DEVICE FOR PRODUCEING A WORKPIECE FROM AMORPHEMICAL METAL AND METHOD FOR PRODUCEING SUCH A WORKPIECE

Description

[0001] The present invention relates to the manufacture of parts in amorphous or partially amorphous metal.

[0002] Amorphous metals, also known as metallic glasses, possess particularly interesting properties, including a high yield strength, excellent resistance to wear and fatigue (due to the absence of grains), high hardness, and good chemical resistance. These properties can be advantageously exploited in various applications, particularly in watchmaking.

[0003] These materials are not easy to machine, however. One way to shape them cleanly, without damaging them, is through molding, particularly injection molding. The equipment and techniques for molding amorphous metals are specific in that they must allow the material to be heated above its melting point, followed by sufficiently rapid cooling of the material introduced into the mold to prevent crystallization.

[0004] An example of an apparatus and method for molding amorphous metals, in accordance with the preamble of the attached claims 1 and 13, is described in US patent application 2021 / 0276079 in the name of Amorphous Metal Solutions GmbH.

[0005] US patent application 2021 / 0181679 describes a clockwork balance wheel made of amorphous metal by casting in a mold made of silicon by DRIE or by machining. Inserts placed in the mold before the introduction of the heated metal allow for the overmolding of functional and / or decorative elements onto the balance wheel.

[0006] Patent application JP 2001-009563 describes a mold comprising an insert in which grooves are formed for producing metal parts, specifically personal computer structures, with ribs. The technical problem addressed in this document is to facilitate the demolding of such ribbed structures. The molten metal introduced into the mold for producing the parts is aluminum, magnesium, zinc, bismuth, or similar materials. The insert is machined.

[0007] Patent application WO 2020 / 031821 describes a mold in two parts that move relative to each other, each part comprising an insert. The two inserts together define a molding cavity. One of the two inserts has grooves on its surface delimiting the molding cavity to reduce thermal stresses that cause cracking.

[0008] US patent application 2019 / 0262896 describes a method for manufacturing a component for a watch or jewelry made of amorphous metal. The method uses a one-piece mold that is destroyed after molding to release the molded component. The mold material is of a specific type, exhibiting a thermal effusivity ranging from 250 to 2500 J / K / m² / s, for example, zircon or plaster. In its introductory section, US patent application 2019 / 0262896 refers to molds and mold inserts made by LIGA.

[0009] Patent application EP3981571 discloses an apparatus for manufacturing a metal watch component, comprising a mold, a device for introducing molten metal into the mold cavity, and a cooling device for solidifying the metal in the mold cavity. The mold comprises at least one intermediate element manufactured at least partially according to the LIGA process and defining at least part of the mold cavity. This application does not describe the manufacture of a part from an amorphous metal.

[0010] The present invention aims, within the framework of an apparatus or method of the type described in US patent application 2021 / 0276079, to improve the manufacturing accuracy of parts made of amorphous or partially amorphous metal.

[0011] To this end, an apparatus according to claim 1 and a method according to claim 13 are proposed.

[0012] Other features and advantages of the present invention will become apparent from the following detailed description, made with reference to the accompanying drawings, in which: there figure 1 shows an apparatus for manufacturing a part in amorphous or partially amorphous metal according to a particular embodiment of the invention; the figure 2 shows in more detail the intermediate elements used in the device according to the invention.

[0013] There figure 1 This shows an apparatus 1 for manufacturing micromechanical parts from amorphous or partially amorphous metal according to a particular embodiment of the invention. This apparatus 1 is based on the teaching of US patent application 2021 / 0276079 and most of its elements are taken from the embodiment shown in Figure 1a of said patent application.

