Coreless molding manufacturing method for hollow metal parts

Abstract

The present invention provides a coreless molding manufacturing method for hollow metal parts. The invention also relates to metal parts obtained according to the method of the invention.

Description

[0001] DESCRIPTION

[0002] PROCESS FOR MANUFACTURING HOLLOW METAL PARTS BY CORELESS CASTING

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a hollow metal part, to methods of manufacturing hollow metal parts by coreless casting. The invention also relates to metal parts obtained according to the method of the invention.

[0005] PREVIOUS ART

[0006] Foundry covers the processes of forming metals, in their pure state or in alloy form, involving a mold into which molten metal is poured to produce, after solidification, a metal part. A multitude of processes have been developed over the last few centuries, capable of producing a wide variety of metal parts.

[0007] Hollow metal parts with a thin shell, for example less than 2 mm, are in particular demand. These parts weigh less 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, uniform, variable and scalable thickness.

[0008] Patent FR 2 646 824 Bl, for example, discloses the manufacture of a hollow one-piece motorcycle frame. The process 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.

[0009] One method of manufacturing hollow metal parts without using a core is to pour molten metal into a mold. A skin of solidified metal forms on the mold surface within seconds, and then the mold is tilted to remove excess liquid metal.

[0010] 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 another side.

[0011] Existing methods do not satisfy the need to provide coreless manufacturing methods by casting hollow metal parts having a shell of controlled low thickness, in particular between 0.2 mm and 10 mm, preferably between 0.5 and 5.0 mm, preferably less than 2 mm, and made of a metal or alloy having a melting point above 180°C.

[0012] There is therefore a need to provide new processes enabling the manufacturing by molding of parts which cannot be obtained by existing molding processes.

[0013] BRIEF OVERVIEW

[0014] In this context, a first aim of the invention is to provide a manufacturing process by molding, without cores, of hollow metal parts having a shell of controlled low thickness, i.e. less than 10 mm and greater than 0.2 mm.

[0015] A second aim of the invention is to provide a manufacturing process by molding metal parts, making it possible to control the shell thickness of the part to be formed.

[0016] Another aim of the invention is to be able to implement the method with metals or metal alloys with a melting point above 180°C, in particular above 320°C. Another aim of the invention is to provide new hollow metal parts.

[0017] DETAILED DESCRIPTION

[0018] A first object of the present invention relates to a molded monocoque hollow metal part comprising:

[0019] - an outer surface comprising metallurgical grains constrained by the surface of the mold in which the part was molded,

[0020] - a crystallographic inner surface, said metal part being made of a metal or an alloy having a melting point above 180°C, in particular above 320°C, in which the topography of said crystallographic inner surface comprises reliefs corresponding to the metallurgical crystals, in particular reliefs corresponding to the dendritic crystals, in particular primary crystals, and / or to the polyhedral crystals, in particular primary crystals, and / or to the eutectic cells, in which said part comprises

[0021] - a thickness e, defined by the minimum distance between said outer surface and said inner surface, with an average value ranging from 0.2 mm to 10.0 mm, in particular from 0.5 to 5.0 mm,

[0022] - a dimension Rt, defined by the difference between the value of the thickness EM and that of the thickness e, the thickness EM being defined as the distance between the point of the inner surface furthest from the outer surface and its orthogonal projection on the outer surface. The present invention relates to a hollow monocoque metal part molded in the absence of a core comprising:

[0023] - an outer surface comprising metallurgical grains constrained by the surface of the mold in which the part was molded,

[0024] - a crystallographic inner surface, said metal part being made of a metal or an alloy having a melting point above 180°C, in particular above 320°C, in which the topography of said crystallographic inner surface comprises reliefs corresponding to the metallurgical crystals, in particular primary crystals, in particular reliefs corresponding to the dendritic crystals, in particular primary crystals, and / or to the polyhedral crystals and / or to the eutectic cells, in which said part comprises

[0025] - a thickness e, defined by the minimum distance between said outer surface and said inner surface, with an average value ranging from 0.2 mm to 10.0 mm, in particular from 0.5 to 5.0 mm,

[0026] - a dimension Rt, surface condition parameter, defined by the difference between the value of the thickness EM and that of the thickness e, the thickness EM being defined as the distance between the point of the interior surface furthest from the exterior surface and its orthogonal projection on the exterior surface.

[0027] A "molded monocoque part" means a part that has been molded from a molten liquid in a single mold, and which is presented as a single piece.

[0028] By "external surface" we mean the surface of the casting which is obtained by overmolding the interior walls of the mold. Its roughness is mainly given by the surface condition of the mold cavity and the grain size of the release agent (called "poteyage" in the foundry trade) deposited inside the mold. In fact, it is generally quite low, or even said to be relatively smooth, for casting with a metal mold and coarser with a sand mold.

[0029] It is understood that for the hollow metal part the external surface is complementary to the geometry of the impression of the mold in which said part was molded. However, this complementarity takes into account the shrinkage during cooling, but also the metallostatic pressure and the surface tension of the molten alloy / metal.

[0030] The term "crystallographic inner surface" refers to the surface not exposed to the mold walls. The inner surface, called crystallographic, is representative of the solidification front (interface between the solidified metal / alloy and the still liquid metal at the core of the mold cavity). The crystallographic inner surface is more or less rough because it is shaped by crystallography and the flow of the alloy. The topography of the inner surface is directly linked to the morphologies of the different phases developed during solidification (crystallographic appearance of the surface) and to the flow of the liquid alloy during emptying.Its roughness is all the lower when the cast metal alloy has a very small solidification interval (difference between liquidus and solidus temperatures very small or zero), when the mold is a good heat conductor (metal mold preferable to sand mold) and when the temperature gradients are high (marked difference between the initial temperature of the mold and that of the cast alloy). In fact, eutectic alloys cast in metal molds are very interesting for the production of technical parts (in particular the A1SH2 alloy used in the tests presented in the examples).

[0031] Advantageously, the outer surface is of lower roughness than the crystallographic inner surface.

[0032] In the present invention, the thickness e of the hollow part is defined by the minimum thickness of said part, namely the minimum distance between the two surfaces.

[0033] Advantageously, this thickness e is controlled.

[0034] By "controlled" we mean that the thickness e can be previously determined and programmed by the manufacturing process and / or by the mold used to obtain the part. In general, the minimum wall thickness is defined by the designer of the part (design office, foundry customer) in order to ensure that the part is correctly held to the mechanical stresses undergone in service. Its value depends mainly on the holding time of the liquid alloy in the mold before emptying and on the solidification rate. The latter is linked to at least one of the following parameters or to the combination of at least two parameters or preferably to all of the following parameters: the nature of the materials, cast alloy and mold, their initial temperatures, the thickness of the mold, the volume of cast alloy present locally in the impression, the nature and thickness of the coating used (mold and alloy / cast metal interface).Advantageously, all of the parameters can be modulated simultaneously to control the thickness e.

[0035] The minimum wall thickness e, its average value and its deviation can be defined and measured by analysis methods used in metallurgy such as binocular microscope microscopy. The parameter Rt can be measured by a roughness tester or a Keyence type digital microscope.

[0036] Analysis methods for metallurgical parts relating to thickness parameters are known to those skilled in the art.

[0037] Advantageously, the average value of the thickness e of a part or of a domain is defined as the average of at least 3, in particular 5, preferably 10, values ​​of minimum thickness recorded equally distributed respectively over the entire part or of a domain of the part. It is understood that the presence of holes or defects is excluded from the average thickness measurements. According to a particular embodiment, the minimum thickness e of the wall of the hollow metal part is homogeneous over the entire part or over the domains constituting said part.

[0038] The thickness e is said to be "homogeneous" if: when the average value of e is 0.2 to 2.0 mm, its deviation is less than 50% when the average value of e is 2.0 (excluded) to 5.0 mm, its deviation is less than 40% when the average value of e is 5.0 (excluded) to 10.0 mm, its deviation is less than 30%.

[0039] The range of "0.2 to 10 mm" includes the following ranges of values: 0.2 to 0.3 mm, 0.3 to 0.4 mm, 0.4 to 0.5 mm, 0.5 to 0.6 mm; 0.6 to 0.7 mm, 0.7 to 0.8 mm, 0.8 to 0.9 mm, 0.9 to 1.0 mm, 1.0 to 1.1 mm, 1.1 to 1.2 mm, 1.2 to 1.3 mm, 1.3 to 1.4 mm, 1.4 to 1.5 mm, 1.5 to 1.6 mm; 1.6 to 1.7 mm, 1.7 to 1.8 mm, 1.8 to 1.9 mm, 1.9 to 2.0 mm, 2.0 to 2.1 mm, 2.1 to 2.2 mm, 2.2 to 2.3 mm, 2.3 to 2.4 mm, 2.4 to 2.5 mm, 2.5 to 2.6 mm; 2.6 to 2.7 mm, 2.7 to 2.8 mm, 2.8 to 2.9 mm, 2.9 to 3.0 mm, 3.0 to 3.1 mm, 3.1 to 3.2 mm, 3.2 to 3.3 mm, 3.3 to 3.4 mm, 3.4 to 3.5 mm, 3.5 to 3.6 mm; 3.6 to 3.7 mm, 3.7 to 3.8 mm, 3.8 to 3.9 mm, 3.9 to 4.0 mm, 4.0 to 4.1 mm, 4.1 to 4.2 mm, 4.2 to 4.3 mm, 4.3 to 4.4 mm, 4.4 to 4.5 mm, 4.5 to 4.6 mm; 4.6 to 4.7 mm, 4.7 to 4.8 mm, 4.8 to 4.9 mm, 4.9 to 5.0 mm, 5.0 to 5.1 mm, 5.1 to 5.2 mm, 5.2 to 5.3 mm, 5.3 to 5.4 mm, 5.4 to 5.5 mm, 5.5 to 5.6 mm;from 5.6 to 5.7 mm, from 5.7 to 5.8 mm, from 5.8 to 5.9 mm, from 5.9 to 6.0 mm, from 6.0 to 6.1 mm, from 6.1 to 6.2 mm, from 6.2 to 6.3 mm, from 6.3 to 6.4 mm, from 6.4 to 6.5 mm, from 6.5 to 6.6 mm; from 6.6 to 6.7 mm, from 6.7 to 6.8 mm, from 6.8 to 6.9 mm, from 6.9 to 7.0 mm, from 7.0 to 7.1 mm, from 7.1 to 7.2 mm, from 7.2 to 7.3 mm, from 7.3 to 7.4 mm, from 7.4 to 7.5 mm, from 7.5 to 7.6 mm; from 7.6 to 7.7 mm, from 7.7 to 7.8 mm, from 7.8 to 7.9 mm, from 7.9 to 8.0 mm, from 8.0 to 8.1 mm, from 8.1 to 8.2 mm, from 8.2 to 8.3 mm, from 8.3 to 8.4 mm, from 8.4 to 8.5 mm, from 8.5 to 8.6 mm; from 8.6 to 8.7 mm, from 8.7 to 8.8 mm, from 8.8 to 8.9 mm, from 8.9 to 9.0 mm, from 9.0 to 9.1 mm, from 9.1 to 9.2 mm, from 9.2 to 9.3 mm, from 9.3 to 9.4 mm, from 9.4 to 9.5 mm, from 9.5 to 9.6 mm; from 9.6 to 9.7 mm, from 9.7 to 9.8 mm, from 9.8 to 9.9 mm, from 9.9 to 10.0 mm;

[0040] At the micrographic scale of the part (small scale), the notion of conventional dimension parameter Rt, relating to the roughness of the surface can be used and defined. The parameter Rt corresponds well to the usual name in mechanical construction, (see example in figure 18). The parameter Rt is defined as the difference in height between the highest and lowest point of the roughness profile. The parameter Rt depends in particular on the crystallography of the alloy, the solidification rate and the flow of the alloy during emptying during the manufacturing process.

