FR3143393A1 - METHOD FOR MANUFACTURING HOLLOW METAL PARTS BY MOLDING, WITHOUT CORE - Google Patents

Abstract

TITLE: METHOD FOR MANUFACTURING HOLLOW METAL PARTS BY MOLDING, WITHOUT CORE FIELD OF INVENTION The present invention relates to a method of manufacturing hollow metal parts by molding, without a core. The invention also relates to metal parts obtained according to the process of the invention. (Figure 1) .

Description

PROCESS FOR MANUFACTURING HOLLOW METAL PARTS BY CASTING, WITHOUT CORE FIELD OF THE INVENTION

The present invention relates to a method of manufacturing by coreless casting of hollow metal parts. The invention also relates to metal parts obtained according to the method of the invention.

PRIOR ART

Foundry covers the processes of forming metals, in pure state or in alloy form, involving a mold into which molten metal is poured to give, after solidification, a metal part. A multitude of processes have been developed over the last few centuries, capable of producing very diverse metal parts.

Hollow metal parts with a thin shell, for example less than 2 mm, are in particular demand. These parts have a lower weight than a solid part with identical external dimensions and metal, or a hollow part with a thicker shell. In particular, there is a real need to be able to have parts with a thin thickness that is homogeneous, variable and scalable.

Patent FR 2 646 824 B1, for example, discloses the manufacture of a hollow motorcycle chassis in one piece. The method uses a core to achieve the hollow character of the part. However, the use of a core, which must be designed and manufactured beforehand, is restrictive.

One method of making hollow metal parts without using a core is to pour molten metal into a mold. A skin of solidified metal forms on the surface of the mold within seconds, and then the mold is tilted to remove excess liquid metal.

In this process, called " reverse casting ", the fact of hollowing out the mold by tilting results in the metal remaining in contact longer with one part of the mold, namely the part onto which the metal flows after tilting, which leads to an asymmetrical shell, thicker on one side compared to the other side.

Existing processes do not satisfy the need to provide coreless manufacturing processes by casting of hollow metal parts having a shell of controlled low thickness (< 2 mm) in particular between 0.2 mm and 2 mm, and made of a metal or alloy having a melting point above 180°C.

There is therefore a need to provide new processes enabling the manufacturing by casting of parts which cannot be obtained by existing casting processes.

BRIEF OVERVIEW

In this context, a first aim of the invention is to provide a method for manufacturing by molding, without cores, hollow metal parts having a thin shell, i.e. less than 2 mm and greater than 0.2 mm. A second aim of the invention is to provide a method for manufacturing by molding metal parts, making it possible to control the shell thickness of the part to be formed. Another aim of the invention is to be able to implement the method with metals or metal alloys with a melting point greater than 180°C, in particular greater than 320°C. Another aim of the invention is to provide new hollow metal parts.

DETAILED DESCRIPTION

• uneétape 1d’injection d’une masse liquide initiale de métal fondu dans un moule, depuis un contenant comprenant ledit métal fondu, pour obtenir un moule comprenant du métal fondu ;
• uneétape 2de solidification partielle dudit métal fondu au sein du moule pendant un temps suffisant pour former une coque métallique solidifiée en contact avec les parois du moule présentant une température inférieure à la température dusolidusdudit métal fondu, et maintenir en phase liquide la partie restante de la masse liquide initiale dudit métal fondu contenue à l’intérieur de la coque métallique solidifiée, pour obtenir une partie solide constituée de la coque métallique solidifiée, et une phase liquide constituée de la partie restante de la masse liquide initiale dudit métal fondu ;
• uneétape 3de soustraction de la susdite phase liquide, ladite étape de soustraction étant effectuée sans basculement du moule ; et
• uneétape 4de récupération de la pièce métallique creuse sous forme de coque métallique solidifiée,

A first object of the present invention is a method of manufacturing a hollow metal part, said method comprising at least the following steps:

• a step 1 of injecting an initial liquid mass of molten metal into a mold, from a container comprising said molten metal, to obtain a mold comprising molten metal;
• a step 2 of partial solidification of said molten metal within the mold for a time sufficient to form a solidified metal shell in contact with the walls of the mold having a temperature lower than the solidus temperature of said molten metal, and maintaining in liquid phase the remaining part of the initial liquid mass of said molten metal contained inside the solidified metal shell, to obtain a solid part consisting of the solidified metal shell, and a liquid phase consisting of the remaining part of the initial liquid mass of said molten metal;
• a step 3 of subtraction of the above-mentioned liquid phase, said subtraction step being carried out without tilting the mold; and
• a step 4 of recovery of the hollow metal part in the form of a solidified metal shell,

wherein the metal has a melting point above 180°C, in particular above 320°C, and wherein the hollow metal part is formed in the absence of a core,

said method having a thousandth ratio of 1:1 to 1.2:1, preferably about 1:1, in particular 1:1.

When implementing the method of the invention, a molten metal, in the liquid state, is injected into a mold. During its stay in the mold, a portion of the initially molten metal solidifies against the inner wall of the mold, or the imprint, to form a solidified metal shell. This solidified shell is delimited on the outside by the mold, and on the inside by liquid metal, not yet solidified.

The mold is then emptied of the still liquid metal, i.e. not yet solidified, which is inside the shell, thus forming a hollow metal part.

The inventors have found that the method according to the invention allows the manufacture of a wide variety of hollow parts, including for example parts having a thin shell, i.e. less than 2 mm and greater than 0.2 mm. Thanks to emptying without tilting the mold, the method is not dependent on unwanted solidification of the metal, said solidification being completely controlled.

By " hollow metal part " is meant a metal part in the form of a shell which surrounds, or partially surrounds, an empty part. As an example, among the parts in the form of a shell which partially surrounds an empty part, we can cite parts such as cups, bowls, bowls and bottles.

By " partial solidification of the molten metal " is meant that the solidification is sufficient to form the solid shell, while leaving a portion of the metal in a liquid state to allow the hollow portion of the part to be obtained after removal, or draining, of said metal in a liquid state.

By "solid part" we mean a solid phase in the metallurgical or thermodynamic sense. Thus the solid part can be composed of several solid phases, which is the case for example of Al-Si alloys.

By " without tilting the mold " it is meant that the removal of the still liquid metal is done without tilting ( i.e. without rotation around an axis) of the mold, which is usual in a " reverse casting " process. To do this, the mold is emptied using techniques set out below. That being said, it is understood that the absence of tilting of the mold does not prevent the entire mold from being able to be translated above an oven or a ladle in order to receive the emptying.

For the purposes of the present invention, the term " metal " means either a single metal or a metal alloy comprising said metal. Among these metal alloys, mention may be made of a eutectic or near-eutectic alloy, otherwise an alloy with a low solidification range ( i.e. with very close liquidus and solidus temperatures).

A " single metal " is a metal that is not mixed with another element, such as another metal. This is a so-called " pure " metal, having a purity greater than 98%, in particular greater than 99%.

Among the (pure) metals which can be used in the part and the method of the invention, we can cite, by way of example: aluminum (Al), lead (Pb), tin (Sn), copper (Cu), zinc (Zn), iron (Fe), nickel (Ni) and magnesium (Mg).

Among the eutectic alloys which can be used in the part and the method of the invention, we can cite, for example: AlSi12, ZnAl5, AlCu33, AlMg32, MgZn37, CuMn37, CuSi16, SnPb38, eutectic cast iron.

Among the alloys with a low solidification interval which can be used in the part and the method of the invention, we can cite, for example: AlSi10, AlSi2, cast iron relatively close to the Fe-C eutectic, or steel with a very low solidification interval.

By " a melting point above 180°C " is meant in particular a melting point above 200°C, above 320°C, above 500°C and in particular above 660°C. The melting point is in particular between 180°C and 1750°C. By " from 180°C to 1750°C " we also mean the following ranges: from 200°C to 1750°C, from 320°C to 1750°C, from 400°C to 1750°C, from 500°C to 1750°C, from 600°C to 1750°C, from 660°C to 1750°C, from 700°C to 1750°C, from 800°C to 1750°C, from 900°C to 1750°C, from 1000°C to 1750°C, from 1100°C to 1750°C, from 1200°C to 1750°C, from 1300°C to 1750°C, from 1400°C to 1750°C, 1500°C to 1750°C, 180°C to 1600°C, 180°C to 1400°C, 180°C to 1200°C, 180°C to 1000°C, 180°C to 800°C, 200°C to 1600°C, 200°C to 1400°C, 200°C to 1200°C, 200°C to 1000°C, 200°C to 800°C, 320°C to 1600°C, 320°C to 1400°C, 320°C to 1200°C, 320°C at 1000°C, from 320°C to 800°C, from 500°C to 1400°C, from 500°C to 1200°C, from 500°C to 1000°C, from 500°C to 800°C, from 660°C to 1400°C, from 660°C to 1200°C, from 660°C to 1000°C, from 660°C to 800°C.

