NL2031608B1

NL2031608B1 - A method to fabricate a thin-walled structure

Info

Publication number: NL2031608B1
Application number: NL2031608A
Authority: NL
Inventors: Geuskens François; Van Der Werff Roelof
Original assignee: Curve Works Holding B V
Priority date: 2022-04-15
Filing date: 2022-04-15
Publication date: 2023-11-06
Also published as: WO2023200341A1

Abstract

The invention relates to a method to fabricate a thin-walled structure comprising the following steps: a. providing a set of elements next to each other on a mold surface having a first shape with a developable surface, b. pressing the set of elongated elements against the mold surface, c. applying an adhesive in between adjacent elements, d. reconfiguring the mold surface to a desired second shape while pressing the set of elements against the mold surface, and e. allowing the adhesive to dry, harden or cure, wherein reconfiguring the mold surface from the first shape to the second shape is carried out before the adhesive has sufficiently dried, hardened, or cured.

Description

TITLE OF THE INVENTION

A method to fabricate a thin-walled structure

BACKGROUND OF THE INVENTION

The invention relates to a method for fabricating a thin-walled structure.

Thin-walled structures are structures of which one dimension is small compared to the other two dimensions. They include shells, domes, arches, articulated plates, and membrane-type structures.

Flat sheets are typically used to fabricate a thin-walled structure with a developable surface, which is a mathematical term to indicate a smooth surface with zero Gaussian curvature. In other words, such a surface can be made by transforming a plane without distortion. Transforming includes operations like folding, bending, rolling, cutting and/or gluing. Examples of shapes having a developable surface include cylinders, cones, oloids, sphericons, or portions thereof.

Since developable surfaces may be constructed by bending a flat sheet, they play an important role in manufacturing objects from e.g. sheet metal, cardboard, and plywood, as for instance extensively used in shipbuilding.

When fabricating a thin-walled structure from a sheet, either laminated or not, a relatively large amount of energy is required to permanently deform the sheet.

Further, applications may require the use of so-called non-developable surfaces. Non- developable surfaces are variously referred to as having “double curvature”, doubly curved”, “compound curvature”, “non-zero Gaussian curvature”, “free-form”, etc. For instance, rotor blades of modern wind turbines have certain non-developable surfaces to use wind energy with maximum efficiency. Likewise, in ship and aircraft construction, as well as in automobile production, engineers are busy with the development and production of non-developable surfaces to minimize flow resistance and improve visual appearance.

Freedom in the creation of shapes also plays an important role in many areas of architecture as well as in the field of interior architecture.

However, a disadvantage of fabricating a thin-walled structure with a non-developable surface is that it requires the in-plane distortion of an initially flat sheet, resulting in typically local stretching and/or compression of the flat sheet. Hence, when there are limits to the amount of stretching and/or compression that can be applied, as is for instance the case for wood, the non-developable surfaces that can be made using an initially flat sheet are limited to relatively simple surfaces having large radii of curvature.

To make more complex non-developable surfaces, i.e., with smaller radii of curvature, expensive manufacturing processes for the individual components or for the individual structural elements of a non-developable surface are required, including but not limited to shaping by means of complex and cost-intensive forming tools such as matrices, dies or formwork.

SUMMARY OF THE INVENTION

In view of the above it is an object of the invention to provide a method to fabricate a thin-walled structure that is easier and less cost-intensive even when producing the thin- walled structure in small quantities (e.g., between 1 and 10 pieces).

According to an embodiment of the invention, there is provided a method to fabricate a thin-walled structure comprising the following steps: a. providing a set of elements next to each other on a mold surface having a first shape with a developable surface, b. pressing the set of elements against the mold surface, c. applying an adhesive in between adjacent elements, d. reconfiguring the mold surface to a desired second shape while pressing the set of elements against the mold surface, and e. allowing the adhesive to dry, harden or cure, wherein reconfiguring the mold surface from the first shape to the second shape is carried out before the adhesive has sufficiently dried, hardened, or cured.

An advantage of this method is that the structure is made of a plurality of elements that during the reconfiguring step from the first shape to the second shape are not yet completely attached to each other as the adhesive has not sufficiently dried, hardened, or cured yet, and thus are able to deform relative to each other without requiring a large amount of energy. Not only are the elements able to move or deform substantially independent of each other, also the adhesive, if present during the reconfiguring step, can be deformed relatively easy.

