Attachment device of a structural component

Abstract

An assembly comprises a structural component having a first substrate and an attachment device bonded to and / or at least partially embedded in the first substrate of the structural component to fix the attachment device to the structural component. The attachment device comprises a housing defining a peripheral surface of the attachment device, a fastener hole in the housing of the attachment device for receiving a mechanical fastener and at least one cavity located within the housing and at least partially enclosed by the peripheral surface. The cavity has at least one dimension larger than a corresponding dimension of any opening through the peripheral surface into the cavity.

Description

[0001] ATTACHMENT DEVICE OF A STRUCTURAL COMPONENT

[0002] FIELD OF THE INVENTION

[0003] The invention relates to attachment devices for structural components. In particular, the invention relates to attachment devices of the sort used to receive mechanical fasteners when attaching secondary components to structural components typically made of multi-layer and / or composite moulded substrates.

[0004] BACKGROUND

[0005] In many industries that use structural components formed of multi-layer and / or composite moulded substrates, it is common to use attachment devices, commonly referred to as “inserts”, provided on or in the structural components to provide a reinforced location for attaching secondary components using mechanical fasteners. These inserts are commonly solid pieces of metal or polymer with a hole for receiving the mechanical fastener. These inserts act to provide a robust member that directly engages with the mechanical fastener and act to distribute any forces transmitted through the mechanical fastener over a larger area formed by the interface between the insert and the multi-layer and / or composite moulded substrates.

[0006] One downside to these simple solid inserts is that they are relatively heavy, particularly for industries such as the automotive industry where lightweighting is a major concern. In some industries, it has become common to form pockets in the surface of the inserts by milling or casting in order to decrease weight of the inserts. These pockets can be back-filled with low-weight filler (syntactic core, paste, glass microsphere paste, foam, etc.) to restore their profile and some of the structural integrity of the insert. However, these techniques now require a multistep manufacture process, which is undesirable for a simple staple component. These techniques also often negatively influence how forces, such as compressive forces, are transmitted through the insert.

[0007] It is desirable to provide attachment devices for structural components that overcome these issues. SUMMARY OF INVENTION

[0008] In accordance with a first aspect of the invention, there is provided an assembly comprising: a structural component having a first substrate; and an attachment device bonded to and / or at least partially embedded in the first substrate of the structural component to fix the attachment device to the structural component, wherein the attachment device comprises: a housing defining a peripheral surface of the attachment device; a fastener hole in the housing of the attachment device for receiving a mechanical fastener; and at least one cavity located within the housing and at least partially enclosed by the peripheral surface, the cavity having at least one dimension larger than a corresponding dimension of any opening through the peripheral surface into the cavity.

[0009] The assembly according to this aspect thus makes use of an attachment device that has an internal cavity that is larger than any opening through the peripheral surface into that cavity. This arrangement saves weight by removing material from the inside of the attachment device while retaining a relatively complete outer surface of the attachment device. Such a cavity is not capable of being formed by conventional casting or milling processes, which are limited in the size of the cavity they can form by the size of the opening through the outer surface connecting into the cavity. Techniques for forming attachment devices with these cavities include additive manufacturing, multi-part construction and special casting processes (lost core, sand core, etc.) in particular. By providing an attachment device of this sort, weight can be kept low, while the larger surface area of the peripheral surface (compared to if the same cavity had been formed by conventional casting or milling processes) ensures that the attachment device is better able to transmit forces around the housing through the peripheral surface and provides a greater surface area for the interface between the structural component and the housing.

[0010] It should be noted that the cavities of the attachment device are defined above by comparing their dimensions with corresponding dimensions of “any opening” through the peripheral surface into the cavity. It will be appreciated that there may be no opening though the peripheral surface into the cavity, i.e. the cavity may be fully enclosed within the housing, and the cavity need only be larger than an opening through the peripheral surface if one is present. It should be noted that, particularly for attachment devices formed by additive manufacture, as will be discussed below, it is common to provide at least one opening into the cavity in order to remove unfused additive manufacture material, such as powders. Where an opening through the peripheral surface into the cavity is present, the dimensions of the opening may be understood to refer to the dimensions of the largest projected area of said opening, and the dimensions of the cavity may be dimensions measured parallel to the corresponding dimensions of the opening, spaced along the direction of the projection. In some embodiments, an opening into the cavity, if present, may have an area on the peripheral surface, and the cavity may have a larger corresponding area, e.g. measured parallel to the area of the opening. Regardless of whether an opening is present into the cavity, preferably each cavity has at least one dimension of at least 2 mm, preferably at least 5 mm, more preferably at least 10 mm. Alternatively, or additionally, one or more of the cavities have at least one dimension that is at least 10% of the largest dimension of the attachment device, preferably at least 20%, more preferably at least 30% of the largest dimension of the attachment device. Preferably, one or more of the cavities have a dimension parallel to an axial direction of the fastener hole that is at least 30% of the largest dimension of the attachment device parallel to the axial direction of the fastener hole, preferably a least 40%, more preferably at least 50%, most preferably at least 60% of the largest dimension of the attachment device parallel to the axial direction of the fastener hole. While small cavities may be used to achieve lightweighting where an array of cavities is present, very small cavities will require a large network of internal housing walls that will limit the lightweighting potential.

[0011] While the first aspect of the invention is defined in some instances by the dimensions of the cavity compared to the dimensions of any opening through the peripheral surface into the cavity, according to other aspects, an assembly may simply comprise a structural component having a first substrate; and an attachment device bonded to and / or at least partially embedded in the first substrate of the structural component to fix the attachment device to the structural component, wherein the attachment device comprises: a housing defining a peripheral surface of the attachment device; a fastener hole in the housing of the attachment device for receiving a mechanical fastener; and at least one cavity located within the housing and substantially fully enclosed by the peripheral surface.

[0012] As indicated above, the present attachment device is bonded to and / or at least partially embedded in the first substrate to fix the attachment device to the structural component. Thus, this refers to fixing of the attachment device by means that do not use separate mechanical fasteners. These fixing methods encompass fixing methods such as bonding by adhesive or co-curing of the first substrate with the material used for the attachment device housing. They also encompass fixing that results from embedding, by which the attachment is prevented from being separated from the first substrate by parts of the first substrate surrounding or otherwise restricting the movement of parts of the attachment device. In the present context, the attachment device may be considered to be fully embedded in the first substrate when substantially the only part of the attachment device exposed by the first substrate is one or more openings into the fastener hole. As will be described below, in many embodiments it is preferred to only partially embed the attachment device in the first substrate.

