EP3700695B1 - Process and apparatus for bulk metallic glass casting - Google Patents

Description

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

In fact, metallic glasses, which are in the form of an amorphous, non-crystallized or partially crystallized metal, which due to the absence of grain boundaries in the structure of the metal, exhibit characteristics of hardness, elasticity. and corrosion resistance, which make them particularly efficient for this type of application and make unnecessary the protective cases in which consumers wrap their smartphone to protect it from bumps, 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 the glass forming processes, in a die in the shape of said shell after having heated said sheet to a relatively low temperature compared to the temperature which it would be necessary to reach with the same crystallized metal alloy in order to obtain an equivalent forming.

According to another embodiment, the methods of the prior art use a vacuum molding technique of a solid metallic glass alloy (“ Bulk Metallic Glass ” or BMG). The use of a BMG makes it possible to reduce the critical cooling rate allowing the material to solidify into an amorphous material. To ensure a low rate of crystallinity or a high rate of amorphization, the material must be molded under conditions which avoid its contamination by impurities, in particular by nitrogen and oxygen. To this end, 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, 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 zirconia hollow, or a cold sectorized copper crucible.

A channel, generally referred to as an injection or casting crucible, enables the contents of the melting crucible to be placed in communication with the cavity of the mold 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 trap, a piston or a movable finger. When the melting crucible is placed vertically, for example above the mold, and gravity tends to bring the molten charge closer to the mobile closing means, the latter must be cooled, in particular so as not to damage the means ensuring the seal between said movable closure means and the injection crucible, The molten charge cools on contact with the movable closure means and during each casting, a wafer of material remains 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 drawback of reacting with certain alloys.

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

The document JPH 0917421 9 discloses a crucible and a mold suitable for shell casting of an aluminum alloy, comprising a crucible disposed horizontally, and in which a previously melted material is dumped.

The document US2015 / 298296 describes 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 molten into the mold by means of a cooled piston.

The document US 5156 202 describes a sectorized mold which is closed in its lower part by a sectorized and cooled plate, comprising an opening in its center. A molten metal is introduced through the upper part of the mold closed 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 supplied with high frequency alternating current.

The document WO2013 / 190020 describes a mold comprising induction heating means and cooling means.

The document US2002 / 122456 describes a melting furnace comprising a sectorized crucible surrounded by an induction coil.

The document JPS61119368 describes a molding device suitable for molding an aluminum alloy and comprising a horizontal pouring tube and a piston comprising induction means capable of causing pseudo-levitation of the material in the pouring tube.

The invention aims to resolve the drawbacks of the prior art and for this purpose relates to a device for producing a part by molding a BMG, which device according to claim 1.

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 gravity in the implementation of several operations. The sectorized crucible makes it possible to remove the molten material from the walls of the crucible and thus to avoid any contamination thereof, while the use of a sectorized piston makes it possible to put the molten load in levitation or pseudo-levitation with respect to said piston by the components of the Laplace forces of the magnetic field created by the circulation of the currents induced on the sectors of said piston. Since the molten charge is not in contact either with the melting crucible or with the piston during melting and casting, the object device of the invention allows the use of BMG comprising reactive components such as titanium or zirconium capable of interacting with a crucible made of refractory material. The charge does not cool on contact with the piston and does not create a wolf.

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

Advantageously, the means for placing the contents of the melting crucible in communication with the molding cavity comprise a device for vertical displacement of the piston. Thus, due to the vertical arrangement of the melting crucible with respect to the mold, said piston makes it possible to carry out the casting 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 which is the subject of the invention comprises a channel, called an injection crucible, between the melting crucible and the molding cavity. This embodiment makes it possible to place the melting device outside the shells, the passage through the shell of the melting device towards the impression being made by this injection crucible.

Advantageously, the device which is the subject 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 molten charge at temperature until it enters the molding cavity as well as to move said molten charge away from the walls of the injection crucible.

Advantageously, the device which is the subject of the invention comprises, according to an embodiment compatible with the previous ones, an injection coil and means for its electrical supply, capable of producing an electromagnetic force for the injection of the contained molten material. in the melting crucible in the molding cavity. This embodiment makes it possible to use the Laplace forces by said coil in order to inject the 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 supplied by a discharge of capacitors. This embodiment uses a configuration similar to that used in magnetoforming to apply a force to the molten material directing it towards the molding cavity.

