Method for manufacturing large seamless domes and corresponding domes

Abstract

The method includes the steps of providing a semi-finished product (11), hot forging the semi-finished product (11) by upsetting to form a blank (13) with a developed surface that is larger than the developed surface of the semi-finished product (11) and smaller than the developed surface of the wall (3) of the dome, hot forming the blank (13) to create a preform (15) with a developed surface that is equal to or smaller than the developed surface of the wall (3), the preform (15) including at least two successive portions (19, 21) extending radially next to each other away from a central axis (AA), the average thickness and / or convexity of the two successive portions (19, 21) being different for all portions (19, 21), and hot deforming the preform (15) under pressure between a die and a punch to form the wall (3).

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing large hollow parts in the shape of a dome. [Background technology]

[0002] Some large pressure tanks consist of two domes assembled by welding or with a cylindrical ring between them. Each end has a dome-shaped bottom or lid secured to the cylindrical body by bolting or welding.

[0003] These pressure tanks are for example high-pressure cryogenic tanks for liquefied gases such as liquid hydrogen, liquid oxygen or liquid nitrogen for applications in the field of space launch vehicles, terrestrial or mobile stores or in the domain of aviation.

[0004] To manufacture such parts, it is known to form machined sheets by stamping to form petals, which are then assembled to form a corolla, and then welded together to form the part.

[0005] This technique has the disadvantage of requiring a series of costly operations, particularly welding of the assembly, which requires specialized, large-scale equipment, and rigorous ultrasonic testing of the weld to ensure that the weld zone is sound and defect-free.

[0006] Single parts in the shape of a dome can also be produced by closed die forging. This technique has the advantage of requiring only a single forming operation, but the disadvantage that it is limited to small parts due to the limited dimensions of existing forging presses and the very large forces required to deform the material and fill the final part. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Yang Shen, "Compportement et endommagement des alliages d'aluminium 6061-T6: Approche micromecanique", 2012 Summary of the Invention [Problem to be solved by the invention]

[0008] The object of the present invention is to remedy these drawbacks by proposing a method for manufacturing parts in the shape of a dome, such as a cryogenic tank dome, that does not require welding and can be realized on available forging presses whose dimensions and / or capacities are limited in terms of force. [Means for solving the problem]

[0009] To this end, the invention has as its object a method for manufacturing a hollow part comprising a seamless, single (integral) wall in the shape of a dome extending around a central axis, this wall being realized in a material consisting of a metal alloy, this wall having an average thickness of less than 50 mm and a major dimension perpendicular to the central axis of between 1500 mm and 3700 mm, the method comprising the following successive steps: providing a semi-finished product of said material; hot forging the blank by upsetting to form a blank with a developed surface that is larger than the developed surface of the blank and smaller than the developed surface of the wall; hot forming the blank to produce a preform having a developed surface below the developed surface of the wall, the preform including at least two successive portions extending radially next to each other away from a central axis, the average thickness and / or convexity of the two successive portions being different for all portions; hot deforming the preform under pressure between a die and a punch to form a wall; Includes:

[0010] Preferably, the method according to the invention may comprise one or more of the following features, taken alone or in any technically possible combination: - the portions include a central portion and at least one intermediate annular portion, the central portion and the intermediate annular portion being of different convex shapes; the portions additionally include a peripheral annular portion, the peripheral annular portion having a convexity different from the convexity of the adjacent intermediate annular portion; The developed surface of the preform is substantially equal to the developed surface of the wall. - the ratio between the projected surface of the preform on the transverse plane and the developed surface of the preform is less than 90%, and the maximum dimension of the projected surface of the preform on the transverse plane is not more than 150% of the maximum dimension of the punch perpendicular to the central axis. The step of deformation of the preform under pressure involves spreading the preform between a die and a punch so that after spreading, the surface of the part facing the punch is concave. The surface of the central part facing the punch has a concave shape. - hot forming the blank, a first stage of forming by hot die forging the blank to produce a first concave blank; a second stage of shaping by hot die forging the first concave blank to produce a preform. The second stage of shaping includes a first intermediate stage of shaping by hot die forging the first concave blank to produce a second blank including a concave center and a convex periphery extending radially from the center, and a second intermediate stage of shaping by hot die forging the second blank to produce a preform. - said part comprises a central part and at least one intermediate annular part, the central part and the intermediate annular part having different average thicknesses, and the developed surface of the preform is less than the developed surface of the wall; - the portion additionally comprises a peripheral annular portion, the intermediate annular portion being a thickened portion, the average thickness of the intermediate annular portion being greater than the average thickness of the central portion and the average thickness of the peripheral annular portion; The preform deformation step includes a forming stage in which at least a portion of the intermediate annular portion is brought into contact with a die by means of a punch, and a die forging stage corresponding to expansion in which at least a portion of the preform is not in contact with the punch. During the expansion stage, the thick-walled intermediate annular portion of the preform is compressed between the die and the punch, and at least a portion of the central portion and / or peripheral annular portion is out of contact with the punch, so that material plastically flows from the intermediate annular portion towards the central portion and the peripheral annular portion and then over the peripheral annular portion to increase the expanded surface of the preform and form the wall. - The material is an aluminum alloy, in particular a 2XXX or 7XXX alloy.

