EP0914221A1 - Method for making a composite part with magnesium matrix by infiltration casting - Google Patents

Method for making a composite part with magnesium matrix by infiltration casting

Info

Publication number
EP0914221A1
EP0914221A1 EP98917209A EP98917209A EP0914221A1 EP 0914221 A1 EP0914221 A1 EP 0914221A1 EP 98917209 A EP98917209 A EP 98917209A EP 98917209 A EP98917209 A EP 98917209A EP 0914221 A1 EP0914221 A1 EP 0914221A1
Authority
EP
European Patent Office
Prior art keywords
magnesium
container
mold
crucible
vacuum
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP98917209A
Other languages
German (de)
French (fr)
Inventor
Laetitia Billaud
Philippe Le Vacon
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Airbus Group SAS
Original Assignee
Airbus Group SAS
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Airbus Group SAS filed Critical Airbus Group SAS
Publication of EP0914221A1 publication Critical patent/EP0914221A1/en
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D18/00—Pressure casting; Vacuum casting
    • B22D18/04—Low pressure casting, i.e. making use of pressures up to a few bars to fill the mould
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D19/00—Casting in, on, or around objects which form part of the product
    • B22D19/14—Casting in, on, or around objects which form part of the product the objects being filamentary or particulate in form

Definitions

  • the invention relates to a method for manufacturing, by pressure foundry, parts made of a magnesium matrix composite material.
  • magnesium is to be understood as also including all magnesium alloys.
  • composite material with a magnesium matrix designates any material comprising a reinforcing structure, generally formed of long fibers such as carbon fibers, alumina, etc., embedded in a magnesium matrix.
  • the volume rate of fibers contained in the material is generally between approximately 40% and approximately 60%.
  • the method according to the invention can be advantageously used to manufacture any foundry part which must have both good mechanical characteristics and a reduced mass. It finds in particular a privileged application in the aeronautical and space industries.
  • the pressure foundry technique (generally between around 30 bars and around 100 bars) has been known for a few years, for manufacturing parts from a metal matrix composite material. According to this technique, a crucible containing blocks of metal intended to form the matrix of the part is placed in the same hermetic container, comparable to an autoclave, as well as a mold into which a fibrous preform has previously been introduced.
  • a vacuum is created inside the container and the mold, the crucible containing the metal blocks is heated and the mold is preheated.
  • the metal in the crucible is completely melted, it is transferred inside the mold. This transfer is carried out automatically by pressurizing the container at a pressure level, generally between approximately 30 bars and approximately 100 bars.
  • the cooling of the part is accelerated by bringing a refrigerating member into contact with a wall of the mold.
  • the pressure is maintained in the container in order to complete the natural shrinkage of the metal.
  • the crucible containing the metal blocks is placed above the mold and the latter is provided in the upper part with a receptacle at the bottom of which opens the imprint of the part to be manufactured.
  • the metal flows into the receptacle through an orifice formed in the bottom of the crucible and initially closed.
  • the molten metal is then transferred into the mold cavity under the effect of the pressurization of the container.
  • the cooling of the part is then obtained by means of a cooling piston brought into contact with the bottom of the mold.
  • This first technique in which the crucible is placed above the mold, has the advantage of allowing the use of a simple mold and therefore inexpensive to produce. It is therefore relatively economical.
  • this technique is difficult to apply to the production of composite parts with magnesium matrices, despite the advantage that such parts would present in certain industries, such as the aeronautical and space industries.
  • the preliminary transfer of the molten metal into the receptacle formed at the upper part of the mold is carried out under vacuum and without any special precautions.
  • the magnesium may then evaporate and come to settle in the entire installation, which would make part of it unusable. .
  • no precaution is taken in order to avoid an explosive reaction of magnesium with oxygen, in particular during the pressurization of the enclosure.
  • the crucible containing the metal blocks is placed below the mold and the bottom of the latter is equipped with a feed tube which initially opens above the crucible. Vacuuming is carried out by a vacuum tube which opens directly into the mold. When the metal is melted, the crucible is lifted so that the mold feed tube plunges into the molten metal. The transfer of the molten metal inside the mold is then obtained by pressurizing the container. The cooling of the part is ensured by a cooling block which is brought into contact with the upper face of the mold.
  • This technique in which the crucible is placed below the mold, is more expensive than the previous one because the mold must include a supply tube. On the other hand, it eliminates an intermediate step of transfer of the molten metal.
  • this technique is also unsuitable for the production of composite parts with a magnesium matrix. Indeed, the melting of the metal takes place entirely under vacuum as in the previous technique, so that vacuum evaporation of magnesium is practically inevitable. In addition, no special precautions are provided to avoid explosive contact with oxygen.
  • the subject of the invention is precisely a method of manufacturing a composite part with a magnesium matrix generally implementing the known techniques of pressure casting, but whose original characteristics make it possible to eliminate any risk of an explosive magnesium reaction. / oxygen, while avoiding evaporation under vacuum of magnesium.
  • this result is obtained by means of a process for manufacturing a fiber-reinforced magnesium part, characterized in that it comprises the following steps:
  • the neutral gas circulation is established under a vacuum of approximately 100 mb.
  • the heating of magnesium is accompanied by an initial pressurization of the container and of the mold to approximately 0.1 mb.
  • the neutral gas circulation preceding the pressurization of the container is ensured until the magnesium reaches a maximum temperature, for example around 700 ° C.
  • the neutral gas used is argon.
  • the container and the mold are evacuated through at least one passage which opens directly into the container.
  • the solid magnesium is brought into contact with the feed tube by moving the crucible upwards as soon as the temperature of the magnesium reaches a threshold lower than its melting temperature.
  • the mold is cooled by establishing contact between an upper wall thereof and a cooling block placed at the top of the container.
  • FIGS 1A to 1D are schematic sectional views which illustrate the main steps of the method according to the invention.
  • FIG. 2 shows respectively in I, II, III and IV, the variation curves, as a function of time t, of the average temperature ⁇ (in ° C) of the metal, of the pressure P (in bars) prevailing in the container, the position of the lower cylinder and the position of the upper cylinder.
  • the installation used to manufacture a fiber-reinforced magnesium composite part, by foundry under pressure has many similarities with the installations usually used for the manufacture of composite parts with metal matrix. Therefore, no detailed description will be given.
  • an airtight container 10 similar to an autoclave.
  • This container 10 is a tubular container centered on a vertical axis. It is closed at its upper part by a cover 12, the opening of which gives access to the volume 14 delimited inside the container. When the cover 12 is closed, it cooperates sealingly with the upper edge of the container 10, so as to hermetically seal the volume 14.
  • the container 10 and its lid 14 are designed to withstand a maximum pressure of about 100 bar in the volume 14.
  • the container 10 is equipped Internal ⁇ quently first means heating 16 placed in the lower part. of the container and second heating means 18 placed in the upper part of the container.
  • These heating means 16 and 18 can be constituted by any suitable devices such as electrical resistors. Their implementation is controlled and regulated from the outside of reci ⁇ tainer 10 by a control unit (not shown).
  • Thermocouples (not shown) are also arranged inside the container 10, to allow the regulation of the heating provided by the heating means 16 and 18.
  • a heat insulator (not shown path) internally covers all the walls of the container 10 in order to provide thermal insulation of the volume 14 from the outside.
  • the container 10 is also equipped with several access passages, only one of which has been shown diagrammatically at 22 in FIGS. 1A to 1D. In practice, several passages are generally arranged in the bottom of the container 10 and in the cover 12. As will appear better in the following description, their main functions are to connect the closed volume 14 delimited by the container 10 either to a vacuum circuit (not shown) is at a source (not shown) of a pressurized neutral gas such as argon.
  • the bottom of the container 10 is internally equipped with a base (not shown) on which a crucible 26 can rest, which initially contains solid magnesium blocks 28. This crucible 26 is placed inside the first heating means 16.
  • the container 10 is provided with at least one support 30 on. which can be placed a mold 32.
  • the mold 32 has internally one or more imprints whose shapes and dimensions are identical to those of the part (s) to be produced.
  • Each impression is filled with a fibrous preform 34 before the mold is introduced into the container 10.
  • the fibrous preforms are generally formed of long fibers of carbon, alumina, or other intended to form the reinforcements of the part to be produced.
