[0001] The invention relates to an improved sandwich panel and to a method of manufacturing the sandwich panel. The panel can be used in vehicle manufacture and the invention also relates to a structure comprising a sandwich panel.

Background of the invention [0002] Honeycomb sandwich (HC) sandwich panels, or sandwich panels such as those produced by Hexcel™ Composites, are used extensively in aerospace technologies because they offer a low weight / high stiffness alternative to conventional structural panel materials. An example of a conventional panel 10 is illustrated in Figures 1a and 1 b and comprises a core 11 with upper and lower skins 12, 13 each bonded 14 to opposing panel surfaces. Different materials can be used for each element of the panel. Examples of the core material include high density foam, organic foam, carbon, fibreglass, Kevlar™, Nomex™ and metallic alloys including aluminium. Examples of the skin materials include alloys such as aluminium, fibreglass, composites, organic materials and wood laminates and examples of the bonding material include tert-butyldimethylsilyl (TBS) and film adhesives.

[0003] Panels are manufactured by applying bonding material to the top and bottom surfaces of the core layer and then laying the skins over their respective bonding layers. The resultant panel can subsequently be milled from either or both sides to create hole mount pockets, for example.

[0004] Despite the advantageous weight to stiffness ratio of these panels, adoption of this technology has been limited in vehicle manufacture to high cost vehicles such as railway trains and airplanes as well as niche car markets such as formula racing cars. The reason for this is that manufacturing processes using these panels are generally labour intensive and so the cost vs. function ratio in vehicle manufacture remains heavily unbalanced.

[0005] In US 5849122 the use of a panel as a floor panel in a car is described for the purposes of vibration and sound absorption. However, the panel is additional to the structural floor panel of the car chassis. A similar use of a panel is also described in US 4898419. Whilst there have been proposals, such as those mentioned above, to the use of panels in car manufacture, such proposals have not been implemented in high volume production.

[0006] Reference is made herein to panels, such as honeycomb panels, honeycomb sandwich panels and sandwich panels. A panel has a core layer sandwiched between facing skin layers. The core material can be an expanded foam, such as Expanded Polypropylene (EPP), an expanded material, a honeycomb-type of material or a combination thereof. These panels are sometimes referred to as honeycomb-type panels. References are intended to encompass any and all forms of expanded panels such as sandwich panels, irrespective of their manner of manufacture or core material. In this regard reference to honeycomb panels and honeycomb sandwich panels is intended to encompass panels comprising a core layer and opposing outer skin layers provided either side of the core layer, the core layer being formed of a cavity containing material, which can involve isolated cavities or interconnected cavities, regularly or irregularly distributed throughout the core material. Panels described herein are described, by way of example, as having expanded polypropelyne (EPP) core panels sandwiched and glued between two sheets of aluminium.

Summary of the invention

[0007] From one aspect, the invention resides in a panel comprising a core layer, and first and second skin layers secured to opposing surfaces of the core layer, wherein the panel is configured to comprise a strengthener configurable to increase the planar strength of a portion of the panel and/or an interface configurable to enable formation of a structure by engagement with another object or panel, wherein the structure is arrangeable either substantially parallel or substantially perpendicular to the plane of the panel.

[0008] The panel can be used in applications where localised strength and/or interconnection with another panel are required. The interconnection can be a perpendicular T-joint, an angular joint or can be a substantially planar connection. [0009] The invention also resides in a structure, or connection, comprising two or more panels. The panels can have reciprocal connectors. The reciprocal connectors can have a fixer and/or a holder. The fixer and/or the holder can be bolt, a glue or any such means for fixing. The fixer and/or the holder can be a latch, or similar type of locking mechanism. The connection can function to strengthen a structure.

[0010] The strengthener can comprise a formation of the surface of the core layer and/or the skin layer. The formation can be wave-shaped, and can comprise a corrugation of the or each surface of the panel. Corrugations of opposing sides of the panel can be configured to be substantially perpendicular to each other to increase strength. The formation can be regular and/or the formation can have symmetry. The formation can comprise a portion of the or each skin layer that extends over an edge of the core layer. The or each skin layer can connect to the other skin layer. The first skin layer can be connected to the second skin layer at point between the planes defined by the skin layers. The connection can comprise a fixing such as a weld.

[0011] The strengthener can comprise a reinforcer. The strengthener can be a metal bar. The strengthener can comprise an inner layer formed between the skin layers. The inner layer formed between the skin layers can be the same area size and/or volume as an outer skin layer. The inner layer can be made of the same material as the or each outer skin layer. The inner layer can be a different material.

[0012] The panel can have an end-cap configured to enclose the core layer between the first and second skin layers. The end cap can function as a strengthener. The end-cap can have arms configured to securably engage with the first and second skin layers. The end-cap can have a protrusion configured to connect with the core layer. The end cap can function to enclose the edge of the panel and/or increase the strength of the panel.

[0013] The interface can comprise a securer. The securer can comprise a recess in the core material. The recess can comprise an enclosed portion. The recess can be enclosed by the or each skin layer. By way of example, the interface can comprise a securer, or mounting located in an aperture of the core layer. The mounting can be located between skin layers of the panel. A portion of the mounting can be accessible through the or each skin layer.

[0014] The mounting can comprise a load-washer. The mounting can comprise a core having a substantially helical surface for receiving a bolt. The mounting can comprise an anti-rotation feature. The anti-rotation feature can comprise a key and/or can be bonded within the panel.

[0015] A securer can be implemented in different ways. By way of example, the securer can be a threaded mount integrated with the panel. In another example, the securer can comprise an interface. The interface can comprise a tongue and/or a groove that can be reciprocal and configurable to be connectable together and locked together with a glue, such as a resin.

[0016] The interface can comprise a tongue configured to be securable in a reciprocal groove located in another panel. The tongue can comprise a channel configured to receive a fixer. The tongue can be securable by a bolt having a substantially helical surface. The tongue can be securable by a bonding material. The tongue can be configured to enable the bonding material to form a mechanical connection with the groove and/or a bonded connection.

[0017] The interface can comprise a groove configured to be securable with a reciprocal tongue in another panel. The groove can comprise a recess and/or step configured to receive a fixer. The groove can be securable by a bonding material. The groove can be configured to enable the bonding material to form a mechanical connection with the tongue. [0018] By way of example, the invention can reside in a structure comprising a first panel having a groove connected with a second panel having a tongue.

[0019] The bonding material can be configured to form a lock at the edge of the tongue and/or groove.

[0020] The interface can comprise a groove having a latch. The latch can be configured adjacent to a perimeter edge of the groove. The groove can be configured to receive a reciprocal tongue and the latch is locatable in a reciprocal socket located on the tongue. The interface can comprise a tongue having a socket. The tongue is configured to be insertable in a reciprocal groove and the socket is configured to receive a reciprocal latch located on the reciprocal groove. The or each panel can comprise an indicator for indicating when the interface has formed a secured connection with another panel. [0021] The latch and the socket can be used to provide sensory feedback to a person connecting a tongue and a groove having a latch and a socket. The sensory feedback can be audible and/or visual and/or tactile.

[0022] The securer can comprise a protrusion of the core material 101 extending beyond the plane defined by the skin layer. The protrusion can comprise a recess configurable to securably locate an object located therein. The protrusion can comprise a negative-angle recess, or a claw. A negative angle recess can function like a claw, or a crab-like pincer. The claw can grip an object like a finger and thumb on a person's hand. The claw can be formed by a recess having a lip. The lip can extend over the recess to partially close the recess. Functionally, an object can be pushed into a claw, the object squeezing past the edge, or lip, of the recess, and when the object has passed the lip the lip returns to its previous position and can hold the object in the recess. By way of example, the recess can be configured to hold a cylindrical pipe. In cross-section, the claw of the recess can be circular in profile and reciprocal to the pipe. [0023] A panel can be provided with a with one or more flaps that are foldably securable with a reciprocal panel. The flap can be inserted through an aperture in a panel. The portion extending beyond the aperture can be folded over to secure a panel having the flap in place. The flap can be secured using a fixing. The fixing can be a rivet and/or an adhesive.

[0024] A flap can be configured on a tongue of a panel. The flap can be inserted through an aperture located in the base of a reciprocal groove in another panel, which receives the tongue. Similarly, the flap can be folded to secure the panels together. The tongue and groove can be configured at the perimeter of a panel, and the flap can be configured to fold around the edge of the panel instead of passing through an aperture.

[0024] The or each feature of the securer and/or interface and/or fixer are combinable in light of the teaching herein.

[0025] The panel can have an interface that is interfacable in planar connection with another panel. The interface can be a jigsaw-puzzle type of connection.

The interface can have a feature that reciprocates with a corresponding feature on another panel. The connection on one panel can interlock with a connection on another panel. In other words, the connection can be an engaging type of connection. The connection may be a ball and socket type of connection. The interface can comprise tabs and/or c-cuts. The connection can have a hook.

The connection can have dovetailing. Functionally, the connection can be a knitted, or sewn, type of connection. [0026] The panel can comprise a plurality of tessellated, or jigsaw-puzzle connected portions of core layers that are securably configured between skin layers.

[0027] In view of these and other variants within the inventive concept, reference should be made to the appended claims rather than the foregoing specific description in determining the inventive concept. [0028] An aspect of the present invention is to provide an improved panel which is suitable for use in high volume vehicle manufacture. A further aspect of the present invention is to provide a method of manufacture of the improved panel that is suitable for integration into in-line vehicle manufacturing facilities. A still further aspect of the present invention is form structures having one or more of the panels as structural elements of a vehicle, the vehicle being suitable for high volume production.

[0029] Thus the present invention provides a honeycomb type panel comprising a core layer comprising a cavity containing material and first and second skin layers bonded to opposing surfaces of the core layer characterised in that the core layer additionally includes a plurality of apertures, the density of the apertures in the core layer varying with respect to the surface of the core layer.

[0030] The plurality of apertures provided in the core layer can extend through the thickness of the core layer and can be closed at opposing surfaces of the core layer by the first and second skin layers. The density of the apertures can vary as a result of the plurality of apertures including at least two different diameters of aperture and / or as a result of the spacing between adjacent apertures of the plurality of apertures in the core layer varying with respect to the position of the apertures in the panel. [0031] The plurality of apertures in the core layer can be bounded by interconnected cavity containing material.

[0032] The honeycomb type panel can further comprise one or more through holes which extend through the core layer and the first and second skin layers and which are open at the first and second skin layers. The one or more through holes can extend coaxially through the core layer and the first and second skin layers. Optionally a strengthening mounting can be embedded within the core layer, the strengthening mounting having one or more through holes coaxially aligned with respective one or more through holes in the first and second skin layers.

[0033] The perimeter of the panel can include at least one edge projecting tab and / or at least one slot can be provided in a peripheral region of the panel, the slot being adapted for engagement with a projecting tab on a further honeycomb type panel.

[0034] In a further aspect the present invention provides a method of manufacturing a honeycomb type panel comprising the steps of: providing a core layer comprising a cavity containing material; providing first and second skin layers; cutting a plurality of apertures in the core layer, the density of apertures in the core layer varying with respect to the surface of the core layer; applying a bonding material to opposing surfaces of the core layer; and bonding the first and second skin layers to the opposing surfaces of the core layer by virtue of the bonding material.

[0035] The plurality of apertures can be cut so as to extend through the core layer whereby the first and second skin layers close the openings to the plurality of apertures. The plurality of apertures cut in the core layer can vary in diameter and / or the distance separating adjacent apertures of the plurality of apertures cut in the core layer can vary with respect to the surface of the core layer. [0036] In another aspect embodiment the method further comprises the initial step of cutting a plurality of core layers from a single sheet of cavity containing material and / or cutting a plurality of first skin layers from a single sheet of skin material and / or cutting a plurality of second skin layers from a single sheet of skin material. Moreover the first and second skin layers can be cut from a single sheet of skin material.