[0013] As indicated above, in some embodiments, one or more of the at least one cavity (preferably each) is either substantially fully enclosed within the housing, i.e. the cavity is an isolated chamber inside the housing, or has at least one dimension at least twice (preferably three times, more preferably four times) as large as a corresponding dimension of an opening through the peripheral surface into the cavity. Cavities that are fully enclosed or much larger than any openings through the peripheral surface provide greater lightweighting with less sacrifice of the strength of the attachment device and the interface area provided by the peripheral surface.

[0014] The attachment device may take any form. In some simple embodiments, the housing may be substantially prism shaped, preferably with the fastener hole substantially aligned along the central axis of the prism. For example, the housing may be substantially cylindrical. The housing may have a largest dimension of no more than 100 mm, preferably no more than 50 mm, more preferably no more than 40 mm, most preferably no more than 30 mm. However, particularly where the attachment device is used to provide other functions or attachment of multiple mechanical fasteners, the housing may have a larger and / or more complex or irregular shape and examples of these will be described below. Nonetheless, in general, the attachment device will have a smaller total mass and / or volume than the structural component or the first substrate.

[0015] The present attachment device is suitable for use with a wide range of materials that may require reinforcement of an attachment location. However, the present device is particularly advantageous where the first substrate comprises a multilayer substrate, which may be particularly vulnerable to forces from mechanical fasteners causing separation or damage to the layers. Multi-layer substrates are also particularly suited to at least partially embedding the attachment device. Preferably, at least part of the attachment device is located between a plurality of the layers of the multi-layer substrate. This may be achieved by incorporating the attachment device into the substrate during a lamination process, i.e. where the multiple layers are being laid up on one another. In some embodiments, at least part of the housing of the attachment device is sandwiched between at least two layers of the multi-layer substrate. Preferably, at least 20% of the volume of the housing is located between a plurality of the layers of the multi-layer substrate, more preferably at least 30%, more preferably at least 40%, most preferably at least 50% of the volume of the housing. As indicated above, in these embodiments, preferably the plurality of layers that the attachment device is located between include one or more openings aligned with the fastener hole. However, in alternative embodiments, it may be intended that an opening is formed during the attachment process.

[0016] The present invention is also particularly suited to structural components in which the first substrate comprises a composite material, preferably a fibre-reinforced polymer, in particular carbon fibre-reinforced polymers. The first substrate may be a multi-layer substrate comprising one or more layers of such a composite material.

[0017] Many of the materials particularly suited to this invention are mouldable materials. Therefore, preferably, the structural component is a moulded structural component, more preferably a thermoset moulded structural component. Such mouldable materials are particularly suited to partially embedding the attachment device in the first substrate, since the structural component may be moulded around a provided attachment device.

[0018] As indicated above, preferably the attachment device housing is an additively manufactured attachment device housing, preferably a 3D-printed attachment device housing.

[0019] Preferably, the attachment device housing is formed of metal or polymer. Some suitable specific materials would be aluminium alloys, stainless steel, steel, titanium, PEEK, PA6, fibre reinforced polymers, or 3D woven fibre reinforced polymers.

[0020] In particularly preferred embodiments, the attachment device housing is formed as one integral piece. As will be described below, the enclosed cavities may be formed in a housing that is formed as one integral piece in particular by forming the housing by additive manufacturing. Other embodiments may make use of more complex milling processes to hollow out an internal cavity that is larger than the opening through the peripheral surface, for example by a multi-axis milling process. Other embodiments are also foreseen in which the attachment device housing is formed of several pieces. For example, the attachment device may be provided by two separate cast parts attached together so as to define an internal cavity that could not be formed by conventional casting of the housing as a single piece.

[0021] In many embodiments, it may be preferred for the housing to define one large empty cavity within the housing. However, in other embodiments, it may be preferred to provide an internal structure that further strengthens the attachment device. The attachment device may therefore comprise an array of cavities located within the housing separated by internal walls of the housing, and / or the housing may comprise one or more internal strengthening members extending across the cavity. For example, the cavity or cavities may be formed with a honeycomb-like structure to strengthen the attachment device while still providing good lightweighting. These internal walls or internal strengthening members would be particularly suitable for forming in an additive manufacturing process.

[0022] Especially where the attachment device is to be produced by additive manufacturing, it is preferred that internal cavities are not isolated from one another. In particular, it is common to provide an opening through the attachment device into the cavity in order to remove unfused additive manufacture material, such as powders. If several isolated cavities were provided, each would need its own opening through the exterior of the attachment device in order to remove excess additive manufacture material. Therefore, preferably one or more internal walls of the attachment device have openings therethrough to provide fluid communication across the internal wall. This may provide that the attachment device has only one internal cavity with continuous fluid communication through the cavity. An array of openings through the internal wall may also allow the internal wall to contribute to supporting the housing, while also maintaining a light weight.

[0023] In some embodiments, a solid portion of the housing or an internal wall is provided between the fastener hole and the peripheral surface along a direction perpendicular to an axis of the fastener hole. This may be provided by providing the fastener hole close to one edge of the attachment device, or providing an internal wall across the cavity between the peripheral edge and material defining the fastener hole, e.g. along a direction perpendicular to the axis of the fastener hole.

[0024] In some cases, the present attachment device, with one or more cavities that are fully enclosed within the housing or larger in at least one dimension than any opening through the peripheral surface into the cavity, may define a substantially hollow attachment device. The at least one cavity may make up at least 30% of the volume of the attachment device, preferably at least 40%, more preferably at least 50%, most preferably at least 60% of the volume of the attachment device. A larger total cavity volume will provide greater lightweighting. Another advantage of a large total cavity volume may be that the attachment device may provide good thermal insulation or temperature management. In some examples, a vacuum can be pulled inside a fully enclosed cavity to provide a thermal barrier.

[0025] The fastener hole of the attachment device may be tailored to a particular mechanical fastener or a particular attachment scenario. For example, the fastener hole may be a blind hole or a through hole. A blind hole may be suitable in some contexts for providing a large surface area opposing the fastener hole to bond the attachment device to the first substrate. A through hole may be suited where the attachment device is embedded in the substrate and it is desirable for the mechanical fastener to pass through the substrate. For example, the mechanical fastener may be a bolt or machine screw and it may be desirable to pair this with a connecting element on the opposing side of the first substrate, for example a nut. It will thus be appreciated that it is particularly preferred that the fastener hole is a threaded hole for receiving a machine screw or bolt; however, this is not essential.

