FR3141867A1 - Injection device for amorphous metal alloy - Google Patents

Abstract

The invention relates to an injection device for the production of at least one molded part made of amorphous metal alloy, comprising: (i) a mold having at least two injection chambers connected to at least one cavity; and (ii) at least one heating means capable of melting metal elements; and a multipiston system comprising: (1) at least two injection pistons whose respective main axes are each aligned with that of their corresponding injection chamber and (2) a support cooperating with each of the injection pistons; And such that the support and/or the mold are able to move along an axis parallel to the main axes of the injection pistons so as to allow the loading of the metal elements and the injection of the molten metal elements into the chambers injection. The invention relates to an injection process for the production of at least one molded part made of amorphous metal alloy.[Fig. 1]

Description

Injection device for amorphous metal alloy

The present invention relates to the field of die-casting production of amorphous metal alloy parts.

“Amorphous metal alloys” (AMAs) or “metallic glasses” exhibit exceptional mechanical properties compared to their traditional crystalline counterparts: high yield strength and hardness, high elastic deformation capacity, high resistance to fatigue, corrosion and abrasion.

Long limited by manufacturing processes inducing geometries that are not very suitable for industrialization, AMA parts can now be obtained industrially, in particular via processes for molding a metal alloy capable of forming a metallic glass. Such processes consist first of all in filling an imprint of a mold with a previously melted metal alloy. The alloy thus molded is then cooled sufficiently quickly to obtain a part with the shape of the imprint, the amorphous phase of which is predominant compared to the crystalline phase. Different types of molding have been developed for the manufacture of AMA parts, such as suction molding, centrifugal molding or even pressure molding.

A "die casting process" is a process in which pressure is applied to the molten alloy during the cavity filling step. The pressure is applied to ensure optimum filling of the cavity and to "compact" the alloy in it. This pressure is generally applied by mechanical action, for example using a piston, and can be reinforced by the joint action of a depression or an overpressure of the atmosphere within the mold or another mechanical system such as, for example, a movable insert in the mold.

The present invention relates more particularly to the die casting of AMA parts, generally considered to be the most suitable process for industrialization. It is indeed known that such a process makes it possible to manufacture parts with complex shapes, but it is however difficult to guarantee excellent quality of these, for example due to crystals or porosities within the parts (Lehua Liu et al. Near-Net Forming Complex Shaped Zr-Based Bulk Metallic Glasses by High Pressure Die Casting. Materials 2018, 11, 2338; doi:10.3390/ma11112338).

Thus, to ensure excellent quality of the AMA parts produced, the quantity of alloy melted and then injected must be limited and the process cycle times generally greater than one minute. The limitation of injectable volume and cycle times therefore impose a limit in terms of production rate and/or volume of AMA parts for industrial production.

Technical problem

There is therefore a need for an injection device and a die casting process for the manufacture of good quality AMA parts, possibly in larger volumes, said process also having a high productivity. The increase in productivity of the process must however not impact the quality of the parts compared to a process with lower productivity because it requires working at smaller volumes.

• au moins deux pistons d’injection 4 dont les axes principaux respectifs sont alignés chacun à celui de leur chambre d’injection 3 correspondantes et
• un support 7 coopérant avec chacun des pistons d’injection 4 ; et
  tel que le support 7 et/ou le moule 1 sont aptes à se déplacer le long d’un axe parallèle aux axes principaux des pistons d’injection 4 de façon à permettre :
  i. le chargement des éléments métalliques 8 ; et
  ii. optionnellement, la mise en fusion desdits éléments métalliques 8 ; et
  iii. l’injection des éléments métalliques 8 en fusion dans les chambres d’injection 3.