[0011] The invention also has as its object a hollow part comprising a single, seamless wall in the shape of a dome, the wall extending around a central axis, the wall being realized in a material consisting of a metal alloy, the wall having an average thickness of less than 50 mm and a major dimension perpendicular to the central axis comprised between 1500 mm and 3700 mm.

[0012] Preferably, the wall exhibits a homogeneous fiber ring about a central axis, and the orientation of the grains (also called fibers) of said metal alloy is such that, in any transverse plane, the angle formed between the direction of elongation of the grain as seen in a cross section of this transverse plane and the tangent to the wall of this grain is substantially constant.

[0013] The invention also has as its object a cryogenic tank comprising a part as defined above or manufactured by a method as defined above. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a schematic perspective view of a hollow part in the shape of a dome according to one embodiment; [Figure 2] FIG. 2 illustrates a schematic diagram of a method according to an embodiment. [Figure 3] 1 is a schematic diagram of a cross section in an axial plane of a preform according to a first embodiment; [Figure 4]4A-4C show schematic diagrams of steps for shaping a blank to form the preform of FIG. 3. [Figure 5] 1 is a schematic perspective view of a preform according to a second embodiment before its hot deformation under a press; FIG. [Figure 6] 4 is a schematic view of a cross section through an axial plane of the preform of FIG. 3 at the beginning of a step of hot deformation. [Figure 7] FIG. 2 shows the orientation of particles in the hollow part of FIG. 1; DETAILED DESCRIPTION OF THE INVENTION

[0015] FIG. 1 represents a hollow part 1 in the shape of a dome according to one embodiment in an axial cross section.

[0016] The hollow part 1 comprises a single, seamless wall 3 in the shape of a dome. "Wall" refers to a part throughout its thickness, as opposed to the terms "surface" or "face".

[0017] The wall 3 includes a convex outer surface oriented towards the outside of the dome and a concave inner surface.

[0018] The wall 3 is seamless and weld-free and is therefore realized in one piece and consists of a single piece of material.

[0019] The hollow part 1 is intended to form, for example, an end dome of a substantially cylindrical pressure vessel.

[0020] The wall 3 extends around the central axis AA between two planes perpendicular to the central axis AA, which planes delimit the wall 3 in the axial direction.

[0021] In the following, we consider an axial direction oriented so that the wall is concave when viewed from above, as in the figure. Furthermore, a plane perpendicular to the central axis AA is called the "lateral plane," and a plane containing this central axis AA is called the "axial plane."

[0022] Thus, with reference to FIG. 1, the wall 3 extends between a lower transverse plane 5 and an upper transverse plane 7 .

[0023] The wall 3 has, for example, a shape of revolution, in other words such that a cross section of the wall 3 passing through any axial plane A has a constant shape.

[0024] The wall 3 is, for example, substantially hemispherical or in the form of a spherical cap.

[0025] Alternatively, the wall 3 is in the form of an elliptical cap, or in the form of a Cassini dome, Cassini cap, or more generally in the form of an oval cap.

[0026] The wall 3 presents a curved shape, for example a circular, oval, in particular a Cassini oval, or an elliptical transverse plane (in other words a plane perpendicular to the central axis AA), for example.

[0027] According to one embodiment, the wall 3 comprises a curved portion such as an elliptical cap, a Cassini dome, a Cassini cap, or an oval cap, and a cylindrical or frustoconical portion following the curved portion.

[0028] The wall 3 is realized in a material consisting of a metal alloy.

[0029] The metal alloy is, for example, an aluminum alloy, in particular a 2XXX alloy such as alloy 2050 or alloy 2219, or a 7XXX alloy such as alloy 7020.

[0030] Alternatively, the metal alloy is a titanium alloy or steel.

[0031] The wall 3 has an average thickness of less than 50 mm, usually greater than 25 mm, in particular greater than 30 mm.

[0032] The wall 3 has a major dimension perpendicular to the central axis AA of between 1500 mm and 3700 mm, by which we mean the largest dimension in any transverse plane, in other words the major dimension in the upper transverse plane 7 in the example represented in Figure 1.

