Method and apparatus for molding composite materials

Abstract

The present invention relates to a method for preforming a composite material (I) into a plate shape, the composite material comprising reinforcing fibers bonded together, particularly by means of a plastic polymer material. Specifically, the method includes an intermediate molding stage (b) comprising at least the following operations: - introducing gas (III) into a second chamber (4) while the external pressure Pext equals atmospheric pressure, simultaneously maintaining the pressure P2 in the second chamber (4) below the external pressure Pext and, in particular, atmospheric pressure, and thus locally maintaining a distance between the upper membrane (2) and the lower membrane (1), and simultaneously maintaining the positioning and contact between the composite material (I) and the two membranes (1 and 2) in the contact area (5); - evacuating gas (III) contained in the first chamber (3) to press the lower membrane (1) onto the entire molding surface (22) present at the bottom (21) of the mold (20). The invention also relates to an apparatus suitable for carrying out this method.

Description

Technical Field

[0001] The present invention relates to the field of methods for forming composite materials and apparatus suitable for such methods. Background Technology

[0002] Composite materials are made by combining a set of reinforcing fibers (notably carbon or aramid) with a polymeric material that at least partially provides the reinforcing fibers. Composite materials are typically intended for the production of composite parts of more or less complex shapes, particularly in the aerospace, automotive, sports, or energy sectors. The manufacture of composite parts or articles can be carried out using two types of methods: the so-called "indirect" method and the so-called "direct" or "LCM" (liquid composite molding) method.

[0003] The indirect method uses a composite material known to be pre-impregnated with a polymer resin, which is then shaped by a compression molding operation to produce a desired composite part. The fiber pre-impregnated material contains the desired amount of resin for the final composite part.

[0004] The direct method is defined by the fact that one or more fiber reinforcements are processed in a “dry” state (i.e., without a final matrix), wherein the resin to be used as the matrix is ​​processed individually, for example, by injection into a mold containing the fiber reinforcement (“RTM” (Resin Transfer Molding) method), by pouring the entire thickness of the fiber reinforcement (“LRI” (Liquid Resin Infusion) method or “RFI” (Resin Film Infusion) method), or by manually coating / impregnating each individual layer of the fiber reinforcement onto the form in turn using rollers or brushes.

[0005] For RTM, LRI, or RFI methods, a preform in the desired finished product shape must typically be manufactured first, and then impregnated with a resin intended to form the matrix (usually a stack of sheets). The resin is injected or infused using pressure and temperature differentials, and after the preform contains the required amount of resin, the assembly is heated to a higher temperature to complete the polymerization / crosslinking cycle and thus harden.

[0006] The starting composite material (whether dry or prepreg) has a flat surface and is provided in the form of a flat structure (also called a sheet), which must be shaped into the desired shape of the final composite part. Typically, the shaped composite material consists of a stack of several layers of material that have been previously combined to form a single sheet, also known as a preform. There are two main types of molding methods in the prior art:

[0007] -A method using an open mold with a non-planar molding surface at the bottom, wherein the open mold is combined with a diaphragm to close the mold, such as... Figure 1 As shown, this will be referred to as the single-diaphragm method, and

[0008] - Using an open mold combined with two diaphragms, the composite material to be formed is placed between the two diaphragms, such as... Figure 2 As shown, this will be referred to as the double-diaphragm method.

[0009] Single-diaphragm methods are suitable for forming convex, single-bend parts. These methods allow for a wide range of deformation possibilities, particularly bending and interlaminar slippage. However, one of their main drawbacks relates to the imbalance of the flat composite material to be preformed, which is simply placed on the convex shape and intended to impart its shape during the first step of the method, such as... Figure 1 As shown. Furthermore, the alignment of the diaphragm on this composite material can also affect its positioning on the bottom of the mold shape. Therefore, the positioning of the starting material, and consequently its deformation, is uncontrolled, which reduces the mechanical properties of the resulting preform. Additionally, in this method, there is a lack of control over the remaining material to be formed in the molding process, and it is difficult to obtain shapes with hyperbolic curvature. Finally, in the single-diaphragm method, for a given starting composite material and geometry, there are no adjustable parameters, which could be a potential source of method optimization.

[0010] To overcome the positioning problem, a so-called double-diaphragm method has been developed. Using the reduced pressure of two diaphragms, this molding method has the advantage of ensuring the composite material remains and is precisely positioned throughout the molding process. It also offers the possibility of forming composite materials with hyperbolic geometries by means of planar shear deformation under transverse stress.

[0011] To this end, the composite material is placed between two diaphragms, and reduced pressure is generated between the two diaphragms to ensure that the composite material is held in place before molding. The dual-diaphragm method provides:

[0012] - Control over the position of the laminations, because in such... Figure 2 As shown, after the planar material is positioned on the lower diaphragm 1, it will not be subject to gravitational displacement as in the single-diaphragm method.

[0013] - Improved ability to implement automation

[0014] - The possibility of modulating the method by changing the pressure applied between the two diaphragms, as proposed in U.S. Patent 9,259,859.

[0015] - This allows for the formation of materials with more complex geometries than in single-septum methods, especially in asymmetric configurations. Indeed, bending deformation is always dominant, but the deformation modes extend to intralaminar and interlaminar sliding as well as planar shearing, which makes it possible to obtain bi-bending shapes.

[0016] However, it has been found that lateral stress restricts interlaminar slippage, which can cause defects (e.g., creases) in the resulting molded material, even under simple bending conditions. Indeed, applying near-vacuum pressure between the two diaphragms increases the compaction of the composite and reduces the fiber slippage ability, and when the composite is in the form of a stack of several laminars, the slippage ability between the laminars is reduced, leading to creases during molding. To mitigate this phenomenon, U.S. Patent 9,259,859 proposes varying the pressure applied in the interlaminar space during the first stage of the method, maintaining it at a high value (500 mbar in the example), and then reducing it to below 10 mbar in the final molding and compaction operation. However, this adjustment does not completely eliminate defects, but reductions can be observed. Depending on the material, its thickness, and the desired geometry, defects may persist.

[0017] In this context, the present invention proposes novel molding methods and apparatus that enable the resolution of molding problems encountered in the prior art. The methods and apparatus developed by the inventors offer greater flexibility and thus allow the benefits of both single-diaphragm and double-diaphragm methods to be enjoyed while compensating for their disadvantages. Summary of the Invention

[0018] This invention relates to a method for preforming a composite material into a sheet form, the composite material comprising reinforcing fibers, particularly bonded together by a plastic polymer material, wherein the composite material to be preformed is placed within a molding apparatus comprising a first sealed chamber formed between a mold having a molding surface and a lower diaphragm, and a second sealed chamber formed between the first diaphragm and a second diaphragm positioned above the first diaphragm, the first chamber defining a first modular volume V1, and the second chamber defining a second modular volume V2 (referred to as the inter-diaphragm volume), the composite material being contained within the inter-diaphragm volume V2. The method according to the invention includes an intermediate molding stage (b) during which gas is introduced into the second chamber when an external pressure Pext equals atmospheric pressure, and the upper diaphragm is thereby locally maintained at a distance from the lower diaphragm, while the pressure P2 in the second chamber is maintained at the molding apparatus below the external pressure Pext, and particularly atmospheric pressure, and the lower diaphragm is positioned adjacent to the molding surface.

[0019] The object of this invention is a method for preforming a composite material into a sheet form, said composite material comprising reinforcing fibers, particularly bonded together by a plastic polymer material, the method comprising the following sequential stages:

[0020] (a) A positioning stage of the composite material within the molding apparatus, the positioning stage comprising the following operations:

[0021] (a1) A mold is provided, the non-planar bottom of which defines a molding surface corresponding to the shape to be given to the composite material to be preformed.

[0022] (a2) A first diaphragm, referred to as the lower diaphragm, is positioned above the bottom of the mold, and a second diaphragm, referred to as the upper diaphragm, extends above the composite material. The composite material to be preformed is deposited on the first diaphragm. Both diaphragms are elastically deformable and impermeable to gas, and the composite material is placed above the molding surface.

[0023] (a3) Position the two diaphragms together with the mold to form:

[0024] -A first sealed chamber between the mold and the lower diaphragm, the first chamber defining a first modular volume V1, and

[0025] - A second sealed chamber between the two diaphragms, the second chamber defining a second variable volume V2, referred to as the interdiaphragm volume, in which the composite material is accommodated.

[0026] (a4) The gas from the second chamber is discharged, thereby reducing the inter-diaphragm volume V2 so that both diaphragms are in contact with the composite material.

[0027] (a5) The lower diaphragm is partially attached to the molded surface in at least one contact area, wherein the composite material is also in contact with both diaphragms at the contact area.

[0028] The positioning phase results in the composite material being placed within the resulting molding apparatus, which itself is placed under an external pressure Pext that can be equal to atmospheric pressure. The placement of the composite material within the molding apparatus corresponds to the composite material being held by the two diaphragms, both in contact with it, wherein in at least one contact area, the lower diaphragm is partially aligned on the molding surface.

[0029] (b) The intermediate forming stage includes at least the following operations:

[0030] When the external pressure Pext equals atmospheric pressure, gas is introduced into the second chamber, while the pressure P2 is maintained below the external pressure Pext, and particularly atmospheric pressure, thereby locally maintaining a certain distance between the upper and lower diaphragms, and simultaneously maintaining alignment and contact between the composite material and the two diaphragms at the contact area.

[0031] - Gas is discharged from the first chamber to press the lower diaphragm onto the entire molding surface at the bottom of the mold.

[0032] (c) The final molding and compaction stage, which produces the desired final shape of the preformed composite material, during which heating is applied and the gas contained in the second chamber is removed to press both the composite material and the upper diaphragm onto the lower diaphragm, which itself is pressed against the bottom of the mold, particularly against the molding surface, and to achieve a reduction in pressure P2 to ensure compaction.

[0033] (d) The cooling stage and demolding stage of the preformed composite material.

[0034] Therefore, the method according to the invention is a hybrid method of forming a composite material under reduced pressure using two diaphragms. It enables a hybridization of the prior art single-diaphragm and double-diaphragm molding methods: initially, the presence of two diaphragms ensures the placement and maintenance of the composite material plane, and this control continues throughout the method, as the two diaphragms maintain contact with the composite material at least at the layer level of the contact area, wherein the diaphragm / composite material assembly is supported on the molding surface. At the end of the positioning stage (a), the composite material remains compressed between the two diaphragms, and after operation (a4), the second diaphragm chamber is advantageously at its minimum volume, and the lower diaphragm abuts the molding surface at at least one contact area (particularly corresponding to the highest area of ​​the molding surface). Subsequently, during intermediate molding (b), the mechanical stress applied to the composite material is reduced by adjusting the volume of the second chamber between the two diaphragms in which the composite material is positioned, thereby altering the mechanical stress experienced by the composite material during molding. In the intermediate molding step (b), the invention provides a reduction in the pressure exerted on the composite material by the two diaphragms, thereby reducing / eliminating the risk of wrinkling, and particularly wrinkling caused by uncontrolled interlaminar slippage due to bending deformation. The method according to the invention provides an intermediate molding step (b) (also called a pre-molding step) during which the composite material regains the freedom of movement to ensure optimal (defect-free) quality. However, its proper positioning is ensured by the pressure exerted on the molding surface by the upper diaphragm and the support at the contact area.

[0035] Specifically, in the intermediate molding stage (b), when the external pressure Pext equals atmospheric pressure, a gaseous medium is introduced into the second chamber, causing an increase in the volume of the second chamber while maintaining the pressure P2 below the external pressure Pext, and particularly atmospheric pressure. Therefore, the upper diaphragm is locally held at a distance from the lower diaphragm, while maintaining alignment and contact between the composite material and the two diaphragms at the contact area. This spacing between the upper and lower membranes on their partial surfaces is achieved by the presence of the gaseous medium added to the second chamber during the intermediate molding stage (b). Specifically, the upper membrane is also locally spaced from the composite material (while maintaining alignment and contact between the composite material and the two membranes at the contact area).

[0036] According to the invention, the approach and positioning of the reinforcing material on the molding surface are controlled. The reinforcing material will follow the movement of the first diaphragm as it descends, and will be pressed more or less completely and rapidly onto the molding surface. On the other hand, by increasing the volume of the second chamber during intermediate molding (b), while maintaining pressure P2 below the external pressure Pext, and especially atmospheric pressure, when the external pressure Pext is equal to atmospheric pressure, the descent of the upper diaphragm does not follow the reinforcing material and the lower diaphragm, and its movement is displaced relative to the lower diaphragm, except over a more or less large area at the contact area corresponding to the initial alignment. During this intermediate molding stage (b), the space maintained between the two diaphragms provides greater freedom of movement for the fibers within the material, and will minimize stress and avoid defects in the final molded material. However, the support at the contact area of ​​the upper diaphragm on the composite material (the composite material itself rests on the lower diaphragm, and the lower diaphragm itself rests on the molding surface) allows the composite material to be positioned and prevented from sliding on the molding surface, ensuring the correct shape is obtained.

