CH716669B1 - Method of manufacturing a balance pivot shaft. - Google Patents

Abstract

The invention relates to a method of manufacturing a balance pivot shaft for a watch movement, comprising a body (12) provided with pivots (13) at the ends of said body (12), characterized in that it comprises the steps following steps: injection of a molten metal alloy into a mold (1), cooling of the molten alloy to obtain a shaft blank (10') comprising at least one part of amorphous non-magnetic metal alloy, and termination of at at least a part of the blank (10') so as to obtain a pivot shaft having finished functional zones.

Description

TECHNICAL AREA

The present invention relates, in general, to the field of watch movements and in particular that of the pivot shafts of regulating members such as balances. More specifically, the present invention relates to a method of manufacturing such a pivot shaft, as well as to a pivot shaft obtained by such a method.

PRIOR ART

[0002] The manufacture of watchmaking shafts or pivot axes, of the balance shaft type, traditionally consists of carrying out a succession of operations allowing, from a bar of raw material, to form a shaft or axis having dimensional characteristics precise as well as sufficient mechanical strength with regard to the intended application. Due to their general shape of revolution, horological shafts or pivot axes are made in known manner by precision turning or precision turning operations, from a martensitic carbon steel bar. These machining operations make it possible to define functional surfaces, such as clearances, stops or pivots, necessary on the one hand for the correct functioning of the axis and on the other hand for the assembly of the various components such as the balance seat. , the range of the plate or the range of the ferrule for example.

[0003] The turned pin then undergoes a deburring operation and then one or more heat treatment operations comprising at least quenching to improve the hardness of the pin and tempering to improve its toughness. A rolling operation of the pivots, intended to improve the surface condition, the hardness and the geometric precision, is generally carried out during or at the end of manufacture. The rolling operation can be likened to a grinding and/or polishing operation of the pivots. To improve the surface conditions and eliminate burrs, it is also possible to undertake a bulk polishing step, of the tribofinishing type carried out before or after rolling.

[0004] The grades of free-cutting steels used in the production of the balance shafts are generally martensitic carbon steels including lead and manganese sulphides to improve their machinability. Steel bearing the trade designation 20AP is typically one of these steels. In addition to being easily machinable, this steel can have very interesting mechanical characteristics for the production of watchmaking pivot axes. Indeed, the Vickers hardness of pivots made of such steel exceeds 600 HV1 after treatment.

[0005] The high mechanical properties of 20AP steels are in line with the stresses encountered by the pivot axes during their operation. The balance shaft, in particular its pivots located at its ends, must be able to withstand shocks equivalent to forces subjected to several hundred times the acceleration of Earth's gravity without breaking or exhibiting permanent deformations. These forces are generated in particular when the rim, namely the flywheel mounted on the balance shaft, has a large mass.

[0006] The wear of the contact between the pivot of a balance shaft and the pivot stone which holds it is a function of numerous chemical parameters, such as the chemical nature of the materials or the lubrication used, but is also a function of parameters mechanical such as the hardness of the elements in contact, the geometry of the contact and the forces exerted on the contact. These mechanical parameters are generally quantified and checked during the calculation of the Hertz pressure at the level of the pivoting of the axis. The maximum pressure is proportional to the square root of the modulus of elasticity used to determine the stiffness of the contact. This modulus of elasticity depends on the Young's modulus of the two materials in contact. It was therefore found that it was very advantageous to have alloys having a low Young's modulus and a high elastic limit. For the record, a material with a low Young's modulus can be qualified as a rather soft or flexible material, while a high elastic limit qualifies a material which, subjected to high stress, exhibits a reversible or elastic deformation upon removal of this constraint.

[0007] Among the materials having a low Young's modulus and a high elastic limit, amorphous metallic alloys are known, also called “metallic glasses” or BMG which is the acronym for “Bulk Metallic Glasses” in English. These types of alloys are alloys with an amorphous structure rather than a crystalline one. An amorphous material is composed of atoms which no longer respect order at medium and long distances. These materials are distinguished from crystalline materials which are endowed with a lattice of atoms exhibiting a very rigorous arrangement. Amorphous metal alloys are for example obtained, from their molten state, by means of extremely rapid cooling. Such a cooling rate aims to deprive the atoms of the time it normally takes them to change from a disordered structure, when the material is molten, to a crystalline structure, when the material is cooled.

