INJECTION DEVICE FOR AMORPHOUS METALLIC ALLOY

Description

TECHNICAL FIELD

The present invention relates to the field of production by press molding of parts made of amorphous metallic alloy.

PRIOR ART

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

Limited for a long time by manufacturing methods inducing geometries not very inclined to industrialization, AMA parts may now be obtained industrially via in particular methods for molding a metallic alloy capable of forming a metallic glass. Such methods consist first of all in filling a cavity of a mold with a previously molten metallic alloy. The alloy thus molded is then cooled sufficiently quickly to obtain a part with the shape of the cavity, 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 press molding.

A “press molding method” is a method in which a pressure is applied to the molten alloy during the step of filling the cavity. The pressure is exerted in order to ensure optimum filling of the cavity and to “compact” the alloy in the latter. This pressure is generally exerted by a mechanical action, for example using a piston, and can be reinforced by the joint action of a depression or of an overpressure of the atmosphere within the mold or other mechanical system such as, for example, a movable insert in the mold.

The present invention relates more particularly to the press molding of AMA parts, generally considered to be the most suitable method for industrialization. It is indeed known that such a method 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 an excellent quality of the produced AMA parts, the quantity of alloy molten and then injected must be limited and the cycle times of the method generally greater than one minute. The limitation of injectable volume and the 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 press molding method for the manufacture of good quality AMA parts, possibly in larger volumes, said method also having a high productivity. The increase in productivity of the method must however not impact the quality of the parts compared to a method with lower productivity because it requires working at smaller volumes.

SUMMARY OF THE INVENTION

An injection device is therefore proposed for the production of at least one molded part made of amorphous metallic alloy, comprising:

• • a mold 1 having at least two injection chambers 3 connected to at least one cavity 2; and
  • at least one heating means 5 capable of melting metallic 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 capable of moving along an axis parallel to the main axes of the injection pistons 4 so as to allow:
  • i. the loading of the metallic elements 8; and
  • ii. optionally, the melting of said metallic elements 8; and
  • iii. the injection of the molten metallic elements 8 into the injection chambers 3.

According to one possibility, the invention proposes an injection device for the production of at least one molded part made of amorphous metallic alloy, comprising:

• • a mold having at least two injection chambers connected to at least one cavity; and
  • at least one heating means capable of melting metallic elements;
  • a multi-piston system comprising:
  • at least two injection pistons whose respective main axes are each aligned with that of their corresponding injection chamber and
  • a support cooperating with each of the injection pistons;
  • 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:
  • i. the loading of metallic elements; and
  • ii. optionally, the melting of said metallic elements; and
  • ii. the injection of the molten metallic elements into the injection chambers, and
  • a single actuator configured to cooperate with the support or with the mold so as to cause the relative displacement of the mold and of the support along the axis parallel to the main axes of the injection pistons.

The relative translation of the mold and of the various pistons mounted on the multi-piston system is thus performed by a single actuator.

This makes possible the translation of the at least two pistons concomitantly along their respective main axes thanks to the action of one single actuator when it acts on the support.

According to another aspect, an injection method is proposed for the production of at least one molded part made of amorphous metallic alloy, comprising the steps of:

• • loading metallic elements 8 into the device described above, the metallic elements 8 being loaded in solid form or in a molten state;
  • optionally, melting 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, through the injection pistons 4, the molten metallic elements into the cavity 2 or the cavities 2 of the device to obtain, after cooling, at least one molded part made of amorphous metallic alloy.

The characteristic disclosed 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 possibility, the single actuator is configured to be positioned at the mold so as to allow relative displacement of the mold and of the support.

According to one variant, the single actuator is configured to be positioned at the support so as to allow the relative displacement of the mold and of the support. This allows the translation of the at least two pistons concomitantly along their respective main axes thanks to the action of one single actuator on the support.

According to one possibility, the single actuator is a translational drive means, in particular a cylinder, a screw-nut system or even a ball screw system.

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, a pressure on the molten metallic 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 possibility, each pre-stressed damping system is disposed between the support and the respective injection piston. This makes it possible to limit the pressure peaks inside the mold, created by the kinetic energy due to the speed of the injection and of the pressure used when filling the at least one cavity. This configuration in fact makes it possible to reduce the mass between the metallic element and the pre-stressed damping system.

According to one arrangement, each pre-stressed damping system is disposed at the base of the respective injection piston.

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 sense of injection from bottom to top or from top to bottom,
  • horizontal,
  • inclined at an angle comprised 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 sense of injection from bottom to top.

According to one possibility, each injection piston comprises an upper end face having a surface configured so that the molten metallic element located on the surface does not protrude laterally from said end face. Thus, each of the molten metallic elements is introduced into their own injection chamber, without touching the peripheral wall of said injection chamber. This makes it possible to avoid the cooling of the metallic element in contact with the injection chamber and to block the injection piston.