[0037] Furthermore, the method according to the invention increases the number of parameters that can be modified during its implementation, thus making it particularly possible to adjust the forming according to the material and the desired final geometry. The method is also ideally suited for automation.

[0038] In the method according to the invention, operation (a5) is performed after operation (a4) by venting the gas in the first chamber, resulting in a decrease in the volume V1 of the first chamber to establish pre-contact between the lower diaphragm and the molding surface, while the volume V2 of the second chamber remains constant.

[0039] According to another embodiment that can be combined with the previous embodiment, during the entire intermediate forming stage (b), when the external pressure Pext is equal to atmospheric pressure, one or more gas introductions and one or more gas extractions are performed in such a way that the pressure P1 in the first chamber and the pressure P2 in the second chamber are controlled and / or modified such that the pressure P1 is kept lower than the pressure P2, which is itself lower than the external pressure Pext and, in particular, lower than atmospheric pressure.

[0040] According to the invention, heating of the composite material can be provided throughout the intermediate molding stage (b) to soften the plastic polymer material. Those skilled in the art will adjust the use of this heating according to the properties of one or more constituent polymers of the plastic polymer material, which can serve as an aid to preforming. Typically, heating can be provided at temperatures ranging from 40°C to 250°C, particularly between 70°C and 200°C. However, the method according to the invention is also perfectly suitable for so-called cold preforming (room temperature, about 25°C), depending on the presence of the polymer plastic material in the composite material. Typically, as with prior art methods, the final stages of molding and compaction are performed thermally, particularly in the temperature range of 40°C to 250°C, particularly between 70°C and 200°C, depending on the presence of the polymer plastic material in the composite material.

[0041] When heating is applied at any stage of the method, the temperature rise alters the mechanical properties of the material, gas volume, and pressure. By changing the interdiaphragm volume and / or the volume of the first chamber, the volume of the first chamber can be better adapted to these modifications.

[0042] According to a particular embodiment, the method according to the invention includes a heating step such that the composite material is heated throughout the intermediate molding stage in order to obtain softening of the plastic polymer material, and wherein, during the heating step to obtain the desired heating temperature, the volumes V1 and V2 of the first chamber and the second chamber are controlled to avoid volume increase.

[0043] According to a first alternative embodiment of the method according to the invention, the intermediate molding stage (b) is carried out by suction to remove the gas contained in the first chamber, pressing the lower diaphragm against the entire molding surface present at the bottom of the mold, while simultaneously introducing gas into the second chamber when the external pressure Pext equals atmospheric pressure, maintaining the pressure P2 in the second chamber below the external pressure Pext, and particularly atmospheric pressure, and thus increasing the inter-diaphragm volume V2, and locally maintaining the distance between the upper and lower diaphragms, while maintaining alignment and contact between the composite material and the two diaphragms at the contact area. Advantageously, the reduction in the volume V1 of the first chamber is equal to or substantially equal to the increase in the volume V2 of the second chamber. According to the invention, substantially equal means equal to plus or minus 5% or even plus or minus 2%.

[0044] According to a second alternative embodiment of the method according to the invention, the intermediate molding stage (b) includes the following continuous operations:

[0045] (b1) The gas contained in the first chamber is discharged, causing the volume V1 to decrease, so that the lower diaphragm descends to the middle position. Simultaneously, when the external pressure Pext equals atmospheric pressure, gas is introduced into the second chamber, and the pressure P2 in the second chamber is maintained below the external pressure Pext, and particularly atmospheric pressure. This increases the inter-diaphragm volume V2 and locally maintains a certain distance between the upper and lower diaphragms, while maintaining alignment and contact between the composite material and the two diaphragms at the contact area.

[0046] (b2) Gas is discharged from the first chamber to press the lower diaphragm against the entire molding surface at the bottom of the mold while keeping the inter-diaphragm volume V2 constant.

[0047] Specifically, step (b2) involves depositing the second diaphragm onto the composite material to be molded, the first diaphragm, and the molding surface in a delayed but simultaneous manner, followed by step (c).

[0048] Advantageously, in a second alternative embodiment of the method according to the invention, also in step (b1), the decrease in the volume V1 of the first chamber is equal to or substantially equal to the increase in the volume V2 of the second chamber.

[0049] According to a third alternative embodiment of the method according to the invention, the intermediate molding stage (b) includes the following continuous operations:

[0050] (b'1) The gas contained in the first chamber is discharged, causing the first volume V1 to decrease, so that the lower diaphragm descends to the middle position. Simultaneously, when the external pressure Pext equals atmospheric pressure, gas is introduced into the second chamber, and the pressure P2 in the second chamber is maintained below the external pressure Pext, and particularly atmospheric pressure. This increases the inter-diaphragm volume V2 and locally maintains a certain distance between the upper and lower diaphragms, while maintaining alignment and contact between the composite material and the two diaphragms at the contact area.

[0051] (b'2) Gas is discharged from the second chamber, thereby reducing the inter-diaphragm volume V2 so that the upper diaphragm descends and positions the two diaphragms in contact with the composite material.

[0052] (b'3) The gas contained in the first chamber is discharged to press the lower diaphragm onto the entire molding surface present at the bottom of the mold, while the gas is introduced into the second chamber when the external pressure Pext is equal to atmospheric pressure and the pressure P2 in the second chamber is maintained below the external pressure Pext, and in particular atmospheric pressure, and thus the inter-diaphragm volume V2 is increased, and the upper diaphragm and the lower diaphragm are locally maintained at a certain distance, while the alignment and contact between the composite material and the two diaphragms are maintained at the contact area.

[0053] Advantageously, in this third alternative embodiment of the method according to the invention, also in operation (b'1) and / or operation (b'3), the decrease in the volume V1 of the first chamber is equal to or substantially equal to the increase in the volume V2 of the second chamber.

[0054] In a third alternative embodiment of the method according to the invention, operations (b'1) to (b'2) may be repeated, for example, one to ten times, to gradually induce the descent of the lower and upper diaphragms.

[0055] In the method according to the invention, regardless of the embodiment or alternative embodiments, typically in steps (a2) and (a3), the two diaphragms are arranged horizontally. This allows for better control over the positioning of the plate-like composite material resting on the lower diaphragm at the start of the method. This horizontal positioning is maintained during step (a3), which is simply composed of a molding chamber, and thus achieves a seal between the diaphragms on the one hand, and a seal between the lower diaphragm and the mold on the other, as will be understood from the explanation in the following description.

[0056] In the method according to the invention, regardless of the embodiment or alternative embodiments, typically at the end of step (a2), both diaphragms are either flat or stretched to minimize bending deformation (out-of-plane) caused by their own weight. However, to maintain their ability to elastically deform or even plastically deform, the diaphragms are stretched, avoiding excessively significant flat elongation (i.e., within the plane of the diaphragms). For this purpose, each diaphragm is stretched, but preferably its planar elongation is less than 5%.

[0057] According to one embodiment compatible with all and alternative embodiments of the method according to the invention, during the cooling phase, the pressure in the first chamber can be increased, specifically to reduce friction with the mold. Then, when the external pressure Pext equals atmospheric pressure (1.013 bar), the pressure P2 in the second chamber will be lower than the pressure P1 in the first chamber, the pressure of which is itself lower than or equal to the external pressure Pext (and particularly atmospheric pressure). Specifically, during the cooling phase, when the external pressure Pext equals atmospheric pressure, a pressure P1 ranging from 850 mbar to atmospheric pressure (1.013 bar) can be obtained in the first chamber. This pressure increase can be achieved by adding gas to the first chamber, particularly by adding air. However, both diaphragms will remain pressed against the composite material and the molding surface, and therefore the volumes V1 and V2 will remain constant.

[0058] The method according to the invention is applicable to the formation of so-called dry composite materials intended for direct manufacturing methods of composite parts. Specifically, the plastic polymer material constitutes at most 10% of the total weight of the composite material, preferably 0.5% to 10% of the total weight of the composite material in sheet form, and more preferably 2% to 6% of the total weight of the composite material. The method according to the invention can also be used to form prepreg composite materials comprising a relatively high plasticity content of greater than 10%. Specifically, in this case, the plastic polymer material can constitute at least 20% and up to 60% of the total weight of the composite material in sheet form, and preferably 20% to 40% of the total weight of the composite material in sheet form.

[0059] Unlike composite materials that exist in sheet form, plastic polymer materials are specifically selected from thermoplastic polymers, thermosetting polymers, polymers comprising thermoplastic and thermosetting or crosslinked portions, and mixtures thereof.

[0060] In addition, the composite material is typically formed from glass fiber, carbon fiber, aramid fiber or ceramic fiber or any other reinforcing fiber known to those skilled in the art, with carbon fiber and glass fiber being particularly preferred.

[0061] According to certain embodiments, as is evident in the examples, the composite material in the form of a sheet comprises a stack of fiber-reinforced layers, which are obviously selected from fabrics and unidirectional sheets of reinforcing fibers. This stack of fiber-reinforced layers has uniform properties and is obtained by polymeric plastic materials and / or by any other means of the stitching or weaving type.

[0062] The present invention also relates to an apparatus for preforming composite materials into plate form, the apparatus comprising:

[0063] - A mold, the non-planar bottom of which defines the molding surface of the composite material to be preformed.

[0064] A first diaphragm, referred to as the lower diaphragm, and a second diaphragm, referred to as the upper diaphragm, are elastically deformable and impermeable to gas, and are positioned one above the other and extend above the bottom of the mold.

[0065] - A positioning device that allows the two diaphragms and the mold to be formed:

[0066] -A first sealed chamber between the mold and the lower diaphragm, the first chamber defining a first variable volume V1, and

[0067] - A second sealed chamber between the two diaphragms, the second chamber defining a second variable volume V2, referred to as the interdiaphragm volume, the second variable volume being designed to receive the composite material to be preformed.

[0068] - Each of the first and second chambers is equipped with an outlet valve to ensure the exit of the gaseous medium contained in the chamber. Each outlet valve is connected to a circuit equipped with a gaseous medium flow and a pressure regulator to ensure the gaseous medium can be discharged from the respective chamber. The second chamber is equipped with an inlet valve to ensure the entry of the gaseous medium into the second chamber. The inlet valve is connected to a circuit equipped with a gaseous medium flow and a pressure regulator to ensure the introduction of the gaseous medium into the second chamber.

[0069] According to a preferred embodiment, the first chamber is equipped with an inlet valve to allow a gaseous medium to enter the first chamber. The inlet valve is connected to a circuit equipped with a gaseous medium flow and pressure regulator, thereby allowing the gaseous medium to be introduced into the first chamber. In particular, this arrangement allows for an increase in pressure within the first chamber, especially for reducing friction with the mold during the cooling phase.

[0070] In the molding apparatus proposed in the prior art, the outlet valve exists only at the level of the two chambers and has the function of removing air from the space between the diaphragms and from the space between the lower diaphragm and the mold. Therefore, the pressure and volume in the two chambers can only be reduced during molding. According to the present invention, an inlet valve has been added at the level of the second chamber (the space between the diaphragms), or even at the level of the first chamber (the chamber located between the lower diaphragm and the mold), thereby allowing the volume and / or pressure in the relevant chambers to be increased, thereby regulating the method and reducing the stress applied to the material during intermediate molding stages or even during cooling.

[0071] In any device according to the invention, some or all of the inlet valve and outlet valve may correspond to various valves or taps. It is also possible that the inlet valve and outlet valve assembled into the same chamber may actually be a single valve comprising an inlet and an outlet, said single valve being connected to a pneumatic system to regulate the valve in either inlet or outlet mode in the direction of the chamber / external circuit.

[0072] In some embodiments, the device can be expected to include an external loop for circulating gas from the first chamber to the second chamber. This configuration facilitates simultaneous modification of the volumes of both chambers. Attached Figure Description

[0073] [ Figure 1 ] Figure 1 This is a cross-sectional view of an apparatus used in the prior art, which is used in a molding method using a single diaphragm (so-called single diaphragm method).

[0074] [ Figure 2 ] Figure 2 This is a cross-sectional view of an apparatus used in the prior art, which is used in a molding method (double diaphragm method) using two superimposed diaphragms.

[0075] [ Figure 3 A] Figure 3 A is a cross-sectional view of the device according to the invention, which is suitable for implementing the molding method according to the invention.