[0037] Also the method can further comprise forming at least one edge projecting tab during the step of cutting the core layer and the first and second skin layers from their respective sheet material and / or forming at least one slot in a peripheral region of the panel shaped to receive an edge projecting tab on a further panel.

[0038] Of course the bonding material can be applied by means of a rotary applicator and the plurality of apertures can be cut simultaneously in the core layer by means of a profiled cutting pallet.

[0039] Ideally the chassis of the vehicle comprises a plurality of interconnected honeycomb type panels and the honeycomb panels can be joined together by means of co-operable tabs and slots provided on peripheral regions of the panels.

[0040] Furthermore a holding strip can be provided over the junction between two honeycomb panels and a foam material provided in the region bounded by the honeycomb panels and the holding strip.

[0041] A further aspect of the present invention is to provide methods of manufacture of panels that is suitable for integration into in-line vehicle manufacturing facilities. A still further aspect of the present invention is to provide panels having means for improving inter-panel bond reliability. [0042] Thus in a first aspect the present invention provides a method of manufacturing a honeycomb type panel comprising the steps of: providing a mould having a first and a second part, at least one of the first and second mould parts including at least one injection port; positioning first and second skin layers on the interior surfaces of the first and second parts of the mould respectively; closing the mould and injecting an expandable material into the mould interior via the at least one injection port; curing the expandable foam material thereby forming a core layer between the first and second skin layers, the core layer comprising a cavity containing material.

[0043] The core material injected into the mould can comprise an expandable foam. The core material can comprise a thermoplastic polymer foam.

[0044] Also, at least one of the first and second parts of the mould can be provided with one or more formations projecting into the interior of the mould and the respective skin layer includes one or more openings corresponding to the one or more formations such that when the skin layer is mounted in the mould, the one or more formations extend through the skin layer and into the space between the first and second skin layers.

[0045] Moreover, at least one of the first and second parts of the mould can be provided with one or more formations projecting into the interior of the mould for which no corresponding opening in the respective skin layer exists such that the skin layer over-lies and confirms to the contours of the one or more projecting formations.

[0046] In a second aspect the present invention provides a honeycomb type panel comprising a core layer comprising a cavity containing material and first and second skin layers bonded to opposing surfaces of the core layer, the panel including one or more tabs projecting from the edge of the panel and characterised by each tab including at least one open channel in its surface defining a bonding fluid pathway.

[0047] The panel can further include one or more slots closed at one end by the first or second skin layers, the slots being sized to receive a projecting tab on a second panel and the skin layer at the rear of the slot including at least one injection opening for the injection of a bonding material and at least one exit opening for the escape of air and excess bonding material. [0048] In a yet further aspect the present invention provides a honeycomb type panel comprising a core layer comprising a cavity containing material and first and second skin layers bonded to opposing surfaces of the core layer characterised in that the core layer additionally includes a plurality of apertures, the density of the apertures in the core layer varying with respect to the surface of the core layer.

[0049] The plurality of apertures provided in the core layer extend through the thickness of the core layer and are closed at opposing surfaces of the core layer by the first and second skin layers. The density of the apertures can vary as a result of the plurality of apertures including at least two different diameters of aperture and / or as a result of the spacing between adjacent apertures of the plurality of apertures in the core layer varying with respect to the position of the apertures in the panel. The plurality of apertures in the core layer can be bounded by interconnected cavity containing material.

[0050] The honeycomb type panel can further comprise one or more through holes which extend through the core layer and the first and second skin layers and which are open at the first and second skin layers. The one or more through holes can extend coaxially through the core layer and the first and second skin layers. Optionally a strengthening mounting can be embedded within the core layer, the strengthening mounting having one or more through holes coaxially aligned with respective one or more through holes in the first and second skin layers.

[0051] Each of the honeycomb type panels can be designed to interconnect with adjacent panels so that integral features of the panel design such as an energy path or a communicating channel align with and interconnect with similar features in adjacent panels so that energy paths, communicating channels and other features can extend continuously across multiple panels. In this respect the panels function as jigsaw elements which when correctly connected together jointly form larger structures and flow / communicating functions.

[0052] In a further embodiment the perimeter of the panel can include at least one edge projecting tab and / or at least one slot can be provided in a peripheral region of the panel, the slot being adapted for engagement with a projecting tab on a further honeycomb type panel.

[0053] In a further aspect the present invention provides a method of manufacturing a honeycomb type panel comprising the steps of: providing a core layer comprising a cavity containing material; providing first and second skin layers; cutting a plurality of apertures in the core layer, the density of apertures in the core layer varying with respect to the surface of the core layer; applying a bonding material to opposing surfaces of the core layer; and bonding the first and second skin layers to the opposing surfaces of the core layer by means of the bonding material. The plurality of apertures can be cut so as to extend through the core layer whereby the first and second skin layers close the openings to the plurality of apertures. In one aspect the plurality of apertures cut in the core layer vary in diameter and / or the distance separating adjacent apertures of the plurality of apertures cut in the core layer varies with respect to the surface of the core layer. [0054] The method can further comprise the step of cutting one or more holes in each of the core layer and the first and second skin layers, the holes in the three layers being aligned when the skin layers are bonded to the core layer so as to form holes extending through the panel. d

[0055] In another aspect, the invention resides in a tool configurably locatable in an aperture of a panel to control the position of the components of a panel with respect to each other during a manufacturing operation, such as pressing. This is achievable by limiting the degree to which panel components can move laterally during when a panel is compressed. The tool can inhibit movement of the skins of a panel during manufacture. The tool can be expandable and collapsible between an open position and a closed position. The tool can have a mechanism, such as an internal resilient bias, that is compressible from an open or expanded position. The mechanism can comprise a spring, rubber or pneumatic component. The cross-sectional profile of the tool can be configured to match the aperture. The tool can be tubular and/or cylindrical. The tool can have at least one reference surface. The end of the tool can be flat, or can be concave, to maximise stability when engaging with press, or convex to minimise contact with a press. The tool can be configured with ribs. The ribs can be configured to improve the control of aperture position in a panel. The tool can have more than one protrusion. The tool can have protrusions at the or each end for engagement with a panel and/or a manufacturing component, such as a press. The tool can have features to improve handling by a machine or a manual operator, such as a handle, roughened surface or a magnetic interface.

[0056] The tool can have a central axis, or datum about which one or more components of the tool are centred. The peripheral edges of the tool can be aligned about the datum, and can be centrally aligned about the datum. During the transition from open to closed position the tool can remain centrally aligned in the aperture. The tool is configurable to inhibit the movement of panel components during an assembly operation, such as pressing. The tool can have a shaped side configured to maintain optimum contact with the panel. The shaped side can self-centre the tool. The side can be substantially flat, or the side can be shaped, such as chamfered edge for self-centring within an aperture. The tool can maintain alignment about the datum throughout compression.

[0057] In another aspect the method further comprises the initial step of cutting a plurality of core layers from a single sheet of cavity containing material and / or cutting a plurality of first skin layers from a single sheet of skin material and / or cutting a plurality of second skin layers from a single sheet of skin material. Moreover the first and second skin layers can be cut from a single sheet of skin material.

[0058] Also the method can further comprise forming at least one edge projecting tab during the step of cutting the core layer and the first and second skin layers from their respective sheet material and/or forming at least one slot in a peripheral region of the panel shaped to receive an edge projecting tab on a further panel. Of course the bonding material can be applied by means of a. rotary applicator and the plurality of apertures can be cut simultaneously in the core layer by means of a profiled cutting pallet.

[0059] With the present invention, by varying the density of the core layer within a single panel the weight of an individual panel can be reduced, in comparison to conventional panels, whilst still meeting the strength requirements for that panel at positions such as hard points. This flexibility in the core density of each panel permits weight control not only across each panel but in the case of vehicle manufacture across the vehicle as a whole without undermining the ability of the panels to withstand and/or transmit complex and multiple directional forces. In this regard panels of the present invention have spherical integrity to externally applied forces. [0060] Moreover, with the methods of manufacturing the panels in accordance with the present invention, both fixed and variable core density panels can be produced using a low energy construction at high rates of repetition making the panels suitable for use in high volume vehicle manufacture. Also, the method enables the panel manufacturing method to be integrated with in-line vehicle manufacturing with differently designed panels being manufactured for specific chassis platforms.

[0061] Overall it will be appreciated that standard honeycomb panels are assembled before being subjected to modification and/or adaptation for use, whereas the panels of the present invention comprise bespoke elements, such as bespoke skins and a bespoke core material, which enables features to be engineered into the product at an earlier stage of the manufacturing process, prior to assembly, bonding, pressing and the like.

[0062] Conventional honeycomb panels are often subject to expensive post purchase machining to create finished structure panels, which can be complex if features are to be embedded into the core material. Further, the core material is subject to a degree of degradation or 'destruction' that occurs to the core after machining, thus the stability of the panel and the anti-peel ability, or ability for the skin to stay attached to the core, is significantly reduced.

[0063] Although conventional honeycomb has a high tensile strength, the failure mode is catastrophic compared to a gradual reduction in performance of the panel of the present invention.

[0064] Although the panels are substantially flat, or two dimensional, the panel, or a portion of the panel, can be a three dimensional shape. In cross-section, the three dimensional shape can be across a single plane, thus creating for example an arch-type structure. Additionally, or alternatively, the three dimensional shape across a two planes can, for example, create a concave or convex structure. [0065] One or more of the above mentioned features and/or panels of the invention provides a low cast panel that is inherently light and easy to handle, yet retaining sufficient strength and handling high static and dynamic loads. The panel can be thicker, while being lighter and stronger than a similar steel structure. It is not simply a flat panel because one or more features can be integrated therein, thus enabling a panel to be customisable. A panel, with integral connecting means, or connection-type interfaces, can reduce the bill-of- materials in an assembly using the panels. [0066] Note that the manufacturing process of the panels can be achieved sequentially, without the need to modify, or customise, the product after assembly of the panel is complete. Therefore, bespoke features such as fluid ducting, wire looms, sensors, fixings and the like can be integrated during the assembly process without the need for a secondary operation in a post- production stage.

[0067] Note that a non-honeycomb type core material, such as EPP, permits lower cost and more efficient manufacture of a panel. Honeycomb panels are often supplied in sheets of a predetermined size, such as 8' x 4' (2.4384m x 1.2192m) and preparation of such a sheet often involves cutting the honeycomb structure using a cutting tool. To achieve sharp corners in apertures cut in the honeycomb panel the cutting tool requires a small radius, which has the effect that a cutting operation takes longer to complete because it physically takes longer or a tool change is required. In contrast, an alternative core material, such as EPP, can be cut using other tools, such as a laser-cutting device.

[0068] Note that the edges of an aperture cut into a honeycomb panel will make point contact with an object located in the aperture. To be clear, if a honeycomb was fabricated using a 0.2mm foil, then a cut across the honeycomb would result in protrusions of the foil that were 0.2mm thick. In contrast, a cut aperture in an alternative core material such as EPP has a substantially flat interface surface. [0069] In light of the teaching of the present invention, the skilled person would appreciate that two or more aspects or objects of the invention can be combined to form an improved panel, or a structure comprising two of more panels.