[0008] The document US8079754B2 discloses the use of an amorphous alloy, in particular metallic glass, for a gear part of a watch movement. This gear piece is formed by a pinion coaxial with a shaft, at the end of which there is a toothed wheel of larger diameter than the pinion. The shaft is made of a crystalline metal containing copper, such as brass, or formed from a steel or other crystalline metal. The pinion and the toothed wheel are obtained by molding by first placing the shaft in a mold, then by injecting into the latter an alloy of the metallic glass type. By manufacturing the pinion and the toothed wheel by molding from an amorphous alloy, this document teaches that the abrasion resistance of the toothed parts can thus be improved and that this gear part can advantageously be produced at low cost of the that the teeth are produced by casting rather than by machining. This document therefore teaches that there is a real interest in the manufacture of gear parts.

[0009] Documents CH713264, CH712718 and CH712720 meanwhile refer to pivot pins made of light material (Ti, Al or Mg) or of copper or aluminum alloy then treated by surface hardening. These documents teach that these pivot axes are in particular intended for the production of pendulum axes and have the advantage of being able to be easily obtained by machining while being made from non-magnetic materials in order to limit their sensitivity to magnetic fields.

[0010] From the prior art, it can be seen that the manufacture of balance pivot shafts for watch movements remains focused on perfectly controlled machining processes which make it possible to obtain very high quality results. However, the satisfaction provided by these processes prevents the exploration of innovative alternative solutions leading to obtaining even more efficient processes, in particular on the qualitative or economic level at least.

[0011] Consequently, there is an interest in finding a solution which makes it possible, at least in part, to resolve the aforementioned drawbacks by proposing a more optimal process for manufacturing balance shafts.

SUMMARY OF THE INVENTION

[0012] For this purpose, the first aspect of the present invention relates to a method of manufacturing a balance pivot shaft for a watch movement, comprising a body provided with pivots at the ends of said body. This method is characterized in that it comprises the following steps: injection of a molten metal alloy into a mould, cooling of the molten alloy to obtain a shaft blank comprising at least one part of amorphous non-magnetic metal alloy, and termination of at least a part of the blank so as to obtain a pivot shaft having terminated functional areas.

[0013] According to the invention, the method of manufacturing a balance pivot shaft (generally called a balance shaft by those skilled in the art) advantageously combines a preliminary molding step followed by at least one termination step in a finishing phase. The molding step advantageously makes it possible to obtain a balance pivot shaft blank made of an amorphous material, such as a metallic glass. This molding step also makes it possible to obtain geometries which are difficult or even impossible to obtain by machining, and to acquire, within the material, atomic structures which cannot be obtained otherwise. In addition, this blank not only has desired physical characteristics in perfect harmony with the function for which this pivot shaft is intended, but also makes it possible to optimize machining by limiting the latter to the functional zones necessary for a balance shaft. The removal of material by machining is minimized and the machining time reduced to a strict minimum. In the end, this process makes it possible to obtain a finished balance pivot shaft (with reference to the finishing step), which benefits from advantageous physical and mechanical characteristics while guaranteeing, in the functional zones, dimensional values of high precision and high quality surface conditions.

[0014] In one embodiment, the termination step is preceded by a machining step so that this method also makes it possible to obtain a machined balance pivot shaft.

[0015] In one embodiment, the cooling of the blank is configured so that the body has partly an amorphous structure, and partly a semi-crystalline or crystalline structure.

In another embodiment, the method of the invention further comprises a preparatory step of structuring said mold.

As a variant or in addition to any one of these embodiments, the method of the invention could comprise an ion implantation step and/or a surface hardening step applied at least to the pivots.