[0076] [ Figure 3 B] Figure 3 B is a cross-sectional view of another apparatus according to the invention suitable for performing the molding method according to the invention, wherein the first chamber is equipped with a valve for the gas inlet.

[0077] [ Figure 4 ] Figure 4 This is a perspective view of a molding apparatus according to the invention, showing a connecting device for forming two chambers and holding two diaphragms on a mold.

[0078] [ Figure 5] Figure 5 It is shown Figure 4 Partial perspective view of the various parts of the connecting device shown.

[0079] [ Figure 6 ] Figure 6 The diagram shows the steps of the method according to the invention based on a first alternative embodiment.

[0080] [ Figure 7 ] Figure 7 This is a diagram illustrating the various steps of the method according to the invention based on a second alternative embodiment.

[0081] [ Figure 8 ] Figure 8 This is a diagram illustrating the various steps of the method according to the invention based on a third alternative embodiment.

[0082] [ Figure 9 ] Figure 9 This is a cross-sectional view of a device according to the invention, the device including an external circuit for circulating gas from a first chamber to a second chamber.

[0083] [Figure 10] Figure 10 is a perspective view of the protrusions present in the molding area of ​​the mold used in Examples 1a to 3.

[0084] [Figure 11] Figure 11 shows the preform material obtained in Comparative Example 1b and shows the presence of creases that constitute defects. Detailed Implementation

[0085] Before describing the various embodiments of the present invention, some concepts and terms will be defined.

[0086] Composite materials existing in the form of plates can consist of a single material based on reinforcing fibers and plastic polymers, or a corresponding stack of such materials. The composite starting material is planar and is referred to as a plate to reflect the fact that its width and length are much greater than its thickness, but it can have a certain thickness. Specifically, the plate-form material can have a width and length, each being at least 10 times or even at least 10 to 1000 times the thickness of the starting composite material. Within the scope of the invention, the plate-form composite starting material particularly has a thickness of 0.2 mm to 50 mm, preferably 0.5 mm to 20 mm.

[0087] Within the scope of this invention, any composite starting material used in the prior art for molding operations can be used. Such material comprises one or more fiber reinforcing layers, particularly one or more reinforcing fiber layers selected from glass fibers, carbon fibers, aramid fibers, or ceramic fibers, with carbon fibers and glass fibers being particularly preferred.

[0088] This type of composite material in the form of a plate can be formed by an assembly of reinforcing fibers bonded together by plastic polymer materials or by a stack of fiber-reinforcing layers comprising plastic polymer materials, said layers being bonded together by plastic polymer materials and / or by any other suitable means, particularly by stitching or weaving.

[0089] Specifically, the fiber composite material comprises fiber-reinforced layers or stacks of fiber-reinforced layers, and is particularly selected from:

[0090] - Unidirectional sheet with structural support provided by polymer adhesive, by stitching or by weaving;

[0091] -Assemblies of stacked unidirectional layers with different orientations constitute multiaxial reinforcements, commonly known as non-crimped fabrics (NCF), which are fixed together by stitching or weaving.

[0092] - Fabrics (or woven fabrics) with an interlaced or ply structure, in which threads (called weft threads) are inserted between the threads they pass through (called warp threads), especially those with taffeta, twill, or satin reinforcement or interlaced types, such as those in the 21st Congrès de Mécanique [French Congress of Mechanics] by C.Dufour, F.Boussu, P.Wang, D.Soulat and X.Legrand: "Analysis of the behavior of interlock woven reinforcements during the preforming process]", 2013, pages 5-6;

[0093] - A knitted fabric with a structure containing interlaced yarns or rovings, wherein the interlocking is not a result of an insertion method. In particular, such a knitted fabric can be biaxial, triaxial, or interlocking. See in particular the paper by Boris Duchamp (https: / / www.theses.fr / 197146112) Contribution to the development of textile preforms for the reinforcement of flexible cavities under the direction of Damien Soulat and Xavier Legrand-Lille 1, 2016 and M. Kowalski, "Développement de croisements de raidisseurs composites [Development of composite stiffener crossings]: Technology, Modeling and Optimization", Thesis, University of Lille 1, 2015 and T. Liao and S. Adanur, "A novel approach to Three-dimensional modeling of interlaced fabric structures", Text.Res.J., Volume 68, Pages 841-847, 1998;

[0094] -Woven fabrics, obtained through interlaced loops. Such woven fabrics can be, in particular, gathered knits (or weft knits), unraveled knits (or warp knits), or interlocking knits. Interlocking knits are variations of the other two structures, featuring interlaced loops in thickness, creating an ordered structure between layers of loops or through repeatable and repetitive three-dimensional patterns.

[0095] Specifically, composite material I comprises a stack of fiber-reinforced layers as defined above and at least one porous layer of plastic polymer material. This porous polymer layer may be in the form of a porous membrane, mesh, powder coating, fabric, or preferably, a nonwoven fabric or veil.

[0096] Specifically, the composite material may consist of fiber-reinforced layers having porous plastic polymer layers on each of its faces, or of a stack of several fiber-reinforced layers with one or more porous plastic polymer layers inserted between them. Before placing the composite material in the device according to the invention, the interrelationship between the layers ensures uniform properties for the composite material, thereby ensuring its shape. The prior bonding between the fibers or even the layers may be achieved solely through the thermal bonding properties of the existing plastic polymer material, or it may be achieved or accomplished by using other types of bonding (such as stitching or weaving).

[0097] Examples of composite materials include:

[0098] - A composite material consisting of unidirectional sheets of reinforcing fibers and their stacks, wherein the reinforcing fibers are associated with one or more porous plastic polymer layers (and particularly nonwovens) on each face.

[0099] - An assembly of several unidirectional sheets of reinforcing fibers oriented in at least two different directions, wherein one or more layers of porous plastic polymer material are present between the unidirectional sheets and on the surface, the assembly being joined together by stitching or weaving.

[0100] These can be dry materials (i.e., plastic polymer materials accounting for up to 10% of the total weight of the composite material, preferably 0.5% to 10% of the total weight of the composite material, and preferably 2% to 6% of the total weight of the composite material in sheet form) or prepregs.

[0101] Such materials are specifically mentioned in patent applications or patents EP 1125728, US 6,828,016, WO 00 / 58083, WO2007 / 015706, WO 2006 / 121961, US 6,503,856, US 2008 / 7435693, WO 2010 / 046609, WO2010 / 061114 and EP 2 547 816, US 2008 / 0289743, US 2007 / 8361262, US 2011 / 9371604, WO2011 / 048340, EP 2547816, WO 2010 / 067003, US 8,361,262, US 9,371,604, WO As described in 2011 / 113751 and EP 2491175, or in U.S. Patent 9,259,859.

[0102] "Plastic polymer material" refers to any polymer or mixture of polymers that can be deformed with or without heating. Therefore, by applying the method according to the invention, a composite material in sheet form containing such a plastic polymer material can be deformed and molded into a desired shape. Thus, it can be a thermoplastic, thermosetting polymer, a polymer comprising a thermoplastic portion and a thermosetting or crosslinked portion, or a mixture of these polymers. Any plastic polymer material conventionally used in the manufacture of composite materials and intended for the production of composite parts is suitable. Examples of thermosetting polymers are epoxy resins, phenolic resins, bismaleimide resins, cyanate ester resins, and mixtures of these resins. Suitable examples of thermoplastic polymers include: polyamides (PA: PA6, PA12, PA11, PA6,6, PA6,10, PA6,12, etc.), polyamides (PA: PA6, PA12, PA11, PA6,6, PA6,10, PA6,12, ...), copolyamides (CoPA), polyamide-ether or ester blocks (PEBAX, PEBA), polyphthalamides (PPA), polyesters (polyethylene terephthalate-PET, polybutylene terephthalate-PBT, ...), copolyesters (CoPE), thermoplastic polyurethanes (TPU), and polyacetals. (POM…), polyolefins (PP, HDPE, LDPE, LLDPE…), polyethersulfone (PES), polysulfone (PSU…), polyphenylene sulfone (PPSU…), polyolefins (PP, HDPE, LDPE, LLDPE), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyphenylene sulfide (PPS), polyetherimide (PEI), thermoplastic polyimide, liquid crystal polymer (LCP), phenoxy, block copolymers such as styrene-butadiene-methyl methacrylate (SBM), methyl methacrylate-butyl methacrylate (MAM) copolymers, and mixtures thereof. The composite material may also be in the form of a sheet comprising a partially crosslinked or partially crosslinkable thermoplastic polymer as the plastic polymer material, as described in application WO 2019 / 102136. According to some embodiments, the plastic polymer material of the composite material in sheet form consists of a thermoplastic polymer or a polymer comprising a thermoplastic portion or a mixture of such polymers.

[0103] "Separator" refers to a thin and flexible separating layer, or in other words, a flexible membrane. Conventional molding methods use an open mold, which is closed by using one diaphragm (single diaphragm method) or two stacked diaphragms (double diaphragm method), said one or more diaphragms capable of elastic deformation. The fact that the diaphragm can undergo elastic deformation is not exclusive; it does not exclude the possibility of plastic deformation. In the case of reusable diaphragms, the deformation is entirely elastic. In the case of disposable, single-use diaphragms, the deformation can be elastoplastic (partially elastic and partially plastic). Therefore, such diaphragms are not necessarily made of elastomeric materials, but can be made of elastomeric materials, as described in U.S. Patent 9,259,859 filed on behalf of Cytec. The diaphragm can be made, in particular, of rubber, nylon, or silicone. Table 1 lists some examples of diaphragms that can be used in the methods and apparatus of the present invention.

[0104] Table 1

[0105]

[0106] The percentages of elongation at break and tensile strength are measured in accordance with ASTM D882.

[0107] Typically, membranes with a thickness of 10 μm to 3000 μm, typically 50 μm to 100 μm, should be used.

[0108] The diaphragms used within the scope of this invention are described as being impermeable to gases because they provide a barrier to gases. In other words, they are non-porous and do not allow gases to pass through their thickness, which makes it possible to obtain a sealed chamber.

[0109] The device according to the invention is in Figure 3 A, Figure 3 B and Figure 9 As shown in the image. Figure 4 and Figure 5 An example of this device is shown in more detail.

[0110] Figure 3A illustrates an apparatus according to the invention after a starting composite material I has been placed in place and two diaphragms 1 and 2 have been positioned on a mold 20 to form two sealed chambers 3 and 4. The mold 20 defines a box or cavity and has a shaped surface at its bottom 21, which forms the shaped surface 22 of the composite material I. In contrast to the initial composite material I, the shaped surface 22 is non-planar and three-dimensional in shape, whereas the initial composite material is planar and typically described by those skilled in the art as two-dimensional, but with a certain thickness. In the example shown, this shaped surface 22 corresponds to a convex protrusion 23 extending into the middle of the bottom 21 of the mold 20. In the example shown, the mold is square in shape, and the protrusion 23 is symmetrical and has axes parallel to the two opposing peripheral walls 25 of the mold, as shown... Figure 4 As shown in Figure 10, this protrusion 23 is shown in perspective, but with a tapered cross-section. Other shapes can also be provided for the molding surface 22, such as U-shaped, C-shaped, L-shaped, or V-shaped shapes after the composite material has been formed. Other more complex shapes with several embossings can also be provided as the molding surface 22.

[0111] The cavity defined by mold 20 is closed by a first diaphragm 1, which extends above the mold and is fixed to the peripheral edge 26 of the mold, as shown. Figure 5 The diagram shown is a partial perspective view of the device according to the invention. The arrangement of the device allows for the creation of a sealed chamber, referred to as the first chamber 3, between the first diaphragm 1 and the mold 20. This seal is provided by any suitable means. Figure 4 and Figure 5 In the example shown, a washer 16 is provided between the peripheral edge 26 of the mold and the diaphragm 1, and the frame 11 is positioned on the diaphragm 1 to rest on the peripheral edge 26 of the mold and clamp the lower diaphragm 1. In the example shown, a clamping hook system 17a (including hooks 18a on the frame 11 and fasteners 19a on the outer surface of the peripheral wall 25 of the mold 20) is used to clamp and secure the diaphragm 1 to the mold 20. In the example shown, a groove 15 is provided on the peripheral edge 26 of the mold to allow insertion of the washer 16. In the embodiment shown, a stop is also provided along the peripheral edge 26 of the mold to facilitate positioning and alignment of the frame 11. Therefore, the thickness of the frame 11 will define the space between the two diaphragms and can be adjusted according to the thickness of the composite material I to be formed.

[0112] The first diaphragm 1 extends horizontally and is designed to support and hold the composite material I in place, the composite material being deposited on the upper surface 1a of the first diaphragm 1.