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

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

The invention also relates to a method as described in claim 11 attached hereto.

The melting device of the molding device that is the subject of the invention makes it possible to keep the molten charge at high temperature until injection, while the preheating of the mold ensures good flow of the material during casting and a total filling of the impression. The sectorized piston of the device which is the subject of the invention prevents the creation of a wolf on the surface of said piston during fusion and the casting and thus the cleaning operations of said piston. The use of induction heating of the mold makes it possible to bring the latter quickly to the appropriate temperature for casting and thus to rapidly chain the cycles while ensuring efficient and rapid cooling of the part after casting.

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

• la figure 1 représente, selon une vue en coupe un schéma de principe d'un mode de réalisation du dispositif objet de l'invention, avec un dispositif de fusion placé au-dessus du moule, au cours de la fusion de la charge ;
• la figure 2 montre le dispositif de la figure 1 en début de coulée ;
• la figure 3 est un schéma de principe, selon une vie en coupe, d'un autre mode de réalisation du dispositif objet de l'invention dans lequel le dispositif de fusion est placé en-dessous du moule ;
• la figure 4 représente schématiquement selon un vue en perspective et en coupe partielle, un exemple de réalisation du piston sectorisé du dispositif objet de l'invention ;
• la figure 5 est une vue en perspective d'un exemple de réalisation d'un secteur du piston tel que représenté figure 4 ;
• la figure 6 montre un synopsis du procédé objet de l'invention ;
• et la figure 7, représente selon une vue partielle du dispositif de fusion, correspondant à la coupe représentée figures 1 et 2, un exemple de réalisation du dispositif objet de l'invention comprenant un piston d'injection.

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

• the figure 1 shows, in a sectional view 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;
• the figure 2 shows the device of the figure 1 at the start of casting;
• the figure 3 is a block diagram, according to a sectional life, of another embodiment of the device according to the invention in which the melting device is placed below the mold;
• the figure 4 shows schematically in a perspective view and in partial section, an exemplary embodiment of the sectorized piston of the device which is the subject of the invention;
• the figure 5 is a perspective view of an exemplary embodiment of a piston sector as shown figure 4 ;
• the figure 6 shows a synopsis of the method which is the subject of the invention;
• and the figure 7 , shows a partial view of the melting device, corresponding to the section shown figures 1 and 2 , an exemplary embodiment of the device which is the subject of the invention comprising an injection piston.

The drawings of figures 1 to 5 and 7 are principle representations of the device which is the subject of the invention, intended for understanding the operation of the essential means of the invention. In all these figures, the y axis represents the vertical direction from bottom to top. In order not to overload the figures, the means for supplying the inductors and coils have not been shown.

Figure 1 , the device is shown during the melting phase of the BMG. According to an exemplary embodiment, the device which is the subject of the invention comprises a mold in two parts (101, 102), or more, which can be separated which, when closed, define a cavity. tight (110) waterproof. 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 in order to allow the opening and the closing of the mold. At least one (101) of the parts of the mold comprises means for heating the surfaces of the molding cavity (110), in the form of inductors (120) extending in ducts made in the mold. These inductors are for example formed by copper tubes or multi-strand copper cables of cross 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 mold is not ferromagnetic, for example if these parts are made of copper, the surfaces of the conduits receiving the inductors (120) are coated with a ferromagnetic material, for example with nickel . The thickness of the coating layer depends on the heating power and the frequency of the current supplied to the inductors, it is typically between 0.1mm and 1mm. When said inductors (120) are supplied with high frequency alternating current, they heat the walls of the conduits, and the heat thus produced is propagated by conduction to the surfaces of the molding cavity (110). Typically the heating inductors of the mold are supplied with an alternating current with a frequency between 10KHz and 200KHz by a generator with a power between 10 KW and 100 KW without these values being limiting, At least one of the parts of the mold comprises channels (125) for the circulation of a heat transfer fluid and the cooling of the molding cavity (110). According to exemplary embodiments, the heat transfer fluid 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 degree of amorphization. The position of the inductors, the installed heating power, the number and distribution of the cooling channels as well as the heat transfer fluid flow rate necessary for cooling, are for example determined by numerical simulation of the mold heating and cooling cycles.

