Method for manufacturing a grill for a reverse thrust device

Abstract

The present invention proposes a method for manufacturing a grille for a cascade type reverse thrust device of a jet engine, the method comprising: a) manufacturing a first element comprising a continuous or long fiber that is impregnated with a thermoplastic or thermosetting resin; b) manufacturing a series of second elements comprising a series of discontinuous fibers that are impregnated with a thermoplastic or thermosetting resin, either after or together with step a), wherein step b) is performed such that the second elements are arranged transversely with respect to the longitudinal direction of the first element on one side thereof and spaced apart from each other along the longitudinal direction thereof to form a comb-like structure, and the second elements are incorporated into the first element.

Description

Technology Field

[0001] The present invention relates particularly to the field of reverse thrust devices in jet engines of aircraft.

[0002] A thrust reverser is used during the landing of an aircraft equipped with jet engines to decelerate the aircraft. More specifically, a thrust reverser can assist in decelerating the aircraft by redirecting the airflow entering the jet engines in a direction substantially opposite to the forward direction of the aircraft during landing. Background Technology

[0003] There are different types of reverse thrust devices.

[0004] A reverse thrust device considered to be more efficient is called a "cascade." A "cascade" is formed by a plurality of grilles positioned on each other's sides around the nacelle of a jet engine, and each grille is attached to the nacelle.

[0005] This type of reverse thrust device is typically installed midway along the length of the jet engine.

[0006] Figure 1 shows a cross-sectional view of an aircraft jet engine, Figure 1a for flight and Figure 1b for landing.

[0007] By comparing the two diagrams, the effect of the "cascade" type reverse thrust device can be seen.

[0008] In fact, during landing, the translational skirt (JT) of the nacelle moves simultaneously with the blocking section (VB), so that the airflow (FA) is redirected toward the grilles (G1, G2) of the reverse thrust device.

[0009] FIG. 2 is a perspective view of a typical grille (G) of a "cascade" type reverse thrust device.

[0010] The grille (G) of a “cascade” type reverse thrust device includes a first element (PC) called a spar or “strongback” that extends along the longitudinal direction of the engine when the reverse thrust device is installed on the jet engine, a second element (SC) called a blade or “vane” that extends transversely to the first element and thus along the periphery of the jet engine, and a frame (C) for the first element (PC) and the second element (SC), generally as in the case of FIG. 2.

[0011] Currently, these grills are made of composite materials, that is, fibers that are pre-impregnated with resin.

[0012] All elements contribute to mechanical strength in redirecting airflow in the opposite forward direction of the airflow during landing. Manufacturing the grille of a "cascade" type reverse thrust device made of composite materials is particularly complex.

[0013] In fact, this requires many steps, and in the special manual, expensive tools are used in some steps.

[0014] Generally, current technology is structured as follows:

[0015] a) On the one hand, to manufacture the first element or strong bag,

[0016] b) on the other hand, to manufacture a second element or vane, and

[0017] c) Assemble the second element into the first element.

[0018] For example, this is proposed in the literature US 9 587 582 B1(D1).

[0019] In this document, the first element is manufactured individually or made as a single part by low-pressure injection molding of resin (more commonly known by the acronym RTM ("Resin Transfer Moulding")), drawing, or compression molding.

[0020] In this document, the second element is also manufactured as a block cut into different individual elements, or manufactured by forming each of the second elements individually. Whichever method is used, the individually manufactured block or each second element can be obtained by RTM or compression molding.

[0021] In this document as well, the assembly of the second element to the first element is performed by sliding each of the second elements into a receiving slot provided in the first element. And, the retention of each of the second elements on the first element must be ensured using a structural adhesive.

[0022] Once steps a), b), and c) are performed, the frame of the grill must finally be formed in the next step.

[0023] In particular, this method takes a long time to execute because each of the second elements (vanes) must be inserted or slid between the two first elements (strongbacks).

[0024] A method according to steps a), b), and c) above is also proposed in literature FR 3 048 025 A1(D2).

[0025] The uniqueness of this method lies in the manufacture of the second element. In fact, to make each of the second elements, it starts with a preform made of a composite material that is pre-impregnated with resin, and then a stamping process is performed to form the desired shape.

