EP3617811A1 - Method for producing friction by indenting - Google Patents

Abstract

Method for producing a tube (1) for a friction system comprising the tube (1) and a shaft (2), in particular a tube intended to rub around a shafted pinion, the method comprising a first step of plastic deformation of the tube, in particular a first stage of plastic deformation of the tube controlled in deformation, then a second stage of hardening of the tube, in particular hardening by heat treatment.

Description

The invention relates to a method for producing a tube for a friction system. It also relates to a method of producing friction between a shaft and such a tube. It also relates to a tube for producing such friction. It also relates to an assembly producing such friction. It also relates to a movement comprising such a tube or such an assembly. Finally, it relates to a timepiece, in particular a wristwatch, comprising such a tube or such an assembly or such a movement.

The driving of the hands or discs allowing the display of the time on a watch is generally done by means of a roadway, which one comes to pinch then drive out on a tigeron of a center pinion. Pinching creates two bumps in the tube or barrel of the roadway which come into contact with the tigeron and thus ensure, by friction of the bumps on the tigeron, the transmission of the rotation of the center pinion to the roadway in normal operating mode time display.

Adjusting the diameter of the tiger and the distance between the bumps ensures the transmission of a torque allowing the rotation of the minute hand. The higher this torque, the better the needles will behave at impact. In time setting mode, the rotation of the rod causes the rotation of the roadway by means of a correction mechanism, which slides on the center pinion to position the hand in the right place relative to the dial.

Such a pavement - center gable structure constitutes, for example, lanterning.

Too much friction or friction torque results in a difficult adjustment feeling and also induces wear on the lanterning.

It is therefore necessary that the torque transmitted by the roadway is large enough to avoid inadvertent slipping of the hands, but not too large so as to obtain a qualitative feeling when setting the time.

For reasons related to the materials and the dimensions of the parts, it is difficult to obtain high friction torques for an internal diameter of roadway of the order of 0.3 to 1 mm with roadways manufactured in the traditional way. This torque is sufficient for conventional needles, but the use of precious metal needles or large needles requires a greater tightening torque to ensure their maintenance, especially to shocks.

When trying to make larger bumps to increase the torque, the material cracks and the results are irregular. It is therefore not possible to guarantee the holding, in particular the impact resistance, of high inertia needles without cracking the roadway at the time of the lanterning operation.

Traditionally, the lanterning operation is carried out by a constriction pinch of a tube of the roadway facing a span or a clearance of the tigeron. This pinching is a manual task, and its result depends on the dexterity and sensitivity of the watchmaker, and is therefore random. This is inconvenient because, as seen previously, the purpose of the lanterning is to ensure a certain level of friction between the tigeron and the roadway during normal operation of the watch in order to display the time, while the manual operations of time setting by the user apply a torque greater than that of friction. The friction torque should therefore not be too high.

Correct adjustment of the friction torque is therefore difficult. Furthermore, the roadway is a fragile component, and the resumption of lanterning after disassembly often results in deterioration requiring the replacement of the roadway.

Precise control of the applied clamping force is therefore important, and conventional manual lanterning does not achieve this precision or the required reproducibility.

In the document CH129931, the roadway is adjusted with greasy friction on the shaft of the minute pinion, which generally comprises a groove (“lantern notch”) making it possible to accommodate two bulges generated in the wall of the roadway. Sufficient quality of such an assembly can only be ensured by pairing the roadway and the center pinion so that the lanterning is perfectly adjusted, on pain of seeing the roadway wobble and the needles move unexpectedly. Document CH129931 presents a solution that has become traditional, consisting in using a pinion with a support cone guaranteeing the centering of the roadway on the center pinion before lanterning.

The lanterning of the roadway is therefore a traditional method which requires skill on the part of the watchmaker who must sometimes return to the roadway to adapt it to the gable, or a perfect mastery of the geometries or the couples obtained in the case of more industrial.

The functional tolerances are small, as are the nominal dimensions of the components. Any modification of a dimension potentially leads to a malfunction of the system, and, in industrial production, it is necessary to pair lots of pavements and gables which are dimensionally compatible before proceeding to assembly. This induces significant logistical constraints.

The pavement is traditionally machined in free-cutting steel (20AP or Finemac) and then hardened by heat treatment according to the supplier's instructions to reach a hardness of 550 ± 50 HV. This hardness corresponds to a compromise to allow both the deformation of the roadway without cracking during the lanterning step, and the maintenance of the torque over time. The material is put in a metallurgical state allowing the lanterning to be corrected by the watchmaker until the correct torque is obtained.