[0041] Its value depends on the crystallography of the alloy used, the solidification rate, the flow of the liquid alloy during emptying and the local orientation of the mold wall (vertical / horizontal / inclined face).

[0042] As a non-limiting example, with a eutectic alloy type A1SH2 (A-S13), experience shows that the higher the solidification rate and the shorter the holding time of the cast alloy in the mold before emptying, the lower the value of Rt.

[0043] For a hollow metal part used as a metal heat exchanger, a high Rt value promotes heat transfer but increases pressure losses for the flow of the internal fluid. Depending on the use, there is therefore a compromise to be made in setting the Rt value and the internal surface condition.

[0044] According to a particular embodiment, the invention relates to a hollow metal part as defined above, in which the ratio between the parameter Rt and the thickness e, hereinafter Rt / e, varies from 0.0 to 500.0%. This ratio is an indicator of the roughness of the interior surface.

[0045] We understand that for a low Rt / e ratio of the order of 0.0 to 50%, the surface is said to be smooth.

[0046] It is understood that for an Rt / e ratio of the order of 100.0 to 500.0%, the surface is said to be rough. A high value is an indicator of a high exchange surface promoting heat transfer, which is particularly sought after, for example, for an application to heat exchangers.

[0047] The Rt value can be determined by performing a topography of the inner surface of the part over a length of at least 10.0 mm by topographic analysis methods known in metallurgy to those skilled in the art such as measurement with a roughness meter, binocular microscopy or Keyence digital microscopy.

[0048] The range of “0.0 to 500%” includes the following ranges: 0.0 to 50.0%, 50.0 to 100.0%, 100.0 to 150.0%, 150.0 to 200.0%, 200.0 to 250.0%, 250.0 to 300.0%, 300.0 to 350.0%, 350.0 to 400.0%, 400.0 to 450.0%, 450.0 to 500.0%.

[0049] On a macroscopic scale (large scale), the concept of geometric tolerance t (used in mechanical design by design offices, in mechanical manufacturing and in metrology) can be introduced for a hollow part according to the invention (see figure 21).

[0050] A linear dimensional tolerance for the wall thickness dimension of the part can also be defined. The geometric tolerance and the linear dimensional tolerance are known parameters and can be determined by those skilled in the art of foundry for castings. The NF EN ISO 8062-3 standard gives the dimensional tolerances and geometric tolerances of the cast products according to the cast alloy, the casting process used and the dimensions of the part; however, this standard only deals with all conventional casting processes. The method according to the invention is an original technique of drained casting, a transposition can be carried out but keeping in mind that it is expected, as shown in Figure 21, that these parameters are higher than those of conventional castings obtained with an internal core.

[0051] Indeed, the hollow metal parts according to the invention, which can be manufactured by the technique according to the invention of drained casting, offer the great advantage of manufacturing parts with a very low minimum wall thickness e without an internal molding element. On the other hand, obtaining a tight geometric tolerance for an internal surface will be a difficulty to be mastered as best as possible. Indeed, in conventional foundry processes, the use of internal metal cores, or those made of sand or ceramic, allows relatively low geometric tolerances t; but the surface tension of the cast alloy and its metallostatic pressure do not allow the production of hollow parts of very low thicknesses e with gravity casting.

[0052] As a non-limiting example, with the tube in figure 19: e= 1.6mm and t=0.9mm, i.e. an average thickness of 2.05 ±0.45 mm (0.9mm can be defined here as the linear dimensional tolerance obtained for the wall thickness in this example).

[0053] According to a particular embodiment, the invention relates to a hollow metal part as defined above, said part being made up of distinct domains of different geometric shapes or relating to a different functionality of the part, each domain of the part having a thickness e in said domain, said average thicknesses e of said domains being identical or different from each other and each having a value in the range from 0.2 mm to 10.0 mm, in particular from 0.5 to 5.0 mm.

[0054] By "domain" we mean the different distinctive parts of said hollow monocoque part differentiated by the geometric shape or by the functionality of the part.

[0055] As a non-limiting example of a geometric shape domain, we can cite:

[0056] - a plate of regular shape such as a square, a rectangle, a circle, which may have a flat surface or present a curve,

[0057] - a cone, a tube

[0058] - the edges and corners.

[0059] As a non-limiting example of a functional domain, we can cite:

[0060] - the ends of the part - the attachment points for an assembly

[0061] - the junctions between two domains.

[0062] According to a particular embodiment, the invention relates to a hollow metal part as defined above, said part not having an axis of symmetry.

[0063] Hollow metal parts of complex shape, namely not having axial or planar symmetry for the entire part, are more difficult to obtain, in particular with a controlled thickness, in particular of thin thickness, by conventional molding methods with a core. One embodiment of the present invention relates to such hollow metal parts.

[0064] According to a particular embodiment, the invention relates to a hollow metal part as defined above, said part being symmetrical and having a plane of symmetry.

[0065] A bicycle frame (example 35) or an elbow-shaped tube are examples of hollow parts that do not include an axis of symmetry but have a plane of symmetry.

[0066] According to a particular embodiment, the invention relates to a hollow metal part as defined above, said part having an axis of symmetry.

[0067] A hollow part of a luminaire (example 9) or a linear tube are examples of hollow parts comprising an axis of symmetry.

[0068] According to a particular embodiment, the invention relates to a hollow metal part as defined above, in which all the areas have the same average thickness value e.

[0069] According to a particular embodiment, the invention relates to a hollow metal part as defined above, in which at least two areas have different average thickness values ​​e.

[0070] Advantageously, the domains relating to a functionality, such as the attachment domains or the ends, have a greater thickness than the geometric domains.

[0071] According to a particular embodiment, the invention relates to a hollow metal part as defined above, in which said part is a mechanical or fluidic functional part, the average value of the thickness e ranging from 0.5 to 10.0 mm.

[0072] By "functional part" is meant a mechanical or fluidic functional part, namely respectively having mechanical resistance properties and fluidic properties (chemical resistance, conductivity). In the present invention, the hollow parts serving as sacrificial molds are not considered to be mechanical or fluidic functional parts. 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 columnar or equiaxed dendritic structures, polyhedral structures and eutectic facet structures or a mixture or combination of these structures.

[0073] These structures are closely related to the crystallography of the metal or metal alloy used.

[0074] According to a particular embodiment, the invention relates to a hollow metal part as defined above, in which the size of the metallurgical grains of the outer surface is smaller than that of the metallurgical crystals of the crystallographic inner surface.

[0075] It is important to note that the hollow part of the casting is obtained without the use of a molding part, destructible (sand core for example, destroyed after molding) or permanent (metal core or pin generally removable in the mold). Furthermore, the hollow part, also called the interior cavity (in whole or in part) of the part, is obtained by draining the unsolidified alloy / liquid metal from the center of the part

[0076] According to a particular embodiment, the invention relates to a hollow metal part as defined above, said metal being aluminum.

[0077] According to a particular embodiment, the invention relates to a hollow metal part as defined above, said alloy being an alloy of aluminum and silicon.

[0078] According to a particular embodiment, the invention relates to a hollow metal part as defined above, said metal or alloy being chosen from: aluminum (Al), lead (Pb), tin (Sn), copper (Cu), zinc (Zn), iron (Fe), nickel (Ni) and magnesium (Mg),

[0079] A1SH2, ZnA15, AlCu33, AlMg32, MgZn37, CuMn37, CuSilo, SnPb38, eutectic cast iron, AlSi0, AlSi2, cast iron relatively close to the Fe-C eutectic, or steel with a very narrow solidification interval.

[0080] According to a particular embodiment, the invention relates to a hollow metal part comprising:

[0081] - a smooth exterior surface

[0082] - a crystallographic interior surface and

[0083] - a homogeneous average thickness, in particular from 0.2 mm to 2 mm, said metal part being made of a metal having a melting point above 180°C, in particular above 320°C, in which the topology or topography of said crystallographic inner surface comprises reliefs corresponding to metallurgical crystals, in particular reliefs corresponding to dendritic crystals or polyhedral crystals or eutectic cells.

[0084] 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.

[0085] In the present invention, topology is assimilated to topography.

[0086] 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.

[0087] According to a particular embodiment, the invention relates to a hollow metal part as defined above, in which the topology or topography 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.

[0088] According to a particular embodiment, the invention relates to a hollow metal part comprising:

[0089] - a smooth outer surface comprising metallurgical grains,

[0090] - a crystallographic interior surface and

[0091] - a homogeneous average thickness, in particular from 0.2 mm to 2 mm, said metal part is made of a metal having a melting point above 180°C, in particular above 320°C, in which the topology or topography of said crystallographic inner surface comprises reliefs corresponding to metallurgical crystals, in particular reliefs corresponding to dendritic crystals and / or polyhedral crystals and / or eutectic cells.

[0092] Advantageously, said smooth outer surface delimits said metallurgical grains. A surface corresponds to a 2D geometry and the grains to a 3D volume, it is understood that the metallurgical grains of the outer surface are constrained by the surface of the mold in which the part was molded.

[0093] Metallurgical crystals internal to the wall of the casting or located on the crystallographic interior surface are the crystals formed freely during solidification of the molten metal from which the part is made, for example without constraint from an applied surface, except those in direct contact with the mold surface of the mold (impression).

[0094] Metallurgical grains are solidification crystals formed in contact with a cooling surface during solidification, particularly located on the smooth outer surface of the part in contact with the impression.

[0095] 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 association of these structures.

[0096] 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, columnar and / or equiaxed structures and eutectic facet structures or a mixture or association of these structures.

[0097] By "association of these structures" we mean, for example, dendritic crystals formed or organized in columns.

[0098] Surface conditions of the product:

[0099] According to the innovative manufacturing process of the invention, the molded part has two types of surface condition.

[0100] 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.

[0101] 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, they have a certain roughness, because they are representative of the morphology of the solid phases developed during solidification and the flow of the molten metal during emptying.

[0102] Visually, it is possible to identify these different surfaces on the product with the naked eye, using comparative reference images of optical microscopy (binocular loupe or optical microscope) or scanning electron microscopy or digital microscope.

[0103] Certain characteristics of the profile of these surfaces are measurable via 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 outer surface is smaller than that of the crystals on the crystallographic inner surface.

[0104] Advantageously the hollow metallurgical part comprises an increase in the size of the crystals in the thickness from the smooth outer surface to the crystallographic inner surface.

[0105] Metallurgical grain size:

[0106] 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.

[0107] 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 of dendritic fineness, measurement of grain size by image analysis).

[0108] 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, in which said metal shell has:

[0109] • a smooth exterior surface,

[0110] • a crystallographic inner surface, in which the metal of said metal shell has a melting point above 180°C, in particular above 320°C.

[0111] According to a particular embodiment, the present invention relates to the metal part, as defined above, having a thickness less than or equal to 10 mm, in particular from 0.2 mm to 5.0 mm, preferably from 0.5 to 2.0 mm, on at least part of the part or the entire part.

