Method of manufacturing a sandwich panel which is locally stiffened, and panel produced thereby

0001The present invention relates generally to the composite panel structure of the sandwich type having a cellular core especially for motor vehicles, more particularly a method for producing a stiffened zone said insert within such a panel for mounting of a fastening system such as for example a screw or clip system.

0002The materials of sandwich honeycomb core have very high stiffness characteristics with regard to their weight.

0003Conventionally, the construction of such materials is to imprison by bonding or welding a cellular core low mechanical characteristics between two skins with a thickness much lower than that of the cellular core but with excellent mechanical characteristics.

0004In addition, document FR - 2711573 belonging to the Applicant, a method for making a composite panel of the sandwich type having a cellular core, wherein said panel is carried out in a single stage, by pressing in a mold cold, of a stack consisting of at least a first skin material stampable reinforced thermoplastic, of a cellular core of thermoplastic material, a second skin material of a stampable reinforced thermoplastic, and a first outer coating layer in woven or nonwoven material, said skins being previously heated outside the mold to a softening temperature.

0005Such a method is particularly advantageous in that it allows in a single operation to generate the coherence between the various layers of the composite structure and shape said panel. The panel thus produced has all the mechanical properties due to the sandwich structure with a honeycomb core.

0006The composite structure of the type sandwich panels with honeycomb core have sufficient rigidity characteristics for structurally reinforce mechanical structures subjected to high stresses without thereby overburdening them. Such panels are then commonly used in the field of shipbuilding, aerospace and rail.

0007Conventionally, to enhance a mechanical structure is then fixed thereto a composite panel of the sandwich type having a cellular core. In this case, the fastening system used to locally transmit the mechanical stresses of the mechanical structure to the sandwich panel.

0008It addition, it may be in a motor vehicle for example, a composite structure of the sandwich type having a cellular core is used instead of a metal structure. This composite structure is then directly attached to the frame of the vehicle by several fixing points.

0009This is the case for example of a rear seat back whose metal structure can be replaced by a composite panel of the sandwich type having a cellular core.

0010The rear seatback can be subjected to since high mechanical stresses on impact, these loads are then absorbed in part by the composite structure, but also partly transmitted to the vehicle frame by means of said structure mounting system to the latter.

0011In general, the forces applied to such a composite structure seatback are directed mainly along the normal to the material surface. This structure then undergoes overall bending. However, depending on the deformation capacity of the fastening system of the composite structure to the vehicle frame and the rigidity thereof, the mechanical stresses exerted at the level of the fastening system may be different.

0012Tensile tests on the attachment point of the belt of a rear seat back, the structure was made of composite material of sandwich honeycomb core, helped highlight the tensile stresses exerted on the said composite structure lead to a shear and a matting skins and the honeycomb core component, essentially due to the forces exerted at the fixing structure of said system. In this case, it is essentially the skin opposing the displacement of the screw fastener system.

0013Furthermore, a composite sandwich panel with a honeycomb core can be also used to perform the sub-floor of a motor vehicle. Such a piece is fixed to the frame of the vehicle by six to eight attachment points.

0014It is mainly subjected to stresses in torsion, for example when the vehicle goes in part on a sidewalk.

0015The attachment points of this structure are generally submitted by the game of the movements of the vehicle in normal use, to phenomena tensile, compression, bending and torsion.

0016Also in this case, tensile test on such a part made of sandwich material made it possible to highlight a skin shear phenomenon and said honeycomb core material.

0017Conventionally, for mounting a system for securing a composite panel of the sandwich on a mechanical structure, one uses inserts which are introduced into the sandwich structure. These inserts are conventionally of inserts or attachment fittings, metallic or not, which constitute supports to localized transmission of mechanical stress.

0018According to the intensity of localized mechanical stresses, the inserts along the length of said panel is distributed.

0019The inserts can lower rates to an eligible localized mechanical stresses transmitted to the sandwich material considered.