A further advantage may be that the method steps are every time the same independent of the desired second shape. The method steps are also simple as they do not require complex adjustments to the elements dependent of the desired second shape as is for instance disclosed in WO2020/064717A where a complex pattern of slots and grooves dependent of the desired shape needs to be made in a plate-like core. it is explicitly noted here that the steps of the method according to the invention may be carried out in any order as is technically possible as will also be described below in exemplary embodiments. The method is not limited to the order of the steps as listed above.

In an embodiment, the desired second shape has a non-developable surface. In this embodiment, the use of separate elements that are sufficiently adhered to each other after reaching the second shape allows to make thin-walled structures, e.g. from wood, with more complex shapes compared to a thin-walled structure made from a single initially flat plate or sheet.

In an embodiment, the developable first surface is a substantially flat surface.

Alternatively, the developable first surface has a partial cylindrical shape, e.g. having a radius of curvature in only one direction. In an embodiment, when the desired second shape has a non-developable surface, the developable first surface may be chosen to have an intermediate shape between a substantially flat surface and the non-developable surface of the second shape, for instance by having a first shape with developable surface that comes closest to the second shape, i.e. requires the least deformation and/or energy required for deformation.

In an embodiment, the adhesive is applied in between adjacent elements before reconfiguring the mold surface from the first shape to the second shape or at least before reaching the second shape. Hence, in an embodiment, the step of applying the adhesive in between adjacent elements (step c.) is completely carried out before, i.e. during lay-up of the set of elements, or at least carried out before completing the step of reconfiguring the mold surface from the first shape to the desired second shape (step d.). This allows to carry out the step of reconfiguring the mold surface to the desired second shape (step d.) at least partially during the step of allowing the adhesive to dry, harden or cure (step e.).

This reduces the time required to complete the process. Another advantage is that the adhesive reduces friction between the elements during reconfiguring the mold surface from the first shape to the desired second shape. This results in even less energy required during shaping of the thin-walled structure.

In an embodiment, the elements of the set of elements are elongated elements, wherein a length of the elements is larger than a width of the elements which in turn is larger than a thickness of the elements. In an embodiment, the elements of the set of elements are strips.

In an embodiment, a spacing between adjacent elements is smaller than a width of the elements, preferably at least five times smaller than a width of the elements, and more preferably smaller than a thickness of the elements.

In an embodiment, the set of elements are arranged in at least two layers of elements, which at least two layers are arranged on top of each other. In other words, the set of elements may form a laminate.

In an embodiment, the elements of the set of elements include the same material.

Alternatively, the set of elements include a first sub-set of elements and a second sub-set of elements, wherein the first sub-set of elements comprise a first material and the second sub-set of elements comprise a second material different from the first material.

When the set of elements are arranged in at least two layers of elements, it is envisaged that one of the at least two layers of elements includes elements from the first sub-set of 5 elements only and another of the at least two layers of elements includes elements from the second sub-set of elements only. Hence, in an exemplary embodiment, the thin- walled structure may include three layers, wherein the outer two layers are made of a first material using a first sub-set of elements and the layer in between the outer two layers is made using a second sub-set of elements. In another more specific example, the thin-walled structure is a laminated product including the following layers from bottom to top: a layer of wood, a flax fiber layer, a foam core, a flax fiber layer, and a layer of wood, wherein each layer is provided as a sub-set of elements together forming a set of elements as described above.

Hence, in an embodiment, the set of elements includes one or more wooden elements.

In an embodiment, a wood grain of the one or more wooden elements is substantially parallel to a longitudinal direction of the one or more wooden elements.

In an embodiment, wooden elements are provided in different layers of the thin-walled structure, wherein the wooden elements are oriented differently in said different layers, for example having a 45-, 60-, 75- or 90-degrees angle relative to each other. This different orientation is preferably applied to adjacent layers.

In an embodiment, the elements of the set of elements are arranged in at least two construction layers of elements and a covering layer, which at least two construction layers and the covering layer are arranged on top of each other, wherein the elements in the at least two construction layers are configured to mainly provide strength and stiffness to the thin-walled structure, and wherein the elements in the covering layer are configured to provide a desired appearance and/or outer surface property to the thin- walled structure.

In an embodiment, the mold surface is defined by a reconfigurable mold, and may be a conformable mold surface. A conformable mold surface is a surface that when reconfigured to a desired shape is not distorted more than required to obtain the non- developable shape. This is for instance the case when using a tool as disclosed in

W02017/153319 which uses a magnetic joint system between a membrane and an array of actuators allowing the joints holding the membrane to slide on the holding surface of the membrane, which holding surface is opposite the mold surface.

