EP3170579A1 - Method for manufacturing a part from amorphous metal - Google Patents

Abstract

The present invention relates to a method for manufacturing a micromechanical part made of a first material, said first material being a material capable of becoming at least partially amorphous, said method comprising the following steps: a) providing a mold made of a second material, said mold having a cavity forming the negative of the micromechanical part; b) providing the first material and forming it in the cavity of said mold, said first material having undergone at the latest at the time of said shaping a treatment enabling it to become at least partially amorphous; c) disconnecting the micromechanical part thus formed from the mold;

Description

The present invention relates to a method for manufacturing a micromechanical piece of amorphous metal.

The technical field of the invention is the technical field of fine mechanics. More specifically, the invention will belong to the technical field of manufacturing methods of amorphous metal parts.

BACKGROUND TECHNOLOGY

Various methods are known for producing micromechanical parts. Indeed, these can be performed by micro-machining or stamping or by injection into a mold.

To make amorphous metal parts, it can also be envisaged to use micromachining or stamping methods.

However, an advantageous solution consists in directly casting the piece of amorphous metal so as to obtain by foundry the final geometry or a geometry close to the final geometry requiring little retouching. The absence of crystalline structure implies that the properties of the amorphous metal part (in particular the mechanical properties, the hardness and the polishability) do not depend on the method of manufacture. This is a major advantage over traditional polycrystalline metals where the castings have lower properties compared to forged parts.

However, for the production of micromechanical parts of very small thicknesses (0.5 to 2 mm), drawbacks appear.

A first problem comes from the cooling of the mold. This disadvantage can be seen in two aspects. A first aspect is that the cooling must not be too slow because there is then a risk of partial or total crystallization and thus lose the properties of the amorphous metals. For some micromechanical parts or some trim parts, the presence of a single crystallite may be unacceptable for reasons of mechanical properties or visual appearance, since such crystallites will inevitably occur during the finishing steps. It is therefore essential to have a sufficiently rapid cooling during casting to ensure the amorphicity of the room. For this reason, the molds are made of metal, for example steel or copper, for quickly extracting heat. Depending on the capacity of the chosen alloy to become amorphous, it is possible with this method to obtain pieces of thickness of the order of 10mm.

The second aspect to consider is that the cooling must not be too fast because there is a risk of solidification before the mold cavity is completely filled. However, with metal molds such as copper or steel, the thermal energy is quickly dispersed causing a risk of early solidification. These two contradictory aspects imply the following compromise: the thickness of the castings must not be too small (risk of solidification before complete filling of the impression), nor too great (risk of crystallization). This is why this process is conventionally limited to pieces of thickness between about 2 and 10 mm.

A second disadvantage is a formatting problem. This formatting problem comes from the small size of the mold and the footprint of the micromechanical part to be manufactured. For some geometries, in particular recessed geometries, indémoulables, it may be necessary to add inserts in the mold to be eliminated after shaping, and lost. For complex shapes, the cost of these inserts and additional operations related thereto can become very high, making the process unusable industrially.

Another advantageous solution is to use the shaping properties of the amorphous metals. Indeed, the amorphous metals have the particular characteristic of softening while remaining amorphous in a given temperature range [Tg - Tx] specific to each alloy and low because these temperatures Tg and Tx are low. This makes it possible to accurately reproduce fine and precise geometries because the viscosity of the alloy decreases sharply and the latter can be easily deformed in order to match all the details of a mold.

However, for the production of micromechanical parts of very small thicknesses (0.5 to 2 mm), the production of suitable molds is here again very complex and has the same limitations as in foundry.

In addition, at a temperature between Tg and Tx, the time available before the alloy crystallizes is limited. If the geometry has many complexities of small thicknesses, the time required for complete filling of the mold may be longer than the time available, resulting in partial or complete crystallization of the part and a loss of its mechanical properties in particular.

A similar known technique is LIGA technology. The LIGA consists of three main stages of treatment; lithography, electroplating and molding. There are two main manufacturing technologies LIGA, the X-Ray LIGA technique, which uses the X-rays produced by a synchrotron to create structures with a high aspect ratio, and the LIGA UV technique, a more accessible method that uses the ultraviolet light to create structures with low aspect ratios.

• des rapports d'aspect élevés, de l'ordre de 100:1 ;
• des parois latérales parallèles avec un angle de flanc de l'ordre de 89,95 °;
• parois latérales lisses avec = 10 nm, adaptées pour les miroirs optiques ;
• hauteurs structurelles de dizaines de micromètres à quelques millimètres ;
• les détails structurels de l'ordre de micromètres sur des distances de centimètres.