According to one arrangement, each injection piston comprises an upper end face having a hollow shape and a peripheral rim capable of preventing metallic elements from falling from the end face of the pistons, in particular metallic elements loaded into the injection device in liquid or solid form, preferably the metallic elements are loaded in solid form.

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

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

Technical Solution

The invention and the variants thereof can make it possible, in general, to propose an injection device for the simultaneous production of a large quantity of AMA molded parts of excellent quality, suitable for industrial rate production, and/or for the production of at least one large volume AMA molded part.

Simultaneous injection of small volumes of molten alloy into one or several cavities seems to be a clever solution to solve the problems of the prior art. However, such simultaneous work involves a number of technical problems to overcome. Firstly, the simultaneous management of means for translating the different injection pistons and/or the mould is extremely complex and these different translation means are too bulky to allow easy mounting on an industrial injection device.

The present inventors have thus developed an injection device for the industrial production of AMA molded parts making it possible to manage the injection parameters as finely as the devices of the prior art such as that disclosed for example in document WO2018/224418 A1. The cited device of the prior art allowed the production of molded parts in good quality but with a lower rate and/or a limited volume.

Thus, to solve these problems, the present inventors have discovered that it is possible to carry out an injection of molten metallic alloy thanks to a multi-piston system comprising a support on which at least two injection pistons are mounted. The relative translation of the mold and of the different pistons mounted on the multi-piston system is thus performed by a single actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

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 metallic elements according to one embodiment of the invention;

FIG. 2 shows an injection device when the multi-piston system is in position for melting the metallic 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 metallic 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 metallic 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 metallic elements, according to one embodiment of the invention;

FIG. 6 shows an injection device comprising a single cavity 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 metallic 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 metallic 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 metallic 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 allowing to evaluate the elastic limit, σel, and the plastic contribution to deflection, fp, of the samples made of amorphous metallic alloy.

DESCRIPTION OF THE EMBODIMENTS

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 metallic alloy” or “AMA” means metals or metallic 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 metallic 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 metallic 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 metallic 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 done on a surface and to avoid the few inevitable metallurgical defects, while only analyzing crystals of significant size, that is to say 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 comprises an illustration of an XRD analysis of a metallic alloy in the “totally amorphous” state, the amorphous fraction being very much in the majority compared to the crystalline fraction. Application WO2020/128170 A1 comprises 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 the amorphous structures, but with the presence of peaks as well. Application WO2020/128170 A1 also comprises 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” means 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, gel, and the plastic contribution to deflection, fp, are evaluated as follows.

The 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 FIG. 10.

The elastic limit, σel, is calculated according to the following formula 1:

σ ⁢ el = 3 × Fe × L 2 × b × h 2 [ Math . 1 ]

• • where Fe is calculated according to the following formula 2:

Fe = 2 ⁢ F ⁢ max 3 [ Math . 2 ]

• • with
    • Fmax: the maximum force value recorded at the force plate.

The plastic contribution to deflection, fp, is calculated according to the following formula 3:

fp = fr - fe [ 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 deflection at break.

The elastic deformation capacity, εe, is calculated according to the following formula 4:

ε ⁢ e = ( 6 × Fe × h ) L 2 - [ Math . 4 ]

The injection device is specifically adapted to the production of at least one molded part made of amorphous metallic 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 it was not possible to produce until now. 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 metallic elements 8. The metallic elements 8 are loaded into the injection device in liquid or solid form, preferably the metallic 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 metallic elements 8” or “metallic elements 8 loaded” into the device means the act of introducing said metallic elements 8 into the device so that they can then be injected, via the injection pistons 4 into the injection chambers 3 and the cavity 2 or the cavities 2 of the mold 1.

Reference is now made to FIGS. 1 to 3 to illustrate one embodiment of the invention. Thus, the metallic elements 8 can be loaded in solid form. The metallic 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 FIGS. 1 to 3, the injection device corresponds to a vertical injection device. The loading position illustrated in FIG. 1 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 metallic 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 metallic 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 represented, 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 metallic elements 8 is located above the end face 9 of an injection piston 4, outside the central hollow shape 11.

According to one variant, the operation of loading, that is to say of depositing each of the metallic 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 metallic element 8 is deposited in an upper portion of the gutter. The metallic 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 metallic element 8 being placed above the central hollow shape 11. After which, the gutter is removed and the containment ring is removed, without striking the deposited metallic element 8.

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

After which, the pistons 4 are moved in translation upwards to an intermediate position illustrated in FIG. 2, in which the metallic 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 metallic elements 8 are heated until they pass into a molten state. Under the effect of the surface tensions, the molten metallic elements 8, although in the liquid state, substantially take the shape 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 metallic 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 FIG. 3, each of the molten metallic 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 clearance 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 metallic elements 8 into the cavity 2 or the cavities 2. One or several 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 cavity 2 or the cavities 2, the molten metallic 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 metallic material does not crystallize.

According to another embodiment illustrated by FIGS. 8 and 9, the metallic elements 8 are loaded into the injection device in liquid form. The heating means 5 then makes it possible to melt the metallic element(s) 8. The metallic alloy in the liquid state is contained in one or several 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 metallic elements 8. The loading can also be performed 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 metallic element 8 in the liquid state.

