WO2012159856A1

WO2012159856A1 - Method for manufacturing inner pressure deformed sheet metal structures

Info

Publication number: WO2012159856A1
Application number: PCT/EP2012/058107
Authority: WO
Inventors: Jakob PRZYBYLO; Haidong MA; Chun-yang WANG
Original assignee: Jakob Przybylo Architekt
Priority date: 2011-05-03
Filing date: 2012-05-03
Publication date: 2012-11-29

Abstract

The invention provides a method for manufacturing an inner pressure deformed sheet metal structure comprising at least one step of applying an inner pressure to at least one cavity of a pre-structure. The cavity is formed from one plate of sheet metal and comprises at least three fixed edges. Also provided is a pre-structure being formed from one plate of sheet metal and comprising at least one cavity, wherein the cavity comprises at least three fixed edges or provided by the method of the invention. And an inner pressure deformed sheet metal structure manufactured by the method of the invention and uses in construction thereof. The invention also provides triangular frames characterized in that one inner pressure deformed sheet metal structure is in triangular configuration or in that at least three inner pressure deformed sheet metal structures are assembled in triangular configuration.

Description

Method for manufacturing inner pressure deformed sheet metal structures

Field of the invention

The invention relates to a method for producing inner pressure deformed sheet metal structures, to the structures and pre-structures and uses thereof.

Background

Sheet metal is a very versatile construction material which may be formed into highly complex three-dimensional structures due to its high deformability. In general, sheet metal is characterized by its thin and flat form which can be cut, bent or fold into a variety of different shapes. Such sheet metal structures, in particular deformed sheet metal structures, may be characterized by a very high stiffness and stability, although having a comparatively low weight.

General methods of metal processing comprise bending, folding, casting and cutting. Another method for metal processing is inner pressure deformation, optionally inflating. Using this method the form of the material is changed in that the sheet metal is pushed outside upon application of an inner pressure. By applying a pressure medium to a principally pressure-tight (e.g. air-tight) closed cavity, the surface of the cavity stretches and pushes to the outside depending on the geometry and size of the pressurized cavity, the thickness of the sheet metal plate, the conditions and parameters of inner pressure deformation and the used material of the sheet metal.

Current techniques use different pressure media for inner pressure metal deformation, such as air or water. In hydroforming, under high pressure a hydraulic fluid is introduced into a chamber above the working material whereby the material is pushed down towards a shaping matrix or die. Thus, for hydro-shaping of a structure, a matrix has to be constructed being the "negative" of the desired form. In this way, 3 -dimensional structures may be formed which are open on one or more sides. However more complex structures have to be assembled in additional working steps afterwards which multiplies the number of working steps and thus increases the error frequency besides the requirement of at least one specifically constructed matrix for each piece.

A variant of hydroforming is the so-called tube hydroforming as described in WO 00/10748 Al . Herein, an even metal tube is fixed inside a chamber which serves as a matrix and a pressure is applied to the inside of the tube by the introduction of a hydraulic fluid. The pressurised fluid leads to an increased inner pressure inside the tube which pushes the walls of the metal tube outside towards a surrounding matrix. Thereby, 3-dimensional structures are possible; however, the number of possibilities is limited and expensive since for each individual piece a specific matrix construction is required. It is also not easily possible to flexibly adjust the resulting form of the structure.

In both variants of hydroforming, good precision of the resulting shape can be achieved. Using a matrix allows the industrial production of high piece numbers, however, the matrix requirement does not allow easy on-site construction or a flexible adaptation of the desired shape of the resulting structure. Even a slightly alternative shape requires new matrix construction. Especially very large or voluminous structures are not easily achievable in a single hydro forming step.

Moreover, these methods require a very high pressure of at least 1000 bar which highly stresses tools and machines. These aspects additionally add to the relatively cost and energy intensiveness of the hydroforming techniques.

EP 2 110 189 Al describes a metal processing technique that uses an inner pressure to achieve a 3-dimensional structure. The technique does not require a 3-dimen- sional matrix but one or more restriction elements instead to guide the deformation of the metal. Herein, two plates of sheet metal are connected along their contour by welding or gluing to form a cavity and further a restriction element is connected between both metal plates. After introduction of an opening into the resulted structure, a pressure medium is applied and the two or more plates are inflated until inflating is restricted by the restriction element. Another aspect of the method described in EP 2 110 189 Al is that the two or more sheet metal plates are assembled simply lying flat onto each other prior to inflating and thus having a principally 2-dimensional form and a single welded un-branched contour after connecting both sheet metal plates by welding. Only by inflating, the structure becomes 3-dimensional. Thus, inflating leads to a structural change in three dimensions, however, the inflating process is only restricted by the single weld and punctual restriction elements.

If - beside the single contour - only a limited number of restriction elements is present to control and restrict the inner pressure deformation, even small irregularities in welding of the contour and positioning of the restriction element may lead to a useless final structure due to undesired deformation upon inflating or variations within a series of construction elements. The use of inner restriction elements also highly limits the possibilities of the resulting shape although the resulting shape is hardly predictable or controllable. The 3-dimensional shape is mainly influenced by the contour of the sheet metal plate and the form, length, number and position of the inner restriction elements may only auxiliary help to achieve a series of equally pressure deformed sheet metal structures. Further, the one or more inner restriction elements have to be attached prior to connecting the at least two plates of sheet metal whereby the cavity to be deformed is formed. This does not allow for on-site modification in order to achieve an alternative final inner pressure deformed structure. This additionally limits the flexibility and options in shaping sheet metal, is error-prone due to the assembling of three distinct pieces and minimal variations in the positioning of the restricting element may result in loss of precision during deformation.

In summary, to date a minimum of two or more plates of sheet metal is used to form the closed cavity to be inflated. Further, either a matrix is applied from the outside to limit the pressure deformation of the sheet metal which is inflated or a restriction element is introduced inside the structure, i.e. inside the cavity, to be inflated which guides and restricts the inflating of the sheet metal cavity according to its position and length. However, the construction of said matrix or said restriction element increases the number of working steps, the cost and the susceptibility to errors of the whole manufacturing process. A matrix has to be constructed for each individual piece, hence individual and flexible adaptation of the desired final 3-dimensional shape is not easily achievable. Using an inner element of any kind to restrict inflating or inner pressure deformation requires very specific determination of the length, properties, form and in particular the position of the element. All techniques in the art require either a matrix to be at the production facility for inflating or assembling of the inner restriction element before closing the cavity to be pressure deformed, i.e. closing the sheet metal pre-structure. This significantly reduces the flexibility of sheet metal structure production.

Thus, there is still a need in the art for a method for manufacturing of inner pressure deformed sheet metal structures which does neither require an outer matrix nor one or more inner elements to restrict inner pressure deformation and which produces inner pressure deformed sheet metal structures that are suitable for construction and other sheet metal structure applications while having a high flexibility with respect to the achievable shapes of the inner pressure deformed sheet metal structures. Moreover, to be suitable for construction and other sheet metal structure applications the resulting structures need to have high precision, i.e. a precision tolerance being in the range of maximal 1%. On the one hand, the 3-dimensional shape of the inner pressure deformed sheet metal structure needs to be predictable from the cut of the sheet metal plate and from the forming of the pre-structure prior to inner pressure deformation, and on the other hand similar pieces within one manufacturing series need to be highly identical to be used in a construction project. Thus, an unpredictable inner pressure deformation and also a high variation of similar pieces within a single product series increases the number of defective parts and rejects which results in higher production, material and energy cost. To reduce cost and energy thereby also protect the environment and supports sustainable use of resources.

Summary of the invention

To overcome the drawbacks of current pressure deforming methods and to achieve metal structures within the 1% tolerance, the invention provides a method for manufacturing an inner pressure deformed sheet metal structure comprising at least one step a) of applying an inner pressure to at least one cavity of a pre-structure; the cavity, optionally also the pre-structure, being formed from one plate of sheet metal; wherein the cavity comprises at least three fixed edges. The inventors have surprisingly found out that a cavity which comprises at least three fixed edges, optionally wherein the at least three fixed edges correspond to the edges of at least three extremities of a pre-structure, is especially beneficial for manufacturing a high precise inner pressure deformed sheet metal structure (optionally inflated sheet metal structure). In the presence of at least three fixed edges, the inner pressure deformation is highly controllable and results in very low deviation in the resulting 3 -dimensional inner pressure deformed sheet metal structures, i.e. results in a deviation or tolerance below 1% in the final structure, so that variations in form and size after inner pressure deformation between single pieces of one manufacturing series are minimal and the precision within the series is appropriately high for construction purposes and other applications. Without intention of being bound by one particular theory, the inventors believe that the high preciseness of the manufacturing method of the invention is based on the characteristic of the cavity which is to be inner pressure deformed comprising at least three fixed edges restricting and guiding the inner pressure deformation of the sheet metal in three directions/dimensions without additional restriction elements or matrices. Thus, the inventors believe that since the application of an inner pressure leads to a deformation of the pre-structure in three dimensions, also at least three restricting parts or edges are necessary to control and stabilize the inner pressure deformation. Optionally, the fixed edges are positioned in parallel and/or correspond to the edges of at least three extremities of the pre- structure which are optionally also in parallel. In an optional embodiment, the at least three edges are in parallel, correspond to the edges of at least three extremities and all extremities have equal size (in length, depth and height).

In contrast to the restriction elements or matrices of the prior art, the restriction edges may be easily applied at any stage of the manufacturing process prior to inner pressure deformation and the number of the restricting edges be increased in order to further increase the preciseness or to achieve an alternative final inner pressure deformed sheet metal structure. Moreover, a wide variety of forms or structures of the final inner pressure deformed structure may be achieved by alternative forming of the pre-structure or by alternative location of the fixed edges or other additional fixed parts of the one plate of sheet metal.

Said one plate of sheet metal may have any form desired by the manufacturer and is not restricted by the exemplary forms depicted herein or presented in the Figures. Prior to inner pressure deformation, the one plate of sheet metal has to be brought in a form that allows for inner pressure deformation, i.e. a pre-structure that comprises at least one cavity which is principally pressure-tight. This is achieved by closing at least part of the surface of said pre-structure by connecting at least part of the contour or inner part of said one plate of sheet metal.

Using a single plate of sheet metal has the advantage that all pieces which are principally necessary to manufacture one inner pressure deformed sheet metal structure are together and already connected so that neither a part can be missing nor the parts of a single structure may be assembled or connected in a wrong way which also significantly reduces the number of defective parts or malfunctions. Another advantage is that transport of the construction elements as flat sheet metal pieces prior to inner pressure deformation require much less space than 3 -dimensional structures which highly reduces transport costs as well. Examples of pre- structures which are flat and thus optimised for transportation are shown in

Figure 14. In principal, any of the pre-structures of the invention can be pressed into a flat form before or after closing of the surface since the volume or final shape is nevertheless achieved again by inner pressure deformation. Especially if a large number of pieces, such as in facades construction in architecture, are required, this may considerably add to the overall cost-effectiveness to the whole construction project.

The present invention provides a method for manufacturing an inner pressure deformed sheet metal structure comprising at least one step a) of applying an inner pressure to at least one cavity of a pre-structure; the cavity, optionally also the pre- structure, is formed from one plate of sheet metal; wherein the cavity comprises at least three fixed edges. Optionally, in step a) a crease, and/or a kink, is formed. Optionally, the cavity, optionally also the pre-structure, is formed from one or more plates of sheet metal. Optionally, the method further comprises step b) and/or step c) prior to step a); wherein in step b) the cavity and the pre-structure is formed from one plate of sheet metal comprising folding and/or bending; and in step c) at least part of the surface of said pre-structure is closed by connecting at least part of the contour or inner part of said one plate of sheet metal, whereby the at least one cavity is obtained. An example of the method steps of an inner pressure deformed sheet metal structure being manufactured by applying an inner pressure to at least one cavity of a pre-structure; the cavity, optionally also the pre-structure, being formed from one plate of sheet metal; wherein the cavity comprises at least three fixed edges is illustrated in Figure 21.