There is therefore proposed an injection device for the production of at least one molded part in amorphous metal alloy, comprising:
- a mold 1 having at least two injection chambers 3 connected to at least one imprint 2; and
- at least one heating means 5 capable of melting metal elements 8; and
- a multi-piston system 6 comprising:

• at least two injection pistons 4 whose respective main axes are each aligned with that of their corresponding injection chamber 3 and
• a support 7 cooperating with each of the injection pistons 4; and
  such that the support 7 and/or the mold 1 are able to move along an axis parallel to the main axes of the injection pistons 4 so as to allow:
  i. loading of metal elements 8; and
  ii. optionally, melting said metallic elements 8; and
  iii. the injection of the molten metal elements 8 into the injection chambers 3.

According to another aspect, there is provided an injection method for producing at least one amorphous metal alloy casting, comprising the steps:
- loading metal elements 8 into the device described above, the metal elements 8 being loaded in solid form or in a molten state;
- optionally, melt the metallic elements introduced in solid form;
- relatively moving the support 7 and the mold 1 along an axis parallel to the main axes of the injection pistons 4 in order to inject substantially simultaneously, via the injection pistons 4, the molten metal elements into the imprint 2 or imprints 2 of the device to obtain, after cooling, at least one molded part made of amorphous metal alloy.

The features set out in the following paragraphs may optionally be implemented. They may be implemented independently of each other or in combination with each other.

According to one embodiment, the injection device is such that each injection piston 4 comprises a pre-stressed damping system 10 capable of exerting, when the injection piston 4 is in the injection position, pressure on the molten metal element 8 corresponding to said injection piston 4, this force, included in a determined force range, possibly being different from that of the other injection piston(s) 4.

According to one embodiment, the pre-stressed damping system 10 is chosen from: mechanical springs, a system using a pressurized gas and a system using a pressurized fluid.

According to one embodiment, the heating means 5 is chosen from: induction heating, electric arc heating, laser beam heating, electron beam heating.

According to one embodiment of the injection device, the injection direction is:
- vertical and the injection direction from bottom to top or from top to bottom,
- horizontal,
- inclined at an angle between 0 and 90 degrees from the vertical,
preferably the injection direction is vertical and even more preferably the injection direction is vertical and the injection direction from bottom to top.

According to one embodiment, the metal elements 8 are loaded into the injection device in liquid or solid form, preferably the metal elements are loaded in solid form.

According to one embodiment, the mold 1 only comprises a single imprint 2.

Other characteristics, details and advantages of the invention will appear on reading the detailed description below, and on analyzing the attached drawings, in which:

Fig. 1

shows an injection device when the multi-piston system is in the position for loading the metal elements according to one embodiment of the invention;

Fig. 2

shows an injection device when the multi-piston system is in position to melt the metal elements according to one embodiment of the invention;

Fig. 3

shows an injection device when the multi-piston system is in the position for injecting the metal elements according to one embodiment of the invention;

Fig. 4

shows an injection device comprising a pre-stressed damping system, the multi-piston system being in the position for loading the metal elements, according to one embodiment of the invention;

Fig. 5

shows an injection device comprising a pre-stressed damping system, the multi-piston system being in the position for injecting the metal elements, according to one embodiment of the invention;

Fig. 6

shows an injection device comprising a single imprint according to one embodiment of the invention;

Fig. 7

shows an injection device when the multi-piston system is in the position for loading the metal elements according to one embodiment of the invention;

Fig. 8

shows an injection device when the multi-piston system is in the injection position, the molten metal elements being loaded in the liquid state according to one embodiment of the invention.

Fig. 9

shows an injection device when the multi-piston system is in the injection position and comprises a pre-stressed damping system, the molten metal elements being loaded in the liquid state according to one embodiment of the invention.

Fig. 10

represents a 3-point bending curve obtained during mechanical tests to evaluate the elastic limit, σel, and the plastic contribution to the deflection, fp, of amorphous metal alloy samples.

The drawings and the description below contain, for the most part, elements of a certain character. They may therefore not only serve to better understand the present invention, but also contribute to its definition, if necessary.

