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

0001The present invention relates generally to composite structure panels type sandwich cellular core especially for motor vehicles, and more particularly a method for producing a area stiffened insert member within such a panel for mounting of a fastening system such as by such as a screw or clip system.

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

0003Conventionally, such construction materials is to imprison by gluing 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 core alveolar, wherein said panel is carried out in a single stage, by pressing in a cold mold, an stack consisting of at least a first skin stampable reinforced thermoplastic material, soul foamed thermoplastic material, a second thermoplastic skin stampable reinforced, and a first layer of outer coating material woven or nonwoven, said skins being previously heated outside the mold to a temperature of softening.

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

0006The panels of composite type structure sandwich honeycomb core with characteristics sufficient rigidity to strengthen structurally mechanical structures subject to without significant constraints for it to overly. Such panels are then commonly used in the sector of shipbuilding, aerospace and rail.

0007Conventionally, for reinforcing a structure Mechanical is then fixed thereto a panel of composite sandwich-type structure with a honeycomb core. In this case, the fastening system used to transmit local mechanical stress of the structure mechanical structure to the sandwich panel.

0008It addition, it may be in a vehicle automobile for example, a composite structure sandwich honeycomb core is used instead a metal structure. This composite structure is then directly fixed to the frame of the vehicle by several attachment points.

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

0010The rear seatback can be subject to high mechanical stresses in case of impact, these stresses are then absorbed in part by the composite structure, but also partially transmitted to the frame of the vehicle through the system securing said structure to the latter.

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

0012Tensile tests on the point of attachment of the belt of a rear seat back, the structure was made of composite material of the sandwich type honeycomb core, helped highlight the tensile stresses exerted on said structure composite lead to a shear and a matting skins and the honeycomb core component, mainly due to the forces exerted at the fastening said structural system. In this case, are essentially the skins who oppose displacement of the screw of the fastening system.

0013Furthermore, a structural composite panel sandwich a honeycomb core can also be used for realize the subfloor of a motor vehicle. A Such a piece is fixed to the frame of the vehicle by six to eight attachment points.

0014It is mainly subjected to forces in twist for example when the vehicle goes in part on a sidewalk.

0015this structure attachment points are usually submitted by the play of vehicle movements in common usage, to tensile phenomena, compression, bending and torsion.

0016Also in this case, tensile tests such a piece made of sandwich material allowed to highlight a phenomenon of shear skins and the honeycomb core of said material.

0017Conventionally, for the mounting of a system for attaching a structural panel Composite sandwich on a mechanical structure, are used inserts which are introduced into the sandwich structure. These inserts are conventionally of inserts or attachment fittings, metallic or not, which constitute supports for the localized transmission of mechanical stress.

0018Depending on the intensity of mechanical loads localized, the inserts along the length of said one distributed sign.

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

0020Various methods already known are implemented to establish such a panel inserts composite sandwich-type structure with a honeycomb core.

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

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

0023It is also possible to reinforce the structure composite by adding skins are bonded by top place to strengthen or butcher.

0024Moreover, it is known from US 5,614,285 a method for producing a composite panel, comprising a linen mat and topped thermoplastic fibers a skin 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 barbs extending perpendicularly to the fastener.

0026The securing element is mounted in the mold, for be placed against the mast, and when the panel pressing by closing the mold, said pins of the element of fixing sinking in the mat being deflected to move in a direction generally parallel to the plane of said panel.

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

0028Such a panel is not usable in the field of the automobile, since its structure to a skin and to a linen mat does not give him strength sought to provide a vehicle part automobile.

0029Finally, document FR - 2686043 a method of making a structural panel composite sandwich honeycomb core comprising metal inserts, which consists in preheating the sandwich material component skins to make them malleable and facilitating their attachment by sealing the cells of the honeycomb core, and preheating the metallic inserts before carry a stack of different elements of that panel in a forming tool thereof.