In an optional embodiment of the method, each of the at least three fixed edges comprises a part of the one plate of sheet metal which is closed, or fixed and optionally folded or bent; optionally wherein a crease is formed along a part of the one plate of sheet metal which is bent. In another embodiment, the pre-structure comprises at least three extremities and the at least three fixed edges of the at least one cavity correspond at least partially to the edges of the at least three extremities of the pre-structure; wherein each extremity comprises two sheet metal layers connected to each other via a fixed edge and each extremity is connected to at least one adjacent extremity via a joining part, the joining part being characterised in that it comprises a part of the one plate of sheet metal which is bent, closed or straight.

Optionally, in the method prior to any one of steps a) to c) at least one opening suitable for applying the inner pressure in step a) is introduced into the one plate of sheet metal so that the at least one opening reaches to the at least one cavity; said opening not being closed in step c).

Optionally, in the method prior to any one of steps a) to c) an elastic coat of paint is applied to the pre-structure.

In an optional embodiment of the method, one or more additional parts of the one plate of sheet metal, of the pre-structure or of the inner pressure deformed sheet metal structure are fixed, thereby leading to a changed rigidity and an alternative shape or form of the inner pressure deformed sheet metal structure.

In the method of the invention optionally for fixing and/or closing a method selected from the group consisting of welding, gluing, riveting, screwing and combinations thereof is used.

In an optional embodiment, the at least one opening is introduced by a method selected from the group consisting of laser cutting, cutting, sawing, plasma arc cutting, water jet cutting, drilling and a combination thereof.

The form of the contour of the one plate of sheet metal optionally comprises a form selected from the group consisting of polygon, square, rectangular, rhombus, triangular, trapezoid, parallelogram, tetragon, round, ellipse, and combinations thereof; further optionally the form of the one plate of sheet metal comprises at least one symmetry axis or point of symmetry; further optionally at least two symmetry axes are rectangular to each other.

In another embodiment of the method of the invention, the pre-structure is formed from the one plate of sheet metal in step b) according to one or more bending lines and/or one or more folding lines, optionally a bending line corresponds to a joining part and/or a folding line corresponds to a fixed edge.

Exemplarily, the bending lines and/or folding lines in the one plate of sheet metal are as follows:

a) b)

c d e f g h . c d e f g h i J wherein folding lines are indicated by and bending lines are indicated by ; wherein in a) c + d + e + f +g + h = b, and in b) c + d + e + f+g + h + i + j

= b, wherein the length of a, b, c, d, e, f, g, h, i and j may be selected independently; optionally wherein in a) a = b, d = e, f = g and/or h = c; and optionally in b) a = b, d = e, f = g, h = i and/or j = c.

Optionally, at least one folding line is perforated prior to folding in step b) and closed in step c). Exemplarily, the pre-structure of the invention and the pre-structure formed in step of the method of the invention may comprise at least one form selected from the group consisting of

a) b)

wherein fixed edges are indicated by and joining parts are indicated by ; wherein the length of a, b, c, d, e, f, g, h, i and j may be selected independently; optionally wherein in a) d = e, f = g and/or h = c; and optionally in b) d = e, f = g, h = i and/or j = c.

Optionally, the pre-structure may further comprise one or more of the following substructures:

1.4. 2.1. 2.2. 11

Further provided is a pre-structure being formed from one plate of sheet metal, or from one or more plates of sheet metal, and comprising at least one cavity, wherein the cavity comprises at least three fixed edges; or a pre-structure formed, and optionally closed, according to any embodiment of the method of the invention mentioned herein.

In another aspect, the invention provides an inner pressure deformed sheet metal structure manufactured by any embodiment of the method of the invention mentioned herein, or obtained by applying a pressure medium to at least one cavity of any pre-structure of the invention. Optionally, the inner pressure deformed sheet metal structure further comprises a crease, and/or a kink, along at least one joining part and/or bending line. In an optional embodiment of the inner pressure deformed sheet metal structure, the inner pressure deformed sheet metal structure further comprises one or more connection elements. Optionally, the connection element comprises an eyelet, loop, thread mount, hook or similar.

Further provided is a triangular frame characterized in that one inner pressure deformed sheet metal structure is in triangular configuration or characterized in that at least three inner pressure deformed sheet metal structures are assembled in triangular configuration.

Any pre-structure and/or any inner pressure deformed sheet metal structure and/or any triangular frame of the invention may be used in construction. Optionally, construction comprises architectural or house building construction, engineering, mechanical engineering, heavy or civil construction, complex form creation, vehicle engineering, ship building and/or industrial construction.

Brief description of the drawings

Figure 1: Schematic representation of a structure having three extremities with one exemplary extremity being labelled. Each extremity comprises two sheet metal layers (1 and 2), i.e. parts, of the same plate of sheet metal and is connected to the two adjacent extremities via a joining part (4), i.e. a part of the same one sheet metal plate which may be bent, optionally along a bending line, or straight. The two layers (1 and 2) of the one plate of sheet metal which belong to the same extremity are connected to each other via a fixed edge (3). The fixed edge (3) is a part of the one plate of sheet metal which is fixed or closed and optionally folded or bent. (A) Front Cross-section, (B) side view. 1 and 2: layers of the one plate of sheet metal; 3: fixed edge; 4: joining part.

Figure 2: Cross-section of an exemplary extremity formed from the end parts or part of the contour of the one sheet metal plate. (A) Extremity prior to closing, (B) extremity after closing by connecting at least part of the contour of said one plate of sheet metal. Herein the fixed edge (3) is a part of the one plate of sheet metal which is closed. 1 and 2: layers of the one plate of sheet metal; 3: fixed edge;

4: joining part.

Figure 3: Cross-section of an example of a pre-structure, wherein two joining parts

(4₁) comprise a part of the one plate of sheet metal which is bent and one joining part

(4₂) comprises a part of the one plate of sheet metal which is straight.

Figure 4: Manufacturing steps of an inner pressure deformed sheet metal structure comprising applying an inner pressure to the cavity of a curved pre-structure. A) Cut plate of sheet metal. B) Cut plate of sheet metal with parts to be folded indicated as dashed lines. C) Formed (left) and closed (right) curved pre-structure (side view and cross-section). D) Inner pressure deformed curved sheet metal structure (side view and cross-section).

Figure 5: Exemplary sheet metal plate with contour and inner part. The contour may also be denoted as end part of the one plate of sheet metal.

Figure 6: Schematic cross-section representation of an inner pressure deformed sheet metal structure after inner pressure deformation with indicated creases

(indicated by arrows). These creases optionally remain in the inner pressure deformed sheet metal structure after inner pressure deformation of the joining part and/or bending line of the pre-structure.

Figure 7: Manufacturing steps of an inner pressure deformed sheet metal structure comprising applying an inner pressure to the cavity of a pre-structure. The cavity is formed from one plate of sheet metal and comprises three fixed edges which correspond to the edges of three extremities of the pre-structure. A) The plate of sheet metal, wherein a and/or b are in general independently selected in the range from 10 cm to 5 m. B) The plate of sheet metal, wherein folding and bending lines are marked. Here, c + d + e + f + g + h = b, and d = e, f = g and h = c are in pairs the layers of the three extremities. Their edges have to be connected for closing the surface of the cavity and pre-structure. C) Pre-structure having three extremities and a cavity which comprises the space between the layers of the extremities and the central part of the pre-structure. D) Inner pressure deformed sheet metal structure. Figure 8: Manufacturing steps of an inner pressure deformed sheet metal structure comprising applying an inner pressure to the cavity of a pre-structure. The cavity is formed from one plate of sheet metal and comprises four fixed edges which corres- pond to the edges of four extremities of the pre-structure. A) The plate of sheet metal, wherein a and b are in general in the range of 10 cm to 5 m. B) The plate of sheet metal, wherein folding and bending lines are marked. Here, c + d + e + f + g + h + i + j = b, and d = e, f = g, h = i and j = c are in pairs the layers of the four extremities. Their edges have to be connected for closing the surface of the cavity and pre-structure. C) Pre-structure having four extremities and a cavity which comprises the space between the layers of the extremities and the central part of the pre- structure. D) Inner pressure deformed sheet metal structure.

Figure 9: Exemplary process of the inner pressure deformation of an exemplary pre- structure having three fixed edges in cross-section and production of the inner pressure deformed sheet metal structure. Here, a pre-structure with an already closed surface having three fixed edges and three extremities is shown, wherein from left to right the inner pressure deformation is illustrated in that the layers of the extremities are pushed to the outside and the cavity more and more (from left to right) resembles a round cross-section and a tube-like overall shape if the pre-structure resembles a rectangular form. The deformation from left to right may be stopped at any time point depending on the manufacturer's needs. The deformation is principally irreversible and is as faster from left (prior to deformation) to right (full inner pressure deformation) the higher the applied pressure or the thinner the material. Alternative forming of the pre-structures/cavities and the addition of additional fixed elements may facilitate (e.g. by partial unfolding or by larger angles between the two layers of sheet metal connected via a fixed edge) or restrict the deformation or make it more difficult (e.g. by addition of fixing elements). This alternative forming is also denoted a sub-structure which may be present in the pre-structure. Exemplary substructures are shown in Figure 10.

Figure 10: Examples of sub-structures of pre-structures of the invention (depicted as cross-sections). By alternative forming of the pre-structure and thus of the cavity to be deformed, an alternative inner pressure deformation of the cavity and the pre- structure can be achieved. A pre-structure of the invention can comprise one or more of these sub-sections in individual combination. 1.0 Geometry. The geometrical form of the cavity and the pre- structure considerably defines the shape of the inner pressure deformed sheet metal structure. In general, the smaller the cavity is the bigger the force has to be which necessary to deform it. The force which is necessary may be influenced in different ways by varying the geometry of the cavity and the pre-structure. 1.1. The bending and folding angles can be chosen individually. The smaller the angle of the joining part, the weaker the deformation of the joining part. 1.2. Fixed edges and joining parts, also folding and bending lines in parallel. 1.3. Fixed edges and joining parts, also folding and bending lines are not parallel. 1.4. Curved fixed edges and joining parts. 2.0. Bending. 2.1. The joining parts may be achieved by bending which can have different radiuses and angles. Alternatively, two or more parts of the sheet metal plate between the fixed edges can be bent (triangulation). The larger the angle of the joining part, the lower the forces which are necessary to deform the respective sub-part of the cavity. 2.2. Large bending angle and radius. 2.3. Triangulation/multiple bending. 2.4. No bending, straight joining part. 2.5. Negative bending angle at the joining part. Here, the joining part can be regarded as already deformed and thus requires only a small pressure increase to be fully deformed. 3.0. Welding. Welding as a fixing tool which does not connect or close the surface of the cavity in the first instance but is used to additionally fix parts of the pre-structures. Additional fixing of the extremities is a strategy of increasing the stiffness of the pre-structure locally. Of course this fixation can also be achieved or combined with other methods of closing and or fixing. 3.1. Welding of the joining part. Here, the joining part is welded and therefore the stiffness is increased. In this case, the deformation of the layers at the respective joining part is reduced. 3.2. Bending and perforated welding in a single joining part. Here, the joining part is partially bent and partially perforated and welded, i.e. fixed. This sub-structure allows a gradual influence of the manufacturer on the deformation of the respective part. 3.3. Bent joining part and perpendicular perforated welding, i.e. fixation. Also here, the deformation of the layers at the respective fixed parts of the joining part is reduced and can be used as a tool for gradual deformation by the manufacturer. 3.4 Branching welding line. Here, the joining part is bent and from the joining part an additional fixing line starts being perforated and welded. Also here, the deformation of the layers at the respective fixed parts of the joining part is reduced or even completely prevented. 4.0. Overlapping. By overlapping at least partially the plate of sheet metal with the layers of the cavity, the layer thickness increases which reduces the deformation extent. In general, the overlapping layer is at least partially connected with the surface of the cavity by welding, gluing, screwing, riveting or similar. Also the overlapping layer can be used to stabilize or fix the geometry of the cavity at the respective part before deformation. 4.1. Overlapping. In the left area (double layer of sheet metal) the deformation of the cavity is decreased. 4.2. Overlapping fixing. Here, no deformation will occur on the left side. 5.0. Cutting. By cutting and subsequent closing of the surface of the cavity, the cavity can be split into one or more spaces of smaller size which also reduces the extent of deformation in this part of the pre-structure. This cutting for reducing the size of the cavity can be performed at any part of the cavity and in any extent. Thereby also the form of the cavity can be changed after forming of the pre-structure. 5.1. Boundary cutting of one layer. Here, only one layer is cut and the cut edge is connected to the respective inner part of the adjacent layer. 5.2. Boundary cutting of both layers. 5.3. Partial cutting of one layer at an inner part of the layer. This one layer will be connected, optionally by welding, to the layer below to close the cavity, subsequently. 5.4. Partial cutting of both layers at an inner part of the layer. This is an option of adding additional parts to the pre- structure. 5.5. Cutting of a single layer at a joining part. 5.6. Cutting of two or more layers at a joining part. 6.0. Complex forms. Many different complex forms can be introduced by adjusting the cutting of the one plate of sheet metal and complex folding. In general, sharp angles of the fixed edges or joining parts and the addition of additional fixing elements reduce the local deformation of the cavity. 6.1. Continuous and discontinuous surface/layers of one extremity. 6.2. Branching of a fixed edge leading to a new sub-structure having three extremities. 6.3. Branching of a fixed edge leading to at least one new extremity. 6.4. Branching of a fixed edge leading to at least one new extremity. 6.5. Branching of a fixed edge leading to a crossed pre-structure. 6.6. Multiple branching of a fixed edge leading to a crossed pre-structure having a I-form. This component achieves a similar form as standard I-shaped profiles. Of course, also variants of this form are possible by small variations. 7.0 Attachment. 7.1. Attachment to an optional surface. All pre- structures may be attached to surfaces or to other structures of any material such as concrete, metal, plastic or else. Of course, this also applies to the inner pressure deformed sheet metal structure. The deformation of the layers which are connected to the other surface is limited depending on the strength of the material of the surface. Optionally, the connection can be permanent or reversible.