The notable features of LIGA structures manufactured by the X-ray method include:

• high aspect ratios of the order of 100: 1;
• parallel side walls with a flank angle of the order of 89.95 °;
• smooth side walls with = 10 nm, suitable for optical mirrors;
• structural heights from tens of microns to a few millimeters;
• the structural details of the order of micrometers over distances of centimeters.

X-Ray LIGA is a microtechnology manufacturing process developed in the early 1980s. In this process, an X-ray sensitive photoresist, typically PMMA (poly (methylmethacrylate)), bonded to an electrically conductive substrate, is exposed to parallel beams of high energy X-rays from a synchrotron radiation source through a mask partly covered with an X-ray absorbing material. Chemical removal from exposed (or unexposed) areas photoresist polymer provides a three-dimensional structure which can be filled by metal plating. The resin is chemically removed to produce a metal mold insert. The mold insert can be used to produce polymer or ceramic parts by injection molding.

The main advantage of the LIGA technique is the precision achieved by the use of X-ray lithography (DXRL). This technique allows for microstructures with high aspect ratios and high accuracy to be manufactured in a variety of materials (metals, plastics and ceramics).

The LIGA UV technique uses an inexpensive ultraviolet light source, such as a mercury lamp, to expose a photoresist, typically SU-8. Because heating and transmission are not a problem in optical masks, a simple chrome mask can be substituted for the sophisticated X-ray mask technique. These simplifications make the technique LIGA UV, a technique much cheaper and more accessible than his counterpart X-ray. However, the LIGA UV technique is not as efficient in producing precision molds and is therefore used when the cost has to be kept low and when very high aspect ratios are not needed.

The disadvantage of such a method is that it does not allow the simple production of three-dimensional parts. Indeed, the manufacture of three-dimensional part via the LIGA process is possible but it is necessary to carry out several successive iterations of photolithography, and galvanic deposition.

Moreover, the LIGA process poses a problem concerning the choice of materials. Indeed, two materials are needed: a material for the substrate and a material that will be deposited. The material for the substrate must be photo-structuring so that the plaster or zircon is not usable. For the deposited material, it must be deposited electroplating so that the metal materials are the only ones that can be envisaged. However, such materials generally have thermal characteristics such that they ensure good heat dissipation and therefore good cooling. This ability to dissipate heat energy would cause, for an amorphous metal alloy formed in the LIGA mold, a hardening too fast and thus prevent good formation of parts.

Finally, the LIGA process for the manufacture of the mold is likely to limit the possible geometries since such a three-dimensional mold would require stratum production by stratum.

SUMMARY OF THE INVENTION

1. a) se munir d'un moule réalisé dans un second matériau, ledit moule comportant une empreinte formant le négatif du composant ;
2. b) se munir du premier matériau et le mettre en forme dans l'empreinte dudit moule, ledit premier matériau ayant subi au plus tard au moment de ladite mise en forme un traitement lui permettant de devenir au moins partiellement amorphe;
3. c) désolidariser le composant ainsi formé du moule ;

caractérisé en ce que le second matériau formant le moule présente une effusivité thermique allant de 250 à 2500 J/K/m²/s^0.5.The invention relates to a method for producing a first part which overcomes the disadvantages of the prior art by making it possible to obtain a method of manufacturing a component made of a first metallic material, said first material being a material capable of becoming at least partially amorphous, said method comprising the following steps:

1. a) providing a mold made of a second material, said mold having a cavity forming the negative of the component;
2. b) providing the first material and forming it in the cavity of said mold, said first material having undergone at the latest at the time of said shaping a treatment enabling it to become at least partially amorphous;
3. c) dissociating the component thus formed from the mold;

characterized in that the second material forming the mold has a thermal effusivity ranging from 250 to 2500 J / K / m ² / s ^0.5 .

In a first advantageous embodiment, step c) consists of dissolving said mold.

In a second advantageous embodiment, said first material is subjected to a rise in temperature above its melting point allowing it to lose locally any crystalline structure, said rise being followed by cooling to a temperature below its temperature. transition glass allowing said first material to become at least partially amorphous.

In a third advantageous embodiment, the shaping step b) is simultaneous with a treatment rendering said first material at least partially amorphous, by subjecting it to a temperature above its melting point followed by cooling to a temperature lower than its glass transition temperature allowing it to become at least partially amorphous, during a casting operation. This embodiment is characterized in that that the critical cooling rate of the first material is less than 10K / s.

