FIELD OF THE INVENTION

The present invention relates to sandwich panels and in particular to sandwich panels for use in building construction, for structures of various different types and shapes. BACKGROUND TO THE INVENTION

Sandwich panels are pre- fabricated elements consisting of a pair of metal sheet layers sandwiching an inner core of insulating, and sometimes structural, non-metal material. This inner core can be made from any material and is, in some implementations, typically a mix of a polymer and another component, such as polyethylene mixed with mineral wool to reduce combustibility. They are cheap to manufacture and have generally good insulation properties, whilst exhibiting excellent compressive and flexural strength, making them ideal for facades, partitioning walls and ceilings in industrial and commercial buildings.

It is important, in any kind of building, including in high rise buildings, to keep weight of non-load bearing materials to a minimum. Doing so reduces cost not only of transporting pre-fabricated items to construction sites, but also reduces load placed on structural elements allowing buildings to be constructed to lower strength specifications. Sandwich panels are generally made to standard specifications and used only to provide structural support and insulation. There is scope for improving on existing sandwich panels and their various uses.

SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided a sandwich panel, comprising a first metal layer; a second metal layer orientated substantially parallel to the first metal layer; a non-metal layer sandwiched between the first metal layer and the second metal layer; and a plurality of openings extending through the non-metal layer in a longitudinal direction, substantially parallel to the planes of the first and second metal layers, wherein the plurality of openings of same, similar, or different geometric forms and shapes, are preferably each surrounded on all lateral sides by the non-metal layer.

Preferably, the invention includes any or all of: a first metal layer;

a second metal layer orientated substantially parallel to the first metal layer; a non-metal layer sandwiched between the first metal layer and the second metal layer; and

a plurality of openings, at least some of the openings each extending through the non-metal layer from a first edge of the non-metal layer to a second edge of the non-metal layer to provide an open-ended channel through the non-metal layer, extending in a longitudinal direction of the openings, substantially parallel to the planes of the first and second metal layers, wherein the plurality of openings are surrounded on all of their lateral sides by the non-metal layer;

the sandwich panel having a length L in a direction substantially parallel to longitudinal direction of the openings, and a width W in a direction substantially perpendicular to the longitudinal direction of the openings, the width W being greater than the length L;

the openings being provided as voids in an otherwise substantially uniform body of the non-metal material, and being substantially regularly spaced from one another in a direction perpendicular to the longitudinal direction of the openings; the first and second edges of the sandwich panel each having a complimentary interlocking form, such that when placed adjacent one another, adjacent panel edges can interlock to prevent relative translation of the panels in at least one direction.

Alternative arrangements may comprise any or all of: a first structural outer layer;

a second structural outer layer orientated substantially parallel to the first structural outer layer;

a core layer sandwiched between the first structural outer layer and the second structural outer layer; and

a plurality of openings, at least some of the openings each extending through the core layer from a first edge of the core layer to a second edge of the core layer to provide an open-ended channel through the core layer, extending in a longitudinal direction of the openings, substantially parallel to the planes of the first and second structural outer layers, wherein the plurality of openings are surrounded on all of their lateral sides by the core layer; the sandwich panel having a length L in a direction substantially parallel to longitudinal direction of the openings, and a width W in a direction substantially perpendicular to the longitudinal direction of the openings, the width W being greater than the length L;

the openings being provided as voids in an otherwise substantially uniform body of the core material, and being substantially regularly spaced from one another in a direction perpendicular to the longitudinal direction of the openings.

The first and /or second metal or structural outer layer(s) may be generally planar, although they may include undulations or non-planar features, such as channels, ridges, recesses or other features as may be included to fulfil their required function. They generally extend in a planar manner, to preferably form a structural outer layer to the sandwich panel. The openings may be provided substantially evenly across a full width of the sandwich panel. However, the openings may be spaced apart by different distances from one another. For example, the openings may be grouped together in sub-groups. Openings within a sub-group may be spaced apart by a first set of distances, which may be equal and which may be less than a first distance. Plural sub-groups of openings may be provided. The sub-groups may be spaced apart by a second distance, which is greater than or equal to the first distance.