[0033] For example, if wall 3 presents a circular transverse plane, the maximum dimension of wall 3 is the diameter of the outer circle in upper transverse plane 7. If wall 3 has an elliptically shaped transverse plane, the maximum dimension of wall 3 is the major diameter of the outer ellipse in upper transverse plane 7.

[0034] Wall 3 optionally includes features arranged on wall 3. These features are intended for connecting equipment such as pipes, for example. These features include, for example, openings, reliefs on the outer surface of wall 3, appendages, protrusions, bosses, spigots and / or ribs. These features are preferably integral to wall 3, of the same material as the wall, and thus realized during the manufacturing of wall 3.

[0035] In particular, the wall 3 preferably includes a feature in its lower portion, such as a tubular opening 9 centered on a central axis AA, which opening 9 may be, for example, circular, elliptical or oval in cross section.

[0036] For example, the opening 9 is bounded by a border whose thickness is greater than the average thickness of the wall 3 .

[0037] With reference to Figures 2 to 6, a method for manufacturing such a hollow part 1 according to one embodiment of the present invention will now be described.

[0038] The method first comprises the step of providing a semi-finished product 11 of the material from which the hollow part 1 is realized.

[0039] The semi-finished product 11 is for example a billet or a slab of said material (as seen from above in Figure 2) The semi-finished product 11 is for example obtained by casting said material.

[0040] The method then includes hot forging the preform 11 by upsetting it to form a blank 13. For example, in the example of Figure 2, a substantially circular blank 13 is formed from the preform 11 by applying pressure between the bottom and top surfaces of the preform 11.

[0041] The blank 13 presents a developed surface that is larger than the semi-finished product 11 and smaller than the developed surface of the wall 3 to be produced.

[0042] The hot forging step is performed at a temperature that depends on the material used. For example, if the material is an aluminum alloy, the hot forging step is usually performed at a temperature between 300°C and 500°C. If the material is a titanium alloy, the hot forging step is usually performed at a temperature between 700°C and 1300°C.

[0043] If the hollow part 1 to be manufactured contains an opening 9 as described above, a circular opening 14 is realized in the blank 13 during this step.

[0044] The blank 13 is then hot formed to create a preform 15 .

[0045] The hot forming step is performed at a temperature that depends on the material used. For example, if the material is an aluminum alloy, the hot forming step is usually performed at a temperature between 300°C and 500°C. If the material is a titanium alloy, the hot forming step is usually performed at a temperature between 700°C and 1300°C.

[0046] The preform 15 has a developed surface that is equal to or smaller than the developed surface of the wall 3 .

[0047] The preform 15 includes at least two successive portions extending radially one after the other away from the central axis AA, and for all portions, the average thickness of the first and second successive portions is different, and / or the first portion is convex, concave or flat while the second portion is concave or flat, convex or flat, or convex or concave, respectively (in other words, if the first portion is convex, the second portion is concave or flat; if the first portion is concave, the second portion is convex or flat; if the first portion is flat, the second portion is convex or concave).

[0048] The preform 15 is then hot deformed under pressure between a die and a punch to form the wall 3 of the hollow part 1, as explained below.

[0049] By convex or concave is meant a part in which the surface of the part intended to face the punch during hot deformation is convex and concave, respectively, and the opposite surface is concave and convex, respectively.

[0050] Furthermore, hereinafter, two parts will be considered to be differently convex if and only if one of the parts is concave and the other is convex, or one of the parts is flat and the other is convex, or one of the parts is concave and the other is flat.

[0051] The preform 15 therefore comprises at least two successive portions extending radially one after the other away from the central axis AA, and for all these portions the average thickness and / or convexity of the two successive portions differ.

[0052] By different average thicknesses is meant that the average thickness of the first portion through at least one axial cross-section and the average thickness of the second portion through this axial cross-section are such that the ratio between the maximum and minimum average thickness is 1.2 or more, preferably 1.3 or more, better still 1.5 or more, or even 2 or more. Generally, this ratio is 5 or less. In other words, the maximum average thickness is 120%, preferably 130%, better still 150% or even 200% or more of the minimum thickness, but remains 500% or less of the minimum thickness.

[0053] Thus, the preform 15 comprises a central portion 19 and at least one annular portion 21 extending radially adjacent to each other away from the central axis AA, the central portion 19 and the annular portion 21 having different convex shapes and / or different average thicknesses.

[0054] If the central portion 19 and annular portion 21 are of different convexities, the central portion 19 is normally concave and the adjacent annular portion 21 is normally convex.

