Method for manufacturing a tubular metal body, configured to form a side wall of a container

Abstract

The present invention relates to a method for manufacturing a tubular metal body (10), configured to form a side wall of a container, preferably a metal can, which method comprises the following steps: - a supplying step, to supply a cylindrical body, with a longitudinal axis, - a radial expansion step, to form a tubular preform (30) from said cylindrical body, and - a final stretching step, to reduce surface marks from said radial expansion step and yielding said tubular metal body (10).

Description

[0001] Description

[0002] Title of the invention: Method for manufacturing a tubular metal body, configured to form a side wall of a container

[0003] Technical field of the invention

[0004] The present invention relates to the technical field of methods for manufacturing a tubular metal body, configured to form a side wall of a container.

[0005] Prior art

[0006] In the field of manufacturing tubular metal bodies, many methods are known for shaping components intended for applications such as containers.

[0007] Traditionally, such tubular bodies are made from flat rectangular blanks rolled and welded.

[0008] The shaping of these tubular bodies often involves a radial expansion step, typically utilizing moving segments or stretching dies, to form the cylindrical body.

[0009] While this conventional process is widely used, it typically leaves surface marks that compromise the perceived quality of the final product.

[0010] Therefore, there is a need to improve the process in order to enhance surface finish and overall product appearance.

[0011] Presentation of the invention

[0012] In order to remedy the aforementioned disadvantage of prior art, the present invention provides a method for manufacturing a tubular metal body, configured to form a side wall of a container, preferably a metal can,

[0013] which method comprises the following steps:

[0014] - a supplying step, to supply a cylindrical body, with a longitudinal axis,

[0015] - a radial expansion step, to form a tubular preform from said cylindrical body, and

[0016] - a final stretching step, to reduce surface marks from said radial expansion step and yielding said tubular metal body.

[0017] The method according to the invention offers multiple advantages over conventional forming techniques used in the manufacture of tubular metal bodies for containers:

[0018] - improved surface quality: by integrating a final stretching step after the radial expansion step, the method significantly reduces or eliminates surface marks induced during the expansion phase, leading to a smoother and more uniform externalappearance of the tubular body; this is particularly valuable for applications where the visual aspect of the container is critical to the end user’s perception of quality;

[0019] - dimensional accuracy and repeatability: the combination of radial expansion followed by controlled final stretching allows for precise shaping of the tubular body, ensuring tight tolerances and reproducible geometries along the entire production series.

[0020] Other non-exhaustive and advantageous features of the process according to the invention, taken individually or in all technically feasible combinations, are the following:

[0021] - said radial expansion step comprises at least two radial expansion operations: a first radial expansion operation, to form a preliminary tubular preform from said cylindrical body, and a second radial expansion operation, to form said tubular preform from said preliminary tubular preform;

[0022] - said radial expansion step comprises a single radial expansion operation; - said radial expansion step is configured to form a tubular preform having a round shape, and one of the following expansion and surface change combinations expressed as a percentage relative to the final geometry: 100% of expansion and less than 100% of surface change, less than 100% of expansion and 100% of surface change, less than 100% of expansion and of surface change; and said final stretching step is configured to form said tubular metal body having a round shape, and both 100% of expansion and 100% of surface change;

[0023] - further comprising, before the radial expansion step, a prior angular indexing step about a longitudinal axis of said cylindrical body;

[0024] - said radial expansion step and said final stretching step are selected from one of the following embodiments: said radial expansion step comprises a single radial expansion operation which is implemented to form a round tubular preform, having less than 100% expansion and / or less than 100% surface change expressed as a percentage relative to the final geometry, then the final stretching step is implemented to form a round tubular metal body with the final shape; said radial expansion step comprises at least two radial expansion operations which are implemented to form a round tubular preform, having less than 100% expansion and / or less than 100% surface change expressed as a percentage relative to the final geometry, then the final stretching step is implemented to form a round tubular metal body with the final shape;- the radial expansion step is performed using radial expansion tools comprising moving segments or stretching dies;

[0025] - the final stretching step is performed using stretching dies;

[0026] - further comprising a prior stretching step for stretching the extremities of said cylindrical body, before the radial expansion step.