[0112] 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, in particular a eutectic type alloy is preferable for the process due to its low solidification interval (low difference between liquidus and solidus temperature) and its good flowability.

[0113] 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 A1SH2 or another Al-Si alloy.

[0114] Another object of the present invention relates to an assembly comprising one, two or more hollow metal parts according to the invention as defined above.

[0115] Another object of the present invention relates to an assembly comprising one, two or more hollow metal parts as obtained according to the method below or according to the invention as defined above.

[0116] As an example, a bicycle frame was designed as exemplified in Figure 7.

[0117] Another object of the present invention relates to a mold of the hollow metal part according to the invention as defined above.

[0118] According to a particular embodiment, the invention relates to the mold as defined above further comprising means for controlling the temperature of said mold.

[0119] Another object of the present invention is a method of manufacturing a hollow metal part, said method comprising at least the following steps:

[0120] • 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;

[0121] • 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;

[0122] • a step 3 of subtraction of the above-mentioned liquid phase, said subtraction step being carried out without tilting the mold; and

[0123] • a step 4 of recovering the hollow metal part in the form of a solidified metal shell, in which the metal has a melting point above 180°C, in particular above 320°C, and in which the hollow metal part is formed in the absence of a core (i.e. without an internal molding element), in particular said method having a casting ratio of 1:1 to 1.2:1, preferably approximately 1:1, in particular 1:1. The casting ratio is defined here as the ratio between the mass of the casting cluster (solidified mass) extracted from the mold and the mass of the finalized raw part (i.e. after cutting any residual casting and draining jets, and deburring if necessary).

[0124] The hollow part of the casting is obtained without using a molding part, destructible (sand core for example, destroyed after molding) or permanent (metal core or pin generally removable in the mold). Furthermore, the hollow part, also called "internal cavity (in whole or in part) of the part", is obtained by emptying the unsolidified alloy / liquid metal from the center of the part.

[0125] According to a particular embodiment, the invention relates to a method as defined above, of a hollow metal part according to the invention as defined above.

[0126] According to a particular embodiment, the invention relates to a method for manufacturing a molded monocoque hollow metal part comprising:

[0127] - an outer surface comprising metallurgical grains constrained by the surface of the mold in which the part was molded,

[0128] - a crystallographic inner surface, said metal part being made of a metal or an alloy having a melting point above 180°C, in particular above 320°C, in which the topography of said crystallographic inner surface comprises reliefs corresponding to the metallurgical crystals, in particular reliefs corresponding to the dendritic crystals, in particular primary crystals, and / or to the polyhedral crystals, in particular primary crystals, and / or to the eutectic cells, in which said part comprises

[0129] - a thickness e, defined by the minimum distance between said outer surface and said inner surface, with an average value ranging from 0.2 mm to 10.0 mm, in particular from 0.5 to 5.0 mm,

[0130] - a dimension Rt, defined by the difference between the value of the thickness EM and that of the thickness e, the thickness EM being defined as the distance between the point of the inner surface furthest from the outer surface and its orthogonal projection on the outer surface, said method comprising at least the following steps:

[0131] • 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;

[0132] • 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;

[0133] • a step 3 of subtraction of the above-mentioned liquid phase, said subtraction step being carried out without tilting the mold; and

[0134] • a step 4 of recovering the hollow metal part in the form of a solidified metal shell, in which the metal has a melting point above 180°C, in particular above 320°C, and in which the hollow metal part is formed in the absence of a core, in particular said method having a casting ratio of 1:1 to 1.2:1, preferably approximately 1:1, in particular 1:1. The casting ratio is defined here as the ratio between the mass of the casting cluster (solidified mass) extracted from the mold and the mass of the finalized raw part (i.e. after cutting any residual casting and draining jets, and deburring if necessary).

[0135] When implementing the method of the invention, a molten metal, in a liquid state, is injected into a mold. While in the mold, a portion of the initially molten metal solidifies against the inner wall of the mold, or the cavity, 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.

[0136] The mold is then emptied of the still liquid, i.e. not yet solidified, metal which is inside the shell, thus forming a hollow metal part.

[0137] 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 10.0 mm and greater than 0.2 mm, in particular from 0.2 to 5.0 mm, preferably from 0.5 to 5.0 mm. Thanks to emptying without tilting the mold, the method is not dependent on unwanted solidification of the metal, said solidification being completely controlled.

[0138] This controlled solidification allows in particular a controlled thickness of said part.

[0139] It is also advantageously possible to obtain different average minimum thicknesses in the different areas of said part at controlled thickness values.

[0140] In particular, a major advantage of the gravity-fed casting according to the invention is that it allows a minimum wall thickness e to be obtained that is much lower than in conventional gravity casting with a metal shell and internal molding element (metal core or sand core).

[0141] Indeed, during conventional shell casting, the surface tension of the alloy and the metallostatic pressure limit the minimum thickness of the cast product; for example, for an aluminum alloy it is very difficult to make parts whose minimum general thickness is less than 2.5 mm. Drained casting makes it possible to have a minimum thickness whose value can be set between 0.3 and 3 mm without difficulty, this due to the drainage of the unsolidified alloy. By "hollow metal part" we therefore mean a metal part in the form of a shell which surrounds, or partially surrounds, an empty part. For example, among the parts in the form of a shell which partially surrounds an empty part, we can cite parts such as cups, cups, bowls and bottles.

[0142] By "partial solidification of the molten metal" is meant that the solidification is sufficient to form the solid shell, while leaving a part of the metal in a liquid state to allow the hollow part of the part to be obtained after removal, or emptying, of said metal in a liquid state.

[0143] By "solid part" we mean a solid state in the metallurgical or thermodynamic sense. Thus the solid part can be composed of several solid phases, which is the case for example with Al-Si alloys.

[0144] 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 explained below. That being said, it is understood that the absence of tilting the mold does not prevent the entire mold from being able to be moved above a furnace or a ladle in order to receive the emptying.

[0145] 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 interval (i.e. with very close liquidus and solidus temperatures).

[0146] A "single metal" is a metal that is not mixed with another element, such as another metal. This is a so-called "pure" metal, with a purity greater than 98%, particularly greater than 99%.

[0147] Among the (pure) metals that 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).

[0148] Among the eutectic alloys that can be used in the part and the method of the invention, we can cite, by way of example: A1SH2, ZnA15, AlCu33, AlMg32, MgZn37, CuMn37, CuSilô, SnPb38, eutectic cast iron. Among the alloys with a low solidification interval that can be used in the part and the method of the invention, we can cite, by way of example: AlSilO, AlSi2, cast iron relatively close to the Fe-C eutectic, or steel with a very low solidification interval.

[0149] 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 to 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.

[0150] 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".

[0151] In general, in foundry work, the "mild weight" refers to the ratio of the mass of the casting sprue to the mass of the finished raw part. The casting sprue corresponds to the part taken out of the mold with all its adhering casting devices (filling system, riser, vents, flash). The mild weight is therefore often greater than 1, and rarely equal to 1.

[0152] In the case of this process, the ratio 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 with no or almost no 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.

[0153] By "close to 1:1" is meant from 1:1 to 1.2:1. By "1:1 to 1.2:1" is also meant the following ranges: "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”, “1:1 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 by several techniques. The injection can be carried out by gravity, by means of a manual or automatic cup, or even a transfer chute.The injection of 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.

[0154] Stage 2 of solidification 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 produced. 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.

[0155] 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 (e.g. induction system). It can also be facilitated by the thrust of a pressurized gas in the upper part of the mold.

[0156] Step 4 of recovering the hollow metal part can be carried out using known demolding methods. Demolding can, for example, be carried out by turning the mold over. A grid can first 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 placed on the grid.

[0157] 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.

[0158] 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 totally surrounds an empty part, in which said metal shell has:

[0159] • a smooth exterior surface,

[0160] • a crystallographic interior surface.

[0161] Thus, the process according to the invention can be implemented in different ways: 1- Gravity casting process

[0162] 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 surplus 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, blocked by a plug, a stopper rod or other closure system which can be opened when emptying the mold.

[0163] Typically, the drain hole closure device is preheated and / or made of thermally insulating materials. Below the mold, a ladle or furnace collects the excess molten alloy.

[0164] The gravity casting process is illustrated in Figure 1. In this regard, it should be noted that the three diagrams present different technical solutions for the drained casting here carried out solely by gravity. The graphics each illustrate a general principle. However, in the majority of cases, the casting is not necessarily of revolution or symmetrical.

[0165] 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 hotter 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.

[0166] 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.

[0167] 2- Low pressure casting process

[0168] Low pressure is a technical device consisting of bringing an inert gas for the metal, such as nitrogen, argon, or other, into the sealed 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 used for injecting the metal. This inlet also serves to drain the 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 from the bottom of the mold, then pressurized during solidification, under a controlled atmosphere (nitrogen, argon or other).

[0169] This technique allows the speed of filling and emptying of the mold to be controlled, and thanks to the neutral gas limits the formation of oxide skins with oxidizable metals, including for example alumina with aluminum alloys.

[0170] This embodiment of the method of the invention is illustrated by Figures 2 and 3.

[0171] 3- Pressure injection molding process

[0172] 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 conduit into the cavity can be separate from the drain conduit. 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). The injection can also be carried out in a controlled atmosphere of neutral gas (nitrogen, argon or other). A die injection molding process is very compatible with so-called hot chamber pressure 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 the 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 emptied through a different conduit from the injection conduit.

[0173] This embodiment of the method of the invention is illustrated by Figures 8 to 14.

[0174] According to a particular embodiment, the present invention relates to the manufacturing method as defined above, 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.

[0175] By "upper part of the mold" we mean the apical part of the mold, namely the part which is furthest from the ground.

[0176] 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.

[0177] 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 (or magnesium) alloys, an inert gas such as nitrogen or argon is preferred in order to avoid the formation of alumina skins (or ignition of the alloy).

[0178] By "the bottom of the mold" we mean the basal part of the mold, namely the part which is closest to the ground.

[0179] According to a particular embodiment, the invention relates to a manufacturing method as defined above, in which in injection step 1 the temperature of the surface of the impression of said mold of said part is controlled and / or the temperature in the thickness of the mold in the vicinity of the impression is controlled and / or the initial temperature of the cast metal is controlled and / or the time and speed of filling of the mold are controlled and / or the heat exchanges between the above-mentioned molten metal and the surface of the impression of said mold are controlled and / or the metallostatic pressure of the above-mentioned molten metal and on the surface of the impression of said mold is controlled in order to control the thickness e of the part.

[0180] The control of these parameters can be carried out, without limitation, by temperature mapping, a coating or a coating deposited on the impression, a mold cooling device. Advantageously, these parameters can be different in certain parts of the mold in order to obtain different average thicknesses in the areas of said hollow part.

[0181] According to a particular embodiment, the invention relates to a manufacturing method as defined above, in which advantageously the thickness e is controlled.

[0182] Advantageously, in a non-limiting manner, the thickness e is controlled using at least one of the following control parameters: the holding time of the liquid alloy in the mold before emptying, the casting time, the solidification rate of the alloy, the nature of the cast alloy and its temperature, the nature of the mold (sand, metal or alloy or fiber mold) and its initial temperature(s), the thickness of the mold, the volume of cast alloy present locally in the impression, the nature and thickness of the coating (metal mold), or of the possible layer (sand mold), used at the mold and alloy / cast metal interface, a possible mold cooling device.