0030All the above methods already known for implement tips in the structural panel composite 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 the implementation of such panels by such methods has a cost too high.

0031In particular, insertion of inserts and reinforcements according to the above methods often requires work manual or special machines, and the matter making link as glues, resins, foams filling. These steps of laying inserts are then mandatory recovery steps that are additional costs in manufacturing processes.

0032Furthermore, according to the above methods already known, used the inserts are generally made often in different materials from those used for realize the composite sandwich panel, it limiting subsequent recycling opportunities of that panel inside which are placed the inserts.

0033The present invention therefore provides a new method for producing a stiffened zone forming insert intended to receive a fastening system within a composite panel of the type sandwich honeycomb core, whose implementation is simple and economical.

0034More particularly, according to the invention, it is provided a method for producing a stiffened zone forming insert to house a system of fixing inside a composite panel of the type sandwich comprising a stack of at least one first skin, a cellular core of thermoplastic material and a second skin, the first and second skins being consisting of reinforcing fibers and a material thermoplastic.

0035It is characterized in that it comprises the steps following:<sl><li>a) is positioned a reinforcing plate to a particular place on the inner face of a portion of a forming mold, said plate being provided with spikes which extend towards the other part of mold,</li><li>b) placed in the said forming mold stacking said first and second skins being previously heated,</li><li>c) press is said stack by closing the forming mold, under a forming pressure range between 1 and 3 MPa, to simultaneously form said panel so that said panel matches the shape of the plate reinforcement which is anchored by means of its pins therein, and perform the specific location is positioned said reinforcing plate, a compaction localized compression of said stack.</li></sl>

0036Thus, advantageously, the method of embodiment of this stiffened zone for accommodate a fastening system is part of the forming process of the panel so that the method Global production of the panel to make a comprises 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 recyclable because the reinforcing plate may be advantageously made of metal, is located outside of the panel and it will later be possible to separate easily the composite of platinum reinforcement.

0039The fact that the plate is anchored in the panel composite, and more particularly in one of the skins sandwich material by means of its pins, allows system during mechanical stress fixing welcome in said stiffened zone, of apply directly pulling the skin against wherein the platen is pressed, the skin of said material sandwich with as best we know tensile mechanical properties.

0040The mechanical attachment via pins of the reinforcing plate on the skin can however surprised the art because it implies a priori affect the integrity of the composite structure the sandwich. But on the contrary, it will subsequently demonstrated by test results that according to the invention, the integrity of the composite panel is not affected.

0041Step c) of the process according to the invention in Also to further increase the resistance to high mechanical stress in the area and stiffened performed.

0042More particularly, the process according to the invention, the reinforcing plate covering the locally compacted composite panel and back on his edges, increases panel bending resistance where it could be weakened by the crash said sign.

0043According to an advantageous characteristic of the process according to the invention, the reinforcing plate being provided at least one through orifice, in step c), simultaneously with forming said panel, is pierced, through said hole of said reinforcing plate, said stack at the location of the compaction achievement localized, discarding at this point the fibers of the first and second skin.

0044Thus, according to the invention, the drilling operation said panel does not involve the cutting of fibers are only apart, and the panel retains where is performed the opening all its qualities mechanical. In addition, the drilling operation is advantageously performed simultaneously with the operation forming said panel, the number of steps to manufacture the part is reduced and thereby its manufacturing cost.

0045Furthermore, the reinforcing plate increases resistance to matting and shear opening thus achieved when the mechanical stress fixing system hosted in this opening stiffened zone.

0046According to a first embodiment of the method according to the invention, a reinforcing plate of which the pins extend in a direction perpendicular to the surface of the plate which carries them.

0047According to another embodiment of the method according to the invention, a reinforcing plate which pins extend in a direction inclined relative to the normal to the surface of the platen which the door.

0048Indeed, the pins placed perpendicular to the surface of the reinforcing plate does not allow in some cases to maintain the plate in place to little it is biased in the direction of the pins at handling and transportation of the formed panel. Of Moreover, in cases of extreme use, it is found that some barbs deform before the panel composite tearing.