[0026] As described above, one of the functions of the attachment device may be to distribute forces transmitted through the mechanical fastener over a relatively large area formed by the interface between the attachment device and the substrate. One way to increase the area of the interface between the attachment device and the substrate is to provide that the peripheral surface comprises one or more projections or recesses for increasing a contact area between the peripheral surface and the first substrate. This may increase the area over which an adhesive may form a bond between the surfaces, for example, or provide a strong connection between the surfaces when the substrate is moulded around the attachment device.

[0027] The attachment device may also provide a compression limiter function. For example, a portion of the peripheral surface of the attachment device surrounding the fastener hole may be exposed relative to the first substrate, and is preferably level with or projects above a surface of the first substrate, such that said portion of the peripheral surface of the attachment device may act as a compression limiter during fastening by a mechanical fastener. In this way, a mechanical fastener, such as a bolt or machine screw, may be prevented from damaging the substrate during attachment of a secondary component.

[0028] An additional function that may be provided by the present attachment device is a way to store or pass a substance or component from one side of the first substrate to the other. Preferably, the attachment device is at least partially embedded in the first substrate of the structural component such that a first portion of the housing is exposed on a first side of the first substrate and such that a second portion of the housing is exposed on a second side of the first substrate, and further comprising a first opening through the peripheral surface into the cavity in the first portion of the housing and comprising a second opening through the peripheral surface into the cavity in the second portion of the housing. This may allow wires or service lines, e.g. hydraulic lines, to be passed through the attachment device from one side of the substrate to the other. Alternatively, this may form part of a fluid flow path for feeding a fluid across the substrate. For example, particularly in an automotive context, fluids such as oil or washer fluids may be passed through the attachment device. While this embodiment has the first and second openings on opposite sides of the substrate, this may not be the case in other embodiments. For example, the attachment may be at least partially embedded in the first substrate of the structural component such that a first portion of the housing is exposed in a first region of the first substrate and such that a second portion of the housing is exposed in a second region of the first substrate, which may both be on the same side, and the housing may further comprise a first opening through the peripheral surface into the cavity in the first portion of the housing and comprising a second opening through the peripheral surface into the cavity in the second portion of the housing. This may use a section of the structural component as a passthrough for a substance or component. For example, in some embodiments, this may be used to pass a coolant through the attachment device to provide cooling to the structural component. Nonetheless, in many embodiments, it may be preferrable for the cavity to be substantially empty, i.e. to include only air.

[0029] In some particularly preferred embodiments, first and second openings are provided through the peripheral surface into the cavity, and the attachment device further comprises a flow control valve located in the cavity for controlling flow of fluid through the cavity between the first and second openings. Thus, this uses the attachment device as an integral part in a fluid flow path and saves space by arranging the flow control valve within the attachment device.

[0030] The above embodiments have featured attachment devices with first and second openings into the cavity that a substance or component may pass between. However, some embodiments may simply use the cavity as a reservoir or storage location, in which case only a single opening into the cavity may be required. For example, the attachment device may comprise an opening through the peripheral surface into the cavity, and the cavity may be filled with fluids such as oil or washer fluids, or mechanical or electronic devices, such as sensors, in order to save space. In other embodiments, the cavity may be filed with an acoustic material to act as a resonator / damper and improve noise, vibration and harshness (NVH) characteristics of the structural component.

[0031] One particularly useful function that may be facilitated by the present attachment device is automatic decoupling of a secondary component attached to the structural component via the attachment device. For example, it may be desirable to allow the doors of a passenger vehicle to be automatically decoupled following a crash to aid with passenger extraction. Therefore, some embodiments further comprise an explosive charge located in the cavity and an initiation device arranged to selectively initiate the explosive charge for decoupling a component attached to the attachment device by a mechanical fastener received in the fastener hole. Such an embodiment is also envisaged to be useful in aerospace contexts, for example by allowing decoupling of components during spaceflight.

[0032] The above embodiments have discussed an attachment device with a single fastener hole, but it will be appreciated that the attachment device may comprise a plurality of fastener holes into the housing of the attachment device, each for receiving a respective mechanical fastener. Each fastener hole may be configured as described above. Preferably, there are at least three fastener holes, or at least four fastener holes. The benefits in lightweighting are greater when multiple fastener holes are incorporated into the same attachment device.

[0033] In particularly preferred embodiments, the attachment device comprises a plurality of fastener holes extending along different directions of the attachment device. Preferably, an angle between two of the fastener holes may be at least 20°, preferably at least 45°, preferably at least 80 °. Most preferably, the fastener holes are substantially orthogonal to one another. In this way, the attachment device may act as a lightweight supporting structure for supporting fastening along multiple different directions, improving the overall strength of the structural device. The cavity located in the attachment device may be arranged anywhere in the housing to achieve the required lightweighting. In some embodiments, the at least one cavity substantially surrounds the fastener hole(s). In embodiments comprising a plurality of fastener holes, preferably the cavity is arranged between at least two fastener holes. In some embodiments, one or more of the fastener holes are arranged around an edge of the attachment device. For one or more of the fastener holes, a solid portion of the housing may be provided between the fastener hole and the peripheral surface along a direction perpendicular to an axis of the fastener hole. This can help improve the strength of attachment devices accommodating multiple fastener holes.

[0034] It will be appreciated that, once in use, the present assembly may further comprise a secondary component, the secondary component being attached to the structural component by a mechanical fastener received in the fastener hole. The secondary component may be any component that must be attached to the structural component. In some cases, the secondary component may comprise an attachment device of the sort described herein bonded to and / or at least partially embedded in a substrate of the secondary component to fix the attachment device to the secondary component. The secondary component may be fixed to the structural component by a mechanical fastener passed through both attachment devices. In this case, at least one of the attachment devices should comprise a through hole for the fastener hole. This may be useful if the secondary component comprises a multi-layer substrate, a composite material and / or is a moulded secondary component, as described above. In other embodiments, the secondary component may not comprise an attachment device of the sort described herein. For example, the secondary component could comprise conventional brackets.

[0035] While the above aspect of the invention has focussed on an assembly comprising a structural component and an attachment device, other aspects may comprise only an attachment device for a structural component comprising a housing defining a peripheral surface of the attachment device; a fastener hole in the housing of the attachment device for receiving a mechanical fastener; and at least one cavity located within the housing and at least partially enclosed by the peripheral surface, each cavity being larger in at least one cross-section than an area of any opening through the peripheral surface into the cavity, said at least one cross-section being measured in a plane parallel to said area. All of the above features in respect of the disclosed assemblies would also apply to the attachment device of this aspect.