[0018] In another embodiment, the blank does not constitute a volume of revolution.

[0019]Preferably, the injection of the molten metal alloy into the mold takes place via at least one mold supply channel arranged outside said functional zones.

[0020]Preferably, said functional zones comprise at least in part: at least one of said pivots, at least one span of the pivot shaft, at least one shoulder and/or one chamfer of the pivot shaft.

In another embodiment, the method of the invention comprises a prior step of placing a central part of the body in the mold before injection, said central part of the body being provided with said pivots at its ends and consisting of a crystalline structure.

[0022] In a second aspect not covered by the appended claims, the disclosure could relate to a method of manufacturing a balance pivot shaft for a watch movement, comprising a body provided with pivots at the ends of said body, in which this process would include the following steps: machining a cylinder at least partly in amorphous non-magnetic metal alloy to obtain a shaft blank comprising at least one part in amorphous non-magnetic metal alloy, and termination of at least a part of the blank so as to obtain a pivot shaft having terminated functional areas.

In a final aspect, the present invention also relates to a balance pivot shaft for a watch movement obtained by the method according to one of said aspects and according to any one of the embodiments from the present description. or according to any possible combination of these embodiments.

BRIEF DESCRIPTION OF FIGURES

Other characteristics and advantages of the present invention will appear more clearly on reading the detailed description which follows and which presents various embodiments of the invention given by way of non-limiting examples and illustrated by the figures. annexes in which: Fig. 1 is a diagrammatic representation of a mold configured for obtaining the blank of a balance pivot shaft of a watch movement in accordance with one of the steps of the method of the invention; Fig. 2 is a schematic illustration of a blank from the mold of FIG. 1; Fig. 3 is a schematic illustration of the balance pivot shaft obtained after the step of machining, or at least finishing, the blank illustrated in FIG. 2; Fig. 4 is a comparative illustration of the profiles of one of the pivots of the balance pivot shaft obtained before and after the machining step, or at least the termination step, of the method of the invention; Fig. 5 is a schematic representation of examples of amorphous alloys that can be used as metal alloy injected during the injection step of the method of the invention, and Fig. 6 is an illustration, in a view in partial vertical section, of a variant of FIG. 3 in which the balance pivot shaft is formed by a central part of the body previously placed in the mold before the injection step.

DETAILED DESCRIPTION

The watch movement to which the pivot shaft of the manufacturing method of the present invention refers is typically that of a wristwatch. However, it could nevertheless refer to the movement of another timepiece. The balance pivot shaft is generally known by the balance pin terminology to those skilled in the art. In the present description, it will be understood that these two designations are equivalent and designate the same element within the movement of the timepiece. Thus, in the expression „axis of a pendulum, „the term „axis“ designates a material object and must therefore not be confused with an immaterial reference such as a line or a straight line of a geometric figure for example.

[0026] FIG. 1 is an illustration of a mold 1 for a balance pivot shaft. This mold is illustrated in a vertical section which reveals two parts 1a, 1b of the mold in which a blank 10' of the balance pivot shaft is still housed there. It should be noted that the number of constituent parts of the mold 1 is of no particular importance in understanding the invention, but rather depends on the complexity and the general shape of the blank 10' to be obtained by molding. As illustrated schematically in FIG. 1, the mold 1 comprises at least one supply channel 2, in this case two supply channels 2 intended for the injection into the mold of a molten metal alloy.

[0027] FIG. 2 is an illustration of the balance pivot shaft blank 10'. This blank 10' corresponds to the part obtained after demolding.

[0028] FIG. 3 gives an illustration of the balance pivot shaft 10 after machining, or at least after completion, of at least part of the blank 10', in accordance with the method of the invention which will now be detailed.