Means (130) make it possible to draw the molding cavity to a vacuum and to introduce therein a neutral gas, such as argon, so as to create therein a slight overpressure with respect to 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 evacuation of the molding cavity also places the melting device 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 melting coil (165) supplied by a very high frequency current generator. Said melting crucible (160) is a sectored crucible, of generally cylindrical shape comprising a plurality of hollow sectors (161), extending along the axis of the cylinder and electrically isolated from one another. Said sectors are made 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 part of the melting crucible communicating with the molding cavity (110) is, during the melting, closed by a piston (180), connected to an operating rod (185) to retract the latter. To this end, the device comprises means (186) acting on the operating rod, such as a rack pinion system, an electric cylinder, a linear motor or any other means known from the prior art for carrying out the displacement of the piston and of the operating rod.

Said piston (180) constitutes, during the melting of the material (190) a hearth 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 metallic material and electrically insulated from each other. Means (175) allow fluid to circulate in the hollow sectors of the piston, for example through the operating rod so as to cool the latter. Unlike a simple sole, the sectorized configuration and the electrically conductive nature of the sectors of the piston (180), by the circulation of the currents induced in its sectors during the supply of the fusion coil (165), to create Laplace forces, repelling the charge molten surface of the piston (180) in the melting crucible. Thus, the molten charge (190) is levitated or in electromagnetic pseudo-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 the BMG, or of several materials whose alloy constitutes the BMG, the alloy being produced during the melting. According to another variant, the charge consists of a single solid piece of land, such as a cylinder.

The solid charge being 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 under vacuum, the melting coil (165) is supplied with very high frequency current. Alternatively, after the evacuation, a neutral gas is introduced into the molding cavity and into the enclosure comprising the melting crucible. The induced currents heat said charge which melts. The sectorized nature of the crucible and the magnetic field which results from it, moves the molten charge away from the walls of the crucible, as well as from the walls of the piston (180), itself sectorized. The melting of the charge is extremely rapid due to its direct heating by induction. The Laplace forces generated keep the molten charge away from the walls of the crucible and the piston, the circulation of the currents induced in the molten charge, also ensure a stirring of said charge, which makes it possible to ensure its homogeneity, particularly when the latter. this comprises several alloying elements of different specific masses.

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

Figure 2 , the device of the figure 1 , is shown during the injection phase. The charge being melted, to perform the injection, the molding cavity is heated beforehand, by means of the inductors (120) to bring it to a temperature equal to or slightly lower than the glass transition temperature of the BMG. According to this exemplary embodiment, where the fusion device is placed above of the mold, the piston (180) is retracted into the mold by moving the latter downwards by its operating rod (185) thus freeing the passage towards the molding cavity (110). The molten charge (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 retaining sufficient fluidity to fill it entirely. An electronic control device (not shown) makes it possible to synchronize and sequence, the supply of the melting coil, the heating of the molding cavity, the retraction of the piston, the stopping of the supply of the melting coil and cooling the mold.

According to an advantageous embodiment, the flat coil (166) is supplied by the discharge of the capacitors in a manner synchronized 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 towards the mold cavity.

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

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

According to one embodiment, the melting crucible (160) is extended by an injection crucible or cylinder (260) which is advantageously surrounded by a coil (265) supplied with 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 part of the mold separating the melting crucible (160) from the molding cavity, while keeping the molten charge sufficiently hot. Thus, the power supply to the coil (265) surrounding the injection crucible (260) has the effect, on the one hand, of moving the molten charge (190) of the walls of the injection crucible (260) and on the other hand to keep, by the effect of inductive heating, the molten charge at a sufficient temperature before it enters the molding cavity.

The supply of the injection inductor, the flat coil (166), the injection coil (266), the coil (265) surrounding the injection crucible (260) as well as 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 which is the subject of the invention comprises a piston (760) capable of pushing the load (190) into the molding cavity. Said piston comprises a head (762) and an operating rod (761) for its vertical displacement, said displacement being carried out by a jack, electric, hydraulic or pneumatic acting on said rod (761), by a rack pinion system, a motor linear 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 melting inductor (165). 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 head of the piston. The dimensioning of the piston head, its constitution and the possible cooling thereof, make it possible to bring the surface of the piston head in contact with the molten load (190) during casting, at) a temperature such as: that this is high enough not to create a wolf on the surface of said head and low enough not to cause the phenomenon of sticking or welding of the molten material 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 for this purpose only comprises the segmented piston (180), or gravity casting assisted by a field. magnetic, combination including 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 which is the subject of the invention comprises the segmented piston (180) which can be retracted acting as a sole in the lower part of the melting crucible and an injection piston (760) pushing the charge into it. 'footprint. According to another variant of the latter embodiment comprising an injection piston (760), the device which is the subject of the invention further comprises an injection coil (266) capable of creating a sliding magnetic field.