  • the volume of fiber in the fiber preform 34 is generally between about 40% and about 60% of the total volume of the impression.
  • the imprint (s) it delimits communicate with the internal volume 14 of the container only by a single passage, materialized by a supply tube 36. More precisely, the tube feed 36 opens into the bottom of the mold 32 and extends downward, preferably along the vertical axis of the container 10. The lower end of the feed tube 36 initially opens at a level close to that of the upper edge of the crucible 26, as illustrated in FIG. 1A.
  • a lower cylinder 38 initially in the low position as illustrated in FIG. 1A, is placed under the bottom of the container 10 so that its rod 38a passes through this bottom in a sealed manner, along the vertical axis of the container. In the initial lower position of the lower cylinder 38, the upper end of its rod 38a occupies a position such that the crucible 26 is not lifted from its base.
  • An upper cylinder 40 initially in the high position, is also mounted above the cover 12 of the container 10.
  • the rod 40a of this cylinder 40 which passes through the cover 12 in a sealed manner along the vertical axis of the container 10, its lower end a cooler block 42.
  • this cooler block 42 In the initial high position of the jack 40, this cooler block 42 is spaced from the upper face of the mold 32.
  • Access passages comparable to passage 22 illustrated in FIGS. 1A to 1D can pass axially through jacks 38 and 40 to open into the volume 14.
  • a passage 23 passing through the upper cylinder 40 is shown in FIGS. 1A to 1D.
  • FIG. 1A illustrates the initial state of the installation, in which magnesium blocks 28 in the solid state have been placed in the crucible 26, the mold 32 containing the fibrous preform 34 has been introduced into the container 10 and the cover 12 has been put in place.
  • the lower cylinder 38 is in the low position and the upper cylinder 40 in the high position.
  • the magnesium 28 contained in the crucible is then heated simultaneously and progressively and the interior volume 14 of the container 10 is evacuated.
  • the heating of magnesium 28 is provided by the first heating means 16 and is accompanied by the preheating of the mold 32 using the second heating means 18.
  • the preheating of the mold 32 aims to prevent the molten metal from solidifies too quickly when it is then transferred to the mold.
  • the preheating temperature of the mold is therefore relatively close to the heating temperature of magnesium 28 (to within a few tens of degrees).
  • the evacuation of the interior volume 14 of the container 10 is ensured by one or more of the access passages which equip the container 10. It is illustrated diagrammatically by the arrow FI in FIG. 1A, opposite the passage 22.
  • the other access passage (s) to the container 10 are then closed by valves (not shown).
  • the vacuum level in the container 10 is stabilized as soon as the pressure reaches a level of about 0.1 mb corresponding to a primary vacuum. This vacuum level is reached well before the beginning of the melting of the magnesium blocks 28 in the crucible 26, which occurs at a temperature of about 600 ° C (curve I). This temperature level is reached after a time which depends in particular on the quantity of magnesium initially placed in the crucible.
  • the evacuation of the interior volume 14 of the container 10 is accompanied by an evacuation of the imprint (s) formed in the mold 32, due to the fact that these communicate with the volume 14 by the tube supply 36.
  • the first step of the process which has just been described with reference to FIG. 1A, is followed by a step which makes it possible to avoid the immediate evaporation of part of the magnesium during its melting , while eliminating any risk of an explosive reaction between magnesium and oxygen and while maintaining a primary vacuum inside the mold 32 ⁇
  • these three objectives are achieved by the fact that a circulation of a neutral gas such as argon is established inside the container 10, under a vacuum level insufficient to cause evaporation of the magnesium, as soon as its temperature reaches a value close to its melting temperature.
  • a neutral gas such as argon
  • the beginning of the melting of the magnesium 28 contained in the crucible 26 is detected and the conditions prevailing in the container 10 are immediately modified, on the one hand, by introducing the lower end of the feed tube 36 into the magnesium melted during melting and, on the other hand, by establishing in volume 14 a circulation of argon under a vacuum level of approximately 100 mb.
  • the plunger of the feed tube 36 in the magnesium being melted is obtained by actuating the lower cylinder 38 so as to raise the crucible 26 as illustrated in FIG. 1B. This eliminates any communication between the interior volume 14 of the container 10 and the imprint (s) formed in the mold 32. The interior of the latter therefore remains under primary vacuum.
  • the circulation of argon is established by injecting argon into the interior volume 14 of the container 10, through one of the access passages, as illustrated by the arrow F2 (opposite the passage 23 formed in the upper cylinder 40) in FIG. 1B, while maintaining in this volume 14 a level of vacuum controlled by at least one other access passage, as illustrated by arrow F3 (opposite passage 22).
  • a neutral gas sweep is thus carried out in the container 10, which avoids any risk of oxygen returning to this container.
  • the vacuum inside the container is insufficient for the molten magnesium to evaporate.
  • the sudden rise in pressure to around 100 mb and the maintenance of the vacuum at this value are illustrated by part IIb of curve II in FIG. 2.
  • the start of melting of magnesium which triggers the step illustrated on FIG.
  • the heating of the magnesium 28 continues until its complete melting in the crucible 26.
  • its temperature is raised to a predetermined value, higher by example of around 100 ° C at its melting temperature.
  • the circulation of argon under a vacuum level of approximately 100 mb is maintained.
  • the time required to obtain this predetermined temperature for example around 700 ° C., varies as appropriate between around 30 minutes and around 60 minutes.
  • the molten magnesium 28 is transferred from the crucible 26 to the mold 32 by the supply tube 36.
  • This transfer is carried out by pressurizing the volume inside 14 of container 10, always under an atmosphere of a neutral gas such as argon. Simultaneously, all the heating means 16 and 18 of the container 10 are stopped.
  • volume 14 is obtained by interrupting all communication between this volume and the vacuum circuit and by connecting it to a pressurized argon circuit, as illustrated by arrow F4 (opposite access passage 23) on Figure 1C.
  • the pressure is thus raised rapidly, for example from about 1 bar / s, to a pressure level generally between about 30 bars and about 100 bars.
  • the rise in pressure to a value of approximately 100 bars is illustrated by the part Ile of curve II in FIG. 2. It takes place, for example, in approximately 1 minute.
  • the speed of pressure build-up in the internal volume 14 of the container 10 can vary according to the nature and the arrangement of the fibers forming the preform 34. In fact, this speed must be as high as possible in order to ensure a efficient filling of the fiber preform, without exceeding a threshold beyond which the fibers forming this preform may be displaced or damaged.
  • the upper cylinder 40 is actuated to accelerate the cooling of the part, as soon as the pressure in the container 10 has reached the predetermined maximum threshold (100 bars in the example represented) .
  • the cooling block 42 then comes into contact with the upper face of the mold 32 (FIG. 1D), so that the magnesium begins to solidify from the top of the mold.
  • the cooling effect can be obtained by a cooling circuit (not shown) housed in the cooling block 42 as well as by a circulation of a neutral cooling gas, such as argon, injected through the access passage 23 ' which passes through the upper cylinder 40.
  • This refrigerant gas then circulates between the refrigerating block 42 and the upper face of the mold 32 in grooves formed radially on the lower face of the cooling block.
  • the cooling of the magnesium in the mold 32 is illustrated by the part 1c of the curve I in FIG. 2.
  • the pressure of approximately 100 bars is maintained until the solidification of the magnesium in the mold 32.
  • the pressure in the container 10 then gradually decreases, while the cooling of the room continues.
  • the jacks 38 and 40 are brought back to their initial positions and the cover 12 of the container 10 is opened to allow the mold 32 to be extracted therefrom.
  • the demolding of the manufactured part or parts is then carried out .
  • the process which has just been described can undergo certain modifications without departing from the scope of the invention.
  • the upper cylinder 40 can be omitted.
  • the cooling of the part is obtained by using a lower cylinder 38 having a greater stroke.
  • the jack 38 is again actuated to raise the crucible 26 beyond the position illustrated in FIGS. 1B and 1C.
  • the crucible 26 then comes to bear against the bottom of the mold 32 and lifts the latter until its upper face comes into contact with the cooler block 42, which is then mounted directly under the cover 12.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Manufacture Of Alloys Or Alloy Compounds (AREA)

Abstract

The invention concerns a method for making a composite part with magnesium matrix by infiltration casting consisting in the following steps: placing in a container (10) a mould (32) provided with a supply tube (36) in its lower part and in which a fibrous preform (34) has been housed. A melting pot (26) containing magnesium blocks (28) is placed beneath the mould (32). The magnesium is heated and the mould is preheated under vacuum until the magnesium starts to melt. The tube (36) is then introduced in the magnesium and neutral gas is circulated in the container, at a vacuum level that is insufficient to cause the magnesium to evaporate. When the magnesium has completely melted, it is transferred into the mould by quick pressurising of the container. The mould is then cooled, and the part is removed therefrom.