[0014] This apparatus 1 comprises, within a housing 2, a mold 3 whose body is in two parts 4, 5 movable relative to each other. In a first relative position of parts 4, 5 (closed position, which is the position illustrated in the figure 1 ), the two parts 4, 5 are against each other and form a molding cavity 17. In a second relative position of parts 4, 5 (open position, not shown), the two parts 4, 5 are separated from each other and the mold 3 is thus open, which allows the shaped and solidified material in the molding cavity 17 to be demolded. The movement of parts 4, 5 is ensured by rods 6, 7 actuated by motors 8, 9 in the direction of the double arrows 10, 11. This movement is horizontal in the illustrated example but it could be vertical as also indicated in US patent application 2021 / 0276079.

[0015] The mold 3 is cooled by a cooling device (not shown) using a cooling fluid such as water, air, and / or oil, and comprising, for example, internal channels for the flow of the cooling fluid formed in the body of the mold 3. To facilitate this cooling, the body of the mold 3 is made of a material with good thermal conductivity, for example, steel, copper, or a copper alloy, preferably copper or a copper alloy. In an alternative, the cooling device may be the mold 3 itself and its surroundings arranged for sufficiently rapid heat dissipation.

[0016] A feeding device 29 is arranged to deposit metal pellets 15 onto the outer surface 12 of the mold 3, opposite an orifice 16 that connects the mold cavity 17 to the outside of the mold 3, in a melting zone 13. Each pellet 15 deposited on the mold 3 is heated by a heating device 31 above, and even well above, its melting temperature. The heating device 31 includes an electrode 32, typically made of tungsten, which can be moved inside the housing 2 by a motor 33 in the direction of the double arrow 34 and can thus move closer to or further from the melting zone 13. When the electrode 32 is above the metal pellet 15 in the melting zone 13, an electric arc is formed between it and the pellet to melt the latter and heat it to a temperature between 75 and 1300°C above its melting temperature.For this purpose, the housing 2, the mold 3 and the granule 15 are electrically connected to form the counter electrode of the electrode 32. After melting, the electrode 32 returns to a position (i.e. that illustrated in the . figure 1 ) distant from the melting zone 13. The melting of the metal could however be achieved in a way other than by an electric arc, for example by means of a laser beam and / or an electron beam.

[0017] An injection piston 20 and a sleeve 19 surrounding it are simultaneously displaceable by a motor 24 inside the housing 2 in the direction of the double arrow 21, the piston 20 being further displaceable in the same direction relative to the sleeve 19 against or by the action of a spring 22. After the metal pellet 15 is melted by the heating device 31, the assembly 19, 20 is moved until an end portion 23 of the sleeve 19 protruding from the piston 20 engages and stops in an annular groove 18 of the mold 3 which surrounds the area 14 of the mold 3 serving as a support for the pellet 15. A further displacement of the piston 20 towards the mold 3 against the action of the spring 22 reduces the space delimited by the end surface 25 of the piston 20 and the internal surface 26 of the sleeve 19, so that the molten metal is pressed and injected into the mold cavity 17 through the orifice 16.

[0018] Once the metal has filled the mold cavity 17 and solidified there, the two parts 4, 5 of the mold body 3 are separated and the part resulting from the solidification of the metal is removed from the mold 3 and the housing 2 by an airlock 37. The whole process described above can then start again with a new metal pellet 15 deposited by the feeding device 29 onto the mold 3 in the melting zone 13.

[0019] The cooling of mold 3 is such that it rapidly lowers the temperature of the metal in the mold cavity 17 to a value below the glass transition temperature. The cooling rate is higher than a critical cooling rate in order to prevent the metal from crystallizing. It therefore retains its amorphous state during solidification.

[0020] Before using the device 1 or at least before the formation of the electric arc between the electrode 32 and the granule 15, the air can be evacuated from the housing 2 and a protective gas, for example argon, can be introduced.

[0021] A degasser 35, made for example of a titanium plate, may be provided inside the housing 2. This degasser 35 may be heated before the metal melts in order to eliminate residual oxygen inside the housing 2.

[0022] Instead of injection, the molten metal could be introduced into the mold cavity 17 by simply letting it flow through the orifice 16 under the effect of gravity.