In a fourth advantageous embodiment, the shaping is done by injection.

In a fifth advantageous embodiment, the shaping is done by centrifugal casting.

In another advantageous embodiment, the second material is zircon having an effusivity of 2300 J / K / m ² / s ^0.5 .

In another advantageous embodiment, the second material is of the plaster type composed mainly of gypsum and / or silica, having an effusivity of between 250 and 1000 J / K / m ² / s ^0.5 .

In another advantageous embodiment, the first material has a critical cooling rate of less than or equal to 10 K / s.

The invention also relates to a component made in a first material being a metallic material capable of becoming at least partially amorphous, characterized in that it is manufactured using the method according to the invention.

The invention further relates to a timepiece or jewelery comprising the component according to the invention, said component is selected from the list comprising a middle part, a bezel, a bracelet link, a cog, a needle, a crown, an escapement anchor or balance, a tourbillon cage, a ring, a cufflink or an earring or a pendant.

BRIEF DESCRIPTION OF THE FIGURES

• les figures 1 à 6 représentent de manière schématique les étapes du procédé selon la présente invention.

The objects, advantages and features of the method of producing a first part according to the present invention will appear more clearly in the following detailed description of at least one form of embodiment of the invention given solely by way of nonlimiting example and illustrated by the appended drawings in which:

• the Figures 1 to 6 show schematically the steps of the method according to the present invention.

DETAILED DESCRIPTION

The Figures 1 to 6 represent the various steps of the method of producing a watchmaking or jewelery component 1 also called first piece 1 according to the present invention. This first piece 1 is made of a first material. This first piece 1 may be a piece of clothing such as a caseband, a bezel, a bracelet link, a ring, cufflinks or earrings or a pendant or a functional piece such as a cogwheel 3, a needle , a crown, an anchor 5 or a balance 7 exhaust system 9, a tourbillon cage.

The first material is advantageously an at least partially amorphous material. More particularly, the material is metallic, it is understood that it comprises at least one metal or metalloid element in a proportion of at least 50% by weight. The first material may be a homogeneous metal alloy or an at least partially or totally amorphous metal. The first material is thus chosen capable of locally losing any crystalline structure during a rise in temperature above its melting temperature followed by sufficiently rapid cooling to a temperature below its glass transition temperature, allowing it to become at least partially amorphous. The metal element may be valuable or not.

The first step, represented at figure 2 is to provide a mold 10. This mold 10 has a cavity 12 which is the negative of the part 1 to achieve. This is a mold called lost wax. This type of mold consists of a mold 10 made of a material that can be destroyed or dissolved after use to release said part. The advantage of this type of mold is its ease of manufacture and demolding, which is independent of the geometry of the print. It is thus possible to easily make fingerprints of complex geometries and / or recesses, without inserts. This mold may be obtained by covering a wax or resin model, itself obtained by injection, additive manufacturing, machining, or sculpture. This mold 10 comprises a conduit 14 so that the liquid metal can be poured therein.

This mold 10 is thus made of a second material. Advantageously, the mold material is chosen to have specific thermal properties. Indeed, the aim here is to have a mold for casting lost wax which is made of a material allowing the amorphous material of the micromechanical part not to crystallize while completely filling the mold cavity.

Crystallization of amorphous metals occurs when these, when in a viscous or liquid state, are not cooled fast enough to prevent the atoms from structuring themselves. For a given alloy, this characteristic is defined by the critical cooling rate, Rc, ie the minimum cooling rate to be respected between the melting point and the glass transition temperature in order to maintain an amorphous state of the material. Therefore, it becomes necessary to have a mold 10 made of a material that dissipates heat energy well enough to ensure a cooling rate R greater than Rc. Conventionally, foundry molds are made of steel or cuprous alloys to have a high R value.

However, for parts of small dimensions or with fine and complex details, this ability to dissipate thermal energy should not be too great. In case this capacity is too much important, the risk is that the first material forming the first piece freeze before being able to completely fill the footprint 12 of the mold 10.

As such, the present invention proposes to use the criterion of thermal effusivity E in combination with Rc.

où :

• λ : est la conductivité thermique du matériau (en W·m^-1·K^-1)
• ρ : la masse volumique du matériau (en kg·m^-3)
• c : la capacité thermique massique du matériau (en J·kg^-1·K^-1)
• L'effusivité se mesure alors en J/K/m²/s^0.5.