0020Various methods already known are employed to implement such inserts in a composite panel of sandwich honeycomb core.

0021One method is to pierce the sandwich panel with a honeycomb core over its entire thickness, positioning the insert in the bore and fill in the emptied remaining between the insert and the material of a filling resin of the epoxide type. Such filling resin can be alleviated by incorporation of phenolic microballoons.

0022Another known method for ajonction an insert in a structural sandwich panel with a honeycomb core, is to weld or glue the insert on the edges of the panel.

0023It is also possible to reinforce the composite structure by adding skins that are glued over the place to strengthen or butcher.

0024Furthermore, document discloses US 5,614,285 a method for producing a composite panel comprising a flax mat and thermoplastic fibers with a drumhead and a decorative layer.

0025According to this method, the fixed panel, the side of the mat, one or more fasteners having a plurality of eyelets with pins extending perpendicularly to the fastening element.

0026The securing element is mounted in the mold, to be placed against the mat, and during the pressing of the panel by closing the mold, said pins of the fastener penetrate into the mat are deflected so as to s orient in a direction generally parallel to the plane of the panel.

0027During cooling of the panel thus formed, the spikes are embedded in the mat and do not come to interfere with the upper layers overlying the mat, that is to say with the skin and the decorative layer.

0028Such a panel can not be used in the automotive field, the fact that its structure with a skin and a flax mat does not give it the desired mechanical resistance to constitute a part of a motor vehicle.

0029Finally, document FR - 2,686,043 a method of producing a composite panel of sandwich honeycomb core, comprising metal inserts, which is to preheat the skins forming the sandwich material to make them malleable and facilitating their attachment by heat to the cells of the honeycomb core, and preheating the metallic inserts before making a stack of different elements of the panel in a shaping tool of it.

0030All the above methods already known to introduce inserts into a composite panel of sandwich honeycomb core, are difficult to apply in the field of automobile manufacturing, where production rates are high, because all these methods are relatively long to implement and implementation of such panels by such methods has too high a cost.

0031In particular, insertion of inserts and reinforcements according to the above methods often require manual labor or special machinery as well as of matter which link such as adhesives, resins, fillers foams. These steps for fitting inserts are then necessarily of recovery steps which represent additional costs in manufacturing processes.

0032In addition, according to the aforementioned methods already known, the inserts used are generally made of materials often differ from those used for making the composite sandwich panel, which limits the subsequent recycling Actions of said panel, inside which are placed the inserts.

0033The present invention therefore provides a novel method for producing a stiffened zone forming an insert for receiving a fastening system inside a composite panel of the sandwich type having a cellular core, the implementation is simple and economic.

0034More particularly, according to the invention, there is provided a method for producing a stiffened zone said insert intended to receive a fastening system inside a composite panel of the sandwich type comprising a stack of at least a first skin, a cellular core of thermoplastic material and a second skin, the first and second skins being constituted by reinforcing fibers and a thermoplastic material.

0035It is characterized in that it comprises the following steps:<sl><li>a) is positioned a reinforcing plate at a determined location on the inside of a portion of a forming mold, said plate being provided with spikes extending towards the other portion of said mold,</li><li>b) are placed in the forming mold said stack, said first and second skins being previously heated,</li><li>c) press is said stack by closing the forming mold, the forming pressure between 1 and 3 MPa, to simultaneously form said panel so that said panel matches the shape of the reinforcing plate which is anchored by the through its pins into the latter, and to perform the specific location is positioned said reinforcing plate, a localized compacting by compressing said stack.</li></sl>

0036Thus, advantageously, the method of achieving this stiffened zone for receiving a fastening system is part of the process of forming the panel so that the overall process of manufacturing the panel to be produced comprises a minimum of steps and is the least expensive possible.

0037Such a method provides a stiffened zone in located in the panel without unnecessarily burdening it.