0049These two above-mentioned problems, a solution can be, as presented above, the use of pins inclined relative to the plane of the surface of the platen wearer.

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

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

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

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

0054According to an advantageous characteristic of the process according to the invention, in step a), one positions a another reinforcing plate on the inner face of the other part of the forming mold, facing the platinum reinforcement 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 direction of the first reinforcing plate, and are for step c), to be anchored in the panel, and secondly accommodation also inserting it into the panel during step c) and in which are intended to engage the greater length of pins worn by the first so that after forming reinforcing plate said panel, the two plates are bonded to the other by crimping.

0055According to other characteristics of the method according to the invention, each reinforcing plate may have a thickness approximately between 0.8 and 1.2 mm and they comprise pins are then performed by stamping the material of said platen. In step c), the localized compacting of said stack may be carried out by means of at least one boss provided on the least part of the forming mold. prior to localized compacting of the panel, a preassembly heated formed by stacking at least the first skin, the cellular core and the second skin. then heating the pre-assembly can be realized a more pronounced heating of the localized area of ​​the pre-assembly where subsequently perform compaction localized 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 takes place in a direction perpendicular to the plane formed by said skins or in a direction obliquely with respect to the normal to the plane formed by said skins.

0057According to the invention there is also provided a device for implementing the aforesaid method which comprises a punch mounted on an inner wall of the mold so that it extends in the direction of the other wall in facing said mold where a housing is provided in which engages when said needle pierces said forming current stack. The needle is advantageously movably mounted on the upper wall of mold so that it sinks towards said housing corresponding after said first and second skins of the stack have been clamped between said walls of the mold. This needle comprises a barrel ending by a tip whose shapes and dimensions are adapted to the shape and dimensions of aperture traversing to realize, this tip having a shape conical or a needle shape with one face flat and a curved surface.

0058Finally, the invention also provides a panel of composite sandwich type structure, with a stacking at least a first skin, a core foamed thermoplastic material and a second skin, said panel being provided with at least one area forming stiffened insert for receiving a fastening system produced according to the aforementioned method.

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

0060In the accompanying drawings:<ul><li>FIG 1 is an exploded schematic sectional view of side of a stiffened zone of a composite panel to honeycomb core sandwich structure according to the invention,</li><li>2a and 2b are schematic views of above a stiffened zone as shown in exploded in Figure 1, on which two positions different pins are shown,</li><li>Figures 3a and 3b are front views and profile of an embodiment of a pin of a plate reinforcement used in the process according to the invention,</li><li>4a and 4b are views from above and side of a positioning mode of a pin reinforcing plate on a weft thread in accordance with method according to the invention,</li><li>5 shows schematically inserting an inclined pin and a pin right in a composite panel of sandwich structure having a core alveolar,</li><li>6 shows the upper and bottom of the forming mold used in accordance with method of the invention, the upper part being provided with a reinforcing plate with inclined spikes,</li><li>7 shows schematically seen in side cutting the stiffened zone of a panel sandwich structure with a honeycomb core upper reinforcing plate and a reinforcing plate lower by the method according to the invention,</li><li>Figures 8a, 8b and 8c show a mode producing a reinforcing plate used the process according to the invention,</li><li>9 shows a test fixture in pull on a test piece made in accordance with method of the invention, and</li><li>10 shows schematically seen over five different reinforcement plates used for tensile tests according to the scheme shown in Figure 9.</li></ul>

0061Figure 1 schematically shows a stiffened area 110 forming insert for accommodating a fastening system 10 within a panel Composite sandwich 100. This composite panel 100 comprises a stack of at least a first skin 101, a honeycomb core 102 and a thermoplastic material second skin 103. honeycomb core 102 is made by geometric cells of determined shape regularly spaced and bounded by thin walls thermoplastic material such as polypropylene. The cells may have a tubular shape or a hexagonal shape, in the latter case, the core alveolar type will honeycomb. The first and second skins 101, 103 of the composite board 100 shown consist of reinforcing fibers, glass, or other inorganic or organic material such as of the plant material, and a thermoplastic material. Advantageously, in the typical case shown 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 as son Chain oriented at 90 ° to each other.