Figure 11: Integration of individual solutions. These and other connection elements can be added before, at or after any step of the method of the invention. A) Fixation of structure corner. B) Eyelet/loop for handrail integration. C) Connection elements for screwing connection.

Figure 12: Schematic representations to explain the influence of the shape of the cavity on its behaviour upon application of an inner pressure. In general, the smaller the cavity is the bigger the force has to be which necessary to deform it. A) The ratio between the length of k and the length of 1 is l(k):3(l). Upon application to the cavity which comprises part k and part 1, the deformation in part k will be negligible whereas part 1 of the same cavity is fully deformed (Compare before and after deformation). B) The deformation of part k decreases the higher the difference between the length of k to the length of 1 (total length). Also here, part 1 of the same cavity is fully deformed. C) Here, part k is already partially unfolded in that the angle of the fixed edges, i.e. between the two layers which are connected to each other via a fixed edge, are increased in comparison the respective angle in part 1 (cf. cross-sections shown). This is an example for alternative folding as also shown in Figure 10 (2.1 to 2.4).

Figure 13: Exemplary triangular frames. If the triangular frame is characterized in that one inner pressure deformed sheet metal structure is in triangular configuration, the cut of the one plate of sheet metal with indicated folding and bending lines (cf. Figure 13 A), the pre-structure (cf. Figure 13 B (side view and cross-section)) and the inner pressure deformed sheet metal structure (cf. Figure 13 C (side view and cross-section)), i.e. the triangular frame, may be manufactured as illustrated in Figure 13 A-C. Here, the whole triangular frame is manufactured according to the method of the invention from a single plate of sheet metal formed into a single pre- structure having one cavity with three fixed edges. In one manufacturing example a may be 540 cm and b = 36 cm. However, these sizes may vary significantly. In an optional embodiment, b is at least 20 cm or 24 cm and a is at least 200 cm or 240 cm. In principle, there is no upper limit, however, it may be better to handle is a is not

RECTIFIED SHEET (RULE 91 )

ISA/EP more than 20 m or not more than 16 m and b is not more than 3 m. In Figure 13 D) to F) alternative examples of triangular frames are shown. Here, the triangular frames are characterized in that three inner pressure deformed sheet metal structures are assembled in a triangular configuration. For the manufacturing steps of each of the three inner pressure deformed sheet metal structures see Figure 18. For assembling of the triangular frame any of the methods mentioned herein for fixing and or closing may be used, in particular welding, gluing, riveting, screwing or combinations thereof. The connection and/or assembling of the frames may also be achieved by connection elements such as eyelets, loops, thread mounts, hooks or similar or any other connection element or tool a person skilled in the art knows. Assembling may be done before or after deformation. D) Assembling by welding; E) Assembling by screwing; F) Mounting (nested facade frame).

Figure 14: Examples of pre-structures which are flat and thus optimised for transportation. A) and B) Exemplary pre-structures having four fixed edges corresponding to the edges of four extremities being optimised for transportation purposes in that it is relatively flat. C) and D) Exemplary pre-structure having three fixed edges corresponding to the edges of three extremities being optimised for transportation purposes in that it is relatively flat. 3: Fixed edge; 4: Joining part. Figure 15: Manufacturing steps of an exemplary inner pressure deformed sheet metal structure comprising applying an inner pressure to the cavity of a pre-structure having a star- shaped form wherein the outer edges resemble a polygon box and 12 extremities. A) Cut plate of sheet metal. B) Cut plate of sheet metal with indicated folding lines and bending lines. C) Pre-structure wherein the complete outer contour is fixed and thus, 12 fixed edges guide the deformation process.

D) Inner pressure deformed sheet metal structure.

Figure 16: Manufacturing steps of an exemplary inner pressure deformed sheet metal structure with curved edges comprising applying an inner pressure to the cavity of a pre-structure having three fixed edges corresponding to the edges of three extremities. A) Cut plate of sheet metal. B) Cut plate of sheet metal with indicated folding lines and bending lines. C) Formed and closed pre-structure (side view and cross-section). D) Inner pressure deformed sheet metal structure (side view and cross-section). Figure 17: Manufacturing steps of an exemplary inner pressure deformed sheet metal structure comprising applying an inner pressure to the cavity of a pre-structure having four fixed edges. A) Cut plate of sheet metal. B) Cut plate of sheet metal with indicated folding lines and bending lines. C) Formed and closed pre-structure (side view and cross-section). D) Inner pressure deformed sheet metal structure (side view and cross-section).

Figure 18: Manufacturing steps of an exemplary inner pressure deformed sheet metal structure which can be used for assembling of a triangular frame. Here, an inner pressure is applied to the cavity of a pre-structure having three fixed edges corresponding to the edges of three extremities. For one triangular frame, three inner pressure deformed sheet metal structures have to be assembled and/or connected. Examples for connecting/assembling are shown in Figure 13 D-F. A) Cut plate of sheet metal. B) Cut plate of sheet metal with indicated folding lines and bending lines. C) Formed and closed pre-structure. D) Inner pressure deformed sheet metal structure. In one manufacturing example may be 180 cm and b = 36 cm. However, these sizes may vary significantly. In an optional embodiment, b is at least 20 cm or 24 cm and a is at least 60 cm or 80 cm. In principle, there is no upper limit, however, it may be better to handle if a is not more than 20 m or 16 m and b is not more than 3 m.

Figure 19: Manufacturing steps of an exemplary inner pressure deformed sheet which may be suitable as basic structure for ship building. A) Cut plate of sheet metal. B) Cut plate of sheet metal with indicated folding lines and bending lines. C) Formed and closed pre-structure (side view and cross-section). D) Inner pressure deformed sheet metal structure (side view and cross-section). E) After removal of part of the upper part of the deformed sheet metal structure, the final structure may be used as ship (side view and cross-section). Of course, this is a basic structure, however, a person skilled in the art knows from the examples and the explanation given in the description how to adapt the method of the invention to achieve more complex and more sophisticated ship structures.

Figure 20: Manufacturing steps of an exemplary inner pressure deformed sheet metal structure comprising applying an inner pressure to the cavity of a pre-structure having three fixed edges at each of the three sub-structures of the pre-structure. A) Cut plate of sheet metal. B) Cut plate of sheet metal with indicated folding lines and bending lines. C) Formed and closed pre-structure (side view and cross-section). D) Inner pressure deformed sheet metal structure (side view and cross-section).

Figure 21: Manufacturing steps of an exemplary inner pressure deformed sheet metal structure comprising applying an inner pressure to the cavity of a pre-structure having three fixed edges. A) Cut plate of sheet metal. B) Cut plate of sheet metal with indicated folding lines and bending lines. C) Formed and closed pre-structure (side view and cross-section). D) Inner pressure deformed sheet metal structure (side view and cross-section).

Figure 22: Illustration of experimental set-up of the testing procedure to determine the deviation of the inner pressure deformed sheet metal structure in comparison to the pre-structure upon inner pressure deformation. Here, a triangular pre-structure is fixed at two corners (left and right corner) via two metal pieces in L-form in a distance of at least 20 cm on the workbench so that the third corner (middle/front) remains unfixed and lifted. The points of distance measurement are indicated with numbers 1 to 9.

Figure 23: Cross-section of a virtual pre-structure having a T-shape.

Figure 24: Manufacturing steps of an exemplary inner pressure deformed sheet metal structure comprising applying an inner pressure to the cavity of a pre-structure having three and/or four fixed edges at each of the five sub-structures of the pre- structure. A) Cut plate of sheet metal. B) Cut plate of sheet metal with indicated folding lines and bending lines. C) Formed and closed pre-structure. D) Inner pressure deformed sheet metal structure (side view and cross-section). This exemplary sheet metal structure may be further processed to be a lampshade.

Figure 25: Manufacturing steps of an exemplary inner pressure deformed sheet metal structure comprising applying an inner pressure to the cavity of a pre-structure having three fixed edges at each of the two sub-structures of the pre-structure. A) Cut plate of sheet metal. B) Cut plate of sheet metal with indicated folding lines and bending lines. C) Formed and closed pre-structure. D) Inner pressure deformed sheet metal structure (side view and cross-section). This exemplary sheet metal structure may be further processed to be a chair or other piece of furniture.

Figure 26: Manufacturing steps of an exemplary inner pressure deformed sheet metal structure comprising applying an inner pressure to the cavity of a pre-structure having multiple fixed edges at the pre-structure. A) Cut plate of sheet metal. B) Cut plate of sheet metal with indicated folding lines and bending lines. C) Formed and closed pre-structure (side view and cross-sections 1 and 2). D) Inner pressure deformed sheet metal structure. This exemplary sheet metal structure may be further processed to be a table, part of a table or other piece of furniture.

Figure 27: Photo documentation of an exemplary crease which can be seen in the final inner pressure deformed sheet metal structure along a joining part of a pre- structure, in particular along a bending line in an inner pressure deformed sheet metal structure.

Figure 28: A) Photo documentation and B) graphic representation of a kink which is a special form of a crease and can be seen in the middle part of an inner pressure deformed sheet metal structure being inner pressure deformed and inflated from a pre-structure comprising at least three sub-structures with at least three fixed edges, in particular having three sub-structures and with three sixed edges each. An arrow indicates the kink in the graphic representation of an inner pressure deformed sheet metal structure. The kink or crease may be formed upon inner pressure deformation in the centre of a joining part (4) as indicated for example in Figures 1 and 2.

Detailed description

A cavity according to the invention comprises at least three fixed edges. A "fixed edge" (see item 3 in Figures 1 to 3) is a part of said cavity which comprises a part of the one plate of sheet metal which is closed, or fixed and optionally folded or bent. Optionally, a fixed edge comprises a part of the one plate of sheet metal which is closed or a part of the one plate of sheet metal which is fixed and folded. Optionally, the at least three fixed edges of a single cavity are individually selected from the group consisting of a part of the one plate of sheet metal which is closed, a part of the one plate of sheet metal which is fixed, a part of the one plate of sheet metal which is fixed and folded and a part of the one plate of sheet metal which is fixed and bent. In an optional embodiment, an edge may be achieved by folding of the one plate of sheet metal along a folding line or by bending of the one plate of sheet metal along a bending line and fixing along the resulting edge after folding or bending. For fixing and/or closing a method selected from the group consisting of welding, gluing, riveting, screwing and combinations thereof may be used. Optionally, a folding line or bending line is perforated prior to folding or bending of the fixed edge, i.e. the folding line or bending line comprises a perforation line. If the folding line or bending line comprises a perforation line, it denotes that first the one plate of sheet metal is perforated along a folding line or bending line, second the one plate of sheet metal is folded or bent along the folding line or bending line, respectively, and third the one plate of sheet metal is fixed and closed along the folding line or bending line.