0038It also allows to obtain a panel easily recycled because the reinforcing plate may be advantageously made of metal, is located outside of the panel and it is subsequently possible to easily separate the composite material of the reinforcing plate.

0039The fact that the plate is anchored in the composite panel, and more particularly in one of the skins of the sandwich material, via its pins, allows during mechanical stress of the fixing system received in said stiffened zone, solicit directly tensile skin against which the plate is plated, the said sandwich skin material having as is known the best mechanical properties in tension.

0040The mechanical latching via the pins of the reinforcing plate on the skin can however catch the art because it requires a priori affect the integrity of the composite structure of the sandwich type. But on the contrary, it is subsequently demonstrated by test results according to the invention, the integrity of the composite panel is unaffected.

0041Step c) of the process according to the invention even allows to further increase resistance to high mechanical stresses of the stiffened zone thus produced.

0042More particularly, the process according to the invention, the reinforcing plate covering the locally compacted composite panel and back on its edges, panel increases flexural strength where it could be weakened by the crushing of said panel.

0043According to an advantageous characteristic of the method according to the invention, the reinforcing plate being provided with at least one through orifice, in step c), simultaneously with forming said panel, is pierced via said port of said reinforcing plate, said stack at the location of the realization of localized compacting, separating at this point the fibers of the first and of the second skin.

0044Thus, according to the invention, the bore of said panel operation does not involve the breaking of fibers which are only eliminated, and maintains the panel where is performed the opening mechanically sound. In addition, the .perçage operation is advantageously carried out simultaneously with the formation of said panel, the number of steps required to manufacture the part is reduced and hence its manufacturing cost.

0045Furthermore, the reinforcing plate increases the resistance to shear and matting of the opening thus made during mechanical stress of the fixing system welcome in this opening of the stiffened area.

0046According to a first embodiment of the process according to the invention, a reinforcing plate is used whose spikes extend in a direction perpendicular to the platen surface that carries them.

0047According to another embodiment of the process according to the invention, a reinforcing plate is used whose spikes extend in a direction inclined to the normal to the plate the surface which bears them.

0048Indeed, the pins placed perpendicularly to the surface of the reinforcing plate does not in certain cases to keep the plate in place provided it is urged in the direction of the barbs, when handling and transporting the formed panel . In addition, in cases of extreme use, it is found that some spikes will deform before the composite panel from tearing.

0049These two above-mentioned problems, a solution can be, as presented above, the use of pins inclined with respect to the plane of the plate the surface which bears them.

0050In this case, in step a), the reinforcing plate is positioned on a movable portion of a part of the forming mold, and in step c), during closure of the forming mold by vertical displacement of said mold part towards the other part, the movable portion moves in a plane inclined relative to the plane of the internal surface of said portion of the mold so that the reinforcing plate has a horizontal movement and the pins are inserted into said following stack their tilt direction.

0051The insertion of the pins into the stack formed is then, without damaging the skin of the reinforcing fibers.

0052According to one characteristic of the method according to the invention, the first and second skins used are constituted by a fabric of reinforcing fibers embedded in a thermoplastic material, wherein the warp son are oriented at 90 ° relative to the weft son, it uses a reinforcing plate of which the pins are positioned so that in step c), they fit into the stack by positioning in abutment on the skin chain son against which the reinforcing plate is pressed .

0053According to a variant of the process according to the invention, the first and second skins used are constituted by a fabric of reinforcing fibers embedded in a thermoplastic material, a plate is used whose spikes are positioned so that in step c ), they fit into the stack by positioning staggered against the weft son of the skin against which the reinforcing plate is pressed.

0054According to an advantageous characteristic of the method according to the invention, in step a), positioning another reinforcing plate on the inner face of the other part of the forming mold, facing the reinforcing plate positioned on the internal face of the first portion of said mold, the other reinforcing plate being provided on the one hand of pins which, when said plates are in position in the mold, extend towards the first reinforcing plate, and are intended in step c), to be anchored in the panel, and the other housing also inserted in the panel during step c) and in which are intended to engage the pins of greater length carried by the first reinforcing plate so that after forming of said panel, the two plates are bonded together by crimping.

