CH711794B1 - Process for manufacturing an amorphous metal part. - Google Patents

Abstract

The present invention relates to a method of 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 (10 ) made of a second material, said mold comprising an imprint forming the negative of the micromechanical part; b) provide the first material and shape 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) separate the micromechanical part thus formed from the mold; the second material forming the mold has an effusivity of between 250 and 1000 J/K/m 2 /s 0.5. The invention also relates to a component manufactured according to this method, as well as a timepiece or a piece of jewelry comprising such a component.

Description

[0001] The present invention relates to a method of manufacturing a micromechanical part made of amorphous metal.

[0002] The technical field of the invention is the technical field of fine mechanics. More precisely, the invention will belong to the technical field of methods of manufacturing amorphous metal parts.

TECHNOLOGICAL BACKGROUND

[0003] Various methods are known for producing micromechanical parts. In fact, the latter can be produced by micro-machining or stamping or by injection into a mold.

[0004] To produce amorphous metal parts, it can also be envisaged to use micro-machining or stamping methods.

However, an advantageous solution consists of directly casting the part in amorphous metal so as to obtain by casting the final geometry or a geometry close to the final geometry requiring little rework. The absence of a crystalline structure implies that the properties of the amorphous metal part (in particular mechanical properties, hardness and polishability) do not depend on the manufacturing method. This is a major advantage compared to traditional polycrystalline metals for which raw casting parts have reduced properties compared to forgings.

[0006] However, for the production of micromechanical parts of very thin thickness (0.5 to 2 mm), disadvantages appear.

[0007] A first problem arises from the cooling of the mold. This disadvantage can be observed 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 therefore losing the properties of amorphous metals. For certain micromechanical parts or certain trim parts, the presence of a single crystallite can be prohibitive for reasons of mechanical properties or visual appearance, given that such crystallites will inevitably appear during the finishing stages. It is therefore essential to have sufficiently rapid cooling during casting to guarantee the amorphicity of the part. For this reason, the molds are made of metal, for example steel or copper, allowing heat to be extracted quickly. Depending on the ability of the chosen alloy to become amorphous, it is possible with this method to obtain parts with a thickness of around 10mm.

[0008] The second aspect to consider comes from the fact that the cooling must not be too rapid 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, leading to a risk of premature solidification. These two contradictory aspects imply the following compromise: the thickness of the castings must be neither too small (risk of solidification before complete filling of the cavity), nor too great (risk of crystallization). This is why this process is conventionally limited to parts with a thickness between approximately 2 and 10mm.

[0009] A second drawback is a formatting problem. This shaping problem comes from the small size of the mold and the footprint of the micromechanical part to be manufactured. For certain geometries, in particular hollow, non-mold geometries, it may be necessary to add inserts in the mold which will have to be eliminated after shaping, and lost. For complex shapes, the cost of these inserts and the additional operations associated with them can become very high, making the process unusable industrially.

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

[0011] However, for the production of micromechanical parts of very thin thickness (0.5 to 2 mm), the production of suitable molds is here again very complex and presents the same limitations as in foundries.

[0012] Furthermore, at a temperature between Tg and Tx, the time available before the alloy ends up crystallizing is limited. If the geometry presents many complexities of small thicknesses, the time required to completely fill the mold may be greater than the time available, leading to partial or complete crystallization of the part and a loss of its mechanical properties in particular.

[0013] A similar known technique is LIGA technology. LIGA consists of three main processing stages; lithography, electroplating and casting. There are two main LIGA fabrication technologies, the X-Ray LIGA technique, which uses 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 ultraviolet light to create structures with low aspect ratios.

[0014] The notable characteristics 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 around 89.95°; -smooth side walls with = 10 nm, suitable for optical mirrors; -structural heights from tens of micrometers to a few millimeters; -structural details of the order of micrometers over distances of centimeters.