[0036] As described above, the present aspects are particularly useful in automotive contexts, where strength and lightweighting are significant concerns. Therefore, preferably the structural component is a frame or bodywork component of a passenger vehicle. Further preferably, the structural component comprises at least a portion of a monocoque of a passenger vehicle. The structural component may also be a frame or bodywork component of any motor vehicle.

[0037] In accordance with a further aspect of the invention, there is provided a method of manufacturing an assembly comprising: providing a structural component having a first substrate; and providing an attachment device bonded to and / or at least partially embedded in the first substrate of the structural component to fix the attachment device to the structural component, wherein the attachment device comprises: a housing defining a peripheral surface of the attachment device; a fastener hole in the housing of the attachment device for receiving a mechanical fastener; and at least one cavity located within the housing and at least partially enclosed by the peripheral surface, the cavity having at least one dimension larger than a corresponding dimension of any opening through the peripheral surface into the cavity.

[0038] It will be appreciated that this method corresponds to a method of manufacturing the assemblies described above, and as such the method may be adapted to provide any of the preferred features described above.

[0039] While the present aspect relates to the manufacture of the assembly, in accordance with other aspects of the invention, there may be provided a method of manufacturing an attachment device, the attachment device comprising a housing defining a peripheral surface of the attachment device; a fastener hole in the housing of the attachment device for receiving a mechanical fastener; and at least one cavity located within the housing and at least partially enclosed by the peripheral surface, the cavity having at least one dimension larger than a corresponding dimension of any opening through the peripheral surface into the cavity.

[0040] As mentioned above, preferably the method comprises forming the housing of the attachment device by additive manufacturing, preferably 3D printing. However, alternatively, the housing could be formed by casting and milling processes and / or with multi-part construction of the housing involving bonding or welding separate attachment device housing sections.

[0041] It should be noted that additive manufacturing generally lacks the tolerances needed to define fastener holes with the required positions and dimensions. Therefore, some embodiments comprise comprises forming the housing of the attachment device by additive manufacturing and subsequently forming the (or each) fastener hole into the attachment device, preferably by a separate machining process, e.g. a milling or drilling process. In these cases, the area intended to have a fastener hole may be formed as a solid region of the attachment device, or could be provided with a pilot hole to save additive manufacture material. Preferably, the method further comprises performing a surface etching process, surface abrasion process, a surface coating process or a surface anodization process on the housing of the attachment device before the attachment device is bonded to and / or at least partially embedded in the first substrate. Such processes may improve the strength of the connection to surrounding substrate (either chemically or mechanically). For example, this may comprise surface projections and / or recesses formed by etching or abrasion. Alternatively, a intermediate coating may be provided on the attachment device housing that improves the strength of the bond chemically.

[0042] Preferably, the method also comprises moulding the structural component, in particular by compression moulding or injection moulding the structural component. Again, this is not essential, and other structural components may also be provided.

[0043] In particularly preferred embodiments, the method comprises forming, preferably moulding, the structural component around the attachment device, such that the attachment device is at least partially embedded in the structural component.

[0044] In some embodiments, the method may comprise bonding the attachment device to the first substrate of the structural component and / or at least partially embedding the attachment device in the first substrate of the structural component. Suitable processes include bonding by adhesives adhesives, mechanical processes such as clinching, or co-moulding and / or co-curing.

[0045] BRIEF DESCRIPTION OF DRAWINGS

[0046] The invention will now be described by reference to the accompanying drawings, of which:

[0047] Figure 1 is a schematic cross-section of a first embodiment of an assembly;

[0048] Figure 2 is a schematic perspective view of an attachment device used in the assembly of Figure 1 ;

[0049] Figure 3 is a schematic cross-section of part of another embodiment of an assembly; Figure 4 is a schematic perspective view of an attachment device used in the assembly of Figure 3;

[0050] Figure 5 is a schematic cross-section of part of another embodiment of an assembly;

[0051] Figure 6 is a schematic cross-section of part of another embodiment of an assembly;

[0052] Figure 7 is a schematic cross-section of another embodiment of an assembly;

[0053] Figure 8 is a schematic cross-section of another embodiment of an assembly;

[0054] Figure 9 is a schematic cross-section of another embodiment of an assembly;

[0055] Figure 10 is a schematic cross-section of another embodiment of an assembly;

[0056] Figure 11 is a schematic perspective view of an attachment device used in the assembly of Figure 10;

[0057] Figure 12 is a schematic cross-section of another embodiment of an assembly;

[0058] Figure 13 is a schematic cross-section of another embodiment of an assembly;

[0059] Figure 14 is a schematic cross-section of part of another embodiment of an assembly;

[0060] Figure 15 is a schematic cross-section of another embodiment of an assembly;

[0061] Figure 16 is a schematic cross-section of another embodiment of an assembly;

[0062] Figure 17 is a schematic cross-section of another embodiment of an assembly;

[0063] Figure 18 is a schematic cross-section of part of another embodiment of an assembly;

[0064] Figure 19 is a schematic perspective view of a structural component forming part of an assembly according to an embodiment

[0065] Figure 20 is a schematic perspective view of another attachment device;

[0066] Figure 21 is a cutaway view of the attachment device of Figure 20;

[0067] Figure 22 is a second cutaway view of the attachment device of Figure 20

[0068] Figure 23 is a schematic perspective view of another attachment device; and

[0069] Figure 24 is a cutaway view of the attachment device of Figure 23.

[0070] DETAILED DESCRIPTION

[0071] Figure 1 shows an assembly according to an embodiment. The main components of the embodiment are the substrate 100 of a structural component, the attachment device 200, the mechanical fastener 251 and the secondary component 300. In this Figure, only a small region of the substrate 100 of a structural component is shown, and it will be appreciated that this substrate could form any desired structural component. An example of the wider structural component is shown in Figure 19.

[0072] The first substrate 100 is a multilayer substrate comprising opposing first and second skins 101 , 103 sandwiching a core layer 102. The first and second skins 101 , 103 also sandwich therebetween the attachment device 200, which is surrounded by the core layer 102. The layers 101 , 102 and 103 may be layers of composite material, such as carbon fibre-reinforced polymer and may be formed by laminating several layers together, with the attachment device laid up during this process. Alternatively, the layers could be compression moulded or injection moulded polymers, for example. In some embodiments, the core layer 102 may be a foam, aramid honeycomb, aluminium honeycomb or the like.