[0055] If the central portion 19 and annular portion 21 have different average thicknesses, the central portion 19 will typically have a lower average thickness than the average thickness of the adjacent annular portion 21 .

[0056] If the hollow part 1 to be manufactured contains an opening 9, the central part 19 is an annular part. The central part 19 therefore contains a recess 22. This recess 22 is intended to form the opening 9 of the hollow part 1.

[0057] Preferably, the preform 15 comprises a plurality of successive portions 19, 21, 23, etc. extending radially one after the other away from the central axis AA, and for all portions the average thickness and / or convexity of two successive portions is different.

[0058] The central portion 19 typically has a developed surface area between 5% and 90% of the developed surface area of ​​the preform 15 .

[0059] If the preform comprises only two parts, the annular part 21 therefore has a developed surface that is between 10% and 95% of the developed surface of the preform 15 .

[0060] Additionally, where N is the number of sections that make up preform 15, and N≧3, each annular section has a developed surface that is between 10% / (N−1) and 100% / (N−1) of the developed surface of preform 15.

[0061] Each consideration portion differs from each adjacent portion in that the average thickness of the consideration portion differs from the average thickness of its adjacent portions and / or in that the convexity of the consideration portion differs from the convexity of its adjacent portions.

[0062] For example, these portions may have different successive convex shapes.

[0063] Preferably, the preform 15 then comprises a sequence of at least three alternating concave and convex portions 19, 21, 23, which form a wave-like pattern, with the central portion preferably having a developed surface area between 10% and 90% of the developed surface area of ​​the preform 15, and each annular portion preferably having a developed surface area between 10% / (N-1) and 50% / (N-1) of the developed surface area of ​​the preform 15.

[0064] According to another example, the portions exhibit different successive average thicknesses.

[0065] According to yet another example, at least one portion has a convex shape identical to that of a first adjacent portion but an average thickness different from that of the first adjacent portion, and a convex shape different from that of a second adjacent portion but an average thickness identical to that of the second adjacent portion.

[0066] In particular, the preform includes a central portion 19, an intermediate annular portion 21 extending radially following the central portion 19 away from the central axis AA, and a peripheral annular portion 23 extending radially following the intermediate annular portion 21 away from the central axis AA, the intermediate annular portion 21 having an average thickness different from the average thicknesses of the central portion 19 and the peripheral annular portion 23 and / or a convex shape different from the convex shapes of the central portion 19 and the peripheral annular portion 23.

[0067] In a first embodiment, an example of which is shown in FIG. 3, the preform 15 comprises a central portion 19 and at least one intermediate annular portion 21, the central portion 19 and the intermediate annular portion 21 having different convex shapes.

[0068] Preferably, as shown in Figure 3, these portions additionally include a peripheral annular portion 23 having a convex shape different from the convex shape of the adjacent intermediate annular portion 21. The preform 15 then includes a series of at least three alternating concave and convex portions, which form a wave-like pattern.

[0069] In the example shown in FIG. 3, the preform 15 includes a single intermediate annular portion 21 .

[0070] Thus, the central portion 19, the intermediate annular portion 21 and the peripheral annular portion 23 extend radially one after the other away from the central axis AA, with the central portion 19 adjacent to the intermediate annular portion 21 and the intermediate annular portion 21 adjacent to the central portion 19 and the peripheral annular portion 23.

[0071] The central portion 19 has, for example, a developed surface that is between 50% and 90% of the developed surface of the preform 15 .

[0072] The intermediate annular portion 21 has, for example, a developed surface that is between 5% and 25% of the developed surface of the preform 15 .

[0073] The peripheral annular portion 23 has, for example, a developed surface that is between 5% and 25% of the developed surface of the preform 15 .

[0074] In this example, the central portion 19 is an annular portion and includes a recess 22 .

[0075] In one alternative, the preform includes at least two intermediate annular portions. In this first embodiment, for all portions, the convexity of two consecutive portions is different. For example, if the preform includes a central portion, a first intermediate annular portion, a second intermediate annular portion, and a peripheral annular portion extending radially consecutively one after the other away from the central axis AA, the first intermediate annular portion has a convexity different from the convexity of the central portion and the second intermediate annular portion, and the peripheral annular portion has a convexity different from that of the second intermediate annular portion.

[0076] Preferably, in this first embodiment, as shown in FIG. 3, the surface of the central portion 19 facing the punch (in other words, when viewed from above downwards) has a concave shape.

[0077] In the example shown in Figure 3, the intermediate annular portion 21 is convex, while the central portion 19 and peripheral annular portion 23 are concave.