Description

PROCEDE DE FABRICATION D'UNE PIECE COMPOSITE A MATRICE MAGNESIUM, PAR FONDERIE SOUS PRESSION PROCESS FOR MANUFACTURING A COMPOSITE PART WITH MAGNESIUM MATRIX, BY PRESSURE FOUNDRY
DESCRIPTIONDESCRIPTION
Domaine techniqueTechnical area
L'invention concerne un procédé permettant de fabriquer, par fonderie sous pression, des pièces en matériau composite à matrice de magnésium. Dans l'ensemble du texte, le termeThe invention relates to a method for manufacturing, by pressure foundry, parts made of a magnesium matrix composite material. Throughout the text, the term
"magnésium" doit être compris comme englobant également tous les alliages à base de magnésium."magnesium" is to be understood as also including all magnesium alloys.
Par ailleurs, l'expression "matériau composite à matrice de magnésium" désigne tout matériau comprenant une structure de renfort, formée généralement de fibres longues telles que des fibres de carbone, d'alumine, etc., noyée dans une matrice de magnésium. Le taux volu ique de fibres contenues dans le matériau est généralement compris entre environ 40 % et environ 60 % .Furthermore, the expression “composite material with a magnesium matrix” designates any material comprising a reinforcing structure, generally formed of long fibers such as carbon fibers, alumina, etc., embedded in a magnesium matrix. The volume rate of fibers contained in the material is generally between approximately 40% and approximately 60%.
Le procédé selon l'invention peut être utilisé avantageusement pour fabriquer toute pièce de fonderie devant présenter à la fois de bonnes caractéristiques mécaniques et une masse réduite. Il trouve notamment une application privilégiée dans les industries aéronautique et spatiale.The method according to the invention can be advantageously used to manufacture any foundry part which must have both good mechanical characteristics and a reduced mass. It finds in particular a privileged application in the aeronautical and space industries.
Etats de la techniqueState of the art
La technique de fonderie sous pression (généralement entre environ 30 bars et environ 100 bars) est connue depuis quelques années, pour fabriquer des pièces en matériau composite à matrice métallique. Selon cette technique, on place dans un même récipient hermétique, comparable à un autoclave, un creuset contenant des blocs du métal destiné à former la matrice de la pièce, ainsi qu'un moule dans lequel on a introduit auparavant une préforme fibreuse.The pressure foundry technique (generally between around 30 bars and around 100 bars) has been known for a few years, for manufacturing parts from a metal matrix composite material. According to this technique, a crucible containing blocks of metal intended to form the matrix of the part is placed in the same hermetic container, comparable to an autoclave, as well as a mold into which a fibrous preform has previously been introduced.
Lors d'une première étape, on fait le vide à l'intérieur du récipient et du moule, on chauffe le creuset contenant les blocs métalliques et on préchauffe le moule. Lorsque le métal contenu dans le creuset est totalement fondu, il est transféré à l'intérieur du moule. Ce transfert est effectué automatiquement en pressurisant le récipient à un niveau de pression, généralement compris entre environ 30 bars et environ 100 bars.During a first step, a vacuum is created inside the container and the mold, the crucible containing the metal blocks is heated and the mold is preheated. When the metal in the crucible is completely melted, it is transferred inside the mold. This transfer is carried out automatically by pressurizing the container at a pressure level, generally between approximately 30 bars and approximately 100 bars.
Dès que le moule est rempli, le refroidissement de la pièce est accéléré en amenant un organe réfrigérant au contact d'une paroi du moule. Tant que la température n'est pas redescendue en dessous de la température de solidification du métal, la pression est maintenue dans le récipient afin de compléter le rétreint naturel du métal.As soon as the mold is filled, the cooling of the part is accelerated by bringing a refrigerating member into contact with a wall of the mold. As long as the temperature has not dropped below the solidification temperature of the metal, the pressure is maintained in the container in order to complete the natural shrinkage of the metal.
Les principales techniques connues de mise en oeuvre de ce procédé sont présentées dans l'article "Pressure Infiltration Casting of Métal Matrix Composites" de Arnold J. COOK et Paul S. ERNER, dans "Materials Science & Engineering" A 144 (Oct. 1991) p. 189-206.The main known techniques for implementing this process are presented in the article "Pressure Infiltration Casting of Metal Matrix Composites" by Arnold J. COOK and Paul S. ERNER, in "Materials Science & Engineering" A 144 (Oct. 1991 ) p. 189-206.
Dans l'une de ces techniques connues, le creuset contenant les blocs métalliques est placé au-dessus du moule et celui-ci est muni en partie haute d'un réceptacle au fond duquel débouche l'empreinte de la pièce à fabriquer. Lors de sa fusion, le métal s'écoule dans le réceptacle par un orifice formé dans le fond du creuset et initialement obturé. Le métal fondu est ensuite transféré dans l'empreinte du moule sous l'effet de la pressurisation du récipient. Le refroidissement de la pièce est alors obtenu au moyen d'un piston réfrigérant amené au contact du fond du moule .In one of these known techniques, the crucible containing the metal blocks is placed above the mold and the latter is provided in the upper part with a receptacle at the bottom of which opens the imprint of the part to be manufactured. When it melts, the metal flows into the receptacle through an orifice formed in the bottom of the crucible and initially closed. The molten metal is then transferred into the mold cavity under the effect of the pressurization of the container. The cooling of the part is then obtained by means of a cooling piston brought into contact with the bottom of the mold.
Cette première technique, dans laquelle le creuset est placé au-dessus du moule, a pour avantage de permettre l'utilisation d'un moule simple et donc peu coûteux à réaliser. Elle est donc relativement économique. Cependant, cette technique est difficilement applicable à la réalisation de pièces composites à matrices de magnésium, malgré l'intérêt que présenteraient de telles pièces dans certaines industries, telles que les industries aéronautique et spatiale. En effet, le transfert préliminaire du métal fondu dans le réceptacle formé à la partie supérieure du moule s'effectue sous vide et sans précaution particulière. Le magnésium risque alors de s'évaporer et de venir se déposer dans l'ensemble de l'installation, ce qui rendrait une partie de celle-ci inutilisable. .Par ailleurs, aucune précaution n'est prise afin d'éviter une réaction explosive du magnésium avec l'oxygène, notamment lors de la mise sous pression de l'enceinte.This first technique, in which the crucible is placed above the mold, has the advantage of allowing the use of a simple mold and therefore inexpensive to produce. It is therefore relatively economical. However, this technique is difficult to apply to the production of composite parts with magnesium matrices, despite the advantage that such parts would present in certain industries, such as the aeronautical and space industries. In fact, the preliminary transfer of the molten metal into the receptacle formed at the upper part of the mold is carried out under vacuum and without any special precautions. The magnesium may then evaporate and come to settle in the entire installation, which would make part of it unusable. .Moreover, no precaution is taken in order to avoid an explosive reaction of magnesium with oxygen, in particular during the pressurization of the enclosure.
Selon une autre technique connue de l'article de COOK et WERNER précité, et du document EP-A-0 388 235, le creuset contenant les blocs métalliques est placé en dessous du moule et le fond de celui-ci est équipé d'un tube d'alimentation qui débouche initialement au-dessus du creuset. La mise sous vide est effectuée par un tube de vide qui débouche directement dans le moule. Lorsque le métal est fondu, le creuset est soulevé de telle sorte que le tube d'alimentation du moule plonge dans le métal fondu. Le transfert du métal fondu à l'intérieur du moule est ensuite obtenu par la pressurisation du récipient. Le refroidissement de la pièce est assuré par un bloc réfrigérant que l'on amène en contact avec la face supérieure du moule.According to another technique known from the aforementioned article by COOK and WERNER, and from document EP-A-0 388 235, the crucible containing the metal blocks is placed below the mold and the bottom of the latter is equipped with a feed tube which initially opens above the crucible. Vacuuming is carried out by a vacuum tube which opens directly into the mold. When the metal is melted, the crucible is lifted so that the mold feed tube plunges into the molten metal. The transfer of the molten metal inside the mold is then obtained by pressurizing the container. The cooling of the part is ensured by a cooling block which is brought into contact with the upper face of the mold.
Cette technique, dans laquelle le creuset est placé en dessous du moule, est plus coûteuse que la précédente du fait que le moule doit comprendre un tube d'alimentation. En revanche, elle supprime une étape intermédiaire de transfert du métal fondu.This technique, in which the crucible is placed below the mold, is more expensive than the previous one because the mold must include a supply tube. On the other hand, it eliminates an intermediate step of transfer of the molten metal.