The thermal effusivity of a material characterizes its ability to exchange thermal energy with its environment. It is given by: $$E=\sqrt{\lambda \rho \mathrm{vs}}$$

or :

• λ: is the thermal conductivity of the material (in W · m ^-1 · K ^-1 )
• ρ: the density of the material (in kg · m ^-3 )
• c: the specific heat capacity of the material (in J · kg ^-1 · K ^-1 )
• The effusivity is then measured in J / K / m ² / s ^0.5 .

This effusivity makes it possible, according to the thickness of the first part to be produced, to obtain a cooling which guarantees an amorphous state of the material, that is to say R> Rc. Indeed, if the criterion of effusiveness is important, the amorphicity is related to the thickness of the part to be manufactured. It is easily understood that, for a given thickness, a high effusivity may result in solidification of the material before it has been able to fill the entire mold while too weak effusivity may cause crystallization. According to the invention, it will be considered that the effusivity will be chosen within a range of 250 to 2500 J / K / m ² / s ^0.5 . As an example of material, the effusivity of plaster type materials is 250 - 1000 J / K / m ² / s ^0.5 while for zircon, it will be 2300 J / K / m ² / s ^0.5 .

With the effusivity characteristics chosen for the invention, it is possible to obtain a first piece having a thickness of 0.5 mm or more without freezing the material before the impression is completely filled. It is clear that parts or parts of 0.5mm can be properly filled if they are point and small details.

The second step is to provide the first material, that is to say the material constituting the first part 1. Once provided with the material, the next step of this second step is to shape it as visible to the Figures 3 and 4 . For this, a casting process is used.

Such a method consists in taking the first material which was provided during the third step without having made it undergo a treatment rendering it at least partially amorphous and put it in liquid form. This liquid forming is done by melting said first material in a pouring container 20.

Once the first material in liquid form, it is poured into the cavity 2 of the mold. When the cavity 2 of the mold is filled or at least partially filled, the first material is then cooled so as to give it an amorphous shape. According to the invention, the cooling is carried out by heat dissipation of the mold 10, that is to say by using the thermal characteristics of the constituent material of the mold.

As a reminder, the constituent material of the mold 10 will be chosen to have an effusivity in the range of 250 to 2500 J / K / m ² / s ^0.5 , this thermal effusivity of a material being the capacity of the latter to exchange thermal energy with its environment. Thus, the greater the effusivity, the greater the cooling will be at equivalent thickness.

With such effusivity values, the cooling rate R is low compared to the traditionally used metal molds. For comparison, the effusivity of the steel is more than 10'000 J / K / m ² / s ^0.5 and copper more than 35'000 J / K / m ² / s ^0.5 . For this reason, it is necessary to use a first material having a low critical cooling rate Rc in order to guarantee an amorphous or partially amorphous state of the piece to realize. This critical cooling rate Rc will be less than 15 K / s. Alloys used are, for example, given by the compositions Zr58.5Cu15.6Ni12.8A110.3Nb2.8 (Rc = 10K / s), Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Rc = 1.4K / s) or else Pd43Cu27Ni10P20 ( rc = 0.10K / s). It will therefore be understood that a mold used in the present invention can not be made of metallic material.

With the effusivity characteristics chosen for the invention, it is thus possible to obtain a first piece of amorphous metal having a thickness of between 0.5 mm and 1.4 mm, being understood as explained above that details of smaller thickness are feasible if they are punctual and limited in size. Similarly, parts or parts of parts greater than 1.4 mm in thickness can be made without crystallization if they are considered as point and small details.

An advantage of casting a metal or alloy capable of being amorphous is to have a low melting point. Indeed, the melting temperatures of metals or alloys capable of having an amorphous form, are in general two to three times lower than those of conventional alloys when one considers compositions of the same types. For example, the melting temperature of Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy is 750 ° C compared to 1500-1700 ° C of zirconium Zr and Ti titanium alloys. This avoids damaging the mold.

Another advantage is that the solidification shrinkage, for an amorphous metal, is very low, less than 1% relative to the shrinkage of 5 to 7% for a crystalline metal. This advantage allows to use the principle of casting without fear of surface defects or significant changes in size that would be the consequence of said withdrawal.

Another advantage is that the mechanical and polishability properties of the amorphous metals do not depend on the process of as long as they are amorphous. Thus the parts obtained by casting will have the same properties as forged parts, machined, or deformed hot, which is a major advantage over crystalline metals whose properties strongly depend on the crystal structure, itself related to the history of the process of obtaining the piece.