[0023] Apparatus 1 enables the production of parts from amorphous metal. The term "metal" refers to a pure metal or a metallic alloy, that is, an alloy comprising at least 50% by mass of one or more metallic elements. An example of an amorphous metallic alloy is Zr 41.2 Be 22.5 Ti 13.8 Cu 12.5 Ni 10, known as Vitreloy 1.

[0024] The remarkable mechanical properties of amorphous metals allow for the creation and integration of very small components into mechanisms, particularly watchmaking mechanisms, thus reducing their overall size. For example, an amorphous metal spring, especially a return spring for a rocker arm or lever in a watch, can exert the same force and with the same resistance to fatigue as a larger crystalline metal spring. Similarly, a mainspring in a watch made of amorphous metal, such as a barrel spring or a spring functioning as a barrel, can store as much energy as a larger crystalline metal mainspring.A rigid part made of amorphous metal, for example a gear wheel or an escapement component (for example an escape wheel, an anchor, a balance wheel plate or a balance wheel pin), may have the same robustness as a corresponding rigid part made of larger crystalline metal.

[0025] However, to produce smaller parts with sufficiently precise dimensions, manufacturing tolerances must be tighter. According to the present invention, one or more intermediate elements 50 are interposed between the two parts 4, 5 of the mold body 3. This or these intermediate elements 50, illustrated in the figure 2 and schematically represented by dotted lines at the figure 1 These are in the form of hollowed-out plates produced at least in part using the LIGA process (lithography, electroplating, electroforming). The hollows 51 of the intermediate elements 50 together constitute at least part of the molding cavity 17. These hollows 51 may or may not be through-holes. Preferably, these hollows 51 together define at least the peripheral surface (perimeter) of the part to be manufactured, the upper and lower surfaces of the part being defined by the two parts 4, 5 when the hollows 51 are through-holes.

[0026] Many configurations are possible, for example: two opposing intermediate elements 50, with their facing recesses, integrated respectively into parts 4, 5, as illustrated by the figure 1; a single intermediate element 50 integrated into one of the parts 4, 5, the other of the parts 4, 5 not comprising an impression participating in the molding cavity but only a flat face which closes the molding cavity; several intermediate elements 50 superimposed, with their recesses at least partially superimposed so as to communicate, integrated into one of the parts 4, 5; several intermediate elements 50 superimposed, with their recesses at least partially superimposed so as to communicate, integrated into each of the parts 4, 5.

[0027] By stacking intermediate elements 50, thick and / or three-dimensional parts can be produced. Three-dimensional parts can also be obtained using a single intermediate element 50 manufactured on multiple levels using the LIGA 2.5D or 3D process. Such a multi-level intermediate element has the advantage of increasing manufacturing accuracy by eliminating the need to align multiple intermediate elements.

[0028] The precision of the LIGA process is ideal for reducing manufacturing tolerances for amorphous metal parts. The intermediate elements 50 can be made of any material suitable for the LIGA process, for example, nickel, copper, or a metal alloy such as nickel-phosphorus. The mold body 3, consisting of parts 4 and 5, can be made of a material with high thermal conductivity and may include one or more internal channels for the flow of a cooling fluid. In this way, the advantages of high dimensional accuracy of the mold cavity and efficient cooling of the metal can be combined.

[0029] Advantageously, each intermediate element 50 is placed in a recess 52 in one of the two parts 4, 5 of the mold body 3 and is held there, for example, by one or more movable stops or fixed by pressing or by means of pins. A single recess 52 can receive several superimposed intermediate elements 50.

[0030] The intermediate element(s) 50 are removable and can therefore be replaced if worn or to manufacture parts of a different shape. This avoids having to replace the entire mold 3, which can be very costly.

[0031] The intermediate element(s) 50 can be manufactured entirely using the LIGA process, or can comprise a base plate surmounted by a LIGA-made portion. This base plate can be the support plate on which electroforming is performed during the LIGA process.

[0032] In one variant of the invention, instead of assembling the / each intermediate element 50 to one of the two parts 4, 5 of the mold body 3, the / each intermediate element 50 is formed by LIGA on one of the two parts 4, 5 used as a support for electroforming.