0055According to other characteristics of the process according to the invention, each reinforcing plate may have a thickness approximately between 0.8 and 1.2 mm, and the spikes they comprise are then formed by stamping the material of said platen. In step c), the localized compacting of said stack may be performed using at least one boss provided on at least a portion of the forming mold. Prior to the localized compacting of the panel, a preassembly consisting heated by stacking at least the first skin, the cellular core and the second skin. Upon heating of the pre-assembly can be realized a more pronounced localized heating of the zone-of the pre-assembly where subsequently perform localized compacting by compression. In step c), the first and second skins have a forming temperature between 160 and 200 ° C.

0056In step c), said stack is pierced which is carried out in a direction perpendicular to the plane formed by said skins or in an oblique direction relative to the normal to the plane formed by said skins.

0057According to the invention there is also provided a device for implementing the above method comprising a forming mold, characterized in that it includes a punch mounted on an inner wall of the mold so that it extends direction of the other facing wall of said mold where a housing is provided which is engaged when said needle pierces said forming current stack. The needle is advantageously mounted on the top wall of the mold so that it sinks toward said corresponding housing after said first and second skins of the stack have been clamped between said walls of the mold. This needle comprises a barrel ending in a tip whose shape and dimensions are adapted to the shape and the through-opening dimensions to achieve this tip having a conical shape or a needle with a flat face and one face curve.

0058Finally, the invention also provides a composite panel of the sandwich type comprising a stack of at least a first skin, a cellular core of thermoplastic material and a second skin, said panel being provided with at least one forming stiffened zone insert intended to receive a fastening system produced according to the aforementioned method.

0059The following description in the accompanying drawings given by way of non-limiting example, explains in what the invention is and how it can be achieved.

0060In the accompanying drawings:<ul><li>FIG 1 is an exploded schematic view in side section of a stiffened zone of a composite sandwich panel with a honeycomb core according to the invention,</li><li>2a and 2b are schematic top views of a stiffened zone as shown exploded in Figure 1, on which two different positions of pins are shown,</li><li>Figures 3a and 3b are front and side views of one embodiment of a stud profile of a reinforcing plate used in the process according to the invention,</li><li>4a and 4b are top and side of a positioning mode of the pins of a reinforcing plate on a weft thread according to the method according to the invention,</li><li>5 schematically shows the insertion of an inclined pin and a pin right in a composite panel of sandwich structure with a honeycomb core,</li><li>6 shows the upper and lower portions of the forming mold used according to the method of the invention, the upper part being provided with a reinforcing plate with inclined spikes,</li><li>7 shows schematically seen in side section the stiffened zone of a sandwich structural panel having a cellular core comprising an upper reinforcing plate and a lower reinforcing plate according to the method according to the invention,</li><li>Figures 8a, 8b and 8c show an embodiment of a reinforcing plate used according to the method according to the invention,</li><li>Figure 9 shows an assembly tensile test on a test piece made according to the method of the invention, and</li><li>10 shows schematically viewed from above five different reinforcing plates used for tensile testing according to the scheme shown in FIG 9.</li></ul>

0061Figure 1 shows diagrammatically a stiffened zone 110 forming insert intended to receive a fastening system 10 within a composite panel of the sandwich type composite 100. This panel 100 includes a stack of at least a first skin 101, a cellular core of thermoplastic material 102 and a second skin 103. the honeycomb core 102 is constituted by cells determined geometric shape of regularly spaced and bounded by thin walls of thermoplastic material such as polypropylene. The cells may have a tubular shape or a hexagonal shape, in this case, the honeycomb core will be the nest type of bees. The first and second skins 101, 103, 100 shown composite panel are constituted of reinforcing fibers, glass, or other inorganic or organic material such as plant material and a thermoplastic material. Advantageously, in the typical case shown in the first and second skins 101, 103 are constituted by a fabric of glass fibers embedded in polypropylene and more particularly to a balanced fabric in which there are as many weft son chain son of that oriented 90 ° relative to each other.