0062Of course, in other embodiments not shown, may be considered for use production of the composite panel, first and second skin whose weaving would be different or constituted by a mat of reinforcing fibers embedded in a thermoplastic material 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, this area compacted being covered with a reinforcing plate 200, preferably of metal, applied against the second 103 skin following the shape of the compacted -area, and anchored by means of pins 201 in said sign.

0064According to the invention, the method for producing a Such stiffened area comprises the following steps:<sl><li>a) positioning the reinforcing plate 200 to a particular place on the inner face of a portion of a forming mold by the upper mold part, said reinforcing plate 200 being provided with spikes 201 extending towards the other party here lower said mold,</li><li>b) placing in the said forming mold stacking said first and second skins 101, 103 being preheated,</li><li>c) pressing said stack by closing the forming mold to form said panel, and simultaneously with forming said panel, is carried out, to the place determined which is positioned said deck reinforcement 200, a compaction made by compression, under a compaction pressure of between 1 and 3 MPa, said stack, placed here in the reinforcing plate, so that it matches the shape of the reinforcing plate preformed which anchor via its pins in said panel.</li></sl>

0065Note, advantageously, according to this method, prior to step b), a pre-assembly is heated formed by stacking at least the first skin 101, the cellular core 102 and the second skin 103. Upon heating of the pre-assembly is carried out cause further heating of the localized area of ​​said pre-assembly where the conduct is later localized compacting by compression. Temperature pre-heating assembly is such that in step c), the first and second skins have a temperature forming between 160 and 200 ° C.

0066As shown in Figure 1, the stiffened zone 110 is pierced by a through orifice 104 for carrying higher instead of a fastening system here, by example, a screw 10. To achieve the stiffened zone breakthrough according to the method according to the invention, the reinforcing plate 200 is provided with at least one orifice through 202, and in step c), simultaneously with forming said panel is pierced via said port 202 of the plate 200, said stack at the location of the realization of localized compaction by spreading this place the fibers of the first and of the second skin 101, 103.

0067Advantageously, it is noted that the embodiment of region stiffened by compression of the panel covered with a reinforcing plate, the bore at that location of the area stiffened, and the panel form are carried out in a single step during the forming by pressing said panel, which allows to obtain a process with a minimum number of steps and therefore to reduced cost.

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

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

0070This boss can preferentially be consisting of 200 preformed reinforcing plate to the shape of the boss if it is sufficiently rigid for, during the pressing step, compacting said stack.

0071As already mentioned above, to fix the reinforcing plate 200 on the skin 103 that the supports, there is provided according to the invention to use a reinforcing plate 200 with barbs 201 for, during the shaping of the panel, to be anchored to inside thereof. For the attachment of spikes of the reinforcing plate 200 is effective without much damage skin fibers they through, it is preferred that the pins have a shape and dimensions suitable to your skin type 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 efforts traction.

00722a and 2b, 4a and 4b show two opportunities available pins on the plate reinforcement used in the process according to the invention and thereby hooking of these pins to skin fiber used.

0073As shown in Figures 2a and 2b, the skin 103 used here is constituted by a balanced fabric Reinforcing fibers 103a, 103b, such as fibers of glass, vegetable fibers or fibers atoms, embedded in a thermoplastic material such as polypropylene, wherein there are as many of son 103b frame as son Chain 103a oriented 90 ° relative to each other. Thus, in a first mode embodiment of the method according to the invention, then uses a reinforcing plate 200 whose pins 201 are positioned so that in step c), they are inserted in the stack being placed in abutment on the son Chain 103a of the skin 103 against which the reinforcing plate 200 is pressed (see 2a).