The manufacturing method of the invention aims to obtain a shaft, in particular a pivot shaft 10 of the balance. This shaft 10 comprises a body 12 provided with pivots 13 or with at least one zone intended for the pivoting of the shaft 10. Such a pivoting zone could for example be a bearing surface intended to be in engagement with a bearing, such as a ball bearing. The pivots 13, or other pivoting zones, are located at the ends of the body 12. The method comprises at least the following three steps:

The first step is to inject a molten metal alloy into the mold. The injection of this alloy implies that the latter is introduced under pressure into the mould. However, the alloy could also be cast by gravity into the mould. During the molding operation, the metal alloy is molten, that is to say it is in a liquid state, at least at a temperature situated beyond that of the glass transition. Finally, in its molten state, the metal alloy can be magnetic or non-magnetic.

The second step consists in cooling the molten alloy in order to obtain a shaft blank 10' comprising at least one part made of amorphous non-magnetic metal alloy. The non-magnetic character of the metal alloy which constitutes the blank 10' aims to obtain a balance pivot pivot shaft 10 insensitive to magnetic fields. This property advantageously makes it possible to guarantee that no disturbance of a magnetic order will be able to disturb or influence the balance axis which is the pivot shaft 10 .

[0032] The balance shaft constitutes the central element of the regulating member in a mechanical movement. It is therefore important that this element be able to guarantee the precision and rate of the movement. The amorphous character of the metal alloy which constitutes at least a part of the blank 10 refers to a non-crystalline structure, in particular to a structure in which the atoms do not respect any order at medium and long distance, contrary to the crystalline structures. .

The third step consists of the termination of at least part of the blank 10 'so as to obtain a pivot shaft 10 having completed functional areas (in reference to the so-called termination operation). In one embodiment, the termination step is preceded by a machining step. The functional zones are portions of the shaft, such as the pivots 13, which have a particularly important function in order to be able to ensure precise operation of the regulating member. These functional zones, which could be described as precision zones, must have dimensions, surface states as well as properties (such as hardness, elasticity, resistance to breakage, wear and shock, etc. .. ) particular. For these reasons, the functional areas are machined, or at least finished, after the blank 10' has been obtained by molding.

[0034] FIG. 4 gives a comparative illustration of the profiles A and B of one of the pivots 13 of the balance pivot shaft 10 obtained respectively before and after the machining step, or at least the termination step, of the method of the invention. Note in this figure that the amount of material removed between the profiles A and B is advantageously minimal. This makes it possible to optimize the resources in terms of quantity of material necessary to obtain the shaft 10 and in terms of machining, compared to obtaining such a part from a bar of raw material. To pass from profile A to profile B, the machining step refers to common machining methods, such as turning, bar turning or bar turning by means of cutting tools, or even laser machining for example. The finishing stage refers to finishing operations such as surface treatment, grinding, rolling, laser or mechanical-chemical polishing, tribofinishing or bulk polishing. Termination operations could further include an ion implantation operation.

Preferably, the non-magnetic metal alloy of the blank 10 comprises a metal base formed of at least one metal from among copper, zirconium, iron, nickel and hafnium. Thus, the amorphous metal alloy which constitutes at least part of the blank can for example be one of the alloys from the following chemical formulas: Copper-Zirconium base alloys (Cu64Zr36, Cu46Zr42Al7Y5, Cu46Zr54, CU50Zr45Ti5), Zirconium alloys divers (Zr2NixCu(1-x), Zr41Ti14Cu13Ni10Be22, Zr55Cu30Al10Ni5, Zr57Nb5Al10CU15,4Ni12,6ou Zr61Ti4Nb4Cu14Ni9Al9) les alliages de Titane - Cuivre - Nickel (Ti34CU47Ni8Zr11, Ti50Cu28Ni15Sn7), les alliages d'Aluminium - Yttrium - Fer (A185Y10Fe5, Al88Y9Fe5, Al88Y5Fe7) or finally Magnesium - Copper alloys (Mg53Cu37Nd10, Mg65Cu25Tb10).