[0073] The attachment device 200 embedded within the substrate 100 has an octagonal polygon shape in this embodiment and may have a width of approximately 30 mm and a depth of 10 mm, for example. This shape of the attachment device 200 is defined by a housing 210 which forms the outer peripheral surface. The housing thus has an octagonal upper surface 211 , eight side surfaces 212 and an octagonal lower surface 213. The housing 210 is a metal or polymer formed as an integral piece by additive manufacturing. In particular, the housing may be an aluminium alloy, stainless steel, steel, titanium, PEEK, PA6, a fibre reinforced polymer, or a 3D woven fibre reinforced polymer. The attachment device has a fastener opening 202 passing between the opposing octagonal faces of the upper and lower surfaces 211 , 213 of the attachment device along a central axis of the attachment device. In this embodiment, the fastener opening 202 is a threaded through hole suitable for receiving a bolt 251 , which may be secured in place by a nut 252. This may be fully or partially machined after the housing has been formed by additive manufacturing. In other embodiments, the fastener opening could be formed as part of the additive manufacturing process. When incorporated into the substrate 100 of the structural component, the openings of the fastener hole in the upper and lower surfaces 211 , 213 are aligned with openings through the first and second skins 101 , 103.

[0074] Within the attachment device 200 is a cavity 203, fully enclosed within the housing. The cavity surrounds the fastener opening 202 so that the attachment device generally torus shaped. The cavity thus has a ceiling that is proximate the upper surface 211 of the housing, a floor that is proximate the lower surface 213 of the housing, eight internal outer sidewalls proximate each side surface 212, and a cylindrical inner sidewall proximate the fastener opening 202. The cavity is formed during additive manufacturing by omitting material from the region that is to form the cavity. The attachment device 200 is thus hollow, providing good lightweighting. However, the intact outer peripheral surface formed by the housing means that the attachment device retains its strength and has a large interface with the substrate 100.

[0075] Figure 1 illustrates an assembly in which the attachment device 200 is used to secure a secondary component 300 to the substrate 100 of the structural component. As shown here, a bracket of the secondary component 300 is aligned with the fastener hole 202 of the attachment device. The bolt 251 is passed through the bracket of the secondary component and through the fastener hole 202 of the attachment device 200. The bolt 251 thus extends through to the opposite side of the substrate 100, where a nut 252 may be used to secure the bolt in place, thus fastening the secondary component 300 to the substrate 100 of the structural component.

[0076] Figures 3 and 4 illustrate another embodiment. In this embodiment, the substrate 100 has been omitted from Figure 3 for clarity. This embodiment shows an attachment device that is substantially as described with reference to Figures 1 and 2. This attachment device 200 differs in that each of the eight side surfaces 212 is provided with an opening 220 through the peripheral surface defined by the housing 210 into the cavity 203. These openings may be formed by milling the attachment device of Figures 1 and 2 to form openings into the cavity. The advantage of these openings is that it provides additional weight saving by removing additional material from the attachment device. However, the strength and rigidity of the housing may be maintained due to the areas where material remains in the final attachment device providing a relatively complete outer peripheral surface, with most of the lightweighting still coming from material absent in the region of the internal cavity 203. In particular, Figure 3 illustrates that each opening 220 through the sidewalls 212 has a diameter Do, whereas the cavity is larger in at least one dimension corresponding to a diameter of the opening. For example, the internal height of the cavity Dcalong the vertical direction is larger than the vertical diameter Do of the opening 220.

[0077] Figure 5 illustrates another alternative embodiment of an attachment device. This attachment device 200 is substantially as described with reference to Figures 1 and 2. This attachment device 200 differs in that the cavity 203 is provided with internal strengthening members 214. These strengthening members are again formed in the additive manufacturing process and may be struts that extend diagonally across the cavity 203. These internal strengthening members 214 are thus integrally formed with the housing 210. Such internal strengthening members 214 further increase the strength of the attachment device while maintaining good lightweighting and a relatively complete outer surface of the attachment device.

[0078] Figure 6 illustrates a further embodiment of an attachment device 200. This attachment device 200 is substantially as described with reference to Figures 1 and 2, and differs in that the housing comprises an array of internal cavities completely separated from one another by internal walls 215 of the housing, such that each cavity is an isolated chamber within the housing 210. These internal walls 215 defining the array of cavities may be arranged as desired. A honeycomb structure may be particularly preferred for strength and since it lends itself particularly well to additive manufacture.

[0079] Figure 7 illustrates another embodiment of an assembly. In this embodiment, the attachment device 200 differs from that of Figures 1 and 2 in that the fastener hole 202 is not a through hole passing between the upper and lower surfaces 211 , 213, but is a threaded blind hole passing only part way from the upper surface 211 towards the lower surface. A blind hole may be preferred in some attachment contexts. Furthermore, as a result of this, the lower surface 213 is completely continuous, which may be preferred when bonding the attachment device onto a flat surface of a substrate 100, as shown in Figure 7, such as by an adhesive.

[0080] Figure 8 illustrates another embodiment of an assembly. Like the embodiment of Figure 1 , the attachment device here is embedded in the substrate 100. In this embodiment, the attachment device 200 is adapted to provide a compression limiter function to protect the substrate 100 from damage by a bolt 251 or nut 252. In particular, in this embodiment, both the upper and lower surfaces 211 , 213 include a projecting portion 216 that project away from the upper and lower surfaces. These projecting portions 216 form a rim on each of the upper and lower surface 211 , 213 surrounding the fastener hole 202. With the attachment device 200 embedded in the substrate 100, the projecting portions 216 form surfaces around the fastener hole that are at least level with the outer surfaces of the substrate 100. Thus, the substrate 100 is at least partially protected from the compressive forces of the bolt 251 or nut 252 by the housing 210 of the attachment device 200.

[0081] Figure 9 illustrates another embodiment particularly suited to embedding in a substrate 100 by moulding. Again, the attachment device 200 may have substantially the same construction as described with respect to Figures 1 and 2. The attachment device 200 of this embodiment differs in that each of the side surfaces 212 includes a plurality of projecting elements 215. Each projecting element may project from its side surface, for example, by 1 mm. These projections may be formed by engraving the side surfaces to form a rough relief structure on the side surfaces 212. When moulding the substrate 100 around an attachment device 200 of this sort, the material of the substrate may fill the gaps around the projections. This increases the surface area of the interface between the substrate 100 and the attachment device 200 and so more firmly joins the two together.