Optionally, the fixed edge, the folding line or bending line is in longitudinal direction of a resulting elongated or linear pre-structure. In another optional embodiment, the fixed edges are positioned so that the distance between parallel fixed edges in the inner pressure deformed sheet metal structure is as large as possible.

In another optional embodiment, all fixed edges except one of a structure of the invention are fixed and folded, optionally along a folding line and optionally after perforation of the folding line, and the remaining fixed edge is closed. The fixed edge which is achieved by closing results from connecting at least part of the contour or part of the end parts of said one plate of sheet metal by closing. Such an exemplary fixed edge is depicted in Figure 2. Figure 2A depicts one extremity of a pre- structure comprising two layers (1,2) of the one plate of sheet metal, however, the two layers not yet being closed or fixed at the contour of the one plate of sheet metal. Figure 2B depicts the extremity comprising two layers (1,2) of the one plate of sheet metal and the fixed edge (3) after closing or fixing at least part of the contour of the one plate of sheet metal. This fixed edge is not bent or folded but closed or fixed. Also, in case of a curved pre-structure to achieve a curved inner pressure deformed sheet metal structure, the fixed edges may be achieved by closing at least part of the contour or end parts of the one plate of sheet metal of the pre-structure (cf. Figure 4).

Optionally, a pre-structure of the invention comprises at least three extremities and the at least three fixed edges of the at least one cavity correspond at least partially to the edges of the at least three extremities of the pre-structure; wherein each extremity comprises two sheet metal layers connected to each other via a fixed edge and each extremity is connected to at least one adjacent extremity via a joining part, the joining part being characterised in that it comprises a part of the one plate of sheet metal which is bent, closed or straight. An extremity is a part of the formed and closed pre-structure and all extremities of a structure are made from the same one plate of sheet metal. In general, an "extremity" comprises two sheet metal layers connected to each other via a fixed edge and each extremity is connected to at least one adjacent extremity via a joining part. An exemplary extremity comprises a form as depicted in Figure 1. In Figure 1 , it can be seen that one extremity in general comprises two parts or "layers" of the one plate of sheet metal (cf. layer 1 (1) and layer 2 (2) in Figures 1 to 3) which are connected to each other via a fixed edge (3).

A "joining part" comprises a part of the one plate of sheet metal which is bent, straight or closed (cf. item 4 in Figures 1 to 3). Optionally bending is performed along a bending line. Optionally all joining parts of a pre-structure are bent, optionally along a bending line. In another optional embodiment, all except one joining part of a structure are bent, optionally along a bending line and the remaining joining part is achieved by closing at least part of the contour or the end parts of the one plate of sheet metal. One or more joining parts may also be closed for achieving a curved pre-structure (cf. Figure 4). Here, for closing, any one of the closing methods mentioned herein may be used. In general, each joining part of any structure of the invention may independently be selected from the group consisting of bent, straight and closed. Optionally, the joining part can be seen in the final inner pressure deformed sheet metal structure in form of a crease along the joining part (see Figures 6 and 27). In particular, the crease is visible along a bending line after inner pressure deformation. As can be seen in Figure 28, a kink may be formed in the centre of a joining part as a special form of a crease.

If a pre-structure comprises at least three extremities, then the fixed edges may correspond to the edges of the extremities and the joining parts are located near the central part of the sheet metal structure and can be regarded as the origin of the extremities. The fixed edge can then be regarded as the part of the structure or of the extremity which is furthest away from the centre of the structure and from the beginning of the extremity. Further, in general in the presence of at least three extremities, the angle a of a joining part is larger than the angle β of a fixed edge. For illustration of inner angle a and angle β please refer to Figures 1 to 3.

In an alternative embodiment, the joining part of one or more of the at least three extremities may be straight. Here two extremities of the pre-structure share a sheet metal layer. This embodiment is illustrated in Figure 3, wherein the joining part 4₂ is straight. Of course, the angles a or β of the joining parts or fixed edges may independently be selected from each other within a single pre-structure.

The 3 -dimensionality may be applied to the structure prior to inner pressure deformation by forming comprising bending and/or folding of the pre-structure and not only by the inner pressure deformation process itself. The overall structure of the resulting "inner pressure deformed sheet metal structure" (herein also denoted as "final sheet metal structure", or simply as "final structure" or "resulting structure", optionally also as "inflated sheet metal structure") is predetermined by the form and thickness of the sheet metal plate, the forming of the pre-structure comprising folding and bending and the parameters of the application of the inner pressure.

"Sheet metal structure", "metal structure" and "structure" are understood as synonyms in the sense of the invention. Upon an inner pressure (optionally upon inflating), the optionally already 3-dimensional form of the pre-structure is deformed whereby the final inner pressure deformed sheet metal structure is manufactured. In addition, depending on alternative forming of the pre-structure from the one plate of sheet metal, variations in the inner pressure deformation conditions and parameters and an alternative positioning of the fixed edges alternative final forms of the inner pressure deformed sheet metal structure are easily achievable. Thereby, the invent- tion also allows for alternative shapes of the final sheet metal structure upon easy and quick on-site adaptation of the manufacturing process and also after closing at least part of the surface of the sheet metal pre-structure. In this way, the method of the invention allows a high level of complexity in 3 -dimensional shapes of the resulting final sheet metal structure.

The term "structure" is used herein for any structure, final structure, pre-structure and intermediate structure. The "surface" of a structure is the outer part of a structure in contrast to a cavity inside the structure. The expression "at least part of the surface" denotes that a cavity of the invention may only be surrounded by a part of the whole surface of a pre-structure.

Also provided is a pre-structure being formed from one plate of sheet metal and comprising at least one cavity, wherein the cavity comprises at least three fixed edges; or a pre-structure formed, and optionally closed, according to any embodiment of the method of the invention. A "pre-structure" in the sense of the invention is formed from one plate of sheet metal comprising folding and/or bending and is understood to mean any structure which is - also temporarily - formed, manufactured, produced and/or obtained in any way or by any technique before the final product, i.e. the inner pressure deformed sheet metal structure, is achieved. A pre- structure may be open or closed depending on the stage of the manufacturing process: for example the pre-structure which is formed by folding and/or bending in step b) of the method of the invention may be regarded as "open", whereas the pre- structure after closing in step c) of the method of the invention, i.e. after connecting at least part of the contour or inner part of the one plate of sheet metal, whereby the at least one cavity is obtained, may be regarded as "closed pre-structure". The overall shape and form, also 3 -dimensional form, of the pre-structure is, however, not significantly changed or not changed by closing the pre-structure in step c) of the method of the invention. Typically, a pre-structure is not yet deformed by an inner pressure, or optionally not yet inflated, as in step a) of the method of the invention. Optionally a pre-structure comprises a star-shaped cross-section due to the presence of at least three extremities.

Principally, to obtain the inner pressure deformed sheet metal structure, a plate of sheet metal comprising any form which can be selected by the manufacturer and not limited to any specific form or shape is formed into a pre-structure comprising at least one cavity comprising at least three fixed edges, which is optionally already 3 -dimensional. The form of this pre-structure is not restricted and may be chosen individually by the manufacturer. However, the skilled person knows that for achieving cavities that may later be deformed by an applied inner pressure, said pre- structure should be formed in a way that the closing at least part of the surface by different closing means, such as welding, gluing and others, is possible.

"Forming" of the pre-structure from one plate of sheet metal in step b) of the method of the invention denotes that the form of a single plate of sheet metal is changed by any method which is known by a person skilled in the art, in particular by folding and/or bending, e.g. by air bending, bottoming, coining, three-point bending, wiping, roll bending, elastomer bending and joggling. Alternatively, a pre-structure may be partially formed by casting and optionally further processed by bending and/or folding, thereby also leading to a pre-structure of the invention.

A structure or any other body is "3 -dimensional" if the structure or else has expansion in all three dimensions according to the general understanding of a person skilled in the art. Said expansion in all three dimensions is generally expressed in length, width and depth (or height).

One very important advantage of using only one plate of sheet metal to be formed into the pre-structure of the invention over the use of two or more plates of sheet metal is that assembling of the parts of the structure is highly facilitated, whereby errors during the manufacturing process of the final structure are reduced. Thereby, the overall industrial process is fastened, the error rate minimized and no additional marks of pieces or the description of now unnecessary working steps is required.

The "plate" of sheet metal or "one plate" of sheet metal of the invention may have every geometrical form or every combination of geometrical forms or every other desired form or shape as pre-determined and desired by the manufacturer. The form of the sheet metal is determined by the form of the contour and the inner part of the plate (see Figure 5). "Contour" in the sense of the invention denotes the end part or outer part of the sheet metal plate of the invention. The form of the contour of the one plate of sheet metal may comprise a form selected from the group consisting of polygon, square, rectangular, rhombus, triangular, trapezoid, parallelogram, tetragon, round, ellipse, and combinations thereof; optionally the form of the one plate of sheet metal comprises at least one symmetry axis or point of symmetry; optionally at least two symmetry axes are rectangular to each other. Optionally, folding lines and/or bending lines are parallel to at least one symmetry axis. The geometrical forms polygon, square, rectangular, rhombus, triangular, trapezoid, parallelogram, tetragon, round and ellipse are to be understood according to their general meaning in the field of geometry.

"Symmetry axis" and "point of symmetry" are to be understood according to their general meaning in geometry. Thus, a symmetry axis is a line such that, if a perpendicular is constructed, any two points lying on the perpendicular at equal distances from the axis of symmetry are identical and a point of symmetry is when every part has a matching part or point that has the same distance from the central point (=symmetry point or point of symmetry) but is in the opposite direction perpendicular to the axis. The point of symmetry is a point about which a figure or graph can be rotated around 180° ending up looking identical to the original.

Although, no symmetry is necessary at all to perform the method of the present invention, it may simplify the closing of at least part of the surface of the pre-struc- ture by connecting at least part of the contour or inner part of the one plate of sheet metal step c) of the method of the invention, whereby the at least one cavity is obtained. If the one plate of sheet metal does not comprise at least one symmetry axis, then the cavity or pre-structure formed in step b) of the method of the invention is not closed at the contour or end part of the sheet metal plate but the respectively shorter layer or part is connected to an inner part of the sheet metal plate and still at least one cavity is obtained in the pre-structure. An edge of a structure may derive from the forming process, such as from folding or bending the plate of sheet metal or from closing at least a part of the contour or part of the end parts of the one plate of sheet metal, optionally, an edge of a structure corresponds to a fixed edge of a pre-structure of the invention if it is at least fixed after folding or bending or closed. The "inner part" (also layer) is principally the remaining part of the sheet metal plate which is surrounded by the contour, however, there is no strict differentiation between the edge or contour and the inner part of the one plate of sheet metal. A person skilled in the art knows very well from his general knowledge which part of a sheet metal plate is regarded as contour and which part is regarded as inner part. Figure 5 presents an exemplary plate of sheet metal. The one plate of sheet metal may have a surface which is not absolutely flat or plain but waved, rough, crimped, corrugated, or else, or a mixture thereof.

In an optional embodiment of the method of the invention, the contour of the one plate of sheet metal is brought or cut in a specific pre-determined form prior to the forming of the pre-structure in step b) of the method of the invention. The determination of the specific form or contour of the one plate of sheet metal which is required to obtain a specific desired pre-structure or inner pressure deformed sheet metal structure can be calculated using engineering and design tool software such as Catia V5 (Dassault Systemes, Velizy-Villacoublay, France), Solidworks (Dassault Systemes, Velizy-Villacoublay, France), ProEngineer (Parametric Technology Corporation, Needham, MA, USA) or Inventor (Autodesk, San Rafael, CA, USA). A person skilled in the art is well familiar with this engineering software and design tools. For a step-by-step calculation, please refer to the examples section.