Here, the term "metallic glass" or "amorphous metal alloy" or "AMA" means metals or metal alloys that are not crystalline, that is to say whose atomic distribution is predominantly random. However, it is difficult to obtain a one hundred percent amorphous metal alloy because there most often remains a fraction of the material that is crystalline in nature. This definition can therefore be generalized to metals or metal alloys that are partially crystalline and which, therefore, contain a fraction of crystals, as long as the amorphous fraction is in the majority compared to the crystalline fraction. The metallic glasses according to the present invention have an amorphous phase fraction greater than 50%, preferably greater than 60%, more preferably still greater than 70% and even greater than 80%.

It is specified here that a metallurgical structure is said to be “completely amorphous” within the meaning of the present invention when an X-ray diffraction analysis as described below does not reveal any crystallization peak. A metallurgical structure is said to be “partially amorphous” within the meaning of the present invention when an X-ray diffraction analysis as described below reveals a few crystallization peaks. Unless otherwise specified, the term “amorphous” is used both for alloys said to be “completely amorphous” and for alloys said to be “partially amorphous” within the meaning of the invention. Such an evaluation of the amorphous nature of a metal alloy is detailed in the article Cheung et al., 2007 (Cheung et al. (2007) “Thermal and mechanical properties of Cu–Zr–Al bulk metallic glasses)” doi:10.1016/j.jallcom.2006.08.109). It allows an average analysis to be carried out on a surface and to avoid the few inevitable metallurgical defects, while only analyzing crystals of significant size, i.e. greater than a few nanometers and/or in significant quantity. Figures in application WO2020/128170 A1 represent an XRD analysis as described above. These figures show the intensity of the diffracted beam as a function of the angle between the incident beam and the diffracted beam. Application WO2020/128170 A1 includes an illustration of an XRD analysis of a metal alloy in the “totally amorphous” state, the amorphous fraction being very much in the majority compared to the crystalline fraction. Application WO2020/128170 A1 includes an illustration of a similar analysis carried out on an alloy in the “partially amorphous” state, the amorphous fraction being in the majority compared to the crystalline fraction. In this figure, we find the characteristic bump of amorphous structures, but with the presence of peaks as well. Application WO2020/128170 A1 also includes an illustration of a similar analysis carried out on a crystalline alloy, the crystalline fraction being in the majority compared to the amorphous fraction. In this last figure, the characteristic bump of AMAs is not present and the crystallinity peaks are clearly visible.

The term "elastic deformation capacity, εe" is here understood to mean the maximum reversible deformation that a material can undergo. Beyond this value, the material will break or plastically deform (irreversible deformation). The elastic deformation is expressed in % and is determined during a bending test. Thus, according to the present description, the elastic limit, σel, and the plastic contribution to the deflection, fp, are evaluated as follows.
Mechanical tests are carried out on a DY34 mechanical testing machine (Adamel Lhomargy). These are 3-point bending tests in the direction of the thickness of the sample.
The test parameters are as follows:
- Length between supports L=10 mm
- Sample width b=10 mm
- Sample thickness h=0.50 mm
- Sample length l=15 mm
- Crosshead speed v=0.005 mm/s
The 3-point bending curve has a first linear elastic part then a plastic plateau, as illustrated in .
The elastic limit, σel, is calculated according to the following formula 1:
[Math. 1]
where Fe is calculated according to the following formula 2:
[Math. 2]
with
- Fmax: the maximum force value recorded at the force plate.
The plastic contribution to the deflection, fp, is calculated according to the following formula 3:
[Math. 3]
with
- fe is the deflection reached at a stress level corresponding to the elastic limit, i.e. 2Fmax/3; and
- fr is the break arrow.
The elastic deformation capacity, ε e, is calculated according to the following formula 4:
[Math. 4]
-

The injection device is specifically adapted to the production of at least one molded part made of amorphous metal alloy. It comprises a mold 1 having at least two injection chambers 3 connected to at least one cavity 2. The device thus makes it possible to produce numerous parts simultaneously and/or to produce large-volume AMA parts that were not previously possible to produce. For the production of large-volume and good-quality parts, at least two injection chambers 3 can be connected to a single cavity 2. In one embodiment, the mold 1 comprises only a single cavity 2, each of the injection chambers 3 therefore being connected to this single cavity 2. This embodiment is illustrated in FIGS. 6 and 7.