[0026] In one embodiment, then each of the second elements is installed on the first element, and finally, welding is performed.

[0027] From these steps a), b), and c), a frame is provided, and the first and second elements can be fixed to this frame.

[0028] Therefore, the manufacturing time can be closer to that of document D1.

[0029] The document EP 2 944 452(D3) proposes a method according to steps a), b), and c) mentioned above.

[0030] However, here, the second element is not given as an individual element assembled to the first element, but as an element (vane) connected together through a frame to form a ladder-type structure or a rack-type structure (Fig. 7 or Fig. 8 of this document). And the ladder-type structure or the rack-type structure is assembled to an assembly comprising a first element (strongback) having a frame (Fig. 6 of this document).

[0031] The assembly of the first element and its frame (Fig. 6 of this document) can be performed by compression molding.

[0032] Similarly, assembling the second element and its frame to form a ladder-type structure or a rack-type structure (Fig. 7 of this document) can be done by compression molding.

[0033] This is advantageous to the solution proposed in Literature D1 or Literature D2, particularly regarding the number of tasks to be performed manually.

[0034] Additionally, finally, in contrast to what is proposed in literature D1 and literature D2, the frame of the grille is formed simultaneously with the first and second elements.

[0035] However, to ensure that the two assemblies (on one hand, the assembly of Fig. 7 or 8, and on the other hand, the assembly of Fig. 6) are integrated together, a special and more complex tool based on a mandrel is used. Furthermore, this mandrel is meltable and therefore not reusable, which increases the cost. The problem to be solved

[0036] The object of the present invention is to propose a method for manufacturing a grille for a "cascade" type reverse thrust device that requires inexpensive and relatively simple tools over time.

[0037] This method can actually reduce the manufacturing cost of such grills. means of solving the problem

[0038] To achieve the above objective, the present invention proposes a method for manufacturing a grille for a cascade type reverse thrust device of a jet engine, the method comprising: a) manufacturing a first element comprising a continuous or long fiber that is impregnated with a thermoplastic or thermosetting resin; b) manufacturing a series of second elements comprising a series of discontinuous fibers that are impregnated with a thermoplastic or thermosetting resin, either after or together with step a), wherein step b) is performed such that the second elements are arranged transversely with respect to the longitudinal direction of the first element on one side thereof and spaced apart from each other along the longitudinal direction thereof to form a comb-like structure, and said second elements are incorporated into the first element.

[0039] The method according to the present invention may also include at least one of the following characteristic features individually or in combination:

[0040] - A first element manufactured during step a) includes a series of notches, and each notch accommodates a second element;

[0041] - Step b) further comprises fixing a second element to the first element on a second side of the related first element, said second side being on the opposite side of the first side;

[0042] - This method is,

[0043] c) a step of repeating steps a) and b) at least once to obtain at least one other comb-shaped structure - said second element is integrated into first element -;

[0044] d) a step of placing a previously obtained comb-shaped structure on a frame configured to be attached to a jet engine; and

[0045] e) further includes the step of fixing the comb-shaped structure to the frame;

[0046] - Two second elements of two different comb-shaped structures, advantageously obtained in step c), are fixed to each other, for example, by welding and / or joining and / or in a complementary shape;

[0047] - The above frame includes, depending on the case of a notch or lug accommodating each comb-shaped structure;

[0048] - The frame includes four sides, two of which are secured by removable fastening means;

[0049] - The frame comprises continuous fibers or long fibers that are pre-impregnated with a thermoplastic or thermosetting resin;

[0050] - Step a) is,

[0051] a1) a substep of providing at least one sheet made of continuous fibers that are previously impregnated with a thermoplastic or thermosetting resin;

[0052] a2) A substep of placing at least one sheet in a mold;

[0053] a3) includes a sub-step of compression molding the at least one sheet in the mold to obtain the first element;

[0054] - Step b) is,

[0055] b1) a substep of providing at least one second sheet made of continuous fibers that are previously impregnated with a thermoplastic or thermosetting resin;