This hardening heat treatment has the consequence, in addition to increasing the hardness of the pavement to make it more resistant to wear, to increase the elastic return and reduce the elongation at break. On the other hand, it only modifies the dimensions of the roadway in a negligible way, even on a watchmaking scale.

In view of industrial manufacturing tolerances for carriageways and center gables, batches of carriageways must be paired with batches of center gables, so as to ensure dimensional correspondence.

The lanterning step generates a narrowing of the internal diameter of the roadway along an axis located in the plane perpendicular to the axis of the roadway, to bring the distance between bumps to a chosen theoretical value.

The parts are then assembled on the movement: the roadway is driven out on the center pinion and the two bumps made during the previous step are slightly elastically spread during insertion on the pinion, then come to be housed in a groove or on a cone made on the pinion, and ensure the relative positioning of the two parts along the axis of the roadway, as well as the relative maintenance of the two parts in rotation until a friction torque defined by the geometry and the rigidity of the parts .

This torque is checked or measured and, if it is not sufficient, the roadway is removed and changed, or pinched again.

The material characteristics of the two components are respectively a hardness of 550 ± 50 HV for the roadway and 650 ± 50 HV for the pinion, both made of 20AP steel.

The document EP2881803 describes a recent alternative to lanterning obtained using a shape memory alloy ring intended to tighten the roadway around the tigeron. The ring is widened at low temperature (martensitic state), placed opposite the pavement area and then heated to reach the austenitic structure allowing its tightening and the controlled maintenance of the pavement on the tigeron.

Document CH41140 presents a longitudinally split barrel carriageway making it easier to insert the carriageway on the center pinion. A circular rim created on the lower part of the roadway is inserted into a groove located between spans of the center pinion.

Several problems arise with the solutions known from the state of the art. First, the typical torques measured on pavements obtained in the traditional way are limited and a high torque could only be obtained by dimensional changes, which are not always possible due to the respective dimensions of the components and the mechanical properties of the matter.

Then, the control of the lanterning torque cannot be industrialized with the known methods without resorting to pairings, because the torque very precisely depends on the internal diameters of the roadway and the external pinion of the center gear. The machining tolerances and the additional dispersion induced by the heat treatment then the nipping are such that it is necessary to pair lots to guarantee a friction torque within the required tolerances. Even with such pairing, the standard deviation of the couples measured on sets of at least 500 tubes assembled on 500 shafts is of the order of 0.3 to 0.35 mNm.

The object of the invention is to provide a lantern friction device which makes it possible to remedy the drawbacks mentioned above and to improve the devices known from the prior art. In particular, the invention provides a simple, reliable and reproducible friction device and a method for producing such a device.

A method according to the invention is defined by claim 1.

Different modes of carrying out the process are defined by claims 2 to 7.

A tube according to the invention is defined by claim 8.

A set of tubes according to the invention is defined by claim 9.

An assembly according to the invention is defined by claim 10.

Different embodiments of the assembly are defined by claims 11 and 12.

A watch movement according to the invention is defined by claim 13.

A timepiece according to the invention is defined by claim 14.

The appended figure shows by way of example an embodiment of a timepiece.

The figure 1 is a diagram of an embodiment of a timepiece.

An embodiment of a timepiece 200 according to the invention is described below with reference to the figure 1 . The timepiece is for example a watch or a wristwatch. The timepiece may include a timepiece movement 100, in particular a mechanical timepiece movement, in particular automatic, or electronic timepiece. The timepiece may also include a timepiece assembly, in particular a watch case intended to contain the movement.

The movement comprises an assembly 3 or a friction system 3 comprising a shaft 2 and a tube 1. The shaft is housed in the tube 1. By example, the tube 1 is a carriageway or a carriageway and the shaft 2 is a center gear, in particular a shafted center gear.

The shaft 2 and the tube 1 each have diameters D which are equal to the ready functional clearance which allow the tube 1 to slide freely relative to the shaft 2 along an axis A and which allow the tube to rotate freely relatively to the shaft 2 around the axis A. The diameters D are for example between 0.3 mm and 2 mm, or even between 0.6 mm and 1 mm. Preferably, the diameters D are less than or equal to 2 mm, or even less than or equal to 1 mm.