It is understood that the melting point may correspond to the melting point of a pure metal, or to the liquidus of an alloy. In the foregoing and following, the expression " melting point " refers to both pure metals and alloys; in which case it is understood to mean " the liquidus ".

In general, in foundry, the " milking ratio " refers to the ratio of the mass of the casting cluster to the mass of the finished raw part. The casting cluster corresponds to the part taken out of the mold with all of its adhering casting devices (filling system, feeder, vents, flashes). The milking ratio is therefore often greater than 1, and rarely equal to 1.

In the case of the present process, the ratio that is obtained is 1:1, or close to 1:1, which is exceptional compared to conventional foundry processes. Indeed, the process makes it possible to obtain a raw part at the exit of the mold without or almost without adhering casting artifice, thus eliminating or greatly limiting the finishing. This is made possible because the volume of liquid metal initially injected into the mold is not completely solidified.

By “ close to 1:1 ” we mean 1:1 to 1.2:1. The following ranges are also understood to mean " 1:1 to 1.01:1", "1:1 to 1.02:1", "1:1 to 1.03:1", "1:1 to 1.04:1", "1:1 to 1.05:1", "1:1 to 1.06:1", "1:1 to 1.07:1", "1:1 to 1.08:1", "1:1 to 1.09:1", "1:1 to 1.10:1", "1:1 to 1.11:1", "1:1 to 1.12:1", "1:1 to 1.13:1", "1:1 to 1.14:1", "1:1 to 1.15:1", "1:1 to 1.16:1". 1.16:1", "1:1 to 1.17:1", "1:1 to 1.18:1", "1:1 to 1.19:1".

Step 1 of injecting a liquid mass of molten metal into a mold can be carried out using several techniques. Injection can be carried out by gravity, using a manual or automatic bucket, or even a transfer chute. Injection of the molten metal into the impression can also be carried out via an injection nozzle or a sleeve with an injection piston; the process is then suitable for molding with a low-pressure machine or a pressure injection press, particularly with a hot chamber.

Solidification step 2 forms a shell, or skin, of metal, solidified against the inner wall of the mold. The holding time of the molten metal in the mold depends on several parameters, including for example the difference in materials and initial temperatures between the mold and the molten metal. The holding time also depends on the thickness of the shell to be manufactured. In general, a time of a few seconds to a few minutes is sufficient to obtain a thin shell , i.e. less than 2 mm and greater than 0.2 mm.

Step 3 of subtraction can be carried out by gravity; the liquid metal exits through an opening in the bottom of the mold, initially obstructed by a stopper, a plug, a hatch, or other heating or thermally insulating device, or other device ( eg induction system). It can also be facilitated by the thrust of a pressurized gas in the upper part of the mold.

Step 4 of recovering the hollow metal part can be carried out by known demolding methods. Demolding can for example be carried out by turning the mold over. Beforehand, a grid can be placed on top of the mold to prevent the part from falling out of the mold, breaking or deforming. After turning the mold over, the ejected part is then on said grid.

According to a particular embodiment, the invention relates to a manufacturing method as defined above for the production of a hollow metal part having a thickness of 0.2 mm to 2 mm.

According to a particular embodiment, the invention relates to a manufacturing method as defined above for the production of a hollow metal part consisting of a metal shell which partially or completely surrounds an empty part,

• une surface extérieure lisse,
• une surface intérieure cristallographique.

in which said metal shell has:

• a smooth exterior surface,
• a crystallographic interior surface.

Thus, the method according to the invention can be implemented in different ways:

1- Gravity casting process

In the case of pouring liquid metal by gravity, a fixed mold must have at least one upper inlet to receive the metal and a lower outlet to evacuate the excess alloy still liquid after formation of a solidified skin. It is therefore open on the upper part of the mold to ensure its filling, and it has at least one orifice in the lower part of the mold, plugged by a stopper, a stopper rod or other sealing system which can be opened when emptying the mold.

Typically, the drain hole plug is preheated and/or made of thermally insulating materials. Below the mold, a ladle or furnace collects excess molten alloy.

The gravity casting process is illustrated by the . In this regard, it should be noted that the three diagrams present different technical solutions of the drained casting here carried out only by gravity. The graphics each illustrate a general principle. However, in the majority of cases, the casting is not necessarily of revolution or symmetrical.

During the short filling and emptying phases, the liquid alloy present in the impression solidifies against the walls of the mold. This can lead to variations in the thickness of the solidified shell in places; in particular, the solidified thickness is often thinner at the top of the mold and thicker in the lower part of the mold. To best manage the thickness of the solidified shell, several process parameters can be used: the thickness of the mold (especially with a metal mold), the introduction of coolers (in steel or cast iron, or silicon carbide, or graphite for example) in a sand mold or cooling devices in a metal mold, the preheating or non-uniform heating of the metal mold (generally the mold temperature is warmer in the lower part), the use of different coatings on the impression of the metal mold (insulating and conductive coatings), the use of different sands (more or less thermally conductive) and/or additives in the composition of the sand mold.

In most cases, the position of the drain hole corresponds to the lowest part of the part in the mold. Generally, this hole is located under the mold; but in some cases it can be located on a low side of the mold. For certain particular part geometries, it may be possible to associate a slight inclination of the mold during draining to best facilitate the total evacuation of the residual liquid metal bath still present in the impression.

2- Low pressure casting process

Low pressure is a technical device consisting of bringing an inert gas for the metal such as nitrogen, argon or other, into the hermetic chamber of the furnace containing the molten metal. The pressure of the gas on the surface of the bath allows the molten metal to rise into an injection nozzle which feeds the mold cavity. In general, the mold is placed above the low pressure furnace and the metal enters the cavity from its lower part or from one side.

In the case of low-pressure casting, the mold is equipped with an inlet at the bottom of the mold for injecting the metal. This inlet also serves as a drain for excess metal, which returns directly to the furnace via the injection nozzle. An air intake device, or other gas, can be installed to facilitate the evacuation of the molten metal. Once the mold and metal temperatures are operational, the molten material is injected through the bottom of the mold, then pressurized during solidification, under a controlled atmosphere (nitrogen, argon or other).

This technique makes it possible to control the speed of filling and emptying of the mold, and thanks to the neutral gas limits the formation of oxide skins with oxidizable metals, including for example alumina with aluminum alloys.

This embodiment of the method of the invention is illustrated by Figures 2 and 3.

3- Pressure injection molding process

In the case of die casting, the mold has an inlet, which can also act as an outlet. An air or neutral gas intake device to facilitate the evacuation of the liquid metal can also be installed. Furthermore, the metal inlet pipe into the cavity can be separate from the drain pipe. Once the mold and metal temperatures are operational, the molten metal is injected by a piston or gas into the mold, under pressure (from 5 to 5,000 bars). Injection can also be done under a controlled atmosphere of neutral gas (nitrogen, argon or other). The die injection molding process is very compatible with so-called hot chamber die injection systems, where the drained liquid metal can return directly to the injection chamber, using an injection piston controlled by a hydraulic cylinder or carrying out injection by gas pressure in the chamber. Less easy to implement, the cold chamber pressure process can also be used, particularly in the case where the excess liquid metal is drained via a different conduit from the injection conduit.

This embodiment of the method of the invention is illustrated by Figures 8 to 14.

According to a particular embodiment, the present invention relates to the manufacturing method as defined above, wherein injection step 1 is carried out by gravity, said injection step 1 being carried out by pouring the liquid metal through an opening in the upper part of the mold.

By " upper part of the mold " we mean the apical part of the mold, namely the part which is furthest from the ground.

According to another particular embodiment, the present invention relates to the manufacturing method as defined above, in which injection step 1 is carried out by injection with a low pressure method, said injection step 1 being carried out by applying a gas pressure in the container comprising the liquid metal, making it possible to push said liquid metal into the mold, through an orifice located in the bottom of said mold.

Among the gases that can be used in injection step 1, we can cite, for example: air, nitrogen, argon. It is understood that in the case of the use of an oxidizable metal, such as aluminum alloys, an inert gas such as nitrogen or argon is preferred in order to avoid the formation of alumina skins.

By " the bottom of the mold " we mean the basal part of the mold, namely the part which is closest to the ground.

According to another particular embodiment, the present invention relates to the manufacturing method as defined above, in which injection step 1 is carried out by injection under pressure, said injection step 1 being carried out by injection of the liquid metal using a piston or a gas.

According to another particular embodiment, the present invention relates to the manufacturing method as defined above, in which injection step 1 is carried out by hot chamber pressure injection, said injection step 1 being carried out by injection of the liquid metal using a piston or a gas.

According to another particular embodiment, the present invention relates to the manufacturing method as defined above, in which injection step 1 is carried out by injection under pressure in a cold chamber, said injection step 1 being carried out by injection of the liquid metal using a piston or a gas.

It should be noted that with regard to these two particular embodiments. The injection pressure values are clearly different (under hot chamber pressure: by gas 5 to 110 bars and by hydraulic piston 100 to 400 bars; under cold chamber pressure: by piston 250 to 5000 bars; low pressure: 1.5 bars). In general, the main parting plane of the mold is horizontal in low pressure and vertical in die casting. In low pressure, the mold can be made of sand or metal; in under pressure the mold is only made of metal. Under pressure allows much shorter cycle times and greater geometric precision than low pressure. The architecture of the injection device is also quite different between these processes.

