Method for producing friction by indenting

Abstract

A method for 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 stage of plastic deformation of the tube, in particular a first stage of plastic deformation of the tube that is controlled in deformation, followed by a second stage of hardening of the tube, in particular hardening by heat treatment.

Claims

1. A method for producing a tube for a friction system comprising the tube and an arbor, the method comprising: performing plastic deformation of the tube, followed by performing hardening the tube, and providing a tube obtained by the implementation of the method and an assembly comprising an arbor and the tube, wherein a diameter of the arbor is less than or equal to 2 mm.

2. The method according to claim 1, wherein said performing plastic deformation of the tube includes the deformation being performed on a portion of the tube wherein at least one of the following: the portion of the tube is in an annealed condition, the portion of the tube has an elastic limit of less than 1000 MPa, the portion of the tube has a hardness of less than 400 HV.

3. The method according to claim 1, wherein the tube is a tube of a cannon pinion or a clutch element or a torque limiter element.

4. The method according to claim 1, wherein the deformation is performed by pinching the tube.

5. The method according to claim 1, wherein the deformation is performed on a tube made of 20AP alloy or Finemac alloy having a hardness of less than or equal to 400 Hv.

6. The method according to claim 1, wherein the deformation is controlled by at least one of the following: optical measurement of the deformation, a template arranged in the tube during the deformation, passing through gauges.

7. The method according to claim 1, wherein the deformation is performed on a portion of the tube having an elongation at break greater than or equal to 2%.

8. A method for producing a tube for a friction system comprising the tube and an arbor, the method comprising: performing plastic deformation of the tube, followed by performing hardening the tube, and providing a set of at least 500 tubes obtained by the implementation of the method, wherein a standard deviation of diameters of circles centered on axes of the tubes and inscribed within straight sections of the tubes at a level of peaks of bulges is less than 0.2 micrometers.

9. The method as claimed in claim 1, wherein a friction torque between the arbor and the tube is greater than or equal to 1.8 mNm.

10. The method as claimed in claim 1, further including providing a watch movement comprising the assembly.

11. The method as claimed in claim 10, further including providing a timepiece comprising the movement.

12. The method as claimed in claim 1, wherein the tube is adapted to rub around a pinion arbor.

13. The method as claimed in claim 1, wherein the plastic deformation is controlled in deformation.

14. The method as claimed in claim 1, wherein the hardening is performed by heat treatment.

15. The method as claimed in claim 2, wherein the tube is adapted to rub around a pinion arbor.

16. The method as claimed in claim 2, wherein the portion of the tube has a hardness is of less than 350 HV.

17. The method according to claim 2, wherein the tube is a tube of a cannon pinion or a clutch element or a torque limiter element.

18. A method for producing a tube for a friction system comprising the tube and an arbor, the method comprising: performing plastic deformation of the tube, followed by performing hardening the tube, wherein the deformation is performed on a tube made of 20AP alloy or Finemac alloy having a hardness of less than or equal to 400 Hv.

19. A method for producing a tube for a friction system comprising the tube and an arbor, the method comprising: performing plastic deformation of the tube, followed by performing hardening the tube, and providing a tube obtained by the implementation of the method and an assembly comprising an arbor and the tube, wherein a friction torque between the arbor and the tube is greater than or equal to 1.8 mNm.

Description

(1) The FIGURE attached hereto represents by way of example an embodiment of a timepiece.

(2) FIG. 1 is a diagram of an embodiment of a timepiece.

(3) An embodiment of a timepiece 200 according to the invention is described below with reference to FIG. 1. The timepiece is a watch or a wristwatch, for example. The timepiece may comprise a watch movement 100, especially a mechanical watch movement, in particular automatic or electronic. The timepiece may further comprise a watch assembly, in particular a watch case intended to contain the movement.

(4) The movement comprises an assembly 3 or a friction system 3 comprising an arbor 2 and a tube 1, in particular a tube provided to rub around a pinion arbor or a tube provided to rub around an arbor of a shafted pinion. The arbor is housed inside the tube 1. For example, the tube 1 is a cannon pinion or a cannon pinion barrel, and the arbor 2 is a center pinion, in particular a shafted center pinion.