[0027] The present invention also relates to:

[0028] - a tubular metal body formed by the method according to the invention;

[0029] - a container comprising a tubular metal body according to the invention.

[0030] Of course, the different features, variants and embodiments of the invention may be associated with each other in various combinations as long as they are not incompatible or exclusive of each other.

[0031] Detailed description of the invention

[0032] In addition, various other features of the invention are apparent from the annexed description made with reference to the drawings which illustrate non-exhaustive forms of embodiment of the invention and where:

[0033] [Fig. 1] is a view of a radial expansion step, to form a tubular preform from a cylindrical body;

[0034] [Fig. 2] is a view of a final stretching step, to reduce surface marks from the radial expansion step of Figure 1 and yielding the tubular metal body;

[0035] [Fig. 3] is a view of a prior stretching step, for stretching the extremities of the cylindrical body, before the radial expansion step of Figure 1.

[0036] It should be noted that, in these figures, the structural and / or functional elements common to the different variants may have the same references.

[0037] As shown schematically in the Figures, the present invention relates to a method for manufacturing a tubular metal body 10, configured to form a side wall of a container, preferably a metal can.

[0038] In general, according to the invention, the method of manufacturing comprises the following steps:

[0039] - a supplying step (Figure 1), to supply a cylindrical body 20, with a longitudinal axis 20’,

[0040] - a radial expansion step (Figure 1), to form a tubular preform 30 from said cylindrical body 20, and- a final stretching step (Figure 2), to reduce surface marks from said radial expansion step and yielding the tubular metal body 10.

[0041] Container

[0042] By “container, preferably a metal can”, it is meant a structure designed to hold and store materials, for food and non-food stuffs, such as powders or other particulate products.

[0043] This container is particularly suitable for industrial, commercial, or consumer applications where durability, structural integrity, and the ability to preserve the contents are critical.

[0044] The container comprises advantageously:

[0045] - a side wall formed by the tubular metal body 10,

[0046] - a bottom wall (not shown), and

[0047] - a cover (not shown).

[0048] The assembly of the bottom wall and the cover to the side wall, is, for example, achieved by metal seaming, ensuring a robust and airtight construction that preserves the integrity of the contents while providing mechanical strength and durability.

[0049] For the purposes of the present invention, the tubular metal body 10 is preferably made from steel alloy or an aluminium alloy.

[0050] By “tubular metal body 10”, it is meant a structure having a hollow, elongated shape with a continuous wall, typically formed from a metallic material.

[0051] In general, a tubular body have advantageously a cross-sectional shape that is axisymmetric (e.g., circular, also named round).

[0052] The diameter of said tubular body may be either constant or variable along its longitudinal height, depending on the functional or aesthetic requirements of the final container design.

[0053] And the side wall of the tubular body is advantageously characterized by a generatrix, which is the line around the longitudinal axis that defines the height of the cylinder. For a constant diameter, the generatrix is straight, while for a variable diameter, the generatrix is non-straight.

[0054] These configurations represent forms of revolution, maintaining symmetry around the longitudinal axis.

[0055] Supplying StageIn the present invention, the supplying step involves supplying a tubular structure known as a cylindrical body 20, possibly a welded cylindrical body, which serves as the foundational element for subsequent processing.

[0056] By “cylindrical body 20”, it is meant a tubular structure with a substantially cylindrical geometry and a longitudinal axis 20’.

[0057] The cross-section of the cylindrical body 20 is preferably circular and may exhibit a diameter that is either constant or variable along its height.

[0058] A variable diameter encompasses, for example, annular features such as shoulders or other geometric transitions. These variations may be introduced to meet specific functional, structural, or aesthetic requirements of the final container.

[0059] By “welded cylindrical body”, it is preferably meant a tubular structure with a substantially cylindrical shape, formed by joining the edges of a metallic sheet or blank along a longitudinal weld line 21 (as shown Figure 3) using a welding process.