[0056] b2) a substep of cutting the second sheet to produce a shaving formed of discontinuous fibers that are previously impregnated with a thermoplastic or thermosetting resin; and

[0057] b3) a substep of placing the above shaving inside a mold; and

[0058] b4) Includes a sub-step of compression molding the shaving in the mold to obtain the second element;

[0059] - Sub-steps a2) and b3) are performed in the same mold, sub-steps a3) and b4) are performed together, and steps a) and b) are performed together;

[0060] - Substep b3) is performed inside the mold in the presence of the first element obtained in substep a3), so steps a) and b) are performed in succession to each other;

[0061] - Step a) is,

[0062] a'1) A substep of providing a sheet made of continuous fibers that are previously impregnated with a thermoplastic or thermosetting resin;

[0063] a'2) A substep of cutting the sheet to produce a shaving formed of long fibers that are pre-impregnated with a thermoplastic or thermosetting resin;

[0064] a'3) a substep of placing the above shaving inside a mold; and

[0065] a'4) includes a sub-step of compression molding the shaving in the mold to obtain the first element;

[0066] - Step b) is,

[0067] b'1) a substep of providing at least one second sheet made of continuous fibers that are previously impregnated with a thermoplastic or thermosetting resin;

[0068] b'2) A substep of cutting the second sheet to produce a shaving formed of long fibers that are previously impregnated with a thermoplastic or thermosetting resin;

[0069] b'3) a substep of placing the above shaving inside a mold; and

[0070] b'4) Includes a sub-step of compression molding the shaving in the mold to obtain the second element;

[0071] - Sub-steps a'3) and b'3) are performed in the same mold, sub-steps a'4) and b'4) are performed together, so steps a) and b) are performed together;

[0072] - Step a) is performed by drawing, and then step b) is performed by injection overmolding for the first element;

[0073] - The injection overmolding step b) is performed with short fibers that are pre-impregnated with a thermoplastic or thermosetting resin, i.e., discontinuous fibers having a length of less than 100 microns. Brief explanation of the drawing

[0074] Other features and advantages of the present invention will become apparent from reading the following detailed description, and reference will be made to the accompanying drawings for understanding the detailed description. Figures 1a and 1b show cross-sectional views of an aircraft's jet engine during flight on one hand and landing on the other. FIG. 2 is a perspective view of a typical grille (G) of a "cascade" type reverse thrust device. FIG. 3 is a perspective view of a comb-shaped structure obtained by the method according to the present invention. Figure 4 shows a side view of a comb-shaped structure obtained by the method according to the present invention. FIG. 5 is a schematic top view of another comb-shaped structure obtained by the method according to the present invention. FIG. 6 illustrates different steps of a first embodiment of the method according to the present invention according to a first variation. FIG. 7 illustrates different steps of this first embodiment of the method according to the present invention, according to a second variation. FIG. 8 illustrates different steps of this first embodiment of the method according to the present invention, according to a third variation. FIG. 9 illustrates different steps of a second embodiment of the method according to the present invention. FIG. 10 is a schematic top view of a grill obtained by the method according to the present invention having a frame. Figure 11 shows a method of fixing two different comb-shaped structures of one identical grill. FIG. 12 schematically shows a perspective view of a set of comb-shaped structures before they are assembled into a specific frame. Specific details for implementing the invention

[0075] In the following description, "long" fibers should be understood as fibers having a length between 1 mm and 70 mm, advantageously between 1 mm and 50 mm, or more advantageously between 1 mm and 30 mm.

[0076] Similarly, in the following description, "short" fibers should be understood as fibers having a length between 1 micron and 1 mm (the latter value (1 mm) is excluded), advantageously between 1 micron and 500 microns, more advantageously between 1 micron and 300 microns, and even between 1 micron and 100 microns.

[0077] In the following description, therefore, discontinuous fibers can be long or short.

[0078] Moreover, non-discontinuous fibers are similar to continuous fibers.

[0079] Finally, the term "sheet" may equally refer to a layer, particularly a layer of unidirectional fibers, or a fabric.