According to another particular embodiment, the present invention relates to the manufacturing method as defined above, in which the demolding step 4 is carried out by turning the mold over. Turning the mold over allows the shell to come out of the mold by gravity. An example of this embodiment is shown schematically in Figure 4C.

According to another particular embodiment, the present invention relates to the manufacturing method as defined above, in which the mold has an opening in the bottom of the mold, which opening is obstructed, during injection step 1 and during solidification step 2, by a closing device, in particular a plug, a stopper or a hatch, subtraction step 3 being initiated by a release of said opening, by removal of said closing device.

This embodiment is illustrated by Figures 1A and 1B. Note that in a particular embodiment, said closing device (stopper, a stopper or hatch) is either preheated, heated or thermally insulating.

According to another particular embodiment, the present invention relates to the manufacturing method as defined above,

in which the mold has air or gas intake means at the top of the mold, said air or gas intake means being closed during injection step 1 and during solidification step 2,

in which subtraction step 3 is facilitated or made possible by the opening of said air or gas intake means causing an intake of air or gas, in particular nitrogen or argon, under pressure, in particular at a pressure equal to or greater than atmospheric pressure.

Advantageously, said air or gas intake means are a trap or plug made of highly thermally insulating material, or of heated or preheated material, locally preventing solidification; or heated metallic or refractory air filter(s); or even an element for piercing the thin skin solidified at this location.

Said air or gas intake means are said to be closed when air or gas cannot penetrate inside the mold.

Said air or gas intake means are said to be open when air or gas can penetrate inside the mold.

In this embodiment, the call or gas means, in particular a plug or a hatch, are made of an insulating material, and/or of heated or preheated material, in order to avoid the solidification of the metal against the part of said device in contact with said metal.

In this way, when the means are removed, an opening is present in the shell formed at the end of solidification step 2. This solution is however generally only used for low pressure and under pressure.

According to another particular embodiment, the present invention relates to the manufacturing method as defined above, in which the melting point of the metal is greater than 180°C, and is in particular between 180°C and 1750°C.

According to another particular embodiment, the present invention relates to the manufacturing method as defined above, in which the melting point of the metal is greater than 320°C, and is in particular between 320°C and 1750°C.

According to another particular embodiment, the present invention relates to the manufacturing method as defined above, in which the melting point of the metal is greater than 500°C, and is in particular between 500°C and 1750°C.

According to another particular embodiment, the present invention relates to the manufacturing method as defined above, in which the melting point of the metal is greater than 660°C, and is in particular between 660 and 1750°C.

According to another particular embodiment, the present invention relates to the method as defined above, in which the metal is pure or alloyed aluminum. In particular, the present invention relates to the method as defined above, in which the metal is pure aluminum. In particular, the present invention also relates to the method as defined above, in which the metal is alloyed aluminum.

According to another particular embodiment, the present invention relates to the method as defined above, in which the metal is the eutectic alloy AlSi12.

According to another particular embodiment, the present invention relates to the method as defined above, in which the mold is made of cast iron, aluminum, steel, metal alloy, and is in particular made of aluminum alloy, or copper alloy.

It is also possible to use other materials constituting the mold, such as: sand, refractory plaster, ceramic, or graphite. The material constituting the mold must be compatible with the metal used in the preparation of the hollow parts. Thus, if the process is used to prepare an aluminum part, whose melting point is around 660°C, it is preferable to choose a mold made of a material with a melting point higher than 660°C, such as, for example, a steel or sand mold, in order to limit the degradation of the mold. For the manufacture of a steel part with a high melting point (casting temperature between 1550°C and 1750°C), a sand or ferrous alloy mold is preferably used.

The method according to the invention allows the manufacture of parts comprising a thin shell. The method also allows the thickness of the solidified shell to be controlled locally. To do this, it is possible to use a mold of variable thickness. The solidified shell will be thicker in the places where the wall of the mold is thicker.

The thickness of the solidified shell can also be controlled by local heating of the mold and/or the coatings deposited in the mold. Thus, the solidified shell will be less thick at the places in contact with the overheated parts of the mold, or in contact with the parts of the impression coated with thermal insulating coating.

According to another particular embodiment, the present invention relates to the method as defined above, in which the mold is a mold of variable thickness. This embodiment makes it possible in particular to better control the thermal mapping of the mold and therefore to better control the thicknesses of the molded metal parts.

According to another particular embodiment, the present invention relates to the method as defined above, in which the mold is locally heated or cooled to a temperature different from that of the rest of the mold. This temperature is dependent on the geometry of the part and the mold, as well as the nature of the materials used (mold and cast metal).

In some cases, this embodiment allows for better control of the thickness (variable or uniform) of the metal parts. Similarly, the use of different coatings and/or a variation in the thickness of the mold and/or the integration of a thermal seal in the mold (air blades or embedded insulating material) and/or a cooling device (circulation of a fluid or embedding of a thermally conductive material) can also allow for better management of the thickness of the solidified shell.

According to another particular embodiment, the present invention relates to the method as defined above, in which the mold is coated with a coating.

The " pot coating " is a coating applied to, or against, the inner face of the mold (impression), i.e. the face that will be in contact with the molten metal. The pot coating facilitates demolding, limits mold-alloy chemical interactions and thermal shocks, and helps control solidification. A pot coating is used when using a metal mold, and is made of an insulating or thermally conductive material. The pot coating has a thickness of 0.2 to 0.5 mm. "0.2 to 0.5 mm" also means the following ranges: 0.3 to 0.5 mm, 0.4 to 0.5 mm, 0.2 to 0.4 mm, 0.2 to 0.3 mm, 0.3 to 0.4 mm.

On this point, it should be noted that a coating, often called a "layer", can also be applied to the imprint of a sand mold. In general, its role is to improve the surface condition of the casting (attenuation of the sand grain size), or sometimes even to accelerate locally and on the surface the solidification of the cast metal. The common composition corresponds to a refractory flour (zircon, graphite, etc.) suspended in a liquid (water, alcohol) which is evaporated after application (by spray gun, brush or dipping). When high thermal conductivity is required for this surface deposit, the layer may contain aluminum powder.

According to another particular embodiment, the present invention relates to the method as defined above, in which the coating material is a thermal insulating material, in particular chosen from talc, kaolin, Spanish white and Meudon white. It should be noted that the thickness of this type of coating material on the mold imprint is often between 0.3 mm and 0.5 mm.

According to another particular embodiment, the present invention relates to the method as defined above, in which the coating material is a thermally conductive material, in particular colloidal graphite. It should be noted that the thickness of this type of coating material on the mold imprint is often of the order of 0.2 to 0.3 mm.

According to another particular embodiment, the present invention relates to the method as defined above, in which, at the start of injection step 1, the mold is at a temperature higher than ambient temperature. The mold is in particular heated when a mold made of a metallic material is used. However, it is not necessary to heat the mold if said mold is a sand mold.

“ Room temperature ” means a temperature between 15°C and 30°C, in particular between 20 and 25°C.

Heating the mold allows the molten metal to be received, while limiting the risks of degradation of the metal mold, eg rupture by thermal shock, cracking due to thermal fatigue. In addition, preheating the mold prevents premature solidification of the poured metal leading to incomplete filling of the mold, called " unwelcome ".

Alloy and mold temperatures can be measured by thermocouples or optical sensors.

According to another particular embodiment, the present invention relates to the method as defined above, in which, during injection step 1, the mold is at a temperature such that the difference between the temperature of the mold and the temperature of the mass of molten metal is between 50°C and 1750°C.

According to this embodiment, it is understood that the temperature of the mold is 50°C to 1750°C lower than the temperature of the mass of molten metal (commonly called "pouring temperature"). On this point, it is necessary to differentiate the pouring temperature (pouring temperature of the molten metal in the mold) from the melting point of said metal (liquidus temperature). The difference between these two temperatures (pouring temperature and liquidus temperature) is called " overheating " in the professional vocabulary of foundries.

• en moulage au sable où le moule est à température ambiante, la surchauffe est couramment comprise de 50°C à 200°C pour une coulée par gravité, et est très souvent comprise de 100°C à 150°C ;
• en moulage avec une coquille métallique et coulée par gravité, la surchauffe pour un alliage coulé d’aluminium est souvent comprise de 50°C à 100°C et la température du moule est de l’ordre de 350°C ; et
• en moulage sous pression, il est parfois possible d’avoir une surchauffe nulle (température d’injection du métal fondu dans le moule métallique égale à la température de liquidus du métal fondu), ou comprise entre 0°C et 150°C, ou plus rarement négative (c’est-à-dire avec une température d’injection du métal fondu comprise entre la température de liquidus et celle de solidus du métal fondu).