[0060] This cylindrical body serves as a precursor or intermediate product in the manufacturing process of tubular components, such as containers or structural elements, and is characterized by its uniform wall thickness and the presence of a longitudinal weld line 21 running along its length.

[0061] Radial expansion step

[0062] Then, a radial expansion step is implemented to form a tubular preform 30 from said cylindrical body 20.

[0063] In general, the method comprises “radial expansion step” which refers to a controlled manufacturing operation in which a tubular structure, such as a cylindrical body or a tubular preform, is subjected to forces that deform it radially outward from its longitudinal axis.

[0064] This process is used to modify the cross-sectional geometry of the structure while preserving its structural integrity and maintaining its longitudinal alignment.

[0065] In particular, the radial expansion step is structured to increase the diameter of the cross-section while maintaining a circular shape throughout the height of the tubular body.

[0066] The resulting geometry may comprise a constant diameter or a variable diameter along the longitudinal axis, depending on design specifications.A variable diameter may include features such as transitions, enabling the formation of containers with functional or decorative shape variations while retaining overall roundness.

[0067] The radial expansion is preferably achieved using specialized tools, such as segmented dies, expandable mandrels, moving segments, stretching dies, or other mechanical devices, including pneumatic and hydraulic systems, which apply outward forces uniformly or selectively along the inner or outer circumference of the tubular body.

[0068] For example, as shown Figure 1 , in first embodiment, these tools 50 operate by employing moving segments 51, which are components that move radially outward or inward in a synchronized manner to deform the tubular body with high precision.

[0069] The moving segments 51 are configured to apply distributed forces along the circumference of the tubular body, ensuring a smooth and precise radial deformation.

[0070] This mechanism allows the tubular body to expand evenly, minimizing risks of defects such as thinning, cracking, or buckling of the material.

[0071] The moving segments 51 can be adjusted to create specific geometries, advantageously round shapes.

[0072] The expansion can result advantageously in round, or in a nearly round, cross-sectional shape, oriented perpendicularly to the longitudinal axis 20’ of the cylindrical body 20, depending on the desired design or functional requirements.

[0073] The radial expansion steps play a pivotal role in forming the tubular metal body 10. They enable precise control over the desired shape by applying targeted forces during the expansion process.

[0074] This ensures that the desired geometries are achieved with accuracy and consistency, while maintaining the structural integrity of the tubular body.

[0075] The radial expansion steps may be defined by at least one of the following parameters expressed as a percentage relative to the final geometry:

[0076] a) percentage of expansion:

[0077] This parameter represents the relative increase in size of the tubular structure during an expansion step, compared to its final form. It describes how much the structure is expanded radially before reaching its target geometry. This parameter is particularly useful for defining controlled deformation steps, ensuring the desired final dimensions are achieved.In particular, by “percentage of expansion”, it is advantageously meant the ratio between the current radial deformation and the maximum radial deformation of the final geometry. This parameter is measured relative to the final radius. A 100% expansion indicates that the tubular preform has achieved its final target dimensions in terms of size for a specific operation, typically the round portion.

[0078] By “percentage of expansion”, it is also advantageously meant the dimensional ratio between the radial envelope of the preform at a given moment and the maximum radial envelope of the final body. Concretely, this parameter measures the attainment of the diameter or overall dimensions of the part. An expansion of 100% means that the preform has reached its final radial footprint, i.e. , its outer diameter corresponds to that of the finished product, regardless of the presence or absence of local deformations on the surface.

[0079] By "100% of expansion", it is advantageously meant that the tubular preform has achieved its final target dimensions in terms of size for a specific operation, such as the completion of a round portion. This value specifically refers to the achievement of the final target radius at the maximum radial points of the cross-section. Such a state corresponds to a preform that has reached its final outer radial envelope, for instance, a smooth cylindrical shape at the final diameter, even if the material has not yet been fully deformed to create the final non-axisym metric contours. In this context, the radial expansion results in a radius that corresponds exactly to the desired final dimensions, representing 100% of the final radius.