0062Of course, according to other embodiments not shown, it is conceivable to use for the production of the composite panel, first and second skins of which would be different weaving or constituted by a mat of reinforcing fibers embedded in a material thermoplastic such as polypropylene.

0063As shown in Figure 1, according to the invention, the stiffened area 110 of the panel 100 is constituted by a localized compacting of the composite panel 100, the compacted area being covered with a reinforcing plate 200, preferably of metal, applied against the second skin 103 following the shape of the compacted area, and anchored by means of pins 201 in said panel.

0064According to the invention, the method for producing such a stiffened area comprises the following steps:<sl><li>a) positioning the reinforcing plate 200 to a specific location on the inner face of a portion of a forming mold by the upper mold part, said reinforcing plate 200 is provided with pins 201 which extend towards the other party, here below, said mold</li><li>b) placing said stack in the forming mold, said first and second skins 101, 103 being pre-heated,</li><li>c) pressing said stack by closing the forming mold to form said panel, and simultaneously with forming said panel, is carried out, the specific location is positioned said reinforcing plate 200, a compaction made by compression, under a compacting pressure between 1 and 3 MPa, said stack, placed here in the reinforcing plate, so that the shape of the preformed reinforcing plate which is anchored by means of its pins into said panel.</li></sl>

0065It should be noted, advantageously, according to this method, prior to step b), a preassembly consisting heated by stacking at least the first skin 101, the honeycomb core 102 and the second skin 103 . Upon heating of the pre-assembly, is provided a more pronounced heating of the localized zone of said preassembly where the localized compacting subsequently effected by compression. The pre-assembly heating temperature is such that in step c), the first and second skins have a forming temperature between 160 and 200 ° C.

0066As shown in Figure 1, the stiffened area 110 is pierced by a through orifice 104 for the subsequent establishment of a fixing system here, for example, a screw 10. To achieve breakthrough stiffened zone in accordance with the method conforming to the invention, the reinforcing plate 200 is provided with at least one through hole 202, and in step c), simultaneously with forming said panel, is pierced via said port 202 of the plate 200, said stack the place of the realization of localized compacting, separating at this point the fibers of the first and of the second skin 101, 103.

0067Advantageously, it is noted that the embodiment of the zone stiffened by compaction of the panel covered with a reinforcing plate, the bore at that location of the stiffened zone, and the forming of the panel take place in a single step during the pressing by forming said panel, which provides a method of manufacturing with a minimum of steps and therefore to reduced cost.

0068The embodiment of the through hole in the stiffened zone, may be carried out according to the invention by piercing said stack in step c) in a direction perpendicular to the plane formed by said skins 101, 103 or in an oblique direction by relative to the normal to the plane formed by said skins. To do this, a not shown pin may be mounted on an inner wall of the mold so that it extends in the direction of the other inner wall facing said mold where it is provided a housing, also not shown, wherein engages when said needle penetrates said stack during forming. The needle may be mounted on the upper wall of the mold so that it sinks toward said corresponding housing after said first and second skins of the stack have been clamped between said walls of the mold. In addition, the needle comprises a barrel ending in a tip whose shape and dimensions are adapted to the shape and the through-opening dimensions to achieve. For example, the tip can have a conical shape or a needle with a flat face and a curve face.

0069Furthermore, it should be noted that in step c), the localized compacting of said stack has been performed using at least one boss provided on at least one wall of the forming mold.

0070This boss can preferentially be constituted by the reinforcing plate 200 preformed to the shape of the projection, if the latter is sufficiently rigid when the pressing step, compacting said stack.