[0080] The present invention relates to a method for manufacturing a grille for a cascade type reverse thrust device of a jet engine, the method comprising the following steps:

[0081] a) a step of manufacturing a first element comprising a continuous or long fiber that is previously impregnated with a thermoplastic or thermosetting resin;

[0082] b) a step of manufacturing a series of discontinuous fibers that are pre-impregnated with a thermoplastic or thermosetting resin, either after or together with step a), wherein (step b) is performed such that the second elements are arranged transversely with respect to the longitudinal direction of the first element on one side of at least one side of the first element and spaced apart from each other along the longitudinal direction on the other side to form a comb-like structure, and the second elements are incorporated into the first element).

[0083] Through this, in contrast to the solutions proposed in the aforementioned prior art literature, no special steps are required when integrating the second element (vane) into the first element (strongback).

[0084] Figure 3 shows the comb-shaped structure (SFP) obtained in step b).

[0085] Additionally, the first element manufactured during step a) may include a series of notches (ENC), and each notch accommodates a second element.

[0086] These notches (ENC) can be seen, for example, in Fig. 3, and in this case, are formed in the mass of the first element, that is, by creating a slot in the thickness of the first element.

[0087] Such notches can also be seen in FIG. 4. However, in FIG. 4, the notches are obtained by creating two lip (L1, L2) in the excess thickness of the first element, thereby creating a slot between the two lip. By creating the notches in this way, the thickness of the first element can be maintained, so there is no risk of the mechanical performance of the first element changing. Additionally, by creating the notches in this way, the joint between the second element and the first element can be strengthened, thus improving the mechanical strength between these elements. Furthermore, creating notches with such lip-like notches does not have a sensitive effect on the airflow passing through the cascade.

[0088] Step b) consists of fixing a second element to the first element on a second side of the related first element, where the second side is on the opposite side of the first side. In this case, as shown in the schematic top view of FIG. 5, the second element (vane) extends from both sides of the first element (strongback).

[0089] Mainly, two embodiments for implementing this method can be considered.

[0090] In the first embodiment, compression molding can be performed to manufacture a first element (step a)) and also to manufacture a second element (step b)).

[0091] More specifically, step a) includes the following sub-steps:

[0092] a1) a substep (101) providing at least one sheet made of continuous fibers that are previously impregnated with a thermoplastic or thermosetting resin;

[0093] a2) A substep (102) of placing at least one sheet inside a mold;

[0094] a3) A substep (103) of compression molding at least one sheet in a mold to obtain a first element.

[0095] It should be noted that due to the problem of mechanical resistance, it is advantageous to use continuous fibers in forming the first element (which is to form the strong bag of the grill).

[0096] More specifically, therefore, step b) also includes the following sub-steps:

[0097] b1) a substep (201) providing at least one second sheet made of continuous fibers that are previously impregnated with a thermoplastic or thermosetting resin;

[0098] b2) a sub-step (202) of cutting a second sheet to produce a shaving formed of discontinuous fibers that are previously impregnated with a thermoplastic or thermosetting resin; and

[0099] b3) a sub-step (203) of placing the shaving inside the mold; and

[0100] b4) A sub-step (204) of compression molding the shaving inside the mold to create the second element.

[0101] When substep b3) (203) is performed in the mold in the presence of the first element obtained in substep a3), substep b3) is performed after substep a3). In fact, steps a) and b) are performed in succession to each other. Thus, there are two compression molding operations, one compression molding operation for the first element and the other compression molding operation for the second element, and over time, the second element may be integrated into the first element. Thus, although, the compression molding operation of the second element performed in the presence of the first element can not only form the second element, but also, at the same time, ensure the integration of the second element (SC) into the first element (PC).

[0102] This option is shown in Fig. 6.

[0103] The advantage of performing the aforementioned steps a) and b) is that, by the first molding, the continuous fibers of the first element can be aligned before the molding of the second element is performed.

[0104] In contrast, when sub-steps a2) (102) and b3) (203) are performed in the same mold, sub-steps a3) (103) and b4) (204) are performed together. In fact, steps a) and b) are performed together. Thus, a comb-shaped structure having a first element and a series of second elements is formed in a single compression molding operation, and furthermore, during the molding operation, the second elements (SC) are fixed to the first elements. This variation is useful because, by finally providing only one compression molding step, manufacturing time can be further reduced and thus manufacturing cost can be further reduced.