[0113] The second diaphragm 2 extends above the first diaphragm 1, with the composite material I located between the two diaphragms. Therefore, the first diaphragm 1 is referred to as the lower diaphragm, and the second diaphragm 2 as the upper diaphragm. In the example shown, the upper diaphragm 2 extends parallel to the lower diaphragm 1, although an offset extension from the horizontal plane can be expected, particularly for the upper diaphragm 2. The two diaphragms 1 and 2 are thus positioned one above the other and extend above the bottom 21 of the mold 20 (and specifically, above the molding surface 22).

[0114] In the same manner as the first diaphragm 1, the positioning device allows a sealed chamber to be created between the lower diaphragm 1 and the upper diaphragm 2. This chamber is referred to as the second chamber 4 or the interdiaphragm chamber. The seal is provided by any suitable means.

[0115] In the example shown, a washer 16 is provided between the upper side of frame 11 and upper diaphragm 2, and frame 12 is placed on upper diaphragm 2 to support frame 11 and clamp upper diaphragm 2. A clamping system 17b, including hooks 18b on frame 12 and fasteners 19b on the outer side of peripheral wall 25 of mold 20, is used to clamp upper diaphragm 2 and secure frame 12. In the example shown, a groove 15 is provided on the top surface of frame 11 to allow insertion of washer 16. Supports are also provided on frame 11 to allow frame 12 to be positioned and adjusted. Any other clamping system (such as bolt or strap clamps) can also be used instead of fasteners 17a and / or 17b. The frame holds the diaphragm on the mold.

[0116] In the example shown, frames 11 and 12, along with gasket 16 and clamping systems 17a and 17b, form positioning device 9 to form two sealed chambers 3 and 4.

[0117] The thickness of frame 11 defines the space between the two diaphragms and thus affects the initial volume V2 of the second chamber 4. The thickness of frame 11 can vary depending on the thickness of the composite material I to be formed and the final desired part size. For example, for parts with a maximum size of 50 cm, the thickness can be only a few centimeters or even less. For parts larger than 2 m, the thickness is increased to facilitate handling and prevent frame deformation (bending or warping under its own weight).

[0118] exist Figure 3In the example shown in A, which illustrates the apparatus at the start of the method (end of operation a3) before any pressure change in any chamber and thus after the assembly of the various components of the device, the lower diaphragm 1 is positioned at a distance from the top 27 of the protrusion 23, which may have already made contact. Similarly, the upper diaphragm 2 is positioned at a distance from the composite material I, which may also have already made contact. Advantageously, the maximum distance between the upper diaphragm 2 and the reinforcing material I, on the one hand, and the maximum distance between the lower diaphragm 1 and the highest part of the bottom 21 of the mold 20 (in the illustrated example, the top 27 of the protrusion 23), will preferably be at most 20 cm, and will preferably correspond to a distance of 0.5 cm to 15 cm.

[0119] The mold 20 is equipped with an outlet valve 32, which allows all or part of the air or gaseous medium III (also referred to as gas III) contained in the first chamber 3 formed by the mold 20 and the lower diaphragm 1 to be removed. Therefore, taking into account the flexibility and elasticity of the lower diaphragm 1, the valve 32 will allow the volume V1 of the first chamber 3 to be reduced, or even its pressure P1, when the minimum volume of the chamber has been reached.

[0120] Conversely, the diaphragm chamber 4 is equipped with an outlet valve 30 that allows the removal of all or part of the air or gaseous medium III contained therein, and also with an inlet valve 31 that allows the addition of air or another gaseous medium III into the diaphragm chamber 4. Therefore, taking into account the flexibility and elasticity of the two diaphragms 1 and 2, these valves will allow for the alteration of the volume V2 and / or its pressure P2 of the second diaphragm chamber 4. In particular, within the scope of the invention, it will be possible to increase the volume V2 at certain stages of the method in order to reduce the mechanical stress applied to the composite material I by controlling the contact area, particularly by compensating for the reduction in volume V1, and to provide additional deformation to the composite material I during intermediate molding stages.

[0121] The two diaphragms 1 and 2 are elastically deformable, or even plastically deformable, but impermeable to gas III, and the chambers formed when the valve is in the closed position are gas-proof, thus preventing gas from passing through the diaphragms or from being transferred due to leakage, especially during gas extraction or injection operations, and thus enabling full control of the volumes V1 and V2 of chambers 3 and 4 by means of the valve.

[0122] In the example shown, the channels for the valves 30 and 31 are arranged in a frame 11, which is positioned between the two diaphragms 1 and 2.

[0123] By comparison, Figure 1 and Figure 2The prior art single-diaphragm device and double-diaphragm device are shown respectively, and the same reference numerals are used for the same parts in the device as those in the present invention.

[0124] According to one embodiment of the device according to the invention, such as Figure 3 As shown in B, the first chamber 3 may also be equipped with an inlet valve 33, thereby allowing gaseous media to enter the chamber 3.

[0125] In the example shown, at the level of the first chamber 3, the outlet valve 32 and inlet valve 33 for gas III are positioned in the bottom 21 of the mold 20 and on both sides of the protrusion 23. However, their positioning is ineffective because balance is established in the first chamber 3. Therefore, they can be positioned on the same side of the protrusion 23. Similarly, one and / or the other can be positioned not on the bottom 21, but on the peripheral wall 25 of the mold 20.

[0126] The inlet and outlet valves allow for adjustment of the displacement of the first diaphragm 1 and the second diaphragm 2, thereby changing the volume and / or pressure of the first chamber 3 and the second chamber 4.

[0127] The first diaphragm 1 initially controls the positioning of composite material I and helps maintain its position during its gravitational displacement, influencing the progression of the molding operation. When the inter-diaphragm pressure P2 is sufficiently low, the first diaphragm 1 facilitates the compaction of composite material I after achieving the minimum volume V1 of the first chamber 3. The second diaphragm 2 helps guide and hold composite material I in place throughout the molding process and plays a role in molding and controlling its progress. When the inter-diaphragm pressure P2 is sufficiently low, the upper diaphragm 2 also facilitates the compaction of composite material I after achieving the volume V1 of the first chamber 3.

[0128] It should be noted that adding gas to the first chamber 1 and the second chamber 2, as well as removing gas from the first chamber and the second chamber, can cause changes in the volume or pressure of these chambers. These changes will affect the pressure, and thus the mechanical forces and stresses applied to the diaphragm and the composite material, and consequently the final properties of the resulting preformed composite material. It should be emphasized that if the volume of the spaces contained within the chamber is difficult to reduce (contact between deformable materials, contact between deformable and rigid materials, low elongation tensile response of the deformable material), the pressure within the chamber will decrease primarily relative to the volume. Conversely, if one or more compressible spaces exist beneath the diaphragm, or if the material has a weak tensile response or a large elongation potential, the volume of the chamber will develop primarily relative to the pressure.

[0129] In the device according to the invention, when the intake valve 31 in the second chamber 4 allows an increase in pressure P2, it enables the mechanical release of the fibers and / or sheets of the composite material I; when it allows a decrease in volume V2, it also enables certain degrees of freedom to be given to the composite material I and the diaphragms 1 and 2, and to adjust the contact interactions between the various components (and in particular, reduce friction).

[0130] When the gas outlet valve 30 from the second chamber 4 causes a decrease in pressure P2, this allows the composite material I to be mechanically constrained (according to conventional double diaphragm operation), and when this causes a decrease in volume V2, this facilitates the formation of composite material I.

[0131] At the level of the first chamber 3, the gas outlet valve 32 from the first chamber 3 has the main function of reducing the volume V1 of the first chamber 3, thereby allowing the molding process to continue until it is finally pressed onto the molding surface 22.

[0132] The gas inlet valve 33 in the first chamber 3 is mainly used to reduce pressure and release the lower diaphragm 1, thereby reducing friction, especially during cooling.

[0133] In comparison, Figure 9 An example of an apparatus according to the invention is shown, comprising an external circuit 34 for circulating gas III from a first chamber 3 to a second chamber 4. Specifically, this circuit connects the outlet valve 32 of the first chamber 3 to the inlet valve 31 of the second chamber 4. This has the advantage that gas discharged from the first chamber 3 is reinjected into the second chamber 4, thereby maintaining a substantially constant total volume of the two chambers during certain stages of the method (such as, as will be explained, the intermediate forming stage).

[0134] Typically, the valve is connected to a circuit equipped with a gaseous medium flow and a pressure regulator, and in particular an air pressure regulator (not shown), which allows the gaseous medium to be drawn in or injected, depending on the nature of the valve (outlet or inlet) in the relevant chamber. The circuit may therefore include a gas injection pump or gas pressure reducing pump connected to the relevant valve, or any other device suitable for injection or suction when the relevant valve is in the open position.

[0135] The apparatus according to the invention is suitable for forming (or preforming) composite materials into sheet form according to the method according to the invention.

[0136] The method according to the invention (and some alternative embodiments thereof) involves steps in Figures 6 to 8 (As shown in the diagram) First, it includes a positioning phase (a), which includes the following operations (steps (a1) and (a2) are not shown):

[0137] (a1) A mold 20 is provided, the non-planar bottom of which defines a molding surface 22 corresponding to the shape to be given to the composite material I to be preformed.

[0138] (a2) A first diaphragm (referred to as lower diaphragm 1) is provided above the bottom 21 of the mold and a second diaphragm (referred to as upper diaphragm 2) extending above the composite material I, the composite material I to be preformed is deposited on the first diaphragm, the two diaphragms 1 and 2 are elastically deformable and impermeable to gas III, and the composite material I is placed above the molding surface 22.

[0139] (a3) Position the two diaphragms 1 and 2 together with the mold 20 to form:

[0140] -A first sealed chamber 3 between the mold 20 and the lower diaphragm 1, the first chamber 3 defining a first modular volume V1, and

[0141] - A second sealed chamber 4 between the two diaphragms 1 and 2, the second chamber 4 defining a second modular volume V2 (referred to as the inter-diaphragm volume), in which the composite material I is housed.

[0142] Typically, in step (a2), the upper diaphragm 1 is first placed above the mold 20, then the composite material I is placed in the desired position relative to the molding surface 22 (particularly by using alignment marks), and finally the upper diaphragm 2 is positioned. Alternatively, depending on any suitable holding or clamping system, the two diaphragms 1 and 2 can be pre-arranged to form a second chamber 4 in which the composite material is positioned, and the assembly is placed on the mold 20 to form a first chamber 3, holding the entire assembly together. It is understood that the composite material I should have the desired dimensions before being placed on the first diaphragm 1, which may require pre-cutting.

[0143] At the end of stage (a3), a device in which the composite material is placed is obtained, such as Figure 3 A or Figure 3 As shown in B. In the example shown, after step (a3), there is no contact between the upper diaphragm 2 and the composite material I, nor between the lower diaphragm 1 and the molding surface 22. However, due to the initial positioning of the individual components and the size of the device, contact at any of these locations can occur from the beginning.

[0144] In the method according to the invention, in order to facilitate the gravitational descent of composite material I while avoiding its slippage on the lower diaphragm 1, especially during steps (a2) and (a3) ​​of the positioning phase, the lower diaphragm 1, or even both diaphragms 1 and 2, are horizontally positioned at the end of step (a3) ​​or even during steps (a2) and (a3).

[0145] Within the scope of this invention, as in the case of prior art methods (referred to as the double-diaphragm method), this positioning stage (a) is accomplished by the following operations:

[0146] (a4) The gas III contained in the second chamber 4 is discharged, thereby reducing the inter-diaphragm volume V2, so that both diaphragms 1 and 2 are in contact with the composite material I.

[0147] (a5) The lower diaphragm 1 on the molded surface 22 is partially aligned in at least one contact area 5, where the composite material I is also in contact with both the diaphragms 1 and 2.

[0148] This alignment can correspond to a single operation and can be achieved by discharging the gas contained in the first chamber 3, which results in a decrease in volume V1 and a drop in the upper diaphragm 2 and the lower diaphragm 1 carrying the reinforcing material therewith, assuming that operation (a4) has been performed according to... Figure 6 The sequential steps (a3) ​​to (a5) shown are performed beforehand. Furthermore, according to a preferred embodiment, operation (a5) is performed after operation (a4) by venting gas III into the first chamber 3, resulting in a reduction in volume V1 to establish pre-contact between the lower diaphragm 1 and the molding surface 22, while the volume V2 of the second chamber 4 remains constant. Gas venting from the second chamber 4 is accomplished by opening outlet valve 30, while gas venting from the first chamber 3 is accomplished by opening outlet valve 32. After the composite material I has been compressed between the two diaphragms, if the desired pressure level has not been reached when volume V1 decreases (if such reduction is necessary for local alignment), outlet valve 30 can be closed or kept open.