[0082] Figures 10 and 11 show another embodiment of an assembly. The attachment device 200 of this embodiment differs from that of Figure 1 in that an opening 221 is provided in the upper surface 211 of the housing 210, offset from the fastener hole 202, which opens into the cavity 203. Furthermore, an opening 222 is also provided through the lower surface 213 of the housing 210, which opens into the cavity 203. The opening 222 in the lower surface 213 is aligned with the opening 221 in the upper surface 211 .

[0083] This attachment device is again embedded in within the substrate 100 of the structural component. The upper and lower surfaces 211 , 213 of the housing are exposed through the upper and lower surfaces of the substrate 100 such that both openings 221 and 222 in the upper and lower surfaces 211 , 213 of the housing are exposed. This, with the attachment device embedded in the substrate, the openings 221 , 222 and the cavity 203 may be used to pass substances or components from one side of the substrate 100 to the other. For example, wiring or hydraulic lines may be passed through the 221 , 222 and the cavity 203 to form connections across the substrate without forming separate holes in the structural component that may weaken the integrity of the structural component.

[0084] Figure 12 shows an embodiment of an assembly 1 , which includes an attachment device 200 tailored for use with a single layer substrate 100. In particular, the attachment device 200 comprises a housing 210 that defines a defines a fastener hole 202 that is again a threaded throughole for a bolt. The housing also defines a hollow cavity 210 within the housing. The cavity 203 in this embodiment is formed on one side of the fastener hole 202, shown on the left side in Figure 12. This attachment device 200 is configured to be embedded at an edge region of the substrate 100, so that the bolt 251 is inserted into the fastener hole 202 where the fastener hole projects from the edge of the substrate 100, with the fastener hole 202 shown projecting from the right edge of the substrate in Figure 12. Where the housing 210 projects beyond the edge of the substrate 100, it defines the fastener hole 202 with a solid wall portion of the housing 210.

[0085] The portion of the housing 210 that is configured to be embedded in the substrate 100 has a wedge shape in cross section. This is formed by the upper surface 211 of the housing 210 extending further to the left in Figure 12 than the lower surface 213 of the housing, and then being connected by a diagonal sidewall 217 extending between the edges of the upper and lower surfaces 211 , 213. The cavity 203 extends from an inside wall that is adjacent to the bolt hole 202 to a diagonal inside sidewall at the diagonal sidewall 217.

[0086] The attachment device 200 of this embodiment is configured to be embedded in a substrate 100 formed by injection moulding. In particular, the attachment device 200 may be positioned at the edge of an injection mould that is configured to mould the substrate 100 around the edge of the attachment device so that the housing portion containing the cavity 203 is embedded in the injection moulded substrate 100 while the portion containing the fastener hole 202 projects from the edge of the injection moulded component to allow a secondary component to by connected by a bolt 251 .

[0087] Another embodiment of an assembly 1 is shown in Figure 13. This embodiment differs from the embodiment of Figure 12 in that the upper and lower surfaces 211 , 213 each include a projecting portion 216 that projects away from the upper and lower surfaces. These projecting portions 216 form a rim on each of the upper and lower surface 211 , 213 surrounding the fastener hole 202. With the attachment device 200 embedded in the substrate 100, the projecting portions 216 form surfaces around the fastener hole that are at least level with the outer surfaces of the substrate 100. Thus, the substrate 100 is at least partially protected from the compressive forces of the bolt 251 or a nut by the housing 210 of the attachment device 200.

[0088] A further attachment device 200 is shown in Figure 14. Whereas the attachment devices of the preceding embodiments have each had a single fastener hole, the embodiment shown here includes first and second fastener holes 202a, 202b, in the form of threaded through holes, for receiving first and second bolts 251 a, 251 b. The first and second fastener holes 202a, 202b are parallel to one another, and each pass from an upper surface 211 of the housing 210 through to the lower surface 213. The housing may have, for example, a generally cuboidal shape, with the fastener holes 202a, 202b offset along the length of the housing. The housing 210 defines a single internal cavity 203, which surrounds both fastener holes 202a, 202b. Another embodiment is shown in Figure 15. This embodiment shows an assembly in which the cavity inside the attachment device is used to store and transmit a fluid, such as oil or washer fluid. In this embodiment, the attachment device 200 is arranged so that an end portion containing the fastener hole 202, shown as the left-side end of the attachment device 200 in Figure 15, is fully embedded in the substrate 100. A right-side end of the attachment device 200 is also shown as fully embedded in the substrate 100 and in some embodiments may comprise a second fastener hole for a second bolt. Between these two fully embedded ends of the attachment device, a first portion 218 of the housing 210, containing the cavity 203, extends above the upper surface of the substrate 100 on a first side while a second portion 219 of the housing extends below the lower surface of the substrate 100 on the opposing side. This increases the volume of the cavity 203 by having it extend out from the inside of the substrate on both sides. The protruding first portion 218 of the housing has a first opening 221 into the cavity through which a fluid may be fed into or out of the cavity 203. Likewise the protruding second portion 219 of the housing has a second opening 222 into the cavity through which a fluid may be fed into or out of the cavity 203. In use, this attachment device may be connected to a fluid flow control system and used to store and transmit fluid. This embodiment provides lightweighting and space saving advantages over assemblies that would otherwise use dedicated attachment devices and reservoirs for the same purposes.

[0089] A further embodiment is shown in Figure 16. This embodiment differs from the embodiment of Figure 15 in that the cavity 203 contains a flow control valve built into the attachment device. This flow control valve divides the cavity 203 in two, each in communication with one of the two openings 21 , 222 and allows for the valve to control of flow from one section to the next and so control flow of fluid between the openings. Therefore, the attachment device forms an integral part of a fluid flow control system. This may be formed by partially 3D printing the housing, inserting the flow control valve with any required connections across the housing wall, and then continuing to 3D print around the inserted flow control valve. While a valve is shown here, other devices may be embedded in the 3D printed housing, including passive devices, such as a shaped orifice between adjacent cavities that may act as a passive flow control valve.