[0080] By "lower than 100% of expansion", it is advantageously meant that the radial expansion of the tubular structure has not yet reached the final target dimensions of the non-axisymmetric tubular metal body.

[0081] b) percentage of surface change:

[0082] This parameter refers to the relative increase in the surface area of the structure during an intermediate stage of expansion, as compared to its final surface area. It provides a measure of the overall material deformation required to achieve the desired final shape, taking into account final geometries.

[0083] This enclose an intermediate shape that is significantly different from the final shape, particularly in scenarios involving two mechanical expansions.

[0084] This encompasses the formation of an intermediate shape that may be different from the final shape, especially in cases involving two mechanical expansions.Unlike expansion, which concerns the global envelope, surface change concerns the topography of the wall.

[0085] In another words, by "percentage of surface change", it is advantageously meant the ratio between the surface area of the structure at a given intermediate stage and the total surface area of the final non-axisymmetric tubular metal body. This parameter provides a measure of the overall material flow and deformation required to form complex geometries. A surface change lower than 100% indicates that while the structure may have reached its maximum radial expansion, the material has not yet been fully deformed to create the radial deformations forming the outward (convex) or inward (concave) contours of the final design.

[0086] By "100% of surface change", it is advantageously meant that the ratio between the surface area of the structure at a given intermediate stage and the total surface area of the final non-axisymmetric tubular metal body is equal to one.

[0087] This parameter specifically refers to the achievement of the total developed surface area of the final product, including all intricate reliefs and non-axisymmetric contours. In this state, preferably, the surface area is fully adjusted to match the final geometry, providing a complete measure of the overall material flow and deformation required to form complex geometries. Reaching 100% of surface change may occur even when the expansion is partial, meaning the structure has not yet been expanded to the full radial distance required to reach the final radius. This configuration is particularly ideal for managing mechanical material stress and preparing the structure for a final finishing step.

[0088] By "lower than 100% of surface change," it is advantageously meant that the total developed surface area of the intermediate structure is less than the total developed surface area of the final non-axisymmetric tubular metal body.

[0089] By "total developed surface area", it is advantageously meant the cumulative surface area of the wall of the non-axisymmetric tubular metal body once it has reached its complete final geometry.

[0090] For the avoidance of doubt, all percentages of expansion and surface change described herein are preferably calculated relative to the final geometry of the finished non-axisymmetric tubular metal body. Preferably, the “100% expansion” value specifically refers to the achievement of the final target radius at the maximum radial points of the cross-section, while “100% surface change” refers to the total developedsurface area of the final product, including all intricate reliefs and non-axisymmetric contours.

[0091] Moreover, the parameters of expansion and surface change are technically decoupled. A state of 100% expansion with lower than 100% surface change corresponds to a preform that has reached its final outer radial envelope (e.g., a smooth cylindrical shape at the final diameter) but lacks the internal or external radial deformations 11, such as embossments or concavities. Conversely, a state of lower than 100% expansion with 100% surface change describes a preform where the metal has been pre-stretched to its final surface area (material flow) but is still contained within a smaller radial footprint to manage mechanical stress before the final shaping.

[0092] In particular, the radial expansion step enables precise control over the expansion process to achieve advantageously round shapes, defined preferably by the following parameter combinations expressed as a percentage relative to the final geometry:

[0093] a) 100% of expansion and less than 100% of surface change

[0094] In this scenario, the tubular structure undergoes full radial expansion, reaching its maximum intermediate size relative to the final shape. The surface area increase is controlled at less than 100%, determined by the marks or positions of the expanding segments for example.

[0095] In another words, preferably, the tubular structure reaches its maximum intermediate size (e.g., a full round shape), but the surface area remains lower than the final state because the specific patterns, reliefs, or non-axisymmetric details (which require additional material stretching) have not yet been created.

[0096] Also in another words, the preform has been expanded to its final diameter (100% expansion), but its wall remains predominantly smooth or simplified. It has not yet undergone the local stretching necessary to form the complex patterns (reliefs) that would increase its total developed surface area. The transition to 100% surface will occur during a subsequent step by local forming without changing the global diameter.