In other words, reconfiguring the mold surface from the first shape to the desired second shape may be carried out using an apparatus for making a three-dimensionally curved object, said apparatus comprising a membrane defining the mold surface and an array of actuators for directly or indirectly acting on a surface of the membrane opposite the mold surface, wherein the apparatus is configured such that the membrane is configurable into a predetermined shape by individually adjusting the array of actuators acting on the surface opposite the mold surface of said membrane.

An advantage of a conformable mold surface is that the strain in the mold surface is kept to a minimum and thus also the shape of the set of elements is less distorted when being formed into the desired shape.

In an embodiment, the step of pressing the set of elements to the mold surface (step b.) includes covering the set of elements with a bag and applying a vacuum between the bag and mold surface. A vacuum in this context is a pressure below atmospheric pressure, preferably below 500 mbar, more preferably below 300 mbar, most preferably below 100 mbar.

In an embodiment, pressing the set of elements against the mold surface is carried out during the step of allowing the adhesive to dry, harden or cure.

In an embodiment, when adhesive is applied before reaching the desired second shape, pressing the set of elements against the mold surface is carried out using a first pressure before reaching the desired second shape and is carried out using a second pressure after reaching the desired second shape, which second pressure is higher than the first pressure. This provides the advantage that the adhesive can more easily flow or deform during the reconfiguring of the mold surface. Another advantage may be that in case the first and second pressure are applied using vacuum, a lower first pressure during reconfiguring of the mold surface may prevent the adhesive from sufficiently drying, hardening, or curing before reaching the second shape.

It is explicitly mentioned here that sufficiently drying, hardening, or curing of the adhesive means that the adhesive provides sufficient strength to the thin-walled structure to maintain the second shape without external pressure. Hence, the process of drying, hardening, or curing may continue after reaching a required level of sufficiently drying, hardening, or curing.

When vacuum is used to apply pressure to the set of elements on the mold surface, this vacuum may also be used to apply the adhesive, which process may be referred to as vacuum injection of the adhesive. However, it is also possible that the set of elements are provided on the mold surface, adhesive is applied to the set of elements, e.g. by applying it to a top or bottom surface of the set of elements, and subsequently a bag is provided over the set of elements to apply the vacuum.

In an embodiment, during the step of allowing the adhesive to dry, harden or cure (step e.) heat is provided to the adhesive, preferably by the mold surface. This will reduce the amount of time required to dry, harden, or cure.

In an embodiment, the set of elements or a sub-set of elements is attached to a carrier first and subsequently provided to the substantially flat mold surface. In this way, the set {or sub-set) of elements and the carrier can be prefabricated at another time and/or location so that the step of providing the set of elements to the substantially mold surface can be carried out in a relatively small time period as the time-consuming sub- step of aligning the set of elements at the mold surface to obtain the desired spacing is carried out with respect to the carrier.

In an embodiment, the carrier is made from a material different from the elements. This can be an organic material like flax, but other materials are also contemplated.

In an embodiment, the carrier is removed before reconfiguring the mold surface in which case the carrier may be non-flexible.

In an embodiment, the carrier is flexible allowing to adjust its shape during reconfiguring the mold surface but also allowing to make transportation of the carrier, possibly including elements attached thereto, easier, for instance by providing the carrier on a roll.

In an embodiment, the carrier may be an adhesive film that is cured by applying heat.

In an embodiment, the carrier may be made flexible or more flexible by applying heat prior to and/or during reconfiguring the mold surface.

In an embodiment, the carrier is removed after the step of allowing the adhesive to dry, harden, or cure {step e.). Alternatively, the carrier remains part of the fabricated thin- walled structure. In an exemplary embodiment, the set of elements is made by a first set of sub-elements and a second set of sub-elements that are positioned at either side of the carrier. In such a case, a sub-element of the first set may be arranged opposite a sub- element of the second set to form an element with the carrier sandwiched in between the two sub-elements. in an embodiment, the adhesive is a resin.

In an embodiment, the desired second shape has a first minimum radius of curvature in a first direction and a second minimum radius of curvature in a second direction that is orthogonal to the first direction, wherein the first minimum radius of curvature is larger than the second minimum radius of curvature, and wherein a longitudinal direction of the elements in at least one layer is arranged substantially parallel to the first direction.