[0070] In the context of this document reference herein to vehicle is intended as reference to any form of conveyance such as, but not limited to, cars, trains, boats and airplanes. [0071] Further aspects of the invention will be from the following description. Brief description of the Figures

[0072] In order that the invention can be more readily understood, reference will now be made, by way of example, to the drawings in which:

Figure 2 is an exploded view of a panel;

Figure 3 is a system diagram of a manufacturing process for making the panel of Figure 2;

Figure 4 is a schematic diagram showing manufacturing apparatus of a manufacturing process for making the panel of Figure 2; Figure 5 is a schematic diagram showing a manufacturing process comparable to Figure 4, but with additional work stations for increased volume manufacture;

Figures 5a to 5c are schematic diagrams of a tool for improving control of the manufacture of the panels, while Figures 5d and 5e show the tool located in a panel; Figures 6a and 6b are a selection of views of panels, moulds, cores, skins and cross-sections of panels formed for an alternative method of manufacture of a panel; Figures 7a and 7b are sectional views of a panel and panel skins having a shaped surface profile;

Figures 8a and 8b are sectional views of a panels enveloped within a skin layer; Figures 9a to 9d are sectional and perspective views of panels having protruding and recessed features formed in the core layer, which are accessible through apertures in the skin layer;

Figures 10a to 10d are sectional and perspective views of panels having recessed channels formed in the core layer that are enclosed within the panel by the skin layer;

Figure 11a is a cross-sectional view of a panel of Figure 11b taken through a threaded screw mounting incorporated therein, while Figure 11b is a perspective exploded view diagram of the components of the panel;

Figures 12a to 12c are cross-sectional views of an end-cap configurable to close the end of a panel, while Figure 12d is a perspective view of a panel fitted with an end-cap;

Figure 13a and 13b are cross-sectional views of known tongue and groove panel connections, while Figures 13c and 13d are sectional views of improved tongue and groove panel connections; Figures 14a and 14b are sectional perspective views of the panel structure of figures 13c and 13d; Figure 14c is a perspective view, with detail, showing an alternative improved tongue and groove panel connection;

Figures 15a and 15b are perspective views of a modified tongue, while Figures 15c and 15d are cross-section views illustrate the step of fixing the tongue of Figure 15b within a groove using a fixing;

Figures 16a and 16c is a perspective views of a tongue and groove configured to provide a fixer, or holder, while Figures 16b and 16d are cross-sectional views highlighting, respectively the features of the fixer and Figure 16e is a cross- sectional view highlighting the interface between the tongue and the groove of Figures 16a and 16c when connected;

Figure 16f is a perspective view of a tongue and groove configured to provide a modified fixer, or holder, using a flap, while Figures 16g and 16h are cross- sectional views of the modified fixer configuration of Figure 16f, and Figure 16i shows a cross-sectional view of a fixer having two flaps;

Figures 16j to 16t show various views depicting alternative configurations of a tongue, groove and flap configured to provide a modified fixer, or holder;

Figures 17a to 17c are views of load-washers, while Figures 17d and 17e are, respectively, cross-sectional views of a load-washer prior to and after fitting within a reciprocal feature in a panel;

Figure 18a and 18b are views of panels configured to connected to other panels; and

Figure 19a to 19e are views of panels having integrated tracks and configured to connect to other panels. [0073] It should be noted that the relative dimensions of features illustrated in the Figures, are not to scale. In particular the thicknesses of certain layers have been enlarged for ease of reference. Detailed description of embodiments

[0074] An improved sandwich panel is shown in Figure 2. The panel 100 comprises a core layer 101, a top skin layer 102, a bottom skin layer 103 and bonding layers 104. The core layer 101 comprises a material in which cavities are distributed throughout the material. The outline or outer perimeter profile of each of the layers is substantially identical but variations exist between the individual layers with respect to patterning of the layers within their perimeters. Thus, the core layer 101 and both of the skin layers 102, 103 have a plurality of through apertures 105 which are common to all layers and which are aligned to form a through aperture (i.e. An aperture open at both ends) in the panel 100. The through apertures extend through the thickness of the core layer i.e. between the opposing surfaces of the core layer.

[0075] Additionally or alternatively the density adjusting holes 106 can be blind apertures which can have the same or varying depths. In both cases the dimensions of the density adjusting holes are larger than the dimensions of the cavities inherent in the core material. By way of example, each of the dimensions of the density adjusting holes is at least three times the corresponding dimensions of the inherent material cavities. Also, a plurality of different shapes can be used for the density adjusting holes in a single panel: it is not a requirement of the improved panel that all the density adjusting holes are of the same shape and/or size.

[0076] Also, the walls of the density adjusting holes 106 are smooth and have a regular and repeated profile. Whilst the density adjusting holes 106 illustrated in

Figure 2 have a hexagonal periphery it is to be understood that the holes 106 are not limited to this shape and can take any shape e.g. circular, quadric or triangular. Also, different density adjusting holes can have different shapes: it is not a requirement of the improved panel that all of the density adjusting holes are of the same shape. A hexagonal periphery has been illustrated in Figure 2 as it is a good illustration of close hole arrangements with a minimum of boundary core material. Corresponding holes are not provided in the top and bottom skin layers 102, 103. Hence, in the panel 100 the top and bottom skin layers 102, 103 cover and close the density adjusting hole apertures 106 in the core layer 101. [0077] Unlike the cavities inherent in the core material, the density adjusting holes 106 have openings in both a first surface and an opposing second surface of the core layer so that the density adjusting holes 106 extend between these openings substantially perpendicular to the first and second surfaces of the core layer. Corresponding holes are not provided in the top and bottom skin layers 102, 103. Hence, in the panel 100 of Figure 2 the top and bottom skin layers 102, 103 cover and close the density adjusting hole apertures 106 in the core layer 101.

[0078] Three different sizes of density adjusting holes 106 in core layer 101 are illustrated in Figure 2. Although only three sizes are shown, it will be immediately apparent that a greater or lesser number of sizes can be employed, as desired.

[0079] Alternatively or in addition the size of the holes can remain the same with only the distance separating adjacent holes varying. It will be apparent from Figure 2 that the effect of this is that a hole area ratio corresponding to the cumulative area of the density adjusting holes 106 (i.e. the total cross-sectional area of the density adjusting holes) relative to cumulative area of the core material (i.e. the total cross-sectional area of the core material remaining around the density adjusting holes) varies with respect to the surface area of the core layer. Thus, in Figure 2 in addition to a peripheral region 107 of the core layer 101 in which no density adjusting holes are present, the core layer has a first region 108 with a high density of holes (corresponding to a higher hole area ratio) and a second region 109 with a lower density of holes 106 (corresponding to a lower hole area ratio). The effect of this variation in the density of the holes 106 or a variation in the hole area ratio is that the density of the core layer 101 varies with the peripheral region 107 having the highest core density and the first region 108 having the lowest core density and the density variation being controllable and selectable. This, in turn, results in a selective variation in the density of the panel 100. In this regard it is to be understood that the variation in density referred to above is measurable at a scale greater than the dimensions of the inherent cavities in the core material.

[0080] By changing the size and/or density and/or position of the holes 106 the characteristics of the panel csπ be changed. By way of example, characteristics such as the relative strength, the resonant frequency, the stiffness, and the sound-absorbing properties can be changeable.

[0081] It will also be apparent from Figure 2 that the density of the holes 106 in the core layer 101 varies with respect to the surface area of the core layer. Thus, in addition to a peripheral region 107 of the core layer 101 in which no density adjusting holes are present, the core layer has a first region 108 with a high density of holes and a second region 109 with a lower density of holes 106.

[0082] By providing a core layer 101 with a variable core density with respect to its surface area, the total weight of the panel can be reduced without loss of the strength characteristics that are advantageous for the panel to be of use in a vehicle in which the panel can experience forces externally applied from three or more different directions. Thus, in Figure 2 the highest core density is provided at the periphery of the panel and around the apertures 105 which will be used for the purposes of attaching the panel to other structural elements. [0083] The lowest core density is provided in regions of the panel where little or no forces are likely to be experienced. Variations in the core density across the panel, which are intermediate the highest and lowest core densities, ensures that forces experienced by the panel are evenly distributed by the panel and that the risk is minimised of weak points arising at the junction between high and low core densities.

[0084] In Figure 2 the core material of the core layer 101 is interconnected around the density adjusting holes 106. This ensures that the core layer 101 remains a single element in the production process. However, the core material can be wholly interconnected across the core layer.

[0085] It is envisaged that the core layer 101 can comprise multiple tiers of core material joined together by thin supporting sheets. With this embodiment each tier of core type material provided either side of a supporting sheet is not required to be interconnected across the entire panel area. Instead the density adjusting holes can result in different portions of the tier of core material being disconnected from the remainder of the tier of core material but with the supporting sheets acting as connecting bridges to the different portions of core material. It will, of course, be apparent that in this embodiment that the density adjusting holes extend through each tier of core material but can not extend continuously across the entire thickness of the core layer.

[0086] The panel can comprise a material such as EPP, or any similar such low density material. Although the invention can comprise honeycomb material, the use of EPP has particular advantages over known panels. EPP enables accurate moulding and tolerance control, while having memory-material properties, returning to a substantially original form after compression. Further, the use of EPP reduces the need for complex slide-arrangements in the tooling because freshly moulded EPP remains sufficiently hot and pliable enough to be withdrawn from a recess within a mould without detrimental degradation. [0087] Known panels such as honeycomb panels are optimised for static applications wherein the properties of a panel are consistent across the panel, with substantially no variation in, for example, stiffness. Thereafter, the panel is modified to achieve specific performance criteria, such as reduced weight, localised energy absorption or fixings. Known panels are considered to be over- specified for their applications. As a consequence, any modification thereto, such as the reduction of material, can result in a compromise in the performance. [0088] A panel comprising a core layer of EPP allows a panel to be fabricated according to the performance criteria required. The consistency can be varied to allow features and specific characteristics to be inherent in the panel, which can be implemented to meet predetermined specifications. This can be achieved in a single, or reduced, manufacturing process because performance, variation and consistency are factored into the panel during manufacture. By implementing varying factors such as different form, different density, different consistency the panel can be manufactured for dynamic and/or static performance. By implementing one or more features of the invention on a panel simultaneously a synergistic benefit is achievable because manufacturing steps are reduced, no inherent weaknesses are created in the panel and dynamic performance can be optimised. By way of example, energy absorption paths can be implemented within the panel.

[0089] A method of manufacturing the panel of Figure 2 is illustrated in the operational flow diagram of Figure 3 and panel manufacturing apparatus is illustrated diagrammatically in Figures 4 and 5. The manufacturing method is divided into three operational sections: panel design; panel element preparation; and panel construction. Each operational section is time independent of the other operational sections and thus at the end of each operational section the manufacturing method can be halted and the beginning of the next operational section can be commenced, as desired. In Figure 3 an estimate of the duration of each operational section is also identified.

[0090] Firstly, a design of a vehicle chassis utilising one or more panels and the design of each panel is prepared S1 using conventional computer aided design (CAD) software. The CAD software can be run using any suitable CAD computer 200 having a user input interface for example, but not limited to, a server system, desktop computer or laptop. The design of each panel S1 includes the design of the core layer 101 and the upper and lower skin layers 102, 103; the positioning of all through apertures 105; and the positioning of density adjusting apertures 106 in the core layer which are to be cut into the core layer of each panel. The selective positioning of the density adjusting apertures 106 enables the weight of each panel to be reduced without loss of the required panel strength. Designs of the one or more panels can be stored in design data memory 201 and communicated, when required, to a computerised control system 202 which can be any suitable computerised control system such as, but not limited to, a server system, desktop computer or laptop. The CAD computer, memory 201 and control system 202 can be implemented in a single electronic system or can be implemented as separate electronic systems in wired or wireless communication with one another.

[0091] The control system 202 is programmed to determine from the CAD panel designs and the dimensions of the source material sheets the number and arrangement (herein referred to as 'nesting') of individual panel layers on the source material sheets S2 so as to minimise wastage. In the case of the panel skin layers 102, 103, based upon the dimensions of the source material sheets for the skin layers the control system 202 will determine the best nesting of the layer designs for a single sheet. Similarly, in the case of the panel core layer 101, based upon the dimensions of the source material sheet for the core layer, the control system 202 will determine the best nesting of the core layer design on a single sheet to minimise wastage. This information is fed from the control system 202 to the milling machines 203 and is used when cutting out the layer designs from the source material sheets. In the case of the skin layers, multiple sheets of the skin material, e.g. five sheets can be stacked and cut simultaneously.