(5) The arbor 2 and the tube 1 each have diameters D which are equal to the finished operating clearance enabling the tube 1 to slide freely relative to the arbor 2 along an axis A and enabling the tube to rotate freely relative to the arbor 2 about the axis A. The diameters D are comprised between 0.3 mm and 2 mm, for example, or are comprised between 0.6 mm and 1 mm. Preferably, the diameters D are less than or equal to 2 mm, or less than or equal to 1 mm.

(6) The assembly comprises an indenting, that is to say the arbor 2 and/or the tube further comprise particular conformations 11, 21 in order to produce friction between the tube and the arbor 2.

(7) The arbor 2 comprises a groove or a conical recess 21.

(8) The tube comprises at least one bulge 11 or at least one boss, and preferably two, three or four bulges produced 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 bulges are produced in a portion 12 of reduced thickness of the cannon pinion.

(9) Advantageously, the groove or the conical recess on the one hand, and the one or more bulges on the other hand, are arranged to interact by contact with one another when the arbor 2 is positioned in the tube 1, in particular when the tube is driven onto the arbor 2 until a shoulder 22 produced on the arbor 2 comes into contact with an abutment surface 13 of the tube.

(10) In the configuration represented in FIG. 1, the one or more bulges are in contact with a portion or a circle of the groove or of the recess having a diameter d1.

(11) Before positioning the arbor 2 in the tube 1, the distance d2 (not represented) between bulges or the diameter d2 of the circle inscribed within the straight cross section of the tube at the level of the peaks of the bulges or in the vicinity of the peaks of the bulges is less than the diameter d1.

(12) For example, 1.01<d1/d2<1.1, or 1.02<d1/d2<1.09, or 1.03<d1/d2<1.08.

(13) Once the tube 1 has been inserted onto the arbor 2, the tube 1 is deformed elastically at the level of the bulges, in such a way that the distance between bulges or the diameter of the circle inscribed within the straight cross section of the tube at the level of the peaks of the bulges or in the vicinity of the peaks of the bulges has a value d1. It follows that the tube 1 exerts radial or substantially radial forces on the arbor 2. When combined with the rubbing between the arbor and the tube, these forces define a friction torque between the arbor and the tube. The torque depends primarily on the stiffness of the bulges and/or on the elastic deformation of the bulges and/or on the coefficient of friction at the interface between the arbor and the tube.

(14) Preferably, the friction torque between the arbor 2 and the tube 1 is greater than or equal to 1.8 mNm, or is greater than or equal to 2.0 mNm. As has already been seen, the tube 1 may be a tube of a cannon pinion. Preferably, a hand may be fixed to a suchlike tube. As an alternative, a hand may be cinematically connected to a suchlike tube. Thus, the assembly may be utilized for the correction of one or a plurality of hands for the indication of watch information. As an alternative, the assembly may be used to correct any type of device for the indication of watch information or information derived from the time, in particular to correct a disc. As a further alternative, the assembly may be a clutch or a torque limiter. In the case of a vertical clutch, the arbor 2 may be mobile axially relative to the tube 1 between a position such as that represented in FIG. 1 (engaged position) and a position in which the bulges are facing towards a deeper groove in the arbor 2 in which they do not rub (disengaged position, in which the tube 1 turns freely about the arbor).

(15) Preferably, the tube 1 is made of 20AP alloy or Finemac alloy. As an alternative, the tube 1 may be made of stainless steel. As a further alternative, the tube 1 may be made of a copper-beryllium alloy such as CuBe2.

(16) For example, the arbor 2 is made of 20AP alloy or Finemac alloy.

(17) Modes of implementation of a method of manufacturing of the tube 1 for a friction system comprising the tube 1 and the arbor 2 are described below.

(18) According to a first mode of implementation, the method of manufacturing the tube 1 comprises: a first stage of plastic deformation of the tube 1, followed by a second stage of hardening of the tube 1, in particular a second stage of hardening by heat treatment.