[0078] In this example, the average thicknesses of the central portion 19, the intermediate annular portion 21 and the peripheral annular portion 23 are substantially the same, in other words, such that the ratio between the maximum average thickness and the minimum average thickness is less than 1.2.

[0079] In this first embodiment, the developed surface of the preform 15 is substantially equal to the developed surface of the normal wall 3 .

[0080] Thus, the hot deformation of the preform 15 to form the wall 3 is achieved without thickness variations and therefore the required force is limited.

[0081] In addition, due to the alternating concave and convex portions, the projected surface of the preform 15 on a transverse plane is less than the developed surface of the preform 15 .

[0082] The ratio between the projected surface and the developed surface of the preform 15 on a transverse plane is typically less than 90%, preferably less than 80%, more preferably less than 50%, and the maximum dimension of the projected surface of the preform on a transverse plane is not more than 150% of the maximum dimension of the punch perpendicular to the central axis AA, in particular not more than 135% of the maximum dimension of the punch perpendicular to the central axis AA, preferably not more than 120% of the maximum dimension of the punch perpendicular to the central axis AA.

[0083] It is therefore possible to achieve hollow parts 1 of large dimensions using a press that is at least 10%, preferably at least 20%, and even better at least 50% smaller than would be necessary when punching out a flat preform of limited size, in particular with an expanded surface equal to the expanded surface of the wall 3.

[0084] FIG. 4 shows the steps for shaping the blank 13 to form the preform 15 according to this first embodiment.

[0085] In the example shown in FIG. 4, the step of hot forming the blank to form the preform 15 includes a first stage of forming by hot die forging or stamping the blank 13 to create a first concave blank 27.

[0086] This first forming step is preferably a step of forming by upsetting material towards the periphery of the blank 13 so that the developed surface of the first concave blank 27 is larger than the developed surface of the blank 13 .

[0087] The hot forming step then includes a second stage of hot forming by hot die forging or hot stamping the first concave blank 27 to create the preform 15 .

[0088] During this step, the periphery of the first concave blank 27 is deformed to form the intermediate annular portion 21 and the peripheral annular portion 23 .

[0089] Preferably, during this second forming step, material is again upset towards the periphery of the first concave blank 27 so that the developed surface of the preform 15 is larger than the developed surface of the first concave blank 27 .

[0090] Preferably, the first and second forming steps are performed by a first auxiliary press 29 and a second auxiliary press 37, respectively.

[0091] As shown in FIG. 4, the first auxiliary press 29 includes a first die 33 and a first punch 31 .

[0092] The first forming step is preferably carried out by hot die forging or stamping the blank 13 between a first die 33 and a first punch 31 .

[0093] The second forming step is carried out in a second auxiliary press 37 between a second die 35 and a second punch 39 .

[0094] The shape of the second die 35 and the second punch 39 can shape the preform 15, particularly the intermediate annular portion 21 and the peripheral annular portion 23.

[0095] The second forming step is then performed by hot die forging or stamping the first concave blank 27 between a second die 35 and a second punch 39 .

[0096] According to one alternative, the second forming step includes a first intermediate forming step by hot die forging or stamping a first concave blank to produce a second blank including a concave center and a convex periphery extending contiguously from the center, and a second intermediate hot forming step by hot die forging or stamping the second blank to produce a preform.

[0097] Figure 5 shows an example of a preform 15 according to the second embodiment. This figure shows, in perspective, only a portion of the preform 15. In addition, Figure 5 shows a press 47 including a die 49 and a punch 51 just before the preform 15 is hot-deformed.

[0098] In this second embodiment, the preform 15 is such that these portions comprise a central portion 19 and at least one intermediate annular portion 21, the central portion 19 and the intermediate annular portion 21 having different average thicknesses.

[0099] The developed surface of the preform 15 is less than the developed surface of the wall 3 .

[0100] In addition, the ratio between the projected surface of the preform 15 on the transverse plane and the developed surface of the preform 15 is typically greater than 90%. Furthermore, the maximum dimension of the projected surface of the preform 15 on the transverse plane is not more than 150% of the maximum dimension of the punch 51, and preferably not more than 120% of the maximum dimension of the punch 51 perpendicular to the central axis AA.

[0101] These sections include at least one thickened section intended to provide excess material that can be used during the hot deformation step to increase the developed surface of the preform 15 by plastic flow.

[0102] Preferably, as shown in Figure 5, these portions additionally include a peripheral annular portion 23 having an average thickness different from the average thickness of the adjacent intermediate annular portion 21. The preform 15 then includes a series of at least three portions of different successive average thicknesses.

[0103] In the example shown in FIG. 5, the preform 15 includes a single intermediate annular portion 21 .