Par ailleurs, cette technique est également inadaptée à la fabrication de pièces composites à matrice de magnésium. En effet, la fusion du métal s'effectue entièrement sous vide comme dans la technique précédente, de sorte qu'une évaporation sous vide du magnésium est pratiquement inévitable. De plus, il n'est pas prévu non plus de précaution particulière pour éviter un contact explosif avec l'oxygène.Furthermore, this technique is also unsuitable for the production of composite parts with a magnesium matrix. Indeed, the melting of the metal takes place entirely under vacuum as in the previous technique, so that vacuum evaporation of magnesium is practically inevitable. In addition, no special precautions are provided to avoid explosive contact with oxygen.
En outre, dans le document EP-A-0 388 235 comme dans la partie de l'article précité relative à cette technique, la mise sous vide du récipient est effectuée par un passage de vide débouchant directement dans le moule. Cela a pour conséquence d'augmenter encore la complexité et le coût du moule. De plus, le métal liquide risque d'être aspiré par le circuit de vide lors du remplissage du moule. En outre, la présence de ce passage de vide conduit à réduire la surface d'échange thermique servant à refroidir le moule lors de la dernière phase du procédé. Cette analyse des techniques existantes de fabrication de pièces métalliques renforcées, par fonderie sous pression, montre qu'aucune d'entre elles n'est adaptée à la fabrication de pièces à matrice de magnésium. De plus, aucune adaptation évidente de ces techniques à la fabrication de pièces à matrice de magnésium n'est suggérée dans l'état de la technique.In addition, in document EP-A-0 388 235 as in the part of the aforementioned article relating to this technique, the evacuation of the container is carried out by a vacuum passage opening directly into the mold. This has the consequence of further increasing the complexity and the cost of the mold. In addition, the liquid metal may be sucked by the vacuum circuit during filling of the mold. In addition, the presence of this vacuum passage leads to reducing the heat exchange surface used to cool the mold during the last phase of the process. This analysis of existing techniques for manufacturing reinforced metal parts, by pressure foundry, shows that none of them is suitable for the manufacture of parts with a magnesium matrix. In addition, no obvious adaptation of these techniques to the manufacture of parts with a magnesium matrix is suggested in the state of the art.
Exposé de l'invention L'invention a précisément pour objet un procédé de fabrication d'une pièce composite à matrice magnésium mettant généralement en oeuvre les techniques connues de fonderie sous pression, mais dont les caractéristiques originales permettent de supprimer tout risque de réaction explosive magnésium/oxygène, tout en évitant une évaporation sous vide du magnésium.SUMMARY OF THE INVENTION The subject of the invention is precisely a method of manufacturing a composite part with a magnesium matrix generally implementing the known techniques of pressure casting, but whose original characteristics make it possible to eliminate any risk of an explosive magnesium reaction. / oxygen, while avoiding evaporation under vacuum of magnesium.
Conformément à l'invention, ce résultat est obtenu au moyen d'un procédé de fabrication d'une pièce en magnésium renforcée de fibres, caractérisé par le fait qu'il comprend les étapes suivantes :In accordance with the invention, this result is obtained by means of a process for manufacturing a fiber-reinforced magnesium part, characterized in that it comprises the following steps:
- introduction d'une préforme fibreuse dans un moule équipé d'un tube d'alimentation en saillie vers le bas ;- introduction of a fiber preform into a mold fitted with a downwardly projecting feed tube;
- introduction du moule au-dessus d'un creuset rempli de magnésium solide, dans un récipient hermétique ;- introduction of the mold above a crucible filled with solid magnesium, in an airtight container;
- mise sous vide du récipient et du moule qu'il contient et chauffage du magnésium ;- evacuating the container and the mold it contains and heating the magnesium;
- dès que la température du magnésium atteint une valeur proche de sa température de fusion, établissement d'une circulation de gaz neutre dans le récipient, sous un niveau de vide insuffisant pour provoquer une évaporation du magnésium, et introduction du tube d'alimentation dans le magnésium fondu contenu dans le creuset ;- as soon as the temperature of the magnesium reaches a value close to its melting temperature, establishment of a neutral gas circulation in the container, under a vacuum level insufficient to cause evaporation of the magnesium, and introduction of the feed tube into the molten magnesium contained in the crucible;
- pressurisation du récipient sous atmosphère de gaz neutre, de façon à transférer le magnésium fondu dans le moule par le tube d'alimentation ;- pressurization of the container under an atmosphere of neutral gas, so as to transfer the molten magnesium into the mold through the supply tube;
- solidification du magnésium par refroidissement du moule ;- solidification of magnesium by cooling the mold;
- ouverture du récipient et du moule .et extraction de la pièce obtenue. Dans ce procédé, l'augmentation de la pression dès que le magnésium commence à fondre permet d'éviter son évaporation sous vide. Par ailleurs, tout risque de retour d'oxygène à l'intérieur du récipient, susceptible de provoquer une réaction explosive magnésium/oxygène, est totalement empêché par le maintien du récipient en légère dépression et par l'injection simultanée d'un gaz neutre dans celui-ci. En effet, une circulation du gaz neutre est ainsi assurée à tout moment jusqu'à la pressurisation du récipient.- opening of the container and the mold. and extraction of the part obtained. In this process, increasing the pressure as soon as the magnesium begins to melt makes it possible to avoid its evaporation under vacuum. Furthermore, any risk of return of oxygen inside the container, liable to cause an explosive magnesium / oxygen reaction, is completely prevented by keeping the container in slight depression and by the simultaneous injection of a neutral gas into this one. Indeed, a circulation of neutral gas is thus ensured at all times until the container is pressurized.
Dans une forme de réalisation préférentielle de l'invention, on établit la circulation de gaz neutre sous un vide d'environ 100 mb. Au contraire, le chauffage du magnésium s'accompagne d'une mise sous pression initiale du récipient et du moule à environ 0,1 mb .In a preferred embodiment of the invention, the neutral gas circulation is established under a vacuum of approximately 100 mb. On the contrary, the heating of magnesium is accompanied by an initial pressurization of the container and of the mold to approximately 0.1 mb.
La circulation de gaz neutre précédent la pressurisation du récipient est assurée jusqu'à ce que le magnésium atteigne une température maximale, par exemple d'environ 700°C.The neutral gas circulation preceding the pressurization of the container is ensured until the magnesium reaches a maximum temperature, for example around 700 ° C.
Dans la forme de réalisation préférentielle, le gaz neutre utilisé est de l'argon. Par ailleurs, on effectue la mise sous vide du récipient et du moule au travers d'au moins un passage qui débouche directement dans le récipient.In the preferred embodiment, the neutral gas used is argon. Furthermore, the container and the mold are evacuated through at least one passage which opens directly into the container.
De préférence, on amène le magnésium solide au contact du tube d'alimentation en déplaçant le creuset vers le haut dès que la température du magnésium atteint un seuil inférieur à sa température de fusion.Preferably, the solid magnesium is brought into contact with the feed tube by moving the crucible upwards as soon as the temperature of the magnesium reaches a threshold lower than its melting temperature.
Par ailleurs, on refroidit le moule en établissant un contact entre une paroi supérieure de celui-ci et un bloc réfrigérant placé dans le haut du récipient .Furthermore, the mold is cooled by establishing contact between an upper wall thereof and a cooling block placed at the top of the container.
Brève description des dessins On décrira à présent, à titre d'exemple non limitatif, un mode de mise en oeuvre préférentiel du procédé selon l'invention, en se référant aux dessins annexés, dans lesquels :Brief description of the drawings A preferred embodiment of the method according to the invention will now be described, by way of non-limiting example, with reference to the appended drawings, in which:
Les figures 1A à 1D sont des vues en coupe schématique qui illustrent les principales étapes du procédé selon l'invention ; etFigures 1A to 1D are schematic sectional views which illustrate the main steps of the method according to the invention; and
- la figure 2 représente respectivement en I, II, III et IV, les courbes de variation, en fonction du temps t, de la température moyenne θ (en °C) du métal, de la pression P (en bars) régnant dans le récipient, de la position du vérin inférieur et de la position du vérin supérieur.- Figure 2 shows respectively in I, II, III and IV, the variation curves, as a function of time t, of the average temperature θ (in ° C) of the metal, of the pressure P (in bars) prevailing in the container, the position of the lower cylinder and the position of the upper cylinder.
Exposé détaillé d'un mode de mise en oeuvre préférentiel de l'inventionDetailed description of a preferred embodiment of the invention
Conformément à l'invention, l'installation utilisée pour fabriquer une pièce composite en magnésium renforcée de fibres, par fonderie sous pression, présente de nombreuses similitudes avec les installations utilisée habituellement pour la fabrication de pièces composites à matrice métallique. C'est pourquoi il n'en sera pas fait de description détaillée.In accordance with the invention, the installation used to manufacture a fiber-reinforced magnesium composite part, by foundry under pressure, has many similarities with the installations usually used for the manufacture of composite parts with metal matrix. Therefore, no detailed description will be given.