The metal layers are preferably made from a metallic material, but in some embodiments can be made from a non-metal material, but preferably having stronger mechanical properties than the core material of the non-metal layer. The core material is primarily insulative, but combines with the outer layers for improved structural strength.

The metal or structural outer layer(s) are preferably metallic, but may be made of any material and are generally intended to provide structural strength to the non-metal or central layer 106, 206, 306, 406, 506.

The first and second metal layers may sandwich respective first and second principal faces of the non-metal layer. The plurality of openings may extend from one lateral side of the non- metal layer to another lateral side of the non-metal layer. The plurality of openings may be positioned substantially equidistant from the first and second principal faces of the non-metal layer. The non-metal layer may comprise a polymer and/or a mineral material and/or polyisocyanurate. The first and/or second metal layers may comprise aluminium or steel.

One or more of the plurality of openings may be polygonal in cross-section or have a closed- curve cross-section, which means that the outer profile of the cross-section is formed from a curve which makes a closed loop and may have any curved profile. Circles and ovals are included as closed curves. The closed curve may include one or more straight sides. One or more of the plurality of openings may be triangular in cross-section. One or more of the plurality of openings may be square or rectangular in cross-section. One or more of the plurality of openings may be hexagonal in cross-section. One or more of the plurality of openings may be circular or oval in cross-section. Two or more adjacent openings of the plurality of openings may have a triangular cross-section, the orientation of which alternates by 180 degrees from one opening to the next.

The sandwich panel may have an overall thickness between outer surfaces of the first and second planar metal layers of around 4 to 25 centimetres, preferably around 10 to 12 centimetres.

One or more of the first and second metal layers may each have a thickness of between 0.5 and 1 millimetre.

The sandwich panel may have a length of 10 to 14 metres, or 12 metres, but this typically depends upon the size of a building to which the panel will be applied. The ratio between the length and the thickness of the sandwich panel may be between 100: 1 and 120: 1. The ratio between the thickness of the sandwich panel and the thickness of the first metal layer and/or the second metal layer may be between 100: 1 and 240: 1.

A ratio of the overall volume of the non-metal layer to the volume of the plurality of openings may be between 1 :0.2 and 1 :0.4. The ratio of the overall volume of the non-metal layer to the volume of the plurality of openings may be between 1 :0.25 and 1 :0.35. Other ratios are possible.

There is further provided a structure comprising a plurality of sandwich panels according to the invention. A gas or water pipe or an electricity cable may be provided in one or more openings in the plurality of sandwich panels. One or more openings in the plurality of sandwich panels may contain a data cable. The data cable may be an electrical cable or an optical cable. A longitudinal plane of one or more of the plurality of panels may be in a substantially horizontal orientation or in a substantially vertical orientation. A longitudinal plane of one or more of the plurality of panels may be orientated substantially between 0 and 45 degrees from the vertical or substantially between 0 and 45 degrees from the horizontal.

One or more of the plurality of panels may form part of a roof of the structure. A building may be provided comprising a structure comprising panels of the invention.

The building or structure may comprise at least one panel, an opening extending through the principal face of the panel being configured to communicate fluid into and/or out of a room around which the panel or panels is/are arranged, via one or more of the openings extending through the panel.

The building or structure may comprise a non-horizontally oriented panel, having a plurality of non-horizontally-oriented openings therein, the openings being open to surrounding air at an upper end and at a lower end, such that heat applied to an outer surface of the panel causes heated air in the openings to circulate to remove heat from the panel. This is preferably due to convection effects or "chimney" effects.