The injection device comprises at least one heating means 5 capable of melting metal elements 8. The metal elements 8 are loaded into the injection device in liquid or solid form, preferably the metal elements 8 are loaded in solid form. This preferred embodiment is illustrated in FIGS. 1 and 7.

For the purposes of the present invention, the term “loading of the metal elements 8” or “loaded metal elements 8” into the device means the act of introducing said metal elements 8 into the device so that they can then be injected, via the injection pistons 4 into the injection chambers 3 and the imprint(s) 2 of the mold 1.

Reference is now made to Figures 1 to 3 to illustrate an embodiment of the invention. Thus, the metal elements 8 can be loaded in solid form. The metal elements 8 can thus be in the form of a grain of more or less spherical shape composed of a material capable of forming a metallic glass. In the embodiment of Figures 1 to 3, the injection device corresponds to a vertical injection device. The loading position illustrated in is such that the upper end faces 9 of the pistons are located below the mold 1 and the heating means 5. In this loading position, the metal elements 8 in the solid state are deposited on the upper end face 9 of the injection pistons 4.

The upper end face 9 of the injection pistons 4 comprises a central hollow shape 11 and a peripheral rim 12 capable of preventing the metal elements 8 from falling from the end face 9 of the pistons 4. For example, the central hollow shape 11 may be in the form of a spherical cap, as shown, or in the form of a cone or a bowl with a radial bottom and a frustoconical peripheral wall. The major part of each of the metal elements 8 is located above the end face 9 of an injection piston 4, outside the central hollow shape 11.

According to an alternative embodiment, the loading operation, that is to say the depositing of each of the metal elements 8 on an end face 9 of a piston 4, can be carried out by a manipulator arm.

According to another embodiment, the loading operation can be carried out in the following manner. A containment ring is brought above and at a short distance from the end face 9 of a piston 4, the lower end of an inclined gutter is brought above the space created by the containment ring. A metal element 8 is deposited in an upper part of the gutter. The metal element 8 slides by gravity in the gutter and is introduced into the space created by the containment ring which prevents it from falling, the metal element 8 being placed above the central hollow shape 11. After which, the gutter is removed and the containment ring is removed, without hitting the deposited metal element 8.

As a guide, the volume of a metal element 8 can be approximately one tenth of a milliliter to five milliliters.

After which, the pistons 4 are moved in translation upwards to an intermediate position illustrated in the , in which the metal elements 8 are located in the interior space of the heating means 5, for example inside the turns of an induction heating means 5.

After which, thanks to the action of the heating means 5, the metal elements 8 are heated until they pass into a molten state. Under the effect of the surface tensions, the molten metal elements 8, although in the liquid state, substantially take the form of a sphere, generally flattened, which rests and naturally takes a central position on the central hollow shape 11. The surface of the upper end face 9 of the injection pistons 4 is such that the molten metal element 8, located on each of these surfaces, does not protrude laterally from said end face 9.

After which, the pistons 4 are moved from the intermediate position towards their respective injection chamber 3. According to an alternative embodiment possibly compatible with the previous one, the mold 1 is moved towards the pistons 4.

In doing so, as illustrated in the , each of the molten metal elements 8 is introduced into their own injection chamber 3, without it touching the peripheral wall of said injection chamber 3, the end face 9 of each of the pistons 4 engages in the injection chamber 3 which corresponds to it forming a sliding fit with little play between these two elements.

After which, the translational movement of each of the pistons 4 towards the mold 1 creates a pressure in each of the injection chambers 3 which causes the injection of each of the molten metal elements 8 into the imprint 2 or imprints 2. One or more vents in the mold 1 are optionally provided. In the final injection position, the end face 9 of the piston 4 preferably does not reach the bottom of its injection chamber 3.

It follows from the above that, until the actual injection phase into the imprint(s) 2, the molten metal elements 8 are only in contact locally with the central hollow shape 11 of the piston 4 on which they are placed, without any other contact, and remain at a distance from the wall of the injection chambers 3 until they reach the bottom of their injection chamber 3, so that the metal material does not crystallize.