[0033] Of course, several parts can be manufactured simultaneously in the same mold. For this purpose, the mold 3 can include several molding cavities 17 and corresponding intermediate elements 50.

Claims

1. Apparatus for the production of a timepiece component in amorphous or partially amorphous metal, comprising: - a mould (3) comprising a body in two parts (4, 5) which can move with respect to each other, the mould (3) being able to adopt a closed state in which the two parts (4, 5) form a moulding cavity (17) between them and an open state in which the two parts (4, 5) are spaced apart from each other to enable demoulding, - a device (20, 31) enabling the introduction of molten metal into the moulding cavity (17), and - a cooling device enabling the metal to solidify in the moulding cavity (17) and, once solidified, to be amorphous or partially amorphous, the mould (3) comprising, between said two parts (4, 5), at least one intermediate element (50) produced at least partially according to the LIGA method, a method defined by steps of lithography, electroplating and electroforming, and at least partially defining the moulding cavity (17), the at least one intermediate element (50) defining at least the peripheral surface of the timepiece component to be produced.

2. Apparatus as claimed in claim 1, characterised in that the mould (3) comprises a plurality of said intermediate elements (50) superimposed.

3. Apparatus as claimed in claim 1 or 2, characterised in that the or each intermediate element (50) is a hollowed-out plate.

4. Apparatus as claimed in any one of claims 1 to 3, characterised in that the or each intermediate element (50) is fitted together with one of the two parts (4, 5) of the body of the mould (3).

5. Apparatus as claimed in any one of claims 1 to 4, characterised in that the or each intermediate element (50) is removable.

6. Apparatus as claimed in any one of claims 1 to 5, characterised in that the or each intermediate element (50) is placed in an aperture (52) of one of the two parts (4, 5) of the body of the mould (3).

7. Apparatus as claimed in claim 1 or 2, characterised in that the or each intermediate element (50) is formed by LIGA on one of the two parts (4, 5) of the body of the mould (3).

8. Apparatus as claimed in any one of claims 1 to 7, characterised in that the body of the mould (3) is made of steel, copper or a copper alloy, preferably copper or a copper alloy.

9. Apparatus as claimed in any one of claims 1 to 8, characterised in that the device (20, 31) enabling the introduction of molten metal into the moulding cavity (17) comprises an injector, for example a piston.

10. Apparatus as claimed in any one of claims 1 to 9, characterised in that the or at least one of the intermediate elements (50) comprises a plurality of levels produced by LIGA.

11. Apparatus as claimed in any one of claims 1 to 10, characterised in that the moulding cavity (17) is shaped for the production of a spring, for example a return spring of a rocker or lever of a timepiece, or a mainspring of a timepiece.

12. Apparatus as claimed in any one of claims 1 to 10, characterised in that the moulding cavity (17) is shaped for the production of a toothed wheel or of an escapement member of a timepiece.

13. Method for the production of a timepiece component in amorphous or partially amorphous metal comprising the following steps: - providing a mould (3) comprising a body in two parts (4, 5) which can move with respect to each other, the mould (3) being able to adopt a closed state in which the two parts (4, 5) form a moulding cavity (17) between them and an open state in which the two parts (4, 5) are spaced apart from each other to enable demoulding, - introducing molten metal into the moulding cavity (17), and cooling it sufficiently rapidly so that, once solidified, the metal is amorphous or partially amorphous, - removing the solidified metal from the mould (3), the mould (3) comprising, between said two parts (4, 5), at least one intermediate element (50) at least partially produced according to the LIGA method, a method defined by steps of lithography, electroplating and electroforming, and at least partially defining the moulding cavity (17), the at least one intermediate element (50) defining at least the peripheral surface of the timepiece component to be produced.

14. Method as claimed in claim 13, characterised in that the timepiece component is a spring, for example a return spring of a rocker or lever of a timepiece, or a mainspring of a timepiece.

15. Method as claimed in claim 13, characterised in that the timepiece component is a toothed wheel or an escapement member of a timepiece.