[0015] X-Ray LIGA is a microtechnology manufacturing process developed in the early 1980s. In this process, a photoresistive polymer sensitive to conductor, is exposed to parallel beams of high energy X-rays from a synchrotron radiation source through a mask partly covered with an not exposed) of the photoresistive polymer makes it possible to obtain a three-dimensional structure which can be filled by metal electrodeposition. 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 obtained by the use of X-ray lithography (DXRL). This technique allows microstructures with high aspect ratios and high precision to be fabricated 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 photoresistive polymer, typically SU-8. Since 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 LIGA UV technique much cheaper and more accessible than its X-ray counterpart. However, the LIGA UV technique is not as effective for producing precision molds and is therefore used when cost must be kept low and very high aspect ratios are not required.

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

[0019] Furthermore, the LIGA process poses a problem concerning the choice of materials. Indeed, two materials are necessary: a material for the substrate and a material which will be deposited. The material for the substrate must be photo-structurable so plaster or zircon are not usable. For the material deposited, it must be able to be deposited via electroplating so that metallic materials are the only ones possible. However, such materials generally have thermal characteristics such that they ensure good heat dissipation and therefore good cooling. This ability to properly dissipate thermal energy would cause, for an amorphous metal alloy shaped in the LIGA mold, too rapid hardening and would therefore prevent good formation of the parts.

[0020] Finally, the LIGA process for manufacturing the mold is likely to limit the possible geometries since such a three-dimensional mold would require manufacturing layer by layer.

SUMMARY OF THE INVENTION

[0021] The invention relates to a method of producing a first part which overcomes the drawbacks 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: a) providing a mold made of a second material, said mold comprising an imprint forming the negative of the component; b) provide the first material and shape 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) separate 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<05>.

[0022] In a first advantageous embodiment, step c) consists of dissolving said mold.

[0023] In an advantageous embodiment, the shaping is done by injection.

[0024] In an advantageous embodiment, the shaping is done by centrifugal casting.

[0025] In another advantageous embodiment, the second material is zircon having an effusivity of 2300 J/K/m<2>/s<0><5>.

[0026] 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>.

[0027] In another advantageous embodiment, the first material has a critical cooling speed less than or equal to 10K/s.

[0028] The invention also relates to a component made from 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.

[0029] The invention further relates to a timepiece or piece of jewelry comprising the component according to the invention, said component is chosen from the list comprising a middle part, a bezel, a bracelet link, a gear train, a hand, a crown, an anchor or an escapement system balance, a tourbillon cage, a ring, a cufflink, an earring and a pendant.

BRIEF DESCRIPTION OF THE FIGURES

The aims, advantages and characteristics of the process for producing a first part according to the present invention will appear more clearly in the following detailed description of at least one embodiment of the invention given solely by way of example, not limiting and illustrated by the appended drawings in which: – Figures 1 to 6 schematically represent the steps of the process according to the present invention.

DETAILED DESCRIPTION

[0031] Figures 1 to 6 represent the different stages of the process for producing a watch or jewelry component 1 also called first part 1 according to the present invention. This first part 1 is made of a first material. This first part 1 can be a decorative part such as a middle part, a bezel, a bracelet link, a ring, cufflinks or earrings or a pendant or a functional part such as a cog 3, a needle , a crown, an anchor 8 or a balance 7 of an escapement system 9, a tourbillon cage.

The first material is advantageously an at least partially amorphous material. More particularly, the material is metallic, which means that it comprises at least one metallic or metalloid element in a proportion of at least 50% by mass. The first material may be a homogeneous metal alloy or a metal that is at least partially or completely amorphous. 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 metallic element may or may not be precious. The first step, shown in Figure 2, consists of providing a mold 10. This mold 10 has an imprint 12 which is the negative of the part 1 to be produced. This is a so-called lost wax mold. This type of mold consists of a mold 10 made of a material which can be destroyed or dissolved after use to release said part. The advantage of this type of mold is its ease of manufacturing and demolding, which is independent of the geometry of the impression. It is thus possible to easily produce impressions with complex and/or hollow geometries, without inserts. This mold can be obtained by covering a wax or resin model, itself obtained by injection, by additive manufacturing, by machining, or by sculpture. This mold 10 includes a conduit 14 so that the liquid metal can be poured into it.

