EP3700695A1

EP3700695A1 - Method and device for moulding, in particular a metallic glass

Info

Publication number: EP3700695A1
Application number: EP18789433.2A
Authority: EP
Inventors: José FEIGENBLUM
Original assignee: RocTool SA
Current assignee: RocTool SA
Priority date: 2017-10-25
Filing date: 2018-10-25
Publication date: 2020-09-02
Anticipated expiration: 2038-10-25
Also published as: FR3072768A1; WO2019081687A1; CN111372705A; EP3700695B1; FR3072768B1; US20210187602A1; TWI787369B; CN111372705B; TW201923110A

Abstract

The invention relates to a device for producing a part by moulding a BMG, comprising: a. a mould comprising two shells defining a sealed moulding cavity; b. a device for melting the BMG comprising: bi. a vertically disposed sectorised cold crucible, called melting crucible, comprising hollow sectors formed by an electrically conductive and non-magnetic material electrically isolated from one another; bii. an inductor in the form of a coil surrounding said melting crucible in order to heat the content thereof; biii. a means for generating ultrahigh frequency current for powering the inductor, characterised in that it comprises a sectorised piston comprising hollow sectors formed by an electrically conductive and non-magnetic material electrically isolated from one another, closing the melting crucible at one of the ends thereof.

Description

METHOD AND DEVICE FOR MOLDING IN PARTICULAR A GLASS

METALLIC

The invention relates to a method and a device for molding, in particular a metallic glass. The invention is more particularly, but not exclusively, adapted to the manufacture of shells for electronic equipment, more particularly for smart phones.

Indeed, the metallic glasses, being in the form of an amorphous metal, not crystallized or partially crystallized, which due to the absence of grain boundaries in the metal structure, have characteristics of hardness, elasticity and corrosion resistance, which makes them particularly effective for this type of application and make it unnecessary protective shells in which consumers wrap their smart phone to protect it from shocks, scratches and make it waterproof.

According to the techniques of the prior art, such shells are obtained from a sheet of an amorphous metal alloy, which is shaped by a blow molding process, similar to glass forming processes, in a die in the form of said shell after heating said sheet to a relatively low temperature compared to the temperature that would be necessary to achieve with the same crystallized metal alloy to obtain equivalent forming.

According to another embodiment, the methods of the prior art, use a vacuum molding technique of a bulk metal glass alloy ("Bulk Metallic Glass" or BMG). The use of a BMG makes it possible to reduce the critical cooling speed allowing the solidification of the material into an amorphous material. To ensure a low level of crystallinity or a high rate of amorphization, the material must be molded under conditions that avoid contamination by impurities, including nitrogen and oxygen. For this purpose, the melting and casting operations are carried out under vacuum or in a neutral atmosphere. The material is melted in a crucible by means of induction heating and then injected into the mold. The techniques of the prior art use either a crucible made of a material transparent to the magnetic field, such as a hollow zirconia, or a cold sectorized copper crucible.

A channel, generally called an injection or casting crucible, makes it possible to place the melting crucible content in communication with the mold cavity while keeping the assembly under vacuum. The communication between the melting crucible and the injection crucible must be closed during the melting operation, and then opened to allow casting, which is achieved by movable closing means, such as a hatch, a piston or a moving finger. When the melting crucible is placed vertically, for example above the mold, and the gravity tends to bring the molten charge of the movable closing means, they must be cooled, in particular not to damage the means ensuring the seal between said movable closure means and the injection crucible, the molten charge is cooled in contact with the movable closing means and during each casting, there remains a wolf of material on the surface thereof, which is likely to interfere with the operation of the device and must be eliminated.

The ceramic crucible also has the disadvantage of reacting with certain alloys.