[0092] The source material for each of the skin layers and the core layer is supplied, for example by a series of conveyors 204 to respective milling stations where the cutting of the source material sheets is under computer numerical control (CNC). The cutting machines 203 at each station are programmed by the control system 202 to cut out S3 from the source material sheets one or more panel layers for use in the manufacture of panels.

[0093] The cutting of the or each layer of the panel can be using laser-cutting, water-cutting, milling, stamping and the like.

[0094] Once cut, the source material wastage is removed S4, using conventional techniques, and the cut panel layers are collected and stored for future use or transported to the next manufacturing stage. The skin layers are, by way of example, lasercut whereas the core layer can be stamped out using a profiled cutting pallet so that the desired design of the core layer is cut out by a single stamping action.

[0095] In the final operational stage, panel construction, the core layer 101 passes through pinch rollers (not illustrated) and a heat curable bonding material is applied S5 to the upper and lower surfaces of the core layer by an applicator 205. Thereafter respective skin layers 102, 103 are aligned with the core layer and laid over the bonding material on the upper and lower surfaces of the core layer. With all three panel layers in place heat and pressure is applied S6 by a clave 206 to thermally cure the bonding material. Once the curing stage is complete e.g. after 30 minutes, the panel is ready for use. [0096] It will be appreciated that the manufacturing method and apparatus described above is particularly suited to full automation enabling energy and material savings and efficiencies. Also, the manufacturing method and apparatus are suited for incorporation into existing and new automated vehicle manufacturing plants.

[0097] As the bonding material is applied to the core layer and not to the skin layers the bonding material is applied only where it is required. This is particularly important as the core layer and skin layers have apertures cut into them prior to construction of the panel and thus the skin layers overlie regions of low density core in which a substantial portion of the core material has been removed.

[0098] In the above described method the layer of core material is provided as a blank of solid cavity containing material which is then cut to the required shape and which has one or more density adjusting holes cut or stamped into the blank.

[0099] In an alternative method, the layer of core material is moulded to the desired shape incorporating the required density adjusting holes. Thus, a moulding process replaces steps S3 and S4 of the first manufacturing method.

[00100] In this alternative method the CAD software is again used to design the required panel but this time the design data is then used to design a mould for the panel. With a mould produced in accordance to the design, core material is injected into the mould via pre-formed injection ports into the interior of the mould. The core material can be Expanded Polypropylene (EPP), or an equivalent expandable material, which is injected into the mould as foam and subsequently cures to form the cavity containing material. [00101] Recycled EPP can also be used as the cavity containing material.

The use of recycled EPP offers the added benefit of being a comparatively cheap material with a low environmental impact. The core material is cured within the mould and is removed from the mould after curing. Thereafter, other than any finishing processes such as edge trimming, subsequent method steps S5 and S6 for fabricating the panel are identical to those described earlier namely applying bonding material to the opposing surfaces of the core layer, applying the outer skin layers over the bonding layers of cured core material and curing the bonding material.

[00102] The thickness of a panel 100 and the position of apertures therein can be controllable during the manufacturing process. The thickness in an area of a panel can be controlled when the core layer 101 , the top skin layer 102, the bottom skin layer 103 and the bonding layers 104 are pressed together. The pressure of the press can be controlled to improve bonding therebetween.

[00103] The skins 102, 103 and core material 101 are bespoke such that a panel can be complete after assembly and require no further processes, such as milling or forming. It is important, therefore, that the positional tolerance of the skins with respect to the core material is optimised such that apertures, and in particular the edges of apertures, are aligned. By way of example, a hole through a panel is defined by the apertures in the skin layers 102, 103 and in the core material 101 and the centre of these apertures must remain aligned during pressing. Similarly, the layers and core must be aligned when assembling a panel having a recess, or groove.

[00104] Figures 5a to 5c show a tool 220 that functions to provide one or more reference dimensions during the manufacture of the panel. By way of example, the tool enables the centres of apertures of a hole, groove or recess or the like to remain substantially aligned during the manufacture of the panel. In this way, the edges of the aperture can be substantially aligned. The tool is configurable to inhibit movement of components of the panel, such as the skins 102, 103 and core material 101 during manufacture. [00105] The tool is shown located in an aperture of a panel 100 in Figures 5d and 5e. The tool 220 is biased towards an open position, as shown in Figures 5a, 5b and 5d, and is collapsible to a closed position as shown in Figure 5c and 5e. An internal mechanism, not shown, functions to control the alignment of the tool as it moves between an open position and a minimum length of the tool in a closed position.

[00106] The tool 220 is substantially cylindrical and has a lower portion, or locator 222, and an upper portion 224, that are movable relative to one another between the open and closed positions. The locator has a protrusion 226, which defines a shoulder 228 on the locator 222. The upper portion 224 has an interface surface 230, and both the locator 226 and the interface 230 have substantially flat surfaces that define substantially parallel planes. [00107] The length of the tool 220 is measurable between the protrusion 226 and the interface 230. The tool has a mechanism, such as an internal resilient bias, that displaces the locator 226 from the interface 230. The mechanism can, for example, comprise a spring, rubber or pneumatic component. The entire tool and/or the bias mechanism can be made of a non- ferrous and/or non-metallic and/or non-conducting material, such as plastic.

[00108] The tool 220 is locatable in an aperture in a panel 100, wherein the aperture has an open end on the upper skin layer 102 and a closed end provided on the lower skin layer 103, through which the tool cannot pass. In the example shown in Figure 5d, the aperture is a through aperture wherein the maximum diameter of the closed end is smaller than the maximum diameter of the open end.

[00109] The shoulder 228 of a tool 220 positioned in a panel 100 locates against the perimeter of the aperture in the lower skin 103 and the locator 226 extends therethrough. The locator 226 can be configured to match a reference feature, such as an aperture in the lower skin. The open length of the tool 220 is such that the upper portion extends out of the aperture beyond the upper skin 102. In other words, the open length of the tool 220 is greater than the depth of the panel adjacent the aperture in which the tool is located. The depth of the locator 226 can be greater than the thickness of the lower skin 103 and is configurable to self-centre on the lower skin layer 103. The longitudinal surface of the upper portion 224 is configurable to remain between the aperture in the upper skin 102 and self-centre in the open end of the aperture. In other words, the tool can be configured to maintain alignment of the skin layers and core material as it is compressed.

[00110] The tool 220 has a central axis, or datum about which one or more components of the tool are centred. k.> particular, the locator 222 and upper portion 224, and their peripheral edges are centrally aligned about the datum.

[00111] A press 232 is configured to apply pressure to the skins layers 102, 103 of a panel, as shown in Figure 5e. A tool 220 located in an aperture of a panel is pressed into the closed position. During the transition from open to closed position, the locator 222 centrally locates the tool 220 in a substantially central position in the aperture. As the tool is compressed, the peripheral edges of the locator 222 and upper portion 224 also remain substantially centrally aligned in the aperture. The tool, therefore, inhibits movement of the skin layer 102 and core material 101 with respect to the skin layer 103 in which the tool is centred. In the closed position, the locator 226 and interface 230 butt against the press 232.

[00112] The tool 220 is configurable with shaped sides to enable self- centring within the aperture and to improve the accuracy with which the skins of the panels can be positioned. The tool maintains alignment throughout compression. [00113] During manufacture, skins 102, 103 that having been coated with adhesive are accurately located with the core 101 before being placed in a press for final compression bonding. The tool 220 enables the position of the core 101 and skins 102, 103 to be accurately controlled without the need of pins or other reference devices within the press. Apertures in the panels that will be used for other functions, such as groves for tongues and apertures for fixings can be utilised for this operation. The tool 220 does not interfere with the press when closed because it collapses to the same level as the skins. The tool reduces the handling time, set-up costs and improves accuracy.

[00114] The tool 220 functions to inhibit displacement of the panel components such that the resulting aperture is substantially orientated about a common axis. [00115] Figures 6a and 6b show a step involving moulding the core layer and/or the entire panel. Figure 6c illustrates, in exploded view, and with the use of cross-sections, a panel produced from the steps of Figures 6a and 6b.

[00116] A panel having a cavity containing core layer 301 and opposing skins 302, 303 is formed using an enclosed moulding (EM) method. Firstly, the design of each panel is prepared using conventional computer aided design

(CAD) software. Again, the CAD software can be run using any suitable CAD computer 200 having a user input interface for example, but not limited to, a server system, desktop computer or laptop. The design data for the panel is then used to design upper 304a and lower 304b parts of a mould for moulding the panel. The upper and lower parts of the mould 304a, 304b include formations

305 which project into the mould interior and which will define features of the panel when moulded. It will be apparent that these method steps equally apply to the previous method described above for moulding the core layer alone. However, this further alternative method of manufacture now departs from the previous moulding method because the skin layers are mounted within the mould prior to formation of the core layer.

[00117] As mentioned earlier, the upper and lower skins 302, 303 can be formed of any suitable material, such as aluminium. The skin material can be selected according to the application and can be glass-reinforced plastic, carbon- fibre, steel, medium density fibreboard and the like. One or more skin layers can be used on one side of the panel. Also, the upper and lower skins 302, 303 have been pre-cut so that pre-formed openings 306 are provided in the skins at positions corresponding to the position of one or more of the formations 305 in the mould 304a, 304b. The upper skin 302 is then mounted in contact with the inner surface of the upper mould 304a and the lower skin 303 is mounted in contact with the lower mould 304b. The skins are positioned so that the p ^' re formed openings 306 surround projecting formations 305 of the mould. However, for projecting formations 305 in the mould where no corresponding pre-formed opening exists in the skin, the skin over-lies the projecting formation and follows the contours of the projecting formation.

[00118] Thus with this alternative method of manufacture an panel is formed as follows: in step S1 , a panel is designed and a mould for the panel is also designed; one or more openings are cut into the skin layers intended for the panel; and in step S10 the upper skin 302 is mounted in the upper part of the mould 304a and the lower skin 303 is mounted in the lower part of the mould

304b. Both the upper skin 302 and the lower skin 303 have a bonding layer 307 applied to one surface of each skin layer and with the skin layers in position within the mould the bond bearing surfaces of the upper and lower skins 302, 303 face towards one another across the interior of the mould.

[00119] One or both of the mould parts, the lower mould 304b in Figure 6a, is also provided with injection ports 305. In step S11, the mould 304a, 304b is shut and the core material is injected into the mould via the injection ports 308 using one or more injection guns 309. Methods particularly suitable for injecting the core material include CF (crack fill) or PF (pressure fill). As with the previous alternative method, the core material is Expanded Polypropylene (EPP), or an equivalent expandable material, which is injected into the mould as foam and subsequently cures to form a cavity containing material 301. Heat and pressure is applied to thermally cure the core material and the bonding material, such that the core material cures to form a core layer 301 sandwiched between opposing skin layers and with the shape of the core layer defined by the upper and lower skins 302, 303, the projections 305 in the mould 304a, 304b and the perimeter of the mould. Ideally, the core material cures ahead of the bonding material on the skin layers. The temperature applied to the mould can be controlled to manage the curing processes of the core material and the bonding material. Thus, an initial temperature can be set to trigger curing of the core material and after a predetermined time period the temperature can be raised to trigger the curing of the bonding material.

[00120] Increasing the temperature can also be used to accelerate the curing process. The projecting formations 305 determine any through holes required in the panel as well as the size and location of the density adjusting holes. In the former case, the upper and lower skin layers have corresponding pre-formed openings whereas in the latter case one or both of the upper and lower skin layers follow the contours of the density adjusting holes. In this respect the panel of this alternative method differs slightly from the panel illustrated in Figure 2 because the upper and lower skin layers 102, 103 in Figure 2 close over the density adjusting holes in the core layer 101 and do not follow the contours of the holes.