[0105] This other option is shown in Fig. 7.

[0106] Other variations for steps a) and b) can also be considered.

[0107] In fact, above, we explained the case where the fiber of the first element is a continuous fiber and the fiber of the second element is discontinuous, that is, short or long.

[0108] However, another useful case is, more specifically, using long fibers for the first element and long fibers for the second element.

[0109] In fact, the long fibers for the first and second elements can maintain useful mechanical properties.

[0110] This can be achieved with two molds, one for the first element and the other for the second element, but this is advantageous when both the first and second elements are molded simultaneously.

[0111] You can refer to Fig. 8.

[0112] Therefore, step a) may include the following sub-steps:

[0113] a'1) a substep (101') providing a sheet made of continuous fibers that are impregnated with a thermoplastic or thermosetting resin beforehand;

[0114] a'2) A substep (102') of cutting a sheet to produce a shaving formed of long fibers that are pre-impregnated with a thermoplastic or thermosetting resin;

[0115] a'3) a sub-step (103') of placing the shaving inside the mold; and

[0116] a'4) A sub-step (104') of compression molding the shaving inside a mold to obtain the first element.

[0117] Step b) may include the following sub-steps:

[0118] b'1) a substep (201') providing at least one second sheet made of continuous fibers that are previously impregnated with a thermoplastic or thermosetting resin;

[0119] b'2) a substep (202') of cutting a second sheet to produce a shaving formed of long fibers that are previously impregnated with a thermoplastic or thermosetting resin;

[0120] b'3) a sub-step (203') of placing the shaving inside the mold; and

[0121] b'4) A sub-step (204') of compression molding the shaving inside a mold to obtain the second element.

[0122] Advantageously, as also shown in FIG. 8, sub-steps a'3)(102') and b'3)(103') are performed in the same mold, and sub-steps a'4)(103') and b'4)(204') are performed together, so steps a) and b) are performed together. This limits the number of tools and also saves time. In a second embodiment, step a)(100') is performed by drawing and then step b)(200') is performed by injection overmolding for the first element.

[0123] You can refer to Fig. 8.

[0124] Therefore, the drawing step a) is advantageously performed with continuous or long fibers that are pre-impregnated with a thermoplastic or thermosetting resin.

[0125] Then, injection overmolding step b) is advantageously performed with short fibers that are pre-impregnated with a thermoplastic or thermosetting resin. In fact, injection overmolding is easier in the case of short fibers.

[0126] Regardless of which embodiment is practiced, the fiber is advantageously selected from carbon fiber, glass fiber, aramid fiber, or a mixture thereof.

[0127] Furthermore, the thermoplastic resin is selected from polyamide (PA), polyphthalamide (PPA), phenylene polysulfide (PPS), polyetherimide (PEI), polyetheretherketone (PEEK) or polyetherketoneketone (PEKK).

[0128] Furthermore, the thermosetting resin can be selected from epoxy or vinyl ester.

[0129] In particular, the carbon fiber may be provided with an epoxy-type thermosetting resin or a polyetherimide (PEI)-type thermoplastic resin.

[0130] Regardless of which embodiment is practiced, the following steps may be further provided to make the grill:

[0131] c) A step of repeating steps a) and b) at least once to obtain a comb-like structure - the second element is integrated into the first element -;

[0132] d) a step of placing a previously obtained comb-shaped structure on a frame configured to be attached to a jet engine; and

[0133] e) Step of fixing the comb-shaped structure to the frame.

[0134] FIG. 10 schematically shows a top view of the grill (G) obtained in step e). In FIG. 10, several comb-shaped structures are shown arranged on each other's sides, and each comb-shaped structure includes a first element (PC), a series of second elements (SC), and a frame (C).

[0135] Additionally, advantageously, an additional step may be provided that is executed after step c), in which two second elements (vanes) of two different comb-shaped structures are fixed to each other, for example, by welding and / or joining and / or in a complementary shape.