The sectorized cold crucible makes it possible to move the melting charge away from the walls of the crucible by the magnetic forces of Laplace, but does not solve the problem of the creation of a wolf. Thus, according to the prior art, said crucible is placed horizontally, and the forces of Lapace compensate gravity, the load being levitated or pseudo-levitation inside the tube constituted by the crucible. The injection of the material into the mold involves the use of a cooled piston, moving in the crucible and pushing the charge into the molding cavity. Alternatively, the crucible is placed vertically and is closed by a removable and cooled hearth, constituting a trap between the melting crucible and the mold. In these embodiments of the prior art the molten material is cooled in contact with the piston or the hatch and there is also a wolf (skull) material in contact with them, which must be removed periodically, or even when of each casting.

JPH 0917421 discloses a crucible and mold suitable for shell molding an aluminum alloy, comprising a crucible disposed horizontally, and wherein a material previously melt is spilled.

Document US2015 / 298296 discloses a device and a method for molding a BMG comprising a melting crucible made of a material transparent to magnetic fields, said BMG being injected into the mold by means of a piston cooled.

US 5156 202 discloses a sectorized mold which is closed in its lower part by a sectorized plate and cooled, comprising an opening in its center. A molten metal is introduced through the upper part of the closed mold in its lower part by the sectorized plate. A piston pushes the material against the walls of the mold and the sectorized plate in contact with which it cools. The mold is surrounded by a coil powered by high frequency alternating current.

WO2013 / 190020 discloses a mold comprising induction heating means and cooling means.

Document US2002 / 122456 discloses a melting furnace comprising a sectorized crucible surrounded by an induction coil.

The invention aims to solve the disadvantages of the prior art and concerns for this purpose a device for producing a part by molding a BMG, which dispositiif comprises:

at. a mold comprising two shells delimiting a sealed molding cavity;

b. a BMG melting device comprising:

bi. a sectorized cold crucible, said melting crucible, arranged vertically comprising hollow sectors consisting of an electrically conductive and non-magnetic material electrically insulated from each other;

bii. an inductor in the form of a coil surrounding said melting crucible for heating its contents;

biii. very high frequency current generating means for supplying the inductor;

which device comprises a sectorized piston comprising hollow sectors consisting of an electrically conductive and non-magnetic material isolated electrically from each other, closing the melting crucible at one end thereof;

d. means for communicating the contents of the melting crucible with the molding cavity and performing the casting of the BMG.

Thus, the vertical arrangement of the melting crucible with respect to the mold facilitates the automation of the casting process by making it possible to take advantage of the gravity in the implementation of several operations. The sectorized crucible makes it possible to keep the molten material away from the walls of the crucible and thus to prevent any contamination thereof, whereas the use of a sectorized piston makes it possible to put the charge in fusion in levitation or pseudo-levitation. relative to said piston by the Laplace force components of the magnetic field created by the circulation of currents induced on the sectors of said piston. Since the molten charge is not in contact with the melting crucible or with the piston during melting and casting, the device that is the subject of the invention makes it possible to use BMG comprising reactive components such as titanium or zirconium may interact with a crucible made of refractory material. The load does not cool in contact with the piston and does not create a wolf.

The invention is advantageously implemented according to the embodiments and variants described below, which are to be considered individually or in any technically operative combination.

Advantageously, the means for communicating the contents of the melting crucible with the molding cavity comprise a device for vertical displacement of the piston. Thus, because of the vertical arrangement of the melting crucible with respect to the mold, said piston allows the casting to be carried out by gravity or by injection, always without contact of the piston with the molten charge.

Thus, according to a first embodiment, the melting crucible is placed above the molding cavity and the piston moves downwards. And according to a second embodiment the melting crucible is placed below the molding cavity and the piston moves upwards.

Advantageously, the device of the invention comprises a channel, said injection crucible between the melting crucible and the molding cavity. This embodiment makes it possible to place the fusion device on the outside of the shells. passing through the shell of the melting device to the cavity being formed by the injection crucible.

Advantageously, the device of the invention comprises a coil surrounding the injection crucible and supplied with high frequency current. The induction effect produced by this coil makes it possible to keep the filler in temperature until it enters the molding cavity and to move said melt load away from the walls of the injection crucible.