A method of manufacturing a sandwich panel is also provided, comprising one or more of the following steps, in any order: providing a first structural outer layer;

providing a second structural outer layer orientated substantially parallel to the first outer structural layer;

providing a core layer sandwiched between the first metal layer and the second metal layer;

providing a plurality of moulding elements each configured to extend through the core layer from a first edge of the core layer to a second edge of the core layer to provide an open- ended channel through the core layer once the core layer is provided between the outer structural layers, the moulding elements extending in a longitudinal direction of the openings, substantially parallel to the planes of the first and second outer structural layers; the sandwich panel having a length L in a direction substantially parallel to

longitudinal direction of the openings, and a width W in a direction substantially

perpendicular to the longitudinal direction of the openings, the width W being greater than the length L; the openings being provided as voids in an otherwise substantially uniform body of the core layer, and being substantially regularly spaced from one another in a direction perpendicular to the longitudinal direction of the openings; and removing the moulding elements from the core layer to leave the openings through the core layer substantially open ended.

According to a further aspect of the present invention there is provided a method of manufacturing a sandwich panel according to the aspects described above, comprising the steps of:

providing a computer-readable medium having computer executable instructions adapted to cause a 3-D printer to print a sandwich panel as defined above; and

printing the sandwich panel.

According to another aspect of the present invention there is provided a computer-readable medium having computer executable instructions adapted to cause a 3-D printer to print a sandwich panel as defined above. As will be apparent in light of this disclosure, any of the features of the methods described herein can used to create features of the products describe herein. Further, any product feature may be created using an equivalent method step to manufacture the products described herein. Therefore any or all of the above features may be combined to arrive at products and/or methods for making such products.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by non-limiting example only, with reference to the accompanying drawings, in which:

Figure la is a perspective view of a sandwich panel according to an embodiment of the present invention; Figure lb is a side view of a sandwich panel according to an embodiment of the present invention;

Figure lc is a plan view of a sandwich panel according to an embodiment of the present invention; Figure 2a is a side view of a sandwich panel according to an embodiment of the present invention;

Figure 2b is a side view of a sandwich panel according to an embodiment of the present invention;

Figure 2c is a side view of a sandwich panel according to an embodiment of the present invention;

Figure 3 shows an alternative arrangement, of offset openings, in a sandwich panel according to the present invention;

Figure 4 shows a further alternative arrangement, of vented openings, in a sandwich panel according to the present invention; Figure 5 shows a further alternative arrangement, of alternating openings, in a sandwich panel according to the present invention;

Figure 6 shows a preferred example of a sandwich panel having features in accordance with embodiments of the invention;

Figure 7 shows a longitudinal cross-section through a panel of figure 6, along a length of the openings;

Figure 8 shows a detailed cross-section of the panel of Figure 6;

Figures 9 to 10 show optional alternative arrangements of the panel of Figures 6 to 8. DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Embodiments of the present invention provide for a novel sandwich panel design which has been found by the inventors to reduce panel mass. The inventors have realised that by adding elongate openings, cavities, or conduits, within the sandwiched non-metal material of a sandwich panel, the overall weight of the panel can be reduced due to the removed material, while other properties of the panel, such as for example thermal insulation properties, are not adversely affected, and may even be improved. New implementations for a panel have also been identified, which provide improved utility.

Figures la, lb and lc graphically illustrate a sandwich panel according to an embodiment of the present invention. As with prior art sandwich panels, the panel 100 comprises a first planar metal layer 102 and a second planar metal layer 104 orientated substantially parallel to the first metal layer 102. Sandwiched between the first and second metal layers 102, 104 is a non-metal layer 106. The metal layers 102, 104 are typically made from lightweight sheet metal such as aluminium or steel or any alloy thereof. The metal layers 102, 104 may be coated on their outside surface for aesthetic benefit using any form of decorative material, such as paints or coatings, for example, polyvinylidene fluoride (PVDF), fluoropolymer resins (FEVE) or polyester paint. The metal layers 102, 104 sandwich respective first and second principal faces 110, 112 of the non-metal layer 106.