[0183] According to a particular embodiment, the invention relates to a manufacturing method as defined above, in which said mold is chosen from a sand mold, a metal mold, a plaster or ceramic mold, a graphite mold, a mold made of more or less thermally conductive refractory fibers, or a mold composed of a combination of these different materials.

[0184] According to a particular embodiment, the invention relates to a manufacturing method as defined above, in which said mold is a metal mold.

[0185] 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.

[0186] 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 or air.

[0187] 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.

[0188] It should be noted that with regard to these two particular embodiments. The injection pressure values ​​are clearly different (under pressure in a hot chamber: by gas 5 to 110 bars in general and by hydraulic piston 100 to 400 bars in general; under pressure in a cold chamber: by piston 250 to 5000 bars in general; low pressure: 1.5 bars in general). In the vast majority of cases, 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 step 4 of demolding is carried out by turning the mold over. Turning the mold over allows the shell to exit the mold by gravity, with the possible assistance of ejectors. An example of this embodiment is shown diagrammatically in Figure 4C.

[0189] 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.

[0190] This embodiment is illustrated by Figures 1A and 1B. Note that in a particular embodiment, said closing device (stopper, stopper or hatch) is either preheated, heated or thermally insulating.

[0191] 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 in 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 favored 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.

[0192] Advantageously, said air or gas intake means are a trapdoor or plug or generally pointed stopper 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.

[0193] Said air or gas intake means are said to be closed when air or gas cannot penetrate inside the mold.

[0194] Said air or gas intake means are said to be open when air or gas can penetrate inside the mold.

[0195] In this embodiment, the call or gas means, in particular a plug or a generally pointed trap or stopper, are made of an insulating material, and / or of heated or preheated material, in order to avoid solidification of the metal against the part of said device in contact with said metal.

[0196] 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.

[0197] 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.

[0198] 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.

[0199] 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.

[0200] According to another particular embodiment, the present invention relates to the method as defined above, wherein the metal is pure or alloyed aluminum. In particular, the present invention relates to the method as defined above, wherein the metal is pure aluminum. In particular, the present invention also relates to the method as defined above, wherein the metal is alloyed aluminum.

[0201] According to another particular embodiment, the present invention relates to the method as defined above, in which the metal is the eutectic alloy A1SH2.

[0202] 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.

[0203] It is also possible to use other materials constituting the mold, such as for example: sand, refractory plaster, ceramic, graphite or refractory fibers. 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 having a melting point above 660°C, such as, for example, a ferrous alloy (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 process according to the invention allows the manufacture of parts comprising a thin shell.The process also allows for local control of the thickness of the solidified shell. This can be achieved by using a mold of variable thickness. The solidified shell will be thicker in areas where the mold wall is thicker.

[0204] 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 in 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.

[0205] 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.

[0206] 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).

[0207] 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 gaps 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.

[0208] According to another particular embodiment, the present invention relates to the method as defined above, in which the mold is coated with a coating.

[0209] The "seal coating" is a coating applied to, or against, the inner face of the mold (cavity), i.e. the face that will be in contact with the molten metal. The seal coating facilitates demolding, limits mold-alloy chemical interactions and thermal shocks, and helps control solidification. A seal coating is used when using a metal mold, and is made of a thermally insulating or conductive material. The seal coating generally has a thickness of 0.2 to 0.5 mm. By "0.2 to 0.5 mm" we also mean 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 "coat", can also be applied to the impression 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 the solidification of the cast metal locally and on the surface. The current 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.

[0210] 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 impression is often between 0.3 mm and 0.5 mm.

[0211] 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 impression is often of the order of 0.2 to 0.3 mm.

[0212] 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 above 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.

[0213] “Room temperature” means a temperature between 15°C and 30°C, in particular between 20 and 25°C.

[0214] Heating the mold allows the molten metal to be received, while limiting the risks of degradation of the metal mold, e.g. 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".

[0215] Alloy and mold temperatures can be measured by thermocouples or optical sensors.

[0216] 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.

[0217] 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 "superheating" in the professional vocabulary of foundries.

[0218] For information purposes:

[0219] • 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;

[0220] • in casting with a metal shell and gravity casting, the superheat for a cast aluminum alloy is often between 50°C and 100°C and the mold temperature is around 350°C; and

[0221] • in die casting, it is sometimes possible to have zero superheating (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).

[0222] Following the experiments, the inventors unexpectedly found that the superheating with the innovative process according to the invention can be lower than that commonly used in conventional foundry processes, whereas 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.

[0223] 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, from 1500 to 1600°C, 1600 to 1700°C, 1700 to 1750°C.

[0224] As an example for the theoretical values ​​in conventional shell casting: in the case where the metal to be poured by gravity is pure aluminum, the metal mold is preferably heated to a temperature of approximately 350°C, the melting point of pure aluminum being approximately 660°C and the superheat often chosen to be approximately 75°C, the temperature of the mold is in this case approximately 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 mold with gravity casting).

[0225] As a non-limiting practical example, corresponding to the embodiment illustrated in Figure 6: when the metal to be cast is the A1SH2 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 A1SH2 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 A1SH2 alloy.

[0226] In view of this Figure 6 and the embodiment of the method of the invention implemented, it is understood that in terms of temperatures, several factors can 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 emptying, in particular the waiting time before emptying.

[0227] 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 Figure 6.

[0228] 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 A1SÜ2, 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, 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 rod or a hatch, subtraction step 3 being initiated by a release of said opening, by removal of said closing device.

[0229] Advantageously in this embodiment (Fig. 6) the time taken to pour the molten metal (mass of approximately 19 to 24 kg) into the mold is 10 to 17 seconds.

[0230] Advantageously in this embodiment the waiting time before emptying into the mold is 10 seconds to one minute.

[0231] Advantageously in this embodiment the emptying time is 11 to 18 seconds.

[0232] According to another particular embodiment, the present invention relates to the method as defined above, in which said mold temperature above ambient temperature is:

[0233] • is reached by a step 0 of preheating the mold, before step 1 of pouring,

[0234] • be the result of a previous production. The preheating of the mold can be carried out, for example, by using gas burners or electric heating devices.

[0235] After an initial production run, the mold may already be at 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 mass production of multiple parts.

[0236] 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.

[0237] 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 of skill and expertise.

[0238] By "from 0°C to 200°C" we also mean the following ranges: from 0°C to 150°C, from 0°C to 100°C, from 0°C to 50°C, from 50°C to 100°C, from 50°C to 150°C, from 50°C to 200°C, from 100°C to 200°C, from 150°C to 200°C, from 100°C to 150°C.

[0239] As an example in classic shell casting, for an A1SH2 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.

[0240] The liquidus of the said alloy being 580°C (solidus 575°C) (cf NFA 57.703), the alloy is therefore heated to a temperature between 630 and 680°C, eg often to a temperature of around 650°C.

[0241] For the implementation of the present invention, in particular to obtain a low thickness of solidified shell and the time required to carry out emptying, higher superheats may be used, e.g. between 100 and 200°C.

[0242] The present invention also relates to a method for mass-producing at least two metal parts, said method comprising at least:

[0243] • 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 process 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.

[0244] In this embodiment, after the first production run, it is no longer necessary to heat the mold. Successive castings into 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 sufficient heat dissipation to solidify the alloy skin, but also ensure that the metal mold remains hot enough to cast the following parts without having to reheat the mold, through 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.

[0245] Another solution consists of emptying the mold directly above the melting-holding furnace, thus limiting the cooling of the recovered metal while still liquid for reuse, and therefore limiting the energy expenditure of the melting means, these solutions being non-exhaustive.

[0246] However, in certain specific cases of parts, a local cooling or heating device can also be installed on the mold.

[0247] For example, for casting an aluminum alloy, an order of magnitude of the mold thickness is given by Jander's formula: [Mathl]

[0248] Shell thickness (in mm) æ 2.5 x Thermal modulus of the part (in mm) + 15mm

[0249] To more optimally size the thickness of the solidified shell, digital foundry simulation software can be used (digital twin of the casting process). Keeping a full cavity of molten alloy before emptying the mold makes it easier to maintain a high mold temperature in service.

[0250] This process also allows for 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.

[0251] 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.

[0252] 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, e.g. close to 1:1. Another object of the present invention relates to a hollow metal part capable of being obtained by the method as defined above.

[0253] The present method makes it possible to obtain a wide variety of hollow metal parts. Depending on the part to be produced, a person skilled in the art is able to choose from the different process options set out in the present application.

[0254] 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.

[0255] Indeed, the produced parts have a smooth exterior surface and a crystallographic interior surface.

[0256] By "smooth exterior surface" we mean 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 ambient temperature.

[0257] The smooth surface is therefore devoid of crystallographic artifices, is not rough and does not have an uneven topology (no pronounced relief due to solidifying crystals).

[0258] The term "crystallographic inner surface" means 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, e.g., dendritic crystals, polyhedral crystals, eutectic cells.

[0259] 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.

[0260] For example, a part produced with the eutectic alloy A1SU2 will have on the inner surface dendritic crystals rich in aluminum, polyhedral crystals rich in silicon, and mostly eutectic cells.

[0261] The size of these different crystals is linked to the solidification speed 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 parts produced by existing techniques.

[0262] 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.

[0263] 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 emptying carried out by gravity.

[0264] 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.

[0265] The inventors have developed an innovative process enabling the implementation of a "drained casting" process with metals with a melting temperature Q above 180°C (in particular above 320°C), without tilting the mold during drainage.

[0266] The implementation of this process 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 conventional manufacturing processes 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.

[0267] Another object of the present invention relates to a device comprising in association the hollow metal part according to the invention as defined above and the mold used for molding said hollow metal part.

[0268] According to a particular embodiment, the invention relates to a device as defined above, in which said mold is a metal mold.

[0269] The following Examples and Figures illustrate the invention, without limiting its scope. LIST OF FIGURES

[0270] Figure 1 shows gravity-drained casting systems

[0271] Figure IA shows an open mold being drained by opening a hatch / plug or other device.101 represents the mold (metallic, or sand, or refractory plaster, or ceramic, or graphite), 102 represents the filling of the mold with the molten metal / metal alloy, 103 represents a trap / plug device (thermal insulating material or metal, heated or preheated as required) or other device placed under the mold or on the side of the mold in certain applications, 104 represents the draining of the molten metal bath, 107 represents a solidified metal shell, 108 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 being cast, 109 represents the outer surface of the solidified metal / alloy shell, which outer surface is complementary to the geometry of the mold cavity.

[0272] Figure 1B shows an open mold emptied by an upper stopper rod. 101 shows the mold (metallic, or sand, or refractory plaster, or ceramic, or graphite), 102 shows the filling of the mold with molten metal / metal alloy, 105 shows an upper stopper rod (refractory material or metal tube with insulating coating, heated or preheated if necessary), 106 shows the withdrawal of the stopper rod upwards to allow the bath to be emptied, 104 shows the draining of the still molten metal bath, 107 shows a solidified metal shell, 108 shows 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 being cast, 109 shows the outer surface of the solidified metal / alloy shell, which outer surface is complementary to the geometry of the mold cavity.