Comme l'illustrent schématiquement les figures 1A à 1D, la mise en oeuvre du procédé selon l'invention est faite dans un récipient hermétique 10 analogue à un autoclave. Ce récipient 10 est un récipient tubulaire centré sur un axe vertical. Il est fermé à sa partie supérieure par un couvercle 12 dont l'ouverture permet d'accéder au volume 14 délimité à l'intérieur du récipient. Lorsque le couvercle 12 est fermé, il coopère de façon étanche avec le bord supérieur du réci- pient 10, de façon à obturer hermétiquement le volume 14.As schematically illustrated in FIGS. 1A to 1D, the implementation of the method according to the invention is carried out in an airtight container 10 similar to an autoclave. This container 10 is a tubular container centered on a vertical axis. It is closed at its upper part by a cover 12, the opening of which gives access to the volume 14 delimited inside the container. When the cover 12 is closed, it cooperates sealingly with the upper edge of the container 10, so as to hermetically seal the volume 14.
Le récipient 10 et son couvercle 14 sont conçus pour supporter une pression maximale d'environ 100 bars dans le volume 14. Comme on l'a illustré schématiquement sur les figures 1A à 1D, le récipient 10 est équipé inté¬ rieurement de premiers moyens de chauffage 16 placés dans la partie basse . du récipient et de deuxièmes moyens de chauffage 18 placés dans la partie haute du récipient. Ces moyens de chauffage 16 et 18 peuvent être constitués par tous dispositifs appropriés tels que des résistances électriques. Leur mise en oeuvre est commandée et régulée depuis l'extérieur du réci¬ pient 10 par une unité de commande (non représentée) . Des thermocouples (non représentés) sont également disposés à l'intérieur du récipient 10, pour permettre la régulation du chauffage assuré par les moyens de chauffage 16 et 18. Un calorifuge (non repré- sente) recouvre intérieurement toutes les parois du récipient 10 afin d'assurer une isolation thermique du volume 14 vis-à-vis de l'extérieur.The container 10 and its lid 14 are designed to withstand a maximum pressure of about 100 bar in the volume 14. As schematically illustrated in Figures 1A to 1D, the container 10 is equipped Internal ¬ quently first means heating 16 placed in the lower part. of the container and second heating means 18 placed in the upper part of the container. These heating means 16 and 18 can be constituted by any suitable devices such as electrical resistors. Their implementation is controlled and regulated from the outside of reci ¬ tainer 10 by a control unit (not shown). Thermocouples (not shown) are also arranged inside the container 10, to allow the regulation of the heating provided by the heating means 16 and 18. A heat insulator (not shown path) internally covers all the walls of the container 10 in order to provide thermal insulation of the volume 14 from the outside.
Le récipient 10 est également équipé de plusieurs passages d'accès dont un seul a été représenté schématiquement en 22 sur les figures 1A à 1D. Dans la pratique, plusieurs passages sont généralement agencés dans le fond du récipient 10 et dans le couvercle 12. Comme cela apparaîtra mieux dans la suite de la description, ils ont pour principale fonctions de relier le volume clos 14 délimité par le récipient 10 soit à un circuit de vide (non représenté) soit à une source (non représentée) d'un gaz neutre sous pression tel que de l'argon. Le fond du récipient 10 est équipé intérieurement d'un socle (non représenté) sur lequel peut reposer un creuset 26 qui contient initialement des blocs de magnésium 28 solide. Ce creuset 26 est placé à l'intérieur des premiers moyens de chauffage 16.The container 10 is also equipped with several access passages, only one of which has been shown diagrammatically at 22 in FIGS. 1A to 1D. In practice, several passages are generally arranged in the bottom of the container 10 and in the cover 12. As will appear better in the following description, their main functions are to connect the closed volume 14 delimited by the container 10 either to a vacuum circuit (not shown) is at a source (not shown) of a pressurized neutral gas such as argon. The bottom of the container 10 is internally equipped with a base (not shown) on which a crucible 26 can rest, which initially contains solid magnesium blocks 28. This crucible 26 is placed inside the first heating means 16.
Dans sa partie haute équipée des deuxièmes moyens de chauffage 18, le récipient 10 est muni d'au moins un support 30 sur. lequel peut être placé un moule 32. Le moulé 32 comporte intérieurement une ou plusieurs empreintes dont les formes et les dimensions sont identiques à celles de la ou des pièce (s) à réaliser. Chaque empreinte est remplie d'une préforme fibreuse 34 avant que le moule ne soit introduit dans le récipient 10. Les préformes fibreuses sont généralement formées de fibres longues de carbone, alumine, ou autre destinées à former les renforts de la pièce à réaliser. Le taux volu ique de fibres de la préforme fibreuse 34 est généralement compris entre environ 40 % et environ 60 % du volume total de 1 ' empreinte .In its upper part equipped with second heating means 18, the container 10 is provided with at least one support 30 on. which can be placed a mold 32. The mold 32 has internally one or more imprints whose shapes and dimensions are identical to those of the part (s) to be produced. Each impression is filled with a fibrous preform 34 before the mold is introduced into the container 10. The fibrous preforms are generally formed of long fibers of carbon, alumina, or other intended to form the reinforcements of the part to be produced. The volume of fiber in the fiber preform 34 is generally between about 40% and about 60% of the total volume of the impression.
Lorsque le moule 32 est placé dans le récipient 10, la ou les empreintes qu'il délimite ne communiquent avec le volume intérieur 14 du récipient que par un seul passage, matérialisé par un tube d'alimentation 36. Plus précisément, le tube d'alimentation 36 débouche dans le fond du moule 32 et se prolonge vers le bas, de préférence selon l'axe vertical du récipient 10. L'extrémité inférieure du tube d'alimentation 36 débouche initialement à un niveau proche de celui du bord supérieur du creuset 26, comme l'illustre la figure 1A. Un vérin inférieur 38, initialement en position basse comme l'illustre la figure 1A, est placé sous le fond du récipient 10 de telle sorte que sa tige 38a traverse ce fond de façon étanche, selon l'axe vertical du récipient. Dans la position basse initiale du vérin inférieur 38, l'extrémité haute de sa tige 38a occupe une position telle que le creuset 26 n'est pas soulevé de son socle.When the mold 32 is placed in the container 10, the imprint (s) it delimits communicate with the internal volume 14 of the container only by a single passage, materialized by a supply tube 36. More precisely, the tube feed 36 opens into the bottom of the mold 32 and extends downward, preferably along the vertical axis of the container 10. The lower end of the feed tube 36 initially opens at a level close to that of the upper edge of the crucible 26, as illustrated in FIG. 1A. A lower cylinder 38, initially in the low position as illustrated in FIG. 1A, is placed under the bottom of the container 10 so that its rod 38a passes through this bottom in a sealed manner, along the vertical axis of the container. In the initial lower position of the lower cylinder 38, the upper end of its rod 38a occupies a position such that the crucible 26 is not lifted from its base.
Un vérin supérieur 40, initialement en position haute, est également monté au-dessus du couvercle 12 du récipient 10. La tige 40a de ce vérin 40, qui traverse le couvercle 12 de façon étanche selon l'axe vertical du récipient 10, porte à son extrémité basse un bloc refroidisseur 42. Dans la position haute initiale du vérin 40, ce bloc refroidisseur 42 est écarté de la face supérieure du moule 32.An upper cylinder 40, initially in the high position, is also mounted above the cover 12 of the container 10. The rod 40a of this cylinder 40, which passes through the cover 12 in a sealed manner along the vertical axis of the container 10, its lower end a cooler block 42. In the initial high position of the jack 40, this cooler block 42 is spaced from the upper face of the mold 32.
Des passages d'accès comparables au passage 22 illustré sur les figures 1A à 1D, peuvent traverser axialement les vérins 38 et 40 pour déboucher dans le volume 14. Ainsi, un passage 23 traversant le vérin supérieur 40 est représenté sur les figures 1A à 1D.Access passages comparable to passage 22 illustrated in FIGS. 1A to 1D, can pass axially through jacks 38 and 40 to open into the volume 14. Thus, a passage 23 passing through the upper cylinder 40 is shown in FIGS. 1A to 1D.
La figure 1A illustre l'état initial de l'installation, dans lequel des blocs de magnésium 28 à l'état solide ont été placés dans le creuset 26, le moule 32 contenant la préforme fibreuse 34 a été introduit dans le récipient 10 et le couvercle 12 a été mis en place. Dans cet état initial, le vérin inférieur 38 est en position basse et le vérin supérieur 40 en position haute.FIG. 1A illustrates the initial state of the installation, in which magnesium blocks 28 in the solid state have been placed in the crucible 26, the mold 32 containing the fibrous preform 34 has been introduced into the container 10 and the cover 12 has been put in place. In this initial state, the lower cylinder 38 is in the low position and the upper cylinder 40 in the high position.
Comme l'illustrent les parties la et lia des courbes I et II sur la figure 2, on réalise alors simultanément et de façon progressive le chauffage du magnésium 28 contenu dans le creuset et la mise sous vide du volume intérieur 14 du récipient 10.As illustrated by the parts la and lia of the curves I and II in FIG. 2, the magnesium 28 contained in the crucible is then heated simultaneously and progressively and the interior volume 14 of the container 10 is evacuated.