The non-metal layer 106 is typically made from a polymer, such as polyethylene, although a popular core material for the non-metal layer 106 is polyisocyanurate, and panels using this material in their non-metal layers are available from producers such as Kingspan™.

Typically, sandwich panels used in the building industry, although they are not limited to such uses, and in particular tho se used for commercial and industrial use, have a thickness of between 4 centimetres and up to around 25 centimetres, and in some examples, between around 10 centimetres and 12 centimetres, measured between the outer surfaces of the first and second metal layers 102, 104 respectively. In some circumstances, the sandwich panel may be up to around 20 centimetres thick. The thickness of the first and/or second metal layer 102, 104 is conventionally between around 0.5 and 1 millimetre, but is not limited to these values and may be thinner or thicker in certain applications, depending upon design and loading criteria. As such, in some embodiments, the sandwich panel 100 can have, for example, an overall thickness of between 8 and 14 centimetres. In other examples, the sandwich panel has a thickness of around 10 to 12 centimetres. The first and/or second metal layers 102, 104 may have a thickness of anywhere between around 0.2 and 2 millimetres and preferably between 0.5 and 1 millimetre. In certain examples, sandwich panels typically have a width (w) of around 1 - 1.2m and a length (1) of between 10 and 14 m and in some embodiments a length and width of 12 m, i.e. a 12 m x 12 m square is possible.

Provided within the non-metal layer 106 are a plurality of openings, cavities, or voids 108. These openings preferably extend through the non-metal layer 106 in a longitudinal direction, substantially parallel to the planes of the first and second metal layers 102, 104. The openings 108 are preferably surrounded on all lateral sides by the non-metal layer 106. In other words, in preferred arrangements, no part of the conduits 108 opens onto the metal layers 102, 104; the conduits 108 are therefore preferably formed completely within the non- metal layer 106, opening only at the edges of the panel 100. In the embodiment shown in Figure la, one or more of the plurality of openings 108 extend completely through the length of the non-metal layer from one edge to the other. In other embodiments, however, the openings may extend only partially through the non-metal layer 106. To this end, the openings 108 may form pockets within the non-metal layer or may terminate at one edge or the other of the non-metal layer 106. Embodiments of the present invention may comprise any combination of closed and/or open openings formed in the non- metal layer, terminating at one or other or both sides or ends of the panel 100.

In the exemplary embodiments shown in Figures la, lb and lc for illustrative purposes, the openings run in a parallel orientation relative to one another from one edge to the other edge of the panel 100. However, in other embodiments, the openings may be orientated in a non- parallel fashion. Additionally or alternatively, instead of being straight openings as shown in Figures la, lb and lc, the conduits 108 may have one or more bends, whilst still extending generally laterally or longitudinally through the non-metal layer 106. In other embodiments, conduits may cross one another in different lateral directions through the panel 100 whilst all still extending in directions parallel to the primary plane of the panel 100. In the embodiment shown in Figures la, lb and lc, the conduits have a triangular cross- section, in particular that of an equilateral triangle. In other embodiments, however, the conduits may have a cross-section of other triangles (isosceles or irregular, for example) or other polygonal or non-polygonal shapes. Examples include squares, circles, ovals, rectangles, pentagons, hexagons, to name a few. Circles may be preferred for ease of manufacture. In some arrangements, however, the conduits are provided with triangular cross-sections similar to those shown in Figures la and lb, and more preferably equilateral triangles. In some examples, alternating orientations of triangular cross-section conduits rotated by 180° with respect to their neighbouring openings can be used. By removing material from the non-metal sandwich layer 106 of the panel 100, the overall volume of material used, and the resulting, weight is also reduced, while other properties, such as thermal insulation, may be enhanced or maintained.