[0090] Figure 17 shows a further embodiment of an assembly 1. In this embodiment, the attachment device 200 is arranged so that an end portion containing the fastener hole 202, shown as the left-side end of the attachment device 200 in Figure 17, is fully embedded in the substrate 100. A section of the housing having the cavity 203 extends away from the left-side end of the attachment device, within the substrate 100 such that most of the housing, running along within the substrate 100, is embedded inside the substrate. In a first location, adjacent to the fastener hole 202 at a left side of the attachment device in the Figure and corresponding to a left most region of the cavity 203, a first portion 218a of the housing is exposed through the uppers surface of the substrate 100 and a first opening 221a is provided through the exposed portion of the housing into the cavity. In a second location, spaced from the first location by a region in which the housing and cavity are fully embedded in the substrate, a second portion 218b of the housing is exposed through the uppers surface of the substrate 100 and a second opening 221 b is provided through the exposed portion of the housing into the cavity. Alternatively, the second portion may be exposed through the lower surface of the substrate so that the two openings open on opposing sides of the substrate 100.

[0091] The embodiment of Figure 17 may serve several functions. Firstly, the attachment device may provide a way of routing fluid along the first substrate from a first location to a second location without the need for separate exposed fluid lines. Secondly, a cooling medium, such as air or liquid coolant, may be directed actively or passively between the openings to provide a cooling effect to the substrate 100 of the structural component.

[0092] Figure 18 shows an embodiment configured for active decoupling of the attached components using the attachment device. In this embodiment, the attachment device 200 has generally the same structure as the embodiment of Figure 14. This embodiment differs from the embodiment of Figure 14 in that an opening 220 is provide into the cavity 203 through the lower surface 213. This opening may be used to provide the cavity with a charge of an explosive 254, such as guanidine nitrate, commonly used in airbags. An initiation device 255 may be arranged through this opening and used to selectively initiate the explosive charge. This arrangement may thus be used to free the bolts from the attachment device and cause a secondary component to be decoupled from the structural component. To facilitate this, the housing may be provided with localised weak points configured to fail during the explosion. For example, the wall of the housing may be thinner along tracks surrounding the fastener hole.

[0093] Figure 19 shows an example of a suitable structural component 10 for use with one of the attachment devices described herein. This embodiment shows an example of a carbon fibre-reinforced polymer forming a frame section of the cabin of a motor vehicle. In particular, the structural component here corresponds to the front portion of the cabin, including the passenger footwell, door sills, and cabin floor. Figure 19 shows that a rear edge of the cabin floor, which is intended to be joined to another frame section of the cabin, is provided with a series of embedded attachment devices, the fastener openings 202 of which are visible through openings in the carbon fibre-reinforced polymer. These attachment devices may thus be used to bolt together two frame section of the cabin while providing lightweight reinforcement to the bolt holes in the carbon fibre-reinforced polymer substrate.

[0094] Figures 20 to 22 show another embodiment of an attachment device 200. This is another attachment device accommodating multiple fastener holes. The attachment has a housing 210, the peripheral surface of which comprises a substantially planar upper surface 211 separated from a parallel lower surface 213, with a peripheral sidewall 212. A projecting portion 223 extends away from the upper surface 211.

[0095] Figure 20 shows the attachment device after forming by additive manufacturing, such as by powder bed fusion. Figure 20 shows the external wall as transparent to reveal the internal structure, and includes a number of solid and hollow regions, as discussed below. The interior of the housing comprises one large internal cavity 203 that extends through much of the interior of the housing. A series of solid regions 202p have been formed using additive manufacture, which are precursors to the fastener holes that will be formed in the attachment device later. Four solid regions 202p are provided in different parts of the housing extending between the upper surface 211 and the lower surface 212. These are regions that will later be provided with the fastener holes 202a-202d, as shown in Figure 21. Three of these solid regions 202p (those corresponding to fastener holes 202a, 202b and 202d) are adjacent to a section of the peripheral sidewall 212, while a fourth (corresponding to fastener hole 202c) is provided with an internal wall 215 bridging between the solod region 202p and the sidewall 212. The projecting portion 223 is also formed as a solid region 202p.

[0096] Figure 21 shows a cutaway view through the attachment device 200, parallel to the upper and lower surfaces 211 , 213 after a machining process is used to form the fastener holes. Figure 22 shows a cutaway view perpendicular to the upper and lower surfaces 211 , 213. This Figure more clearly demonstrates the solid regions, identified with hatching, and the hollow region, i.e. mainly the cavity 203. Each of the solid precursor regions 202p is drilled in a machining process to form a fastener hole 202a-202e with a high tolerance for position and dimension. Each of the four fastener holes 202a-202d in the solid precursor regions 202p extending between the upper and lower surfaces 211 , 213 is drilled with a respective though hole for a fastener. The solid precursor region 202p in the projecting portion 223 is drilled with a threaded blind hole 202e. It will be noted that the blind hole 202e is drilled along a direction that is substantially perpendicular to the direction of the other four through holes 202a-202d. This allows the attachment device to be used to attach structural components along different directions while retaining a light weight. As shown best in these two Figures, the cavity 203 extends between the and around the various through holes 202a-202e to provide the attachment device with a light weight.

[0097] Figures 23 and 24 show another attachment device comprising multiple fastener holes. The attachment deice has a complex L-shaped main body portion including a side section 301 and a base section 302 extending generally perpendicular to the side section 301. A smaller projecting portion 303 extends from both the side section 301 and base section 302, approximately perpendicular to both. Figure 23 again shows the outer surface as transparent to reveal the internal structure, and depicts a number of solid regions, mainly regions 202p, with the majority of the inside being hollow cavity. Figure 23 shows the attachment device after additive manufacturing and before machining of through holes. Again, it comprises a series of solid precursor regions 202p, including one such solid region in the projecting portion 303 and five in the base section 302.

[0098] Figure 24 shows a cutaway view through the base portion 302 after fastener holes have been machined, only fastener holes 202a-202e machine into the solid precursor regions 202p of the base are visible in this Figure; however, a fastener hole would also be machined in an orthogonal direction into the projecting portion 303. In this embodiment, each of the fastener holes may be threaded blind holes.

[0099] Of note in this embodiment is the three internal walls 215 extending across the cavity 203. These internal walls 215 are provided with small openings through the walls to allow fluid communication across the walls. This allows the loose powder that remains in the cavity 203 after manufacture by powder bed fusion to be removed from the cavity 203 through one opening (not shown) that may be provided anywhere into the cavity through the housing. These walls 215 also act to internally strengthen the attachment device, preventing it from caving in when subject to high pressure manufacturing processes, e.g. when incorporating into a structural component. Finally, these walls 215 also act as supporting structures during additive manufacturing.