However, alternatively, orientations of elements may differ depending on the expected loads applied to the thin-walled structure during use after fabricating. The longitudinal direction of the elements may then be substantially parallel to a direction of the expected loads.

In an embodiment, a length of the elements is equal to or larger than a desired dimension of the thin-walled structure in the longitudinal direction of the elements.

In an embodiment, a thickness of the thin-walled structure is substantially constant.

In an embodiment, dimensions of the elements of the set of elements are chosen such that preferably: 1. an out-of-plane deformation of said elements when reaching the desired second shape is smaller than a thickness of the to be formed thin-walled structure, and/or 2. an out-of-plane deformation of said elements when reaching the desired second shape is within predetermined allowable maximum values for said material, which are typically determined by maximum values to maintain structural integrity and material properties including a safety margin, and/or 3. the elements do not break or buckle during the fabricating process.

Any material such as metals, plastics, ceramics, wood, and fiber reinforced plastics (composites) of a combination thereof can be used for the elements. As an example, the fabricating method according to the invention can be used to fabricate laminated glass (combination of thin glass sheets together with polycarbonate).

In the case of wood, it has been found that it is possible to fabricate curved thin-walled structures from plywood with similar strength as normal plywood since adhesives can be chosen that are stronger than the lignin in the plywood, which is the natural binder of wood fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in a non-limiting way by reference to the accompanying drawings in which like parts are indicated by like reference symbols, and in which:

Fig.1 schematically depicts a perspective view of a mold surface provided with a set of elements next to each other,

Fig. 2 schematically depicts in more detail a cross-sectional view of a portion of the mold surface of Fig.,

Fig. 3 schematically depicts a perspective view of the mold surface of Fig. 1 after reconfiguring the shape of the mold surface,

Fig. 4 schematically depicts a cross-sectional view of a portion of the reconfigured mold surface of Fig. 3,

Fig. 5 schematically depicts a cross-sectional view of a portion of a mold surface with a set of elements provided to the mold surface in three layers according to another embodiment of the invention, and

Fig. 6 schematically depicts a top view of a set of elements arranged on a mold surface according to a further embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 schematically depicts a perspective view of a membrane 1 with a mold surface 1a provided with a set of elements 2 next to each other on the mold surface 1a. Fig. 2 schematically depicts in more detail a cross-sectional view of a portion of the membrane 1 of Fig. 1 with some of the elements 2 of the set of elements. The situation in Figs. 1 and 2 may depict a first step in a method to fabricate a thin-walled structure.

The mold surface 1a in Figs. 1 and 2 has a first shape with a developable surface. A developable surface is a mathematical term to indicate a smooth surface with zero

Gaussian curvature. In other words, such a surface can be made by transforming a plane without distortion. Transforming includes operations like folding, bending, rolling, cutting and/or gluing. Examples of shapes having a developable surface include cylinders, cones, oloids, sphericons, or portions thereof.

Non-developable surfaces are variously referred to as having “double curvature”, doubly curved”, “compound curvature”, “non-zero Gaussian curvature”, “free-form”, etc. For instance, rotor blades of modern wind turbines have certain non-developable surfaces to use wind energy with maximum efficiency. Likewise, in ship and aircraft construction, as well as in automobile production, engineers are busy with the development and production of non-developable surfaces to minimize flow resistance and improve visual appearance.

Thin-walled structures are structures of which one dimension is small compared to the other two dimensions. They include shells, domes, arches, articulated plates, and membrane-type structures. The term “small” in this context may be quantified as that the smallest dimension is at least five times smaller than any other dimension, preferably at least ten times smaller, more preferably at least twenty times smaller, and most preferably at least fifty times smaller, e.g., a hundred times smaller. The dimension that is small compared to the other two dimensions will typically be referred to as the thickness of the thin-walled structure. The other dimensions will typically be referred to as the width and length of the thin-walled structure.

The elements 2 have a dimension in x-, y- and z-direction corresponding to a width, length, and thickness of the elements 2. In this example, the length of the elements 2 is larger than the width of the elements, which in turn is larger than the thickness of the elements. The elements 2 in Figs. 1 and 2 may therefore also be referred to as elongated elements 2 or strips 2. A longitudinal direction of the elements 2 is in this example parallel to the y-direction. The dimension of the elements in the longitudinal direction is equal to or larger than a desired dimension of the thin-walled structure fabricated with the described method.

The elements 2 may be attached to a carrier 3, see Fig. 2, which may be a flexible carrier 3 and allows to preposition the elements 2 relative to each other by attaching the elements 2 to the desired locations, respectively, on the carrier 3 and providing the assembly of elements 2 and carrier 3 to the mold surface 1a.