Plus précisément, le chauffage du magnésium 28 est assuré par les premiers moyens de chauffage 16 et s'accompagne du préchauffage du moule 32 à l'aide des deuxièmes moyens de chauffage 18. Le préchauffage du moule 32 vise à éviter que le métal fondu se solidifie trop rapidement lorsqu'il est transféré ensuite dans le moule. La température de préchauffage du moule est donc relativement proche de la température de chauffage du magnésium 28 (à quelques dizaines de degrés près) .More specifically, the heating of magnesium 28 is provided by the first heating means 16 and is accompanied by the preheating of the mold 32 using the second heating means 18. The preheating of the mold 32 aims to prevent the molten metal from solidifies too quickly when it is then transferred to the mold. The preheating temperature of the mold is therefore relatively close to the heating temperature of magnesium 28 (to within a few tens of degrees).
Par ailleurs, la mise sous vide du volume intérieur 14 du récipient 10 est assurée par un ou plusieurs des passages d'accès qui équipent le récipient 10. Elle est illustrée schématiquement par la flèche FI sur la figure 1A, en face du passage 22. Le ou les autres passages d'accès au récipient 10 sont alors fermés par des vannes (non représentées) . Comme l'illustre la partie lia de la courbe II sur la figure 2, le niveau de vide dans le récipient 10 est stabilisé dès que la pression atteint un niveau d'environ 0,1 mb correspondant à un vide primaire. Ce niveau de vide est atteint bien avant le début de la fusion des blocs de magnésium 28 dans le creuset 26, qui se produit à une température d'environ 600°C (courbe I) . Ce niveau de température est atteint au bout d'un temps qui dépend notamment de la quantité de magnésium placée initialement dans le creuset.Furthermore, the evacuation of the interior volume 14 of the container 10 is ensured by one or more of the access passages which equip the container 10. It is illustrated diagrammatically by the arrow FI in FIG. 1A, opposite the passage 22. The other access passage (s) to the container 10 are then closed by valves (not shown). As illustrated in part 11a of curve II in FIG. 2, the vacuum level in the container 10 is stabilized as soon as the pressure reaches a level of about 0.1 mb corresponding to a primary vacuum. This vacuum level is reached well before the beginning of the melting of the magnesium blocks 28 in the crucible 26, which occurs at a temperature of about 600 ° C (curve I). This temperature level is reached after a time which depends in particular on the quantity of magnesium initially placed in the crucible.
Il est à noter que la mise sous vide du volume intérieur 14 du récipient 10 s'accompagne d'une mise sous vide de la ou des empreintes formées dans le moule 32, du fait que celles-ci communiquent avec le volume 14 par le tube d'alimentation 36.It should be noted that the evacuation of the interior volume 14 of the container 10 is accompanied by an evacuation of the imprint (s) formed in the mold 32, due to the fact that these communicate with the volume 14 by the tube supply 36.
Conformément à l'invention, la première étape du procédé qui vient d'être décrite en se référant à la figure 1A, est suivie d'une étape qui permet d'éviter 1 ' évaporation immédiate d'une partie du magnésium lors de sa fusion, tout en supprimant tout risque de réaction explosive entre le magnésium et l'oxygène et tout en maintenant un vide primaire à l'intérieur du moule 32^ According to the invention, the first step of the process which has just been described with reference to FIG. 1A, is followed by a step which makes it possible to avoid the immediate evaporation of part of the magnesium during its melting , while eliminating any risk of an explosive reaction between magnesium and oxygen and while maintaining a primary vacuum inside the mold 32 ^
En effet, si la fusion du magnésium se produisait sous vide primaire, une partie du magnésium serait évaporée dans l'installation et notamment dans le circuit de vide, ce qui risquerait de rendre cette installation inopérante pour toute utilisation ultérieure. Par ailleurs, la suppression du vide lors de la fusion du magnésium risquerait d'avoir pour conséquence un retour d'air à l'intérieur du récipient 10, ce qui est inacceptable compte tenu du caractère explosif de la réaction magnésium/oxygène. En outre, il est indispensable de maintenir un vide primaire à l'intérieur du moule 32, afin d'être certain que le remplissage de celui-ci s'effectue correctement.Indeed, if the melting of magnesium occurs under primary vacuum, part of the magnesium would be evaporated in the installation and in particular in the vacuum circuit, which would risk making this installation inoperative for any subsequent use. Furthermore, the removal of the vacuum during the melting of the magnesium would risk having the consequence of a return of air inside the container 10, which is unacceptable given the explosive nature of the magnesium / oxygen reaction. Furthermore, it it is essential to maintain a primary vacuum inside the mold 32, in order to be certain that the filling thereof takes place correctly.
Conformément à l'invention, ces trois objectifs sont atteints par le fait qu'on établit une circulation d'un gaz neutre tel que de l'argon à l'intérieur du récipient 10, sous un niveau de vide insuffisant pour provoquer une évaporation du magnésium, dès que la température de celui-ci atteint une valeur proche de sa température de fusion.In accordance with the invention, these three objectives are achieved by the fact that a circulation of a neutral gas such as argon is established inside the container 10, under a vacuum level insufficient to cause evaporation of the magnesium, as soon as its temperature reaches a value close to its melting temperature.
Plus précisément, on détecte le début de la fusion du magnésium 28 contenu dans le creuset 26 et on modifie immédiatement les conditions régnant dans le récipient 10, d'une part, en introduisant l'extrémité basse du tube d'alimentation 36 dans le magnésium fondu en cours de fusion et, d'autre part, en établissant dans le volume 14 une circulation d'argon sous un niveau de vide d'environ 100 mb.More precisely, the beginning of the melting of the magnesium 28 contained in the crucible 26 is detected and the conditions prevailing in the container 10 are immediately modified, on the one hand, by introducing the lower end of the feed tube 36 into the magnesium melted during melting and, on the other hand, by establishing in volume 14 a circulation of argon under a vacuum level of approximately 100 mb.
La plongée du tube d'alimentation 36 dans le magnésium en cours de fusion est obtenue en actionnant le vérin inférieur 38 de façon à soulever le creuset 26 comme l'illustre la figure 1B. Cela permet de supprimer toute communication entre le volume intérieure 14 du récipient 10 et la ou les empreintes formées dans le moule 32. L'intérieur de celui-ci reste donc sous vide primaire.The plunger of the feed tube 36 in the magnesium being melted is obtained by actuating the lower cylinder 38 so as to raise the crucible 26 as illustrated in FIG. 1B. This eliminates any communication between the interior volume 14 of the container 10 and the imprint (s) formed in the mold 32. The interior of the latter therefore remains under primary vacuum.
Par ailleurs, la circulation d'argon est établie en injectant de l'argon dans le volume intérieur 14 du récipient 10, par l'un des passages d'accès, comme on l'a illustré par la flèche F2 (en face du passage 23 formé dans le vérin supérieur 40) sur la figure 1B, tout en maintenant dans ce volume 14 un niveau de vide contrôlé, par au moins un autre passage d'accès, comme on l'a illustré par la flèche F3 (en face du passage 22) . On réalise ainsi un balayage de gaz neutre dans le récipient 10, qui évite tout risque de retour d'oxygène vers ce récipient. Cependant, la dépression à l'intérieur du récipient est insuffisante pour que le magnésium fondu s'évapore. La remontée brutale de la pression jusqu'à environ 100 mb et le maintien du vide à cette valeur sont illustrés par la partie Ilb de la courbe II sur la figure 2. Le début de fusion du magnésium, qui déclenche l'étape illustrée sur la figure 1B, peut être avantageusement détecté en utilisant le vérin inférieur 38. A cet effet, ce vérin 38 est actionné bien avant que la température du magnésium n'atteigne 600°C. Cet actionnement est illustré par la courbe III sur la figure 2. Il a pour effet d'amener l'extrémité inférieure du tube d'alimentation 36 en appui contre les blocs de magnésium 28 contenus dans le creuset 26. Celui-ci s'élève ensuite progressivement dès que la fusion du magnésium débute. Un détecteur judicieusement placé déclenche simultanément l'injection de l'argon et la remontée de la pression, dès que la montée du creuset 26 révèle le début de la fusion du magnésium. La position haute du creuset, illustrée sur la figure 1B, peut être définie par une butée ou par un détecteur (non représenté) .Furthermore, the circulation of argon is established by injecting argon into the interior volume 14 of the container 10, through one of the access passages, as illustrated by the arrow F2 (opposite the passage 23 formed in the upper cylinder 40) in FIG. 1B, while maintaining in this volume 14 a level of vacuum controlled by at least one other access passage, as illustrated by arrow F3 (opposite passage 22). A neutral gas sweep is thus carried out in the container 10, which avoids any risk of oxygen returning to this container. However, the vacuum inside the container is insufficient for the molten magnesium to evaporate. The sudden rise in pressure to around 100 mb and the maintenance of the vacuum at this value are illustrated by part IIb of curve II in FIG. 2. The start of melting of magnesium, which triggers the step illustrated on FIG. 1B can be advantageously detected by using the lower cylinder 38. To this end, this cylinder 38 is actuated well before the temperature of the magnesium reaches 600 ° C. This actuation is illustrated by curve III in FIG. 2. Its effect is to bring the lower end of the supply tube 36 to bear against the magnesium blocks 28 contained in the crucible 26. The latter rises then gradually as soon as the fusion of magnesium begins. A judiciously placed detector simultaneously triggers the injection of argon and the rise in pressure, as soon as the rise of crucible 26 reveals the beginning of the melting of magnesium. The high position of the crucible, illustrated in FIG. 1B, can be defined by a stop or by a detector (not shown).