Claims

CLAIMS1 . An assembly comprising: a structural component having a first substrate; and an attachment device bonded to and / or at least partially embedded in the first substrate of the structural component to fix the attachment device to the structural component, wherein the attachment device comprises: a housing defining a peripheral surface of the attachment device; a fastener hole in the housing of the attachment device for receiving a mechanical fastener; and at least one cavity located within the housing and at least partially enclosed by the peripheral surface, the cavity having at least one dimension larger than a corresponding dimension of any opening through the peripheral surface into the cavity.

2. The assembly of claim 1 , wherein one or more of the at least one cavity is substantially fully enclosed within the housing, or has at least one dimension at least twice as large as a corresponding dimension of an opening through the peripheral surface into the cavity.

3. The assembly of claim 1 or claim 2, wherein the first substrate comprises a multi-layer substrate, and wherein preferably at least part of the attachment device is located between a plurality of the layers of the multi-layer substrate.

4. The assembly of any of the preceding claims, wherein the first substrate comprises a composite material, preferably a fibre-reinforced polymer.

5. The assembly of any of the preceding claims, wherein the structural component is a moulded structural component, preferably a thermoset moulded structural component.

6. The assembly of any of the preceding claims, wherein the attachment device housing is an additively manufactured attachment device housing, preferably a 3D-printed attachment device housing.

7. The assembly of any of the preceding claims, wherein the attachment device housing is formed of metal or polymer.

8. The assembly of any of the preceding claims, wherein the attachment device housing is formed as one integral piece.

9. The assembly of any of the preceding claims, comprising an array of cavities located within the housing separated by internal walls of the housing, and / or wherein the housing comprises one or more internal strengthening members extending across the cavity.

10. The assembly of any of the preceding claims, comprising an internal wall of the housing, wherein the internal wall comprises one or more openings therethrough to provide fluid communication across the internal wall.

11. The assembly of any of the preceding claims, wherein the at least one cavity makes up at least 30% of the volume of the attachment device, preferably at least 40%, more preferably at least 50%, most preferably at least 60% of the volume of the attachment device.

12. The assembly of any of the preceding claims, wherein the fastener hole is a blind hole or a through hole.

13. The assembly of any of the preceding claims, wherein the fastener hole is a threaded hole for receiving a machine screw or bolt.

14. The assembly of any of the preceding claims, wherein the peripheral surface comprises one or more projections or recesses for increasing a contact area between the peripheral surface and the first substrate.

15. The assembly of any of the preceding claims, wherein a portion of the peripheral surface of the attachment device surrounding the fastener hole is exposed relative to the first substrate, and is preferably level with or projects above a surface of the first substrate, such that said portion of the peripheral surface of the attachment device may act as a compression limiter during fastening by a mechanical fastener.

16. The assembly of any of the preceding claims, wherein the attachment device is at least partially embedded in the first substrate of the structural component such that a first portion of the housing is exposed on a first side of the first substrate and such that a second portion of the housing is exposed on a second side of the first substrate, and further comprising a first opening through the peripheral surface into the cavity in the first portion of the housing and comprising a second opening through the peripheral surface into the cavity in the second portion of the housing.

17. The assembly of any of the preceding claims, further comprising first and second openings through the peripheral surface into the cavity, and further comprising a flow control valve located in the cavity for controlling flow of fluid through the cavity between the first and second openings.

18. The assembly of any of the preceding claims, wherein a first part of the housing comprises the fastener hole and wherein a second part of the housing comprises at least some of the at least one cavity, wherein the first part of the housing is embedded within the first substrate, and wherein the second part of the housing extends outside of the first substrate.

19. The assembly of any of the preceding claims, further comprising an explosive charge located in the cavity and an initiation device arranged to selectively initiate the explosive charge for decoupling a component attached to the attachment device by a mechanical fastener received in the fastener hole.

20. The assembly of any of the preceding claims, wherein the attachment device comprises a plurality of fastener holes into the housing of the attachment device, each for receiving a respective mechanical fastener.

21. The assembly of claim 20, wherein at least two of the fastener holes extend along different directions of the attachment device.

22. The assembly of claim 21 , wherein an angle between two of fastener holes is at least 20°, preferably at least 45°, preferably at least 80 °, wherein most preferably two of the fastener holes are substantially orthogonal to one another.

23. The assembly of any of claims 20 to 22, wherein the cavity is arranged between at least two of the fastener holes.

24. The assembly of any of the preceding claims, wherein the at least one cavity substantially surrounds the fastener hole(s).

25. The assembly of any of the preceding claims, further comprising a secondary component, the secondary component being attached to the structural component by a mechanical fastener received in the fastener hole.

26. The assembly of any of the preceding claims, wherein the structural component is a frame or bodywork component of a passenger vehicle, wherein preferably the structural component comprises at least a portion of a monocoque of a passenger vehicle.

27. A method of manufacturing an assembly comprising: providing a structural component having a first substrate; and providing an attachment device bonded to and / or at least partially embedded in the first substrate of the structural component to fix the attachment device to the structural component, wherein the attachment device comprises: a housing defining a peripheral surface of the attachment device; a fastener hole in the housing of the attachment device for receiving a mechanical fastener; and at least one cavity located within the housing and at least partially enclosed by the peripheral surface, the cavity having at least one dimension larger than a corresponding dimension of any opening through the peripheral surface into the cavity.

28. The method according to claim 27, adapted to provide an assembly according to any of claims 1 to 26.

29. The method according to claim 27 or claim 28, further comprising forming the housing of the attachment device by additive manufacturing, preferably 3D printing.

30. The method according to claim 29, comprising, subsequent to the additive manufacturing step, forming the fastener hole into the attachment device, preferably by a separate machining process.

31. The method according to any of claims 27 to 30, further comprising performing a surface etching process, surface abrasion process, a surface coating process or a surface anodization process on the housing of the attachment device before the attachment device is bonded to and / or at least partially embedded in the first substrate.

32. The method according to any of claims 27 to 31 , further comprising moulding the structural component, preferably comprising compression moulding or injection moulding the structural component.

33. The method according to any of claims 27 to 32, further comprising forming the structural component around the attachment device, such that the attachment device is at least partially embedded in the structural component.

34. The method according to any of claims 27 to 32, further comprising bonding the attachment device to the first substrate of the structural component and / or at least partially embedding the attachment device in the first substrate of the structural component.

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