According to another embodiment illustrated by FIGS. 8 and 9, the metal elements 8 are loaded into the injection device in liquid form. The heating means 5 then makes it possible to melt the metal element(s) 8. The metal alloy in the liquid state is contained in one or more crucibles. According to one embodiment, gutters make it possible to connect the crucible(s) to the upper end face 9 of each of the injection pistons 4 to allow the loading of the metal elements 8. The loading can also be carried out by pouring a given volume of alloy onto the upper end face 9 of each of the injection pistons 4 or by any other equivalent means. The upper end face 9 of the pistons 4 comprises a central hollow shape 11 capable of containing the desired volume of metal element 8 in the liquid state.

For the purposes of this description and regardless of the embodiment, the term “upper end face 9” of the injection pistons 4 means the face of the pistons 4 opposite the injection chamber 3 which corresponds to them.

The device comprises at least one heating means 5 capable of melting the metal elements 8. The heating means 5 is preferably chosen from induction heating, electric arc heating, laser beam heating or electron beam heating. For example, according to an embodiment of the device where the injection is a vertical injection and the metal elements 8 are loaded in the solid state, the heating means 5 is preferably located below the mold 1, constituted for example by induction coils coaxial with each of the pistons 4, wound for example in a cylinder or a truncated cone. According to this embodiment, the metal elements 8 can be melted quickly and homogeneously, knowing that the majority of these elements 8 can be located directly in the space heated by the heating means 5. Indeed, as indicated previously, only the lower faces of the metal elements 8 bear on the surface of the upper end face 9 of each of the pistons 4. Under the effect of surface tensions, the molten metal elements 8, although in the liquid state, substantially take the shape of a sphere, generally flattened and do not protrude laterally from said end face 9.

The device may further comprise a means for heating and/or cooling at least a portion of each of the pistons 4, this portion being closest to their upper end face 9.

Advantageously, the mold 1 is equipped with controlled heating and/or cooling means (not shown) so that the material constituting the AMA molded part obtained in the imprint(s) 2 does not crystallize and that after extraction, said part has the characteristics of a metallic glass, that is to say the characteristics of an amorphous or at least partially amorphous or predominantly amorphous metal or metal alloy.

Advantageously, the injection device comprises ejectors 14 in order to be able to easily remove the molded and cooled parts at the end of the injection process. The ejectors 1' can for example be pistons and/or pressurized air nozzles.

The device comprises a multi-piston system 6. The simultaneous injection of metal elements 8 in volume fusion capable of forming one or more good quality AMA molded parts seemed until now an excellent technical solution for increasing the productivity of injection processes and/or for imagining producing larger volume AMA molded parts while maintaining excellent quality of amorphization of the alloy but also seemed unrealistic to adapt to an injection device. Indeed, piston actuators are complex and bulky systems and the present inventors have found that their simultaneous operation was difficult to achieve. This difficulty is even greater in particular in the case where the device comprises only one large volume imprint. In addition, this involves the use of multiple actuators, generates an extremely complex actuator management system and a very high financial cost. A multi-piston system 6 is therefore proposed comprising at least two injection pistons 4 whose respective main axes are each aligned with the main axis of their corresponding injection chamber 3 and a support 7 cooperating with each of the injection pistons 4. The support 7 and/or the mold 1 are thus able to move along an axis parallel to the main axes of the injection pistons 4 using a single actuator 13 moving the support 7 or the mold 1 or two actuators 13 only able to move simultaneously or separately one the support 7 and the other the mold 1 so as to allow the operation of the injection device (loading, optionally melting of the metal elements, concomitant injection of the different metal elements 8 into the injection chambers 3).