Advantageously, the device according to an embodiment of the invention comprises, according to an embodiment compatible with the preceding, an injection coil and means for its electrical supply, capable of producing an electromagnetic force for the injection of the molten material contained therein. in the melting crucible in the molding cavity. This embodiment allows Laplace forces to be used by said coil to inject molten material into the mold without contact with said material at the time of injection.

According to a first variant, the injection coil is a flat coil fed by a capacitor discharge. This embodiment uses a configuration similar to what is used in magnetoforming to apply a force to the molten material directing it to the molding cavity.

According to a second variant, compatible with the first, the injection coil comprises a nested coil in the coil forming the fusion coil, said injection coil being powered by a high frequency alternating current out of phase with the alternating current supplying the coil. fusion coil so as to create a slippery field. Thus the combined action of the coil forming the melting inductor and said injection coil creates a sliding field promoting the injection of the material into the molding cavity.

Advantageously, the sectors of the melting crucible and the piston are made of stainless steel, thus providing a greater durability than copper, generally used for this purpose and also allowing to lighten the piston for a faster movement thereof during the casting process.

Advantageously, the mold comprises a heating means by induction of the molding cavity. Said heating means makes it possible to rapidly bring the molding cavity to a suitable temperature at the moment of casting, in order to promote the filling of said cavity.

Advantageously, the mold of the device which is the subject of the invention furthermore comprises means for cooling the molding cavity. Thus, the cycle times are reduced.

The invention also relates to a method implementing any of the embodiments of the device according to the invention, for molding a part from a BMG and comprising the steps of:

i. charge of crucible;

ii. close the mold and pull the molding cavity to vacuum;

iii. carry the charge in fusion;

iv. preheating the mold by means of the induction circuit of the mold; v. perform the casting by moving the sectorized piston;

vi. cooling the mold by the circulation of a coolant in the induction circuit of the mold;

vii. open the mold and unmould the piece.

The melting device of the molding device which is the subject of the invention makes it possible to keep the filler at high temperature until injection, while the preheating of the mold ensures a good flow of the material during casting and a full filling of the impression. The sectorized piston of the device object of the invention avoids the creation of a wolf on the surface of said piston during melting and casting and thus the cleaning operations of said piston. The use of induction heating of the mold allows it to bring it quickly to the temperature suitable for casting and thus quickly chain cycles while ensuring efficient and rapid cooling of the workpiece after casting.

Advantageously, steps iii) and iv) are performed in parallel, so as to further reduce the cycle time.

The invention is explained below according to its preferred embodiments, in no way limiting, and with reference to FIGS. 1 to 7, in which:

- Figure 1 shows, in a sectional view of a block diagram of an embodiment of the device according to the invention, with a melting device placed above the mold, during the melting of the load;

- Figure 2 shows the device of Figure 1 at the start of casting; - Figure 3 is a block diagram, in a sectional life, of another embodiment of the device of the invention wherein the melter is placed below the mold;

- Figure 4 shows schematically in a perspective view and in partial section, an embodiment of the sectorized piston device object of the invention;

- Figure 5 is a perspective view of an embodiment of a sector of the piston as shown in Figure 4;

FIG. 6 shows a synopsis of the method which is the subject of the invention;

and FIG. 7 shows, in a partial view of the melting device, corresponding to the section shown in FIGS. 1 and 2, an exemplary embodiment of the device according to the invention comprising an injection piston. The drawings of FIGS. 1 to 5 and 7 are representations of principle of the device which is the subject of the invention, intended to understand the operation of the essential means of the invention. In all these figures, the y axis represents the vertical direction from bottom to top. To avoid overloading the figures, the power supply means of the inductors and coils have not been shown.