[0273] Figure IC represents a mold allowing the preparation of a substantially closed solidified shell. 101 represents the mold (metal recommended), 102 represents the filling of the mold with the molten metal / metal alloy, 103 represents 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, 104 represents the draining of the molten metal bath, 111 represents a thermally insulated or heated part of the mold (no or very little solidified alloy), 110 represents the upper ceiling of the cavity, 112 represents a column of liquid metal 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 cavity for the correct arrival of the geometry of the molded part, 107 represents a solidified metal shell,108 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 being cast, 109 represents the outer surface of the solidified metal / alloy shell, which outer surface is complementary to the geometry of the mold cavity.,

[0274] 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).

[0275] Figure 2 shows a low pressure casting system with an air or gas inlet located locally in the mold to provide drainage.

[0276] Figure 2A shows the mold filling.

[0277] Figure 2B shows the filled mold.

[0278] Figure 2C shows the mold emptying.

[0279] Figure 2D shows the mold emptied of molten metal / alloy, comprising a shell of metal / alloy solidified against the inner wall of the mold.

[0280] Key: 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 point); or heated air metal or refractory filter(s) 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.

[0281] Figure 3 shows a low pressure casting system with an air or gas supply through the injection nozzle to ensure emptying.

[0282] Figure 3A shows the mold filling.

[0283] Figure 3B shows the filled mold.

[0284] Figure 3C shows the mold emptying.

[0285] Figure 3D shows the mold emptied of molten metal / alloy, comprising a shell of metal / alloy solidified against the inner wall of the mold.

[0286] Key: 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.

[0287] Figure 4 shows the principle of a mass production device for an example part.

[0288] Figure 4A shows the mold filling.

[0289] Figure 4B shows the mold emptying.

[0290] Figure 4C shows the demolding of the solidified shell and the filling of the casting cup.

[0291] Key: 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 emptying of the 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 during demolding of the part, 412 represents the demolding of the part onto a support, 413 represents a support of the metal grid type, 414 represents the solidified metal / alloy shell and unmolded,415 represents the rotation of the ladle / bucket system for drawing molten metal from the furnace in parallel with the part demolding operation.

[0292] Figure 5 shows photographs of a sand casting process according to Example 5.

[0293] Figure 5A shows a photograph of a wooden template.

[0294] Figure 5B shows a photograph of the making of a sand mold / extraction of the wooden template.

[0295] Figure 5C shows a photograph of the filling of the sand mold with molten aluminum alloy.

[0296] Figure 5D shows a photograph of the liquid metal being held in the mold for solidification.

[0297] Figure 5E shows a photograph of the liquid metal being drained from the bottom of the mold.

[0298] Figure 5F shows a photograph of the hull obtained using the sand casting process.

[0299] Figure 6 shows photographs of a casting process with an aluminum alloy shell.

[0300] Figure 6A represents a photograph of an emptied casting test bench. 601 represents a mold (shell) made of aluminum alloy. 602 represents an orifice allowing the emptying of the molten metal bath, which will be obstructed by a stopper rod, a hatch or other system, 603 represents a pivoting mold support, allowing the solidified shell to be demolded, 604 represents the pivot for the rotation of the mold support, 605 represents a lever arm allowing the mold to be pivoted during demolding, 606 represents a fixed frame (mechanically welded structure), 607 represents a sand bed, 608 represents a casting ladle, collecting the molten metal during the emptying of the mold, 609 represents a stretcher allowing the ladle to be transported with the molten metal, to transfer it back into the furnace.

[0301] Figure 6B shows a photograph of the exterior surface of a solidified metal shell.

[0302] Figure 6C shows a photograph of the crystallographic interior surface of a solidified metal shell.

[0303] Figure 7 shows an assembly comprising a part (bicycle frame) which can be manufactured by the method of the invention.

[0304] Figure 8 shows a hot chamber die casting system with an injection piston controlled by a hydraulic (or pneumatic) cylinder.

[0305] Figure 8A shows the injection of molten metal into the mold and its maintenance under pressure during the formation of the solidified shell.

[0306] Figure 8B shows the emptying of the mold, the feeding of the molten metal jacket and the resulting solidified shell.

[0307] Legend: 801 represents the moving part of the mold, 802 represents the fixed part of the mold, 803 represents the hatch or the 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) 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 filling of the injection jacket 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 solidification of the metal / alloy in the injection nozzle (generally temperature equal to or higher than the liquidus), 812 represents the supply of molten metal / alloy to the injection jacket 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 refilled with molten metal, 818 represents the main joint plane of the mold (here vertical).,

[0308] Figure 9 shows a hot chamber die casting system with injection of molten metal by air or gas (nitrogen, argon, or other) under pressure.

[0309] Legend: 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.

[0310] 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 through the nose of the swan neck. In this particular case, the orifice mentioned 921 then corresponds to the injection nozzle noted 810 in figure 8.

[0311] Figure 10 shows a cold chamber die casting system with a conventional horizontal injection sleeve by piston controlled by a hydraulic (or pneumatic) cylinder, and with a vertical main mold joint plane.

[0312] Figure 10A shows the feeding of the injection jacket with molten metal with the mold previously closed.

[0313] Figure 10B shows the injection of molten metal into the mold and its maintenance under pressure during the formation of the solidified shell.

[0314] Figure 10C shows the emptying of the mold and the resulting solidified shell.

[0315] 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 achieve the call for air or gas (nitrogen, argon, or other) 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 that controls the injection, 1009 represents the closable port allowing the filling of the injection jacket with the molten metal / alloy, 1010 represents the thermally insulating closing system (plug, hatch, stopper rod, other), which can be heated or preheated, 1011 represents the casting attack, 1012 represents the movement of the cylinder rod allowing the cavity to be filled 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 cavity, 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 pressure or higher) 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 moving part of the mold in order to extract the solidified shell.

[0316] Figure 11 shows 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 parting line.

[0317] Figure 11A shows the feeding of the heated / thermo-regulated injection jacket with molten metal with the mold previously closed.

[0318] Figure 11B shows the injection of molten metal into the mold and its maintenance under pressure during the formation of the solidified shell.

[0319] Figure 11C shows the emptying of the mold and the resulting solidified shell.

[0320] 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 that controls the injection, 1109 represents the closable port allowing the filling of the injection sleeve with the molten metal / alloy, 1111 represents the casting attack, 1112 represents the movement of the cylinder rod allowing the cavity to be filled in a controlled manner, 1113 represents the outer surface of the solidified metal / alloy shell, which outer surface is complementary to the geometry of the mold cavity, 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 solidified metal shell against the inner wall of the mold,1116 represents the arrival of air or gas (atmospheric pressure or higher) 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 joint plane of the mold (here horizontal), 1119 represents the opening of the mold allowing the solidified shell to be ejected.

[0321] Figure 12 shows 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.

[0322] Figure 12A shows the feeding of the injection jacket with molten metal, just before closing the mold.

[0323] Figure 12B shows the injection of molten metal into the mold and its maintenance under pressure during the formation of the solidified shell.

[0324] Figure 12C shows the emptying of the mold and the solidified part obtained (part + residual injection pellet).

[0325] Legend: 1200 represents the return of the cylinder rod in order to supply the injection sleeve 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 the 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) under pressure (atmospheric or higher) in order to promote / make possible emptying, 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 cavity, 1213 represents the outer surface of the solidified metal / alloy shell, which outer surface is complementary to the geometry of the mold cavity, 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 solidified metal shell against the inner wall of the mold,1216 represents the arrival of air or gas (atmospheric pressure or higher) to promote / allow the emptying 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 ejection of the solidified shell following emptying, 1219 represents the emptying by gravity of the still liquid metal.

[0326] Figure 13 shows 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 parting line. 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 gas / air pressure.

[0327] Figure 13A shows the feeding of the injection jacket with molten metal, just before closing the mold.

[0328] Figure 13B shows the injection of molten metal into the mold and its maintenance under pressure during the formation of the solidified shell.

[0329] Figure 13C shows the emptying of the mold and the resulting solidified shell.

[0330] 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 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 cavity, 1313 represents the outer surface of the solidified metal / alloy shell, which outer surface is complementary to the geometry of the mold cavity, 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 solidified metal shell against the inner wall of the mold, 1316 represents the arrival of air or gas (atmospheric pressure or higher) to promote / allow the emptying of the still liquid metal / alloy,1317 represents the main joint 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.

[0331] Figure 14 shows 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 parting line. 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 gas / air pressure.

[0332] Figure 14A shows the feeding of the injection jacket with molten metal, just before closing the mold.

[0333] Figure 14B shows the injection of molten metal into the mold and its maintenance under pressure during the formation of the solidified shell.

[0334] Figure 14C shows the emptying of the mold and the resulting solidified shell.

[0335] 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 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 arrival of air or gas (atmospheric pressure or higher) 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 ejection of the solidified shell following emptying and the supply of molten metal to the injection jacket. Figure 15: Photographs of crystallographic surface and cross-sectional view of samples from gravity-emptied castings with A1SÜ2 (A-S13) alloy:,

[0336] Part A is a photo of an interior crystallographic surface of sample A from a parallelepiped piece (135x60x35 mm 3) cast in a cast iron mold (grey cast iron with lamellar graphite, mold thickness 10 to 20 mm) at an initial temperature of 450 ° C and coated with a conductive coating (colloidal graphite base, thickness of approximately 0.2 mm). Alloy temperature at casting between 650 and 720 ° C. Mold filling time of the order of 1 to 3 seconds, holding time of the liquid alloy in the cavity between 5 and 60 s, complete emptying time of approximately 1 to 2 s.

[0337] Sample A: e = 1.5 mm; Rt = 1.6 mm (binocular loupe) / l.3 mm < Rt < 1.4 mm (Keyence digital microscope); i.e. Rt / e = approximately 100%

[0338] Part B is a photo of an interior crystallographic surface of a sample B from a cylindrical part (diameter = 205mm, height = 180mm) cast in a thermal insulating mineral fiber mold. Initial mold temperature 40°C, alloy temperature during filling about 700°C.

[0339] Sample B: e = 0.25 mm; 1.20 mm < Rt < 1.25 mm; or Rt / e = 490%

[0340] Part C is a photo of an interior crystallographic surface of a sample C from a semi-spherical luminaire (diameter 52 cm) cast in a 35 mm thick AlSi7Mg aluminum alloy mold coated with graphite-based conductive coating (initial mold temperature = 160°C, alloy pouring temperature = 700°C, mold filling time = 10 s, holding time of the liquid alloy in the mold = 19 s, emptying time = 11 s).

[0341] Sample C: e = 1.3mm; Rt = 0.5mm (binocular magnifier) ​​ / 0.4mm < Rt < 0.5mm (Keyence digital microscope); i.e. Rt / e = approximately 37%

[0342] Part D is a photo of a cross-sectional view of a tubular heat exchanger obtained by drain casting (gravity process, outer diameter of the tube = 22mm, length of the tube = 360mm) with eutectic alloy A1SH2 (A-S13) cast at 744°C in a steel mold with an initial temperature of 195°C. DI: crystallographic inner surface (low roughness due to a strong temperature gradient during casting); D2: smooth outer surface in contact with the mold.

[0343] Figure 16 shows surface photographs of samples obtained by gravity-drained casting with A1SH2 (A-S13) alloy:

[0344] Part A is a photograph of an interior crystallographic surface of sample A from a parallelepiped piece (135x60x35mm 3) cast in a cast iron mold (grey cast iron with lamellar graphite, mold thickness 10 to 20mm) at an initial temperature of 450°C and coated with a conductive coating (colloidal graphite base, thickness of approximately 0.2mm). Alloy temperature at casting between 650 and 720°C. Mold filling time of the order of 1 to 3 seconds, holding time of the liquid alloy in the cavity between 5 and 60 s, complete emptying time of approximately 1 to 2 s.