0074Such an arrangement of the pins on the plate is expected when the mechanical stresses exerted on said stiffened zone are directed mainly the direction of the son of chain.

0075According to another embodiment, it may be provided that the pins 201 are placed on the plate reinforcement 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 expected when the mechanical stresses exerted on said stiffened zone are directed mainly the direction of the weft son.

0077Of course, for distributed mechanical efforts more complex way on the stiffened zone, we can consider the invention to use a platinum reinforcement provided so distributed over pins or less uniform, which is positioned against the son of chain and staggered against the frame of the son skin of said area.

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

0079Moreover, according to an embodiment of the method of the invention, there is provided use of a reinforcing plate with the pins extend in a direction perpendicular to the surface of the platen which the door.

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

0081The pins 201 then away skin fibers By driving as little as possible during their penetration therein. The barbs 201 have sufficient matting surface rely on the fibers without slicing.

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

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

0084To overcome this problem, according to a variant of the method according to the invention a plate is used reinforcement whose barbs extend in a direction inclined with respect to the normal to the surface of the platinum wearer.

0085Figure 5 depicts the insertion of a pin 201 a reinforcing plate 200, right and tilted, 100 in the composite panel. We can see this figure that the area of ​​skin pierced by the pins, is much greater when the pin 201 is inclined that when the pin 201 is right. Indeed, when the pin 201 is inclined with respect to the normal to the surface of the reinforcing plate which carries them, the Zone D₁ concerned of the skin is greater than the Zone D₂ pierced by a pin 201 law. to limit this zone D₁ pierced by inclined pins of the reinforcing plate used, must be introduced pins in the stack during the pressing step said panel, depending on their direction of inclination. So, 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 it is more particularly shown in Figure 6, in step a), the reinforcing plate 200 comprising the 201 pins inclined, here is positioned on a portion mobile M3 of the upper M₁ the forming mold and in step c), during closure of the forming mold by vertical movement according to the arrows F of Part top M₁ to the lower part M₂, the part Mobile M₃ moves on an inclined plane I with respect to plane of the inner surface of the upper part M₁ of so that said reinforcing plate 200 has a horizontal movement along arrow F₁ and the pins 201 fit into said stack along their direction of inclination.

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

0088That the pins are inclined or not, positioned so as to build on the sense son or frame chain they pierce the skin, they may may not, in some cases solicitations high mechanical, ensure by themselves the fixing the reinforcing plate in the stack.

0089Advantageously, it is then planned to link this 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 internal face of the other part of the forming mold, here the lower part, facing the reinforcing plate 200 positioned on the inner face of the part upper mold, the other reinforcing plate 200 ' being also provided with pins 201 'which, when the plates are in position in the mold, extend direction of the first reinforcing plate 200. These pins are intended to step c) to be anchored in the sign. The other reinforcing plate 200 'comprises 20l'a further housing is also featured within the panel during step c) and in which are for engaging the barbs 201a larger 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 reinforcement plates are solidarity, and so avoids the shearing of said panel thanks to the deformation of the assembly.

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

0092The pins 201a of greater length, used for crimping must be provided sufficiently fine to pass through the fabric constituting said skins without damaging them. These pins can be any 201 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 internal face of the other part- the forming mold is provided with at least one orifice through 202 'which is positioned next to the through hole 202 of the first platinum reinforcement 200 so that in step c), simultaneously forming said panel is pierced via said orifices of the plates, said stack at the location of the realization of localized compaction by spreading this place the fibers of the first and of the second skin.

0095The reinforcing plates 200, 200 'used have a thickness which is included here about between 0.8 and 1.2 mm, and the spikes they comprise are made by stamping the material of the plates. Indeed, for a large scale production, the pins are made by stamping. This requires that the Platinum is drawable, which sets the thickness maximum thereof.