[0104] Thus, the central portion 19, the intermediate annular portion 21 and the peripheral annular portion 23 extend radially one after the other away from the central axis AA, with the central portion 19 adjacent to the intermediate annular portion 21 and the intermediate annular portion 21 adjacent to the central portion 19 and the peripheral annular portion 23.

[0105] The central portion 19 has, for example, a developed surface that is between 5% and 90% of the developed surface of the preform 15 .

[0106] The intermediate annular portion 21 has, for example, a developed surface that is between 5% and 50% of the developed surface of the preform 15 .

[0107] The peripheral annular portion 23 has, for example, a developed surface that is between 5% and 50% of the developed surface of the preform 15 .

[0108] In this example, the central portion 19 is an annular portion and includes a recess 22 .

[0109] Additionally, in this example, the intermediate annular portion 21 exhibits an average thickness that differs from the average thickness of the central portion 19 and from the average thickness of the peripheral annular portion 23 .

[0110] In particular, the intermediate annular portion 21 is a thickened portion, in other words with an average thickness that is greater than the average thickness of the central portion 19 and the average thickness of the peripheral annular portion 23 .

[0111] In this example, the average thicknesses of the central portion 19, intermediate annular portion 21 and peripheral annular portion 23 are such that the ratio between the maximum average thickness and the minimum thickness is 1.2 or greater, preferably 1.3 or greater, more preferably 1.5 or greater, or even 2. Preferably, this ratio is 5 or less.

[0112] Shaping of the blank 13 to form the preform 15 is achieved by upsetting, for example, by means of a die ring or a flat disk.

[0113] After hot forming the blank 13 to create the preform 15 , the method includes hot deforming the preform 15 under a press 47 between a die 49 and a punch 51 to form the wall 3 .

[0114] The hot deformation step is performed at a temperature that depends on the material used. For example, if the material is an aluminum alloy, the hot deformation step is usually performed at a temperature between 300°C and 500°C. If the material is a titanium alloy, the hot deformation step is usually performed at a temperature between 700°C and 1300°C.

[0115] Typically, the die 49 has a major diameter that is less than the maximum diameter of the developed surface of the wall 3 .

[0116] The hot deformation step involves stamping and optionally die forging the preform 15 to form the wall 3 .

[0117] During stamping, the shape of the preform 15 is modified to take the shape of the contours of the die 49 and / or punch 51 without any significant variation in thickness.

[0118] During die forging, the wall 3 is shaped and the local and average thickness is modified.

[0119] In the first embodiment described above, in which the preform 15 comprises at least two portions of different convex shapes, the hot deformation step comprises stamping.

[0120] In particular, if the developed surface of the preform 15 is equal to the developed surface of the wall 3, the hot deformation step consists of stamping.

[0121] In particular, the hot deformation step involves spreading the preform 15 between the die 49 and the punch 51 so that after spreading, the surface of the convex part of the preform facing the punch 51 becomes concave.

[0122] In particular, in the example shown in FIG. 3, the preform 15 is widened during the hot deformation step so that the surface of the intermediate annular portion 21 facing the punch 51 is concave.

[0123] If the preform 15 has a developed surface equal to the developed surface of the wall 3, this step of hot deformation does not involve any change in thickness, and therefore the pressing force required in such a step is reduced.

[0124] In addition, the projected surface of the preform 15 on the transverse plane is less than the developed surface of the preform 15, and during this step it is possible to achieve hollow parts 1 of large dimensions by pressing with a limited size, in particular at least 50% smaller than would be necessary when punching a flat preform with a developed surface equal to the developed surface of the wall 3.

[0125] FIG. 6 shows, by way of example, a schematic representation of the first stage of the hot deformation step for the preform 15 of FIG.

[0126] As shown in this figure, the deformation step involves first bringing a punch 51 into contact with the preform 15 and, in particular, the central portion 19 .

[0127] The punch 51 then continues its stroke, inverting the convex shape of the intermediate annular portion 21 and widening the preform 15 so that the intermediate annular portion 21 becomes concave. At the end of the punch stroke, the surface of the wall 3 in contact with the punch is concave.

[0128] In the second embodiment described above, in which the preform 15 comprises at least two portions of different average thickness, the hot deformation step comprises, for example, die forging and stamping the preform 15 between a die 49 and a punch 51.

[0129] In particular, stamping the preform 15 includes a forming step in which the preform 15 is brought into contact with the die 49 by a punch 51 .

[0130] At the end of this stage, for example, the underside of at least one portion of preform 15, preferably all portions of the preform, is in contact with die 49, and the upper surface of at least one portion is not in contact with punch 51. Preferably, at the end of this stage, at least a portion of intermediate annular portion 21 is in contact with die 49 and punch 51.