The form or contour of the sheet metal plate can be achieved by any "cutting" technique known to a person skilled in the art such as shearing, blanking, plasma arc cutting, plasma cutting, cutting, laser cutting, sawing, punching or stamping, water jet cutting and combinations thereof, or other methods which are known to a person skilled in the art. In general, shearing, blanking, plasma arc cutting, plasma cutting, cutting, laser cutting, sawing, punching or stamping and water jet cutting are to be understood according to the general knowledge of a person skilled in the art. A person skilled in the art knows which methods and devices are to be used for shearing, blanking, plasma arc cutting, plasma cutting, cutting, laser cutting, sawing, punching or stamping and water jet cutting. Punching machines can for example be obtained from Trumpf (Ditzingen, Germany), machines for plasma cutting from Migatronic (Wettenberg, Germany) or from Rehm (Uhingen, Germany). Further information thereon can also be taken from D.A. Stephenson and J.S. Agapiou "Metal cutting theory and practice" (CRC Taylor & Francis, 2006). The aforementioned cutting techniques may also be used for introducing the at least one opening suitable in the one plate of sheet metal or in the open or closed pre-structure for applying an inner pressure to at least one cavity of a pre-structure and for perforating a folding line. Optionally, the one plate of sheet metal is cut into a pre-determined form, i.e. the contour of the one plate of sheet metal is achieved by laser cutting. For this purpose, a standard industrial laser may be used, such as obtainable from Trumpf (Ditzingen, Germany; e.g. TRUMATIC L 3030), Bystronic (Niederonz, Switzerland), Amada (Haan, Germany) or others. In general, laser cutting uses a high powered laser to cut through the sheet metal according the operator's settings. A laser beam is typically 0.2 mm or 0.4 mm in diameter at the cutting surface with a power of 1000 to 2000 W. A series of mirrors and lenses direct and focus a high- energy laser beam onto the surface of the sheet where it is to be cut by melting the material and leads to a very specific cut profile. The resulting contour of the sheet metal plate may be individually chosen by the skilled person performing the method of the invention.

"Sheet metal" principally denotes any metal in form of a plate. The sheet metal of the invention may comprise different metals such as aluminium, brass, copper, steel, tin, nickel, titanium, silver, gold, platinum and mixtures thereof. Optionally, the sheet metal is aluminium or steel sheet metal, or the sheet metal is steel. The thicknesses of the sheet metal of the invention can also vary significantly. The sheet metal of the invention and in particular the one plate of sheet metal has a thickness in the range of 0.5 mm to 3 mm, or of 0.55 mm to 2.5 mm, or of 0.6 mm to 2 mm or of 0.6 mm to 1.5 mm, or of 0.6 mm to 1 mm, or a thickness of 0.6 mm, 0.65 mm, 0.7 mm, 0.75 mm, 0.8 mm, 0.85 mm, 0.9 mm, 0.95 mm, 1 mm or of 1.5 mm. The size, i.e. length and width of the sheet metal is principally not limited. A typical proportion of a rectangular sheet metal plates is 1 : 1.5 or 1 :2 prior to cutting of the plate to gain the desired contour of the one plate of sheet metal for the method of the invention. The length and/or width of the sheet metal plate may typically vary independently between 0.05 m and 30 m, between 0.1 m and 20 m, between 0.2 m and 15 m, between 0.3 m and 10 m, between 0.5 m and 8 m, between 0.5 m and 6 m, between 1 m and 3 m, between 1.5 m and 3 m or between 1.5 and 2 m. Exemplarily, the sheet metal plate may have a size of 0.2 m x 0.5 m, 1 m x 1.25 m, 1 m x 1.5 m, 1 m x 1 m, 1 m x 3 m, 0.5 m x 3 m, 0.5 m x 4 m, 0.5 m x 5 m, 1 m x 5 m, 1 m x 6 m, 1 m x 4.5 m, 1 m x 4 m or 1.5 m x 3 m or 1.25 m x 2.5 m. Another exemplary sheet metal plate has a thickness of 0.8 mm and a size of 1.5 m x 3 m or 1.25 m x 2.5 m.

"Bending", "folding" and "casting" are to be understood according to their general meaning in the field of metal processing and not be understood in a restricting or narrow way. Using different dies, bending of sheet metals as well as casting allows for forming of 3 -dimensional structures with a customized mould. Further information can also be taken from the literature, e.g. from O.W. Boston "Metal processing" (Wiley, 1955), R. Fournier and S. Fournier "Sheet metal handbook" (Penguin, 1989), H. Tschatsch "Metal forming practise: processes - machines - tools" (Springer, 2006), M.P. Groover "Fundamentals of Modern Manufacturing: Materials, Processes and Systems" (John Wiley and Sons, 2010), J. Beddoes, M.J. Bibby "Principles of metal manufacturing processes" (Butterworth-Heinemann, 1999) or W.F. Hosford and R. Caddell "Metal Forming: Mechanics and Metallurgy"

(Cambridge University Press, 2011).

"Casting" is a metal manufacturing process by which liquid metal is usually poured into a mould containing a hollow cavity of the desired shape, and then the liquid metal is allowed to solidify. The solidified metal is also known as a casting and is ejected or broken out of the mould to complete the process. Further information can be taken e.g. from T.V. Ramana Rao "Metal Casting: Principles and Practice" (New Age International, 2007) and R.A. Flinn "Fundamentals of metal casting" (Addison- Wesley Pub. Co., 1963). "Bending" is a manufacturing process of sheet metal whereby metal is plastically deformed and its shape is changed. It allows for bringing sheet metal into a specific angle and creates precise metal parts for construction. In general, bending refers to the change of the shape about one axis or bending line, whereby the material surface is not or only marginally changed. Bending is a simple, cheap and convenient way for industry. Further information can be taken e.g. from M.P. Groover "Fundamentals of Modern Manufacturing: Materials, Processes and Systems" (John Wiley and Sons, 2010), J. Beddoes, M.J. Bibby "Principles of metal manufacturing processes" (Butterworth-Heinemann, 1999) or O.D. Lascoe "Handbook of fabrication processes" (ASM International, 1988). Typically standard die sets and bending brakes, such as press brakes are used (cf. for example S.D. Benson "Press brake technology: a guide to precision sheet metal bending", SME, 1997). For this, the sheet metal is placed on the die and fixed and either the die or a negative of the die is moved so that the shape of the sheet metal is changed according to the form of the die. During bending, the inside surface of the metal is compressed whereas the outside of the metal is stretched. The "bending line" in the sense of the invention denotes the line along which the sheet metal plate is bent.

Bending is generally achieved by the use of different dies. A person skilled in the art knows which die should be used for a specific purpose and how to determine the maximal bending radius of a specific material to achieve a specific angle of the bent metal and thus a specific pre-structure of the invention. Dies for bending which may be used in the invention are for example 90° V-shape dies, acute angle dies, gooseneck dies or offset dies. Using a 90° V-shape die, in particular 90° angles may be formed. Using an acute angle die, the operator can apply a specific angle or radius to the sheet metal depending on the applied pressure. The higher the pressure the sharper the angle of the sheet metal will be. It is a convenient way to bend sheet metal; however, this kind of metal processing requires an experienced operator to achieve a specific bending angle. Especially, 90° V-shape and acute angle dies may be used to bend the sheet metal at preselected bending line. With gooseneck dies, U-shape parts are formed. Rotary bending dies are also applicable for bending sheet metal into a specific angle. For specific die design and manufacture it is exemplarily referred to D.A. Smith "Die design handbook" (SME, 1990), I. Suchy "Handbook of die design" (McGraw-Hill Professional, 1998) and V. Boljanovic "Sheet metal forming processes and die design" (Industrial Press Inc., 2004). In the method of the invention, bending may for example be achieved using a TruBend 5000 of Trump f (Ditzingen, Germany).

"Folding" is the pressing and shaping of sheet metal on a press brake usually also into an inner angle close to 0° or at 0° or outer angle close to 180°. It is not as commonly used as bending although very similar to it. By folding, the material is stressed beyond the yield strength and partly beyond the ultimate tensile strength. Like for bending, the change of the shape appears about one axis or folding line, whereby the material surface which is not in the area of the folding line is not or only marginally changed along the folding line where the material is even thinner after folding than after bending and thus once sheet metal has been folded in a outer 180° angle, i.e. an inner angle close to 0° or at 0°, the flexibility of the metal especially in the area of the folding line is greatly reduced so that the metal breaks on the outside surface. In the method of the invention, folding may for example be achieved using a TruBend 5000 of Trump f (Ditzingen, Germany).

For achieving an "fixed edge" the one plate of sheet metal is fixed or closed and optionally bent or folded in an inner angle β (cf. Figure 1) which is 90° or smaller than 90°, smaller than or exactly 80°, 75°, 70°, 65°, 60°, 55°, 50°, 45°, 40°, 35°, 30°, 25°, 20°, 18°, 16°, 14°, 12° or 10°, or smaller than or exactly 9°, 8°, 7°, 6°, 5°, 4°, 3°, 2°, 1° or close to 0° or 0°. "Close to 0°" denotes typically an angle below 1°.

However, an inner angle β = 0° might not be possible due to the presence of the two sheet metal layers, thus 0° denotes the maximal bending or folding which may be performed by any bending or folding technique known in the art. In general, the method of the invention uses folding for forming a fixed edge. Nevertheless, the person skilled in the art knows which technique, e.g. folding or bending or a combination thereof, is to be applied to result at a certain inner angle β of two sheet metal layers of a pre-structure of the invention. The "folding line" in the sense of the invention denotes the line along which the sheet metal plate is folded. Its shape depends on the applied die, tool or machine and can thus be selected according to the specific demands of the manufacturer. In general, the folding line and the bending are linear. Further information on metal folding can be taken from "Producing Sheet Metal Components and Assemblies" (Benchmark Media UK, 2008), B.J. Black "Workshop Processes, Practices and Materials" (Elsevier, 2004) or S. Chatti "Production of Profiles for Lightweight Structures" (BoD, 2006).

Optionally, at least one folding line or bending line is perforated prior to folding and closed in step c) of the method of the invention when at least part of the surface of the pre-structure is closed by connecting at least part of the contour or inner part of the one plate of sheet metal, whereby the at least one cavity is obtained. In this case at least one folding line or bending line comprises a perforation line. In this case, prior to folding the folding line, or prior to bending the bending line, the respective line is "perforated", i.e. partially cut or slit which facilitates the folding by significantly reducing the forces which are required for the folding process. Thereby, also the accuracy of the folding process is increased. A perforated bending line or perforated folding line is also denoted as "perforation line". After perforating, the respective parts are still connected and need not to be identified or assigned to each other. The perforation of the sheet metal plate may be done by any cutting technique known to a person skilled in the art as mentioned above, optionally by laser cutting, plasma arc cutting, plasma cutting, cutting, water jet cutting or else. Optionally, the slits are introduced, i.e. the folding or bending line is perforated, using laser cutting with a standard laser obtainable from Trumpf (Ditzingen, Germany), Bystronic (Niederonz, Switzerland), Amada (Haan, Germany) or others. The slits (= cuts) along the folding or bending line are typically 5 mm to 20 cm in length, 1 cm to 15 cm in length, 3 cm to 12 cm in length, 5 cm to 10 cm in length or 10 cm. The slit width is typically the width of a standard laser beam partially depending on the laser heat or the slit width is in the range of 0.1 mm to 10 mm, in the range of 0.2 mm to 8 mm, or in the range of 0.3 mm to 5 mm, or 0.4 mm. In this respect it should be noted that the width of a standard laser (i.e. in the range of 0.1 mm to 0.4 mm) is suitable to perforate a sheet metal plate having a thickness in the range of 0.1 mm to 0.5 mm, in case of thicker sheet metal plates, the width of the cuts or slits typically corresponds to the thickness of the sheet metal plate, i.e. if the sheet metal plate has a thickness of 3 mm, then the width of the cuts should be 3 mm. The distance between two slits is generally in the range from 1 mm to 5 cm, from 2 mm to 1 cm, from 3 mm to 8 mm or the distance between two slits is 5 mm. A typical example of a perforation line is a slit length of 10 cm, a slit width of 0.4 mm and a distance between two slits of 5 mm. In general, the depth of a slit corresponds to the thickness of the sheet metal plate. The skilled person is well aware of the fact that the dimensions of the slits may vary depending on the dimensions of the metal plate. Optionally, the folding line is perforated over the complete length of the bending or folding line; however, it may also be sufficient if the folding line is only partially perforated. Within one plate of sheet metal, one or one or more or all folding lines or bending lines may be perforated. Bending lines may be perforated according to folding lines.

