EP0270466B1 - Pressure die casting machine for metallic articles which may contain ceramic fibres - Google Patents

Description

The present invention relates to a machine for the pressure molding of metal parts, in particular of aluminum and lithium alloys or of magnesium alloys, said alloys possibly containing ceramic fibers, according to the preamble of claim 1.

Those skilled in the art of permanent mold molding know well the methods of pressure molding of metal parts using in particular cold room machines in which an alloy in the liquid state, placed in a container secured to a mold, is pushed by a piston into a cavity in a relatively short time.

The exercise of a pressure which can exceed 10 ² MPa then ensures the supply of the part in liquid alloy during its solidification.

Such methods make it possible to obtain parts with high dimensional accuracy with a very good surface condition, which avoids the need for costly machining later. In addition, the absence of weights leads to a much better mileage than in gravity casting. Finally, it is not necessary to carry out heat treatments because of the good mechanical characteristics presented by the raw molding parts.

All of these advantages make pressure molding an increasingly used process, particularly in the foundries of light metals such as aluminum and magnesium.

However, certain difficulties appeared during the extension of this molding process to new products such as, for example, aluminum-lithium alloys, certain magnesium alloys and composite products containing, in addition to these metals, ceramic fibers.

It is known, in fact, that aluminum-lithium and magnesium alloys are particularly sensitive to oxidation and that the fiber-metal bond in composites can be greatly weakened by the presence in the metal of oxides or other compounds. resulting from an environmental action.

However, most cold room pressure molding machines have not, until now, taken into account this interaction between the molded products and the air.

Thus, for example, in the pressure molding machine described in patent US-A 4,088,178, the metal supply of the container is effected by separation of the injection system from the mold then, tilting by vertical and filling the container with a ladle. It is obvious that by operating in this way, it is not possible to obtain suitable parts from very easily oxidizable alloys.

Prior to the previous patent, US-A 3,058,179 had already, for an entirely different purpose, produced a machine which partially addresses the interaction problem. In fact, the container is here supplied, sheltered from air, by means of a piping plunging into a sealed container containing the metal to be molded in the liquid state and provided at its upper part with an inlet for pressurized inert gas by means of which an overpressure is created on the surface of the liquid to send the latter into the container. According to this arrangement, contact of the liquid metal is avoided with the atmosphere when the container is filled, but the interaction problem is not solved. Indeed, during the upward movement of the piston in the container, in order to compress the metal in the impression, the air contained in the cylinder where the piston slides and which surrounds the piston rod, is found to be put in relation with the liquid supply piping to the container. As at this instant the metal contained in the piping begins to flow back towards the container, it sucks this air and is thus oxidized.

Another even more worrying difficulty is the following: given the high speed of displacement of the piston (more than 0.5 m / sec), the connection of the piping with the atmosphere of the piston cylinder is very rapid so that initially the metal has not yet started to flow back to the container when this connection takes place. This then results in a flow of metal inside the cylinder which quickly compromises the smooth running of the piston and most often results in a stop of the machine. It was to overcome these difficulties that the plaintiff sought and found a new machine.

This falls within the framework of US Pat. No. 3,058,179, that is to say that it combines with the die-casting device a metal supply by means of a pipe immersed in a container from which the metal is forced back towards the container by the action of a pressure P2 of gas. It is characterized in that said piping is equipped at a point on its wall adjacent to the container with an inert gas supply and with a pressure bag P1 depending on the position of the piston and P2.

Under these conditions, assuming the mold ready to be supplied, the molding takes place as follows: inert gas is blown under a pressure Pi into the piping. As the piston is then in the low position, the connection between the container and the piping exists and this gas can spread into the mold cavity thereby purging it of the air it contains.

Then, an overpressure is established on the surface of the metal bath contained in the container. So that the metal rises in the pipework, this excess pressure P ₂ must then be greater than P _i . When the metal has filled the piping, and the container, the piston rises quickly to ensure the compression of the metal. As soon as the piston masks the connection orifice between the piping and the container, which is detected by means of a probe or any detector, the gas is immediately blown in such a way that Pi becomes greater than P ₂ . At this time, the metal is discharged towards the container and any flow of metal towards the cylinder is prevented at the moment when the piston rod appears at the level of the orifice. This gas then fills the entire volume bonded between the metal and its pressure expels the air which comes from the piston cylinder. It should be noted that the length of the piston must be greater than the height of the orifice both in relation to the piping with the container so that the metal is pushed back before the cylinder is put in relation to the piping. Subsequently, when the piston goes down and unmask the orifice, the gas blown then under low pressure will enter the container and prevent any entry of air from the mold which is then opened and this until the value of P ₂ which has been reduced to 0 to facilitate the return of the metal to the container is increased to start a new molding cycle.