[0149] The lower diaphragm 1 can also be in contact with the molding surface 22 from the beginning. Initial alignment can be achieved at the end of operation (a3) ​​and maintained at the end of operation (a4). Alternatively, even after operation (a3), the diaphragm 1 may be in contact with the molding surface 22, and during operation (a4), the diaphragm may be slightly lifted from the molding surface, in which case a subsequent alignment step (a5) will be necessary.

[0150] Regardless of the implementation scheme, the alignment corresponds to a pre-contact between the lower diaphragms 1, which will abut against the highest portion of the molding surface 22. It is a partial contact rather than pressing against the entire molding surface, unlike what would be obtained at the end of an intermediate molding stage. If there are several protrusions on the molding surface 22, alignment is possible in several contact areas 5.

[0151] At the end of step (a5), when the external pressure Pext equals atmospheric pressure, the pressure P2 in the second chamber 4 is lower than the pressure P1 in the first chamber 3, and the pressure in the first chamber is itself lower than the external pressure Pext, and in particular atmospheric pressure.

[0152] Instead, operation (a4) involves reducing the volume V2 of the inter-diaphragm chamber, particularly to its minimum volume, to tightly hold the composite material between the two diaphragms 1 and 2. Thus, at the end of operation (a4) and consequently at the end of stage (a), the composite material I is compressed between the two diaphragms 1 and 2, having the maximum contact surface with the latter.

[0153] At the end of step (a), a contact is established between the lower diaphragm 1 and the highest portion 27 of the molding surface 22 at the contact area 5. However, at this contact area 5, as a result of step (a4), the assembly of the lower diaphragm 1 / composite material I / upper diaphragm 2 is positioned to contact the highest portion 27 of the molding surface 22.

[0154] Step (a4) may result in a more or less reduction in the pressure P2 in the inter-diaphragm chamber 4. At the end of step (a4) and at the end of step (a5), and thus at the end of positioning stage (a), composite material I is firmly held between the two diaphragms 1 and 2, thereby ensuring good positioning on the molding surface 22. However, at the end of step (a4) and at the end of step (a5), and thus at the end of positioning (a), it is preferable that the pressure P2 in the inter-diaphragm chamber 4 is moderate to avoid excessive stress on the composite material. In particular, if the external pressure is equal to atmospheric pressure, the pressure P2 is preferably between 600 mbar and 950 mbar. Such a pressure allows for the limitation of mechanical stress within composite material I, especially at the sandwich level where the composite material is the most common case of a stack of several reinforcing sheets. However, if the external pressure is equal to atmospheric pressure, a pressure P2 in the range of 2 mbar to 1000 mbar can also be provided.

[0155] At the end of positioning phase (a), the molding apparatus is thus constructed and the material is in place therein, and molding can then begin. The molding apparatus / composite material I assembly can be placed in the ambient atmosphere such that the external pressure of the apparatus (referred to as Pext) is equal to atmospheric pressure (or 1.013 bar). Alternatively, the molding apparatus / composite material I assembly can be placed in a variable pressure enclosure (such as an autoclave). The pressures given in the remainder of the specification are particularly suitable for cases where the molding apparatus / composite material I assembly is placed at atmospheric pressure, but these pressures can be readily modified by those skilled in the art based on external pressure if necessary.

[0156] Following the positioning stage (a), the method according to the invention includes an intermediate forming stage (b), during which at least the following operations are performed:

[0157] When the external pressure Pext equals atmospheric pressure, gas III is introduced into the second chamber 4, while the pressure P2 is maintained below the external pressure Pext (and especially atmospheric pressure). This locally maintains a certain distance between the upper diaphragm 2 and the lower diaphragm 1 and the composite material I, while maintaining the alignment and contact between the composite material I and the two diaphragms 1 and 2 in the contact area 5.

[0158] - The gas III contained in the first chamber 3 is discharged to press the lower diaphragm 1 onto the entire molding surface 22 present at the bottom 21 of the mold 20.

[0159] Within the scope of this invention, controlling the pressure and introducing gas into the second chamber 4 (which allows for an increase in the volume of the chamber 4) enables the composite material and the diaphragm to have a certain degree of freedom and allows for the mechanical release of the fibers or even sheets constituting the composite material. Therefore, compared to prior art dual-diaphragm methods, defects in the final material can be reduced.

[0160] However, by maintaining the first diaphragm 1 / composite material I / second diaphragm 2 in contact at least in the contact area 5, the positioning of the composite material and the desired shape can be controlled, as is the case with the double diaphragm in the prior art. Throughout the method, and particularly throughout the intermediate molding stage (b), at least in the contact area 5, the two diaphragms 1 and 2 are maintained in contact with the composite material I, wherein the diaphragm / composite material assembly rests on the molding surface 22. At the highest region of the molding surface, maintaining the alignment and contact between the composite material I and the two diaphragms 1 and 2 secures the material's positioning on the mold and on the molding surface and prevents displacement due to the weight of the composite material I.

[0161] Typically, when the external pressure Pext equals atmospheric pressure, one or more introductions and one or more extractions of gas III are performed in such a manner that the pressure P1 in the first chamber 3 and the pressure P2 in the second chamber 4 are controlled and / or modified, and the pressure P1 is kept lower than the pressure P2, which itself is lower than the external pressure Pext (and in particular atmospheric pressure).

[0162] When heating is used, it will affect the gas volume and / or gas pressure in the chambers, or even the volume occupied by the composite material. Typically, the final heating temperature will be gradually reached, and the volume of the first chamber or even the second chamber will be adjusted during this temperature rise until the desired final temperature is reached to avoid an increase in the volume of the relevant chamber. Furthermore, when the temperature rises to the desired heating temperature, the outlet valve 32 can be opened and gas can be extracted from the first chamber 3 to control the volume V1 and prevent its increase, thereby maintaining it substantially constant. Similarly, the outlet valve 30 can be opened and gas can be extracted from the diaphragm chamber 4 to control the volume V2 and prevent its increase, thereby maintaining it substantially constant.

[0163] When heating is applied, it affects the gas volume and / or gas pressure in the chambers, or even the volume occupied by the composite material. Typically, the final heating temperature is gradually reached, and the volume of the first chamber or even the second chamber is adjusted during this temperature rise until the desired final temperature is reached to avoid an increase in the volume of the relevant chamber. Furthermore, when the temperature rises to the desired heating temperature, the outlet valve 32 can be opened and gas can be extracted from the first chamber 3 to control the volume V1 and prevent its increase, thereby maintaining it substantially constant. Similarly, the outlet valve 30 can be opened and gas can be extracted from the diaphragm chamber 4 to control the volume V2 and prevent its increase, thereby maintaining it substantially constant.

[0164] according to Figure 6 In one embodiment of the invention shown, gas III is introduced into the second chamber 4 to locally maintain the upper diaphragm 2 and the lower diaphragm 1 at a certain distance, while gas III contained in the first chamber 3 is discharged, pressing the lower diaphragm 1 against the bottom of the mold 21, which can be done simultaneously. In this case, an intermediate molding stage is performed by discharging gas III contained in the first chamber 3 to press the lower diaphragm 1 against the molding surface 22 located at the bottom 21 of the mold. Simultaneously, when the external pressure Pext equals atmospheric pressure, gas III is introduced into the second chamber 4, and the pressure P2 in the second chamber 4 is maintained below the external pressure Pext (and particularly atmospheric pressure), thus increasing the inter-diaphragm volume V2 and locally maintaining the upper diaphragm 2 and the lower diaphragm 1 and composite material I at a certain distance, while maintaining the alignment and contact between composite material I and both diaphragms 1 and 2 in the contact area 5. In fact, under the action of gravity, composite material I deforms according to its bending properties and according to the geometry and surface of the contact area 5. As a result, separation occurs between the upper diaphragm 2 and the composite material I, with the end of the composite material I moving away from the upper diaphragm 2, such as... Figure 6As shown. By simultaneously keeping the inlet valve 31 at the diaphragm chamber 4 and the outlet valve 32 at the first chamber 3 open, a certain degree of freedom can be allowed for the composite material I during the final molding and compaction steps, before it is placed on the lower diaphragm 1 and thus on the molding surface. Furthermore, after stage (b) has begun, the pressure P2 will, in most cases, remain substantially constant during this pre-forming stage (b) to prevent displacement of the upper diaphragm 2.

[0165] Typically, in the method according to the invention, those skilled in the art will vary the gas injection or suction flow rate in the chamber according to various parameters (in particular the selected valve, the diameter of the pipe in the gas circulation loop, the size of the mold, any pressure drop in the loop, etc.).

[0166] During and therefore at the end of the preforming stage (b), the pressure P1 in the first chamber 3 is lower than the pressure P2 in the second chamber 4. At the end of the preforming stage (b), the preforming pressure P1(b) is typically in the range of 2 mbar to 50 mbar.

[0167] In this embodiment, the decrease in the volume V1 of the first chamber 3 can be equal to or approximately equal to the increase in the volume V2 of the second chamber 4. For example... Figure 6 As shown, it is also possible that the increase in volume V2 of the second chamber 4 is lower (especially 5% to 10% lower) compared to the decrease in volume V1 of the first chamber 3, which would result in more or less noticeable movement of the upper diaphragm 2 toward the bottom of the mold, but the upper diaphragm maintains a certain distance from certain areas of the molding surface.

[0168] according to Figure 7 The second alternative embodiment shown includes, or even only includes, the following sequential operations in the intermediate molding stage (b):

[0169] (b1) Gas III contained in the first chamber 3 is discharged, causing the volume V1 to decrease and the lower diaphragm 1 to descend to the middle position. At the same time, when the external pressure Pext equals atmospheric pressure, gas III is introduced into the second chamber 4 and the pressure P2 in the second chamber 4 is maintained below the external pressure Pext (and especially atmospheric pressure), thereby increasing the inter-diaphragm volume V2 and locally maintaining a certain distance between the upper diaphragm 2 and the lower diaphragm 1 and composite material I. Meanwhile, in the contact area 5, the composite material I is maintained in alignment and contact with both diaphragms 1 and 2.

[0170] (b2) The gas III contained in the first chamber 3 is discharged, thereby pressing the lower diaphragm 1 onto the entire molding surface 22 present at the bottom 21 of the mold 20, while keeping the inter-diaphragm volume V2 constant.

[0171] Here again, in step (b1), the decrease in the volume V1 of the first chamber 3 can be equal to or approximately equal to the increase in the volume V2 of the second chamber 4, such as... Figure 7 As shown. It is also possible that the increase in volume V2 of the second chamber 4 may be lower (especially 5% to 10% lower) compared to the decrease in volume V1 of the first chamber 3, which would result in more or less noticeable movement of the upper diaphragm 2 toward the bottom of the mold, but the upper diaphragm would maintain a certain distance from certain areas of the molding surface. The displacement of the upper diaphragm 2 will also depend on the pressure balance between chambers 3 and 4. Step (b1) is performed by simultaneously keeping the inlet valve 31 at the level of the diaphragm chamber 4 and the outlet valve 32 at the level of the first chamber 3 open, and in step (b2), the inlet valve 31 is closed while the outlet valve remains open to obtain the pressing of the lower diaphragm 1 on the molding surface.

[0172] Therefore, in Figure 7 In the method shown, the upper diaphragm 2 moves in accordance with the movement of the lower diaphragm 1 (which has moved forward from step (a5) to step (b1)). In this case, the upper diaphragm 2 deforms and becomes increasingly tight during the progress of step (b), and particularly step (b2), which leads to a change in the pressure P2 of the second chamber 4. Advantageously, the volume V2 remains substantially constant or even constant throughout stage (b).

[0173] During step (b1), the pressure in the chamber depends particularly on the mechanical properties of the diaphragm. In step (b2), when the lower diaphragm 1 contacts the molding surface 22, the pressure P1 in the first chamber 3 can be between 2 mbar and 50 mbar. In step (c), when the upper diaphragm 2 contacts the composite material I, which is itself pressed against the lower diaphragm 1 and the molding surface 22, the pressure P2 in the second chamber 4 can be between 2 mbar and 50 mbar.

[0174] according to Figure 8 The third alternative embodiment shown includes, or even only includes, the following sequential operations in the intermediate molding stage (b):

[0175] (b'1) Gas III contained in the first chamber 3 is discharged, causing the first volume V1 to decrease and the lower diaphragm 1 to descend to the middle position. Simultaneously, when the external pressure Pext equals atmospheric pressure, gas III is introduced into the second chamber 4, and the pressure P2 in the second chamber 4 is maintained below the external pressure Pext (and particularly atmospheric pressure), thus increasing the inter-diaphragm volume V2. This also locally maintains a certain distance between the upper diaphragm 2 and the lower diaphragm 1 and composite material I, while maintaining alignment and contact between composite material I and both diaphragms 1 and 2 in the contact area 5.