[0131] Alternatively, at the end of this stage, the upper surface of at least one portion of the preform 15, and preferably all portions of the preform 15, is in contact with the punch 51 and the lower surface of the at least one portion is not in contact with the die 49.

[0132] Die forging is an expansion stage during which the material is upset until it assumes the shape of the surfaces of the punch 51 and die 49.

[0133] According to one embodiment, during this stage, at least a portion of the preform 15 does not come into contact with the punch 51 until expansion is complete.

[0134] In this way, the force to be applied by the press is reduced. In addition, the projected surface of the preform 15 on the transverse plane is less than the developed surface of the preform 15, making it possible to realize hollow parts 1 of large dimensions using a press that is at least 50% smaller than would be required to stamp a flat preform of limited size, in particular with a developed surface equal to the developed area of ​​the wall 3.

[0135] 5, during the expansion stage, the thick-walled intermediate annular portion 21 of the preform 15 is compressed between the die 49 and the punch 51, and at least a portion of the central portion 19 and / or the peripheral annular portion 23 does not contact the punch 51. Thus, material plastically flows from the intermediate annular portion 21 toward the central portion 19 and the peripheral annular portion 23, and then over the peripheral annular portion 23, increasing the expanded surface of the preform 15 and forming the wall 3.

[0136] The method according to the invention therefore makes it possible to manufacture large parts in the shape of domes, such as cryogenic tank domes, without the need for welding and which can be realized on available forging presses whose dimensions are limited, in particular whose maximum diameter is less than the maximum diameter of the developed surface of the wall 3 and / or whose capacity is limited in terms of force.

[0137] In addition, this method makes it possible to achieve a part whose grain is homogeneous, so that the mechanical properties of the part are homogeneous, from the lower transverse plane 5 towards the upper transverse plane 7 around the central axis AA and along the wall 3, as shown in FIG. 7.

[0138] In particular, the orientation of the grains is homogeneous both about the central axis in any axial plane containing the axis AA and in any plane transverse to the axis AA.

[0139] Typically, in any transverse plane, the angle α formed between the direction of elongation (longitudinal direction) of the particle as seen in cross section in that plane and a tangent to the wall surface of that particle is substantially constant (e.g., ±10°), as shown in Figure 7.

[0140] Indeed, as a result of the deformation applied by the method according to the invention, the particles are elongated in a preferred direction.

[0141] The direction of elongation of a particle as seen in a cross section of a transverse plane means the direction in which the largest dimension (length) of the particle as seen in this cross section of a transverse plane extends.

[0142] Non-Patent Document 1 particularly illustrates the microstructural characteristics of the particles, especially the direction of elongation.

[0143] As far as fiberization is concerned, the tangential direction is preferably more pronounced than the axial direction, and the axial direction is more pronounced than the radial direction, which generally means that the particles extend more tangentially than axially and more axially than radially. "Radial" here generally means a direction extending through the thickness of the wall, or in other words, perpendicular to the plane tangent to the wall through the thickness (and therefore not necessarily perpendicular to the axis AA).

[0144] Generally speaking, if one considers a particle viewed in three dimensions, the maximum direction of particle elongation is tangential, contained in the horizontal plane and tangent to the surface of wall 3 (in other words, the angle α formed between the direction of particle elongation seen in a cross section in this horizontal plane and the tangent to the surface of the wall at this particle is substantially zero).

[0145] The mechanical properties of the resulting part are high in the tangential direction, which is the highest stress mode for this type of part.

[0146] The particle is preferably symmetrical about a central axis AA.

[0147] Generally speaking, a person skilled in the art will be able to adapt the shape of the preform and the dimensions of its different parts, in particular the diameter and thickness, as well as the number of parts, depending on the shape and dimensions of the wall to be produced and depending on the maximum dimensions and capacity of the press.

[0148] Furthermore, this method is not limited to the production of large size domes for pressure vessels, but can be adapted to any large size part that can be produced by stamping / die forging.

[0149] Parts that can be produced by this method are usually, but not necessarily, parts of revolution. The walls can also contain additional features such as openings, surface reliefs, especially bosses, pits and ribs.