For information purposes:

• in sand casting where the mold is at room temperature, the superheat is commonly between 50°C and 200°C for gravity casting, and is very often between 100°C and 150°C;
• in metal shell casting and gravity casting, the superheat for a cast aluminum alloy is often between 50°C and 100°C and the mold temperature is of the order of 350°C; and
• in die casting, it is sometimes possible to have zero superheat (injection temperature of the molten metal into the metal mold equal to the liquidus temperature of the molten metal), or between 0°C and 150°C, or more rarely negative (i.e. with an injection temperature of the molten metal between the liquidus temperature and the solidus temperature of the molten metal).

Following the experiments, the inventors unexpectedly found that the superheating with the innovative method according to the invention can be lower than that commonly used in conventional foundry processes, while in general it is expected that a thin part requires high superheating. This allows energy savings and improves the service life of the metal mold.

By "from 50°C to 1750°C" we also mean the following ranges: from 50 to 75°C, from 75 to 100°C, from 100 to 200°C, from 200 to 300°C, from 300 to 400°C, from 400 to 500°C, from 500 to 600°C, from 600 to 700°C, from 700 to 800°C, from 800 to 900°C, from 900 to 1000°C, from 1000 to 1100°C, from 1100 to 1200°C, from 1200 to 1300°C, from 1300 to 1400 °C, from 1400 to 1500°C, 1500 to 1600°C, 1600 to 1700°C, 1700 to 1750°C.

As an example for the theoretical values in classic shell casting: in the case where the metal to be cast by gravity is pure aluminium, the metal mould is preferably heated to a temperature of around 350°C, the melting point of pure aluminium being around 660°C and the superheat often chosen to be around 75°C, the temperature of the mould is in this case around 385°C lower than the casting temperature of the molten metal. These values correspond to the temperatures commonly used in so-called “shell” casting (i.e. in a metal mould with gravity casting).

As a non-limiting practical example, corresponding to the embodiment illustrated in : when the metal to be cast is the AlSi12 alloy, the metal mold (here made of AlSi7Mg alloy) is preferably heated to a temperature of approximately 169.5°C, the casting temperature of the alloy being 719°C. The temperature of the mold is in this case approximately 549.5°C lower than the casting temperature of the AlSi12 alloy, and 407.5°C lower than the liquidus temperature (called in this text "melting point", equal to 577°C without metallurgical treatment to modify the eutectic) of the AlSi12 alloy.

In view of this and the embodiment of the method of the invention implemented, it is understood that in terms of temperatures, several factors may intervene such as: the initial thermal mapping of the mold, the liquidus temperature of the cast metal (value fixed by the nature of the material) and the superheat used (fixing the pouring temperature of said molten metal). Also, three other parameters intervene for the quality of the molded part obtained: the pouring time of the molten metal into the mold, the following waiting time before emptying and the duration of the emptying, in particular the waiting time before emptying.

These five parameters make it possible to influence the steps of the process according to the invention in order to ensure the quality of the molded part, particularly in the case presented in .

According to a particular embodiment, the present invention relates to the method as defined above, in which said metal is aluminum or an aluminum alloy, in particular AlSi12,

in which injection step 1 is carried out by gravity, said injection step 1 being carried out by pouring the liquid metal through an opening in the upper part of the mold,

wherein the mold has an opening in the bottom of the mold, which opening is obstructed, during injection step 1 and during solidification step 2, by a closing device, in particular a plug, a stopper or a hatch, subtraction step 3 being initiated by a release of said opening, by removal of said closing device.

Advantageously in this embodiment ( ) the time for pouring the molten metal (mass of approximately 19 to 24 kg) into the mold is 10 to 17 seconds.

Advantageously in this embodiment the waiting time before emptying into the mold is 10 seconds to one minute.

Advantageously in this embodiment the draining time is 11 to 18 seconds.

• soit atteinte par une étape 0 de préchauffage du moule, avant l’étape 1 de versement,
• soit le résultat d’une production précédente.

According to another particular embodiment, the present invention relates to the method as defined above, in which said mold temperature above ambient temperature is:

• is reached by a step 0 of preheating the mold, before step 1 of pouring,
• either the result of a previous production.

Preheating of the mold can be carried out, for example, by using gas burners or electric heating devices.

After a first production, it is possible that the mold already has the desired temperature. In this case, the mold can be used without additional heating. This feature is particularly interesting and sought after in the case of a series production of multiple parts.

According to another particular embodiment, the present invention relates to the method as defined above, in which the molten metal, injected during injection step 1, is at a temperature equal to or greater than the melting point of said metal,

said temperature, called “ casting/injection temperature ”, being equal to or greater than 0°C to 200°C relative to said melting point.

Overheating above the melting point depends on the geometry of the part to be cast, the nature of the alloy and that of the mold. The choice of the temperature to which the metal is heated is a matter for the skilled person.

By “ 0°C to 200°C ” we also mean the following ranges: 0°C to 150°C, 0°C to 100°C, 0°C to 50°C, 50°C to 100°C, 50°C to 150°C, 50°C to 200°C, 100°C to 200°C, 150°C to 200°C, 100°C to 150°C.

As an example in classic shell casting, for an AlSi12 alloy cast by gravity in the metal mold, the difference between the casting temperature and the liquidus (called “superheat”) is often between 50°C and 100°C.

The liquidus of said alloy being 580°C (solidus 575°C) (cf NFA 57.703), the alloy is therefore heated to a temperature of between 630 and 680°C, eg often to a temperature of around 650°C.

For the implementation of the present invention, in particular to obtain low thickness of solidified shell and the time required to carry out the draining, higher superheats can be used, eg between 100 and 200°C.

• la fabrication d’une première pièce métallique selon le procédé de fabrication tel que défini ci-dessus, et
• la fabrication d’une deuxième pièce métallique, selon le procédé de fabrication tel que défini ci-dessus, dans lequel le métal utilisé versé dans l’étape 1 de versement est le métal soustrait lors de l’étape 3 de soustraction de la fabrication de la première pièce.

The present invention also relates to a method for mass-producing at least two metal parts, said method comprising at least:

• the manufacture of a first metal part according to the manufacturing process as defined above, and
• the manufacture of a second metal part, according to the manufacturing method as defined above, in which the metal used poured in pouring step 1 is the metal subtracted during subtraction step 3 of the manufacture of the first part.

In this embodiment, after the first production, it is no longer necessary to heat the mold. The successive castings in the metal mold keep the mold hot. The mass production process is a relatively economical process (limiting energy consumption). The thickness of the mold and the preheating temperature therefore allow the heat to dissipate sufficiently to solidify the alloy skin, but also ensure that the metal mold is kept hot enough to cast the following parts without having to reheat the mold, by thermal self-regulation of the mold: the heat supplied to the mold by each part produced then corresponds substantially to the heat exchanged by the mold with its external environment during the cycle time.

Another solution is to empty the mold directly above the melting-holding furnace, thus limiting the cooling of the recovered metal while it is still liquid for reuse, and therefore limiting the energy expenditure of the melting means, these solutions being non-exhaustive.

However, in some special cases of parts, a local cooling or heating device can also be installed on the mold.

For example, for casting an aluminum alloy, an order of magnitude of the thickness of the mold is given by the Jander formula:

To dimension the thickness of the solidified shell more optimally, a numerical foundry simulation software can be used (digital twin of the casting process). Keeping a full impression of molten alloy before emptying the mold makes it easier to maintain a high mold temperature in service.

This process also allows continuous production at a high rate. The rate depends on several parameters including the geometry of the part and its dimensions, as well as the nature of the cast alloy and the mold material.

As a guide, for small to medium sized parts with cast aluminum alloy and metal mold the cycle time can be from a few seconds to 5 minutes.

The method according to the present invention is less expensive, less energy-intensive and less polluting than conventional methods. This is the result of the absence of a core in the method of the invention and the very low milling ratio, eg close to 1:1.

A second object of the present invention relates to a hollow metal part capable of being obtained by the method as defined above.

The present method makes it possible to obtain a wide variety of hollow metal parts. Depending on the part to be produced, the person skilled in the art is able to choose from the different process options set out in the present application.

The characteristics of the process, namely the absence of a core and the formation of a solidified shell of metal against the inner wall of the mold, give the cast metal parts exterior and especially interior surfaces of specific structure compared to parts produced by conventional techniques.

Indeed, the produced parts have a smooth exterior surface and a crystallographic interior surface.

By " smooth exterior surface " is meant a surface corresponding to the complementary shape of the geometry of the interior surface of the mold (cavity). The exterior surface of the produced part is however slightly reduced by linear shrinkage, i.e. the contraction of the solidified metal between the solidus temperature and room temperature.

The smooth surface is therefore free of crystallographic artifices, is not rough and does not have an uneven topology (no pronounced relief due to the solidifying crystals).

By " crystallographic inner surface " is meant a surface that is not smooth, rough and has a chaotic relief. The topology of the crystallographic surface has reliefs corresponding to the crystals formed during solidification, eg dendritic crystals, polyhedral crystals, eutectic cells.