[0036] As other examples, taken from the work entitled “Mechanical Properties and Deformation Behavior of Bulk Metallic Glasses” (Dmitri V. Louzguine-Luzgin, Larissa V. Louzguina-Luzgina and Alexander Yu. Churyumov), we can cite: AlLaCu; CuHfAl; CuHfTi; CuZrAg; CuZrAl; CuZrGa; CuZrTi; ZrCoAl; ZrFeAlCu; ZrCuNiAl; ZrAlNiPd; ZrAlCoCu; TiNiCuSn; PdCuSiP; NiNbTiZr; MgCuNiGd.

For example, the Zr57Cu20Al10Ni8Ti5 alloy, which is particularly interesting because it is non-magnetic and stainless, has the following characteristics in the amorphous state: Density: 6.6 Young's modulus: 64 GPa Elastic limit: 1560 N/mm<2> Breaking strength: 1650 N/mm<2> Vickers hardness: 520 HV1000 Glass transition temperature: 650 K Crystallization temperature: 705 K.

[0038] Other possible alloys are further indicated in FIG. 5, in particular in the oval zone Z delimited by a broken line in this figure which gives a schematic representation of examples of known amorphous alloys which can be used as metal alloy injected during the injection step of the process of invention.

According to at least one of the embodiments, the step of injecting the molten metal alloy is done in an empty mold.

[0040] Preferably, the body 12 and the pivots 13 constitute a solid in one piece, in particular a solid which can be obtained entirely by molding, apart from the termination operations including, where appropriate, the machining operations. .

The cooling step is at least partly obtained by the contact of the molten metal alloy with the mold into which it is injected. Thus, the cooling takes place mainly in contact with the mould. This cooling could however be accentuated by an additional complementary action. For example, this cooling could be accentuated by environmental conditions of use and/or storage of the mold at a deliberately lower temperature compared to the usual conditions. In this case, the mold could then be cooled beforehand before its use in order to accentuate the cooling of the alloy once injected. In another embodiment, the mold could also be provided with or in contact with a cooling circuit during the injection of the alloy. Such a cooling circuit could be obtained by means of any heat transfer fluid.

Preferably again, the step of cooling the alloy aims to obtain a blank 10 of which at least the pivots 13 are made of an amorphous non-magnetic metal alloy and therefore have a non-crystalline structure.

In an advantageous embodiment, the cooling of the blank 10 could be configured so that the body 12 has partly an amorphous structure and partly a semi-crystalline or crystalline structure. For example, the amorphous structure could be obtained at the surface of the blank, whereas at the core this same blank could have a semi-crystalline or crystalline structure. Such differentiated structures for the same part could be obtained by acting on parameters such as the cooling rate of the blank and/or the choice of zones cooled at different rates. Advantageously, it is thus possible to obtain, relatively easily, in particular thanks to the molding step, a solid in one piece provided with two different (atomic) structures. This solid refers in particular to the balance pivot shaft 10 which can thus acquire particular physico-mechanical characteristics via a relatively simple manufacturing process.

To do this, it will be noted that this process refers more particularly to: the injection of a metallic alloy of metallic glass type (BMG), a specific cooling step configured so that at least part of the blank 10 can be amorphous and non-magnetic, and a step of terminating at least part of the blank in order to be able to guarantee, to the functional zones of the pivot shaft, the current characteristics required for this shaft to be able to be used as a balance shaft.

In a preferred embodiment, the termination step is preceded by a machining step.

In another embodiment, the method of the invention further comprises a preparatory step for structuring the mold 1. Performed prior to the injection step, this preparatory step could for example consist of being able to obtain, by surface of the blank 10, ridges, cavities or any other lines or structural shapes which mark the surface of certain parts, zones or portions of the blank. Such structural shapes can be intended to promote the assembly (maintenance) of the pivot shaft 10 with one or more subsequent assembly elements, such as the plate (or double plate), the balance ring or the spiral-ferrule assembly. Typically, the subsequent assembly of these elements to the balance shaft is done by driving in. These structural shapes could, additionally or alternatively, constitute useful oil reserves for lubrication.

In one embodiment, the method further comprises a surface hardening step applied at least to the pivots. This hardening could for example be obtained by a surface coating process, typically a coating obtained by physical vapor deposition known by the acronym PVD. Such a process would consist of hard metal deposition from ionized metal vapor.