[0176] (b'2) The gas III contained in the second chamber 4 is discharged, thereby reducing the inter-diaphragm volume V2, and causing the upper diaphragm 2 to descend and both diaphragms 1 and 2 to be positioned in contact with the composite material I.

[0177] (b'3) The gas III contained in the first chamber 3 is discharged, thereby pressing the lower diaphragm 1 onto the entire molding surface 22 present at the bottom 21 of the mold 20. At the same time, when the external pressure Pext is equal to the atmospheric pressure, the gas III is introduced into the second chamber 4 and the pressure P2 in the second chamber 4 is maintained below the external pressure Pext (and especially the atmospheric pressure), thereby increasing the inter-diaphragm volume V2 and locally maintaining a certain distance between the upper diaphragm 2 and the lower diaphragm 1, while maintaining the alignment and contact between the composite material I and the diaphragms 1 and 2 in the contact area 5.

[0178] Again, in operation (b'1) and / or operation (b'3), the reduction in volume V1 in the first chamber 3 can be equal to or substantially equal to the reduction in volume V2 in the second chamber 4, such as... Figure 8 As shown. It is also possible that the reduction in volume V2 of the second chamber 4 may be less than the reduction in volume V1 of the first chamber 3 (especially 5% to 10%), which would result in more or less noticeable movement of the upper diaphragm 2 toward the bottom of the mold, but the upper diaphragm would maintain a certain distance from certain areas of the molding surface. The displacement of the upper diaphragm 2 will also depend on the pressure balance between chambers 3 and 4. Step (b'1) is performed by simultaneously keeping the inlet valve 31 at the level of the diaphragm chamber 4 and the outlet valve 32 at the level of the first chamber 3 in the open position. Then, in step (b'2), both valves are closed and the outlet valve 30 at the level of the second chamber 4 is opened, thereby allowing the upper diaphragm 2 to descend onto the composite material I. In step (b'3), the outlet valve 30 is closed and valves 31 and 32 are opened again, as in step (b'1).

[0179] As in Figure 8 As can be seen in the diagram, the upper diaphragm 2 does not move between steps (b'2) and (b'3), but then moves downward in step (b'3) and may move upstream in the repetition of steps (b'1) and (b'2) until the final compression of the composite material in step (c).

[0180] Steps (b'1) to (b'2) can be repeated, for example, one to ten times, and thereby gradually cause the descent of the lower diaphragm 1, and then cause the descent of the upper diaphragm 2 until the lower diaphragm 1 is pressed against the molding surface 22. According to the third alternative embodiment, the intermediate molding stage (b) can consist only of the repetition of operations (b'1) to (b'2), followed by the final operation (b'3). The number of repetitions will depend on the reduction of the volume V1 obtained at the end of each step (b'1). During step (b'1), the first diaphragm 1 gradually descends, except for the part on the molding area at the contact zone(s) 5 which gradually extends. Step (b'2) requires the upper diaphragm 2 and the composite material I to follow the movement of the lower diaphragm 1, although the descent of the lower diaphragm 1 in step (b'1) is usually accompanied by the descent of the reinforcing material, as Figure 8 shown.

[0181] In particular in Figure 8 this third alternative embodiment shown, generally, during step (b'1), P1 < P2 < P 大气 , where in particular, 50 mbar < P1 < 950 mbar and 50 mbar < P2 < P 大气 , and during step (b'2), 50 mbar < P1 < 950 mbar and 50 mbar < P2 < 950 mbar. In step (b'3), the pressure in the chamber can be such that 2 mbar < P1 < 50 mbar and 50 mbar < P2 < 950 mbar.

[0182] Generally, in the method according to the invention, the two diaphragms only move downwards throughout the method. However, it is not excluded that the upper diaphragm 2 may rise slightly, especially when gas is added to the inter-diaphragm space.

[0183] Similarly, in the method according to the invention, in the contact zone 5, the contact 6 between the lower diaphragm 1 and the molding zone 22 is maintained, the contact 7 between the lower diaphragm 1 and the composite material I is maintained, and the contact 8 between the composite material I and the upper diaphragm 2 is maintained. As the method progresses, this contact area between the respective elements expands until the lower diaphragm 1 / composite material I / upper diaphragm 2 assembly is fully pressed against the entire molding area 22 (or even more).

[0184] At the end of the intermediate molding stage (b), regardless of the alternative embodiment, the pressure P1 in the first chamber 3 will advantageously be in the range of 2 mbar to 50 mbar, typically 2 mbar to 5 mbar.

[0185] The method according to the invention, regardless of the intermediate molding stage (b) used, comprises the following steps:

[0186] - Final molding and compaction stage (c), which produces the desired final shape of the preformed composite material II, during which heating is applied and gas III contained in the second chamber 4 is removed to press both composite material I and the upper diaphragm 2 onto the lower diaphragm 1, which itself is pressed against the bottom of the mold 21, particularly against the molding surface 22, and to achieve a reduction in pressure P2 to ensure compaction.

[0187] - Cooling and demolding stage of preformed composite material II (d).

[0188] At stage (c), outlet valve 30 is opened to expel gas III contained in diaphragm chamber 4, thereby achieving the minimum volume V2. After this volume is achieved, pressure P2 also decreases. During final molding and compaction, the pressure P2 in diaphragm chamber 4 is typically in the range of 2 mbar to 50 mbar, with a typical range of 2 mbar to 5 mbar. Once this pressure has been reached, outlet valve 30 can be closed. Typically, suction is maintained to ensure operational safety.

[0189] As a function of the dimensions of the molding surface 22 and the intermediate material I, when pressure is obtained in step (c), the lower diaphragm 1 / composite material I / upper diaphragm 2 assembly may cover only the molding surface 22 or a portion thereof, such as Figure 6 and Figure 7 As shown in the final step, the flat portion of the bottom of the mold or even the entire bottom 21 of the mold 20 can be covered, which reduces the risk of diaphragm rupture.

[0190] During step (c), the outlet valve 32 of the first chamber 3 may be closed or remain open. During final molding and compaction, the pressure P1 in the first chamber 3 is typically in the range of 2 mbar to 50 mbar, typically 5 mbar.

[0191] To achieve part consolidation, in stage (c) where the composite material is kept compressed between two diaphragms to achieve the desired final shape, the time required to maintain heating under reduced pressure depends particularly on the thickness of the composite material and the properties of the polymer thermoplastic. Typically, stage (c) will last from 2 minutes to 5 hours. Afterward, cooling can be performed before demolding to freeze the shape obtained in stage (c). For this purpose, simply turn off the heating and allow it to naturally return to room temperature.

[0192] Regardless of the method according to the invention (and particularly the intermediate molding stage implemented), during the cooling stage, methods such as... Figure 3The device shown in B increases the pressure in the first chamber 3 by opening the inlet valve 33 at the level of the first chamber 3. This increase in pressure (especially values ​​in the range of 850 mbar at atmospheric pressure) reduces the friction between the lower diaphragm 1 and the mold 20, thereby promoting sliding between the diaphragm / composite assembly and the mold, and further reducing the risk of defects. This sliding occurs due to the difference in thermal expansion between the mold and the diaphragm / composite assembly.

[0193] After cooling and freezing to obtain the desired shape, and once the apparatus has been restored to external pressure (specifically atmospheric pressure), the pre-formed composite material II can be removed from the mold. If the properties of the diaphragm permit, the apparatus can be reused.

[0194] The external pressure Pext can be varied. If the external pressure Pext changes during the process, particularly if the apparatus is placed in an autoclave, the increase in external pressure Pext can be achieved before the implementation of stage (b) and / or stage (c). On the other hand, typically, the external pressure Pext remains constant throughout stage (b) and throughout stage (c), even if the external pressure is increased before either of these stages. For example, if the apparatus is placed in an autoclave, the external pressure Pext can be increased to a value in the range of 1 bar to 20 bar and maintained at that value during stages (b) and (c) or even during the cooling stage. The pressures P1 and P2 given above will, for example, be changed accordingly.

[0195] Based on the foregoing description, the methods and apparatus according to the invention offer great flexibility. They allow for both control and positioning of the composite material I to be molded throughout the method, resulting in molding to the desired shape without displacement. Conversely, the possibility of increasing the volume of the interdiaphragm chamber 4 during the descent of the lower diaphragm 1, during one or more preforming (b) stages, allows for a degree of freedom to be given to the fibers of the composite material or even the laminations of the composite material (if the composite material is in a laminated form), and can avoid lamination or other defects caused by excessive mechanical stress applied to the composite material I during molding. Therefore, the invention provides many possible optimization paths by adjusting these parameters.

[0196] Furthermore, considering the reliability of the placement of composite material I, the implementation of the method and apparatus according to the invention can be fully automated by using two diaphragms 1 and 2 and controlling various parameters of a fully computerized method. Typically, the molding cycle using the method according to the invention is on the order of 5 to 15 minutes without heating, and can reach 1 to 12 hours when heating is used. When using prepreg of composite material I, the method according to the invention can produce a final part. When the composite material is considered "dry," the method according to the invention will produce a preform by implementing a direct method well known to those skilled in the art, which will then be bonded to a polymer matrix to obtain the desired final part.

[0197] The following examples illustrate the invention, but are by no means limiting.

[0198] Example

[0199] In this embodiment, composite material stacks were used, each stack consisting of a unidirectional mesh of IMA 12K carbon fiber sold by Hexcel, and bonded to each side with Protechnic's 4g / m 2 Copolyamide 1R8 fiber web bonding. According to application WO 2010 / 046609, a polymer yarn is combined with a unidirectional carbon web.

[0200] Comparative tests 1a, 1b, and 1c, as well as Examples 1 and 2, were conducted using 16 stacked sheets of this material, joined together automatically via AFP without heating to form a stack I in the form of a plate with dimensions of 750 mm * 450 mm * 3.1 mm. Based on the weight of the stack, the final weight percentage of plastic (copolyamide) in stack I was 3.6%.

[0201] In all cases, regardless of whether one or multiple diaphragms are used, they are all 75μm thick Ipplon DP1000 nylon diaphragms distributed by Airtech in the UK.

[0202] The temperature used for intermediate and final molding and compaction operations is 170°C, and the demolding temperature is 25°C. The temperature is increased to 170°C at a rate of 1.5°C / min and takes 6 hours.

[0203] The mold 20 used is in the form of a box with dimensions of 2000mm * 1000mm * 320mm. At the bottom 21 of the mold, extending parallel to its long side, there is a protrusion 23 corresponding to the molding surface 22. The shape and size of this protrusion are shown in Figure 10. A seal between the mold 20 and the diaphragm, and a seal between the two diaphragms 1 and 2 for forming a closed inter-diaphragm space (referred to as the second chamber 4) when using two diaphragms 1 and 2, are ensured by using two washers 16 and by the superposition of the frames 11 and 12 with clamping systems 17a and 17b. Figure 4 and Figure 5 As shown. When using a single diaphragm, only one sealing gasket 16 is used, which extends along the peripheral edge 26 of the mold 20 and is positioned between the edge of the mold and the diaphragm. Then, the equivalent of... Figure 5 The frame of frame 11 is positioned and tightened onto the diaphragm.

[0204] In the comparative embodiment and according to the present invention, the molding apparatus is placed in the ambient atmosphere such that the pressure outside the molding apparatus is equal to the atmospheric pressure, i.e., 1.013 bar or 1013 hPa.

[0205] Surface analysis was performed using a 3D scanner based on Créaform technology to determine the presence or absence of defects.

[0206] Comparative Example 1a

[0207] Using previous simple diaphragm technology and therefore using, for example Figure 1 The apparatus described herein is used to perform this comparative embodiment. The stack is positioned directly on top of a protrusion present at the bottom of the mold. It is positioned symmetrically relative to the protrusion such that the top of the protrusion forming a line is parallel to its two large sides and extends between them. However, it is difficult to maintain the balance of the stack. A diaphragm is then positioned above the top to hold the stack against the top of the protrusion.

[0208] The temperature is then raised to 170°C, and the air trapped between the mold and the diaphragm is expelled. Compaction is performed by maintaining a pressure of 5 mbar and a temperature of 170°C for 30 minutes. Heating is then stopped, and the resulting molded stack is removed from the mold after the temperature has returned to room temperature.

[0209] The analysis yielded a preform corresponding to 284750 mm. 2 The total surface area (i.e., the inner and outer sides) is shown, and it is completely free of defects.