Comme l'illustre la partie Ib de la courbe I sur la figure 2, le chauffage du magnésium 28 se poursuit jusqu'à sa fusion complète dans le creuset 26. Afin de garantir cette fusion complète et de permettre un transfert du magnésium dans le moule sans risque de solidification prématurée, sa température est élevée jusqu'à une valeur prédéterminée, supérieure par exemple d'environ 100°C à sa température de fusion. Simultanément, la circulation d'argon sous un niveau de vide d'environ 100 mb est maintenue.As illustrated in part Ib of curve I in FIG. 2, the heating of the magnesium 28 continues until its complete melting in the crucible 26. In order to guarantee this complete melting and to allow transfer of the magnesium into the mold without risk of premature solidification, its temperature is raised to a predetermined value, higher by example of around 100 ° C at its melting temperature. At the same time, the circulation of argon under a vacuum level of approximately 100 mb is maintained.
Le temps nécessaire à l'obtention de cette température prédéterminée, par exemple d'environ 700°C, varie selon le cas entre environ 30 minutes et environ 60 minutes.The time required to obtain this predetermined temperature, for example around 700 ° C., varies as appropriate between around 30 minutes and around 60 minutes.
Lorsque la température du magnésium atteint cette valeur prédéterminée, par exemple d'environ 700°C, on réalise le transfert du magnésium fondu 28 du creuset 26 dans le moule 32 par le tube d'alimentation 36. Ce transfert est réalisé en pressurisant le volume intérieur 14 du récipient 10, toujours sous atmosphère d'un gaz neutre tel que de l'argon. Simultanément, tous les moyens de chauffage 16 et 18 du récipient 10 sont stoppés .When the temperature of the magnesium reaches this predetermined value, for example around 700 ° C., the molten magnesium 28 is transferred from the crucible 26 to the mold 32 by the supply tube 36. This transfer is carried out by pressurizing the volume inside 14 of container 10, always under an atmosphere of a neutral gas such as argon. Simultaneously, all the heating means 16 and 18 of the container 10 are stopped.
La pressurisation du volume 14 est obtenue en interrompant toute communication entre ce volume et le circuit de vide et en le reliant à un circuit d'argon sous pression, comme l'illustre la flèche F4 (en face du passage d'accès 23) sur la figure 1C. On élève ainsi rapidement la pression, par exemple d'environ 1 bar/s, jusqu'à un niveau de pression généralement compris entre environ 30 bars et environ 100 bars. La montée en pression jusqu'à une valeur d'environ 100 bars est illustrée par la partie Ile de la courbe II sur la figure 2. Elle s'effectue, par exemple, en environ 1 minute.The pressurization of volume 14 is obtained by interrupting all communication between this volume and the vacuum circuit and by connecting it to a pressurized argon circuit, as illustrated by arrow F4 (opposite access passage 23) on Figure 1C. The pressure is thus raised rapidly, for example from about 1 bar / s, to a pressure level generally between about 30 bars and about 100 bars. The rise in pressure to a value of approximately 100 bars is illustrated by the part Ile of curve II in FIG. 2. It takes place, for example, in approximately 1 minute.
La pressurisation du volume intérieur 14 du récipient 10 crée une différence importante de pression entre ce volume et l'intérieur du moule 32, toujours sous vide primaire. Sous l'effet de cette différence de pression, le magnésium liquide est transféré rapidement dans le moule 32 par le tube d'alimentation 36, comme le montre la figure 1C.The pressurization of the interior volume 14 of the container 10 creates a significant difference in pressure between this volume and the interior of the mold 32, always under primary vacuum. Under the effect of this pressure difference, the liquid magnesium is transferred quickly in the mold 32 by the feed tube 36, as shown in Figure 1C.
Il est à noter que la vitesse de montée en pression dans le volume intérieur 14 du récipient 10 peut varier selon la nature et la disposition des fibres formant la préforme 34. En effet, cette vitesse doit être aussi élevée que possible afin d'assurer un remplissage efficace de la préforme fibreuse, sans pour autant excéder un seuil au-delà duquel les fibres formant cette préforme risquent d'être déplacées ou endommagées .It should be noted that the speed of pressure build-up in the internal volume 14 of the container 10 can vary according to the nature and the arrangement of the fibers forming the preform 34. In fact, this speed must be as high as possible in order to ensure a efficient filling of the fiber preform, without exceeding a threshold beyond which the fibers forming this preform may be displaced or damaged.
Comme on l'a illustré par la courbe IV sur la figure 2, le vérin supérieur 40 est actionné pour accélérer le refroidissement de la pièce, dès que la pression dans le récipient 10 a atteint le seuil maximal prédéterminé (100 bars dans l'exemple représenté) . Le bloc réfrigérant 42 vient alors au contact de la face supérieure du moule 32 (figure 1D) , de sorte que le magnésium commence à se solidifier à partir du haut du moule.As illustrated by curve IV in FIG. 2, the upper cylinder 40 is actuated to accelerate the cooling of the part, as soon as the pressure in the container 10 has reached the predetermined maximum threshold (100 bars in the example represented) . The cooling block 42 then comes into contact with the upper face of the mold 32 (FIG. 1D), so that the magnesium begins to solidify from the top of the mold.
L'effet réfrigérant peut être obtenu par un circuit réfrigérant (non représenté) logé dans le bloc refroidisseur 42 ainsi que par une circulation d'un gaz neutre réfrigérant, tel que de l'argon, injecté par le passage d'accès 23 'qui traverse le vérin supérieur 40. Ce gaz réfrigérant circule alors entre le bloc réfrigérant 42 et la face supérieure du moule 32 dans des rainures formées radialement sur la face inférieure du bloc réfrigérant. Le refroidissement du magnésium dans le moule 32 est illustré par la partie le de la courbe I sur la figure 2. Comme l'illustre la partie Ild de la courbe II sur la figure 2, la pression d'environ 100 bars est maintenue jusqu'à la solidification complète du magnésium dans le moule 32. La pression dans le récipient 10 redescend ensuite progressivement, alors que le refroidissement de la pièce se poursuit.The cooling effect can be obtained by a cooling circuit (not shown) housed in the cooling block 42 as well as by a circulation of a neutral cooling gas, such as argon, injected through the access passage 23 ' which passes through the upper cylinder 40. This refrigerant gas then circulates between the refrigerating block 42 and the upper face of the mold 32 in grooves formed radially on the lower face of the cooling block. The cooling of the magnesium in the mold 32 is illustrated by the part 1c of the curve I in FIG. 2. As illustrated in part Ild of curve II in FIG. 2, the pressure of approximately 100 bars is maintained until the solidification of the magnesium in the mold 32. The pressure in the container 10 then gradually decreases, while the cooling of the room continues.
Lorsque le refroidissement de la pièce est terminé, les vérins 38 et 40 sont ramenés dans leurs positions initiales et le couvercle 12 du récipient 10 est ouvert pour permettre d'en extraire le moule 32. Le démoulage de la ou des pièces fabriquées est ensuite effectué .When the cooling of the part is finished, the jacks 38 and 40 are brought back to their initial positions and the cover 12 of the container 10 is opened to allow the mold 32 to be extracted therefrom. The demolding of the manufactured part or parts is then carried out .
Bien entendu, le procédé qui vient d'être décrit peut subir certaines modifications sans sortir du cadre de l'invention. Ainsi, le vérin supérieur 40 peut être supprimé. Dans ce cas, le refroidissement de la pièce est obtenu en utilisant un vérin inférieur 38 présentant une plus grande course. Lorsqu'on désire commencer le refroidissement, le vérin 38 est à nouveau actionné pour soulever le creuset 26 au-delà de la position illustrée sur les figures IB et 1C. Le creuset 26 vient alors en appui contre le fond du moule 32 et soulève celui-ci jusqu-'à ce que sa face supérieure vienne en contact avec le bloc refroidisseur 42, qui est alors monté directement sous le couvercle 12.Of course, the process which has just been described can undergo certain modifications without departing from the scope of the invention. Thus, the upper cylinder 40 can be omitted. In this case, the cooling of the part is obtained by using a lower cylinder 38 having a greater stroke. When it is desired to start cooling, the jack 38 is again actuated to raise the crucible 26 beyond the position illustrated in FIGS. 1B and 1C. The crucible 26 then comes to bear against the bottom of the mold 32 and lifts the latter until its upper face comes into contact with the cooler block 42, which is then mounted directly under the cover 12.
Par ailleurs, les niveaux de pression et de température indiqués à titre d'exemple en se référant à la figure 2 peuvent être sensiblement modifiés sans sortir du cadre de l'invention. Il en est de même de la vitesse de montée en pression lors de l'étape illustrée sur la figure 1C. Furthermore, the pressure and temperature levels indicated by way of example with reference to FIG. 2 can be substantially modified without departing from the scope of the invention. The same is true of the pressure build-up speed during the step illustrated in FIG. 1C.