0071As already mentioned above, to fix the platinum Reinforcement 200 on the skin 103 which supports it, is provided according to the invention to use a reinforcing plate 200 on the pins 201 for, when setting shape of the panel, to be anchored inside thereof. For the attachment of the pins of the reinforcing plate 200 is effective without damaging the fibers of the skin through which they pass, it is preferred that the pins have a shape and dimensions adapted to the type of skin used. Furthermore, their provision with each other on the reinforcing plate, is also important because it determines in part the ability of the plate to resist tensile forces.

00722a and 2b, 4a and 4b show two possibilities of disposition of the pins on the reinforcing plate used in the process according to the invention and of this coupling makes these pins to the skin used fibers.

0073As shown in Figures 2a and 2b, the skin 103 used is constituted here by a balanced fabric 103a reinforcing fibers, 103b, such as glass fibers, vegetable fibers or carbon fibers embedded in a thermoplastic material such as polypropylene, wherein there are as many weft son 103b 103a that chain son oriented at 90 ° to each other. Thus, according to a first embodiment of the process according to the invention, when using a reinforcing plate 200 whose pins 201 are positioned so that in step c), they fit into the stack placing in abutment on the chain 103a son skin 103 against which the reinforcing plate 200 is pressed (see 2a).

0074Such an arrangement of the pins on the plate is provided when the mechanical stresses exerted on said stiffened zone are predominantly directed in the direction of the warp son.

0075According to another embodiment, provision can be made that the pins 201 are placed on the reinforcing plate 200 used so that during step c), said pins 201 are inserted into the stack by positioning staggered against the frame 103b son skin 103 against which the reinforcing plate 200 is pressed (see figures 2b, 4a and 4b).

0076Such an arrangement of the pins on the plate is provided when the mechanical stresses exerted on said stiffened zone are predominantly directed in the direction of the weft son.

0077Of course, for distributed mechanical forces more complex way on the stiffened zone, may be considered according to the invention to use a reinforcing plate provided with spikes distributed more or less uniformly, which is positioned against the warp son and staggered against skin weft son of said zone.

0078Furthermore, for other types of weaves or mats of glass fibers embedded in polypropylene, the positioning pins on the reinforcing plate used according to the method of the invention, will be different.

0079Furthermore, according to one embodiment of the method according to the invention, there is provided use of a reinforcing plate of which the pins extend in a direction perpendicular to the platen surface that carries them.

0080In this case, as shown in Figures 3a and 3b, the pins 201 of the reinforcing plate used are shaped tip whose base has a width smaller than or substantially equal to the width of a wire of a calendered fabric glass fibers embedded in a thermoplastic material.

0081The barbs 201 then diverge the fibers of the skin resulting in the least possible during their penetration in the latter. The pins 201 have sufficient matting surface to press the fibers without slicing.

0082Of course, for other types of weaves, or mats, the size and shape of the pins will be adapted accordingly.

0083However, such pins placed perpendicularly to the surface of the reinforcing plate which carries them, do not allow in some cases to maintain the plate in place against the skin of the stack provided it is urged in the direction of the pins , during handling and transportation. In some use cases, there may be some barbs deform before the composite thermoformed panel from tearing.

0084To overcome this problem, according to a variant of the process according to the invention, a reinforcing plate is used whose spikes extend in a direction inclined to the normal to the plate the surface which bears them.

0085Figure 5 depicts the insertion of a pin 201 of a reinforcing plate 200, and right inclined in the composite panel 100. One can see in this figure that the area of ​​skin pierced by the pins, is much greater when the pin 201 is inclined when the pin 201 is straight. In fact, when the pin 201 is inclined with respect to the normal to the surface of the reinforcing plate which carries them, Zone D₁ concerned of the skin is greater than the area D₂ pierced by a pin 201 law. To limit this zone D₁ pierced by pins inclined in the reinforcing plate used, it is necessary to introduce the pins into the stack during the pressing step of said panel, according to their direction of inclination. Thus, the pins 201 penetrate the stack without damaging the fibers of the skin they pierce.