[0210] Comparative Example 1b

[0211] This comparative embodiment uses a double diaphragm with prior art and therefore employs... Figure 2The apparatus described herein is used. In contrast to Comparative Embodiment 1a, the lower diaphragm 1 is then positioned above the mold 20 to close it and form the first chamber 3. It is placed 2 cm from the top of the protrusion at the bottom of the mold. The stack I is positioned directly on the lower diaphragm 1 above the top of the protrusion, such that the lower diaphragm 1 contacts the top of the protrusion present at the bottom of the mold. It is positioned symmetrically relative to the protrusion 23, such that the top of the protrusion forming a line is parallel to its two large sides and extends between them. It is held in place by the lower diaphragm 1. The upper diaphragm 2 is then positioned above it to capture the stack I between the two diaphragms forming the second chamber 4, with a 40 mm space between diaphragms 1 and 2. Then, using… Figure 4 and Figure 5 The clamping systems 17a and 17b shown lock the entire device in place. The method then continues as follows: heating to a temperature of 170°C is maintained until the compaction step is completed, and air contained in the diaphragm chamber 4 is vented by means of an outlet valve 30 connected to the diaphragm chamber space until a pressure of 5 mbar is obtained in the diaphragm chamber 4: the stacked position is thus secured and disengaged from the protrusion 23. The valve 30 then remains open to maintain pressure regulation.

[0212] With the aid of a suction rate of 7.5 m / s connected to the first chamber 3, 3 The outlet valve 32 discharges the air contained between the mold and the lower diaphragm 1 until a pressure of 5 mbar is achieved. Thus, the diaphragm / stack assembly conforms to the shape of the protrusion 23. A final molding and compaction stage is then performed, while maintaining this 5 mbar pressure and a temperature of 170°C for 30 minutes. Afterward, heating is stopped, and the formed stack II is removed from the mold after the temperature has returned to room temperature.

[0213] During the various stages of the method, the volumes and pressures in the two chambers 3 and 4 are summarized in Table 2 below.

[0214] Table 2

[0215]

[0216] In the table of embodiments, P 大气 =Atmospheric pressure, V 模具 = The air volume in the space between the lower diaphragm and the mold at the start of the method, Vx = the feed volume associated with the first chamber (located between the mold and the lower diaphragm), v1 min = Minimum value of volume V1, V2 min = Minimum value of volume V2.

[0217] The obtained preforms corresponding to 285943 mm were analyzed. 2The total surface area (i.e., outer surface 101 and inner surface 102) of the preform II is shown to be 32812 mm. 2 Defects on both the inner and outer surfaces of the surface area (i.e., 11.5% of the surface area). Figure 11 shows the sheet 200 present on the outer surface 102 of preform II.

[0218] Comparative Example 1c

[0219] This comparative embodiment is equivalent to Comparative Embodiment 1b, except that: firstly, air is expelled into the inter-diaphragm space to achieve a pressure of 850 mbar instead of 5 mbar. Therefore, this modification conforms to the recommendations of U.S. Patent 9,259,859 and is designed to limit the compaction of the stack during intermediate forming, thereby promoting the sliding of the sheets relative to each other.

[0220] During the various stages of the method, the volumes and pressures in the two chambers 3 and 4 are summarized in Table 3 below.

[0221] Table 3

[0222]

[0223] In this case, the total surface area of ​​the preform analyzed is 284247 mm². 2 And the defect accounts for 14178mm. 2 Area (or 5% of the total surface area).

[0224] Example 1

[0225] Example 1 is based on Figure 6 The method shown is used.

[0226] After positioning diaphragms 1 and 2 and stack I, as in Comparative Example 1b, air is expelled into the diaphragm space (second chamber 4) to reach a pressure of 850 mbar by opening outlet valve 30 and closing inlet valve 31, as in Comparative Example 1c. Then, outlet valve 30 is closed. Next, partial alignment of the diaphragm 1 and 2 / stack I assembly is performed on the top 27 of protrusion 23 by expelling the air contained in the first chamber 3 formed by mold 20 and lower diaphragm 1 (for less than 10 seconds). This suction is achieved by opening outlet valve 32. Suction continues until lower diaphragm 1 is pressed against the bottom of protrusion 23 and mold 21, while the total volume of chambers 3 and 4 remains substantially constant (injection time 5 minutes, injection flow rate 7.5 m³ / s) due to air being injected into the second diaphragm chamber 4 by inlet valve 31. 3 / h. After the minimum volume of the first chamber 3 is reached, the pressure in the first chamber 3 is equal to 5 mbar. The outlet valve 32 is closed, and the inlet valve 31 is also closed. Then, by means of the outlet valve 30, the air contained in the second diaphragm chamber 4 is vented until the minimum volume of this chamber is reached and a pressure of 5 mbar is obtained therein. Therefore, the final molding and compaction stage is carried out in both the first chamber 3 and the second chamber 4 at a pressure of 5 mbar. Its duration is 30 minutes.

[0227] Cooling and demolding were performed in the same manner as in Comparative Example 1a.

[0228] During the various stages of the method, the volumes and pressures in the two chambers 3 and 4 are summarized in Table 4 below.

[0229] Table 4

[0230]

[0231] The analysis of the obtained preform corresponding to 284750 mm 2 The total surface area (i.e., the outer and inner sides) was measured, revealing that there were no defects at all.

[0232] Example 2

[0233] Example 2 is based on Figure 7 The method shown is used.

[0234] The method is the same as in Example 1, until diaphragms 1 and 2 / stack I are positioned on the top 27 of protrusion 23. Then, air is continuously vented from the first chamber 3 formed by mold 20 and lower diaphragm 1 until an intermediate pressure and volume of 850 mbar are achieved in the first chamber 3, while air is injected into the second diaphragm chamber 4 through inlet valve 31 to compensate for the decrease in volume of the first chamber 3 by increasing the volume of the second chamber 4. Thus, pressure P2 is maintained at a substantially constant value of 850 mbar, and the two diaphragms are kept approximately 15 cm apart in their furthest regions. Inlet valve 31 is then closed, and air continues to be vented through outlet valve 32 until lower diaphragm 1 is pressed against both the bottom of mold 21 and protrusion 23. After reaching the minimum volume of the first chamber 3, the pressure in the first chamber 3 is equal to 5 mbar. Outlet valve 32 is then closed. The air contained in the second diaphragm chamber 4 is then vented through the outlet valve 30 until the minimum volume of the chamber is reached and a pressure of 5 mbar is obtained in the subsequent chamber. Therefore, as in Example 1, the final molding and compaction operation is performed at a pressure of 5 mbar in both the first chamber 3 and the second chamber 4.

[0235] Cooling and demolding were performed as in Comparative Example 1a.

[0236] During the various stages of the method, the volumes and pressures in the two chambers 3 and 4 are summarized in Table 5 below.

[0237] Table 5

[0238]

[0239] In the table of the embodiment, ΔVx = propulsion volume associated with the second chamber 4 (diaphragm space).

[0240] The analysis yielded a preform corresponding to 284750 mm. 2 The total surface area (i.e., the outer and inner sides) was measured, revealing that there were no defects at all.

[0241] Example 3

[0242] Example 3 was performed using the same method and under the same conditions as Example 2, but on a different stack. Instead of a stack of 16 layers, the stack consisted of 96 layers, resulting in a 20mm thick plate.

[0243] Again, there are no defects in the preforms produced as a result.

[0244] Example 4

[0245] Example 4 was performed using the same stacking as in Examples 1 and 2, but with displacement of the stack relative to the tops of protrusions of a different shape. The tops of the protrusions form a 90° angle. In this case, a 300mm x 180mm plate was positioned such that the tops of the protrusions forming a line divided the plate into two parallel strips: one 120mm wide and the other 60mm wide. Implementation of the simple diaphragm method of the prior art resulted in a displaced preform, where the stack had moved 47mm from its initial position, but without defects. Using the double diaphragm method according to Comparative Examples 1b or 1c allows for proper positioning and thus avoids displacement. However, this method results in defects.

[0246] The implementation of the method described in Example 2 results in the absence of both displacement and defects.

Claims

1. A method for preforming a composite material (I) into a plate form, said composite material (I) comprising reinforcing fibers bonded together, said method comprising the following sequential stages: (a) The stage of positioning the composite material (I) within the molding apparatus, the stage comprising the following operations: (a1) A mold (20) is provided, the non-planar bottom of which defines a molding surface (22) corresponding to the shape to be given to the composite material (I) to be preformed. (a2) A first diaphragm, referred to as the lower diaphragm (1), and a second diaphragm, referred to as the upper diaphragm (2), extending above the composite material (I), are positioned above the bottom (21) of the mold. The composite material (I) to be preformed is deposited on the first diaphragm. The two diaphragms (1 and 2) are elastically deformable and impermeable to gas (III), and the composite material (I) is placed above the molding surface (22). (a3) Position the two diaphragms (1 and 2) together with the mold (20) to form: - A first sealed chamber (3) between the mold (20) and the lower diaphragm (1), the first sealed chamber (3) defining a first variable volume (V1), and - A second sealed chamber (4) between the two diaphragms (1 and 2), the second sealed chamber (4) defining a second variable volume (V2) referred to as the interdiaphragm volume, in which the composite material (I) is contained. (a4) The gas (III) from the second sealed chamber (4) is discharged, thereby reducing the inter-diaphragm volume (V2) so that both diaphragms (1 and 2) are in contact with the composite material (I). (a5) The lower diaphragm (1) on the molded surface (22) is partially aligned in at least one contact area (5), wherein the composite material is also in contact with the two diaphragms at the contact area (5). The positioning stage (a) results in the composite material (I) being placed within the resulting molding apparatus, which itself is placed under an external pressure Pext equal to atmospheric pressure. The placement of the composite material within the molding apparatus corresponds to the composite material being held by two diaphragms, both in contact with the composite material, wherein in at least one contact area, the lower diaphragm is partially aligned on the molding surface. (b) The intermediate forming stage includes at least the following operations: - When the external pressure Pext equals atmospheric pressure, gas (III) is introduced into the second sealed chamber (4), while the pressure P2 in the second sealed chamber (4) is maintained below the external pressure Pext, thereby locally maintaining a certain distance between the upper diaphragm (2) and the lower diaphragm (1) and the composite material (I), and simultaneously maintaining alignment and contact between the composite material (I) and the two diaphragms (1 and 2) at the contact area (5). - Expel the gas (III) contained in the first sealed chamber (3) to press the lower diaphragm (1) onto the entire molding surface (22) present at the bottom (21) of the mold (20). (c) The final molding and compaction stage, which produces the desired final shape of the preformed composite material (II), during which heating is applied and the gas (III) contained in the second sealed chamber (4) is removed to press both the composite material (I) and the upper diaphragm (2) onto the lower diaphragm (1), which itself is pressed onto the bottom (21) of the mold, and to achieve a reduction in the pressure P2 in the second sealed chamber (4) to ensure compaction. (d) Cooling and demolding stages of the preformed composite material (II).

2. The method according to claim 1, characterized in that, The composite material (I) comprises reinforcing fibers bonded together by a plastic polymer material.

3. The method according to claim 1, characterized in that, When the external pressure Pext is equal to atmospheric pressure, gas (III) is introduced into the second sealed chamber (4), while the pressure P2 in the second sealed chamber (4) is maintained below atmospheric pressure.

4. The method according to claim 1, characterized in that, The lower diaphragm (1) itself is pressed onto the molded surface (22).

5. The method according to any one of claims 1 to 4, characterized in that, Throughout the method, the two diaphragms (1 and 2) are maintained in contact with the composite material (I) at least in the contact area (5), wherein the diaphragm / composite material assembly rests on the molding surface (22).

6. The method according to any one of claims 1 to 5, characterized in that, After operation (a4), operation (a5) is performed by venting gas (III) into the first sealed chamber (3), resulting in a reduction in its volume (V1) to establish pre-contact between the lower diaphragm (1) and the shaped surface (22), while the volume (V2) of the second sealed chamber (4) remains constant.

7. The method according to any one of claims 1 to 6, characterized in that, Throughout the intermediate forming stage, when the external pressure Pext is equal to atmospheric pressure, one or more introductions and one or more extractions of gas (III) are performed in such a manner that the pressure P1 in the first sealed chamber (3) and the pressure P2 in the second sealed chamber (4) are controlled and / or modified such that the pressure P1 is kept lower than the pressure P2, which is itself lower than the external pressure Pext.