The assembly comprises a lanterning, that is to say that the shaft 2 and / or the tube further comprise particular conformations 11, 21 in order to produce friction between the tube and the shaft 2.

The shaft 2 comprises a groove or a conical clearance 21.

The tube comprises at least one boss 11 or at least one boss, preferably two, three or four bosses 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 boss or bosses are made in a portion 12 of lesser thickness of the roadway.

Advantageously, the groove or the conical clearance on the one hand, and the bump (s) on the other hand are arranged to cooperate by contact with each other when the shaft 2 is positioned in the tube 1, in particular when the tube is driven into the shaft 2 until a shoulder 22 formed on the shaft 2 comes into contact against an abutment surface 13 of the tube.

In the configuration shown in the figure 1 , the bump (s) are in contact with a portion or a circle of the groove or the clearance having a diameter d1.

Before positioning the shaft 2 in the tube 1, the distance d2 (not shown) between bumps or the diameter d2 of the circle inscribed in the right cross section of the tube at the tops of the bumps or in the vicinity of the tops of the bumps is less than the diameter d1.

For example, 1.01 <d1 / d2 <1.1, even 1.02 <d1 / d2 <1.09, even 1.03 <d1 / d2 <1.08.

Once the tube 1 is inserted on the shaft 2, the tube 1 is elastically deformed at the level of the bumps, so that the distance between bumps or the diameter of the circle inscribed in the right cross section of the tube at the tops of the bumps or near the peaks of the bumps is d1. It follows that the tube 1 exerts on the shaft 2 radial or substantially radial forces. Combined with shaft-tube friction, these forces define a shaft-tube friction couple. The torque mainly depends on the stiffness of the bumps and / or the elastic deformation of the bumps and / or the coefficient of friction at the shaft-tube interface.

Preferably, the friction torque between the shaft 2 and the tube 1 is greater than or equal to 1.8 mNm, or even greater than or equal to 2.0 mNm.

As seen previously, the tube 1 can be a roadway tube. Preferably, a needle can be fixed on such a tube. Alternatively, a needle can be in kinematic connection with such a tube. Thus, the assembly can be used for the correction of one or more hands for indicating watch information. Alternately, the assembly can be used to correct any type of organ for indicating watchmaking information or derived from the time, in particular to correct a disc. Alternatively again, the assembly can be a clutch or a torque limiter. In the case of a vertical clutch, the shaft 2 can be axially movable relative to the tube 1 between a position such as that shown on the figure 1 (engaged position) and a position in which the bumps are opposite a deeper groove in the shaft 2 in which they do not rub (disengaged position in which the tube 1 rotates freely around the shaft).

Preferably, the tube 1 is made of 20AP alloy or of Finemac alloy. Alternatively, the tube 1 can be made of stainless steel. Alternatively again, the tube 1 can be made of a beryllium copper alloy such as CuBe2.

For example, the shaft 2 is made of 20AP alloy or of Finemac alloy.

Embodiments of a method for producing the tube 1 for a friction system comprising the tube 1 and the shaft 2 are described below.

• une première étape de déformation plastique du tube 1, puis
• une deuxième étape de durcissement du tube 1, notamment une deuxième étape de durcissement par traitement thermique.

According to a first embodiment, the method for producing the tube 1 comprises:

• a first step of plastic deformation of the tube 1, then
• a second step of hardening the tube 1, in particular a second step of hardening by heat treatment.

According to a second embodiment, the method for producing the tube 1 comprises a step of plastic deformation of the tube 1, in particular a step of plastic deformation of the tube 1 controlled in deformation, the deformation step being carried out on a portion of the tube in the annealed condition and / or whose elastic limit is less than 1000 MPa and / or whose hardness is less than 400 HV or less than 350 HV.

After study, it turns out that the control of the pinching of the tube 1 in size (and not in force as known from the prior art) makes it possible to give a clearer instruction to the equipment and to partially tighten the standard deviation final dimensions of the tube 1, in particular of the distance between bumps d2 (not illustrated).

• une première étape de déformation plastique du tube 1, notamment contrôlée en déformée, l'étape de déformation étant réalisée sur une portion du tube à l'état recuit et/ou dont la limite élastique est inférieure à 1000 MPa et/ou dont la dureté est inférieure à 400 HV ou inférieure à 350 HV, puis
• une deuxième étape de durcissement du tube, notamment une deuxième étape de durcissement par traitement thermique.