(19) According to a second mode of implementation, the method of manufacturing the tube 1 comprises a stage of plastic deformation of the tube 1, in particular a stage of plastic deformation of the tube 1 that is controlled in deformation, the deformation stage being performed on a portion of the tube in the annealed condition, and/or of which the elastic limit is less than 1000 MPa and/or of which the hardness is less than 400 HV or less than 350 HV.

(20) Studies have shown that the control of the pinching of the tube 1 in respect of dimension (and not in respect of force, as known from the prior art) allows a better control of the equipment and to some extent narrows the standard deviation of the final dimensions of the tube 1, in particular the distance between bulges d2 (not illustrated).

(21) Thus, according to a third mode of implementation, the method of manufacturing the tube 1 comprises: a first stage of plastic deformation of the tube 1, in particular controlled in deformation, the deformation stage being performed on a portion of the tube in the annealed condition, and/or of which the elastic limit is less than 1000 MPa and/or of which the hardness is less than 400 HV or less than 350 HV, followed by a second stage of hardening of the tube, in particular a second stage of hardening by heat treatment.

(22) Surprisingly, the applied heat treatment has practically no influence on the dimensions of the part, while it results in a modification of the response of the part to mechanical stresses. The response to the torque is thus more homogeneous in the case of parts that are pinched in the annealed condition or in the state of delivery than in the case of parts that have been previously hardened and then pinched.

(23) Furthermore, the performance of the controlled pinching in respect of dimension improves the dimensional regularity of the space between the bulges. Finally, the dispersion induced by pinching of the non-hardened material is less than in the case of hardened material. As a consequence, pinching has a more homogeneous and repeatable behavior than in the case of thermally hardened material, and the dispersion of the final dimensions of the tube 1, in particular the dimension between bulges d2, associated with the method, is significantly lower.

(24) Thus, the material worked is more ductile and is less subject to variations than material that has been thermally hardened. For example, the stage of plastic deformation is performed on the material as delivered, lightly cold-worked or in the annealed condition. This allows plastic deformations of greater amplitude, which makes it possible subsequently to obtain higher friction torques, for example above 1.6 mNm. When associated with control of the pinching in respect of dimension, and not in respect of force, this solution makes it possible further to reduce the dispersion within batches of cannon pinions and to avoid matching of the tubes 1 and the arbors 2.

(25) In the different embodiments, the stage of plastic deformation of the tube 1 comprises the production of at least one bulge in the tube. This deformation is preferably produced by pinching.

(26) In the different modes of implementation, and depending on the type of alloy, the stage of hardening of the tube may comprise quenching treatment followed by stress relief annealing and, if necessary, tempering treatment, or annealing treatment for structural hardening.

(27) By proceeding according to the modes of implementation described previously, it is possible to obtain a higher friction torque for the tube/arbor assembly. In order to do this, the manufacturing range of the tubes is modified, and the bulges are produced on the tubes before the hardening heat treatment. The higher the friction torque, the more the risks of sliding of the minutes hand relative to the center pinion are prevented, in particular in the event of shock. If the hand is heavy (made of precious metals) or large in size, the risk of sliding in the event of shock is high for a given friction torque.

(28) By proceeding according to the modes of implementation described previously, it is possible to obtain a different microstructure at the level of the bulges than by proceeding according to the ranges of the prior art, for example with carbides of a slightly larger size for the Finemac alloy but without impact on the behavior of the assembly.

(29) Preferably, the plastic deformation of the tube 1 in order to form the bulges is performed not by controlling the force of a pinching tool pressing on the tube, but rather by controlling and/or measuring the displacement of the material in the interior of the tube 1. As an alternative, it is possible to measure and/or to control the distance present between the bulges in the course of the realization or formation thereof.

(30) When the bulges on the tube 1 are produced on a portion of material in the annealed condition or more generally before hardening, the necessary forces are weaker, the material springback is lower and the material is more ductile, and it is thus possible to prevent cracking and to create bulges of larger dimensions, that is to say a smaller dimension d2 between the bulges.