Thus, a metal shell obtained by the process of the present invention therefore presents in relief on its interior surface dendritic, columnar and/or equiaxed structures, and eutectic facets for hypoeutectic alloys.

For example, a part produced with the eutectic alloy AlSi12 will present on the interior surface dendritic crystals rich in aluminum, polyhedral crystals rich in silicon, and mainly eutectic cells.

The size of these different crystals is linked to the speed of solidification of the metal; the higher the speed, the finer the crystal grains.

The parts produced according to the process of the invention can also have a very low, homogeneous and controllable thickness compared to the parts produced by existing techniques.

For example, when implementing a so-called " reverse casting " process, during the tilting of the mold for emptying, part of the mold cavity is in contact with the poured metal for longer than the rest of the cavity. The result is a non-symmetrical part with non-uniform thickness.

For certain types of parts produced, a solidified shell thickness of less than 2 mm can be obtained over the entire part; this even with casting, solidification and draining carried out by gravity.

Since the shell is of variable thickness, said shell is clearly not thin over its entire surface. The above sentence therefore corresponds to a preferred embodiment of the invention which ultimately relates to thin parts.

The inventors have developed an innovative process enabling the implementation of a " drained casting " process with metals with a melting temperature greater than 180°C (in particular greater than 320°C), without tilting the mold during draining.

The implementation of this method has therefore made it possible to have hollow metal parts having a crystallographic interior surface as well as a very low thickness, impossible to obtain with the conventional manufacturing methods known from the prior art such as molding, machining, plastic deformation. The presence of this crystallographic interior surface is interesting for certain applications, in particular in heat transfer (heat exchangers), light reflection (decoration, lighting fixtures), roughness (non-slip parts), etc.

Another object of the present invention relates to a hollow metal part comprising:

- a smooth exterior surface

- a crystallographic inner surface and

- a uniform average thickness,

According to a particular embodiment, the invention relates to a hollow metal part as defined above in which the metal of said metal part has a melting point greater than 180°C, in particular greater than 320°C.

According to a particular embodiment, the invention relates to a hollow metal part as defined above in which the homogeneous average thickness is from 0.2 mm to 2 mm.

According to a particular embodiment, the invention relates to a hollow metal part as defined above, in which the topology of said crystallographic interior surface comprises reliefs corresponding to the crystals formed during solidification, in particular reliefs corresponding to the dendritic crystals or to the polyhedral crystals or to the eutectic cells.

According to a particular embodiment, the invention relates to a hollow metal part

including:

- a smooth exterior surface comprising metallurgical grains,

- a crystallographic inner surface and

- a uniform average thickness, in particular from 0.2 mm to 2 mm,

said metal part is made of a metal having a melting point greater than 180°C, in particular greater than 320°C,

wherein the topology of said crystallographic inner surface comprises reliefs corresponding to metallurgical crystals, in particular reliefs corresponding to dendritic crystals or polyhedral crystals or eutectic cells.

Metallurgical crystals are those crystals formed freely during solidification of the molten metal from which the part is made, for example without the constraint of an applied surface.

Metallurgical grains are solidification crystals formed in contact with a surface during solidification.

According to a particular embodiment, the invention relates to a hollow metal part as defined above, in which said hollow metal part comprises in relief on its crystallographic interior surface structures chosen from dendritic structures, columnar structures, equiaxed structures and eutectic facet structures or a mixture or an association of these structures.

By "association of these structures" we mean, for example, dendritic crystals made up of columns.

Product surface conditions:

According to the innovative manufacturing process of the invention, the molded part has two types of surface condition.

The surfaces of the product in direct contact with the molding elements (mold cavity, pins) are “smooth”. These “smooth” surfaces are mainly external; their roughness is relatively low because it is representative of the surface condition of the interior of the mold.

The surfaces of the product that are not in direct contact with the molding elements, generally the interior surfaces of the product, are called "crystallographic". These "crystallographic" surfaces are chaotic, that is to say of significant roughness, because they are representative of the morphology of the solid phases developed during solidification and the flow of the molten metal during emptying.

Visually, it is possible to identify these different surfaces on the product with the naked eye, using comparative reference images of optical microscopy or scanning electron microscopy.

The profile of these surfaces can be measured using a roughness meter or metallographic images:

In a particular embodiment, the invention relates to a hollow metal part as defined above in which the size of the metallurgical grains of the smooth exterior surface is smaller than that of the crystals on the crystallographic interior surface.

Advantageously the hollow metallurgical part includes an increase in the size of the crystals in the thickness from the smooth outer surface to the crystallographic inner surface.

Metallurgical grain size:

The rapid cooling of the molten metal in direct contact with the mold generates a small size of the primary solidification crystals (dendritic crystals, polyhedral, etc. depending on the nature of the molten metal). Conversely, in the vicinity of the “crystallographic” surfaces, where the solidification time is longer, the size of these primary solidification crystals is coarser.

By metallographic observation, on a cut and polished sample, it is possible to perceive this evolution of grain size and to measure it (DAS measurement, image analysis).

According to a particular embodiment, the present invention relates to a hollow metal part consisting of a metal shell which surrounds, or which partially surrounds an empty part,

• une surface extérieure lisse,
• une surface intérieure cristallographique,

in which said metal shell has:

• a smooth exterior surface,
• a crystallographic inner surface,

wherein the metal of said metal shell has a melting point greater than 180°C, in particular greater than 320°C.

According to a particular embodiment, the present invention relates to the metal part, as defined above, having a thickness less than or equal to 2 mm, in particular from 0.2 mm to 2 mm, on at least part of the part or the entire part.

According to a particular embodiment, the present invention relates to the metal part as defined above, in which the metal is a pure metal or an alloy of said metal, a eutectic type alloy being preferable.

According to another particular embodiment, the present invention relates to the metal part as defined above, in which the metal is aluminum.

According to another particular embodiment, the present invention relates to the metal part as defined above, in which the metal is the eutectic alloy AlSi12.

Another object of the present invention relates to an assembly comprising one, two or more hollow metal parts as obtained according to the above method or according to the invention as defined above.

As an example, a bicycle frame was designed as exemplified in the .

The following Examples and Figures illustrate the invention, without limiting its scope.

LIST OF FIGURES

represents gravity-fed pouring systems

ThereFigure 1A shows an open mold being drained by opening a hatch/plug or other device.101represents the mold (metallic, or sand, or refractory plaster, or ceramic, or graphite),102represents the filling of the mold with the molten metal/metal alloy,103represents a trap/plug device (thermal or metallic insulating material, heated or preheated as required) or other device placed under the mold or on the side of the mold in certain applications,104represents the emptying of the molten metal bath,107represents a solidified metal shell,108represents the inner surface of the solidified metal/alloy shell, which inner surface is in the form of a crystallographic surface whose surface condition depends on the type of metal alloy cast,109represents the outer surface of the solidified metal/alloy shell, which outer surface is complementary to the geometry of the mold cavity.

ThereFigure 1B shows an open mold drained by an upper stopper.101represents the mold (metallic, or sand, or refractory plaster, or ceramic, or graphite),102represents the filling of the mold with the molten metal/metal alloy,105represents an upper stopper (refractory material or metal tube with insulating coating, heated or preheated if necessary),106represents the withdrawal of the distaff upwards to allow the bath to drain,104represents the emptying of the still molten metal bath,107a solidified metal shell,108represents the inner surface of the solidified metal/alloy shell, which inner surface is in the form of a crystallographic surface whose surface condition depends on the type of metal alloy cast,109represents the outer surface of the solidified metal/alloy shell, which outer surface is complementary to the geometry of the mold cavity.

ThereFigure 1C shows a mold for preparing a substantially closed solidified shell.101represents the mold (metal recommended),102represents the filling of the mold with the molten metal/metal alloy,103represents a trap/plug device (thermal or metallic insulating material, heated or preheated as required) or other device placed under the mold or on the side of the mold in certain applications,104represents the draining of the molten metal bath,111represents a thermally insulated or heated part of the mold (no or very little solidified alloy),110represents the upper ceiling of the footprint,112represents a column of liquid metal allowing to compensate for the volume shrinkage of the liquid alloy during its cooling and to ensure a minimum of metallostatic pressure in the upper part of the imprint for the correct arrival of the geometry of the molded part,107represents a solidified metal shell,108represents the inner surface of the solidified metal/alloy shell, which inner surface is in the form of a crystallographic surface whose surface condition depends on the type of metal alloy cast,109represents the outer surface of the solidified metal/alloy shell, which outer surface is complementary to the geometry of the mold cavity.

Note that the dimensions of the column ( 112 ) of liquid metal are a function of the density in the liquid state of the metal or metal alloy, the volume shrinkage of the liquid metal or alloy during its cooling and the geometry of the part (volume in particular, thermal modulus).

represents a low pressure casting system with an air or gas inlet located locally in the mold to ensure drainage.

Figure 2A shows the mold filling.

Figure 2B shows the filled mold.

Figure 2C shows the mold draining.

Figure 2D shows the mold emptied of molten metal/alloy, comprising a shell of metal/alloy solidified against the inner wall of the mold.