[0097] b) less than 100% of expansion and 100% of surface change

[0098] Here, the expansion is partial, defined by less than 100% of the total radial increase required to reach the final shape. However, the surface area is fully adjusted to match the final geometry.Preferably, the surface area is fully adjusted to match the final geometry (often to prepare for a finishing step and manage material stress), but the structure has not yet been expanded to the full radial distance required to reach the final radius.

[0099] Preferably also, the material has been pre-stretched to reach its final developed surface area (all patterns are formed), but the part is maintained within a restricted radial envelope (reduced diameter). The next step will consist of “unfolding” or expanding this shape to reach the final diameter without further stretching the material locally.

[0100] c) less than 100% of expansion and of surface change

[0101] This scenario allows for customized combinations of partial expansion and partial surface adjustments, enabling flexibility in tailoring the intermediate shape.

[0102] These scenarios provide a versatile framework for shaping tubular bodies into preferable round geometries, balancing radial deformation and surface control to meet specific design and functional requirements.

[0103] Moreover, these parameters allow precise calibration of the expansion process, optimizing the control over the geometry of the intermediate and final shapes. They also help minimize mechanical stresses and surface defects while ensuring consistent quality of the final product.

[0104] The radial expansion step results in a tubular preform 30, preferably with a specific shape that can be classified as:

[0105] - final / full

[0106] or

[0107] - near-final I near-full,

[0108] based on its degree of conformity to the desired end geometry.

[0109] A shape is considered “final” when it matches 100% of the intended final geometry, as defined by the application's design and functional requirements. The final shape is the completed product, fully meeting all geometric and functional requirements.

[0110] This corresponds to a full radial expansion process, where the deformation reaches the complete target dimensions in all sections of the tubular preform.

[0111] A shape is deemed “non-final” or “near-final” when it is less than 100% of the final geometry.In some embodiments, this occurs when at least a part of the metal piece conforms to the final shape, while other parts remain in an intermediate state requiring further processing.

[0112] The percentage of finality can vary, with non-final shapes typically representing a deformation that is less than 100% of the target geometry.

[0113] In other words, the degree of finality is thus defined as a percentage of the final shape:

[0114] - 100% indicates the preform has achieved its final geometry in terms of both size and shape,

[0115] - less than 100% indicates a partially final shape, where the deformation has not yet reached the full dimensions of the final geometry (i.e. the deformation has not yet reached the full size and shape), preferably for a part or all the shapes.

[0116] Moreover, radial expansion is also measured relative to the final radius:

[0117] -for final shapes, the radial expansion results in a radius that corresponds exactly to the desired final dimensions (100% of the final radius),

[0118] - for non-final shapes, the radial expansion produces a radius that is smaller than the final target radius, corresponding to the percentage of finality achieved during the process.

[0119] In other words, “100% of a final shape” means achieving the final shape for a specific operation.

[0120] Preferably, said radial expansion step is thus configured to form a tubular preform 30 having:

[0121] - a round shape,

[0122] and

[0123] - one of the following expansion and surface change combinations expressed as a percentage relative to the final geometry:

[0124] -- 100% of expansion and less than 100% of surface change,

[0125] -- less than 100% of expansion and 100% of surface change,

[0126] -- less than 100% of expansion and of surface change,

[0127] In particular, even when the first radial expansion step achieves 100% of the expansion (the final radius), the second radial expansion step transforms the intermediate geometry into the non-axisymmetric final shape. Preferably, in this specific sequence, the first step establishes the overall size, while the second stepperforms the localized material redistribution required to create non-round contours without exceeding the material's structural limits.

[0128] Moreover, radial expansion step may be implemented according to alternative embodiments.

[0129] In a first embodiment, said radial expansion step comprises at least two radial expansion operations:

[0130] - a first radial expansion operation, to form a preliminary tubular preform (not shown) from said cylindrical body 20, and

[0131] - a second radial expansion operation, to form said tubular preform 30 from said preliminary tubular preform.