Figure 1, the device is shown during the BMG melting phase. According to an exemplary embodiment, the device according to the invention comprises a mold in two parts (101, 102), or more, separable which, closed, define a tight molding cavity (1 10). Sealing means (103) make it possible to seal the cavity under a primary vacuum, and under a slight overpressure of a neutral gas. The two parts (101, 102) of the mold are for example fixed on the plates of a press to allow the opening and closing of the mold. At least one (101) of the mold parts comprises means for heating the surfaces of the molding cavity (1 10), for example in the form of inductors (120) extending into ducts in the mold. Inductive ledits are for example constituted by copper tubes or multi-stranded copper cables of section adapted to the electric induction current used. The inductors (120) are connected to a high frequency current generator (not shown). The two parts (101, 102) of the mold are made of a metallic material, for example steel or copper. In the case where the material constituting said parts of the The mold is not ferromagnetic, for example if these parts consist of copper, the surfaces of the ducts receiving the inductors (120) are coated with a ferromagnetic material, for example with nickel. The thickness of the coating layer is a function of the heating power and the frequency of the current supplying the inductors, it is typically between 0.1 mm and 1 mm. When said inductors (120) are powered by a high frequency alternating current, they heat the walls of the ducts, and the heat thus produced is propagated by conduction to the surfaces of the molding cavity (1 10). Typically, the heating inductors of the mold are powered by an alternating current of a frequency of between 10 KHz and 200 KHz by a generator with a power of between 10 KW and 100 KW without these values being limiting. According to an exemplary embodiment, at least one of the mold parts comprises channels (125) for circulating a coolant and cooling the molding cavity (1 10). According to exemplary embodiments, the coolant is a liquid such as water or oil, or a gas. According to this exemplary embodiment, the cooling channels (125) are placed between the molding cavity and the inductors, as close as possible to the surface of the molding cavity so as to ensure rapid cooling and a high rate of amorphization. The position of the inductors, the heating power installed, the number and the distribution of the cooling channels as well as the coolant flow required for cooling, are for example determined by numerical simulation of the heating and cooling cycles of the mold.

Means (130) are provided for drawing the mold cavity to vacuum and introducing a neutral gas, such as argon so as to create therein a slight overpressure with respect to the atmospheric pressure.

Said mold comprises a melting device (150), located above the mold, according to this exemplary embodiment. This device is in communication with the molding cavity and confined in an enclosure (155) sealingly assembled with the mold so that the vacuum draw of the molding cavity also places the melter under vacuum, and that it is also in slight overpressure in the case of the injection of a neutral gas. This melting device (150) comprises a melting crucible (160) surrounded by a generator-fed fusion coil (165) current at very high frequency. Said melting crucible (160) is a sectorized crucible of generally cylindrical shape comprising a plurality of hollow sectors (161) extending along the axis of the cylinder and electrically insulated from each other. Said sectors consist of a non-magnetic metallic material, for example copper or stainless steel. Cooling means (170) make it possible to circulate a heat-transfer fluid in said hollow sectors in order to cool them. According to an exemplary embodiment, the portion of the melting crucible communicating with the molding cavity (1 10) is, during melting, closed by a piston (180), connected to an operating rod (185) to retract it. The device comprises for this purpose means (186) acting on the actuating rod, such as a rack pinion system, an electric jack, a linear motor or any other means known in the prior art for effecting the displacement of the piston and of the operating rod.

Said piston (180) is, during the melting of the material (190) a sole vis-à-vis the melting crucible (160). However, said piston (180) is sectored and comprises, similarly to the melting crucible, a plurality of hollow sectors, made of an electrically conductive metal material and electrically insulated from each other. Means (175) make it possible to circulate fluid in the hollow sectors of the piston, for example through the operating rod so as to cool them. Unlike a single sole, the sectorized configuration and the electrically conductive nature of the sectors of the piston (180), allows, by the circulation of currents induced in its sectors during the supply of the coil (165) of fusion, to create Laplace forces, repelling the molten charge of the piston surface (180) in the melting crucible. Thus, the melt load (190) is levitated or pseudo-electromagnetic levitation in the crucible, without contact with the walls.

The arrangement of the melting crucible in a vertical position above the mold makes it possible to load the crucible by gravity, the mold being closed. The filler consists of granules of the constituent material of BMG, or of several materials whose alloy constitutes BMG, the alloy being produced during melting. According to another variant, the charge consists of a single solid piece, such as a cylinder.