[0345] Part B is a photograph of an interior crystallographic surface of sample B from a cylindrical part (diameter=205mm, height=180mm) cast in a thermal insulating mineral fiber mold. Initial mold temperature 40°C, alloy temperature during filling about 700°C.

[0346] Part C is a photograph of a smooth exterior surface, sample from a semi-spherical luminaire (diameter 52 cm) cast in a 35 mm thick AlSi7Mg aluminum alloy mold coated with graphite-based conductive coating (initial mold temperature = 160°C, alloy casting temperature = 700°C, mold filling time = 10 s, holding time of the liquid alloy in the mold = 19 s, draining time = 11 s).

[0347] The roughness of the outer surface is representative of the quality of the coating deposit in the metal mold. In this example, it is coarse because it is accentuated by an excess of coating, a so-called "orange peel" appearance on the part. Otherwise, in general, the roughness is rather very low on the outer surface of the part (see following figures).

[0348] Figure 17 shows binocular microscope observation images of the wall section of parts cast by gravity drain casting process with A1SH2 (A-S13) alloy:

[0349] Part A is a photograph of sample A from a hollow parallelepiped piece (external dimensions = 135x60x35 mm 3 ) cast in a cast iron mold (grey cast iron with lamellar graphite, mold thickness 10 to 20 mm) at an initial temperature of 450 ° C and coated with a conductive coating (colloidal graphite base, thickness of approximately 0.2 mm). Alloy temperature at casting between 650 and 720 ° C. Mold filling time of the order of 1 to 3 seconds, holding time of the liquid alloy in the cavity between 5 and 60 s, complete emptying time of approximately 1 to 2 s. Al: interior crystallographic surface; A2: smooth exterior surface (in contact with the mold).

[0350] Part C is a photograph of a sample C from a semi-spherical luminaire (diameter 52 cm) cast in a 35 mm thick AlSi7Mg aluminum alloy mold coated with graphite-based conductive coating (initial mold temperature = 160°C, alloy casting temperature = 700°C, mold filling time = 10 s, holding time of the liquid alloy in the mold = 19 s, emptying time = 11 s). Cl: crystallographic inner surface; C2: smooth outer surface (in contact with the mold). The aluminum mold being more thermally conductive than the cast iron mold, and its initial temperature being lower than that of the cast iron mold, sample C solidified more quickly than sample A. In fact, for a fairly similar minimum wall thickness e, the roughness (see parameter Rt in the following figure) is more pronounced on the interior surface of sample A than on the interior surface of sample C.

[0351] On the profile observed here with a binocular loupe (figure 17), the following measurements can be made:

[0352] Sample A: e = 1.5mm and Rt = 1.6mm

[0353] Sample C: e = 1.3mm and Rt = 0.5mm

[0354] Figure 18 shows a diagram illustrating the roughness of the inner surface 1 of the casting and the difference Rt in height between the highest and lowest point of the profile (small scale / micrographic scale view).

[0355] 2: represents the smooth outer surface of the casting, in contact with the mold cavity. e: represents the minimum wall thickness. In general, it will be defined by the designer of the part (design office, foundry customer) in order to ensure that the part is correctly held to the mechanical stresses undergone in service. Its value will depend mainly on the holding time of the liquid alloy in the mold before emptying and the solidification rate. The latter is linked to the nature of the materials, cast alloy and mold, and their initial temperatures, as well as to the thickness of the mold, the volume of cast alloy present locally in the cavity, and the nature and thickness of the coating used (mold and alloy / cast metal interface).

[0356] In particular, a major advantage of gravity-fed casting is that it allows for a much lower minimum wall thickness e to be obtained than in conventional gravity casting with a metal shell and an internal molding element (metal core or sand core). Indeed, during conventional shell molding, the surface tension of the alloy and the metallostatic pressure limit the minimum thickness of the molded product; for example, for an aluminum alloy, it is very difficult to make parts with a minimum general thickness of less than 2.5 mm. The drained casting allows for a minimum thickness whose value can be set between 0.3 and 3 mm without difficulty, due to the emptying of the unsolidified alloy.

[0357] Rt: represents the difference in height between the highest and lowest point of the roughness profile. Its value depends on the crystallography of the alloy used, the solidification rate, the flow of the liquid alloy during emptying and the local orientation of the mold wall (vertical / horizontal / inclined face). With a eutectic alloy type A1SÜ2 (AS 13), experience shows that the higher the solidification rate and the shorter the holding time of the cast alloy in the mold before emptying, the lower the value of Rt.

[0358] For an application of the drained casting process to the manufacture of metal heat exchangers, a high Rt value promotes heat transfer but increases the pressure losses for the flow of the internal fluid. Depending on the use, there is therefore a compromise to be made to fix the Rt value and the internal surface condition.

[0359] Figure 19 shows a binocular microscope observation photograph of a local section D of a tubular heat exchanger obtained by gravity-drained casting (outer diameter of the tube = 22mm, length of the tube = 360mm). The eutectic alloy A1SH2 (designation A-S13 according to AFNOR standard) cast at 744°C in a steel mold at an initial temperature of 195°C. Conductive graphite-based coating deposited by spray gun on the impression (regular deposit thickness of approximately 0.2mm). Mold filling time of approximately 1.5s; holding time of the liquid alloy in the mold before draining = 3 to 5s; draining time of approximately 1s.

[0360] Part D 1 represents the crystallographic interior surface (Rt criterion of low roughness because of strong temperature gradient during casting); D2 represents the smooth exterior surface in contact with the mold.

[0361] In the tube section shown in Figure 19, the following measurements can be made:

[0362] Minimum tube thickness: e = 1.6mm; maximum thickness: e + 1 = 2.5mm;

[0363] Here we have a geometric tolerance of circularity of the internal profile obtained with the value: t = 0.9mm.

[0364] The general geometry of the outer surface D2 being obtained by contact with the cooling metal mold, it is precisely cylindrical. The general geometry of the inner surface DI being obtained after draining the unsolidified alloy, it has a less perfect cylindricity.

[0365] The wall thickness here depends on the filling time of the cavity, the holding time of the liquid alloy in the mold and the emptying time. The axis of the tube whose section is shown in Figure 5 was vertical during the filling, holding and emptying of the cast alloy in the mold.

[0366] Figure 20 shows a complete CAD of the drain casting bench for heat exchanger tube (thickness of the octagonal steel mold: minimum distance between the inner surface of the cavity and the outer surface of the mold = 37mm; height of the cylindrical cavity: 360mm). Experimental mold for making the tubular sample D shown above (figures 15 and 19). Figure 21 shows a diagram illustrating the geometric tolerance “t” of cylindricity and flatness for the inner surface of castings by drain casting (large scale view / macro scale).

[0367] 1: crystallographic interior surface

[0368] 2: smooth external surface in contact with the mold e: minimum wall thickness t: geometric tolerance of cylindricity / flatness obtained inside the molded part

[0369] Drained casting offers the great advantage of manufacturing parts with a very low minimum wall thickness e without internal molding elements. Indeed, in conventional foundry processes, the use of internal metal, sand or ceramic cores allows relatively low geometric tolerances t; but the surface tension of the cast alloy and its metallostatic pressure do not allow the production of very low thicknesses e with gravity casting.

[0370] For example, when producing rectangular section tubes by drain casting (illustration in figure 6 on the right), the solidification of the cast alloy is always faster in the corners than in the middle of the flat faces.

[0371] Experiments show that the orientation (vertical / horizontal / inclined) of the internal face of the part during the mold filling and emptying phases, as well as the mold assembly planes (thermal seals by micro-air blades), also play a role in the degradation of the geometric tolerance t of the internal surfaces. When molding by empty casting of a tubular, circular or rectangular part, the position with its vertical axis makes it possible to obtain the lowest geometric tolerance of concentricity and coaxiality or parallelism of the internal surface 1 with respect to the external surface 2, for a mold at a homogeneous initial temperature.

[0372] Figure 22 represents an observation image with an optical microscope at the heart of the wall of a part cast by pouring emptied with the eutectic alloy A1SH2 (A-S13 in AFNOR standard) in a metal mold.

[0373] 3: polyhedral primary crystals rich in silicon;

[0374] 4: primary dendritic crystal rich in aluminum (equiaxed crystals here); 5: eutectic mixture (acicular or lamellar crystals rich in silicon in white matrix rich in aluminum) formed at the eutectic temperature of 577°C (solidus of the A1SH2 alloy). These eutectic cells are predominant in this alloy.

[0375] Figure 23 shows optical microscope images of the smooth outer surface (indicated as "2" in the micrographs) of a part cast by gravity drain casting with the alloy A1SH2 (A-S13) in a metal mold (on the left, a gray cast iron mold with lamellar graphite at an initial temperature of 450°C was used, and on the right, an aluminum alloy AlSi7Mg mold at an initial temperature of 160°C was used). The phases present are finer in the right micrograph because the solidification rate is faster.

[0376] 5: eutectic mixture (acicular or lamellar crystals rich in silicon in a white matrix rich in aluminum) predominant in this alloy.

[0377] Figure 24 shows optical microscope observation images of the smooth outer surface (indicated as “2” in the micrograph) of a tubular heat exchanger (samples shown in Figures 1 and 5a, outer diameter = 22mm) produced by gravity drain casting with A1SH2 alloy (AS 13, casting temperature = 744°C) in a steel mold (initial temperature of 195°C, graphite-based coating applied to the impression).

[0378] 4: Primary dendritic crystals rich in aluminum oriented (columnar crystals) from the smooth outer surface due here to the strong temperature gradient in the cast alloy in contact with the mold. The gray background between these dendritic crystals corresponds to the predominant eutectic mixture in this type of alloy.

[0379] Figure 25 shows optical microscope observation images of the crystallographic inner surface (indicated as “1” in the micrograph) of a hollow parallelepiped part (external dimensions = 135x60x35 mm 3 ) cast by gravity-drained casting in a cast iron mold (shell made of gray cast iron with lamellar graphite at an initial temperature of 450°C and coated with a thermally conductive coating, based on colloidal graphite, approximately 0.2 mm thick) with A1SÜ2 (AS 13) alloy. Sample indicated A in figures 15, 16 and 17.

[0380] 4: Primary dendritic crystals rich in aluminum in relief of the interior surface following the emptying of the unsolidified alloy / metal. These crystals participate in the topography of the resulting interior crystallographic surface.

[0381] 5: Eutectic cells predominant in this type of alloy. Figure 26 shows optical microscope observation images of the crystallographic interior surfaces (indicated as “1” in both micrographs) of hollow parts cast by gravity drain casting with A1SH2 (A-S13) alloy.

[0382] Micrograph on the left: casting in a thermal insulating mineral fiber mold (at an initial temperature of 40°C, without coating). Sample indicated B in figures 15 and 16.

[0383] Micrograph on the right: use of a cast iron mold (grey cast iron with lamellar graphite) at an initial temperature of 450°C and coated with a thermally conductive coating based on colloidal graphite (deposit thickness of approximately 0.2 mm). Sample indicated A in figures 15, 16 and 17.

[0384] 3: silicon-rich polyhedral primary crystals participating in the topography of the interior surface.