8. The method according to any one of claims 1 to 6, characterized in that, Throughout the intermediate forming stage, when the external pressure Pext is equal to atmospheric pressure, one or more introductions and one or more extractions of gas (III) are performed in such a manner that the pressure P1 in the first sealed chamber (3) and the pressure P2 in the second sealed chamber (4) are controlled and / or modified such that the pressure P1 is kept lower than the pressure P2, which itself is lower than atmospheric pressure.

9. The method according to claim 2, characterized in that, Throughout the intermediate molding stage (b), the composite material (I) is heated to soften the plastic polymer material.

10. The method according to claim 9, characterized in that, The method includes a heating step, which provides heating to the composite material (I) throughout the intermediate molding stage to soften the plastic polymer material, and is characterized in that the volumes (V1 and V2) of the first sealed chamber (3) and the second sealed chamber (4) are controlled during the heating step to prevent them from increasing.

11. The method according to any one of claims 1 to 10, characterized in that, The intermediate molding stage (b) is performed by: venting the gas (III) contained in the first sealed chamber (3) to press the lower diaphragm (1) onto the entire molding surface (22) present at the bottom (21) of the mold (20), while introducing the gas (III) into the second sealed chamber (4) when the external pressure Pext is equal to atmospheric pressure and maintaining the pressure P2 in the second sealed chamber (4) below the external pressure Pext, thereby increasing the inter-diaphragm volume (V2) and locally maintaining a certain distance between the upper diaphragm (2) and the lower diaphragm (1), while maintaining alignment and contact between the composite material (I) and the two diaphragms (1 and 2) at the contact area (5).

12. The method according to any one of claims 1 to 10, characterized in that, The intermediate molding stage (b) is performed by: venting the gas (III) contained in the first sealed chamber (3) to press the lower diaphragm (1) onto the entire molding surface (22) present at the bottom (21) of the mold (20), while introducing the gas (III) into the second sealed chamber (4) when the external pressure Pext is equal to atmospheric pressure and maintaining the pressure P2 in the second sealed chamber (4) below atmospheric pressure, thereby increasing the inter-diaphragm volume (V2), and locally maintaining a certain distance between the upper diaphragm (2) and the lower diaphragm (1), while maintaining alignment and contact between the composite material (I) and the two diaphragms (1 and 2) at the contact area (5).

13. The method according to claim 11 or 12, characterized in that, The decrease in the volume (V1) of the first sealed chamber (3) is substantially equal to the increase in the volume (V2) of the second sealed chamber (4).

14. The method according to any one of claims 1 to 10, characterized in that, The intermediate forming step (b) includes the following sequential steps: (b1) The gas (III) contained in the first sealed chamber (3) is discharged, causing the volume (V1) to decrease, so that the lower diaphragm (1) drops to the middle position. At the same time, when the external pressure Pext is equal to the atmospheric pressure, the gas (III) is introduced into the second sealed chamber (4) and the pressure P2 in the second sealed chamber (4) is maintained below the external pressure Pext, thereby increasing the volume (V2) between the diaphragms and locally maintaining a certain distance between the upper diaphragm (2) and the lower diaphragm (1), while maintaining the alignment and contact between the composite material (I) and the two diaphragms (1 and 2) at the contact area (5). (b2) The gas (III) contained in the first sealed chamber (3) is discharged to press the lower diaphragm (1) onto the entire molding surface (22) present at the bottom (21) of the mold (20) while maintaining the inter-diaphragm volume (V2) constant.

15. The method according to any one of claims 1 to 10, characterized in that, The intermediate forming step (b) includes the following sequential steps: (b1) The gas (III) contained in the first sealed chamber (3) is discharged, causing the volume (V1) to decrease, so that the lower diaphragm (1) drops to the middle position. At the same time, when the external pressure Pext is equal to the atmospheric pressure, the gas (III) is introduced into the second sealed chamber (4) and the pressure P2 in the second sealed chamber (4) is maintained below the atmospheric pressure, thereby increasing the volume (V2) between the diaphragms and locally maintaining a certain distance between the upper diaphragm (2) and the lower diaphragm (1), while maintaining the alignment and contact between the composite material (I) and the two diaphragms (1 and 2) at the contact area (5). (b2) The gas (III) contained in the first sealed chamber (3) is discharged to press the lower diaphragm (1) onto the entire molding surface (22) present at the bottom (21) of the mold (20) while maintaining the inter-diaphragm volume (V2) constant.

16. The method according to claim 14 or 15, characterized in that, In step (b1), the decrease in the volume (V1) of the first sealed chamber (3) is substantially equal to the increase in the volume (V2) of the second sealed chamber (4).

17. The method according to any one of claims 1 to 10, characterized in that, The intermediate forming step (b) includes the following sequential steps: (b'1) The gas (III) contained in the first sealed chamber (3) is discharged, causing its volume (V1) to decrease, so that the lower diaphragm (1) drops to the middle position. At the same time, when the external pressure Pext is equal to the atmospheric pressure, the gas (III) is introduced into the second sealed chamber (4) and the pressure P2 in the second sealed chamber (4) is maintained below the external pressure Pext, thereby increasing the volume between the diaphragms (V2) and locally maintaining a certain distance between the upper diaphragm (2) and the lower diaphragm (1), while maintaining the alignment and contact between the composite material (I) and the two diaphragms (1 and 2) at the contact area (5). (b'2) Gas (III) is discharged from the second sealed chamber (4), thereby reducing the inter-diaphragm volume (V2) so that the upper diaphragm (2) descends and the two diaphragms (1 and 2) are positioned to contact the composite material (I). (b'3) The gas (III) contained in the first sealed chamber (3) is discharged to press the lower diaphragm (1) onto the entire molding surface (22) present at the bottom (21) of the mold (20), while the gas (III) is introduced into the second sealed chamber (4) when the external pressure Pext is equal to atmospheric pressure and the pressure P2 in the second sealed chamber (4) is maintained below the external pressure Pext, thereby increasing the inter-diaphragm volume (V2) and locally maintaining a certain distance between the upper diaphragm (2) and the lower diaphragm (1), while maintaining the alignment and contact between the composite material (I) and the two diaphragms (1 and 2) at the contact area (5).

18. The method according to any one of claims 1 to 10, characterized in that, The intermediate forming step (b) includes the following sequential steps: (b'1) The gas (III) contained in the first sealed chamber (3) is discharged, causing its volume (V1) to decrease, so that the lower diaphragm (1) drops to the middle position. At the same time, when the external pressure Pext is equal to atmospheric pressure, the gas (III) is introduced into the second sealed chamber (4) and the pressure P2 in the second sealed chamber (4) is maintained below atmospheric pressure, thereby increasing the volume between the diaphragms (V2) and locally maintaining a certain distance between the upper diaphragm (2) and the lower diaphragm (1), while maintaining the alignment and contact between the composite material (I) and the two diaphragms (1 and 2) at the contact area (5). (b'2) Gas (III) is discharged from the second sealed chamber (4), thereby reducing the inter-diaphragm volume (V2) so that the upper diaphragm (2) descends and the two diaphragms (1 and 2) are positioned to contact the composite material (I). (b'3) The gas (III) contained in the first sealed chamber (3) is discharged to press the lower diaphragm (1) onto the entire molding surface (22) present at the bottom (21) of the mold (20), while the gas (III) is introduced into the second sealed chamber (4) when the external pressure Pext is equal to atmospheric pressure and the pressure P2 in the second sealed chamber (4) is maintained below the external pressure Pext, thereby increasing the inter-diaphragm volume (V2) and locally maintaining a certain distance between the upper diaphragm (2) and the lower diaphragm (1), while maintaining the alignment and contact between the composite material (I) and the two diaphragms (1 and 2) at the contact area (5).

19. The method according to any one of claims 1 to 10, characterized in that, The intermediate forming step (b) includes the following sequential steps: (b'1) The gas (III) contained in the first sealed chamber (3) is discharged, causing its volume (V1) to decrease, so that the lower diaphragm (1) drops to the middle position. At the same time, when the external pressure Pext is equal to the atmospheric pressure, the gas (III) is introduced into the second sealed chamber (4) and the pressure P2 in the second sealed chamber (4) is maintained below the external pressure Pext, thereby increasing the volume between the diaphragms (V2) and locally maintaining a certain distance between the upper diaphragm (2) and the lower diaphragm (1), while maintaining the alignment and contact between the composite material (I) and the two diaphragms (1 and 2) at the contact area (5). (b'2) Gas (III) is discharged from the second sealed chamber (4), thereby reducing the inter-diaphragm volume (V2) so that the upper diaphragm (2) descends and the two diaphragms (1 and 2) are positioned to contact the composite material (I). (b'3) The gas (III) contained in the first sealed chamber (3) is discharged to press the lower diaphragm (1) onto the entire molding surface (22) present at the bottom (21) of the mold (20), while the gas (III) is introduced into the second sealed chamber (4) when the external pressure Pext is equal to atmospheric pressure and the pressure P2 in the second sealed chamber (4) is maintained below atmospheric pressure, thereby increasing the inter-diaphragm volume (V2) and locally maintaining a certain distance between the upper diaphragm (2) and the lower diaphragm (1), while maintaining alignment and contact between the composite material (I) and the two diaphragms (1 and 2) at the contact area (5).

20. The method according to any one of claims 1 to 10, characterized in that, The intermediate forming step (b) includes the following sequential steps: (b'1) The gas (III) contained in the first sealed chamber (3) is discharged, causing its volume (V1) to decrease, so that the lower diaphragm (1) drops to the middle position. At the same time, when the external pressure Pext is equal to atmospheric pressure, the gas (III) is introduced into the second sealed chamber (4) and the pressure P2 in the second sealed chamber (4) is maintained below atmospheric pressure, thereby increasing the volume between the diaphragms (V2) and locally maintaining a certain distance between the upper diaphragm (2) and the lower diaphragm (1), while maintaining the alignment and contact between the composite material (I) and the two diaphragms (1 and 2) at the contact area (5). (b'2) Gas (III) is discharged from the second sealed chamber (4), thereby reducing the inter-diaphragm volume (V2) so that the upper diaphragm (2) descends and the two diaphragms (1 and 2) are positioned to contact the composite material (I). (b'3) The gas (III) contained in the first sealed chamber (3) is discharged to press the lower diaphragm (1) onto the entire molding surface (22) present at the bottom (21) of the mold (20), while the gas (III) is introduced into the second sealed chamber (4) when the external pressure Pext is equal to atmospheric pressure and the pressure P2 in the second sealed chamber (4) is maintained below atmospheric pressure, thereby increasing the inter-diaphragm volume (V2) and locally maintaining a certain distance between the upper diaphragm (2) and the lower diaphragm (1), while maintaining alignment and contact between the composite material (I) and the two diaphragms (1 and 2) at the contact area (5).

21. The method according to any one of claims 17 to 20, characterized in that, In operation (b'1) and / or in operation (b'3), the decrease in the volume (V1) of the first sealed chamber (3) is substantially equal to the increase in the volume (V2) of the second sealed chamber (4).

22. The method according to any one of claims 17 to 21, characterized in that, Repeat the operation (b'1) to (b'2) to cause the lower diaphragm (1) and the upper diaphragm (2) to gradually descend.

23. The method according to any one of claims 17 to 21, characterized in that, Repeat the operation (b'1) to (b'2) one to ten times to cause the lower diaphragm (1) and the upper diaphragm (2) to gradually descend.

24. The method according to any one of claims 1 to 23, characterized in that, In steps (a2) and (a3), the two diaphragms (1 and 2) are positioned horizontally.

25. The method according to any one of claims 1 to 24, characterized in that, During the cooling phase, the pressure in the first sealed chamber (3) is increased to reduce friction with the mold (20).

26. The method according to claim 2, characterized in that, The plastic polymer material accounts for up to 10% of the total weight of the composite material (I).

27. The method according to claim 2, characterized in that, The plastic polymer material accounts for 0.5% to 10% of the total weight of the composite material (I).

28. The method according to claim 2, characterized in that, The plastic polymer material accounts for 2% to 6% of the total weight of the composite material (I).

29. The method according to claim 2, characterized in that, The plastic polymer material is selected from thermoplastic polymers, thermosetting polymers, polymers comprising thermoplastic and thermosetting or thermally crosslinked portions, and mixtures thereof.

30. The method according to any one of claims 1 to 29, characterized in that, The composite material (I) comprises a stack of fiber-reinforced layers.

31. The method according to claim 30, characterized in that, The fiber reinforcement layer is selected from fabrics of reinforcing fibers and unidirectional sheets of reinforcing fibers.

32. The method according to any one of claims 1 to 31, characterized in that, The reinforcing fiber is glass fiber, carbon fiber, aramid fiber, or ceramic fiber.

33. The method according to any one of claims 1 to 31, characterized in that, The reinforcing fiber is carbon fiber.

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