[0150] Furthermore, the two embodiments described above can be combined, in particular with reference to the first embodiment, where at least one portion has an average thickness that is different from the average thickness of another portion. [Explanation of symbols]

[0151] 1 Hollow parts 3. Wall 5 Lower horizontal plane 7 Upper horizontal plane 9 aperture 11 Semi-finished products 13 Blank 14 Aperture 15 Preform 19 Center part 21 Intermediate annular section 22 depression 23 Peripheral annular part 27 First concave blank 29 First auxiliary press 31 First Punch 33 First Die 35 Second Die 37 Second auxiliary press 39 Second Punch 47 Press 49 Die 51 Punch

Claims

1. A method for manufacturing a hollow part (1) comprising a single, seamless wall (3) in the shape of a dome extending around a central axis (A-A), said wall (3) being realized in a material consisting of a metal alloy, said wall (3) having an average thickness of less than 50 mm and a major dimension perpendicular to said central axis (A-A) between 1500 mm and 3700 mm, said method comprising the following successive steps: providing a semi-finished product (11) of said material; hot forging the semi-finished product (11) by upsetting to form a blank (13) with a developed surface that is larger than the developed surface of the semi-finished product (11) and smaller than the developed surface of the wall (3); hot forming said blank (13) to produce a preform (15) having a developed surface below the developed surface of said wall (3), said preform (15) comprising at least two successive portions (19, 21) extending radially one after the other away from said central axis (A-A), and for all said portions (19, 21) the average thickness and / or convexity of the two successive portions (19, 21) are different; hot deforming said preform (15) under a press (47) between a die (49) and a punch (51) to form said wall (3); A manufacturing method comprising:

2. 2. A method according to claim 1, characterized in that said part comprises a central part (19) and at least one intermediate annular part (21), said central part (19) and said intermediate annular part (21) being of different convex shapes.

3. 3. The method of claim 2, wherein said portion further comprises a peripheral annular portion (23), said peripheral annular portion (23) having a convexity different from that of the adjacent intermediate annular portion (21).

4. 4. The method according to claim 2 or 3, characterized in that the ratio between the projected surface of the preform (15) on a transverse plane and the developed surface of the preform (15) is less than 90%, and the maximum dimension of the projected surface of the preform (15) on a transverse plane is not more than 150% of the maximum dimension of the punch (51) perpendicular to the central axis (A-A).

5. 5. A method according to any one of claims 2 to 4, characterized in that the step of deformation of the preform (15) under the press comprises spreading the preform (15) between the die (49) and the punch (51) so that after spreading, the surface of the part facing the punch (51) is concave.

6. A method according to any one of claims 2 to 5, characterized in that the surface of the central part (19) facing the punch (51) has a concave shape.

7. 2. The method according to claim 1, wherein said portion comprises a central portion (19) and at least one intermediate annular portion (21), said central portion (19) and said intermediate annular portion (21) having different average thicknesses, and wherein the developed surface of said preform (15) is less than the developed surface of said wall (3).

8. 8. The method of claim 7, wherein the portion further comprises a peripheral annular portion (23), the intermediate annular portion (21) being a thickened portion, the average thickness of the intermediate annular portion (21) being greater than the average thickness of the central portion (19) and the average thickness of the peripheral annular portion (23).

9. 9. The method according to claim 7, wherein the step of deformation of the preform (15) comprises a forming stage in which at least a part of the intermediate annular portion (21) is brought into contact with the die (49) by the punch (51), and a die forging stage corresponding to expansion in which at least a part of the preform (15) is not in contact with the punch (51).

10. 10. The method according to claim 9, characterized in that during the expansion step, the thick-walled intermediate annular portion (21) of the preform (15) is compressed between the die (49) and the punch (51), and at least part of the central portion (19) and / or the peripheral annular portion (23) is not in contact with the punch (51), so that the material plastically flows from the intermediate annular portion (21) towards the central portion (19) and the peripheral annular portion (23), and then over the peripheral annular portion (23), increasing the developed surface of the preform and forming the wall (3).

11. 11. A method according to any one of claims 1 to 10, characterized in that the material is an aluminium alloy, in particular a 2XXX or 7XXX alloy.

12. A hollow part (1) comprising a single seamless wall (3) in the shape of a dome, said wall (3) extending around a central axis (A-A), said wall (3) being realized in a material consisting of a metal alloy, said wall having an average thickness of less than 50 mm and a major dimension perpendicular to said central axis (A-A) between 1500 mm and 3700 mm.

13. 13. A hollow part according to claim 12, characterized in that the wall (3) presents a homogeneous fiber ring around the central axis (A-A) and the orientation of the grains of the metal alloy is such that, in any transverse plane, the angle formed between the direction of elongation of the grain as seen in a cross section of this transverse plane and the tangent of this grain to the wall (3) is substantially constant.

14. Component according to claim 12 or 13, characterized in that the material is an aluminum alloy, in particular a 2XXX or 7XXX alloy.

15. A cryogenic tank comprising a component (1) according to any one of claims 12 to 14 or a component (1) manufactured by the method according to any one of claims 1 to 11.

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