In a first alternative, the casting may be of the gravitational type. In such casting the metal fills the mold under the effect of gravity.

In a second alternative, the casting may be of the centrifugal type. Such centrifugal casting utilizes the principle that the mold is rotated rapidly. The liquid metal poured inside sticks to the wall by centrifugal force and solidifies. This technique allows a centrifugation and a pressure on the material which causes a degassing and expels to the external part the impurities contained in the bath of liquid metal. Smaller cavities can be filled compared to simple gravitational casting.

In a third alternative, the casting may be of the injection type. Such injection molding uses the principle that the mold is filled with a piston that applies a very large force to push the liquid metal. This thrust then makes it possible to introduce the liquid metal into the mold in order to better fill it. In other alternatives, the casting may be of the counter-gravity type, by die casting, by vacuum casting.

The third step, represented at figure 5 consists in separating the first piece 1 from the mold 10. For this, the mold 10, in which the amorphous metal has been overmolded to form the first part 1, is destroyed using a jet of water under high pressure, by dissolved in water or chemical solution, or by mechanical removal. In the case of the use of a chemical solution, it is chosen to specifically attack the mold 10. Indeed, the purpose of this step is to dissolve the negative 1 without dissolving the first piece 5 made of amorphous metal. For example, in the case of a mold made of plaster with phosphate binder, a solution of hydrofluoric acid is used to dissolve the mold. The final result is then obtaining the first piece of amorphous metal.

Next, it is planned to remove the excess material by mechanical or chemical means as shown in figure 6 .

It will be understood that various modifications and / or improvements and / or combinations obvious to those skilled in the art can be made to the various embodiments of the invention set forth above without departing from the scope of the invention defined by the appended claims.

It can also be understood that the first step consisting in acquiring the negative 1 can also include the fact of preparing the negative. Indeed, it is possible to decorate the negative 1 so that surface states can be directly made on the first part. . These surface conditions can be a decoration "Geneva coast", beaded, snailed diamond or satin.

Claims (12)

A method of manufacturing a component (1) made of a first material, said first material being a metallic material capable of becoming at least partially amorphous, said method comprising the following steps: a) providing a mold (10) made of a second material, said mold having a cavity (12) forming the negative of the component; b) providing the first material and forming it in the cavity of said mold, said first material having undergone at the latest at the time of said shaping a treatment enabling it to become at least partially amorphous; c) dissociating the component thus formed from the mold; characterized in that the second material forming the mold has a thermal effusivity ranging from 250 to 2500 J / K / m ² / s ^0.5 . Manufacturing method according to claim 1, characterized in that step c) consists in dissolving said mold. Manufacturing method according to claims 1 or 2, characterized in that said first material is subjected to a rise in temperature above its melting temperature allowing it to lose locally any crystalline structure, said rise being followed by cooling to a temperature below its glass transition temperature allowing said first material to become at least partially amorphous, the first material has a critical cooling rate of less than 15 K / s. Manufacturing method according to claim 3, characterized in that the first material has a critical cooling rate less than or equal to 10K / s. Manufacturing method according to one of claims 1 to 4, characterized in that the shaping step b) is simultaneous with a treatment rendering said first material at least partially amorphous, by subjecting it to a temperature above its temperature. melting followed by cooling to a temperature below its glass transition temperature allowing it to become at least partially amorphous, during a casting operation. Manufacturing method according to claim 5, characterized in that the shaping is done by injection. Manufacturing process according to claim 5, characterized in that the shaping is done by centrifugal casting. Manufacturing method according to one of the preceding claims, characterized in that the second material is zircon having an effusivity of 2300 J / K / m ² / s ^0.5 . Manufacturing method according to one of claims 1 to 8, characterized in that the second material is a plaster mainly composed of gypsum and / or silica, having an effusivity of between 250 and 1000 J / K / m ² / s ^0.5 . Component (1) made of a first material being a metallic material capable of becoming at least partially amorphous, characterized in that it is manufactured using the method according to one of the preceding claims. Timepiece comprising the component according to claim 10, characterized in that said component (1) is chosen from the list comprising a middle part, a bezel, a bracelet link, a gear train (3), a needle, a crown, an anchor (5) or a rocker (7) of exhaust system (9), a tourbillon cage. Jewelery piece comprising the component according to claim 10, characterized in that said component (1) is chosen from the list comprising a ring, a cufflink or an earring or a pendant.

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