The solid charge is introduced into the melting crucible, the latter being closed at its lower end by the piston (180) and the mold being closed, the assembly being drawn to vacuum, the fusion coil (165) is supplied with very high frequency current. Alternatively, after drawing in a vacuum, a neutral gas is introduced into the molding cavity and into the enclosure comprising the melting crucible. The induced currents heat said charge that melt. The sectorized nature of the crucible and the resulting magnetic field, removes the molten charge from the walls of the crucible, as well as the walls of the piston (180) itself sectorized. The melting of the charge is extremely fast because of its direct heating by induction. The Laplace forces generated maintain the molten charge spaced from the walls of the crucible and the piston, the circulation of the currents induced in the molten charge, also ensure a mixing of said charge, which ensures its homogeneity particularly when the latter it comprises several alloy elements of different specific masses.

According to this embodiment, a flat coil (166) connected to a series of capacitors and placed just above the melting crucible.

Figure 2, the device of Figure 1, is shown during the injection phase. The charge being melted, to perform the injection, the molding cavity is preheated by means of the inductors (120) to bring it to a temperature equal to or slightly less than the glass transition temperature BMG. According to this embodiment, where the melting device is placed above the mold, the piston (180) is retracted into the mold by moving it downwards by its operating rod (185) thus releasing the passage to the molding cavity (1 10). The melt load (190) then flows by gravity into the molding cavity. The surfaces of said molding cavity having been preheated, the molten material flows into the cavity while maintaining sufficient fluidity to fill it completely. Then, the cooling of the molding cavity is achieved by circulating a coolant in the channels (125) of cooling. An electronic control device (not shown) is used to synchronize and sequence the feed of the fusion coil, the heating of the molding cavity, the retraction of the piston, the stop of the supply of the fusion coil and cooling the mold.

According to an advantageous embodiment, the flat coil (166) is powered by discharging the capacitors synchronously with the descent of the piston (180). Feeding said flat coil (166) creates an electromagnetic force acting on the molten charge, which pushes said charge toward the molding cavity.

According to an advantageous embodiment, an injection coil (266) is nested in the melting coil and fed at the moment of injection by a high-frequency alternating current simultaneously with the supply of the coil (165). two coils (165, 266) being fed by alternating currents out of phase, so as to create a sliding field which tends to eject the molten charge from the melting crucible to the molding cavity.

The use of such an injection coil, is, according to one embodiment, complementary to the use of the flat coil, for performing the injection of the molten charge into the molding cavity.

According to one embodiment, the melting crucible (160) is extended by a crucible or injection cylinder (260) which is advantageously surrounded by a coil (265) fed by a high frequency current and forming an inductor. Said injection crucible is for example made of a refractory material transparent to the electromagnetic field, without this configuration being limiting. This injection crucible makes it possible to pass through the thickness of the portion of the mold separating the melting crucible (160) from the molding cavity, while keeping the hot melt load sufficiently hot. Thus, the power supply of the coil (265) surrounding the injection crucible (260) has the effect, on the one hand, of moving the melt load (190) away from the walls of the injection crucible (260). and secondly to maintain, by the inductive heating effect, the molten charge at a sufficient temperature before entering the molding cavity.

Feeding of the injection inductor, the flat coil (166), the injection coil (266), the coil (265) surrounding the injection crucible (260) and the movement of the piston are controlled, sequenced and synchronized, by electronic means, for example by a programmable controller (not shown).