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

[0034] The crystallization of amorphous metals occurs when these, when they are in a viscous or liquid state, are not cooled quickly enough to prevent the atoms from structuring themselves. For a given alloy, this characteristic is defined by the critical cooling rate, Rc, i.e. the minimum cooling rate to be respected between the melting temperature and the glass transition temperature in order to maintain an amorphous state of the material. Consequently, it becomes necessary to have a mold 10 made of a material which dissipates thermal energy sufficiently well to guarantee a cooling speed R greater than Rc. Conventionally, foundry molds are made of steel or copper alloys in order to have a high R value.

However, for parts of small dimensions or with fine and complex details, this capacity to dissipate thermal energy should not be too great. In the case where this capacity is too large, the risk is that the first material forming the first part freezes before being able to completely fill the cavity 12 of the mold 10.

[0036] As such, the present invention proposes to use the thermal effusivity criterion E in combination with Rc.

[0037] The thermal effusivity of a material characterizes its capacity to exchange thermal energy with its environment. It is given by:

[0038] where: λ. is the thermal conductivity of the material (in W·m<-1>.K<-1>) p: the density of the material (in kg.m<-3>) c: the specific heat capacity of the material (in J ·kg<-1>·K<-1>) Effusivity is then measured in J/K/m<2>/s<0><5>.

[0039] This effusivity allows, depending on the thickness of the first part to be produced, to obtain cooling which guarantees an amorphous state of the material, that is to say R > Rc. Indeed, if the effusivity criterion is important, amorphicity is linked to the thickness of the part to be manufactured. It is easy to understand that, for a given thickness, high effusivity risks leading to solidification of the material before it has been able to fill the entire mold, whereas too low effusivity risks leading to crystallization. According to the invention, we will consider that the effusivity will be chosen in a range going from 250 to 2500 J/K/m<2>/s<05>. 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>.

[0040] With the effusivity characteristics chosen for the invention, it is possible to obtain a first part 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 parts with a thickness of less than 0.5mm can be correctly filled if they are point details and small in size.

[0041] The second step consists of providing the first material, that is to say the material constituting the first part 1. Once provided with the material, the continuation of this second step consists of shaping it as visible in Figures 3 and 4. For this, a casting process is used.

[0042] Such a process consists of taking the first material which was provided during the second step without having subjected it to a treatment making it at least partially amorphous and putting it in liquid form. This putting into liquid form is done by melting said first material in a pouring container 20.

[0043] Once the first material is in liquid form, it is poured into 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 from the mold 10, that is to say by using the thermal characteristics of the material constituting the mold.

[0044] As a reminder, the material constituting the mold 10 will be chosen to have an effusivity comprised in a range ranging from 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.

[0045] With such effusivity values, the cooling speed R is low compared to the molds traditionally used in metal. For comparison, the effusivity of steel is more than 10,000 J/K/m<2>/s<0><5> and of 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 speed Rc in order to guarantee an amorphous or partially amorphous state of the part to be produced. This critical cooling speed Rc will be less than 15 K/s. The alloys used are for example given by the compositions Zr58.5Cu15.6Ni12.8AI10.3Nb2.8 (Rc=10K/s), Zr41.2Ti13.8Cu12.5Ni10Be22.5 (Rc=1.4K/s) or even Pd43Cu27Ni10P20 ( Rc=0.10K/s). It will therefore be understood that a mold used in the present invention cannot be made of metallic material.

[0046] With the effusivity characteristics chosen for the invention, it is thus possible to obtain a first part of amorphous metal having a thickness of between 0.5mm and 1.4mm, it being understood as explained above that details of Lower thickness are achievable if they are specific and limited in size. Similarly, parts or parts of parts with a thickness greater than 1.4mm can be produced without crystallization if they are considered as point details and small dimensions.