[0385] 4: Primary dendritic crystals rich in aluminum in relief of the interior surface following the emptying of the unsolidified alloy / metal. These crystals also participate in the topography of the resulting interior crystallographic surface.

[0386] 5: eutectic cells predominant in this type of alloy (acicular or lamellar crystals rich in silicon in a white matrix rich in aluminum) formed at the eutectic temperature of 577°C (solidus temperature of the alloy).

[0387] 6: locally hollow shape of the interior surface. If this very local geometry has undercuts, its profile will then be difficult to capture with the Keyence digital microscope used in figures 12, 14 and 15.

[0388] Figure 27 shows a Keyence digital microscope analysis image of the crystallographic inner surface topography of a semi-spherical luminaire (diameter 52 cm) cast by gravity drain casting with A1SÜ2 alloy (AS 13, casting temperature = 700°C) in a metal mold (AlSi7Mg alloy shell coated with graphite-based conductive coating, initial mold temperature = 160°C). The sample marked "C" in Figure 1 also corresponds to the crystallographic inner surface of this same casting.

[0389] Digital acquisition of the surface:

[0390] Digitized area = 22.6455 x 17.7492 mm 2

[0391] Difference in altitude between lowest point and highest point = 1.233 mm

[0392] Figure 28 shows Keyence digital microscope analysis images of the crystallographic inner surface topography of a semi-spherical luminaire (diameter 52 cm) cast by gravity drain casting with A1SÜ2 alloy (AS 13, casting temperature = 700°C) in a metal mold (AlSi7Mg alloy shell coated with graphite-based conductive coating, initial mold temperature = 160°C). The sample marked "C" in Figure 15 also corresponds to the crystallographic inner surface of this same casting.

[0393] Analysis of the scanned surface:

[0394] A: Top view of the scanned surface (22.6455 x 17.7492 mm 2 )

[0395] B: image of the overall surface specifying the 2D profiling line Cl of the sample

[0396] Cl: curve obtained from local roughness (surface condition), which allows us to observe: 0.4mm <Rt<0,5mm sur la longueur du profil Cl de 17,74mm.

[0397] Figure 29 shows Keyence digital microscope analysis images of the crystallographic inner surface topography of a semi-spherical luminaire (diameter 52 cm) cast by gravity drain casting with A1SÜ2 alloy (AS 13, casting temperature = 700°C) in a metal mold (AlSi7Mg alloy shell coated with graphite-based conductive coating, initial mold temperature = 160°C). The sample marked "C" in Figure 15 also corresponds to the crystallographic inner surface of this same casting.

[0398] Detailed analysis (high magnification) of the scanned surface:

[0399] Local surface analyzed = 1 x 0.8 mm 2

[0400] Difference in altitude between lowest point and highest point = 0.222 mm

[0401] Zoom 3: highlighting two polyhedral primary crystals rich in silicon and a dendritic primary crystal nose rich in aluminum.

[0402] Zoom 5: highlighting the majority eutectic cells in the A1SH2 (A-S13) alloy.

[0403] Indication 6: presence of a locally undercut shape that is difficult to scan with a microscope.

[0404] Figure 30 shows an optical microscope observation image of the crystallographic inner surface of a cylindrical part (diameter = 205mm, height = 180mm) molded by gravity drain casting with A1SH2 (A-S13) alloy in a thermal insulating mineral fiber mold (initial mold temperature = 40°C, no potting). The sample indicated "B" in figures 15 and 16 also corresponds to the crystallographic inner surface of this same molded part.

[0405] Highlighting of hollow shape presenting local undercuts, indicated “6” on the micrograph, difficult to capture by the Keyence digital microscope.

[0406] 1: indication of the crystallographic inner surface of the casting. 3: silicon-rich polyhedral primary crystal

[0407] 4: Aluminum-rich dendritic primary crystal arm

[0408] 5: majority eutectic cells in the A1SH2 (A-S13) alloy

[0409] Figure 31 shows an analysis image with a Keyence digital microscope of the topography of the crystallographic interior surface of a parallelepiped part (135x60x35mm 3) cast by gravity drain casting with A1SÜ2 alloy (AS 13, casting temperature between 650 and 720 °C) in a cast iron mold (shell in gray cast iron with lamellar graphite, 10 to 20 mm thick, at an initial temperature of 450 °C, and coated with a conductive coating based on colloidal graphite with a thickness of approximately 0.2 mm). The sample indicated "A" in figures 15 and 16 also corresponds to the crystallographic interior surface of this same casting.

[0410] Digital acquisition of the surface:

[0411] Digitized area = 22.6486 x 9.0376 mm 2

[0412] Difference in altitude between lowest point and highest point = 2.4463 mm

[0413] Figure 32 shows Keyence digital microscope analysis images of the crystallographic inner surface topography of a parallelepiped part (135x60x35mm 3) cast by gravity drain casting with A1SÜ2 alloy (AS 13, casting temperature between 650 and 720 °C) in a cast iron mold (shell in gray cast iron with lamellar graphite, 10 to 20 mm thick, at an initial temperature of 450 °C, and coated with a conductive coating based on colloidal graphite with a thickness of approximately 0.2 mm). The sample indicated "A" in figures 15 and 16 also corresponds to the crystallographic interior surface of this same casting.

[0414] Analysis of the scanned surface:

[0415] A: Top view of the scanned surface (22.6486 x 9.0376 mm 2 )

[0416] B: image of the overall surface specifying the 2D profiling line Cl of the sample

[0417] Cl: curve obtained from local roughness (surface condition), which allows us to observe: l.3mm <Rt< 1,4mm sur la longueur du profil Cl d’environ 22mm.

[0418] Figure 33 shows Keyence digital microscope analysis images of the crystallographic inner surface topography of a cylindrical part (outer diameter = 205mm, height = 180mm) cast by gravity drain casting with A1SH2 alloy (A-S13, casting temperature of approximately 700°C) in a thermal insulating mineral fiber mold (mold at initial temperature of 40°C, without potting deposit). The flat sample marked "B" in Figures 15 and 16 also corresponds to the crystallographic inner surface of this same casting.

[0419] Digital acquisition of the surface:

[0420] Digitized area = 22.6432 x 17.7430 mm 2

[0421] Difference in altitude between lowest point and highest point = 1.5616 mm

[0422] Figure 34 shows Keyence digital microscope analysis images of the crystallographic inner surface topography of a cylindrical part (outer diameter = 205mm, height = 180mm) cast by gravity drain casting with A1SH2 alloy (A-S13, casting temperature of approximately 700°C) in a thermal insulating mineral fiber mold (mold at initial temperature of 40°C, without potting deposit). The flat sample marked "B" in Figures 15 and 16 also corresponds to the crystallographic inner surface of this same casting.

[0423] Analysis of the scanned surface:

[0424] A: Top view of the scanned surface (22.6432 x 17.7430 mm 2 )

[0425] B: image of the overall surface specifying the 2D profiling line Cl of the sample

[0426] Cl: curve obtained from local roughness (surface condition), which allows us to observe: l.20mm <Rt< 1,25mm sur la longueur du profil Cl de 21,9mm.

[0427] Figure 35 shows an exploded view of an electric bicycle frame that can be made by drain casting.

[0428] Construction of the bicycle frame with cast aluminum alloy drained into a metal mold.

[0429] Use of the drained casting process in low pressure casting to make the frame in order to limit the inclusion of oxide skins in the part which would then lower the mechanical performance.

[0430] Steel revolution insert for the front fork axle, placed in the mold when it is closed and then embedded in the alloy.

[0431] Figures 36 and 37 show perspective views of the aluminum alloy electric bicycle frame produced by drain casting in a metal mold using a low-pressure process.

[0432] Lower attachment for fixing the electric motor and battery added later, after finishing and machining the frame.

[0433] Figure 38 shows a schematic diagram of the low-pressure mold for empty casting of the bicycle frame (sectional view). The metal mold (steel / cast iron) is composed of three main parts, as well as a sliding core for the rear fork (slide for demolding the undercut shape) and a pin for holding the steel front fork insert. The cut wall of the hollow molded part is shown in gray color in the diagram.

[0434] The injection nozzle is located in the lower part of the mold (lower main part of the mold). On the resulting casting, the discharge hole for the unsolidified alloy (drain hole) is plugged after machining operations.

[0435] The air in the impression is washed during injection using air drafts (0.2 mm deep grooves made on the assembly planes of the different parts of the mold), or even metal air filters embedded in the mold (air draft pins, etc.).

[0436] The low pressure process allows the filling and emptying of the part cavity with controlled speeds, as well as the use of a non-oxidizing atmosphere for the aluminum alloy (nitrogen gas for example, avoiding the inclusion of oxide skins).

[0437] Figure 39 shows an exterior view and different sections of the low-pressure mold for the empty casting of the bicycle frame.

[0438] Figure 40 shows an exploded perspective view of the low pressure mold and the drain casting bicycle frame.

[0439] 4001: steel insert for front fork bearing (axle inserted during casting)

[0440] 4002: positioning pin between main parts of the mold

[0441] 4003: drawer, metal core molding the middle of the rear fork (undercut shape)

[0442] 4004: upper right mold yoke

[0443] 4005: raw bicycle frame obtained by drained casting

[0444] 4006: Positioning and holding pin for the steel insert for the front fork bearing

[0445] 4007: injection nozzle, connected to the upper end of the dip tube in the crucible of the low pressure furnace

[0446] 4008: drawer extraction plate

[0447] 4009: travel stop for drawer guide

[0448] 4010: upper left mold yoke

[0449] 4011: screw for fixing the travel stop in the drawer guide

[0450] 4012: sole, lower part of the mold mounted above or on the side of the low pressure furnace EXAMPLES

[0451] Example 1. General procedure for melting metallic matter

[0452] 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 heated and then maintained at a temperature above the liquidus of the alloy by a so-called superheat value plus an estimated value of temperature loss due to transfer into the ladle / pouring ladle. The superheat above the liquidus retained was between 0 and 200°C.

[0453] 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 in the furnace too much when transferring the mold drains.

[0454] Example 2. Mold preparation

[0455] In parallel with the melting of the alloy according to example 1, the mold was prepared.

[0456] The metal mold was preheated before the first casting, to a temperature of approximately 350°C for casting aluminum alloys. To bring the mold up to temperature, gas burners or electric heating devices were used.

[0457] The impressions of the metal molds were coated with a thin layer of potting compound, 0.2 to 0.5 mm thick.

[0458] In the case of a sand mold, no preheating was implemented.

[0459] Example 3. Filling the mold

[0460] 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).

[0461] Example 4. Emptying the mold

[0462] 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 desired shell thickness.

[0463] Example 5. Manufacturing of a hollow part by a sand casting process

[0464] A wooden model was made to create a sand mold (Figure 5A). After the sand mold was made, the aluminum alloy AlSil2 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 ladle using a large ladle, so that the metal could be brought to the mold using a stretcher. The aluminum temperature 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.

[0465] 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 (e.g. with a metal point) to pierce this skin. After an emptying 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 impression (Figure 6B) and a crystallographic internal surface, resulting from the natural mode of solidification of the metal / alloy used (Figure 6C).

[0466] Example 6. Mass production of multiple parts

[0467] A series production of several parts was carried out as shown in Figure 6.