Such a multi-piston system 6 makes it possible to solve the problems of the prior art. It can in fact be actuated by a single actuator 13 thus allowing the relative movement of the support 7, and therefore of the injection pistons 4 simultaneously, and of the mold 1 along an axis parallel to the main axes of the injection pistons 4. In an alternative embodiment, the actuator 13 can be positioned at the mold 1 so as to allow the relative movement of the mold 1 and the support 7, and therefore of the injection pistons 4 simultaneously, along an axis parallel to the main axes of the injection pistons 4. In yet another alternative but with the same objective, an actuator 13 can be positioned at the mold 1 and a second at the support 7. The actuator 13 can be any translational drive means such as, in particular, a jack, a screw-nut system or a ball screw system.

According to an advantageous embodiment, illustrated in FIGS. 4 and 5, each injection piston 4 of the device comprises a pre-stressed damping system 10 capable of exerting, when the injection piston 4 is in the injection position, a force on the molten metal element 8 corresponding to said injection piston 4 ( ). This effort, included in a determined effort range, can thus be different from that of the other injection piston(s) 4.

Such a pre-stressed damping system 10 makes it possible to ensure that, in all cases, a minimum pressure (set by the user with the pre-stress) will be applied to the molten metal elements 14 in each of the injection chambers 3. Indeed, a height difference, even small (dimensional tolerances) of the pistons 4 between them or of the injection chambers 3, of the mass of the different metal elements 8 and/or of any other element of said device can cause an imprint 2 of the mold 1 to fill before the others. In the absence of a damping system 10, the other pistons 4, cooperating with the other imprints 2 not completely filled, can then find themselves blocked and said imprints 2 will then remain partially filled. The activation of at least one of the pre-stressed damping systems 10 then makes it possible to generate a relative movement of the piston associated with this system with respect to the others. The other pistons 4 can thus continue their stroke until their cavity is completely filled. Similarly, in the case of an cavity 2 connected to at least two injection chambers 3, the damping systems 10 make it possible to apply a minimum pressure to the alloy in each of the injection chambers 3 and to ensure uniform pressurization of the alloy in the cavity 2. Advantageously, the prestresses of the damping systems 10 are defined so as to generate a pressure on the alloy during injection greater than 5 MPa, preferably between 5 MPa and 300 MPa, even more preferably between 10 MPa and 250 MPa.

The pre-stressed damping system 10 is advantageously chosen from: mechanical springs (helical spring type, spring washers), a system using a pressurized gas (gas cylinder) and a system using a pressurized fluid (hydraulic cylinder).

Although the embodiments illustrated in this document correspond to vertical injection devices, the invention is not limited to this single injection mode. Thus, the injection direction can be vertical and the injection direction from bottom to top or from top to bottom, horizontal or even inclined at an angle between 0 and 90 degrees relative to the vertical. Preferably, the injection direction is vertical and, even more preferably, the injection direction is vertical and the injection direction from bottom to top.

Reference is now made to the . There illustrates an injection device comprising a single cavity 2. Different injection chambers 3 are connected to a single cavity 2 so as to be able to produce a large-volume, high-quality AMA part. Simultaneous injection was not possible industrially until now. Indeed, the simultaneous management of translation means of the different injection pistons 4 and/or the mold 1 is extremely complex and these different translation means are too bulky to allow easy assembly on an industrial injection device. The present inventors have however developed a multi-piston system 6 comprising a support 7 on which the injection pistons 4 are mounted. The relative translation of the mold 1 and the multi-piston system 6 can thus be carried out by a single actuator 13. In an alternative embodiment, several actuators 13 may be included in the device, for example one for translating the mold 1 and the other for translating the multi-piston system 6. In an embodiment compatible with the previous one, there may be several multi-piston systems 6, each being translated by its own actuator 13.

Reference is now made to the . There illustrates an injection device when the multi-piston system 6 is in the loading position of the metal elements 8 according to an embodiment of the invention. The mold 1 (and this regardless of the embodiment of the invention) is made up of at least two parts that can be separated from each other along a plane intersecting each of the cavities 2 so as to allow the demolding of the AMA molded parts. The loading of the metal elements 8, in the solid or liquid state, can be carried out in a position where the upper end face 9 of the pistons 4 is located in a space located between the different parts of the mold 1 when the latter is in the open position, that is to say that these different parts are separated so as to allow the demolding and/or loading of the metal elements 8. Such an embodiment makes it possible in particular to have the possibility of carrying out the depositing of the metal elements 8 on the pistons 4 just after or at the same time as the molded parts are ejected and recovered. The part recovery system can in fact be the same as that used to remove the metal elements 8 (with a robotic arm for example).