[00121] It is also envisaged that one or more regions of the core layer can be left exposed, i.e. these regions are not covered by the skin layer. This has the effect in the cured panel of the core material protruding through the skin layer. Such protrusions can be used to provide fixing points and other functions directly to the core layer or the core layer protrusions can be moulded so that, in use, the core layer protrusion conforms with and fills a cavity adjacent the panel. Thus, in the case of a vehicle chassis a core layer protrusion can be used to fill an adjacent crash zone or crumple zone cavity.

[00122] In step S12, once curing is complete the panel is removed from the mould and any finishing treatments are performed on the panel, such as edge trimming, before the panel is ready for use. [00123] In both of the alternative methods described above different panels can be selectively designed to withstand different stresses and strains by varying the density of the core material injected into the mould, and / or the size and density of holes in the core material defined by the formations 305 in the mould and / or the distance between the upper and lower skin layers 302, 303 when the mould 304a, 304b is shut. The greater the thickness of the core layer and / or the density of the core layer 301, the greater the strength of the panel. Also, variation in the core material density and the size and density of the holes in the core material can be used to form energy paths in the resultant panel. The energy paths are interconnected regions of higher core material density and / or interconnected regions of the core material with smaller sized holes and / or lower hole density along which load and / or impact forces can be transmitted or dissipated across or through the panel.

[00124] The energy paths are included in the initial design of the panel and can include shaped regions and channels to control the direction of transmission of energy along the energy paths. The panels can be designed so that the energy path in one panel is arranged so as to connect with an energy path in an adjacent connected panel thereby forming energy channels extending across two or more panels. [00125] It is envisaged that the panels manufactured according to the methods described above can be stacked and bonded together to form a multiple thickness panel. When the panels are stacked together all through holes will, of course, be aligned. However, the density adjusting holes in each individual panel in the stack need not be aligned and the design of each of the individual panels in the stack is required to be identical to the other panels although using an identical or substantially identical panel design for each panel offers costs savings in reducing the number of moulds required. [00126] The skilled person would appreciate in light of the teaching herein that a panel can comprise elements that are assembled and/or milled and elements that are moulded. By way of example, skin layers can be assembled together with a core layer to form a panel using the process in relation to Figures 3, 4 and 5. However, once assembled, the panel can comprise a void, which is configured to be fillable. Thereafter, the void is filled using a moulding process, such as that described in relation to Figure 6a and 6b, wherein material is injected within the mould and processed to fill the space.

[00127] Figures 7a to 8b shows a way in which forming panel components to control performance parameters of a panel, such as flexural strength, resonance and the like.

[00128] Figures 7a and 7b illustrate the use of corrugations. Figure 7a shows a core layer 101 that is shaped to engage with a shaped skin layer 102 to which it interfaces. The bonding layer is not shown. However, the assembled panel 100 and the layers forming the panel are configured such that the engagement between the layers provides optimum performance. Figure 7b shows a selection of top skin layers 102 having a various shaped profiles. [00129] The engagement between the layers can be configured such that there is sufficient contact and, therefore, sufficient adhesion, between a skin layer 102, 103, a bonding layer 104 and a core layer 101. The bonding layer 104 can comprise a pliable sheet that can adjust in size to enable sufficient contact with the skin layer and the core layer. The bonding layer can comprise a sprayed-on layer. The degree of contact and/or adhesion can vary according to the strength and/or performance required of the panel. Strength and/or performance can be maximisable when the degree of contact and/or adhesion is maximised.

[00130] In cross-section, the shaped profile has a series of peaks and troughs, and can have a wave shaped profile, such as those shown in Figure 7b, which have a symmetrical pattern. The wave shape can have a square, rectangular, triangular or sinusoidal profile, or a combination thereof. Alternatively or in addition to regular and/or symmetrical profiles the profile can have an asymmetrical and/or irregular form. The wave shaped profiles travel, as shown, in a left to right direction, whereas the peaks and troughs extend substantially perpendicularly from the page as viewed.

[00131] A shaped profile has an advantage in that it can change the properties of the panel 100. One or more of the above-described profile features can be combined to modify the characteristics of the panel.

[00132] By way of example, the panel shown in Figure 7a is able to flex more in a direction perpendicular to the waves (i.e. across the page as viewed) than in a direction parallel to the waves. By configuring the waves in a particular direction, the edges of the panel can be displaceable with respect to the centre panel such that the panel is curvable. In contrast, the panel is less flexible in the direction parallel to the peaks and troughs, in a direction perpendicular to the page as viewed, thus inhibiting flexibility and/or the ability to curve in said direction. [00133] The shaped profile is not restricted to a series of parallel waves. The shaped profile can be configured such that a panel, as viewed from above, has an area having concentric circles. By controlling the pattern of peaks and troughs that covers the surface of a panel the flexibility in specific areas such as interface or connection points can be adjustable accordingly. [00134] The strength of a panel can be increased by implementing corrugations on opposing sides of the panel, or on an internal layer within the panel, which run in counter direction to each other. In other words, the corrugations on one side of the panel are arranged substantially perpendicularly to corrugations on the other side of the panel.

[00135] The formation and/or pattern of corrugations enables multi-axis strength to be achievable because, by way of example, the flexural strength in one or more of the X-, Y- and Z- axes is controllable. [00136] Figures 8a and 8b show in cross-section a core layer 101 that is enclosable between skin layers 102, 103. As shown in cross-section in Figure 2a, a flat skin layer 103 and a formed skinned layer 102 can be configured to enclose a core layer, the edges of the skin layers extending from the core layer. The edges of the skin layers are adjacent. Arrows indicate fixation points that secure the adjacent points of the skin layers together. The adjacent points lie on substantially the same plane as one of the surfaces of the core layer 101. Fixation can be achievable using spot welds, crimping or similar fixation.

[00137] In Figure 8a the core layer 101 is received within a recess of a shaped skin layer 102, while the other skin layer 103 remains substantially flat.

Alternatively, both skin layers can be provided with recesses, as shown in Figure

8b, such that the adjacent portions of the skin layers, where the fixation is to be applied, are positioned at an intermediate point between the planes of the surfaces of the core layer 101. The intermediate point is adjustable around the perimeter of the core layer. The edge of the core layer can be additionally bonded to skin layers 102, 103. [00138] All or part of the panel can comprise an enclosed portion, where the skin layers 102, 103 wrap around the edge of the core layer 101 and are fixed together. By way of example, the core layer is enclosed along two opposing sides of a square-shaped panel.

[00139] Similarly, all or part of the panel edge can comprise a portion wherein the or each skin layer 102, 103 wraps over the edge of the core material. At said portion, a skin layer can contact the other skin. By way of example, a skin layer is wrapped over the edge of the core layer and extends down the side of the core layer for a distance equivalent to one fifth of the core layer total depth.

[00140] Figures 9a to 11b are examples of a securer comprising formation or additions that can be made to a panel 100 to facilitate connection to other features.

[00141] Figures 9a to 9d show features comprising recesses and/or protrusions of the core layer 101 that are provided on the panel. The skin layer is configured with apertures 400 to expose these features. The or each recess and/or profile can have shape configured to receive a specific object, such as a fixing, cable, pipe, mounting and the like.

[00142] Figure 9a is a perspective view of fixer, or securer, comprising protrusions 402 of the core material 101 extending beyond the plane defined by the skin layer 102. Figure 9b shows the panel of Figure 9a in cross-section. The apertures 400 are configured in the skin layer 102, through which the core layer 101 extends. In the example shown, the protrusions 402 are substantially rectangular blocks. The blocks are configured with recesses 404 into which an object can be fixed. [00143] One of the protrusions has two elongate holes extending into the protrusion to a depth beyond the skin layer 102. This protrusion is suitable for receiving a fixing, such as a self-tapping coach-screw or bolt. [00144] In comparison, the other cuboid-shaped protrusion has a substantially cylindrically shaped recess 406 that is substantially circular in cross- section profile. The cylinder 406 has an open side enabling a pipe-shaped object of smaller diameter to be pushed in to the recess. The material of the core layer 101 provides resilient bias to secure a pipe trapped therein. The material of the core layer 104 is sufficiently elastic and flexible enough to enable the walls of the protrusion to be displaced temporarily by a pipe inserted there between. After insertion, the material is biased towards its original position and holds the object in place.

[00145] The properties or the core material, which can be EPP, are such that a vibration proof fixing can be provided. By way of example, a motor can be snap-fix mounted or screwed to the EPP material. Not only is the complexity of the fixing reduced but the interface with the EPP functions to absorb vibrations and can be configured to eliminate resonant frequencies generated by the motor.

[00146] Note that the core layer material can achieve resilient bias by comprising a material that enables a negative angle release, such as EPP. The negative angle release enables a grab aperture to be configured for mounting and attaching functionality. A push clip fit action type of mounting can be implemented by the material of the core layer.

[00147] Further, the core layer material and/or the form of the protrusion can be configured to provide a vibration absorber such as a dampening mount suitable for sensitive elements such as electronic systems or, by way of example, a crash-sensor mount that requires negligible damping to the impulse caused by a crash. [00148] The protrusions can be shaped to accommodate the object that is to be secured thereon and the shapes illustrated have been provided merely by way of example. [00149] Figure 9c shows in perspective view recesses 404 set within the core material 101 located between the planes defined by the skin layers 102, 103. Figure 9d shows the panel section 100 of figure 9c in cross-section. The apertures 400 provided in the skin layer 102 enable access to the recesses 404 in the core material 101.

[00150] The recess can be open along its length, or partially covered, as shown in Figure 9c. Once again, as with the configurations described above in Figures 9a and 9b, the core layer 101 is sufficiently elastic and flexible.

[00151] The recesses 404 comprise portions, in cross-section, wherein the aperture 400 in the skin layer 102 is partially closed by core material extending into the aperture. The material extending into the aperture is displaceable, temporarily, by an object inserted into the recess. Once positioned in the recess the material is biased towards its original position and holds the object in place.

[00152] The opening of the recess is slightly smaller that that provided by the aperture 400 in the skin layer 102 and defined by the walls of the core layer 101. The shape of the walls of the core layer forms a circular or pincer-like formation, the opening of which can be defined by an angle in degrees. The angle is definable by the intersection of tangents extending from the wall of the recess adjacent the open side. [00153] It would be clear to the skilled person that the abovementioned features of Figures 9a to 9d are interchangeable and combinable to provide a securer on a panel. Note that such features, suitable scaled, can advantageously reduce the number of clips, brackets or such attachments required when an object such as a pipe or cable-loom is to be secured to a panel 100. [00154] Figures 10a to 10d show perspective and cross-sectional views of recesses 404 within the core layer 101 that are enclosed by skin layers 102 and 103. Figures 10c and 10d illustrate pipes 408 having square-section and cylindrical-section positioned in recesses 404.

[00155] The panel 100 can be configured with one or more additional features that enhance its performance and/or enable improved connectivity with objects or similar panels. [00156] As illustrated in Figures 11a and 11b, the panel can additionally be provided with one or more connector or mounting 500 (only one connection mounting is illustrated in the Figure). The connection mountings 500 can provide additional support at a contact point in the panel which is likely to experience high externally applied stresses. The connection mounting 500 can be in the form of a bar or billet, which can comprise a strong metallic material, which is embedded in the panel during construction. The connection mounting 500 can include one or more through holes for receiving connectors such as screws or rivets to enable the panel to be attached to a strut or other structural element, for example. The mounting can be shaped to inhibit rotation within the core material, e.g. the mounting can have a square-shaped footprint.