Legend: 201 represents the mold/impression, 202 represents the gas-tight furnace or crucible containing the molten metal or metal alloy, 203 represents the molten metal/alloy, 204 represents the air or gas inlet (nitrogen, argon, or other) whose pressure can increase to allow the impression to be filled in a controlled manner, 205 represents the solidified metal/metal alloy, 206 represents the trapdoor or plug made of highly thermally insulating material, or of heated or preheated material, preventing solidification (or even piercing the thin solidified skin at this location); or metal or refractory filter(s) with heated air to create the air or gas intake, 207 represents the air or gas inlet (atmospheric pressure or higher) to promote/allow the emptying of the still liquid alloy.

represents a low pressure casting system with an air or gas supply through the injection nozzle to ensure emptying.

Figure 3A shows the mold filling.

Figure 3B shows the filled mold.

Figure 3C shows the mold draining.

Figure 3D shows the mold emptied of molten metal/alloy, comprising a shell of metal/alloy solidified against the inner wall of the mold.

Legend: 301 represents the mold/cavity, 302 represents the gas-tight furnace or crucible containing the molten metal or metal alloy, 303 represents the molten metal/alloy, 304 represents the air or gas inlet (nitrogen, argon, or other) whose pressure can increase to allow the cavity to be filled in a controlled manner, 305 represents the metal/metal alloy solidified against the inner wall of the mold, 308 represents the gas valve located on the injection nozzle, 309 represents the gas or air inlet under pressure (atmospheric or higher) to promote/enable emptying.

represents the principle of a series production device for an example part.

Figure 4A shows the mold filling.

Figure 4B shows the mold draining.

Figure 4C shows the demolding of the solidified shell and the filling of the casting cup.

Legend: 400 represents the holding furnace, 401 represents the large capacity holding furnace bath, 402 represents the mold/cavity, 403 represents the obstruction system (plug, trapdoor, stopper rod, other), 404 represents a pivot connection, 405 represents a cup, 406 represents a transfer chute, 407 represents the transfer of molten metal from the cup to the cavity, 408 represents the progressive inclination to allow the cavity to be filled correctly, 409 represents the draining of excess molten liquid contained in the cavity, recovered in the holding furnace bath, 410 represents a pivot connection of the mold to allow the cavity to be turned over, 411 represents the rotation of the mold when the part is demolded, 412 represents the demolding of the part on a support, 413 represents a support of the metal grid type, 414 represents the solidified metal/alloy shell and demolded, 415 represents the rotation of the ladle/bucket system for drawing molten metal from the furnace in parallel with the part demolding operation.

represents photographs of a sand casting process according to Example 5.

Figure 5A shows a photograph of a wooden template.

Figure 5B shows a photograph of the making of a sand mold/extraction of the wooden template.

Figure 5C shows a photograph of the filling of the sand mold with molten aluminum alloy.

Figure 5D shows a photograph of the liquid metal being held in the mold for solidification.

Figure 5E shows a photograph of the liquid metal draining from the bottom of the mold.

Figure 5F shows a photograph of the hull obtained using the sand casting process.

depicts photographs of a casting process with an aluminum alloy shell.

Figure 6A shows a photograph of a drained casting test bench. 601 shows a mold (shell) made of aluminum alloy. 602 shows an orifice for draining the molten metal bath, which will be obstructed by a stopper, a hatch or other system, 603 shows a pivoting mold support, for demolding the solidified shell, 604 shows the pivot for rotating the mold support, 605 shows a lever arm for pivoting the mold during demolding, 606 shows a fixed frame (mechanically welded structure), 607 shows a sand bed, 608 shows a casting ladle, collecting the molten metal during the emptying of the mold, 609 shows a stretcher for transporting the ladle with the molten metal, to transfer it back into the furnace.

Figure 6B shows a photograph of the exterior surface of a solidified metal shell.

Figure 6C shows a photograph of the crystallographic interior surface of a solidified metal shell.

represents an assembly comprising a part (bicycle frame) which can be manufactured by the method of the invention.

represents a hot chamber die casting system with injection piston controlled by a hydraulic (or pneumatic) cylinder.

Figure 8A shows the injection of molten metal into the mold and its maintenance under pressure during the formation of the solidified shell.

Figure 8B shows the emptying of the mold, the feeding of the molten metal jacket and the resulting solidified shell.

Legend: 801 represents the moving part of the mold, 802 represents the fixed part of the mold, 803 represents the hatch or plug made of highly thermally insulating material, or of heated or preheated material, locally avoiding solidification (or even piercing of the thin skin solidified at this location); or the heated metallic or refractory air filter(s) to create the air or gas (nitrogen, argon, or other) call under pressure (atmospheric or higher) in order to promote/make possible the emptying, 804 represents the crucible of the holding furnace, 805 represents the molten metal/alloy maintained at the casting temperature, 806 represents the injection chamber usually called "the gooseneck", 807 represents the injection piston, 808 represents the rod of the hydraulic or pneumatic cylinder which controls the injection, 809 represents the closable port allowing the injection jacket to be filled with the molten metal/alloy, 810 represents the nose of the swan neck (end of the gooseneck) often called "injection nozzle", 811 represents the insulating or heating sleeve preventing the metal/alloy from solidifying in the injection nozzle (generally temperature equal to or higher than the liquidus), 812 represents the feeding of the injection jacket with molten metal/alloy from the furnace bath, 813 represents the outer surface of the solidified metal/alloy shell, which outer surface is complementary to the geometry of the mold cavity, 814 represents the inner surface of the solidified metal/alloy shell, which inner surface is in the form of a crystallographic surface whose surface condition depends on the type of metal alloy cast, 815 represents the solidified metal shell against the inner wall of the mold, 816 represents the movement of the cylinder rod allowing the cavity to be filled in a controlled manner, 817 represents the return of the cylinder rod allowing the mold to be emptied of the still liquid metal and the injection jacket to be reloaded with molten metal, 818 represents the main parting plane of the mold (here vertical).

represents a hot chamber die casting system with injection of molten metal by air or gas (nitrogen, argon, or other) under pressure.

Caption : 906 represents the injection chamber usually called "the gooseneck", 919 represents the air or gas pocket, the pressurization of which allows the controlled filling of the mold cavity, 920 represents the valve controlling the arrival of air or gas under pressure, 921 represents the closable port allowing the injection jacket to be supplied with molten metal contained in the holding furnace.

Note that in die casting with air or gas injection, there are systems where the gooseneck is mounted on a horizontal pivot, allowing by its rotation the filling of the jacket by the nose of the swan neck. In this particular case, the orifice mentioned 921 then corresponds to the injection nozzle noted 810 in the .

represents a cold chamber die casting system with a conventional horizontal injection jacket by piston controlled by a hydraulic (or pneumatic) cylinder, and with a vertical main mold joint plane.

Figure 10A shows the feeding of the injection jacket with molten metal with the mold previously closed.

Figure 10B shows the injection of molten metal into the mold and its maintenance under pressure during the formation of the solidified shell.

Figure 10C shows the emptying of the mold and the resulting solidified shell.

Legend : 1000 represents the return of the cylinder rod in order to reload the injection sleeve with molten metal, 1001 represents the moving part of the mold, 1002 represents the fixed part of the mold, 1003 represents the hatch or plug made of highly thermally insulating material, or of heated or preheated material, locally avoiding solidification (or even piercing of the thin skin solidified at this location); or the heated metallic or refractory air filter(s) to create the air or gas (nitrogen, argon, or other) call under pressure (atmospheric or higher) in order to promote/make possible the emptying, 1004 represents the filling of the injection jacket with molten metal, using a manual ladle, an automatic cup or other device from the holding furnace, 1005 represents the molten metal/alloy in the jacket before injection, 1006 represents the injection chamber, 1007 represents the injection piston, 1008 represents the rod of the hydraulic or pneumatic cylinder which controls the injection, 1009 represents the closable light allowing the filling of the injection jacket with the molten metal/alloy, 1010 represents the thermally insulating closure system (plug, hatch, stopper rod, other), which can be heated or preheated, 1011 represents the casting attack, 1012 represents the movement of the ram rod to fill the impression in a controlled manner, 1013 represents the outer surface of the solidified metal/alloy shell, which outer surface is complementary to the geometry of the mold impression, 1014 represents the inner surface of the solidified metal/alloy shell, which inner surface is in the form of a crystallographic surface whose surface condition depends on the type of metal alloy cast, 1015 represents the solidified metal shell against the inner wall of the mold, 1016 represents the arrival of air or gas (atmospheric or higher pressure) to promote/allow the emptying of the still liquid metal/alloy, 1017 represents the emptying by gravity of the still liquid metal in the mold, 1018 represents the main parting plane of the mold (here vertical), 1019 represents the movement of the movable part of the mold in order to extract the solidified shell.

represents a die-casting system with a horizontal heating/thermo-regulated jacket, an injection piston controlled by a hydraulic (or pneumatic) cylinder, and a horizontal main mold joint plane.