[0132] Different radial expansion tools 50 may be used in each said radial expansion operations.

[0133] This refers to the use of distinct sets of radial expansion tools 50 in each said radial expansion operations. Each set of tools is specifically designed or configured to perform a targeted operation, adapting to the evolving geometry and requirements of the tubular body as it progresses through different radial expansion operations.

[0134] The tools vary in design, size, and functionality to accommodate changes in the shape, dimensions, and material characteristics of the tubular body.

[0135] In other words, and for example, the first radial expansion operation is configured to form a preliminary tubular preform from the cylindrical body using tools 50 designed for uniform expansion, achieving a final or near-final percentage of expansion. The second radial expansion operation then employs a different set of tools 50, including customized segments, to refine the geometry of the preform and accurately form the desired final shape.

[0136] In a second embodiment, said radial expansion step comprises a single radial expansion operation.

[0137] This operation is advantageously implemented using radial expansion tools configured to apply a controlled radial deformation in a single stage, such that a tubular preform is obtained directly from the cylindrical body.

[0138] This operation is optionally performed with tools adapted for uniform expansion and / or partially customized segments depending on the desired geometry.

[0139] Final stretching stepThe process then comprises a final stretching step (Figure 2), to reduce surface marks from said radial expansion step and yielding said tubular metal body 10.

[0140] By “reduce surface marks from said radial expansion step”, it is advantageously meant to lessen or eliminate visual or tactile irregularities that may appear on the outer and / or inner surface of the tubular preform as a result of the mechanical deformation forces applied during the radial expansion step.

[0141] These marks may originate from contact with said radial expansion tools (e.g., moving segments), local variations in strain distribution, or discontinuities in material flow.

[0142] The reduction of such marks leads to an improved surface finish, enhancing both the functional quality and the aesthetic appearance of the final tubular metal body.

[0143] This final stretching step is preferably performed using stretching dies 60, which are carried by two opposing die elements (not shown).

[0144] These die elements are designed to move towards each other in a controlled manner, applying symmetrical and uniform radial forces onto the tubular preform 30.

[0145] This operation results in a smoothing effect that not only eliminates surface irregularities but also ensures a 100% expansion and 100% surface change (expressed as a percentage relative to the final geometry), yielding a tubular metal body 10 with a high-quality finish and precise dimensional conformity.

[0146] In other words, said final stretching step is configured to form said tubular metal body 10 having:

[0147] - a round shape,

[0148] and

[0149] - both 100% of expansion and 100% of surface change.

[0150] Possible prior angular indexing step

[0151] In a preferred implementation, the method comprises, before the radial expansion step, a prior angular indexing step about the longitudinal axis 20’ of the cylindrical body 20.

[0152] This operation is configured to precisely orient the cylindrical body in rotation, so that its peripheral geometry, notably the location of its longitudinal weld seam, is brought into a predetermined angular position.This angular positioning is particularly advantageous when specific expansion segments are configured to apply greater or lesser deformation at defined circumferential positions.

[0153] By aligning the weld seam relative to the expansion tooling - especially when using segmented expansion dies or moving segments - it becomes possible to control the strain distribution more effectively, to minimize mechanical stress concentration in the region of the weld, and to reduce the formation of surface marks or material thinning along the seam.

[0154] Such an indexing step therefore contributes to optimizing the overall quality and repeatability of the expansion process, particularly in applications where the weld line defines a mechanical or visual sensitivity zone in the final tubular metal body.

[0155] Possible prior stretching step

[0156] Preferably, as shown Figure 3, the method comprises a prior stretching step for stretching the extremities 25 of the cylindrical body 20, before the radial expansion step.

[0157] This optional stretching step involves elongating the extremities 25, located at both axial ends of the cylindrical body 20, preferably through a die process.

[0158] The die operation is carried out by two opposing die elements T that move towards each other, applying controlled forces to the ends of the cylindrical body 20.

[0159] This die operation is an advantageous preparatory step that enhances the ability of the cylindrical body 20 to withstand the stresses of radial expansion.