The elements 2 are subsequently pressed against the mold surface 1a, for instance using a vacuum bag 4. Spaces 5, which may alternatively be referred to as seams, interfaces or joints, are present between adjacent elements 2, which spaces 5 are smaller than a width of the elements 2, preferably at least five times smaller than a width of the elements 2, and more preferably smaller than a thickness of the elements 2.

Fig. 3 schematically depicts a perspective view of the membrane 1 of Fig. 1 after reconfiguring the shape of the mold surface 1a into a desired second shape, which second shape may have a developable surface, or a non-developable surface as is depicted as an example in Fig. 3. The elements 2 are omitted from Fig. 3 and the mold surface 1a is provided with a grid of lines extending in x-direction and grid lines extending in y- direction to clearly show the shape of the mold surface la after reconfiguring,

The mold surface 1a is reconfigured from an initial flat shape as first shape in Fig. 1 to the desired second shape as depicted in Fig. 3 while pressing the set of elements 2 against the mold surface 1a. In this way, the elements 2 deform along with the mold surface 1a. An example of the resulting deformation of the mold surface 1a and the elements 2 is shown in Fig. 4 in which the membrane 1 and the elements 2 pressed against the mold surface 1a are bend about a bending axis extending in y-direction, i.e. perpendicular to the plane of drawing. However, although not shown, the membrane 1 may also be bend about a bending axis extending in x-direction simultaneously thereby resulting in a non- developable surface la. The elements 2 are able to bend in one direction due to their elongated shape and the spaces 5 allow the set of elements 2 to bend in another direction.

Before or after reaching the desired second shape of the mold surface 1a, an adhesive is applied to the spaces 5 between adjacent elements 2. When the adhesive is applied prior to reconfiguring the shape of the mold surface 1a, the adhesive may act as a friction reducing material during the reconfiguring step. The adhesive is applied to adhere the elements 2 together to form the thin-walled structure. After applying the adhesive, the adhesive is allowed to dry, harden, or cure, depending on the type of adhesive. In any case, reconfiguring the mold surface to a desired shape is carried out before the adhesive has sufficiently dried, hardened, or cured.

The embodiment of Fig. 1 and 2 relates to a set of elements 2 provided to the mold surface in a single layer. However, the set of elements 2 can be provided in at least two layers, for instance three as depicted in Fig. 5 for a similar cross-sectional view as Fig. 2.

Fig. 5 depicts a membrane 1 with a mold surface 1a provided with a set of elements 2. A first sub-set of elements is provided directly on the mold surface 1a with their longitudinal axis parallel to a y-direction similar to the situation of the elements 2 in Figs. 1 and 2. The first sub-set of elements may be referred to as the bottom layer BL of elements 2. On top of the bottom layer BL, an intermediate layer IL of elements 2 is provided. This intermediate layer IL overlaps with the bottom layer BL and is formed by a second sub-set of elements 2 extending in an x-direction perpendicular to the elements in the bottom layer BL. A top layer TL is formed by a third sub-set of elements 2 having an orientation similar to the elements 2 in the bottom layer BL. The top layer TP overlaps with the intermediate layer IL and the bottom layer BL.

The set of elements 2 may again be pressed against the mold surface 1a using a vacuum bagi.

Spaces 5 are present between the elements 2. Spaces 5 are present between adjacent elements within the same layer, in which case we may refer to them as seams 5 or joints 5, but also between adjacent elements of different layers, in which case we may refer to them as interfaces 5. An adhesive applied to the spaces 5 will thus not only adhere elements in the same layer to each other, but also adhere the different layers to each other thereby forming a rigid thin-walled structure. In an embodiment, the adhesive may be applied only to the spaces 5 in between different layer and not necessarily to the spaces 5 in between adjacent elements within the same layer.

Although the orientations of the elements in adjacent layers differ 90 degrees, other overlapping configurations are also possible, for instance using 45-, 60-, or 75-degrees differences in orientation, or a multiple thereof.

Fig. 6 depicts a top view of a mold surface 1a and a set of elements 2 arranged on top of the mold surface 1a according to a further embodiment of the invention. The set of elements 2 are arranged in an array of elements 2 with spaces 5 in between the elements 2, which may alternatively be referred to as seams, joints or interfaces 5. Only some of the spaces 5 have been indicated with a corresponding reference symbol.