After filling the molding cavity, the circulation of a heat transfer fluid in the cooling channels (125) of the mold makes it possible to rapidly cool the molding cavity and the part it contains, thus ensuring a high rate of amorphization of the mold. -this. The mold is then opened, the part removed from the mold and the cycle resumes.

even though figures 1 and 2 represent the device which is 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, the person skilled in the art understands that these characteristics are improvements and are not essential to the operation of the device which is the subject of the invention, the simple movement of the piston (180) making it possible to carry out the casting by gravity, the latter possibly being assisted by the mechanical effect of a 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. figure 3 , but with the piston (180) positioned under the melting crucible, on the side of the molding cavity (110).

Figure 3 , according to another embodiment of the device which is the subject of the invention, the melting device (350) is positioned vertically under the molding cavity (310) of the mold. Similarly 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 parts define between them a cavity tight fitting (310), capable of being evacuated by suitable means, and of being filled with a neutral gas at a 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 parts of the mold advantageously comprise means for heating the surfaces of the molding cavity (310), for example in the form of inductors (320) extending in ducts made in the mold. At least one of the parts of the mold advantageously comprises cooling channels (325) making it possible to rapidly cool the molding cavity (310).

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

The solid charge being placed in the melting crucible, closed by the sectorized piston (380), the mold is closed and vacuumed. Depending on the material injected, the evacuation is followed by the injection of an inert gas into the molding cavity (310) and into the melting chamber (355). Feeding the fusion coil (365) allows the charge (190) to melt. The Laplace forces resulting from the induced currents flowing in the sectors of the melting crucible (360) and of the sectorized piston (380), move the molten charge away from their walls, so that said molten charge is levitated or pseudo- contactless electromagnetic levitation.

To carry out the 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 load in pseudo-levitation fusion, is sufficient to avoid the creation of a wolf, but not too high to avoid sticking or welding of 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 lower than the glass transition temperature of the BMG used, by the high-frequency current supply to the inductors (320), of the mold, so as to promote uniform filling of the impression. Then, the molding cavity is cooled rapidly, by the circulation of a heat transfer fluid in the cooling channels (125) of the mold. The mold is then opened, the part unmolded and the cycle resumes.

According to a variant of this embodiment, the device which is the subject of the invention comprises an injection crucible placing the melting crucible and the molding cavity in communication, and a coil surrounding said injection crucible making it possible to maintain the temperature of the molten charge as it travels 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 fusion and injection devices to ensure better filling of the impression.

Figure 4 , according to an exemplary embodiment, the piston (185, 385) comprises a plurality of hollow sectors (481, ..., 486) made of stainless steel or another electrically conductive and non-magnetic material, perforated at both of them side ends and electrically insulated from each other by a layer of insulating material, such as ceramic. Said layer of insulating material also provides sealing between the sectors. The sectors are linked to the operating rod (185, 385) by means of 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) made in the operating rod, and distributes the heat transfer fluid in all sectors (481, .. ., 486) to ensure their cooling. To this end, said sectors comprise on their underside, an orifice (493) bringing the interior of the sector into contact with the water box (490). A second orifice (494) at the inner radial end of the sector, communicates the interior of each sector with an orifice (492) made in the operating rod, itself in hydraulic communication with the circulation means, which allows the circulation of a heat transfer fluid in the sectors of the piston.

Figures 4 and 5 , when such a sector (486) of the piston is placed in the alternating magnetic field generated by the melting coil of the melting device, induced currents (500) circulate on its surface over its entire perimeter. These induced currents generate a Laplace force oriented in the direction of positive ys on the figure 5 , which keeps the molten charge away from the piston surface.