Any or all of the openings 108 may be provided with a liner or insert 111. This liner or insert can have a number of functions. A first function is where pipes or cables are to be placed in the openings. Here they inserts of liners can protect the non-metal layer from wear and tear or damage in use or during the insertion process. Further, the inserts or liners may be fire retardant or fire resistant and so, in the event of a fire, such as a gas or electrical fire, due to the pipes or cables being located in the openings, the liners or inserts can reduce or prevent damage to the panel 100. The insert may be a pipe suitable for carrying fluids such as gas or liquids, in isolation from the non-metal layer, and so it can form an integral pipe for carrying fluids through the panel.

The following calculations provide quantitative examples of the reduction in volume of a non-metal layer, and therefore its weight, when various openings or different shapes and sizes are formed therein. For simplicity of calculation and for illustrative purposes only, these calculations assume that the non-metal layer 106 of the sandwich panel 100 is, for example, 10 centimetres thick from its first principal face 110 to its second principal face 112. As mentioned above, however, the non-metal layer 106 may have a different thickness in other embodiments.

Generic equations are considered in the following section, for comparing the volume of material removed from the non-metal layer by use of some examples of the openings described herein. In the following we consider, for illustrative purposes only, a section of a non-metal layer of sandwich panel 100, having a volume Vp (calculated by conventional methods, i.e., for example, length x width x height) and a thickness T, and we assume a length L of each of the sides of each of the equilateral triangles forming the cross-section of the openings in the non-metal layer. A longitudinal distance D along the longitudinal length of the opening is assumed. . The total volume VT of N openings formed in the non-metal layer and having an equilateral-triangular cross-section can then be calculated as follows:

V _T x L ² x D x N For any type of triangular cross-section, where the triangle has a base

4

b and a height h, the volume can be calculated as:

This results in a reduction in the overall volume Vp of the space occupied by the non-metal layer. Therefore, a corresponding volume or weight reduction ratio, compared to a panel without the triangular voids being provided in the non-metal layer, can be also calculated as: Figure 2a shows a side view of a side panel in accordance with a further embodiment of the present invention, comprising openings 1 14 having circular cross-sections. Elements of the panel 200 shown in Figure 2a common to Figure l a have been provided with like numbering. Again, assuming an overall thickness of the non-metal layer of T, each of the circular openings 1 14 have a diameter of d and the spacing distance between the edges of each of the adjacent openings 1 14 is s. Accordingly, N parallel openings, of length L can be provided in a selected section of sandwich panel. The total volume Vc of the openings provided in the sandwich panel may therefore be calculated as follows:

V _r = N x π

This translates into a volume and weight reduction ratio of the non-metal layer of

∑c_

V _P

Turning now to Figure 2b, a side view of a sandwich panel 300 according to a further embodiment of the present invention is shown comprising a plurality of square openings 1 16 disposed within the non-metal layer 106. In this embodiment and for the following calculations, the non-metal layer 106 is again considered to have a thickness from its first principal face to its second principal face of T and the cross-section of the square openings S ² , the gap between the edges of each of the adjacent openings 116 being s. With this configuration, as with the example shown in Figure 2b, N openings can be provided in a selected section of sandwich panel 300. The total volume Vs of the square voids making up the openings of length L can be calculated as follows:

V _s = L x S ² x N

This translates into a weight and volume reduction ratio of the non-metal layer of .