The elements 2 have an elongated diamond shape and are provided in a single layer. This layer may be a covering layer provided over other, e.g. constructional layers, to provide a desired appearance and/or outer surface property to the thin-walled structure formed using the set of elements 2. The desired appearance may be simply the pattern of diamond shapes arranged in an array.

As an example, the end product may need to have a rectangular-like shape 100 seen in top view. When only diamond shaped elements are used, the array of elements 2 may extend beyond this rectangular shape 100 and additional machining, e.g. sawing or cutting, may be applied to remove material outside the rectangular shape 100 after fabricating a thin-walled structure according to the invention, examples of which are described in relation to Figs. 1-5. The excess material has been indicated using dashed lines in Fig. 6.

Although no material properties have been mentioned, it will be apparent to the skilled person that any material such as metals, plastics, ceramics, wood, and fiber reinforced plastics {composites) of a combination thereof can be used for the elements or a sub-set thereof. It has been found that the invention provides significant advantages when using wood, e.g. plywood, allowing to fabricate curved thin-walled structures from plywood with similar strength as normal plywood since adhesives can be chosen that are stronger than the lignin in the plywood, which is the natural binder of wood fibers.

Claims

CONCLUSIONS

1. A method for manufacturing a thin-walled structure comprising the following steps:

a. providing a collection of elements next to each other on a mold surface that has a first shape with a developable surface,

b. pressing the collection of elements against the mold surface,

¢. applying an adhesive between adjacent elements,

d. reconfiguring the mold surface to a desired second shape during pressing the set of elements against the mold surface, and e. allowing the adhesive to dry, harden or harden where reconfiguring the mold surface from the first shape to the second shape is performed before the adhesive has sufficiently dried, hardened or hardened.

A method according to claim 1, wherein the desired second surface has a non-developable surface.

A method according to claim 1 or 2, wherein the developable first surface is a substantially planar surface.

A method according to any one of claims 1 to 3, wherein the step of applying the adhesives between adjacent elements is completely performed prior to or performed before the step of reconfiguring the mold surface from the first mold to the desired second shape is completed.

A method according to any one of claims 1 to 4, wherein the elements are elongated elements, wherein a length of the elements is greater than a width of the elements, which in turn is greater than a thickness of the elements.

A method according to any one of claims 1 to 5, wherein a spacing between adjacent elements is smaller than a width of the elements, preferably at least five times smaller than a width of the elements, and more preferably smaller than a thickness of the elements.

A method according to any one of claims 1 to 6, wherein the set of elements are arranged in at least two layers of elements, wherein the at least two layers are arranged on top of each other.

A method according to any one of claims 1 to 7, wherein the set of elements comprise one or more wooden elements.

A method according to claim 8, wherein a wood fiber of the one or more wooden elements is substantially parallel to a longitudinal direction of the one or more wooden elements.

A method according to any of claims 8 or 9, wherein wooden elements are provided in different layers of the thin-walled structure, and wherein the wooden elements are oriented differently in the different layers, for example by having a 60 or 90 degree angle to each other.

A method according to any one of claims 1 to 10, wherein the elements of the set of elements are arranged in at least two construction layers of elements and a covering layer, wherein the at least two construction layers and the covering layer are arranged on top of each other, wherein the elements in the at least two construction layers are designed to provide essentially strength and stiffness to the thin-walled structure, and wherein the elements in the covering layer are designed to provide a desired appearance and/or property of the outer surface of the thin-walled structure structure.

A method according to any one of claims 1 to 11, wherein the mold surface is a conformable mold surface.

A method according to any one of claims 1 to 12, wherein step b. involves covering the collection of elements with a bag and applying a vacuum between the bag and the mold surface.

A method according to any one of claims 1 to 13, wherein during step e. heat is supplied to the adhesive, preferably via the mold surface.

A method according to any one of claims 1 to 14, wherein the set of elements is first connected to a carrier and then provided to the substantially mold surface,

A method according to claim 15, wherein the carrier is removed after step e.

A method according to any one of claims 1 to 16, wherein step d. is performed during step e.

A method according to any one of claims 1 to 17, wherein the adhesive is a resin.

A method according to any one of claims 1 to 18, wherein the desired second shape has a first minimum radius of curvature in a first direction, a second minimum radius of curvature in a second direction orthogonal to the first direction, wherein the first minimum radius of curvature is greater than the second minimum radius of curvature, and wherein a longitudinal direction of the elements in at least one layer is arranged substantially parallel to the first direction.