obtained without the risk of cracking the pinion wall. In addition, in view of the natural variations in the diameter of the center wheel cone, it is necessary to match the intended pinion batch with the pinion batch in order to guarantee the torque, and likewise the tightening must be corrected during the assembly stage. For this reason, the manufacturing method according to the prior art is complex and requires repeated torque measurements as the method progresses to check the match of the two batches during assembly. In particular, the manufacturing method limits the tightening torque when it is required to prevent the appearance of cracks on the pinion. With the manufacturing methods known from the prior art, high friction torques are only achievable in a manual manner by handling the assemblies one by one.

[0069] In various embodiments, the deformation step is performed, for example, by clamping the tube 1 .

[0070] In various embodiments, the deformation step is performed on a section 12 of the tube having an elongation at break of, for example, 2% or more, or 5% or more.

[0071] In various embodiments, the deformation stage may be controlled by optical measurement of the deformation. Alternatively, in various embodiments, the deformation stage may be controlled by a template placed on the tube during the deformation stage or by passing a gauge. In such a case, during the action of the clamping tool, the tube is deformed until the ridges formed on the tube come into contact with the template. The template is selected from a diameter smaller than the diameter d2 such that after elastic withdrawal of the material at the end of the deformation operation, the distance between the ridges or the diameter of a circle inscribed in a horizontal cross section of the tube at a height at or near the apex of the ridges has a value d2.

[0072] The embodiment of the tube according to the invention is obtained by carrying out the method described above.

[0073] All tubes 1 in a batch provided in the annealed state may be deformed in a repeatable manner. Contrary to the variations induced by heat treatment upon plastic deformation, heat treatment applied after plastic deformation has no strong influence on the dimensions of the tube 1, resulting in smaller tolerances. The described method makes it possible to obtain a set of at least 500 tubes, in which the standard deviation of the diameter of a circle inscribed in a horizontal section centered on the axis A and at the height of the apex of the ridge is less than 0.2 μm for a nominal value of 0.758 mm. For a tube with two opposing ridges to the axis A, the standard deviation of the dimension between the apexes of the ridges is less than 0.2 μm for a nominal value of 0.758 mm. The described method makes it possible to obtain a set of at least 500 tubes assembled on 500 mandrels, with an average standard deviation of the measured torque of 0.20 mNm for a nominal value of 2.0 mNm.

[0074] The implementation of the method for generating friction between the mandrel 2 and the tube 1 includes implementing the method for manufacturing the tube 1 described above and positioning the mandrel 2 within the tube 1 .

[0075] According to the above mentioned solution, the range change with respect to the prior art results in a surprising behavior of the material, in that the response to tightening is more uniform in the cold-worked material than in the hardened material, and the heat treatment during the hardening process does not affect the dimensions of the part. The range change therefore allows an increase in the deformation of the tube, starting from the same initial dimensions, and allows the formation of larger and more uniform protuberances that induce a more significant final torque. However, this ensures a sufficiently high torque between the tube and the mandrel, which allows to support a heavier needle. In addition, the degree of rework is significantly lower. [Explanation of symbols]

[0076] 1 tube 2 Mandrel 3 assembly

Claims

1. A method for manufacturing a tube (1) for a friction system comprising a tube (1) and a mandrel (2), said method comprising the steps of: a stage of plastic deformation of the tube, the deformation being controlled to form at least one ridge in the tube; and thereafter hardening the tube; Including, the ridge is positioned to contact a groove or conical recess in the mandrel when the tube is driven onto the mandrel; The plastic deformation stage is controlled by optical measurement of the deformation, or the plastic deformation stage is controlled by a template which is placed on the tube during the plastic deformation stage or by gauge passage, or the plastic deformation stage is controlled by deforming a ridge formed on the tube until it contacts a template, the template being selected from a diameter smaller than the diameter of a circle inscribed in a horizontal cross section of the tube.

2. A method for manufacturing a tube (1) for a friction system comprising a tube and a mandrel (2), said method comprising the steps of: a step of plastic deformation of the tube, the deformation being controlled to form at least one ridge in the tube, said step of plastic deformation being carried out on a portion of the tube in an annealed state and / or having an elastic limit less than 1000 MPa and / or a hardness less than 400 HV or less than 350 HV, the ridge is positioned to contact a groove or conical recess in the mandrel when the tube is driven onto the mandrel; The stage of plastic deformation is controlled by optical measurement of the deformation, or the stage of plastic deformation is controlled by a template placed on the tube during the stage of plastic deformation or by gauge passage, or the stage of plastic deformation is controlled by deforming a ridge formed on the tube until it contacts a template, the template being selected from a diameter smaller than the diameter of a circle inscribed in a horizontal cross section of the tube. method.

3. The tube is a tube that slides around a pinion axle. The method according to claim 1 or 2.

4. The step of hardening the tube is a step of hardening by heat treatment. The method of claim 1.

5. The tube is a tube of a cannula, or of a clutch element, and / or of a torque limiter element, 5. The method according to any one of claims 1 to 4.

6. The step of plastic deformation is carried out by clamping the tube.

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

7. The step of plastic deformation is carried out on a tube made of 20AP alloy or Finemac alloy, having a hardness of 400 Hv or less, or 350 Hv or less; 7. The method according to any one of claims 1 to 6.

8. The deformation is performed on a section of the tube having an elongation at break of 2% or more, or 3% or more; 8. The method according to any one of claims 1 to 7.

9. A tube (1) obtainable by carrying out the method according to any one of claims 1 to 8.

10. the standard deviation of the diameter of a circle inscribed in a horizontal cross section of the tube, centered on the axis (A) of the tube, at the height of the apex of the ridge is less than 0.2 micrometers; A set of at least 500 tubes (1) according to claim 9.

11. An assembly (3) comprising a tube and a mandrel according to claim 9.

12. The friction torque between the mandrel (2) and the tube (1) is 1.8 mNm or more, or 2.0 mNm or more. Assembly (3) according to claim 11.

13. The diameter of the mandrel is 2 mm or less, or 1 mm or less; Assembly (3) according to claim 11 or 12.

14. A miniature clock movement (100) comprising a tube (1) according to claim 9 or an assembly according to any one of claims 11 to 13.

15. A timepiece (200) comprising a movement (100) according to claim 14 or a tube (1) according to claim 9 or an assembly according to any one of claims 11 to 13.

Images