∑s_

V _P

Therefore, in order to calculate the volume of material removed by including the openings, where a mixture of the above shapes is used, for example, square, circular and/or triangular cross-section openings, the overall volume V _v removed from the non-metal layer can be calculated as follows: = v _T + v _c +v _s and the ratio of the volume of non-metal material removed from the non-metal layer in relation to the volume of the non-metal layer in the absence of the openings is: The skilled reader will be able to calculate the volume of other forms of opening by multiplication of the cross-section area by the overall length of the opening, and can find the ratio of volume of material removed to the total volume of the non-metal layer in the absence of the openings, as shown above. From the above calculations it has been found that a possible ratio of overall volume of the non-metal layer to the volume of the plurality of openings provided therein is between 1 :0.1 and 1 :0.5 and more preferably between 1 :0.2 and 1 :0.4. Further, even more preferably the ratio of the overall volume of the non-metal layer to the volume of the plurality of openings is between 1 :0.25 and 1 :0.35. Other ratios can be advantageous for certain implementations. Having regard for the above examples, it is clear that by providing openings within the non- metal layer 106, a significant reduction in weight and positive environmental impact due to decreased material usage can be achieved. Further, as mentioned above and described with reference to Figure la, the removal of material from the non-metal layer does not necessarily result in a significant reduction in strength of the panel and, in some circumstances, such as in particular the triangular configuration of Figure la, the provision of such openings provides no measurable decrease in the flexural strength of the panel 100 under normal loading. In practice, therefore, the provision of the openings in accordance with embodiments of the present invention enables panels to be made which are lighter and therefore easier to transport and install and reduce the overall strength requirements of building foundations or other supporting elements. Additionally, panels use less material for the non-metal layer 106, thus reducing the use of materials and especially, hydrocarbon-based materials such as the polymer, which may be any type of polyethylene. Further, in embodiments where the openings extend all the way through the panel from one side to the other, these openings can be used to carry gas or water pipes or electricity cables as well as other cables such as data cables for electrical or optical data transfer. The openings can also be used to carry fluids for ventilation, heat transfer or humidity control.

It will be appreciated that the cross-section of openings provided within the non-metal layer 106 of the material need not necessarily be all the same shape and size and can be of different shapes and sizes. Further, the openings need not necessarily be located at a centre point through the thickness of the panel either, one or more of the openings may be located toward a first metallic layer or a second metallic layer of the panel. The openings may not necessarily be of constant cross-section along their length and could have a varying, increasing or decreasing cross-section along their length. Figures 2c and 2d provide just two of many examples of sandwich panels falling within the scope of the present invention comprising openings having different shapes and sizes. Any combination of size and/or shape of openings in any possible configuration may be provided within the non-metal layer 106, and the extent to which each of these openings extends through the length or width of the non-metal layer 106 may vary in any manner from opening to opening. For example, one or more of the plurality of openings may extend all the way through and others may not; one or more of the plurality of openings may be completely encapsulated within the non-metal layer, and others may not; one or more of the plurality of openings may run in a different direction through the non-metal layer to others of the plurality of openings. Preferably, however, all of the openings extend through the non-metal layer in a longitudinal direction substantially parallel to the plane of the first and second planar metal layers.

Additionally, it is optional for the plurality of openings to be positioned substantially equidistant from the first and second principal faces of the non-metal layer. In other words, each of the plurality of openings running through the non-metal layer may be at different relative distances from the first and/or second in a direction parallel to the plane of the first and second planar metal layers but preferably not in a direction perpendicular to the plane of the first and/or second metal layers. Figure 3 shows an alternative arrangement in which the openings are located in closer proximity to a first metallic layer 302 than to a second metallic layer 304. This configuration can be useful for certain arrangements in a structure. In particular, as will be explained in more detail in relation to the following figures, where heat is impinging upon metallic layer 304 and an opposite side 302 of the panel is to be kept as cool as possible. By passing a heat transfer fluid such as gas, air or liquid through the openings 308, heat delivered to layer 304 can be removed from the panel by the flow of fluid through openings 308. The heat removed from the panel can be dissipated to the atmosphere at another location, for example by routing it to another channel which is simply out of direct sunlight, in a shaded area, or alternatively, a heat engine, such as a powered refrigeration unit could be used to remove heat from the fluid once the heat is removed from the panel. This arrangement can therefore remove heat from the panel and reduce the amount of heat energy reaching the cooler side 302 of the panel. This can effectively increase the insulating effect of the panel and is particularly useful in cold rooms or cold stores, for example, since in such instances, it is particularly advantageous to remove heat from the panel before it has a chance to reach the internal side of the panel when it provides a wall or ceiling for a cold store or cold room or other space to be kept at a set temperature. The openings can therefore act as conduits for a heat transfer fluid for the removal of heat from the panel. The conduits are advantageously placed in a path of heat transfer from a heated side to a cooler side of the panel. The conduits may advantageously be located closer to the heated side of the panel than to the cooled side of the panel, although they can in some implementations be located nearer to the cooled side of the panel. If the conduits are oriented vertically, or in any non-horizontal configuration, then a 'chimney effect' can be created, in which heat applied to the panel heats the heat transfer fluid. This causes the heated fluid to be less dense and so causes the fluid to rise, pushed upwards by heavier, denser fluid acting at a bottom or lower end of the conduit. This can occur because the heat transfer fluid in another part of the conduit, or fluid outside of the conduit, or fluid in a part of a circuit to which the conduit is connected is denser and so heavier, which causes the lighter heated fluid to rise.