Optionally, to facilitate folding of the one plate of sheet metal to achieve a fixed edge of a cavity of pre-structure, folding is performed along a folding line which is to be determined by the manufacturer according to the desired final inner pressure deformed sheet metal structure and the folding line further comprises a perforation line.

It may be necessary to close the slits prior to inner pressure deforming of the cavities in case that the slits are located or have a size so that they might prevent the increase of the pressure inside the cavity, i.e. the cavity is not pressure-tight or air-tight without closing the slits. The closing of the slits is performed according to the closing at least part of the surface of the pre-structure by connecting at least part of the contour or inner part of said one plate of sheet metal, whereby the at least one cavity is obtained, optionally one, two, three, four, five or more cavities. In general, closing of the slits of a perforation line may be performed by any of the closing methods described below, comprising e.g. welding, gluing, riveting, screwing and combinations thereof. Optionally, welding is used for closing the slits. The closing of the perforation lines also has a double effect: On the one hand, the cavity is made pressure- tight and, on the other hand, the fixed edges are applied. That means if a fixed edge is folded along a folding line or bent along a bending line and this folding line or bending line comprises a perforation line, then the closing of the slits of the perforation line corresponds to the fixing or closing of the fixed edge. Thereby, the closed perforation line may serve as fixed edge for guiding the inner pressure deformation of the at least on cavity of the pre-structure in three dimensions. If a fixed edge is not folded or bent along a bending or folding line which does comprise a perforation line, then the fixing is achieved by additionally fixing the edge by a fixing method of the invention. If a fixed edge is neither folded nor bent, the fixed edge is achieved by closing, i.e. by connecting at least part of the contour or inner part of said one plate of sheet metal (see Figure 3). Thus, fixing or closing, both which are achieved by similar methods, such as welding, gluing, riveting, screwing and combinations thereof, is the most important element for guiding and restricting the inner pressure deformation of the cavity and thereby also of the pre-structure of the invention to arrive at the inner pressure deformed sheet metal structure of the invention.

The closing of the slits along the folding line or bending line due after perforation, leads to a fixation of parts of the sheet metal plate and of the structures of the invention and to an increased stiffness or rigidity in the area or region of the folding line or bending line, i.e. to a fixed edge of the invention. In the same manner, also folding or bending lines with or without being perforated before can be fixed and/or stiffened. In summary, all parts of the sheet metal plate and of the structures of the invention can be fixed by a method such as welding, gluing, riveting, screwing and mixtures thereof and thereby the area around the fixation is stiffened and has an increased rigidity. The stiffened areas or parts influence the unfolding behaviour upon inner pressure deformation in this local region, normally the inner pressure deformation is restricted in such a stiffened area. Therefore, fixing is an optional tool for the manufacturer to determine the final structure of the inner pressure deformed sheet metal structure and thus to control the deformation process. Fixing may be irreversible, such as by welding, or reversible, such as by screwing. Gluing may be reversible or irreversible depending on the glue which is used for fixing and/or closing. Thus, "fixing" denotes the use of a technique such as welding, gluing, riveting, screwing and mixtures thereof of to stiffen or fix pre-determined parts of the sheet metal plate and the pre-structure prior to applying the inner pressure to the at least one cavity which produces the inner pressure deformed sheet metal structure. In principle, an equal effect is achieved by closing which will be explained in more detail below.

Thus, fixing is a tool to limit or restrict the deformation upon pressure. Fixing may also be used after inner pressure deformation to additionally stiffen the manufactured inner pressure deformed sheet metal structure and/or to fix the final structure. The fixed edges or fixed parts may later be used as connection areas for connection elements and for connecting one or more inner pressure deformed sheet metal structures to each other or to connect the inner pressure deformed sheet metal structure to other construction elements, such as walls, metal constructions or else, or for the addition of other metal or non-metal parts or elements. Exemplary connection elements comprise eyelets, loops, thread mounts, hooks or similar.

In one embodiment of the method of the invention, one or more additional parts of the one plate of sheet metal, of the pre-structure or of the inner pressure deformed sheet metal structure are fixed, thereby leading to a changed rigidity and an alternative shape or form of the inner pressure deformed sheet metal structure of the invention. Optionally, fixing is performed by welding using a welding station such as obtainable from Fronius International (Pettenbach, Austria) or EWM Group (Mun- dersbach, Germany) or similar, optionally as a welding system in connection with a robot such as obtainable from KUKA (Augsburg, Germany) or ABB (Zurich, Switzerland).

The closing of at least part of the surface of the pre-structure of the invention by connecting at least part of the contour or inner part of the one plate of sheet metal, whereby the at least one cavity is obtained, is achieved by connecting at least part of the contour or inner part of said one plate of sheet metal which already comprises at least three fixed edges or gains at least three fixed edges by any closing method mentioned herein. Via applying a pressure medium to at least one cavity of the closed or pressure-tight pre-structure, the inner pressure deformed sheet metal structure is produced. Prior to applying an inner pressure to a cavity, optionally prior to inflating, at least part of the surface of the structure has to be closed in order to achieve a pressure-tight cavity. Thus, "closing" connects at least part of the contour or end parts or inner part of said one plate of sheet metal, whereby at least one cavity is obtained, optionally two, three, four, five, six, seven, eight or more cavities are obtained which may then be deformed upon an inner pressure, or optionally be inflated, to produce the inner pressure deformed sheet metal structure. Hence, at least part of the surface of the pre-structure is closed. For closing the same methods as for fixing may be used, e.g. a technique such as welding, gluing, riveting, screwing and mixtures thereof. Aforementioned methods are also denoted as closing and fixing methods. Closing may for example be performed using a welding station such as obtainable from Fronius International (Pettenbach, Austria) or EWM Group (Mundersbach, Germany) or similar, optionally in connection with a robot such as obtainable from KUKA (Augsburg, Germany) or ABB (Zurich, Switzerland).

Welding, gluing, riveting, screwing are to be understood according to the general knowledge of a person skilled in the art. A person skilled in the art knows which methods and devices are to be used for welding, gluing, riveting and/or screwing.

In general, the one plate of sheet metal, the pre-structure and the inner pressure deformed sheet metal structure can be covered with a paint, coat of paint, priming paint, coating, rust protection, weather protection, heat protection, cold protection or be anodised. Optionally, the paint is an elastic paint and applied to the one plate of sheet metal and/or to the pre-structure. The elastic paint may for example be obtained from OWATROL INTERNATIONAL (Barcelona, Spain) or Ronald Hoeseler-POR15 GmbH (Berlin, Germany). This is additionally advantageous to facilitate construction processes since the structures can be transported as pre- structures and be inner pressure deformed on the construction site. They do not have to be painted after deformation but are ready for their respective final use in construction. "Inner pressure deformed sheet metal structure" or also "final structure" denotes a 3 -dimensional sheet metal structure which may be manufactured by any embodiment of the method of the invention. Said inner pressure deformed sheet metal structure is at least partially deformed by the application of an inner pressure to the inside of the structure, namely to a cavity of the structure in step a) of the method of the invention. A "cavity" or also "inner compartment" of a structure or pre-structure of the present invention denotes a hollow or space which is principally enclosed, i.e. pressure-tight, except of the opening which is required for applying an inner pressure and which is surrounded by at least part of the one plate of sheet metal. The "opening" is a hole in the one plate of sheet metal through which the pressurised medium may be applied to the cavity. In general, an opening is "suitable for applying the inner pressure" if the hole in the sheet metal plate has a size and form which is appropriate to connect or adapt a tube or pipe which is connected to the device for introducing a pressurised medium. An exemplary opening has a round form and is between 1 to 20 cm, or 5 to 15 cm or 7 to 12 cm or 8 to 11 cm or 9 cm or 10 cm in diameter. However, a person skilled in the art is well aware of the fact that the opening may have another form or a smaller or bigger size depending on the pressure medium used. For example, in case of a highly viscous medium or a foam being used for inner pressure deformation, the size of the opening may be up to 50 cm or more in diameter. The opening may also be equipped with a device which facilitates the connection of the device for introducing the pressurised medium, such as an elastic item or a hollow riveting or a metal piece of pipe connected to the plate of sheet metal at the opening by a closing or fixing method mentioned herein, such as by welding or gluing. A device for introducing a pressurised medium may be a pump, compressor or similar. A cavity to be inner pressure deformed by the method of the invention comprises at least three fixed edges. In an optional embodiment, the fixed edges correspond at least partially to the edges of at least three extremities of a pre-structure. In this case, the cavity comprises at least the space between the layers of the extremities and the central part of the pre-structure which are connected to the cavity. In Figures 1 to 3 exemplary cavities are shown as a grey area. Here, the cavity comprises the space of the extremities. By applying an inner pressure to the cavity, the cavity is deformed which means that the sheet metal or parts of the sheet metal plate surrounding the cavity (these parts may also be denoted as "walls" of a cavity), optionally comprising one or more extremities, are pushed to the outside, and the walls or sheet metal layers or parts of sheet metal which are located opposite to each other move away from each other, thereby producing said inner pressure deformed sheet metal structure. Upon application of the inner pressure, the structure more and more becomes round on the outside, i.e. resemble a sphere/globe or tube/pipe depending on the more square or more rectangular extension of the cavity in two dimensions. In Figure 9, the process of inner pressure deformation is exemplarily shown in cross-section. In the sense of the present invention, "inner pressure deformed", "deformed" and "pressure deformed" are meant as synonyms. In particular, if the expression "inner pressure deformed sheet metal structure" is used, the final structure of the method of the invention, i.e. the end product, is meant.

The inner pressure deformation of at least one cavity of the pre-structure has a number of advantageous effects which come to light in the final inner pressure deformed sheet metal structure. First only by inner pressure deformation the structure becomes significantly stiff and highly rigid; and second only after inner pressure deformation, the structure has its desired functional form. Although the functional form of the inner pressure deformed sheet metal structure is principally pre-determined in the specific form or contour of the one plate of sheet metal and by forming the plate into the pre-structure in step b) of the method of the invention, it only becomes functional by inner pressure deformation or "unfolding". This procedure also allows for alternative forms of the final inner pressure deformed sheet metal structure depending on the inner pressure deformation conditions and parameters. Inner pressure deformation "conditions" or "parameter" are for example the pressure medium which is introduced through the opening into the cavity to be deformed, the strength of the pressure applied to at least one cavity of the pre-structure, the time period of application of the inner pressure, i.e. the time period of deformation, the temperature, the dimension, size and local form of the cavity, thickness of the one plate of sheet metal surrounding the cavity and the material of the sheet metal. Also temperature plays a role, however, the method of the invention is principally to be performed at general working temperatures, i.e. in the range of 0 °C to 50 °C, 5 °C to 40 °C, 10 °C to 35 °C or 15 °C to 30 °C. As already mentions, the specific form of the structure itself has an influence on the resulting final structure. It is also obvious to a person skilled in the art, that many different pre-structures can be formed from sheet metal plates having the same pre-determined shape or cut (compare Figures 7 and 8).

In general, the deformation requires a higher pressure, a longer period of time and/or a higher working temperature the thicker the sheet metal plate, the higher the stiffness of the material of the sheet metal plate, the smaller the cavity of the pre-struc- ture and/or the more parts of the at least one cavity are fixed and/or the more fixed edges a cavity comprises. The strength or stiffness of the sheet metal material decreases in the following order: strong - ferritic steel > copper > titanium > brass > aluminium > lead - weak.