(31) On the other hand, according to the prior art, the operation of pinching the tube is performed on the hardened material (for example Rp0.2[20AP]>1800 MPa and Rp0.2[Finemac]>1600 MPa after hardening heat treatment). This limits the admissible deformation to about 3%, while requiring a high force. A larger deformation in this material state causes cracking of the tube.

(32) Thus, according to the prior art, when a machined and finished, thermally hardened cannon pinion is pinched in the traditional manner, the deformation required in order to obtain a sufficiently high torque to prevent hands of great mass from sliding may not be obtained without the risk of cracking the wall of the cannon pinion. In addition, in the light of the natural dispersion of the diameters of the cones of the center pinions, it is necessary to match the batches of indented cannon pinions and the batches of pinions in order to guarantee the torque, and likewise to revise the pinching in the course of the assembly stage. The method of manufacture according to the prior art is therefore complicated and requires measurements of the torque to be repeated as the method proceeds in order to validate the matching of the two batches in the course of assembly. It limits the tightening torque in particular if it is wished to prevent the appearance of cracks on the cannon pinions. High friction torques are accessible with the method of production that is known from the prior art only in a manual manner, by treating the assemblies one by one.

(33) In the different modes of implementation, the deformation stage is performed, for example, by pinching the tube 1.

(34) In the different modes of implementation, the deformation stage is performed, for example, on a portion 12 of the tube, of which the elongation at break is greater than or equal to 2%, or greater than or equal to 5%.

(35) In the different modes of implementation, the deformation stage may be controlled by optical measurement of the deformation. As an alternative, in the different modes of implementation, the deformation stage may be controlled by a template arranged in the tube during the deformation stage or by passage through gauges. In a suchlike case, in the course of the action of the pinching tool, the tube is deformed until the bulges formed in the tube come into contact with the template. The template is selected with a diameter less than the diameter d2, such that, after the elastic withdrawal of the material at the end of the deformation action, the distance between the bulges or the diameter of the circle inscribed within the straight cross section of the tube at the level of the peaks of the bulges or in the vicinity of the peaks of the bulges has a value d2.

(36) An embodiment of a tube according to the invention is obtained by the implementation of the method described previously.

(37) All the tubes 1 in a batch supplied in the annealed condition may be deformed in a repeatable manner. A contrario the dispersions induced by the heat treatment in response to the plastic deformation, this heat treatment applied after plastic deformation has a weak influence on the dimensions of the tube 1, and the tolerances are narrower as a result. According to the methods described, it is thus possible to obtain a set of at least 500 tubes, of which the standard deviation of the diameters of the circles centered on the axes A and inscribed within the straight sections of the tubes at the level of the peaks of the bulges is less than 0.2 μm for a nominal value of 0.758 mm. In the case of a tube with two opposing bulges relative to the axis A, it is the standard deviation of the dimensions between peaks of the bulges that is less than 0.2 μm for a nominal value of 0.758 mm. According to the methods described, it is thus possible to obtain a set of at least 500 tubes assembled on 500 arbors, having a mean standard deviation of the measured torques of 0.20 mNm for a nominal value of 2.0 mNm.

(38) A mode of implementation of a method for producing friction between the arbor 2 and the tube 1 comprises a phase of implementation of the method for producing a tube 1 described previously and a stage of positioning the arbor 2 in the tube 1.

(39) According to the solution described previously, the range change in relation to the prior art has given rise to a surprising behavior of the material, in that the response to pinching is more homogeneous on a cold-worked material than on a hardened material, and in that the heat treatment of the hardening process does not influence the dimensions of the part. The range change thus makes it possible to increase the deformation of the tube and to generate, starting with equal initial dimensions, larger and more homogeneous bulges which will induce a more important final torque. This makes it possible, however, to ensure a sufficiently high torque between the tube and the arbor, so as to be able subsequently to support heavier hands. In addition, the level of reworking is significantly lower.