0086To do so, in accordance with the invention, and as is shown more particularly in FIG 6, in step a), the reinforcing plate 200 with the pins 201 inclined, is positioned here on a movable portion M₃ the upper part M₁ the forming mold and at step c), during closure of the forming mold by vertical displacement according to the arrows F of the upper part M₁ to the lower part M₂The movable portion M₃ moves on an inclined plane I with respect to the plane of the inner surface of the upper part M₁ so that said reinforcing plate 200 has a horizontal movement according to arrow F₁ and the pins 201 are inserted into said stack along their direction of inclination.

0087These pins then penetrate the skin, as in the case of vertical pins, depending on their direction of orientation.

0088That the pins are inclined or not, positioned to build on the frame meaning son or chain they pierce the skin, they may not be able, in some cases of high mechanical stress, ensure by them -Same fixing the reinforcing plate to the stack.

0089Advantageously, it is then provided to connect the reinforcing plate 200 to another plate.

0090Thus, in this case, as shown in Figure 7, the process according to the invention, in step a), positioning another reinforcing plate 200 'on the inner face of the other part of the forming mold , here the lower part, opposite the reinforcing plate 200 positioned on the inner face of the upper mold, the other reinforcing plate 200 'is also provided with spikes 201' which, when the plates are in position in the mold, extend towards the first reinforcing plate 200. These pins are used in step c) to be anchored in the panel. The other reinforcing plate 200 'further includes 20l'a housing is also inserted in the panel during step c), and which are intended to engage the pins 201a of greater length carried by said first reinforcing plate 200 so that after the forming of said panel, the two plates 200, 200 'are bonded to each other by crimping. Thus, in the event of bending deformation of the formed panel, the two reinforcing plates are fixed, and then avoid the shearing of said panel through the deformation of the assembly.

0091It will be noted here that the panel is not compacted in the area of ​​the stiffened zone then comprises only the two reinforcing plates placed on both sides of the formed panel, bonded to each other by crimping. In some cases however, it may be useful to compact the panel where are placed the two reinforcement plates to further increase the mechanical strength of the stiffened area thus achieved.

0092The pins 201a of greater length, used for crimping, must be provided fine enough to pass through the fabric constituting the skins without damaging them. These pins 201a may be just the same shape as the pins 201.

0093They can also be crimping nails.

0094It is well understood that the other reinforcing plate 200 ', positioned on the inner face of the other part of the forming mold is provided with at least a through hole 202' which is positioned opposite the orifice through 202 of the first reinforcing plate 200 so that in step c), simultaneously with forming said panel, is pierced via said orifices of the plates, said stack at the location of the realization of localized compacting, discarding at this point the fibers of the first and of the second skin.

0095The reinforcing plates 200, 200 'used have a thickness which lies within about 0.8 to 1.2 mm, and the spikes they comprise are made by stamping the material of the plates. Indeed, for mass production, the barbs are formed by stamping. It is necessary that the plate is deep-drawn, which fixes the maximum thickness thereof.

0096The resistance of the stiffened region comprising the fastening system, to mechanical stresses, depends on the nature of the skins of the stack, the quality of the attachment of the plate or plates to the skin, but also the ability of (have) the plate or plates to withstand the stresses, especially at the through hole through which the fixing screw 10 connecting said panel to a frame.

0097To increase the resistance of the plates, it may be the need, in some cases, to increase the thickness of the plate beyond the maximum allowable limit, so that said plate can be made by stamping.