Figure 7, according to another embodiment, the device of the invention comprises a piston (760) adapted to push the load (190) in the molding cavity. Said piston comprises a head (762) and an operating rod (761) for its vertical displacement, said displacement being achieved by an actuator, electric, hydraulic or pneumatic acting on said rod (761), by a rack pinion system, a linear motor or any other suitable means. The head (762) of the piston is, according to exemplary embodiments, a solid head or a hollow head, made of a ferromagnetic material or coated with a ferromagnetic material. Maneuvered by the operating rod (761), said head (762) moves axially in the melting crucible, where it is subjected to the effect of the induced currents generated by the inductor (165) of fusion. The response of the material constituting the piston head or its coating to the induced currents causes rapid heating of the surface of said head. According to an exemplary embodiment, said head (762) is further cooled by the circulation of a heat transfer fluid circulated by means (not shown) between the operating rod (761) and the piston head. The design of the piston head, its constitution and the possible cooling thereof, make it possible to bring the surface of the piston head into contact with the molten charge (190) during casting, at a temperature such as that it is high enough not to create a wolf on the surface of said head and low enough not to cause gluing phenomenon or welding of the melt on said head.

According to variant combinations of these embodiments described above, the device which is the subject of the invention allows simple gravity casting and comprises for this purpose only the segmented piston (180), or a gravity-assisted casting. a magnetic field, a combination comprising the segmented piston (180) associated with the injection coil (266) and / or the flat coil (166). According to another variant corresponding to a mechanical injection, the device according to the invention comprises the segmented piston (180) retractable acting as sole in the lower part of the melting crucible and an injection piston (760) pushing the load in the 'footprint. According to another variant of this last embodiment comprising an injection piston (760), the device according to the invention further comprises an injection coil (266) adapted to create a sliding magnetic plate.

After filling the molding cavity, the circulation of a heat transfer fluid in the cooling channels (125) of the mold rapidly cooling the molding cavity and the part it contains, thus ensuring a high rate amorphization thereof. The mold is then opened, the part demolded and the cycle resumes.

Although FIGS. 1 and 2 show the device forming the subject of the invention in an embodiment comprising an injection crucible and coils (166, 266) making it possible to promote the injection of the molten charge into the molding cavity, those skilled in the art understand that these characteristics are improvements and are not indispensable to the operation of the device which is the subject of the invention, the simple displacement of the piston (180) making it possible to carry out gravity casting, the latter possibly being assisted by the mechanical effect of an injection piston. In this case, the melting device is placed, for example, directly in the lower part (102) of the mold, similarly to the embodiment shown in FIG. 3, but with the piston (180) positioned under the melting crucible, on the side of the molding cavity (1 10).

Figure 3, according to another embodiment of the device of the invention, the melting device (350) is positioned vertically under the molding cavity (310) of the mold. In a manner similar to the other embodiments, the mold comprises at least two separable parts (301, 302) and associated sealing means (303), so that, when the mold is closed, said portions define between them a cavity molding (310) tight, capable of being drawn by vacuum by appropriate means, and to be filled with a neutral gas in slight overpressure. The two parts (301, 302) of the mold are for example mounted on the plates of a press, which allows the opening and closing of the mold. At least one (301) of the mold parts advantageously comprises means for heating the surfaces of the molding cavity (310), for example in the form of inductors (320) extending in ducts formed in the mold. At least one of the mold parts advantageously comprises cooling channels (325) (325) for rapidly cooling the molding cavity (310).

The vertical arrangement of the melting device (350) in the mold allows the charge to be delivered to the gravity melter, open mold. The melting device (350) comprises a sectorized and cooled melting crucible (360) comprising hollow sectors, for example made of stainless steel and electrically insulated from each other. The melting crucible (360) is in communication with the molding cavity (310) at its upper end, and closed at its lower end by a sectorized piston (380). Said sectorized piston is fixed on an operating rod (385) and operating means (386) allow to move vertically said operating rod (386) and therefore said piston (380). An induction coil (365), referred to as a fusion coil, connected to a high frequency current generator (not shown), is used to generate a high frequency alternating magnetic field in the melting crucible and to melt the charge (190). that it contains. The melter (350) is inserted into a sealed enclosure (355).

The solid charge being placed in the melting crucible closed by the sectorized piston (380), the mold is closed and drawn to vacuum. Depending on the material injected, the vacuum draw is followed by the injection of a neutral gas into the molding cavity (310) and into the melting chamber (355). Feeding the melting coil (365) allows the charge (190) to be melted. The Laplace forces resulting from the induced currents flowing in the sectors of the melting crucible (360) and the sectorized piston (380), move the molten charge away from their walls, so that said molten charge is levitated or pseudo-fused. electromagnetic levitation without contact.