[00157] As shown in Figures 11a a mounting aperture 502 is cut in the core layer 101 and is sized to receive the connection mounting 500. Apertures 504 are also cut in the or each of the skin layers 102, 103 but the position and size of these apertures 504 do not correspond to the mounting aperture 502 but instead correspond to the or each aperture 506 in the connection mounting 500 (three apertures are illustrated in Figure11b). With the apertures 105 in the skin layers 102, 103 aligned with the apertures in the connection mounting an aperture extending through the panel 100 is provided for a connection member. [00158] When the panel 100 is constructed, the aperture in a connection mounting 500 is aligned with the or each aperture 502 in one of the skin layers and the connection mounting 500 is secured to the skin layer 103, for example by a bonding material. Figure 11a illustrates in cross-section a connection mounting 500 with a threaded screw hole in position in the core layer and aligned with apertures 105 in both skin layers 102, 103. Such connection mountings can also be used with panels manufactured in accordance with the final alternative method of manufacture described herein although in this latter example, the skin layer lies intermediate the connection mounting and the core layer.

[00159] As mentioned earlier, the panels manufactured according to the method described above are intended for use in the manufacture of vehicles where the panels are used as part or all of the structural support for the vehicle such as a car or van chassis. It is envisaged that 22 mm thickness panels could be used in the manufacture of a car chassis resulting of a chassis weight of as little as 70 Kg. This would enable the weight of smaller cars to be reduced to around 186 Kg.

[00160] Figures 12a to 12c show cross-sectional views of a panel 100 edge and a cap 600 configurable to be placed on the edge of the panel 100, while Figure 12d shows the cap 600 positioned on a square corner of a panel to illustrate the cap 600 fitted to a panel in perspective view.

[00161] The core layer 101 can be prepared with a slot 602 or similar receiver feature for receiving a fixer comprising a fixing 604 of the cap. The cap is elongate and shaped to extend along the edge of the panel. In cross-section, the cap 600 has a body 606, from which the fixing 604 extends, for covering the edge face of the panel 100 where the core layer 101 is exposed between the skin layers 102, 103. The fixing 604 is in the form of a protrusion that extends substantially perpendicularly from the body 606, although it can protrude at an angle. The fixing 604 is shaped to be securable in the core layer material 101 and is insertable with or without the slot 602. The fixing can have a barbed, or fir- tree type profile to inhibit removal of the cap from the panel 100 after it has been inserted in the core material. [00162] Extending in the same direction from the body 606 as the fixing 604 are arms 608. The arms are configured to engage with the edge of the panel 100 by holding and/or biting onto the skin layers 102, 103. The point at which the arms 608 engage with the skin layer 102, 103, the skin layer compresses the core material 101 in the vicinity of the compression point. The compression of the core material can provide resilient bias against the arms and provide improved fixing between the cap and the panel.

[00163] To aid connection between the cap 600 and the panel 100, the skin layer 102, 103 and/or the surface of the arm 608 with which it contacts has a surface configured to increase frictional contact between the cap 600 and the panel 100. By way of example, the arms 608 of the cap 600 and the panel 100 comprise serrated surfaces. Further, to aid fixation, the cap 600 and/or the edge face of the panel 100 can be provided with an adhesive 610 that provides a bond between the cap 600 and the panel 100. The adhesive and/or the protrusion and/or the arms 608 can provide the fixer. Figure 12c illustrates an interface between one of the arms 608 and the skin layer 102. In particular, the arm is configured to apply pressure to the skin layer 102 such that the core material is compressed. The core material can have resilient bias and push against the arm 608 thus functioning to fix the cap 600 to the panel 100.

[00164] Figures 13a through to 19e show various connectors. A connection is configurable to enable one panel 100 to be connected to another. Panels 100 can be connected at an angle to each other and are described herein in substantially perpendicular arrangements or panels can be connected to define a plane. [00165] A conventional tab and slot connection is illustrated in Figures 13a and 13b. With the conventional tab and slot connection 700 a projecting tongue or tab 702 is provided on the edge of a panel and a reciprocating slot 704, sized to receive the tab 700, is provided in another panel. A bonding material 706 is applied to either or both of the contacting surfaces of the tab 702 and the slot 704, and the tab 702 is then inserted into the slot 704. The action of inserting the tab 702 into the slot 704 can cause the bonding material 405 to spread along the contacting surfaces between the tab 702 and the slot 704. However, this spreading of the bonding material 706 is not controlled and can be uneven leaving regions of the contacting surfaces with too little or too much bonding material 706.

[00166] In Figures 13c and 13d an improved tab and slot connection 800 is shown which can be implemented using the improved panels described herein. The improved connection 800 has a tongue 802 projecting from the edge of a first panel 804 and a reciprocating groove 806 sized to receive the tongue 802 is provided in a second panel 808. The tongue 802 has one or more interconnected open channels 810 on its exterior and remote from the main body of the panel which, when the tongue 802 is inserted into the groove 806, form bond material pathways 812 along which bonding material 814 can flow.

[00167] The core material 101 that defines the groove 806 can additionally, or alternatively, be slightly recessed beneath the skin layer that defines the edge of the groove. Bonding material, therefore, can flow around the entire tongue 802 when securably fixed in the groove 804.

[00168] The second panel 808 includes a one or more injection ports 816

(only one is shown in Figure 13c and 13d) in the skin 103 of the panel 808 at the rear of the groove 806. This injection port 816 is positioned so as to be aligned with one of the interconnected channels 810 so that when the tongue 802 is inserted into the groove 806 and bonding material 814 is injected through the opening 816, the bonding material 814 enters the pathway, or channels 810 and flows along the channels around the tongue 802 and the groove 806. One or more exit openings 818 are also provided (two are shown in Figure 13c) in the skin 103 of the panel 808 at the rear of the groove 806. The exit openings 818 are aligned with the channels 810 to permit the escape of air and any excess bonding material. By means of the channels 810 in the tongue 802 a more even distribution of bonding material can be achieved ensuring a more reliable bond between the two panels. Although the channels can be interconnected, it is also envisaged a series of separate channels can be provided on the tongue 802 each aligned with an injection port 816. The position of the injection ports 816 and exit openings 818, and pathways therebetween are described by way of example. Bonding material can be injected to apertures at the sides of the tongue/groove and excess material can exit from a point elsewhere, such as the centre of the tongue/groove. Alternatively or additionally, the edge of the core layer of each panel can be moulded so as to include an irregular profile, such as a lateral or longitudinal stepped profile, which is designed to inter-engage with an associated edge profile of an adjacent panel. Such inter-engagement of the panel edges further improves the reliability and strength of the junction between adjacent panels.

[00169] Alternatively or additionally, the slot connection 800 can comprise a cage (not shown) that functions to improve and strengthen the connection between the tongue 802 and the groove 806 by providing enhanced structure to the bonding material 814 that resides in the material pathways. The cage can be secureably held in the channel 810 prior to insertion of the tongue 802 into the groove 806. Bonding material 814 passes through the pathways, filling the gaps between the tongue 802 and the groove 806 and encompassing the cage before passing through the exit opening. The cage can be configured to self locate and overlap with the boundary of the groove 806. The cage can be formed of a resilient material. The cage is positionable such that it further inhibits the extraction of the tongue 802 from the groove 806. By way of example, the cage functions as a gasket, or similar seal.

[00170] Note that as well as, or alternatively to, the bonding material functioning to glue the tongue 802 in the groove 806, the bonding material sets, or cures, to become a solid block. Functionally, the solid block mechanically locks the tongue 802 within the groove 806 because it creates a barrier that overlaps the boundary between the tongue 802 and the groove 806. [00171] Figure 14a is a perspective view of the tongue 802 in the first panel 804 prior to insertion into the groove 806 of the second panel 806. For clarity skin layers have been selectively removed/made transparent in order that the features of the connection 800 can be viewed. ^; [00172] Figure 14b is a perspective view of the tongue 802 in the first panel 804 after insertion into the groove 806 of the second panel 808. For clarity, skin layers have been selectively removed/made transparent in order that the tongue 802 can be seen in position within the groove 806. [00173] In particular, the connection 800 of Figures 14a and 14b is configured to receive bonding material 814 via two openings 816. The arrows indicate where bonding material 814 is injected. Two openings 818 are located adjacent the channel 812 into which material 814 is injected. [00174] The process of forming the connection is now described by way of example using the structures shown Figures 14a and 14b. It is to be appreciated, however, that the form of the channels and the position and/or number of openings 816, 818 can be altered. [00175] As viewed, the tongue 802 is inserted into the groove 806 until the edge of the first panel 804 adjacent the tongue abuts against the skin 102 of the second panel 808. Note that the tip of the tongue 802 does not contact the skin layer 103 of the second panel 808 that defines the floor of the groove 806.

[00176] Material 814 is injected into the openings 816 and passes into the channels 810 that begin in the centre of the tip of the tongue 802. At the point, the channels are adjacent the skin layers 102, 103. As more material is injected into the channels, material is displaced along the channel towards the outer edges of the tongue. As viewed, there are upper and lower channels 810 on the tongue 802, located against the skin layers 102 and 103 respectively.

[00177] The channels 810 are connected in the groove 806 in an area outside the tongue 802. This area is defined by a step 820 in the core layer 101 that is located beneath the skin layer 102 of the second panel 808. The material 814 from each channel in the tongue 802 merges in the step 820 area in the groove 806, filling the void defined by the tongue, channels, groove and skin layer 103 of the panel 808.

[00178] The material 814 is injected under sufficient pressure that it fills the voids and flows out of openings 818 adjacent the step 820. Material flowing from openings 816, 818 is indicative that sufficient bonding material has been inserted into the connection 800. The channels are configured to isometric specification principles such that the quality of the bond can be determined.

After setting, the material 814 functions to bond the materials in the connection 800 together and/or mechanically plug the tongue 802 within the groove 806. The material forms a plug that functions as a fixing, holding the tongue within the groove.

[00179] An alternative connection 800 configured to receive bonding material 814 is shown in Figure 14c. This particular configuration has a simple construction and is easier to manufacture than those shown in Figures 14b and 14c because no additional shaping of the tongue/groove and/or inserts in the moulding tool are required and, therefore, this assembly has a lower production cost. In comparison to the shaped channels 810, and step 820, shown in Figures 14a and 14b, the tongue is unmodified. To be clear, the tongue is a simple block-shaped structure with no channels incorporated therein. The groove has a step, or cavity 820, behind the skin layer defining the aperture.

[00180] The groove 806 is configured with an aperture substantially matched to the dimensions of the tongue 802 to be secured therein. The dimensions are such that the gap between the tongue and aperture of the groove is minimal. The walls of the groove 806 defined by the core 101 are recessed, on at least one side, from the aperture of the groove 806 such that a space exists around the tongue. In the example shown, two spaces, or pathways 812 are configured in the groove 806 such that a pathway is created adjacent the skin layers 102,103 of the tongue 802. The pathway 812 defines and step 820 in the groove.

[00181] Inlet openings 816 and an outlet opening 818 are provided on the floor of the groove. The inlets 816 are configured above the pathway 812 to fill the step 820, around a tongue inserted in the groove, directly. As described above, bonding material is injected into the pathways 812 such that it fills the void around the tongue. The material can be injected under pressure. The pathway is configured such that after the tongue is sufficiently surrounded by bonding material the excess material can flow from the opening 818. The pathways and inlets and outlets can be configured such that excess material flowing from the outlet 818 indicates that bonding material has been sufficiently applied.

[00182] The openings 816 and 818 are shown by way of example. Alternative configurations can be implemented to direct bonding material to specific locations, or channels, in the groove. For example, inlet holes 816 can be configured at each corner of a rectangular shaped groove. [00183] Figure 14c shows a cross-sectional detail of the tongue 802 of a first panel 804 located in the groove 806 of a second panel 808. The bonding material 814 can be seen occupying the pathways 812 adjacent the skin layers of the tongue. The bonding material 814 functions to secure the skin layers of the tongue 802 to the skin layers and core material of the panel 808. This creates a mechanical bond and/or a mechanical block between the panels. One or more surfaces of the tongue and/or the groove can be roughed to improve bonding.