Claims

REVENDICATIONS
1. Procédé de fabrication d'une pièce en magnésium renforcée de fibres, caractérisé par le fait qu'il comprend les étapes suivantes :1. Method for manufacturing a fiber-reinforced magnesium part, characterized in that it comprises the following stages:
- introduction d'une préforme fibreuse (34) dans un moule (32) équipé d'un tube d'alimentation (36) en saillie vers le bas ;- introduction of a fiber preform (34) into a mold (32) equipped with a feed tube (36) projecting downward;
- introduction du moule (32) au-dessus d'un creuset (26) rempli de magnésium (28) solide, dans un récipient hermétique (10) ;- introduction of the mold (32) above a crucible (26) filled with solid magnesium (28), in an airtight container (10);
- mise sous vide du récipient (10) et du moule (32) qu'il contient et chauffage du magnésium ;- Vacuuming the container (10) and the mold (32) it contains and heating the magnesium;
- dès que la température du magnésium (28) atteint une valeur proche de sa température de fusion, établissement d'une circulation de gaz neutre dans le récipient (10), sous un niveau de vide insuffisant pour provoquer une évaporation du magnésium, et introduction du tube d'alimentation (36) dans le magnésium fondu contenu dans le creuset (26) ;- as soon as the magnesium temperature (28) reaches a value close to its melting temperature, establishment of a neutral gas circulation in the container (10), under a vacuum level insufficient to cause evaporation of the magnesium, and introduction supply tube (36) in the molten magnesium contained in the crucible (26);
- pressurisation du récipient (10) sous atmosphère de gaz neutre, de façon à transférer le magnésium fondu dans le moule (32) par le tube d'alimentation (36) ;- pressurization of the container (10) under an atmosphere of neutral gas, so as to transfer the molten magnesium into the mold (32) through the supply tube (36);
- solidification du magnésium par refroidissement du moule (32) ;- solidification of magnesium by cooling the mold (32);
- ouverture du récipient (10) et du moule (32) et extraction de la pièce obtenue.- opening of the container (10) and of the mold (32) and extraction of the part obtained.
2. Procédé selon la revendication 1, dans lequel on établit la circulation de gaz neutre sous un vide d'environ 100 mb . 2. Method according to claim 1, in which the circulation of neutral gas is established under a vacuum of approximately 100 mb.
3. Procédé selon l'une quelconque des revendications 1 et 2, dans lequel le chauffage du magnésium s'accompagne d'une mise sous vide du récipient (10) et du moule (32) à environ 0,1 mb. 3. Method according to any one of claims 1 and 2, wherein the heating of magnesium is accompanied by a vacuum of the container (10) and the mold (32) to about 0.1 mb.
4. Procédé selon l'une quelconque des revendications 1 à 3, dans lequel on chauffe le magnésium (28) jusqu'à une température maximale, à laquelle on réalise la pressurisation du récipient (10) . 4. Method according to any one of claims 1 to 3, in which the magnesium (28) is heated to a maximum temperature, at which the container (10) is pressurized.
5. Procédé selon la revendication 4, dans lequel on chauffe le magnésium (28) jusqu'à environ 700°C.5. The method of claim 4, wherein the magnesium (28) is heated to about 700 ° C.
6. Procédé selon l'une quelconque des revendications précédentes, dans lequel on amène le magnésium solide au contact du tube d'alimentation (36) en déplaçant le creuset (26) vers le haut dès que la température du magnésium atteint un seuil inférieur à sa température de fusion.6. Method according to any one of the preceding claims, in which the solid magnesium is brought into contact with the supply tube (36) by moving the crucible (26) upwards as soon as the temperature of the magnesium reaches a threshold below its melting temperature.
7. Procédé selon l'une quelconque des revendications précédentes, dans lequel on refroidit le moule (32) en établissant un contact entre une paroi supérieure de celui-ci et un bloc réfrigérant (42) placé dans le haut du récipient (10) .7. Method according to any one of the preceding claims, in which the mold is cooled (32) by establishing contact between an upper wall thereof and a cooling block (42) placed in the top of the container (10).
8. Procédé selon l'une quelconque des revendications précédentes, dans lequel on utilise l'argon comme gaz neutre.8. Method according to any one of the preceding claims, in which argon is used as neutral gas.
9. Procédé selon l'une quelconque des revendications précédentes, dans lequel on effectue la mise sous vide du récipient (10) et du moule (32) au travers d'au moins un passage (22) qui débouche directement dans le récipient (10) . 9. Method according to any one of the preceding claims, in which the container (10) and the mold (32) are evacuated through at least one passage (22) which opens directly into the container (10 ).
EP98917209A 1997-03-24 1998-03-23 Method for making a composite part with magnesium matrix by infiltration casting Withdrawn EP0914221A1 (en)

Applications Claiming Priority (3)

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FR9703551 1997-03-24
FR9703551A FR2760984B1 (en) 1997-03-24 1997-03-24 PROCESS FOR MANUFACTURING A COMPOSITE PART WITH MAGNESIUM MATRIX, BY PRESSURE FOUNDRY
PCT/FR1998/000579 WO1998042463A1 (en) 1997-03-24 1998-03-23 Method for making a composite part with magnesium matrix by infiltration casting

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US6247519B1 (en) 1999-07-19 2001-06-19 Her Majesty The Queen In Right Of Canada, As Represented By The Minister Of Natural Resources Preform for magnesium metal matrix composites
US6193915B1 (en) 1999-09-03 2001-02-27 Her Majesty The Queen In Right Of Canada, As Represented By The Minister Of Natural Resources Process for fabricating low volume fraction metal matrix preforms
KR101167838B1 (en) * 2010-05-07 2012-07-24 한국기계연구원 Method for manufacturing metal infiltration casting product using carbon mold
CN103934434A (en) * 2014-05-07 2014-07-23 广西玉柴机器股份有限公司 Die heating device
RU2573283C1 (en) * 2015-06-11 2016-01-20 Цоло Вълков Рашев Method of producing of metallurgical blanks, shaped castings, and device for its implementation
US11040913B1 (en) * 2020-08-14 2021-06-22 Fireline, Inc. Ceramic-metallic composites devoid of porosity and their methods of manufacture

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US3828839A (en) * 1973-04-11 1974-08-13 Du Pont Process for preparing fiber reinforced metal composite structures
ATE125476T1 (en) * 1989-03-17 1995-08-15 Pcc Composites Inc CASTING APPARATUS AND METHOD.
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FR2760984B1 (en) 1999-06-25
JP2000511826A (en) 2000-09-12

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