[0160] By conditioning the material at the extremities 25, it ensures uniform expansion behavior and prevents localized weaknesses that could otherwise compromise the final geometry or structural performance.

[0161] Embodiments

[0162] The method of manufacturing is advantageously configured to achieve varying levels of finality in the geometry of the tubular metal body 10, depending on the desired final shape and the manufacturing strategy.

[0163] The levels of finality are defined for example in terms of the percentage of the final geometry achieved during each step.

[0164] Thus, according to the invention, the radial expansion step and the final stretching step are for example selected from one of the following embodiments.In a first embodiment, the radial expansion step comprises a single radial expansion operation, which is implemented to form a round tubular preform 30 having less than 100% expansion and / or less than 100% surface change, relative to the final geometry.

[0165] Subsequently, the final stretching step is carried out to complete the forming of the tubular metal body 10, resulting in a round shape with 100% expansion and 100% surface change, corresponding to the final desired shape.

[0166] In a second embodiment, the radial expansion step comprises at least two successive radial expansion operations, which are implemented to form a round tubular preform 30 having less than 100% expansion and / or less than 100% surface change, relative to the final geometry.

[0167] The final stretching step is then carried out to complete the forming of the tubular metal body 10, resulting in a round shape with 100% expansion and 100% surface change, corresponding to the final desired shape.

[0168] Of course, various other amendments may be made to the invention within the framework of the annexed claims.

Claims

Claims

1. A method for manufacturing a tubular metal body (10), configured to form a side wall of a container, preferably a metal can,which method comprises the following steps:- a supplying step, to supply a cylindrical body (20), with a longitudinal axis (20’), - a radial expansion step, to form a tubular preform (30) from said cylindrical body (20), and- a final stretching step, to reduce surface marks from said radial expansion step and yielding said tubular metal body (10).

2. The method according to claim 1 , wherein said radial expansion step comprises at least two radial expansion operations:- a first radial expansion operation, to form a preliminary tubular preform from said cylindrical body (20), and- a second radial expansion operation, to form said tubular preform (30) from said preliminary tubular preform (30).

3. The method according to claim 1, wherein said radial expansion step comprises a single radial expansion operation.

4. The method according to any one of the claims 1 to 3, wherein said radial expansion step is configured to form a tubular preform (30) having:- a round shape,and- one of the following expansion and surface change combinations, expressed as a percentage relative to the final geometry:-- 100% of expansion and less than 100% of surface change,-- less than 100% of expansion and 100% of surface change,-- less than 100% of expansion and of surface change,and said final stretching step is configured to form said tubular metal body (10) having: - a round shape,and- both 100% of expansion and 100% of surface change, expressed as a percentage relative to the final geometry.

5. The method according to any one of claims 1 to 4, further comprising, before the radial expansion step, a prior angular indexing step about a longitudinal axis (20’) of said cylindrical body (20).

6. The method according to any one of the claims 1 to 5, wherein said radial expansion step and said final stretching step are selected from one of the following embodiments:- said radial expansion step comprises a single radial expansion operation which is implemented to form a round tubular preform (30), having less than 100% expansion and / or less than 100% surface change, expressed as a percentage relative to the final geometry,then the final stretching step is implemented to form a round tubular metal body (10) with the final shape;- said radial expansion step comprises at least two radial expansion operations which are implemented to form a round tubular preform (30), having less than 100% expansion and / or less than 100% surface change expressed as a percentage relative to the final geometry,then the final stretching step is implemented to form a round tubular metal body (10) with the final shape.

7. The method according to any one of claims 1 to 6, wherein the radial expansion step is performed using radial expansion tools (50) comprising moving segments (51) or stretching dies.

8. The method according to any one of claims 1 to 7, wherein the final stretching step is performed using stretching dies (60).

9. The method according to any one of claims 1 to 8, further comprising a prior stretching step for stretching the extremities (25) of said cylindrical body (20), before the radial expansion step.18

10. A tubular metal body (10) formed by the method according to any one of claims 1 to 9.

11. A container comprising a tubular metal body (10) according to claim 10.

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