[00184] Another connector or securer is shown in Figures 15a to 15d, which illustrate a tongue and a groove type engagement 850 between panels. The core layer 101 , skin layers 102, 103 and bonding layer 104 are configured to form a tongue 852 a first panel 854 and a groove 856 in a second panel 858. A fixer

860 can be used to secure the tongue within the groove and secure the panels together. The tongue and groove shown has a rectangular cross-sectional profile, although other shapes can be implementable.

[00185] Figure 15a shows an exploded view of a panel 854 and, in particular, an elongate slit 862 in the tongue 852, which extends from the tip of the tongue into the core layer 101. The slit 862 can be enclosed by the skin layers 102, 103, as shown. The slit 862 is configured to receive the fixer 860.

[00186] By way of example, the fixer 860 comprises a bolt 864 and a washer 866. The dimension of the root 868 of the bolt corresponds to size of a portion of the slit 862 that is adapted to receive the root 868. The maximum width of the washer 866 is greater than the maximum width of the tongue and/or groove. The slot is sized such that the crest 870 of the thread of the bolt 864 engages with the walls of the slit 862 without detriment to the structure of the tongue. [00187] Figure 15b shows the components of Figure 15a assembled together to form the tongue 852, while Figure 15c is a cross-sectional view of the tongue prior to insertion into the reciprocal groove 856. Note that the length of the tongue is shorter than the maximum depth of the groove. This configuration allows the shoulders or edge of the panel adjacent the tongue to substantially abut against the perimeter edge of the groove.

[00188] The groove 856 is formed in a panel 100 having the same structure as the interconnecting tongue, although grooves can be configured in other materials having the same configuration. The groove is comparatively sized to receive the tongue and configured such that the tongue can be easily inserted therein, while minimising the gap, or play, in the groove and thus optimising the structural integrity of the connection when the tongue is secured in the groove.

[00189] The floor of the groove 856 is defined by a skin-layer 103. The walls of the groove 856 are defined by the core layer 101 and top of the walls, or groove edges are defined by the skin layer in which the groove is formed. The floor of the groove has a bolt-hole 872 to receive the bolt 864 there through.

[00190] Figure 15d shows the tongue 852 assembled in the groove 856 and a fixer 860 positioned prior to being inserted into the slit 862 of the tongue.

[00191] During assembly, the tongue 852 is inserted into the groove 856 until the shoulders abut against the edge of the groove in the panel receiving the tongue. From the opposite side of the panel, the bolt is passed through the washer 866 and then through the bolt-hole 872 in the skin layer 103 and received in the slit 862 of the tongue and secured therein. The application of the fixing biases the tongue into the groove. The washer functions to distribute the load applied to the tongue across the surface area of the skin layer 103. The washer extends substantially perpendicularly from the bolt according to the load to be distributed, and may or may not extend beyond the perimeter of the groove.

[00192] Figures 16a to 16i show a number of views of a holder 880 implemented on reciprocal panels 882, 884. The holder is applied, by way of example, applied to the connection of a tongue 886 and a groove 888. The footprint of the tongue 886 is marginally smaller than the footprint defined by the groove 888, thus the tongue can slide into the groove. [00193] Each panel 100 includes the core layer 101, skin layers 102, 103 and a bonding layer 104. When the tongue 886 is inserted in the groove 888 positive feedback is provided by the holder 880 by a click-vibration, such as a snap-fit and/or an audible click. The holder is configured to provide positive, or confirmatory, feedback when the tongue has been correctly inserted into the groove. This type of feedback is advantageous for applications such as quality control, or in a manufacturing production line environment wherein semi-skilled or unskilled workers must determine when a tongue has been correctly inserted. Such operations must often be carried out in short time frames and within a noisy and often hostile working environment.

[00194] The holder illustrated in perspective view in Figure 16a comprises a socket 890 and a latch 892 configured on the tongue 886 and the groove 888 respectively. Figure 16b is a sectional view taken, in a plane parallel with the panel 882 having the tongue, through the skin layer of the tongue 886 and through the mid-point of the groove 888 in the reciprocating panel 884, prior to insertion of the tongue.

[00195] Figure 16c is a perspective view on an alternative configuration. Figure 16d is sectional view taken through the alternative configuration.

[00196] Figure 16e is a cross-sectional view taken through the tongue when fully inserted into the groove, said Figure being provided with detailed-view of the interface between the latch 892 and the socket 890. [00197] The socket 890 is configured on the tongue 886 and comprises an indentation, or slot 890 formed in the skin layer and/or the core layer. The slot is elongate and positioned such that the opening of the slot is located on the tongue itself. The skin layer of the tongue remains connected to the panel via a bridge 894 of the skin layer.

[00198] On one side of the tongue, the narrowest point of the bridge can be defined by a point extending from the end of the elongate slot 890 to the closest edge of the tongue 886. The bridge 894 is configured to maintain sufficient strength in the tongue.

[00199] In Figures 16a and 16b, two bridges 894 are configured either side of the socket 890, whereas the configuration of Figures 16c and 16d has a single bridge 894 dividing two sockets 890.

[00200] The latch 892 is configured on the skin layer 102of the panel 884 having the groove 888, on the side of the groove that faces the socket when the tongue is inserted therein. The latch protrudes from the perimeter of the aperture of the groove. The length of the latch 892 is shorter than the depth of the socket 890.

[00201] During assembly, the tongue 886 is forcibly inserted into the groove 888, pushing past the latches 892, displaying the latches 892 until sufficient space is created to allow the tongue to slide into the groove. At the same time, the core layer material in the tongue can compress, or can be configured to facilitate compression, to enable the tongue to be inserted in the groove beyond the latch.

[00202] The latches are also resiliently biased and apply force to, and compress, the core layer beneath the latch to allow the tongue to be pushed into the groove recess. The latches are resiliently biased against the tongue. Note that the core layer 101 can comprise local modifications in the region beneath the latch to facilitate movement of the latch to allow insertion of the tongue. By way of example, local modifications can comprise formations and/or voids in the core layer to permit greater displacement of the latch portion of the skin layer. [00203] After the tongue 886 has been inserted to a certain depth, the latch 892 becomes aligned with the socket 890 and is located therein. The location of the latch within the socket functions to provide positive affirmation such as acoustic affirmation of the location. As the latch 892 slides up the skin layer 102, 103 it moves and/or snaps into the socket 890. The snap can be achieved by various mechanisms, including: the resilient bias of the latch compressed against the core layer 101 ; the contact between the latch 892 and the socket 890; the speed at which the tongue is inserted; the shape of the edge of the socket; and the material properties of the tongue and groove. The audible and/or tactile signal created by the location of the latch within the socket can be tuned, and can be tuned by configuring/adjusting material properties

[00204] The socket 890 is configured to allow the latch 892 to return to its previous position. After insertion, the socket can be configured to prevent the tip of the tongue from touching the floor of the groove. Bias is provided against the latch by the pressure applied by the tongue in the groove, via gravity of other such assembly conditions, or by a secondary fixing (not shown). [00205] The substantially elongate latch 892 and socket 890 are described merely by way of example. Alternative shapes of reciprocal latches and sockets can comprise three-dimensional portions, or can be provided by a plurality of smaller reciprocal latches and sockets. [00206] The or each side of the tongue and groove can have reciprocal latches and sockets. The reciprocal latches and sockets can be configured to provide baka-yoke, or poka-yoke type features that support mistake or fool proofing assembly methods to eliminate product defects by preventing, correcting, or drawing attention to human errors as they occur. Therefore, the tongue can be inhibited from being wrongly inserted in the groove. [00207] The tongue 886 is shown located adjacent the edge of a panel 100 and is configured to be insertable into a corresponding groove 888 of another panel. The tongue and groove shown has a rectangular cross-sectional footprint, although other shapes of can be implementable, such as hexagonal, triangular or circular shaped tongues, or objects.

[00208] The groove is defined by a recess in the panel. The floor of the recess is defined by one of the skin-layers. The walls of the recess are defined by the core layer 101 and top of the walls, or recess edges are defined by the skin layer in which the recess is formed. Note that the length of the tongue is shorter than the maximum depth of the groove. This configuration is advantageous when a secondary fixing, or securer, is used in conjunction with the above-mentioned locator. [00209] The locator, or holder, enables a tongue to be secured in a groove prior to an operator securing the tongue in place in a separate operation. The separate operation can comprise one or more of the fixer and/or connecter disclosed herein. By way of example, the holder can be combined with the bonding arrangement in Figure 13d comprising features such as those disclosed in Figures 14a and 14b, or the holder can be combined with the fixing connection disclosed in Figure 15d.

[00210] Figures 16f to 16i show an alternative holder configuration applied in conjunction with the above-mentioned latch and socket function, although it can be used independently without a latch and socket function. In this configuration, the skin layer of one of the panels, and in particular in the region of the tongue 886, is extended beyond the body of the panel/tongue to provide a flap 896. The flap 896 is receivable in a reciprocal flap aperture 897 located on the floor of the groove 888. [00211] The tongue 886 is inserted into the groove 888 as described above in relation to Figures 16a to 16e. In this case, however, the flap 896 extends through the flap aperture 897 when the tongue 886 is located in the groove 888. The tongue 886 is configured with a socket 890 adjacent the tip of the tongue body such that the socket aligns with the skin layer 103 defining the lower floor of the groove when inserted therein. The flap aperture 897 has a latch 892 that engages with the socket 890 on the tongue 886 in the same way as the latch and socket arrangement as described above in relation to Figures 16a to 16e.After insertion, the flap 896 extends substantially perpendicularly from the skin layer 103 of the panel having the groove 888. Thereafter, the flap can be folded over to lie substantially flat against the skin layer of the receiving panel and secured thereto. The flap can be folded by approximately 90-degrees.

[00212] The socket 890 can form an aperture through the skin layer. Alternatively, it can define a shallow recess. The location of a tongue 886 within a socket 890 allows the panels to be secureably held together prior to an operator, or similar manufacturing process, folding and securing the flap in place.

[00213] Additionally, or alternatively, a fold-line (not shown) can be configured to improve and/or control folding of a flap. A fold-line facilitates the bending of the skin when there is no hard-surface, or reference point about which the flap is required to fold. The fold-line can be a perforation, a laser-cut line, stamped area or combination thereof. The fold-line can include the socket and/or a recessed area 890, or be independent of the socket.

[00214] Figure 16g shows the tongue 886 of Figure 16f installed in the groove 888, wherein the flap 896 extends through the flap aperture 897 and beyond the skin layer 103. Figure 16h shows, using the hashed line, the position of the flap 896 before being folded over to lie substantially flat against the skin layer of the receiving panel. After folding, a rivet 898 is insertable through a rivet aperture 899 located in the skin layers to secure the flap 896 to the skin layer 103. Figures 16f to 16h show a single-flap configuration while Figure 16i shows a dual-flap configuration wherein the flap 896 extends on both sides of the tongue 886. The rivet, or other suitable fixing device, can be applied to secure the flap in place. The rivet, or other suitable fixing device, can be applied before, during or after an optional bonding process has been applied to secure the tongue in the groove.

[00215] The flap 896 can be configured to secure two panels together in a number of configurations. Three examples are shown in Figures 16j to 16m, Figures 16n to 16q and Figures 16r to 16t.