Figure 11A shows the feeding of the heated/thermo-regulated injection jacket with molten metal with the mold previously closed.

Figure 11B shows the injection of molten metal into the mold and its maintenance under pressure during the formation of the solidified shell.

Figure 11C shows the emptying of the mold and the resulting solidified shell.

Legend : 1100 represents the return of the cylinder rod in order to empty the mold and reload the injection jacket with molten metal, 1101 represents the moving part of the mold, 1102 represents the fixed part of the mold, 1103 represents the hatch or plug made of highly thermally insulating material, or of heated or preheated material, locally avoiding solidification (or even piercing of the thin skin solidified at this location); or the heated metallic or refractory air filter(s) to create the air or gas (nitrogen, argon, or other) call under pressure (atmospheric or higher) in order to promote/make possible the emptying, 1104 represents the filling of the injection jacket with molten metal, using a manual ladle, an automatic cup or other device from the holding furnace, 1105 represents the molten metal/alloy in the jacket before injection, 1106 represents the heated/thermo-regulated injection chamber, 1107 represents the injection piston, 1108 represents the rod of the hydraulic or pneumatic cylinder which controls the injection, 1109 represents the closable port allowing the filling of the injection jacket with the molten metal/alloy, 1111 represents the casting attack, 1112 represents the movement of the cylinder rod allowing the impression to be filled in a controlled, 1113 represents the outer surface of the solidified metal/alloy shell, which outer surface is complementary to the geometry of the mold imprint, 1114 represents the inner surface of the solidified metal/alloy shell, which inner surface is in the form of a crystallographic surface whose surface condition depends on the type of metal alloy cast, 1115 represents the metal shell solidified against the inner wall of the mold, 1116 represents the arrival of air or gas (atmospheric or higher pressure) to promote/allow the emptying of the still liquid metal/alloy, 1117 represents the return by gravity of the still liquid metal into the heated/thermo-regulated jacket following emptying, 1118 represents the main parting plane of the mold (here horizontal), 1119 represents the opening of the mold allowing the ejection of the solidified shell.

represents a cold chamber die casting system with a vertical injection jacket, piston controlled by a hydraulic (or pneumatic) cylinder and horizontal main parting plane of the mold. The jacket can be integrated into the molding tooling and this device has an external evacuation of the unsolidified metal.

Figure 12A shows the feeding of the injection jacket with molten metal, just before the closing of the mold.

Figure 12B shows the injection of molten metal into the mold and its maintenance under pressure during the formation of the solidified shell.

Figure 12C shows the emptying of the mold and the solidified part obtained (part + residual injection pellet).

Legend: 1200 represents the return of the cylinder rod in order to supply the injection jacket with molten metal before closing the mold, 1201 represents the movable upper part of the mold, 1202 represents the fixed lower part of the mold, 1203 represents the hatch or plug made of highly thermally insulating material, or of heated or preheated material, locally avoiding solidification (or even piercing of the thin skin solidified at this location); or the heated metallic or refractory air filter(s) to create the air or gas (nitrogen, argon, or other) call under pressure (atmospheric or higher) in order to promote/make emptying possible, 1204 represents the filling of the injection jacket with molten metal, using a manual ladle, an automatic cup or other device from the holding furnace, 1205 represents the molten metal/alloy in the jacket before injection, 1206 represents the injection chamber here integrated into the mold, 1207 represents the injection piston, 1208 represents the rod of the hydraulic or pneumatic cylinder which controls the injection, 1209 represents the thermally insulating sealing system (plug, hatch, stopper rod, other), which can be heated or preheated, 1210 represents the injection pellet, solidified residual, adhering to the molded part during its ejection, 1211 represents the drain core, 1212 represents the movement of the cylinder rod allowing the controlled filling of the impression, 1213 represents the outer surface of the solidified metal/alloy shell, which outer surface is complementary to the geometry of the mold impression, 1214 represents the inner surface of the solidified metal/alloy shell, which inner surface is in the form of a crystallographic surface whose surface condition depends on the type of metal alloy cast, 1215 represents the metal shell solidified against the inner wall of the mold, 1216 represents the arrival of air or gas (atmospheric or higher pressure) to promote/allow the draining of the still liquid metal/alloy, 1217 represents the main parting plane of the mold (here horizontal), 1218 represents the opening of the mold allowing the solidified shell to be ejected following draining, 1219 represents the draining by gravity of the still liquid metal.

represents a first die-casting system with a vertical heating/thermo-regulated jacket, an injection piston controlled by a hydraulic (or pneumatic) cylinder, and a horizontal main mold joint plane. The injection jacket is integrated into the molding tooling and this device ensures a gravity return of the non-solidified metal into the jacket during emptying, this return being facilitated by the gas/air pressure.

Figure 13A shows the feeding of the injection jacket with molten metal, just before the closing of the mold.

Figure 13B shows the injection of molten metal into the mold and its maintenance under pressure during the formation of the solidified shell.

Figure 13C shows the emptying of the mold and the resulting solidified shell.

Legend: 1300 represents the return of the cylinder rod in order to supply the injection jacket with molten metal before closing the mold and to drain the solidified shell before opening the mold, 1301 represents the movable upper part of the mold, 1302 represents the fixed lower part of the mold, 1303 represents the hatch or plug made of highly thermally insulating material, or of heated or preheated material, locally avoiding solidification (or even piercing of the thin skin solidified at this location); or the heated metallic or refractory air filter(s) to create the air or gas (nitrogen, argon, or other) call under pressure (atmospheric or higher) in order to promote/make possible the emptying, 1304 represents the filling of the injection jacket with molten metal, using a manual ladle, an automatic cup or other device from the holding furnace, 1305 represents the molten metal/alloy in the jacket before injection, 1306 represents the heated/thermo-regulated injection chamber here integrated into the mold, 1307 represents the injection piston, 1308 represents the rod of the hydraulic or pneumatic cylinder which controls the injection, 1309 represents the casting attack, 1312 represents the movement of the cylinder rod allowing the controlled filling of the impression, 1313 represents the outer surface of the solidified metal/alloy shell, which outer surface is complementary to the geometry of the mold imprint, 1314 represents the inner surface of the solidified metal/alloy shell, which inner surface is in the form of a crystallographic surface whose surface condition depends on the type of metal alloy cast, 1315 represents the metal shell solidified against the inner wall of the mold, 1316 represents the air or gas inlet (atmospheric or higher pressure) to promote/enable the emptying of the still liquid metal/alloy, 1317 represents the main parting plane of the mold (here horizontal), 1318 represents the opening of the mold allowing the solidified shell to be ejected following emptying and to supply molten metal to the injection jacket.

represents a second die-casting system with a vertical heating/thermo-regulated jacket, an injection piston controlled by a hydraulic (or pneumatic) cylinder, and a horizontal main mold joint plane. The injection jacket is integrated into the molding tooling and this device ensures a gravity return of the unsolidified metal into the jacket during emptying, this return being facilitated by the gas/air pressure.

Figure 14A shows the feeding of the injection jacket with molten metal, just before the closing of the mold.

Figure 14B shows the injection of molten metal into the mold and its maintenance under pressure during the formation of the solidified shell.

Figure 14C shows the emptying of the mold and the resulting solidified shell.

Legend: 1400 represents the return of the cylinder rod in order to supply the injection jacket with molten metal before closing the mold and to drain the solidified shell before opening the mold, 1401 represents the movable upper part of the mold, 1402 represents the fixed lower part of the mold, 1403 represents the hatch or plug made of highly thermally insulating material, or of heated or preheated material, locally avoiding solidification (or even piercing of the thin skin solidified at this location); or the heated metallic or refractory air filter(s) to create the air or gas (nitrogen, argon, or other) call under pressure (atmospheric or higher) in order to promote/make possible the emptying, 1404 represents the filling of the injection jacket with molten metal, using a manual ladle, an automatic cup or other device from the holding furnace, 1405 represents the molten metal/alloy in the jacket before injection, 1406 represents the heated/thermo-regulated injection chamber here integrated into the mold, 1407 represents the injection piston, 1408 represents the rod of the hydraulic or pneumatic cylinder which controls the injection, 1412 represents the movement of the cylinder rod allowing the controlled filling of the cavity, 1413 represents the outer surface of the solidified metal/alloy shell, which outer surface is complementary to the geometry of the mold cavity, 1414 represents the inner surface of the solidified metal/alloy shell, which inner surface is in the form of a crystallographic surface whose surface condition depends on the type of metal alloy cast, 1415 represents the solidified metal shell against the inner wall of the mold, 1416 represents the air or gas inlet (atmospheric or higher pressure) to promote/allow the emptying of the still liquid metal/alloy, 1417 represents the main parting plane of the mold (here horizontal), 1418 represents the opening of the mold allowing the solidified shell to be ejected following emptying and to supply molten metal to the injection jacket.