Figure 6 , according to an exemplary implementation of the method which is the subject of the invention, whatever the embodiment of the device, the latter comprises a first step (610) of loading the melting crucible. This step is carried out with a closed mold or an open mold in the case where the melting device is placed above the mold and the mold open when the crucible is placed below the mold According to a closing step (620) the mold is closed and the cavity tight, as well as the melting crucible are evacuated. According to a variant, after the evacuation and possibly a sweep, consisting of a succession of evacuations 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 at a slight overpressure with respect to atmospheric pressure. According to a melting step (630) the feed is melted by supplying the melting coil of the melting device. In a parallel or concomitant manner, the mold is preheated by the inductors during a heating step (640) in order to protect the surfaces of the molding cavity at a temperature equal to or slightly lower 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 indentation. According to a casting step (650), the piston is moved from top to bottom or from bottom to top, depending on the embodiment of the mold, and the injection coil is supplied, as well as the coil surrounding the injection crucible, if the device is so provided in order to fill the preheated molding cavity with the molten material. 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 heat transfer fluid is circulated. in the cooling channels of the mold, providing rapid cooling of the part, until 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 parts in amorphous metal at high speed, more particularly thin parts, while ensuring a high rate of amorphization thereof.

Claims (12)

1. Device for producing a part by molding a bulk metal glass (BMG) alloy, comprising:

   a. a mold comprising two dies shells (101, 102, 301, 302) delimiting a sealed molding cavity (110, 310);

   b. a device for melting the bulk metal glass (BMG) alloy comprising:

   bi. a cold sectorized crucible (160, 360), called melting crucible, arranged vertically comprising hollow sectors (161) formed from an electrically conductive and

   non-magnetic material electrically insulated from one another;

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

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

   c. means for connecting the content of the melting crucible (160, 360) with the molding cavity (110, 310) and casting the BMG;

   and comprising a sectorized piston (180, 380) forming the melting crucible (160, 360) at one of its ends, said piston comprises hollow sectors (481...486) made of an electrically conductive and non-magnetic material electrically insulated from one another, said piston (180, 360) being configured in such a way that when it is subjected to the alternating magnetic field of the inductor (165, 365) powered by the means for generating a high-frequency current, induced currents (500) circulate in the sectors of said piston (180, 380) and create a force that repels from the surface of the piston (180, 380) the bulk metal glass (BMG) alloy being located in the melting crucible, characterized in that it comprises induction heating means (120, 320) of the molding cavity (110, 310) and channels (125, 325) for circulating a coolant and cooling said molding cavity.
2. Device according to claim 1, wherein the means for connecting the content of the melting crucible with the molding cavity (110, 310) comprise a device (186, 386) for vertical movement of the piston (180, 380).
3. Device according to claim 2, wherein the melting crucible (160) is positioned above the molding cavity (110) and the piston (180) moves downwards.
4. Device according to claim 2, wherein the melting crucible (360) is positioned below the molding cavity (310) and the piston (380) moves upwards.
5. Device according to claim 2 or claim 3 comprising a channel, called injection crucible (260), between the melting crucible (160) and the molding cavity (110).
6. Device according to claim 5, comprising a coil (265) surrounding the injection crucible and powered with high-frequency current.
7. Device according to claim 5, comprising a coil, called injection coil (166, 266) and means for the electrical power supply thereof, suitable for producing an electromagnetic force for the injection of the molten material (190) contained in the melting crucible (160), into the molding cavity, through the injection crucible.
8. Device according to claim 7, wherein the injection coil is a flat coil (166) powered by a capacitor discharge.
9. Device according to claim 7, wherein the injection coil comprises a coil (266) imbricated in the coil forming the melting coil, said injection coil being powered by a high-frequency alternating current out of phase with respect to the alternating current powering the melting coil so as to create a sliding field.
10. Device according to claim 1, wherein the sectors (481...486) of the melting crucible and the piston (180) are made of stainless steel.
11. Method for molding a part from a bulk metal glass (BMG) alloy implementing a device according to claims 1 and comprising steps of:

    i. charging (610) the melting crucible (160, 360) closed by the sectorized piston (180, 380);

    ii. closing the mold (620) and evacuating the molding cavity and the melting crucible (160, 369);

    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 mold induction circuit (120, 320), so as to bring the surfaces of the molding cavity to a temperature equal to or slightly less than the glass transition temperature of the bulk metal glass (BMG) alloy;

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

    vi. cooling the mold (660) by circulating a coolant in the cooling channels (125, 325) of the mold;

    vii. opening the mold and releasing the part (670).
12. Method according to claim 11 wherein steps iii) and iv) are carried out in parallel.

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