[00216] Figure 16j shows a tongue 886 configured for insertion into a groove 888 that is located at the edge of a panel. The groove is defined by walls, on three sides, of the core material 101 and by a skin layer 103 forming the base of the groove. Instead of a flap 896 being configured on the tongue 886, it is configured in the panel comprising the groove and configured to extend beyond the edge of the panel. The flap is configured, as indicated in Figure 16k, to fold around the edge of the panel such that a portion of the flap 896 forms the fourth wall of the groove 888. The length of the flap 896 is configured to be longer than the length of the tongue, or longer than the depth of the panel, such that the flap can be folded around the edge of the panel and lie flat against the surface of the panel having the tongue. The flap can extend beyond the edge of the panel comprising the tongue to enable the flap to be securably fixed thereto. [00217] Figures 161 and 16m show, respectively, a cross-sectional view of the assembly of Figure 16k before and after the flap 896 has been folded. In particular, Figure 16m shows that the apertures 899 are configured on the flap 896 and the panel such said apertures are aligned when the flap has been folded. Thereafter, a fixing 898 can secure the flap 896 to the panel surface. [00218] Alternatively, the flap can extend from the panel having the tongue and fold over the edge of the panel having the groove.

[00219] Figures 16n to 16q show a comparable configuration to that shown in Figures 16j to 16m. In this configuration, however, the groove 888 is set back from the edge of the panel and is defined on four sides by core material 101. Figures 16n and 16o show the tongue 886 before and after insertion into the groove 888. [00220] The key difference in this configuration can be appreciated from Figures 16p and 16q, wherein the panel 884 is offset from the edge of the panel 882. The flap 896 extends around the edge of the panel 882 and is folded back against panel 884 to be secured thereto. The flap, in effect, is wrapped around the edge of the panel. The flap creates a three-dimensional form and can be configured to add structural strength to the assembled panels.

[00221] Note that the flap function to provide increased strength at the edge of the panel and/or encloses the core 101 of the panel around which it wraps. [00222] Figures 16r to 16t show an assembly in which the flap arrangement of Figures 16f to 16i is combined with the flap arrangement of Figures 16n to 16q.

[00223] The flap configuration can be used alone or in combination with one or more of the other holding or fixing configurations disclosed herein.

[00224] Another connector is shown in Figures 17a to 17e. The connector, like the other connectors, enables an object to be connected to a panel while maintaining the structural integrity of said panel. [00225] A cross-section of a load washer 930 is shown in Figure 17a, while a perspective view of the same washer is shown in Figure 17b. The washer 930 has a circular flange 932 connected to and extending from a substantially cylindrical body 934. The core of the body comprises a threaded portion 936, although the threaded portion can extend through the body 934.

[00226] . The load washers 930 are configured to be fitted in a reciprocal hole 942 within a panel 100. The load-washer 930 has an anti-rotation feature that inhibits turning or rotation of the load-washer when located in the hole. The anti-rotation feature is shown, by way of example, in the form of protrusions, or teeth 938, provided on side of the flange 932 that faces the body 934. Figure 17c shows a load washer 930 also having an anti-rotation feature in the form of a key, in the form of a shoulder 940, cut into the body 934. In the example shown, the body is provided with a symmetrical anti-rotation feature in the form of shoulders. The body of the load-washer can be provided with an asymmetrical anti-rotation feature. . [00227] The washers 930 enable objects to be secured to a panel 100. The threaded core 936 is configured to receive a fixer, such as an M8-type bolt.

[00228] Figure 17d shows the load-washer of Figures 17a and 17b arranged to be inserted in an aperture 942 in the panel 100, or any such board material. The aperture is sized and shaped to match the cross-sectional profile of the body 934 of the load-washer such that when the load-washer is inserted in the aperture the gap, or play, in the aperture is minimised.

[00229] The floor of the aperture 942 is defined by one of the skin layers 103. The walls of the aperture are defined by the core layer 101 and the top of the walls, or aperture edges are defined by the skin layer 102 in which the aperture is formed. The floor of the recess has a hole, or aperture 922 to receive a fixer in the form of a bolt that connects to the body 934. [00230] Figure 17e shows the load-washer 930 fitted in the aperture 942 in a panel 100. When located in an aperture, the flange of the load-washer abuts against the surrounding area of the aperture while the body extends into the aperture. The body does not contact the floor of the aperture.

[00231] One or more rotation inhibitors, or features, can be provided on the load-washers.

[00232] Figure 17e shows the teeth 938 provided on the surface of the flange in contact with the panel in which it is mounted. The teeth function to bite into the skin layer 102. The teeth shown in the Figures are circumferential arc- shaped teeth. However, the teeth can comprise one or more alternative shapes and can be profile to maximise a biting, or clamping, action against the skin layer, while inhibiting rotation and unclamping. The teeth can take any shape, such as spherical, cuboid, pyramidal etc. The flange can comprise protrusions that are functionally comparable to weld-bolts to enable the load-washer to be welded to the skin layer.

[00233] The load-washer 930 can be provided with a holder that functions to hold it within the aperture prior to being held by the fixing that it will secure in place. The holder can comprise spurs, or barbs, that connect with the material of the core layer. The holder can inhibit removal of the washer after insertion into the aperture. The holder can be a compression fit between the load-washer and the wall of the aperture. The body 934 can be provided with ribs.

[00234] The holder can be implemented by a lip 944, shown by way of example on Figure 17c, located on the body 934 of the load washer 930. The lip is configured such that the skin layer in the fitted condition of Figure 17e resides between the lip and the flange 932. The lip functions to latch over the skin layer and hold removably hold the washer 930 in place. The lip can function as a holder and/or an anti-rotation feature.

[00235] The load-washer 930 can be bonded in place, and the teeth 938 can be configurable to control the position of the washer during bonding. [00236] During assembly, the load-washer 930 is inserted into the aperture until the shoulders abut against the edge of the 942 aperture in receiving panel.

From the opposite side of the panel, a bolt (not shown) is passed through the aperture 922 in the skin layer and then threaded into the core 936 of the body, thus securing an object in place. As the bolt is tightened, the teeth 938 bite into the skin layer 102. The tightening of the bolt applies pressure to the surface of the panel 100 beneath the flange and compresses the core layer 101, drawing the body of the load-washer towards the floor of the aperture and reducing the volume between the body and the floor.

[00237] Figures 18a to 19e illustrate care layers of panels 100 that have been adapted to connect on substantially the some plane with an adjacent panel. The panels are provided with tabs 950 and/or c-cuts 952, wherein the tab on a first panel is configured to be received by the c-cut on an adjacent panel.

[00238] The connection can comprise: an interlock, which connects with another panel; a ball and socket type of connection; a hook; dovetailing; a knitted configuration; a sewn configuration. Functionally, the connection can be an engaging type of connection.

[00239] A plurality of core layers of panels can be configured to tessellate and create a jigsaw-puzzle type of formation. The panels can comprise integral latch features to provide a releasably securable connection between core layers of panels.

[00240] Figure 18a shows an arrangement of nine panels, each provided with tabs 950 and c-cuts 952, connected to form a larger square panel. As shown in Figure 18b, by selecting particular panel configurations, the number of different shapes of panels can be reduced. In this example only six different panels, namely A, B, C, D, E and F as shown are required to form a three-panel by three-panel square. Applying this pattern reduces the number of different types of panel required to form a larger panel.

[00241] Further, according to the functionality required by the core layers, the core of the panels can remain blank, as shown in Figures 19a and 19b, or have tracks 954 formed in the surface as shown in Figure 19c and 19d. The tracks 954 are configured such that they align with tracks on adjacent panels.

Figure 19e shows a three-panel by four-panel array in which a mixture of plain and tracked panels has been selected to provide a particular path via which a pipe or wiring loom can be routed. The tracks can be configured to create a three-dimensional path through the core material.

[00242] After a tessellated panel of core layers has been assembled, the panel is assembled together with skin layers 102, 103. The skin layers can include access holes to enable objects, such as pipes or wiring looms to be fed through the tracks 954.

[00243] The assembled panel forms a larger panel that can not be manufacturable using conventional moulding machines. By way of example, each panel A to F in Figure 18a is 600mm by 600mm in size. Once connected, panels A to F form an 1800mm by 1800mm panel, which is then assembled with skins to form a panel 100. The time and cost associated with producing a 600mm by 600mm is lower than that required to produce an 1800mm by 1800mm panel. Above a certain size, a machine can be prohibitively expensive, or may not exist or be available locally.

[00244] One or both skin layers of a honeycomb type panel can include a pressed edge profile to accommodate the overlapping edges at the junction of two interconnected panels. Also, once two panels are connected along an edge by means of the inter-engagement of a series of respective tabs and slots a plastics strip, such as a Vacform™ strip (not illustrated), can be applied so as to bridge over the junction between two panels. The plastics strip is adhered to each of the panels either side of their junction. This creates an enclosed space around the junction which can be filled with an injection foam to further strengthen the junction and provides a bridge for dispersing externally applied forces through the covering plastics strip. The plastics strip can further include dimpling on its inner surface to maintain the cavity prior to injection of the injection foam.

[00245] It will be apparent from the above that with the present invention a panel, such as a honeycomb sandwich type of panel, can be provided with a core layer of at least three different densities that is suitable for use in the manufacture of vehicle chassis. The method of manufacture of the honeycomb sandwich panel enables the production of bespoke panels where the positional variation in density is adjusted to reflect the multi-directional forces the panel is expected to experience.

[00246] Although the above description is specific to the use of flat panels in the manufacture of a car chassis, it is envisaged that the panels described herein can also be shaped so as to be non-flat. Also it is to be understood that the panels in accordance with the present invention are suitable for use in the manufacture of other vehicles such as vans, trains, airplanes, boats and dwellings. In all such cases the panels are adapted to absorb and/or and transmit forces externally applied in a plurality of different directions and specifically to absorb and/or transmit forces externally applied from three or more different directions.

[00247] The panels can also be adapted for rapid construction applications, or Greenfield developments, where no infrastructure exists. A selection of flat- packed panels can be configured to be shipped on a pallet and snapped together manually to form a substantially secure and rigid emergency-type of dwelling. The properties of the panel enable a tensile structure, with insulating properties therein to be fabricated with or without bonding.

[00248] It will, of course, be apparent that changes can be made to the panels described herein, to the method of their manufacture and to vehicles manufactured using such panels. Thus, although specific reference is made herein to laser-cutting the skin layers and stamping the core layer, alternative milling techniques for either or both materials can be employed with departing from the present invention. Also the manner of interconnection of the panels in the manufacture of a vehicle is not limited to the use of inter-engaging tabs and slots. Such changes and others not described herein are encompassed without departing from the scope of the invention as defined in the appended claims.

[00249] Furthermore, the methods of manufacture of the honeycomb sandwich panels described herein enable the production of bespoke panels where the positional variation in density is adjusted to reflect the multi-directional forces the panel is expected to experience. The methods of manufacture are also suitable for use in the manufacture of conventional panels of constant density. Furthermore, the manufacturing methods described herein enable high- speed manufacture of shaped panels available for immediate use and which avoid the need for individual cutting.

[00250] The varying density core can additionally be used to provide communicating channels or profiles within the core layer or between the core layer and a skin layer that can be used as communicating paths e.g. for the circulation of a fluid such as air or another gas or to house parts such as wiring. Separate panels can have inter-panel communicating channels so that when the panels are connected together, a communicating channel in one panel aligns with a communicating channel in a connected panel so as to form a continuous communicating channel or profile extending across two or more panels. Similarly, where the skin layers are attached to the core layer after separate moulding of the core layer, the skin layers can be treated so as to be pre-shaped. The structures formed by the pre-shaping of the skin layer are then aligned with mimicking structures in the surface of the core layer so as to enhance structural integrity and / or to form communicating paths or channels which extend between the skin layer and the core layer. In this regard it will be apparent that the structures formed by the pre-shaping of the skin layer can project into or away from the core layer surface.

[00251] The present invention has been described above purely by way of example, and modifications can be made within the spirit and scope of the invention, which extends to equivalents of the features described. The invention also consists in any individual features described or implicit herein or shown or implicit in the drawings or any combination of any such features or any generalisation of any such features or combination.