An inner pressure may be applied to a cavity of a pre-structure of the invention by applying gases, such as compressed air, or liquid substances, such as water or any other hydraulic fluid, for example oil or water-oil-suspensions. Further, chemical reactions which lead to a volume increase, for example, by the production of gas or else may be used to apply an inner pressure to the at least one cavity of a pre-structure. For this purpose, the reaction educt or educts mixture have to be introduced in a suitable stoichiometrical ratio into the cavity through the opening. The reaction may be initiated by, for example, increasing the temperature of the introduced mixture inside the at least one cavity or by addition of a starter component immediately prior to introducing the mixture into the cavity. Thereby, also a pressure is applied to the inside of a cavity which is then inner pressure deformed. Examples for pressure media leading to a deformation of the cavity and pre-structure by chemical reaction are polyurethane foam, concrete foam or aluminium foam. These materials will remain inside the cavity of the sheet metal structure after the volumetric increase and thus after deforming the structure. Gases, liquid substances and other substances as mentioned above which may lead to a volume increase or are applied under pressure are denoted as "pressure medium" or "pressurised medium". The inner pressure deformation of the cavity or also pre-structure upon the application of an inner pressure by the application of a pressure medium is denoted as "inner pressure deforming" or "deforming". Preferably, compressed air is used as pressure medium for applying an inner pressure to the at least one cavity of a pre- structure, in this case, the inner pressure deformation may also be denoted as "inflating". The skilled person knows that also a pressure medium which is applied to the one plate of sheet metal from the outside of the pre-structure can be used as a mean of design and/or for forming or changing the shape of the structure, however, the application of a pressure from the outside is not meant to form an inner pressure deformed sheet metal structure according to the invention.

The deformation, optionally inflating, may also be achieved when the pre-structure is not completely pressure-tightly closed, then the pressure has to be increased significantly. Of course, a person skilled in the art is also well-aware of the fact that holes or slits in the surface of the cavity to be inner pressure deformed may be larger depending on the pressurised medium that is used. In case of air or water, the holes or slits should be minimal or closed, however, in case of e.g. polyurethane foam, concrete foam or aluminium foam, the slits or holes may be larger and still the cavity is deformed. The applied inner pressure, for example the compressed air, is generally applied at above 4 bar, optionally between 5 bar and 30 bar, between 5 and 20 bar, between 5 and 15 bar or around 9 ± 1 bar or 10 bar. For applying an inner pressure to a cavity by compressed air, a standard compressor such as obtainable from Einhell Germany AG (Landau, Germany) or from GLIDE GmbH & Co. KG (Wolpertshausen, Germany).

The skilled person knows that the pressure might have to be adjusted according to the form of the cavity of the pre-structure to be deformed, the thickness of the one plate of sheet metal, i.e. the thicker the plate, the higher the pressure needed, and other parameters, however, the above given ranges and pressure values are applicable for any embodiment of the present invention. In general, the longer the time of applying an inner pressure to the cavity, the higher the extent of deformation. The time which is required for full inner pressure deformation also depends on the material and also on the shape of the cavity to be deformed (cf. Figure 10 and 12). In general, the inner pressure is applied until no further deformation of the pre-structure is desired or may be achieved, simply due to the fact that the maximal deformation which can be achieved by a particular inner pressure is already reached.

Optionally, the fixed edges are in longitudinal direction of the cavity with respect to the shape of the pre-structure. Additionally, further fixed parts may be introduced to achieve alternative inner pressure deformed sheet metal structures. Alternative inner pressure deformed sheet metal structure may also be achieved by alternative forming of the pre-structure, e.g. by increasing the angles of the fixed edges and/or of the joining parts of the pre-structure. Sub-structures which may be comprised in the pre- structure comprising the cavity to be deformed exemplify such alternative forming of the pre-structure and thus of the cavity to be deformed upon an inner pressure are depicted in cross-sections in Figures 10. One pre-structure may comprise one or more same or different sub-structures.

In Figure 12, schematic representations are shown which are meant to explain the principle that the shape of the cavity influences its behaviour upon application of an inner pressure. In Figure 12 A), the ratio between the length of k and the length of 1 is l(k):3(l). Upon application to the cavity which comprises part k and part 1, the deformation in part k will be negligible whereas part 1 of the same cavity is fully deformed. From Figure 12 B) it can be learned that the deformation of part k decreases the higher the difference between the length of k to the length of 1 (total length). Also here, part 1 of the same cavity is fully deformed. In Figure 12 C) part k is already partially unfolded in that the angle of the fixed edges, i.e. between the two layers which are connected to each other via a fixed edge, are increased in comparison the respective angle in part 1 (cf. cross-sections shown). This is an example for alternative folding as also shown in Figure 10 (2.1 to 2.4).

Also provided is a triangular frame characterized in that one inner pressure deformed sheet metal structure is in triangular configuration or in that at least three inner pressure deformed sheet metal structures are assembled in triangular configuration. If the triangular frame is characterized in that one inner pressure deformed sheet metal structure is in triangular configuration, the cut of the one plate of sheet metal with indicated folding and bending lines (Figure 13 A), the pre-structure

(Figure 13 B) and the inner pressure deformed sheet metal structure (Figure 13 C), i.e. the triangular frame may be as depicted in Figure 13 A-C. Here, the whole triangular frame is manufactured according to the method of the invention from a single plate of sheet metal. Of course, a person skilled in the art knows that a facade frame may also resemble a square, rectangle, pentagon, hexagon or polygon. It is apparent to a person skilled in the art that the cut of the sheet metal plate can easily be adapted to manufacture an inner pressure deformed sheet metal structure being in the form of a square, rectangle, pentagon, hexagon or polygon frame. Further, the length of the inner pressure deformed sheet metal structures may be different from each other.

If the triangular frame is characterized in that at least three inner pressure deformed sheet metal structures are assembled in a triangular configuration, the triangular frame may comprise a form as depicted in Figure 13 D-F. For assembling of the triangular frame any of the methods mentioned herein for fixing and or closing may be used, in particular welding, gluing, riveting, screwing or combinations thereof. The connection and/or assembling of the frames may also be achieved by connection elements such as eyelets, loops, thread mounts, hooks or similar or any other connection element or tool a person skilled in the art knows. In Figure 18, the manufacturing steps of an exemplary inner pressure deformed sheet metal structure which can be used for assembling of a triangular frame. Here, an inner pressure is applied to the cavity of a pre-structure having three fixed edges corresponding to the edges of three extremities. For one triangular frame, three inner pressure deformed sheet metal structures have to be assembled and/or connected. All triangular frames of the invention are especially useful as facade frames. Of course, a person skilled in the art knows that a facade frame may also be assembled from more than three inner pressure deformed sheet metal structures. Then, the frame resembles a square, rectangle, pentagon, hexagon or polygon. It is also apparent that the length of the inner pressure deformed sheet metal structures may be different from each other. The inner pressure deformed sheet metal structure may have a wide variety of applications in any field where metal structures are used. In general, the inner pressure deformed sheet metal structures of the invention are for use in construction. Preferably, construction comprises architectural or house building construction, engineering, mechanical engineering, heavy or civil construction, complex form creation, such as furniture (e.g. chairs, tables, benches, urban furniture and/or interior furniture) or design and art sculpture manufacturing, vehicle engineering, ship building and/or industrial construction, e.g. mould construction and manufacturing. In general, "construction" in the sense of the invention means any kind of construction, engineering or building. "Complex form creation" denotes furniture manufacturing and/or design and art sculpture manufacturing.

For these applications one or more inner pressure deformed sheet metal structures may be connected or assembled in any way which is known to a person skilled in the art. Logically, one or more structures of the invention can also be connected or assembled with or to other structures, elements or vehicles. The connection and/or assembling of the structures may be done before or after the inner pressure deformation by any of the methods mentioned herein for fixing and or closing, in particular by welding, gluing, riveting, screwing or combinations thereof. The connection and/or assembling of the structures may also be achieved by connection elements such as eyelets, loops, thread mounts, hooks or similar or any other connection element or tool a person skilled in the art knows. These connection elements may be considered and added to the structure already during cut of the one plate of sheet metal prior to forming of the pre-structure or later at any step of the method of the invention or even after inner pressure deformation of the pre-structure at the final structure by a fixing or closing method mentioned herein, in particular by welding, gluing, riveting, screwing or combinations thereof. An optional assembling of at least three inner pressure deformed sheet metal structures is a triangular frame.

As already mentioned above, final structures to be suitable for construction and other sheet metal structure applications need to have a high precision, i.e. a precision tolerance being in the range of maximal 1%. The tolerance may be determined as described in the experimental section.

Exemplary contours of the one plate of sheet metal comprise a form as follows a)

wherein a=b, a<b or b<a.

In the following, exemplary examples of bending lines and/or folding lines of the one plate of sheet metal for forming of the pre-structure in step b) of the invention are presented, wherein folding lines are indicated by and bending lines are indicated by . The length of a, b, c, d, e, f, g, h, i and j may be selected independently: a)

c d e f g h

wherein c + d + e + f +g + h = b, optionally wherein a = b, d = e, f = g and/or h = c; b)

b

c d e f g h i j

wherein c + d + e + f +g + h + i + j = b, optionally wherein a = b, d = e, f = g, h = i and/or j = c.

Also here, one or more folding lines or bending lines may be perforated and closed before applying the inner pressure.

Exemplary pre-structures of the invention comprises a form selected from the group consisting of

a) b)

wherein fixed edges are indicated by and joining parts are indicated by ; wherein the length of a, b, c, d, e, f, g, h, i and j may be selected independently; optionally wherein in a) d = e, f = g and/or h = c; and in b) d = e, f = g, h = i and/or j = c.

Further exemplary contours/cut of sheet metal plates, plates with indicated bending and folding lines, exemplary pre-structures and exemplary inner pressure deformed sheet metal plates of the invention and exemplary manufacturing steps of the method of the invention are illustrated in the Figures. A person skilled in the art of course knows that the manufacturing examples and other structures are given for illustration purposes. They can be combined and varied in any way.

The invention is further described by the following examples and by the Figures which are solely for the purpose of illustrating specific embodiments of the invention, and are not to be construed as limiting the scope of the invention in any way.

Examples

1. Testing procedure for determining the deviation within the desired tolerance of maximally 1% in case of a pre-structure in triangular frame configuration (single inner pressure deformed sheet metal structure, no assembling of more than one structure)

The tested pre-structure is in triangular configuration and especially useful as a facade frame as shown in Figure 13 A-C. Here, the pre-structure has three fixed edges which correspond to the edges of three extremities at each of the three parts of the frame. For this purpose, two of the three corners of the triangular pre-structure (frame) are fixed via two metal pieces in L-form in a distance of at least 20 cm to the workbench so that the third corner remains unfixed and lifted as illustrated in Figure 22. The closed pre-structure relies on usual steel production tolerances. First the distance between the lifted corner and the two other corners and the distance between the lifted corned and the table is measured. Second an inner pressure of 10 bar is applied to the cavity of the pre-structure by pressurised air, thereby the pre-structure is deformed and the inner pressure deformed final structure is produced. At the time point where no further deformation at 10 bar occurs, here after 13 seconds, the distance between the lifted corner and the two other corners and the distance between the lifted corned and the table is measured again and compared to the first measurement. The deviation of the distances after deformation and before should not be more than 1% of the distance before the deformation.

2. Production of an exemplary elongated/linear inner pressure deformed sheet metal structure comprising three fixed edges which correspond to the edges of three extremities

This exemplary manufacturing process is also illustrated in Figure 18.

2.1 Determination of sheet metal cut parameters and parameters for pre-structure forming

First a basic design model of the pre-structure is generated. Using the 3d modelling software Rhinoceros (Robert McNeel & Associates, Seattle, WA, USA) three single surfaces are drawn in 3-dimensional mode. The surfaces illustrate the fixed edges and the layers between them. Thereby the size (i.e. length, width, height) and geometry of the parts of sheet metal between the fixed edges are defined, the material thickness is not yet considered. The height/width of each part here is 24 cm, the height/width from the fixed edge to a joining part 6±1 cm, the length is 180 cm. These dimensions are suitable for an inner pressure deformation with a pressure below 10 bar which can be applied by a compressor, here Einhell Profi Compressor RT-AC 250/24/10 (Einhell Germany AG, Landau, Germany).