Figure 4 shows a further alternative arrangement in which one or more of openings 408 is/are provided with vents passing through outer layer 402. This is to permit a fluid such as air to be delivered through the openings 408, to a space adjacent layer 402. This can be useful for delivering a fluid, such as air, to a room around which one or more of the panels is installed, for example. Other fluids could be delivered through the openings 409, to generally heat, cool control humidity, to generally air-condition, or to control any aspect of the atmosphere in the room. Fluid can, or course, also be aspirated through the openings 409 if desired, to extract air, smoke, or generally to extract fluid from the room around which the panel or panels are assembled. Figure 5 shows an arrangement which combines the functionality of Figures 3 and 4. Therefore, the panel 500 may comprise a first set of one or more openings or conduits 508 located toward a first side of the panel and a second set of one or more openings or conduits 511 located toward a second side of the panel. The first set of openings or conduits may comprise openings 509 through a side of the panel as described in respect of Figure 4. The second set of conduits or openings may be used as described in relation to Figure 3. Figure 6 shows a preferred example of a sandwich panel in accordance with embodiments of the invention. The panel 600 has a width w in a direction substantially perpendicular to a longitudinal axis of the openings 601 to 610. The panel 600 has a length / in a direction substantially parallel to a longitudinal axis of the openings 601 to 610. Although ten openings are labelled in Figure 6, any number of openings may be provided, running substantially parallel to one another along the length direction of the panel 600. As can be seen in the Figure, the illustrated example shows triangular openings similarly configured to those shown in Figure lb. As will be appreciated, a range of openings as shown and described in relation to earlier Figures can be employed in any configuration across the width w of the panel 600. A shown in relation to Figures 9 and 10, openings having circular or hexagonal openings are possible, as are openings having any of the forms described in relation to earlier figures, combined with the features of the panel 600 of Figure 6.

The any or all of the openings 601 to 610 may have a form of liner inserted inside it as indicated by numerals 601a and 601b, for example. As will be appreciated, the liner is preferably formed to mate with the inner profile of the opening and preferably contacts the walls of the opening on all sides, along some or all of the length of the openings. However, the openings may be left with no liner inside them in some examples.

The liner or liners preferably are provided as only a thin film for only the purpose of permitting removal of any structural moulding element provided inside the openings during manufacture of the panel. The film may be of a sheet material having a sufficiently low coefficient of friction to allow easier removal of the moulding element. Therefore the liner may have a lower coefficient of friction than the material of the non-structural core layer 620 of the panel 600. This can help the moulding element to be removed from the panel 600 after manufacture. It is envisaged that such a liner may not be necessary. Additions or alternatives to such a liner may be for example the application of a friction reducing chemical treatment or anti-adhesive material on the moulding element before the core layer 620 is moulded around the moulding element may be beneficial. Such materials or treatments can be selected to prevent adhesion of the material of the core non-metallic layer 620 to the moulding element. The moulding elements may be tapered from one end to another to facilitate their removal from the core layer 620 from their large end. As can be seen in Figures 6 and 7, each end of the panel 600, at end faces of its length /, the panel may be provided with a channel formation 631 at a first end 630 of the openings and with a corresponding ridge formation 641 at a second end 640 of the openings. The ridge formation 641 may be configured to fit into the channel formation 631 to locate the first end 630 of the panel into the second end 640 of an adjoining panel. The openings may be provided running from a bottom of the channel formation 631 , to a top of the ridge formation 641 , so as to provide substantially continuous openings through adjacent panels when located with the ridge formation of a first panel located in a channel formation of a second panel. Such an arrangement of a panel similar to that shown in Figure 6 is illustrated in lateral cross- section in Figure 7.