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

The device comprises at least one heating means 5 capable of melting the metallic elements 8. The heating means 5 is preferably chosen from induction heating, electric arc heating, laser beam heating or electron beam heating. As an example, according to an embodiment of the device where the injection is a vertical injection and the metallic 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 metallic elements 8 can be molten 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 metallic elements 8 bear on the surface of the upper end face 9 of each of the pistons 4. Under the effect of the surface tensions, the molten metallic 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 one part of each of the pistons 4, this part being closest to their upper end face 9.

Advantageously, the mold 1 is equipped with controlled heating and/or cooling means (not represented) so that the material constituting the AMA molded part obtained in the cavity 2 or the cavities 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 metallic alloy or metal.

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 method. 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 metallic elements 8 in volume fusion capable of forming one or several good quality AMA molded parts seemed until now to be an excellent technical solution for increasing the productivity of injection methods 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, the 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 cavity. 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 the metallic elements, concomitant injection of the different metallic 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 displacement 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 one variant, the actuator 13 can be positioned at the mold 1 so as to allow the relative displacement of the mold 1 and of 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 variant 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 cylinder, 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 metallic element 8 corresponding to said injection piston 4 (FIG. 5). This force, included in a determined force 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 metallic 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 metallic elements 8 and/or of any other element of said device can cause a cavity 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 cavities 2 not completely filled, can then find themselves blocked and said cavities 2 will then remain partially filled. The activation of at least one of the pre-stressed damping systems 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 10 thus continue their stroke until their cavity is completely filled. In the same way, in the case of a 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 comprised 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 (spring washers, helical spring type), a system using a pressurized gas (gas cylinder) and a system using a pressurized fluid (hydraulic cylinder).

Although the embodiments illustrated in the present 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 sense of injection from bottom to top or from top to bottom, horizontal or even inclined at an angle comprised 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 sense of injection from bottom to top.

Reference is now made to FIG. 6. FIG. 6 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 previously possible industrially. Indeed, the simultaneous management of translation means of the different injection pistons 4 and/or of the mold 1 is extremely complex and these different translation means are too bulky to allow easy mounting 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 of the multi-piston system 6 can thus be performed 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 FIG. 7. FIG. 7 illustrates an injection device when the multi-piston system 6 is in the position for loading the metallic elements 8 according to one embodiment of the invention. The mold 1 (and this regardless of the embodiment of the invention) is made up of at least two portions 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 metallic elements 8, in the solid or liquid state, can be performed in a position where the upper end face 9 of the pistons 4 is located in a space located between the different portions of the mold 1 when the latter is in the open position, that is to say that these different portions are separated so as to allow the demolding and/or loading of the metallic elements 8. Such an embodiment makes it possible in particular to have the possibility of carrying out the depositing of the metallic elements 8 on the pistons 4 just after or at the same time as the molded parts are ejected and recovered. The system for recovering the parts can in fact be the same as that carrying out the depositing of the metallic elements 8 (with a robotic arm for example).

Reference is now made to FIG. 8. FIG. 8 illustrates an injection device into which the metallic elements 8 are loaded in the liquid state, therefore molten. The represented device corresponds to a vertical injection device but any other injection orientation can also be envisaged.

According to FIG. 8, the metallic elements 8 can be molten in a crucible using a heating means 5, both not represented. The resulting molten metallic 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 represented embodiment, 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 represented in FIGS. 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 metallic elements 14 in each of the injection chambers 3. FIG. 8 illustrate a height difference between the pistons 4. As represented in FIG. 9, the damping system 10 allows complete filling of each of the cavities 2 even in the case of a height difference between 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 metallic alloy, comprising the steps of:

• • loading metallic elements 8 into the device described above, the metallic elements 8 being loaded in solid form or in a molten state;
  • optionally, melting 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, through the injection pistons 4, the molten metallic elements 8 into the cavity 2 or the cavities 2 of the device in order to obtain, after cooling, at least one molded part made of amorphous metallic alloy.

The term “substantially simultaneously” means that the metallic elements 8, due to their possible volume differences and/or share of the differences of pressure 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 metallic 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 metallic element injected by the piston is conventionally used in conventional foundry/molding, that is to say 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 metallic elements. The melting cycle can thus be carried out on several small volume/small mass metallic 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 molten pool. Indeed, control the melt quality of the alloy elements thus makes it possible to guarantee a level of metallurgical quality and to have a more homogeneous viscosity during molding, thus improving the filling and repeatability of the injection method.

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 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 of 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 metallic 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 method rate).

INDUSTRIAL APPLICATION

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 rate 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 sought protection.

LIST OF THE REFERENCE SIGNS

• • 1: mold
  • 2: cavity
  • 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 rim of the end face 9
  • 13: actuator (of the injection pistons and/or of the mold)
  • 14: ejector
  • 15: main axis of a piston and its corresponding injection chamber