Thus, according to a third embodiment, the method for producing the tube 1 comprises:

• a first step of plastic deformation of the tube 1, in particular controlled in deformation, the deformation step being carried out on a portion of the tube in the annealed state and / or whose elastic limit is less than 1000 MPa and / or whose hardness is less than 400 HV or less than 350 HV, then
• a second step of hardening the tube, in particular a second step of hardening by heat treatment.

Surprisingly, the heat treatment applied has almost no influence on the dimensions of the part, whereas it induces a modification of the response of the part to mechanical stresses. The response to torque is thus more homogeneous on parts pinched in the annealed state or in the delivery state than on parts previously hardened and then pinched.

In addition, the realization of the controlled pinching in dimension improves the dimensional regularity of the inter-bosses. In the end, the dispersion induced by the pinching of the uncured material is less than on the cured material. Consequently, pinching has a more homogeneous and repeatable behavior than on hardened material thermally, and the dispersion of the final dimensions of the tube 1, in particular of the dimension between bosses d2, linked to the process, is much lower.

Thus, a material is more ductile and less subject to variations than thermally hardened material. The plastic deformation step is for example carried out on the material as delivered, slightly hardened or in the annealed state. It makes it possible to obtain plastic deformations of greater amplitude, which then makes it possible to obtain greater friction torques, for example beyond 1.6 mNm. Associated with the pinch control in size and no longer in force, this solution also makes it possible to reduce the dispersion within batches of roadways and to avoid pairing of tubes 1 and trees 2.

In the various embodiments, the step of plastic deformation of the tube 1 comprises the production of at least one bump in the tube. This deformation is preferably carried out by pinching.

In the different embodiments and depending on the type of alloy, the tube hardening step may include a quenching treatment followed by a stress relief annealing and if necessary an tempering treatment, or a treatment of structural hardening annealing.

By proceeding according to the embodiments described above, it is possible to obtain a higher friction torque of the tube-shaft assembly. To do this, the manufacturing range of the tubes is modified, and the bumps on the tubes are made before the hardening heat treatment. The higher the friction torque, the greater the risk of the minutes hand slipping relative to the center pinion, in particular in the event of an impact. If the needle is heavy (in precious metals) or large, the risk of slipping in the event of impact is high, for a given friction torque.

By proceeding according to the embodiments described above, a different microstructure is obtained at the level of the bumps than when one proceeds according to the ranges of the state of the art, for example with carbides of slightly larger size for the Finemac alloy but without impact on the behavior of the assembly.

Preferably, the plastic deformation of the tube 1 to form the bumps is carried out not by controlling the force of a clamp pressing on the tube, but by controlling and / or measuring the displacement of the material inside the tube 1. Alternatively, one can measure and / or control the distance between the bumps during the realization or formation of these.

When the bosses are made on the tube 1 on a portion of material in the annealed state or more generally before hardening, the forces required are lower, the elastic return of material is less and the material is more ductile, it is therefore possible to avoid cracking and to create bumps of larger dimensions, that is to say a dimension between dimples d2 smaller.

On the contrary, according to the prior art, the pinching of the tube is carried out on the hardened material (for example Rp0.2 [20AP]> 1800 MPa and Rp0.2 [Finemac]> 1600 MPa after curing heat treatment). This limits the allowable deformation to around 3%, while requiring significant force. A greater deformation in this state of matter generates a cracking of the tube.

Thus, according to the prior art, when traditionally pinching a finished and thermally hardened pavement, the deformation necessary to obtain a torque high enough to prevent the sliding of large mass needles cannot be obtained without risk of cracking the road wall. In addition, in view of the natural dispersion of the diameters of the cones of the center gables, it is necessary to pair the lots of lanterned pavements and the lots of gables to guarantee the torque, and also to correct the pinching during the step assembly. The production method according to the prior art is therefore complex and requires repeating the torque measurements throughout the process to validate the pairing of the two lots during assembly. It especially limits the tightening torque if one wants to avoid seeing cracks appear on the roadways. High friction torques are only accessible with the known prior art production method manually, by treating the assemblies one by one.

In the various embodiments, the deformation step is for example carried out by pinching the tube 1.

In the various embodiments, the deformation step is for example carried out on a portion 12 of the tube whose elongation at break is greater than or equal to 2%, or even greater than or equal to 5%.