Furthermore, there has been provided at the gas blowing point a kind of pocket placed on top of the piping and inside which a gas blanket is kept to prevent the entry of metal into the system. insufflation. This pocket is equipped with a probe which detects an abnormal reduction in the height of the gas mattress and then commands the opening of a special valve responsible for ensuring the additional pressure necessary to maintain the desired height.

The establishment of the suitable pressure differences Pi and P ₂ is obtained using a differential pressure gauge controlled by a probe or any position detector which acts on the opening or closing of suitable valves.

The value of P ₂ must be at least equal to the value of the metallostatic pressure exerted by the metal when it fills the imprint. As for the difference Pi - P ₂ it is of the order of 0.01 MPa.

• . Figure 1 : une vue en coupe verticale axiale d'une installation de moulage.
• . Figure 2 : un schéma de l'installation de l'alimentation en gaz du récipient et de la tuyauterie.

The invention can be illustrated by means of the attached drawings which represent:

• . Figure 1: a view in axial vertical section of a molding installation.
• . Figure 2: a diagram of the installation of the gas supply to the container and the piping.

In FIG. 1, a distinction is made between the fixed lower plate 1 and the mobile upper plate 2 of a vertical die-casting machine. Between these plates is placed the mold 3 having an imprint 4. The lower plate is equipped with an injection device constituted by the container 5 in which slides the piston 6 supported by the rod 7 driven by a reciprocating movement and comes under the effect of the jack 18. Said container is connected via the orifice 8 to the pipe 9 which plunges into the bath 10 of metal to be molded contained in the crucible 11 placed in the sealed container 12 which can be pressurized via the gas inlet 13 in order to send the metal through the piping 9 to the container 5. According to the invention, an inert gas is blown into the pipeline 14 at a point 15 in the piping 9 according to a pressure linked to the pressure prevailing in the container as a function of the position of the piston detected by the probe 17, pressure which can be controlled by the differential pressure regulator 16.

In Figure 2 we find the elements of Figure 1 namely the container 5, the piston 6, the rod 7, the orifice 8, the piping 9, the metal bath 10, the crucible 11, the container 12, l gas inlet 13, the pipe 14, the blowing point 15, the pressure gauge 16 and the probe 17.

• - sur l'arrivée de gaz 13 :
• . le détendeur haute pression 20
• . le détendeur basse pression 21
• l'électrovanne 22 qui assure soit le passage du gaz vers le récipient, soit la mise à l'air du récipient
• . le régleur de débit 23
• . le clapet antiretour 24
• - sur la canalisation 14 :
• . le détendeur haute pression 25
• . le détendeur basse pression 26
• l'électrovanne 27 à 2 voies
• l'électrovanne 28 à 3 voies dont l'une communique avec l'atmosphère. Ce couple de vannes permet de régler la pression P_i dans la tuyauterie par rapport à la pression P2 dans le récipient par l'intermédiaire du manomètre différentiel 16.

Beside these elements, are represented all those which make it possible to operate the installation. These are, in the direction of gas flow:

• - on gas supply 13:
• . the high pressure regulator 20
• . the low pressure regulator 21
• the solenoid valve 22 which ensures either the passage of the gas towards the container, or the venting of the container
• . the flow regulator 23
• . the non-return valve 24
• - on line 14:
• . the high pressure regulator 25
• . the low pressure regulator 26
• 2-way solenoid valve 27
• the 3-way solenoid valve 28, one of which communicates with the atmosphere. This pair of valves makes it possible to adjust the pressure P _i in the piping relative to the pressure P2 in the container by means of the differential pressure gauge 16.

Indeed, if Pi is correct, these two valves are closed, if P ₁ is too low, the valve 27 is open and the venting of the valve 28 is closed; if P ₁ is too strong, the valve 27 is closed and the venting of the valve 28 is open.

• . le régleur de débit 30
• . le clapet antiretour 31
• . le débitmètre 32
• l'électrovanne 33 qui assure l'arrêt ou le passage de gaz insufflé vers 15
• . l'électrovanne 34 avec son régleur de débit 35 qui par suite d'une défaillance du circuit de gaz insufflé s'ouvre uniquement si la sonde 36 indique une montée de métal au niveau du point 15 et le risque d'un bouchage de la canalisation.

the solenoid valve 29, the opening of which allows a high flow of blown gas

• . the flow regulator 30
• . the non-return valve 31
• . the flow meter 32
• the solenoid valve 33 which stops or passes the gas supplied to 15
• . the solenoid valve 34 with its flow regulator 35 which due to a failure of the blown gas circuit opens only if the probe 36 indicates a rise in metal at point 15 and the risk of blockage of the pipe .