Second the material model is generated. The basic design model geometry as generated above is transferred to the programme Catia V5 (Dassault Systemes, Velizy- Villacoublay, France). Using the Generative Sheet Metal Design workbench of Catia V5 a new model is generated based on the coordinates from the previous surface model which now also considers the material of the sheet metal as well as material thickness, weight, the size of the layers and production parameters such as the bending radius and folding angles.

Finally, the 2-dimensional cutting data for cutting of the sheet metal plate are calculated by Catia V5. Thereby cutting files in dxf- format are generated which can be used by the laser cutter TRUMATIC L 3030 of Trumpf (Ditzingen, Germany). The 2-dimensional cutting data contain information regarding the cutting of the sheet metal plate for the laser cutter, folding lines, bending lines, the direction of folding and bending and the position of perforation lines. Further, the positioning of the opening into the later formed cavity for applying the pressure medium is determined.

2.2 Cutting of the sheet metal plate

Steel sheet metal plates having a size of 3 m x 1.5 m and a thickness of 1 mm were used. Cutting of the sheet metal plate and the introduction of perforation lines according the dxf-cutting data (cf. item 2.1) was performed using a laser cutting machine TRUMATIC L 3030 of Trumpf (Ditzingen, Germany). Thereby, the sheet metal plate is cut into the form and shape desired by the manufacturer and determined by the material model (cf. item 2.1), also an opening is introduced by cutting.

2.3 Forming of the pre-structure

According to the material model determined by the manufacturer in item 2.1, the sheet metal plate, now having the desired cut form, is formed into the pre-structure by bending and/or folding. Bending is performed using a TruBend 5000 of Trumpf (Ditzingen, Germany) along the determined bending lines. After bending, the sheet metal plate is folded according to the dxf-cutting data also using TruBend 5000 of Trumpf (Ditzingen, Germany). Folding lines which were perforated in item 3.2 require a very low energy intake for folding the metal so that folding may even be performed manually. The slits of the perforation lines are closed in item 2.4 (see below).

2.4 Closing of the surface of the pre-structure

The surface of the pre-structure is closed by welding along the contour of the pre- structure and connecting the edges of the plate of sheet metal. This procedure connects the edges of the sheet metal layers and creates the cavity inside the closed pre-structure. Welding can be performed using for instance a Fronius MAGIC WAVE 220 station (Fronius International, Pettenbach, Austria) or a robot as KUKA 240 robot (KUKA, Augsburg, Germany) having a Fronius RCU 5001 welding station from Fronius International (Pettenbach, Austria) attached.

2.5 Inner pressure deformation

An inner pressure of approx. 10 bar is applied for 10 to 15 seconds by compressed air through the opening of the cavity using an Einhell Profi Compressor RT-AC

250/24/10 (Einhell Germany AG, Landau, Germany). Thereby the cavity and also the pre-structure is inflated and deformed and the inner pressure deformed sheet metal structure is produced.

3. Production of an exemplary triangular frame (cf. Figure 13 A-C) being based on one inner pressure deformed sheet metal structure comprising three fixed edges each of which corresponds to an edge of one extremity

3.1 Pre-structure forming parameters and determination of the sheet metal plate cutting

First a basic design model of the pre-structure is generated. Using the 3d modelling software Rhinoceros (Robert McNeel & Associates, Seattle, WA, USA) three single surfaces are drawn in 3-dimensional mode. The surfaces illustrate the fixed edges and the layers between them. Thereby the size (i.e. length, width, height) and geometry of the parts of sheet metal between the fixed edges are defined, the material thickness is not yet considered. Here, the cross-section of the virtual pre-structure has a T-shape (with joining angles al= 90°; a2= 90°; a3= 180° on the bottom) (cf. Figure 23). This element is further defined in three linear elements (mullions) by cutting out one extremity (flanked by al= 90°; a2= 90°). The 3-dimensional basic design model contains the design driving geometry of the element only. This means the most fundamental geometry as the size of the parts (length, width, and height) is determined, but not the material thickness for instance. The height/width of each part here is 24 cm, the height/width from the fixed edge to a joining part 6±1 cm, the length is 180 cm. The length of the 3 single mullions of the frame is supposed to consist of min. 1 m each and therefore a total triangular frame perimeter of 3 m. For this size an appropriate deformation may be achieved with an inner pressure below 10 bar by Einhell Profi Compressor RT-AC 250/24/10 (Einhell Germany AG, Landau, Germany).

Second the material model is generated. The basic design model geometry is transferred to Catia V5 (Dassault Systemes, Velizy-Villacoublay, France). Using the Generative Sheet Metal Design workbench of Catia V5 a new model is generated which also considers the materiality of the 3-dimensional model as material thickness, weight, the layers of the sheet metal plate and also production parameters as the bending radius and folding angles.

Finally, the 2-dimensional cutting data for cutting of the sheet metal plate are calculated by Catia V5. CatiaV5 uses the material model to calculate the 2-dimensional cutting pattern and to generate 2-dimensional cutting files in dxf- format. These data contain information regarding the cutting of the sheet metal plate for the laser cutter, folding lines, bending lines, the direction of folding and bending and of perforation lines. Further, the positioning of the opening into the later formed cavity for applying the pressure medium is determined.

3.2 Cutting of the sheet metal plate

Steel sheet metal plates having a size of 3 m x 1.5 m and a thickness of 1 mm were used. Cutting of the sheet metal plate and the introduction of perforation lines according the dxf-cutting data is performed using a laser cutting machine

TRUMATIC L 3030 by Trumpf (Ditzingen, Germany). Thereby, the sheet metal plate gets the form and shape desired by the manufacturer and determined by the material model (cf. item 3.1).

3.3 Forming of the pre-structure

According to the material model determined by the manufacturer in item 3.1, the sheet metal plate, now having the desired shape and contour, is formed into the 3-dimensional pre-structure by bending and/or folding. Bending is performed using a TruBend 5000 of Trumpf (Ditzingen, Germany) along the determined bending lines. After bending, the sheet metal plate is folded according to the dxf-cutting data also using TruBend 5000 of Trumpf (Ditzingen, Germany). Folding lines which were perforated in item 3.2 require a very low energy intake for folding the metal so that folding may even be performed manually. The slits of the perforation lines are closed in item 3.4 (see below).

3.4 Closing of the surface of the pre-structure

The surface of the pre-structure is closed by welding along the contour of the pre- structure and connecting the edges of the plate of sheet metal. This procedure connects the edges of the sheet metal layers and creates the cavity inside the closed pre-structure. This can be done using for instance a Fronius MAGIC WAVE 220 station (Fronius International, Pettenbach, Austria) or a robot such as Kuka 240 (KUKA, Augsburg, Germany) having a welding tool or welding station attached such as from Fronius International (Pettenbach, Austria). It should be noted that the triangular frame contains a single cavity so that all three parts of the frame are meant to be inner pressure deformed in a single pressure application step and not separately. For this purpose, care should be taken so that during closing the surface of the cavity and thus also of the pre-structure the cavity is not interrupted. In this way, the pressure is applied through one opening all over the frame.

3.5 Inner pressure deformation

Claims

1. A method for manufacturing an inner pressure deformed sheet metal structure comprising at least one step a) of applying an inner pressure to at least one cavity of a pre-structure; the cavity, optionally also the pre-structure, being formed from one plate of sheet metal; wherein the cavity comprises at least three fixed edges.

2. The method of claim 1 , further comprising step b) and/or step c) prior to step a); wherein in step b) the cavity and the pre-structure is formed from one plate of sheet metal comprising folding and/or bending;

and in step c) at least part of the surface of said pre-structure is closed by connecting at least part of the contour or inner part of said one plate of sheet metal, whereby the at least one cavity is obtained.

3. The method of claim 1 or 2, wherein each of the at least three fixed edges comprises a part of the one plate of sheet metal which is closed, or fixed and optionally folded or bent; optionally wherein a crease is formed along a part of the one plate of sheet metal which is bent.

4. The method of any one of claims 1 to 3, wherein the pre-structure comprises at least three extremities and the at least three fixed edges of the at least one cavity correspond at least partially to the edges of the at least three extremities of the pre- structure; wherein each extremity comprises two sheet metal layers connected to each other via a fixed edge and each extremity is connected to at least one adjacent extremity via a joining part, the joining part being characterised in that it comprises a part of the one plate of sheet metal which is bent, closed or straight.

5. The method of any one of the preceding claims, wherein prior to any one of steps a) to c) at least one opening suitable for applying the inner pressure in step a) is introduced into the one plate of sheet metal so that the at least one opening reaches to the at least one cavity; said opening not being closed in step c).

6. The method of any one of the preceding claims, wherein one or more additional parts of the one plate of sheet metal, of the pre-structure or of the inner pressure deformed sheet metal structure are fixed, thereby leading to a changed rigidity and an alternative shape or form of the inner pressure deformed sheet metal structure.

7. The method of any one of the preceding claims, wherein for fixing and/or closing a method selected from the group consisting of welding, gluing, riveting, screwing and combinations thereof is used.

8. The method of any one of the preceding claims, wherein the at least one opening is introduced by a method selected from the group consisting of laser cutting, cutting, sawing, plasma arc cutting, water jet cutting, drilling and a combination thereof.

9. The method of any one of the preceding claims, wherein the form of the contour of the one plate of sheet metal comprises a form selected from the group consisting of polygon, square, rectangular, rhombus, triangular, trapezoid, parallelogram, tetragon, round, ellipse, and combinations thereof; optionally the form of the one plate of sheet metal comprises at least one symmetry axis or point of symmetry; optionally at least two symmetry axes are rectangular to each other.

10. The method of any one of the preceding claims, wherein the pre-structure is formed from the one plate of sheet metal in step b) according to one or more bending lines and/or one or more folding lines, optionally a bending line corresponds to a joining part and/or a folding line corresponds to a fixed edge.

11. The method of claim 10, wherein the bending lines and/or folding lines in the one plate of sheet metal are as follows:

a) b)

wherein folding lines are indicated by and bending lines are indicated by ,

wherein in a) c + d + e + f +g + h = b, and in b) c + d + e + f+g + h + i + j = b, wherein the length of a, b, c, d, e, f, g, h, i and j may be selected independently.

12. The method of claim 10 or 11, wherein at least one folding line is perforated prior to folding in step b) and closed in step c).

13. The method of any one of the preceding claims, wherein the pre-structure comprises at least one form selected from the group consisting of

a) b)

14. The method of any one of the preceding claims, wherein the pre-structure further comprises one or more of the following sub-structures:

1 .4. 2.1 . 2.2.

2.5.

3.1. 3.2. 3.3.

and/or

7.1.

15. A pre-structure being formed from one plate of sheet metal and comprising at least one cavity, wherein the cavity comprises at least three fixed edges; or a pre- structure formed, and optionally closed, according to the method of any one of the preceding claims.

16. An inner pressure deformed sheet metal structure manufactured by a method of any one of claims 1 to 14, or obtained by applying a pressure medium to at least one cavity of the pre-structure of claim 15.

17. The inner pressure deformed sheet metal structure of claim 16 further comprising a crease along at least one joining part and/or bending line.

18. The pre-structure of claim 15 or the inner pressure deformed sheet metal structure of claim 16 or 17, further comprising one or more connection elements.

19. The pre-structure or inner pressure deformed sheet metal structure of claim 18, wherein the connection element comprises an eyelet, loop, thread mount, hook or similar.

20. A triangular frame characterized in that one inner pressure deformed sheet metal structure is in triangular configuration or characterized in that at least three inner pressure deformed sheet metal structures are assembled in triangular configuration.

21. Use of the pre-structure of any one of claims 15, 18 or 19 or of the inner pressure deformed sheet metal structure of any one of claims 16 to 19 or of the triangular frame of claim 20 in construction.

22. Use according to claim 21, wherein construction comprises architectural or house building construction, engineering, mechanical engineering, heavy or civil construction, complex form creation, vehicle engineering, ship building and/or industrial construction.