In the various embodiments, the deformation step can be controlled by optical measurement of the deformation. Alternatively, in the different embodiments, the deformation step can be controlled by a template placed in the tube during the deformation step or by passing gauges. In such a case, during the action of the clamp, the tube is deformed until the bumps formed in the tube come into contact with the template. The template is chosen with a diameter smaller than the diameter d2, so that after the elastic withdrawal of the material at the end of the deformation action, the distance between the bumps or the diameter of the circle inscribed in the right cross section of the tube at the tops of the bumps or near the peaks of the bumps is worth d2.

An embodiment of a tube according to the invention is obtained by implementing the method described above.

All the tubes 1 of a batch delivered in the annealed condition can be deformed repeatedly. In contrast to the dispersions induced by the heat treatment on the response to plastic deformation, this heat treatment applied after plastic deformation has a small influence on the dimensions of the tube 1, and the tolerances are thereby tightened. It is therefore possible, according to the methods described, 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 in the straight sections of the tubes at the tops of the bumps is less at 0.2 µm for a nominal value of 0.758 mm. In the case of a tube with two opposite bumps relative to the axis A, it is the standard deviation of the dimensions between the tops of the bumps which is less than 0.2 μm for a nominal value of 0.758 mm. Thus, it is possible to obtain, according to the methods described, a set of at least 500 tubes assembled on 500 shafts, having an average standard deviation of the measured torques of 0.20 mNm for a nominal value of 2.0 mNm.

An embodiment of a method of producing a friction between the shaft 2 and the tube 1 comprises a phase of implementation of the method of producing a tube 1 described above and a step of placing shaft 2 in tube 1.

According to the solution described above, the change in range compared to the prior art has revealed a surprising behavior of the material in that the response to pinching is more homogeneous on a work hardened material than on a hardened material and in that the hardening heat treatment does not influence the dimensions of the part. The change of range thus makes it possible to increase the deformation of the tube and to generate, with equal initial dimensions, larger and more homogeneous bumps which will induce a greater final torque. This therefore ensures a sufficiently high torque between the tube and the shaft, capable of subsequently supporting heavier needles. In addition, the retouch rate is significantly lower.

Claims (14)

Method for producing a tube (1) for a friction system comprising the tube (1) and a shaft (2), in particular a tube intended to rub around a shafted pinion, the method comprising a first step of plastic deformation of the tube, in particular a first stage of plastic deformation of the tube controlled in deformation, then a second stage of hardening of the tube, in particular hardening by heat treatment. Method for producing a tube (1) for a friction system comprising the tube and a shaft (2), in particular a tube intended to rub around a shafted pinion, the method comprising a step of plastic deformation of the tube, controlled by deformed, the deformation step being performed on a portion of the tube in the annealed state and / or whose elastic limit is less than 1000 MPa and / or whose hardness is less than 400 HV or less than 350 HV. Method according to one of the preceding claims, characterized in that the tube is a road tube or a clutch element and / or a torque limiter element. Method according to one of the preceding claims, characterized in that the deformation step is carried out by pinching the tube. Method according to one of the preceding claims, characterized in that the deformation step is carried out on a tube of 20AP alloy or of Finemac alloy having a hardness less than or equal to 400 Hv, or even less than or equal to 350 Hv. Method according to one of the preceding claims, characterized in that the deformation step is controlled by optical measurement of the deformation or by a template arranged in the tube during the deformation step or by passing gauges. Method according to one of the preceding claims, characterized in that the deformation is carried out on a portion of the tube whose elongation at break is greater than or equal to 2%, or even greater than or equal to 3%. Tube (1), in particular roadway, in particular lanterned roadway, obtained by implementing the method according to one of claims 1 to 7. Set of at least 500 tubes (1) according to claim 8, the standard deviation of the diameters of the circles centered on the axes (A) and inscribed in the straight sections of the tubes at the tops of the bumps being less than 0.2 micrometers . Assembly (3), in particular center pinion assembly, comprising a shaft and a tube according to claim 8. Assembly (3) according to the preceding claim, characterized in that the friction torque between the shaft (2) and the tube (1) is greater than or equal to 1.8 mNm, or even greater than or equal to 2.0 mNm. Assembly (3) according to claim 10 or 11, characterized in that the diameter of the shaft is less than or equal to 2 mm, or even less than or equal to 1 mm. Watch movement (100), comprising a tube (1) according to claim 8 and / or an assembly according to one of claims 10 to 12. Timepiece (200), in particular wristwatch, comprising a movement (100) according to the preceding claim and / or a tube according to one of claims 8 and / or an assembly according to one of claims 10 to 12.

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