0098Thus, according to the invention, to increase the thickness of the reinforcing plate made by stamping, using a reinforcing plate 200 as shown in Figures 8a to 8c, which has a first portion 200a provided with pins 201 and a through hole 202a, and a second flap portion 200b formed with a hole 202b coming opposite the one provided in the first portion 200a (see Figure 8b) when it is folded on the first part. This flap portion 200b may have a different thickness of the first portion with the pins 201 and thus it is possible to modulate the total thickness of the platinum. In the case shown, the folding part does not entirely cover the first part of the stage, but for aesthetic reasons, it can be expected that this folding part comes completely cover the first portion with barbs.

0099The method according to the invention, as described above, to produce a composite panel of the sandwich type having a cellular core provided with a stiffened zone, has the following advantages.

0100The realization of the stiffened zone provided with one or two reinforcement plates is carried out in a single step during the forming of said panel, by performing a localized compacting, and simultaneously to the bore of said area. It is therefore not necessary to perform the establishment of the plate during a step of recovery, and the method for manufacturing the thermoformed panel is done in a minimum of steps and thus has a minimum cost. The turntables or preformed or not, are positioned in the mold before closing said mold during the heating time of the soul and skin constituting said stack. The use of a turntable with spikes used to hang and to seek the fibers of the skin against which it rests, in traction. This is particularly advantageous when it is known that the skins of the stack have a better quality of the tensile strength that the cellular core. The pins used are studied form so they slip and get stuck between two longitidinaux son and rely on a cross wire breaking at least fibers. The integrity of the fabric constituting the skins is then almost preserved. The reinforcing plate fitted on the compacted stack and used with another platinum positioned vis-a-vis, includes part of the bending forces exerted on said panel, giving back to the latter part of its lost rigidity by locally compaction. Since the thickness of these reinforcing plates determines the value of the stiffness that is desired to make in the workpiece, it can modulate, to avoid mechanical stresses at high shear of said workpiece at its fixing system.

0101The reinforcing plate, for example made of metal, is the only different material added to the composite panel of the sandwich type. It is deposited by the outside or below the sandwich material. It can be then easily removed at the part of recycling operations. In the case of a plate with vertical pins, it has a low tensile strength to remove by hand or using a lever, but sufficient to hold it in place during handling and assembly. In the case of an inclined pin deck, the load is greater but does not require other thing, again, a lever or a chisel to remove the plate of the stack during a recycling operation. If the plates are crimped to one another dismantling probably require a tool that will separate them.

0102However, in all these cases, once this transaction is completed, the metal parts are completely separated from the composite material. The reinforcing plates used are relatively simple to realize by stamping and therefore inexpensive. They can be produced in large series.

0103Tensile tests were conducted on a test piece of a composite panel of the sandwich type according to the invention wherein the first and second skins are constituted by a balanced fabric density of 1,420 g / m². Five kinds of plates were used, shown more particularly in Figure 10, and referenced 1 to 5. In the various plates, the quantity of pins and their respective position with each other, vary.

0104The tensile testing device is shown more particularly in Figure 9.

0105As shown in this figure, in order to test said plates 1-5 shown in Figure 10, the against-plates 20 have been manufactured specifically for these tests. The latter, once installed, completely cover or the pin plates 200, thus preventing their being deformed during the test. Thus, in tests in tension, every effort is absorbed by the barbs of said plates, and the hole that was made in éprouvett These tests were used to assess the ability of such a basic system (pimple-skins ) to withstand stress, depending on the number of pins of the reinforcing plates used, and their respective positions. From a fixing jaw 40, was performed push-ups on the turntables 200 through against-plates 20.

0106Comparing the tensile test results on different decks 1, 2, 4, 1, 3, 5, one could get the value of the minimum number of pins required per line. In addition, by comparing the results of tests conducted on the plates 2, 3 or 4, 5, there was obtained an indication of the influence of the relative position of the pins between them. It was found a row of six pins and an 8 per plate diameter hole allows to withstand a breaking load of 1200 daN, and to reach 2000 daN with four rows before the platinum metal reinforcement is second.