To effect casting, the sectorized piston (380) is moved upwards by the means (386) acting on the operating rod (385), which has the effect of pushing the load (190) into the molding cavity, always without contact between said load and said piston (380). The cooling of the piston (380) is controlled so that the temperature at the surface of the piston likely to come into contact with the melt load in pseudo-levitation is sufficient to prevent the creation of a wolf, but not too high. to avoid sticking or welding the molten charge to the surface of said piston.

Prior to casting, the surfaces of the molding cavity (310) are brought to a temperature equal to or slightly less than the glass transition temperature of the BMG used, by the high frequency current supply of the inductors (320), mold, so as to promote a uniform filling of the impression. Then, the molding cavity is cooled rapidly, by the circulation of a coolant in the cooling channels (125) of the mold. The mold is then opened, the part demolded and the cycle resumes. According to a variant of this embodiment, the device according to the invention comprises an injection crucible placing the melting crucible in communication with the molding cavity, and a coil surrounding said injection crucible making it possible to maintain the temperature of the molten charge during its path between the melting crucible and the molding cavity.

According to a variant of any one of the embodiments of the device which is the subject of the invention, the latter comprises several parallel melting and injection devices to ensure better filling of the impression.

FIG. 4, according to an example embodiment, the piston (185, 385) comprises a plurality of hollow sectors (481, ..., 486) made of stainless steel or of another electrically conductive and non-magnetic material, perforated with their two lateral ends and electrically insulated from each other by a layer of insulating material, such as a ceramic. Said layer of insulating material also provides sealing between the sectors. The sectors are connected to the operating rod (185, 385) via a water box (490) made of an electrically insulating material. Said water box is in hydraulic communication with fluid circulation means (not shown) via an orifice (491) formed in the operating rod, and distributes the coolant in all sectors (481, 486) to ensure their cooling. To this end, said sector comprises on their underside, an orifice (493) bringing into contact the interior of the sector with the water box (490). A second orifice (494) at the radially inner end of the sector communicates the interior of each sector with an orifice (492) made in the actuating rod, itself in hydraulic communication with the circulation means, which allows the circulation of a coolant in the sectors of the piston.

Figures 4 and 5, when such sector (486) of the piston is placed in the alternating magnetic field generated by the fusion coil of the fusion device, induced currents (500) circulate on its surface throughout its perimeter. These induced currents generate a Laplace positive y-direction force in Figure 5, which keeps the melt load away from the piston surface.

FIG. 6, according to an exemplary implementation of the method that is the subject of the invention, whatever the embodiment of the device, this device comprises a first embodiment step (610) of loading the melting crucible. This step is performed closed mold or open mold in the case where the melting device is placed above the mold and open mold when the crucible is placed below the mold According to a closing step (620) the mold is closed and the cavity and the melting crucible are drawn to vacuum. According to a variant, after the vacuum extraction and possibly a sweep, consisting of a succession of vacuum draws and injection of a neutral gas, a neutral gas such as argon is injected into the molding cavity and the enclosure of the melting device, said gas being slightly overpressured relative to the atmospheric pressure. According to a melting step (630) the charge is melted by feeding the fusion coil of the melter. In parallel or concomitant manner, the mold is preheated by the inductors during a heating step (640) to protect the surfaces of the molding cavity at a temperature equal to or slightly less than the glass transition temperature of the BMG. Induction heating achieves such a temperature in 1 minute or less depending on the size of the impression. According to a casting step (650) the piston is moved up or down, according to the embodiment of the mold, and the injection coil is fed, as well as the coil surrounding the injection crucible, if the device is provided to fill the molding cavity preheated with the melt. Depending on the characteristics of the operation, the heating of the molding cavity is maintained or not during the casting step. According to a cooling step (660), the supply of the inductors of the mold is stopped and the coolant coolant is circulated in the cooling channels of the mold, providing rapid cooling of the part, until the it reaches its demolding temperature. According to a demolding step (670) the cooled mold is opened, the part is demolded, and the cycle resumes.