[0468] A metal mold made of AlSi7Mg aluminum alloy was produced by sand casting and machining. This shell was installed on a test bench, a partially articulated mechanically welded frame to allow rotation of the mold in order to demold the produced part. This bench has burners, located under the mold, to heat (or even maintain) the impression at the desired temperature before pouring 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.

[0469] Before the first casting, the aluminum alloy (AISi 12) 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 mold was heated to a temperature of 164°C to 243°C. Similarly, 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 was reached in the furnace, the casting ladle was filled and then brought close to the mold using a stretcher. The temperature of the molten metal in the ladle was then around 720°C just before pouring.This ladle was quickly poured into the mold, for 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 obstructed the mold orifice was removed, allowing the still molten metal 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 into the furnace was between 577°C and 588°C. Finally, to demold 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 placed on the grid was moved elsewhere in the workshop for cooling. The solidified metal shell thus produced has an outer surface complementary to the mold impression (Figure 6B) and a crystallographic inner surface, resulting from the natural solidification mode of the metal / alloy used (Figure 6C).

[0470] The process can be repeated to produce successive pieces. Successive castings thus help maintain the mold temperature.

[0471] Example 7. Production of a parallelepiped part by a gravity-drained casting process in a cast iron mold

[0472] A cast iron mold was made from gray cast iron with lamellar graphite to achieve a mold thickness of 10 to 20 mm and allow the manufacture of a parallelepiped part with dimensions of 135x60x35mm 3The cast iron mold was heated to 450°C and coated with a conductive coating based on colloidal graphite to a thickness of approximately 0.2 mm. The aluminum alloy A1SU2 was melted and heated to a temperature between 650°C and 720°C. The molten aluminum alloy (between 650 and 720°C) was poured by gravity into the cast iron mold (mold at 450°C). The mold filling time was approximately 1 to 3 seconds, followed by a holding time of the liquid alloy in the cavity between 5 and 60 seconds. The excess liquid alloy was drained in 1 to 2 seconds to obtain a minimum thickness e of approximately 1.5 mm. After solidification, the parallelepiped part is demolded.This comprises an external surface complementary to the mold imprint (figure 17 part A surface A2) and a crystallographic internal surface (figure 15 part A, figure 16 part A, figure 17 part A surface Al) resulting from the natural mode of solidification of the alloy used comprising reliefs corresponding to the metallurgical crystals (figure 17 part A surface Al, figure 25, figure 31, figure 32).

[0473] Example 8. Manufacture of a cylindrical part by a gravity-drained casting process in a thermal insulating mineral fiber mold A thermal insulating mineral fiber mold was made to allow the manufacture of a cylindrical part with a diameter of 205 mm and a height of 180 mm. The aluminum alloy A1SU2 was melted and heated to a temperature above 700°C. The molten aluminum alloy (at approximately 700°C) was poured by gravity into the thermal insulating mineral fiber mold (mold at 40°C) without potting. After a time of a few seconds to a few minutes in the mold, the unsolidified alloy, still liquid, was drained. After complete solidification, the cylindrical part was removed from the mold.This comprises an external surface complementary to the mold imprint and a crystallographic internal surface (figure 15 part B, figure 16 part B) resulting from the natural mode of solidification of the alloy used including reliefs corresponding to the metallurgical crystals, (figure 30, figure 33, figure 34).

[0474] Example 9. Manufacture of a semi-spherical luminaire by a gravity-fed casting process in an AlSi7Mg aluminum alloy mold

[0475] A mold was made of 35 mm thick AlSi7Mg aluminum alloy to allow the manufacture of a 52 cm diameter semi-spherical luminaire. The aluminum mold was heated to a temperature above 160°C and coated with a graphite-based conductive coating to a thickness of approximately 0.2 mm. The aluminum alloy A1SU2 was melted and heated to a temperature above 700°C. The molten aluminum alloy (approximately 700°C) was poured by gravity into the aluminum mold (mold at 160°C). The mold filling time was 10 seconds, followed by a holding time of 19 seconds for the liquid alloy in the mold. The excess unsolidified liquid alloy was drained in 11 seconds. After complete solidification, the semi-spherical part was demolded. This has an external surface complementary to the mold impression and a crystallographic internal surface resulting from the natural solidification mode of the alloy used.A sample of the semi-spherical luminaire was cut to visualize the outer surface complementary to the mold impression (figure 16 part C, figure 17 part C surface C2) and the crystallographic inner surface (figure 15 part C, figure 17 part C surface Cl) including reliefs corresponding to the metallurgical crystals (figure 27, figure 28, figure 29).

[0476] Example 10. Manufacture of a tubular heat exchanger obtained by a gravity-fed casting process with a steel mold

[0477] A steel mold was made to allow the manufacture of a tubular heat exchanger whose tube has an external diameter of 22 mm, a length of 360 mm and a minimum thickness e of 1.6 mm. This mold was installed on a drained casting test bench for exchanger tubes (figure 20). This bench has a receiving ladle placed under the mold, in order to recover the cast alloy still liquid after draining which will be transferred back into the melting-holding furnace. Before casting, the steel mold was preheated to more than 195 ° C. The aluminum alloy A1SH2 was melted to reach a temperature of 744 ° C and was poured through the funnel into the steel mold (mold at 195 ° C). Then the drain hatch was opened to drain by gravity the unsolidified aluminum alloy and therefore still liquid in the mold. After solidification, the tubular heat exchanger is demolded.This has a relatively smooth outer surface complementary to the mold cavity and a crystallographic inner surface with low roughness due to the strong temperature gradient during casting. A sample of the tubular heat exchanger was cut to visualize the outer surface complementary to the mold cavity (figure 15 part D surface D2, figure 19 surface D2, figure 24) and the crystallographic inner surface (figure 15 part D surface D1, figure 19 part D surface D1).

Claims

CLAIMS 1. Hollow monocoque cast metal part comprising: - an outer surface comprising metallurgical grains constrained by the surface of the mold in which the part was molded, - a crystallographic inner surface, said metal part being made of a metal or an alloy having a melting point above 180°C, in particular above 320°C, in which the topography of said crystallographic inner surface comprises reliefs corresponding to the metallurgical crystals, in particular reliefs corresponding to the dendritic crystals, in particular primary crystals, and / or to the polyhedral crystals, in particular primary crystals, and / or to the eutectic cells, in which said part comprises - a thickness e, defined by the minimum distance between said outer surface and said inner surface, with an average value ranging from 0.2 mm to 10.0 mm, in particular from 0.5 to 5.0 mm - a dimension Rt, defined by the difference between the value of the thickness EM and that of the thickness e, the thickness EM being defined as the distance between the point of the interior surface furthest from the exterior surface and its orthogonal projection on the exterior surface.

2. Hollow single-shell metal part molded in the absence of a core and comprising: - an outer surface comprising metallurgical grains constrained by the surface of the mold in which the part was molded, - a crystallographic inner surface, said metal part being made of a metal or an alloy having a melting point above 180°C, in particular above 320°C, in which the topography of said crystallographic inner surface comprises reliefs corresponding to the metallurgical crystals, in particular reliefs corresponding to the dendritic crystals, in particular primary crystals, and / or to the polyhedral crystals, in particular primary crystals, and / or to the eutectic cells, in which said part comprises - a thickness e, defined by the minimum distance between said outer surface and said inner surface, with an average value ranging from 0.2 mm to 10.0 mm, in particular from 0.5 to 5.0 mm - a dimension Rt, defined by the difference between the value of the thickness EM and that of the thickness e, the thickness EM being defined as the distance between the point of the interior surface furthest from the exterior surface and its orthogonal projection on the exterior surface.

3. Metal part according to one of claims 1 or 2, said part being made up of distinct domains of different geometric shapes or relating to a different functionality of the part, each domain of the part having a thickness e in said domain, said average thicknesses e of said domains being identical or different from each other and each having a value in the range from 0.2 mm to 10.0 mm, in particular from 0.5 to 5.0 mm.

4. Metal part according to claim 3, in which all the areas have the same average thickness value e.

5. Metal part according to claim 3, in which at least two areas have different average thickness values ​​e.

6. Metal part according to one of claims 1 to 5, in which said part is a mechanical or fluidic functional part, the average value of the thickness e ranging from 0.5 to 10.0 mm.

7. Hollow metal part according to one of claims 1 to 6, in which said hollow metal part comprises in relief on its crystallographic interior surface structures chosen from dendritic, columnar and / or equiaxed structures and eutectic facet structures or a mixture or association of these structures.

8. A hollow metal part according to any one of claims 1 to 7, wherein the size of the metallurgical grains of the outer surface is smaller than that of the metallurgical crystals of the crystallographic inner surface.

9. Hollow metal part according to any one of claims 1 to 8, said metal or alloy being chosen from: aluminum (Al), lead (Pb), tin (Sn), copper (Cu), zinc (Zn), iron (Fe), nickel (Ni) and magnesium (Mg), A1SH2, ZnA15, AlCu33, AlMg32, MgZn37, CuMn37, CuSilô, SnPb38, eutectic cast iron, especially aluminum and aluminum-silicon alloys.

10. Assembly comprising one, two or more hollow metal parts according to any one of claims 1 to 9. Method for manufacturing a hollow metal part according to any one of claims 1 to 9, 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 recovering the hollow metal part in the form of a solidified metal shell, in which the metal has a melting point greater than 180°C, in particular greater than 320°C, and in which the hollow metal part is formed in the absence of a core. Manufacturing method according to claim 11, in which in the injection step 1: the temperature of the surface of the impression of said mold of said part is controlled and / or the temperature in the thickness of the mold in the vicinity of the impression is controlled and / or the initial temperature of the cast metal is controlled and / or the time and speed of filling of the mold are controlled and / or the heat exchanges between the above-mentioned molten metal and the surface of the impression of said mold are controlled and / or the metallostatic pressure of the above-mentioned molten metal and on the surface of the impression of said mold is controlled in order to control the thickness e of the part.Manufacturing method according to one of claims 11 or 12, said method having a milling ratio of 1:1 to 1.2:1, preferably about 1:1, in particular 1:

1. Manufacturing method according to claim 11 to 13, 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. Manufacturing method according to any one of claims 11 to 14, wherein injection step 1 is carried out by injection with a low pressure method, said injection step 1 being carried out by applying 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 11 to 15, wherein injection step 1 is carried out by injection under pressure, said injection step 1 being carried out by injecting the liquid metal using a piston or a gas.Manufacturing method according to any one of claims 11 to 16, wherein step 4 of demolding is carried out by turning the mold over. Manufacturing method according to any one of claims 11 to 17, wherein the mold has an opening in the bottom of the mold, which opening is obstructed, during step 1 of injection and during step 2 of solidification, by a closing device, in particular a plug, a stopper or a hatch, step 3 of subtraction being initiated by a release of said opening, by removal of said closing device.Manufacturing method according to any one of claims 11 to 18, wherein the mold has air or gas intake means in the top of the mold, said air or gas intake means being closed during injection step 1 and during solidification step 2, wherein subtraction step 3 is favored 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 manufacturing at least two metal parts according to any one of claims 1 to 9, said method comprising at least:. • the manufacture of a first metal part according to the manufacturing method according to any one of claims 11 to 19, and • the manufacture of a second metal part, according to the manufacturing method according to any one of claims 11 to 19, in which the metal used poured in the pouring step 1 is the metal subtracted during the 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 11 to 19. Device comprising in association the hollow metal part according to one of claims 1 to 9 and 21 and the mold used for molding said hollow metal part.

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