EXAMPLES

Example 1 . General procedure for melting metallic material

The charge (ingots and/or recycled parts) was melted in an electric or fuel-fired melting furnace. The furnace used corresponds to a conventional foundry furnace. The molten bath was brought and then maintained at a temperature higher than the liquidus of the alloy by a so-called superheat value plus an estimated value of temperature loss linked to transfer into the casting ladle/bag. The superheat above the liquidus retained was between 0 and 200°C.

For mass production, the capacity of the holding and drawing furnace must be large enough in relation to the mold footprint so as not to cool the bath too much in the furnace when transferring the mold drains.

Example 2. Preparing the mold

In parallel with the melting of the alloy according to example 1, the mold was prepared.

The metal mold was preheated before the first casting, at an approximate temperature of 350°C for casting aluminum alloys. To bring the mold up to temperature, gas burners or electric heating devices were used.

The impressions of the metal molds were coated with a thin layer of potting compound, 0.2 to 0.5 mm thick.

In the case of a sand mold, no preheating was implemented.

Example 3. Filling the mold

The mold was filled with molten metal when the temperature of the metal or metal alloy had stabilized in the melting-holding furnace (example 1), and when the initial temperature of the mold preheated for the start of the cycle had been reached (example 2).

Example 4. Emptying the mold

The mold was drained of residual molten metal when the solidified shell was formed against the inner wall of the mold. The length of time the molten metal remains in the mold depends on the thickness of the desired shell.

Example 5. Manufacturing of a hollow part by a sand casting process

A wooden model was made to make a sand mold (Figure 5A). After the sand mold was made, the aluminum alloy AlSi12 was melted and heated to a temperature of about 700 °C, about 40 °C above the desired casting temperature. The molten metal was transferred to a casting ladle using a large ladle, in order to be able to bring the metal to the mold using a stretcher. The temperature of the aluminum was about 660 °C when poured into the sand mold (unheated mold, at room temperature, about 20 °C). The filling time was less than 10 seconds, followed by a holding time of the molten metal in the mold of about 2 minutes.

During the holding time of the molten metal in the mold, the upper surface of the metal bath in contact with the air was skimmed, in order to remove the thick oxide skins (floating and from the filling). A pouring ladle was installed under the mold, in order to collect the metal still molten during emptying. Once the time of approximately 2 minutes had elapsed, the insulating hatch located under the mold was opened, thus allowing the emptying of the still liquid metal bath in the ladle. Despite the insulating material of the hatch, a skin of solidified metal could form against it, possibly requiring intervention ( eg with a metal point) to pierce this skin. After a draining time of less than 10 seconds, the molten aluminum alloy collected in the ladle under the mold was transported and then poured back into the furnace crucible. After cooling of the solidified shell, the sand mold was detached in order to recover the part. This has an external surface complementary to the mold imprint (Figure 6B) and a crystallographic internal surface, resulting from the natural mode of solidification of the metal/alloy used (Figure 6C).

Example 6. Mass production of multiple parts

A series production of several parts was carried out as shown in the diagram. .

A metal mold made of AlSi7Mg aluminum alloy was produced by sand casting and machining. This shell was installed on a test bench, a partly articulated mechanically welded frame to allow the rotation of the mold in order to unmold the part produced. This bench has burners, located under the mold, in order to heat (or even maintain) the impression at the desired temperature before casting the metal. The mold was raised to accommodate a casting ladle, located below the mold, the whole resting on a bed of sand for safety reasons.

Before the first casting, the aluminium alloy (AlSi12) was melted in the furnace crucible and heated to a temperature of 750°C to 790°C, approximately 50°C above the desired casting temperature. During this time, the metal casting shell was sandblasted, installed on the test bench, heated by gas burners, and potted. For casting, the mould was heated to a temperature of 164°C to 243°C. In the same way, the stopper rod (steel tube coated with insulating potting) was heated to a temperature significantly higher than the liquidus temperature of the alloy, so that the molten metal could not solidify on contact with it. Once the desired temperature of the molten metal had been reached in the furnace, the casting ladle was filled and then brought close to the mould using a stretcher. The temperature of the molten metal in the ladle was then about 720°C just before casting. This ladle was quickly poured into the mold, about 17 seconds. Then the holding time of the molten metal/alloy in the metal mold was about 14 seconds ( according to different tests, this time can vary from 14 seconds to 1 minute). Then the stopper that was blocking the mold orifice was removed, allowing the metal still molten in the mold to be drained, in order to pour it into the casting ladle located below (Figure 1B). This ladle was then removed and transported with a stretcher to the furnace crucible. The temperature of the aluminum alloy just before its transfer to the furnace was between 577°C and 588°C. Finally, to unmold the part, a metal grid was installed above the mold; then the mold and its support were rotated 180°C to allow the demolding of the hot part produced without deforming it (Figures 4C, 6B and 6C). The part deposited on the grid was moved elsewhere in the workshop for cooling. The solidified metal shell, thus produced, has an external surface complementary to the mold imprint (Figure 6B) and a crystallographic internal surface, resulting from the natural mode of solidification of the metal/alloy used (Figure 6C).

The process can be repeated to produce successive parts. The successive castings thus help to maintain the temperature of the mold.

Claims (14)

Hollow metal part comprising:
- a smooth outer surface comprising metallurgical grains,
- a crystallographic interior surface, and
- a uniform average thickness, in particular from 0.2 mm to 2 mm,
said metal part being made of a metal having a melting point greater than 180°C, in particular greater than 320°C,
wherein the topology of said crystallographic inner surface comprises reliefs corresponding to metallurgical crystals, in particular reliefs corresponding to dendritic crystals or polyhedral crystals or eutectic cells. Hollow metal part according to claim 1, wherein said hollow metal part comprises in relief on its crystallographic interior surface structures selected from dendritic structures, columnar structures, equiaxed structures and eutectic facet structures or a mixture or combination of these structures. A hollow metal part according to any one of claims 1 or 2, wherein the size of the metallurgical grains of the smooth outer surface is smaller than that of the metallurgical crystals of the crystallographic inner surface. Assembly comprising one, two or more hollow metal parts according to any one of claims 1 to 3. Method of manufacturing a hollow metal part according to any one of claims 1 to 3, said method comprising at least the following steps:

• a step 1 of injecting a liquid mass of molten metal into a mold, from a container comprising said molten metal, to obtain a mold comprising molten metal;
• a step 2 of partial solidification of said molten metal within the mold for a time sufficient to form a solidified metal shell in contact with the walls of the mold having a temperature lower than the solidus temperature of said molten metal, and maintaining in liquid phase the remaining part of the initial liquid mass of said molten metal contained inside the solidified metal shell, to obtain a solid part consisting of the solidified metal shell, and a liquid phase consisting of the remaining part of the initial liquid mass of said molten metal;
• a step 3 of subtraction of the above-mentioned liquid phase, said subtraction step being carried out without tilting the mold; and
• a step 4 of recovery of the hollow metal part in the form of a solidified metal shell,

wherein the metal has a melting point above 180°C, in particular above 320°C, and wherein the hollow metal part is formed in the absence of a core,
said method having a ratio of 1:1 to 1.2:1, preferably about 1:1, particularly 1:1. Manufacturing method according to claim 5, for producing a hollow metal part having a thickness of 0.2 mm to 2 mm. Manufacturing method according to claim 5 or 6, in which injection step 1 is carried out by gravity, said injection step 1 being carried out by pouring the liquid metal through an opening in the upper part of the mold. Manufacturing method according to any one of claims 5 to 7, wherein injection step 1 is carried out by injection with a low pressure process, said injection step 1 being carried out by applying a gas pressure in the container comprising the liquid metal, making it possible to push said liquid metal into the mold, through an orifice located in the bottom of said mold. Manufacturing method according to any one of claims 5 to 8, in which injection step 1 is carried out by injection under pressure, said injection step 1 being carried out by injection of the liquid metal using a piston or a gas. Manufacturing method according to any one of claims 5 to 9, in which step 4 of demolding is carried out by turning the mold over. Manufacturing method according to any one of claims 5 to 10, in which the mold has an opening in the bottom of the mold, which opening is obstructed, during injection step 1 and during solidification step 2, by a closing device, in particular a plug, a stopper or a hatch, subtraction step 3 being initiated by a release of said opening, by removal of said closing device. Manufacturing method according to any one of claims 5 to 11,
in which the mold has air or gas intake means at the top of the mold, said air or gas intake means being closed during injection step 1 and during solidification step 2,
in which subtraction step 3 is facilitated or made possible by the opening of said air or gas intake means causing an intake of air or gas, in particular nitrogen or argon, under pressure, in particular at a pressure equal to or greater than atmospheric pressure. Method for mass-producing at least two metal parts according to any one of claims 1 to 3, said method comprising at least:

• the manufacture of a first metal part according to the manufacturing method according to any one of claims 5 to 12, and
• the manufacture of a second metal part, according to the manufacturing method according to any one of claims 5 to 12, in which the metal used poured in pouring step 1 is the metal subtracted during subtraction step 3 of the manufacture of the first part.

Hollow metal part capable of being obtained by the method according to any one of claims 5 to 12.