0096The resistance of the stiffened region comprising the fixing system, to mechanical stresses, depends on the nature of the skins of the stack, of the quality of the attachment of the plate or plates with the skin, but also the ability of (have) or the turntables withstand the stresses, particularly at the through hole through which the fastening 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, for said platinum could be produced 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 200a first part equipped with pegs 201 and an orifice through 202a, and a second flap portion 200b pierced with an orifice 202b coming opposite that provided in the first portion 200a (see Figure 8b) when the latter is folded on the first part. This folding part 200b may have a thickness different from the first portion with the pins 201 and therefore it is possible to modulate the total thickness of the platinum. In the case shown, the flap portion does not entirely cover the first portion of the plate but for aesthetic reasons, it may be expected that this folding part comes completely cover the first portion with barbs.

0099The method according to the invention, as described above, to provide a composite panel type sandwich with a honeycomb core area stiffened, has the following advantages.

0100The realization of the stiffened zone provided with one or two reinforcement plates is carried out in one step during the forming of said panel, by carrying out a localized compacting, and simultaneously the drilling said zone. 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 made minimal stages and thus has a cost minimum. The turntables or preformed or not, positioned in the mold before closing said mold during the heating time of the soul and skin constituting said stack. The use of a platinum equipped with pegs used to hang and solicit fibers of the skin against which it is based, in traction. This is particularly advantageous when it is known that the skins of the stack have a better quality of tensile strength than the core alveolar. The pins have used a form studied so they slip and get stuck between two son longitidinaux and rely on a transverse wire a minimum breaking fibers. The integrity of the fabric constituting said skin 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 efforts exerted flexion on said panel, giving back to the latter part of its rigidity locally lost by compaction. As the thickness of these reinforcing plates determines the value of the rigidity which is desired to bring the piece, it can modulate, in order to avoid when high mechanical stress shear said piece at its attachment system.

0101The reinforcing plate, made of metal by example, is the only different material added to the composite sandwich panel. It is deposited by outside or below the sandwich material. She can then easily be removed during operations recycling of the part. In the case of a pin platinum vertical, the latter has a low tensile strength to remove by hand or using a lever, but enough to keep it in place during its handling and mounting. In the case of a inclined pin deck, the effort is more important but does not require anything else, again, a lever or chisel to remove the plate the stack during a recycling operation. If the plates are crimped to one another dismantling probably require a tool that will help the to separate.

0102However, in all these cases, once This operation performed, metal parts completely separated from the composite material. the plates reinforcement used are relatively simple to make by stamping and therefore inexpensive. They can be made in large series.

0103Tensile tests were performed on a test of a composite sandwich panel according the invention wherein the first and second skins are constituted by a balanced fabric of density 1420 g / m². Five kinds of plates were used, shown more particularly in Figure 10, and referenced 1 to 5. In the various plates, the amount of pins and their respective position each relative to 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, against the 20-plates have been manufactured specifically for these tests. These, once mounted, completely cover or the pin plates 200, their thereby avoiding deforming during the test. Thus, in tests in tension, every effort is absorbed by the pins of said plates, and the hole was made in the specimen. These tests to evaluate the ability of such a basic system (pimple-skins) to withstand the force, depending on the number of pins of the reinforcing plates used and their respective positions. From a fixing jaws 40, was performed tractions on the turntables 200 via-plates 20 against.

0106Comparing the tensile test results carried out on the different plates 1, 2, 4 or 1, 3, 5, one could get the value of the minimum number of pins needed per line. In addition, by comparing results of tests conducted on the plates 2, 3 or 4, 5, there was obtained an indication of the influence of relative position of the pins between them. It was found a row of six pins and a hole diameter of 8 by Platinum allows withstanding a dependent about 1200 daN, and achieve the 2000 daN four rows before the reinforcing plate metal does not yield.

0107The present invention is not limited to described and illustrated embodiments, but man the art will bring them any variant within the mind.