In another embodiment, the method of the invention further comprises an ion implantation step. Such a step consists of implanting ions of an additional material in at least part of the blank 10' or of the balance pivot shaft 10, in particular to change its physical properties. In particular, this implantation has the advantage of preventing the propagation of cracks and makes the material more resistant to breakage, wear and corrosion. The ion implantation could preferably be implemented by bombarding at least one surface of the pivot shaft 10, or of its blank 10', with ions of carbon, nitrogen and/or oxygen. .

The method of the invention could also comprise a step of chemical hardening of the surface, such as a cementation operation typically.

[0050] In a particular embodiment, the blank 10' could not constitute a volume of revolution. Such a blank 10' would therefore constitute a solid which would differ from a body of revolution since the latter is, by definition, a volume which is obtained by rotating a two-dimensional curve (typically that of the profile of the body) around an axis of rotation. It will then be understood that it is sufficient for the blank 10' to have any asymmetrical part for it to no longer be considered as being a body of revolution, in the geometric sense of the term.

[0051] Such an asymmetrical part could be comparable to the peg or ruby actuating the anchor of the escapement and which is integral with the plate (or double plate) driven onto the balance staff. As another example of a possible asymmetrical part, we will cite an incision or a slot which could be made in the balance shaft, in a manner similar to that sometimes made in the ferrule (driven onto the balance shaft) to hold the end there. internal balance spring. Finally one could also consider a cavity or a hole (even blind) arranged in the balance shaft to accommodate a pin therein for example. Advantageously, it is noted that the process of the invention, in particular the step of molding the blank 10', would make it possible to obtain directly (namely without requiring subsequent machining) a blank 10' having, as a whole , a general shape devoid of an axis of revolution.

In another possible embodiment, the step of injecting the molten metal alloy into the mold 1 could be done by at least one supply channel 2 arranged outside the functional areas of the shaft. 10 balance swivel. Advantageously, this characteristic would make it possible to preserve these functional zones from any imperfection resulting from the attachment of the supply channel to the blank 10'. Alternatively, it could nevertheless be possible to provide the arrangement of such supply channels 2 at the level of zones intended to be machined during the machining step of the process.

[0053] Typically and as best illustrated in FIG. 3, the functional zones of the balance pivot shaft 10 comprise at least in part: at least one of the pivots 13, at least one bearing surface 14 of the pivot shaft 10, at least one shoulder 15 and/or a chamfer 16 of this tree 10.

[0054] With reference to FIG. 6, this illustrates, in a view in partial vertical section, a variant of FIG. 3 in accordance with another embodiment of the method of the invention. This embodiment incorporates, in the manufacturing method of the balance pivot shaft 10, a preliminary step of placing a central part 11 of the body 12 of the shaft 10 in the mold 1 before the step of injection . As shown in FIG. 6, the central part 11 of the body 12 is provided with pivots 13 at its ends. Moreover, this central part 11 consists of a crystalline structure, namely of a non-amorphous material. Preferably, the crystalline structure of the material which constitutes the central part 11 is a free-cutting steel. This free-cutting steel is preferably a martensitic carbon steel including lead and generally manganese sulphides. Such a steel is known to those skilled in the art under the terminology of 20AP steel. This steel has the advantage of lending itself easily to bar turning. In addition, after treatments, such as quenching and tempering, 20AP steel has high mechanical properties, particularly in terms of wear resistance and hardness. These characteristics remain adequate for the production of balance shafts.

[0055] Thus, according to the embodiment illustrated through FIG. 6, the method of the invention makes it possible to obtain a balance pivot shaft 10 which is produced in two inseparable parts which are, on the one hand, the central part 11 and, on the other hand, the overmolding 12 'of this central part 11 which, together with the latter constitute the body 12 of the balance shaft. Advantageously, this embodiment would make it possible, for example, to overcome the difficulties associated with making an extremely small and precise diameter hole in the outer part of the body 12 to guarantee insertion and holding of each pivot 13 in the body. , especially in the case where pivots 13 and body 12 do not constitute one and the same solid. Vis-à-vis this case, the present embodiment of the invention also makes it possible to obtain an overall improvement in the concentricity between pivots 13 and body 12.