In summary, the method and the device which are the subject of the invention make it possible to produce high-speed amorphous metal parts, more particularly thin parts, while ensuring a high degree of amorphization thereof.

Claims

Device for producing a part by molding a BMG, comprising:

at. a mold comprising two shells (101, 102, 301, 302) defining a sealed molding cavity (1 10, 310);

b. a BMG melting device comprising:

bi. a sectorized cold crucible (160, 360), said melting crucible, arranged vertically comprising hollow sectors (161) made of an electrically conductive and non-magnetic material and electrically isolated from each other;

bii. an inductor (165, 365) in the form of a coil surrounding said melting crucible for heating its contents;

biii. very high frequency current generating means for supplying the inductor;

d. means for communicating the contents of the melting crucible (160,360) with the molding cavity (1,10,310) and casting the BMG;

characterized in that it comprises a sectorized piston (180, 380) comprising hollow sectors (481 ... 486) made of an electrically conductive and non-magnetic material, electrically insulated from each other, closing the melting crucible ( 160, 360) at one of its ends, said piston (180, 380) being configured so that when subjected to the alternating magnetic field of the inductor (165, 365) supplied by the high frequency current generating means induced currents (500) circulate in the sectors of said piston (180, 380) and create a repelling force of the piston surface (180, 380) on the BMG in the melting crucible. An apparatus according to claim 1, wherein the means for communicating the contents of the melting crucible with the molding cavity (1 10, 310) comprises a device (186, 386) for vertical displacement of the piston (180, 380).

An apparatus according to claim 2, wherein the melting crucible (160) is placed above the molding cavity (1 10) and the piston (180) moves downwardly.

Apparatus according to claim 2, wherein the melting crucible (360) is located below the molding cavity (310) and the piston (380) is moving upwardly.

Device according to claim 2 or claim 3 comprising a channel, said injection crucible (260) between the melting crucible (160) and the molding cavity (1 10).

Device according to claim 5, comprising a coil (265) surrounding the injection crucible and supplied with high frequency current.

Device according to claim 5, comprising a coil, called an injection coil (166, 266) and means for its power supply, capable of producing an electromagnetic force for injecting the molten material (190) contained in the crucible melting (160) in the molding cavity by the injection crucible.

An apparatus according to claim 7, wherein the injection coil is a flat coil (166) fed by a capacitor discharge.

An apparatus according to claim 7, wherein the injection coil comprises a nested coil (266) in the coil forming the fusion coil, said injection coil being powered by a high frequency alternating current out of phase with the alternating current supplying the fusion coil so as to create a field sliding.

10. Device according to claim 1, wherein the sectors (481 ... 486) of the melting crucible and the piston (180) consist of stainless steel. 11. Device according to claim 1, wherein the mold comprises induction heating means (120, 320) of the molding cavity (110, 310).

12. Device according to claim 1 1, wherein the mold comprises a cooling means (125, 325) of the molding cavity. 13. A method for molding a workpiece from a BMG employing a device according to claims 11 and 12 and comprising the steps of:

i. charging (610) a melting crucible closed by the sectorized piston (180, 380);

ii. closing the mold and pulling the molding cavity to vacuum (620);

iii. melting the charge contained in the melting crucible (630) by means of the inductor, the sectorized piston (180, 380) being subjected to the magnetic field of said inductor;

iv. preheating (640) the mold by means of the induction circuit (120, 320) of the mold, to bring the surfaces of the molding cavity to a temperature equal to or slightly less than the glass transition temperature of the BMG;

v. performing the casting (650) by moving the sectorized piston;

vi. cooling the mold (660) by circulating a coolant in the cooling circuit (125, 315) of the mold;

vii. open the mold and unmould the piece (670).

The method of claim 13 wherein steps iii) and iv) are performed in parallel.