Reference is now made to the . There illustrates an injection device in which the metal elements 8 are loaded in the liquid state, therefore in fusion. The device shown corresponds to a vertical injection device but any other injection orientation can also be envisaged.

According to the , the metal elements 8 can be melted in a crucible using a heating means 5, both not shown. The resulting molten metal alloy can be brought into a hollow shape 12 of the end face 9 of the injection pistons 4 by any suitable means, for example using chutes extending from the crucible to each of the end faces 9 of the pistons 4. According to the embodiment shown, an actuator 13 makes it possible to move the multi-piston system 6 along a longitudinal axis parallel to the direction of the pistons 4. The multi-piston system 6 can thus be translated vertically in order to inject the molten alloy into the injection chambers 3.

The embodiment of the device shown in Figures 8 and 9 comprises a pre-stressed damping system 10 at the base of each injection piston 4. The pre-stressed damping system 10 makes it possible to ensure a minimum pressure applied to the molten metal elements 14 in each of the injection chambers 3. Figures 8 illustrate a height difference between the pistons 4. As shown in , the damping system 10 allows a complete filling of each of the impressions 2 even in the case of a difference in height of the pistons 4 whatever the reason.

The invention also relates to an injection method for the production of at least one molded part made of amorphous metal alloy, comprising the steps:
- loading metal elements 8 into the device described above, the metal elements 8 being loaded in solid form or in a molten state;
- optionally, melt the metallic elements 8 introduced in solid form;
- relatively moving the support 7 and the mold 1 along an axis parallel to the main axes of the injection pistons 4 in order to inject substantially simultaneously, via the injection pistons 4, the molten metal elements 8 into the imprint 2 or imprints 2 of the device to obtain, after cooling, at least one molded part made of amorphous metal alloy.

“Substantially simultaneously” means that the metal elements 8, due to their possible volume differences and/or share of pressure differences within the injection chambers 3, height of the pistons 4 between them, and/or possible geometry defects of the pistons 4, the injection chambers 3 and/or any other element of the device, can be injected concomitantly to within a few milliseconds or microseconds.

AMAs are alloys whose metallurgical quality can be difficult to control. Thus, according to a preferred embodiment of the invention, compatible with the previous embodiments, the device is configured so that the steps where the metal elements are melting, such as the actual melting, the possible transport of the molten elements for example in chutes, their injection, are carried out under a controlled atmosphere. This may be a high vacuum, in particular a vacuum of less than 1.10 ^-1 mbar, preferably less than 1.10 ^-2 mbar, more preferably less than 5.10 ^-3 mbar and even more preferably less than 1.10 ^-3 mbar. It may also be a neutral gas atmosphere, for example an argon or nitrogen atmosphere, the pressure then being able to be lower or higher than atmospheric pressure.

To improve production rates or manufacture larger volume parts, an approach consisting of increasing the volumes/masses of the metal element injected by the piston is conventionally used in conventional foundry/casting, i.e. in the field of crystalline materials. Unlike this conventional approach, the previous device and the present method propose a multiplication and parallel operation of the injection pistons. The same volume of alloy to be injected can thus be divided into several smaller volume metal elements. The melting cycle can thus be carried out on several small volume/small mass metal elements (for example less than 200 g, preferably less than 100 g, more preferably less than 75 g and even more preferably less than 50 g) instead of a larger one. Thus, the melting temperatures are better controlled and this also ensures good homogenization of the weld pool. Indeed, controlling the melting quality of the alloy elements makes it possible to guarantee a level of metallurgical quality and to have a more homogeneous viscosity during molding, thus improving the filling and the repeatability of the injection process.