• 1. Le moule étant ouvert pour extraire la pièce, le récipient est à la pression atmosphèrique par l'intermédiaire de la vanne 22, le piston en position basse, la vanne 29 fermée, le manomètre différentiel 16 sur la position Pi > P₂ de sorte qu'un faible débit de gaz arrive en 15 par l'intermédiaire du régleur de débit 30 et de la vanne 33.
• 2. Le moule est refermé, prêt pour une nouvelle injection. La situation des éléments précédents reste identique de sorte que le gaz balaye l'empreinte et en chasse l'air.
• 3. L'ordre d'injection étant donné, la vanne 33 se ferme isolant la chambre 15, ce qui annule la condition P1 > P2 tandis que la vanne 29 s'ouvre. La vanne 22 assure le passage du gaz vers le récipient et provoque la montée de métal liquide vers le conteneur. Lorsque le piston commence son ascension la vanne 29 étant ouverte est prête à assurer la pression de gaz Pi > P₂ suffisante pour empêcher l'introduction de métal dans le circuit d'insufflation de gaz par formation d'un matelas protecteur au point 15.
• 4. Dès que le piston obture l'orifice 8, la vanne 33 est ouverte de sorte que Pi devienne supérieure à P₂ et accélère le retour de métal vers le récipient pour éviter tout épanchement de métal dans le cylindre au moment où la tige de piston apparaît au niveau de l'orifice 8 et toute entrée d'air provenant dudit cylindre.
• 5. Le piston continue sa progression vers le haut pendant la solidification de la pièce tandis que la vanne 22 est mise à l'air pour faire chuter P₂. Pi est modulée sur P₂ de manière à avoir constamment Pi > P₂.
• 6. Les vannes restant dans la même position, le moule est ouvert et le piston dans son mouvement ascendant chasse la pastille d'injection.
• 7. Le piston revient à la position basse. Au moment où il démasque l'orifice 8, la vanne 29 se ferme de sorte qu'une légère pression de gaz est assurée par le régleur 30 afin de purger le conteneur.

During a molding cycle, the installation operates as follows:

• 1. The mold being opened to extract the part, the container is at atmospheric pressure via the valve 22, the piston in the low position, the valve 29 closed, the differential pressure gauge 16 in the position Pi> P ₂ of so that a low gas flow rate arrives at 15 via the flow regulator 30 and the valve 33.
• 2. The mold is closed, ready for a new injection. The situation of the preceding elements remains identical so that the gas sweeps the footprint and expels the air.
• 3. The injection order being given, the valve 33 closes isolating the chamber 15, which cancels the condition P1> P2 while the valve 29 opens. The valve 22 ensures the passage of the gas towards the container and causes the rise of liquid metal towards the container. When the piston begins to climb, the valve 29 being open is ready to ensure the gas pressure Pi> P ₂ sufficient to prevent the introduction of metal into the gas insufflation circuit by forming a protective mattress at point 15.
• 4. As soon as the piston closes the orifice 8, the valve 33 is opened so that Pi becomes greater than P ₂ and accelerates the return of metal to the container to avoid any effusion of metal in the cylin dre when the piston rod appears at the opening 8 and any air intake from said cylinder.
• 5. The piston continues its upward progression during the solidification of the part while the valve 22 is vented to cause P ₂ to drop. Pi is modulated on P ₂ so as to constantly have Pi> P ₂ .
• 6. The valves remaining in the same position, the mold is opened and the piston in its upward movement drives out the injection tablet.
• 7. The piston returns to the low position. When it unmasks the orifice 8, the valve 29 closes so that a slight gas pressure is ensured by the regulator 30 in order to purge the container.

The molding cycle is then restarted.

It is clear that all these operations are made automatic using regulation and control devices well known to those skilled in the art.

Claims (4)

1. A cold-chamber pressure casting machine for the production of metal parts possibly containing fibres of ceramic materials formed by a lower fixed plate (1) and an upper movable plate (2) between which is disposed a die (3) having a cavity (4) in the form of the part to be cast, said lower plate being provided with an injection means formed by a container (5) in which is slidable a piston (6) supported by a rod (7), said container being connected by the orifice (8) to a conduit (9) which dips into a liquid bath (10) of the metal to be cast, which is contained in a sealed vessel (12), which vessel can be put under a pressure P2 by way of a gas intake (13) so as to pass the metal towards the container, characterised in that in order to prevent any flow of liquid metal the rod of the piston and any intake of air into the conduit (9), said conduit is provided at a point (15) on its wall which is adjacent to the container (5) with an inert gas feed (14) and a pocket under a pressure Pi dependent on the position of the piston (6) and the pressure P2.

2. A machine according to claim 1 characterised in that P2 being higher than P₁ during the period of feeding metal to the container and the cavity, P₁ becomes higher than P2 at the time when the piston in its upward movement masks the orifice (8).

3. A machine according to claim 1 characterised in that the value of Pi is reduced at the time at which the piston in its downward movement opens the orifice (8), until P2 increases.

4. A machine according to claim 1 characterised in that the differences in the pressures P1 and P2 are obtained by means of a differential manometer (16) controlled by a sensor (17).

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