[0047] An advantage of casting a metal or alloy capable of being amorphous is to have a low melting temperature. Indeed, the melting temperatures of metals or alloys capable of having an amorphous form are generally two to three times lower than those of conventional alloys when considering compositions of the same types. For example, the melting temperature of the alloy Zr41.2Ti13.8Cu12.5Ni10Be22.5 is 750°C compared to 1500-1700°C of crystalline alloys based on zirconium Zr and titanium Ti. This helps prevent damage to the mold.

Another advantage is that the solidification shrinkage, for an amorphous metal, is very low, less than 1% compared to the shrinkage of 5 to 7% for a crystalline metal. This advantage makes it possible to use the principle of casting without fear of surface defects or notable changes in dimensions which would be the consequence of said shrinkage.

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

[0050] In a first alternative, the casting could be of the gravitational type. In such casting the metal fills the mold under the effect of gravity.

[0051] In a second alternative, the casting could be of the centrifugal type. Such centrifugal casting uses the principle whereby the mold is driven into rapid rotation. The liquid metal poured inside sticks to the wall by centrifugal force and solidifies. This technique allows centrifugation and pressure on the material which causes degassing and expels the impurities contained in the liquid metal bath to the external part. Smaller cavities can be filled compared to simple gravity casting.

[0052] In a third alternative, the casting could be of the injection type. Such injection casting uses the principle according to which the mold is filled using a piston which applies a very significant 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 could be of the counter-gravity type, by pressure casting, by vacuum casting.

[0053] The third step, shown in Figure 5, consists of separating the first part 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 by use by a jet of water under high pressure, by dissolution in water or in a chemical solution, or by mechanical removal. In the case of using a chemical solution, this is chosen to specifically attack the mold 10. In fact, the aim of this step is to dissolve the negative 10 without dissolving the first part 1 made of amorphous metal. For example, in the case of a mold made of plaster with a phosphate binder, a hydrofluoric acid solution is used to dissolve the mold. The end result is then obtaining the first amorphous metal part.

[0054] Next, it is planned to remove the excess material by mechanical or chemical means as shown in Figure 6.

[0055] 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 different embodiments of the invention explained above without departing from the scope of the invention defined by the appended claims.

[0056] It can also be understood that the first step consisting of providing the negative 10 can also include the fact of preparing said negative. Indeed, it is possible to decorate the negative 10 so that surface conditions can be directly produced on the first piece. These surface conditions can be a “Côte de Genève” decoration, pearled, diamond snailed or satin finishing.

Claims (10)

1. Method for 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) provide yourself with a mold (10) made of a second material, said mold comprising an imprint (12) forming the negative of the component; b) provide the first material and shape 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) separate 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<05>. 2. Manufacturing method according to claim 1, characterized in that step c) consists of dissolving said mold. 3. Manufacturing method according to claim 2, characterized in that the first material has a critical cooling speed less than or equal to 10K/s. 4. Manufacturing process according to claim 1, characterized in that the shaping is done by injection. 5. Manufacturing method according to claim 1, characterized in that the shaping is done by centrifugal casting. 6. 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>. 7. Manufacturing method according to one of claims 1 to 5, characterized in that the second material is a plaster having an effusivity of between 250 and 1000 J/K/m<2>/s<0><5>. 8. Component (1) made from a first 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. 9. Timepiece comprising the component according to claim 8, characterized in that said component (1) is chosen from the list consisting of a middle part, a bezel, a bracelet link, a gear train (3), a needle, a crown, an anchor (5), a balance (7), an escapement system (9) and a tourbillon cage. 10. Piece of jewelry comprising the component according to claim 8, characterized in that said component (1) is chosen from the list consisting of a ring, a cufflink, an earrings and a pendant.