The pressure injection of AMA also ideally requires management of "cold spots" which are the contact areas of the molten alloy with the various elements of the device, in particular the piston(s). At these "cold spots", part of the heat supplied to melt the AMA is dissipated. Control of the melting cycle in these areas can therefore hardly be guaranteed. Managing a small volume of alloy allows better control of these "cold spots" as well as thermal gradients in the AMA.

According to a preferred embodiment, the device is a vertical injection device. Thus, the joint use of a multi-piston system for simultaneously injecting small volumes of molten AMA and a vertical injection device, for example such as that described in application WO2018/224418 A1, makes it possible to limit "cold spots", thus guaranteeing the quality of molded parts. Such an embodiment also makes it possible to avoid potential chemical interactions which could then lead to pollution of the metal elements and/or rapid deterioration of the elements of the device (thermal is indeed more difficult to manage with higher alloy volumes per cycle or an increased process rate).

The invention may find application in particular in the field of industrial devices for manufacturing molded AMA parts. Such an invention makes it possible to produce molded AMA parts at high speed and/or in larger volumes than was previously possible using a single injection piston.

The invention is not limited to the embodiments described above, only as an example, but it encompasses all the variants that a person skilled in the art may envisage within the framework of the protection sought.

List of reference signs
- 1: mold
- 2: footprint
- 3: injection chamber
- 4: injection piston
- 5: heating means
- 6: multi-piston system
- 7: support (of the injection pistons)
- 8: metallic element
- 9: end face (of an injection piston)
- 10: pre-stressed damping system (of an injection piston)
- 11: central hollow shape of the end face 9
- 12: peripheral edge of the end face 9
- 13: actuator (of the injection pistons and/or the mold)
- 14: ejector
- 15: main axis of a piston and its corresponding injection chamber

Claims (7)

Injection device for the production of at least one molded part made of amorphous metal alloy, comprising:
- a mold (1) having at least two injection chambers (3) connected to at least one imprint (2); and
- at least one heating means (5) capable of melting metal elements (8);
- a multi-piston system (6) comprising:
- at least two injection pistons (4) whose respective main axes are each aligned with that of their corresponding injection chamber (3) and
- a support (7) cooperating with each of the injection pistons (4); and
such that the support (7) and/or the mold (1) are able to move along an axis parallel to the main axes of the injection pistons (4) so as to allow:
i. loading of metal elements (8); and
ii. optionally, melting said metallic elements (8); and
iii. injection of the molten metal elements (8) into the injection chambers (3). Injection device according to claim 1 such that each injection piston (4) comprises a pre-stressed damping system (10) capable of exerting, when the injection piston (4) is in the injection position, pressure on the molten metal element (8) corresponding to said injection piston (4), this force, included in a determined force range, possibly being different from that of the other injection piston(s) (4). Injection device according to claim 2 such that the pre-stressed damping system (10) is chosen from: mechanical springs, a system using a pressurized gas and a system using a pressurized fluid. Injection device according to any one of the preceding claims such that the heating means (5) is chosen from: induction heating, electric arc heating, laser beam heating, electron beam heating. Injection device according to any one of the preceding claims such that the injection direction is:
- vertical and the injection direction from bottom to top or from top to bottom,
- horizontal,
- inclined at an angle between 0 and 90 degrees from the vertical,
preferably the injection direction is vertical and even more preferably the injection direction is vertical and the injection direction from bottom to top. Injection device according to any one of the preceding claims such that the mold (1) comprises only a single imprint (2). Injection process for the production of at least one casting made of an amorphous metal alloy, comprising the steps:
- loading metal elements (8) into the device according to any one of claims 1 to 7, the metal elements (8) being loaded in solid form or in a molten state;
- optionally, melt the metallic elements introduced in solid form;
- relatively moving the support (7) and the mold (1) along an axis parallel to the main axes of the injection pistons (4) in order to inject substantially simultaneously, via the injection pistons (4), the molten metal elements into the imprint (2) or imprints (2) of the device to obtain, after cooling, at least one molded part made of amorphous metal alloy.