[0056]Also advantageously, the embodiment illustrated by FIG. 6 makes it easy to obtain, namely without machining holes for the arrangement of the pivots in the body, a balance pivot shaft 10 which, on the one hand, benefits from the qualities of steel (such as steel 20AP) for the pivots and which, on the other hand, is almost insensitive to magnetic fields. Indeed, the sensitivity to magnetic fields of such a shaft 10 is negligible since it also benefits from the qualities of the amorphous non-magnetic metal alloy given by the molding 12 ', which molding remains the largest mass of the shaft 10 .

[0057] In a second aspect not covered by the claims, the disclosure could relate to a method of manufacturing a balance pivot shaft 10 for a watch movement, comprising a body 12 provided with pivots 13 at the ends of said body 12, wherein said method would comprise the following steps: machining a cylinder at least partly in amorphous non-magnetic metal alloy to obtain a blank 10' of shaft 10 comprising at least one part in amorphous non-magnetic metal alloy, and termination of at least a part of the blank 10' so as to obtain a pivot shaft having completed functional zones.

The method according to this aspect could also comprise at least one step or characteristic already described in the present description which would lead to a variant or to an embodiment compatible with the method of this second aspect. By way of example, this method could also comprise a step of ion implantation and/or surface treatment or hardening applied at least to the pivots 13. In addition, the method according to this second aspect could also comprise any combination possible of the embodiments described in this description.

In a final aspect, the invention also relates to a balance pivot shaft 10 for a watch movement, obtained by the method of manufacturing this shaft according to any one of the embodiments taken from the present description or according to any possible combination of these embodiments. The aforementioned method refers in particular to the method described according to any one of said aspects.

Although the objects of the present invention have been described with reference to specific examples, various obvious modifications and/or improvements could be made to the described embodiments without departing from the spirit and scope of the invention as defined by the claims.

Claims (10)

1. A method of manufacturing a balance pivot shaft (10) for a watch movement, comprising a body (12) provided with pivots (13) at the ends of said body (12), characterized in that it comprises the steps following: – injection of a molten metal alloy into a mold (1), – cooling of the molten alloy to obtain a blank (10') of a shaft (10) comprising at least one part in amorphous non-magnetic metal alloy, and – termination of at least a part of the blank (10') so as to obtain a pivot shaft (10) having completed functional zones. 2. Method according to claim 1, characterized in that the termination step is preceded by a step of machining at least a part of the shaft (10) corresponding to the finished functional zones. 3. Method according to claim 2, characterized in that the cooling of the blank (10') is configured so that the body (12) has partly an amorphous structure and partly a semi-crystalline or crystalline structure. 4. Method according to one of the preceding claims, characterized in that it further comprises a preparatory step of structuring said mold (1). 5. Method according to one of the preceding claims, characterized in that the termination step further comprises an ion implantation step and/or a surface hardening step applied at least to the pivots (13). 6. Method according to one of the preceding claims, characterized in that the blank (10 ') does not constitute a volume of revolution. 7. Method according to one of the preceding claims, characterized in that the injection of the molten metal alloy into the mold (1) is done by at least one supply channel (2) of the mold disposed outside said functional areas. 8. Method according to one of the preceding claims, characterized in that said functional zones comprise at least in part: at least one of said pivots (3), at least one bearing surface (14) of the pivot shaft (1), at least one shoulder (15) and/or chamfer (16) of the pivot shaft (10). 9. Method according to one of the preceding claims, characterized in that it comprises a preliminary step of placing a central part (11) of the body (12) in the mold (1) before injection, said central part (11) of the body (12) being provided with said pivots (13) at its ends and being made up of a crystalline structure. 10. Pendulum pivot shaft (10), for a watch movement, obtained by the method according to one of claims 1 to 9.