Figure 8 shows a detailed cross-section illustrating an example of an arrangement of openings suitable for use in particular examples of sandwich panels according to embodiments of the invention. As can be seen, in cross-section, the openings describe opposing rows of triangles, with the tips of the triangles oriented toward the centre of the panel and intermeshing such that tips of a first row of triangles are located in between walls of opposing triangles. The triangles may be substantially equilateral, but may have a height B of the triangles which is larger or smaller than the width El to E6 of one or more bases of respective triangles of the array of openings. The height B of one or more of the triangles may be equal to the width El of the base of one or more of the triangles. In a particular example, a gap Fl to Fl 1 between a tip of a triangle and a base of an adjacent triangle may be around half the width of the base El to E6 of the triangle or triangles.

A depth A of the non-metal core material between the row of openings and a first face 81 of the panel may be the same as or different to a depth C of the core between a second face 82 and the row of openings. A may be less than C or vice versa, to provide an array of openings located nearer to one face than the other of the panel as described in relation to Figure 3 above, for example. A, B and C may also be equal in some arrangements. These features are all optional and may be incorporated into any embodiment of the panels described herein.

As illustrated in Figures 9 and 10, alternative panels 900 and 10, may be provided with similar arrangements of openings as shown in relation to Figures 6 to 8, but with circular, in the case of Figure 10, or hexagonal, in the case of Figure 9, openings. As a skilled person familiar with sandwich panels of the type discussed herein will appreciate, the non-metal/core/insulative layer of the panel may comprise a polyurethane material, and/or one or more of polyurethane foam, expanded polystyrene foam, phenolic foam, cellular glass and mineral wool. It is preferred in some embodiments to use a core comprising a polyurethane material, preferably a majority polyurethane, although the invention can be implemented with a core comprising any of the core materials discussed herein.

One method for producing the openings can include providing at least one, or preferably an array of, moulding element(s) having the shape of the desired openings, moulding the core/non-metal/insulative layer around the moulding elements and removing the moulding elements from the core, providing the metallic/structural elements to opposing principal faces of the core layer and once the core layer has cured, removing the moulding elements to leave the openings extending through the core layer from a first edge of the core layer to a second edge of the core layer. The core layer may therefore be initially provided in liquid or foamed form and allowed to set before removing the moulding elements to leave the desired openings through the core layer 620. As the skilled reader will appreciate, the steps may be carried out in various different orders, for example the core may be injected between the outer structural layers. However, the core may be formed and then the outer structural layers applied to its outer surfaces. Alternatively, the core layer may be provided on one outer structural layer and then a second structural outer layer may be provided to an opposing side of the core. The moulding elements may also be removed from the core independently of when the outer structural layers and the core layer are brought together, i.e. before or after depending on the chosen manufacturing process. As the skilled reader will appreciate, other permutations of the steps described will be practicable. 3D printing methods are increasingly prevalent and as will be appreciated in light of the present disclosure, sandwich panels as described herein may be fabricated by 3D printing methods in certain examples. Such 3D printing methods are well known for a number of types of materials and so a person skilled in the art of additive manufacturing processes will appreciate that one or more sub-components, such as the core layer or the outer structural layer(s) of the panel may be manufactured by 3D printing of the materials in the required configuration as described in relation to the figures. Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.