[0136] This is shown in FIG. 11. In FIG. 11, the second element (SC1) of the first comb structure and the second element (SC2) of the second comb structure can actually be seen. Here, the second elements (SC1, SC2) have both complementary shapes and welds.

[0137] Thus, the structure becomes stronger, and consequently, its mechanical properties can be improved. As a result, the continuity of the grille can also be ensured without obstructing the airflow being redirected toward the forward of the aircraft during landing when in use.

[0138] To facilitate the execution of step e), the frame (C) may include a notch that accommodates each comb-shaped structure. Thus, this notch is similar to the notch on the first part shown in FIG. 3 or 4.

[0139] Frames can be made in different ways.

[0140] Accordingly, the frame may include four sides (C1, C2, C3, C4), and these sides are advantageously secured in pairs by removable fastening means (MAV) (schematically shown in FIG. 10). The fastening means may be rivets (non-removable method) or corners secured by a bolt system (removable method). By making the frame after making different comb-shaped structures, easier adjustment of the grille is made possible.

[0141] The frame may also be made as shown in Fig. 12.

[0142] In FIG. 12, the presence of a plurality of comb-shaped structures (SPF1 to SPF7) can be seen. Each comb-shaped structure is formed according to steps a) and b) of the method according to the present invention.

[0143] Therefore, the assembly shown in Fig. 12 is the one that can be seen during assembly step d) before integration step e).

[0144] The presence of notches (ENC) can also be observed in comb-shaped structures (SPF2 to SPF7).

[0145] The first element (PC1) of the comb-shaped structure (SPF1) forms an element of the frame.

[0146] The remainder of the frame includes three different parts (P1, P2, P3).

[0147] Part (P3) is actually a first element, and there is no second element, and the first element includes a notch (ENC) capable of accommodating the second element (SC) of the comb-shaped structure (SPF7). This is advantageously positioned on the opposite side of the first element (PC1).

[0148] Part (P2) is similar to a strip having lugs (E1 to E7) that are inserted into corresponding orifices (O1 to O7) of different comb-shaped structures. This part (P2) allows all comb-shaped structures to be connected. Furthermore, the strip shape is simple to manufacture and, for example, can be made of continuous fibers to ensure good mechanical strength.

[0149] Finally, part (P1) has a series of notches (ENC') for joining with corresponding elements (EC1-EC7) provided at each end of each first element of different comb structures. By this corresponding shape, part (P1) can be accurately positioned against different comb structures. This also allows the joint to be strengthened by mechanical support.

[0150] The frame is advantageously made of a composite material. In particular, the frame advantageously comprises continuous fibers or long fibers that are pre-impregnated with a thermoplastic or thermosetting resin.

[0151] Now, an example is described.

[0152] In this embodiment, steps a) and b) of the method are performed together.

[0153] The sheet, in this case, starts with a layer of continuous unidirectional carbon fibers (UD). This layer is pre-impregnated with a thermoplastic resin of the polyetherimide (PEI) type.

[0154] This layer is cut by shaving, in this case, to form long fibers of 12.7 mm x 12.7 mm.

[0155] The shaving is introduced into a mold having a shape complementary to the shape of the comb, forming both a strongback (first element) and a set of vanes (second element).

[0156] The mold is closed to ensure a pressure of about 30 bar and heated to a temperature higher than the melting temperature of the polyetherimide used as the resin.

[0157] Therefore, this is compression molding.

[0158] Then, although it is absolutely standard practice, the mold is cooled to the glass transition temperature of the polyetherimide used as the resin to ensure demolding of the comb-shaped part.

[0159] This process can be repeated several times according to step c) to obtain all parts that can be used for the complete formation of the grill.

[0160] Then, step d) of placing on the frame is executed.

[0161] Therefore, the final assembly step e) is performed by welding using conventional dedicated tools.

[0162] Whatever the embodiment being considered, finally, it should be noted that the method according to the present invention can manufacture a portion including a region with many undercuts.

Claims

Claim 1 A method for manufacturing a grille for a cascade type thrust reverse device of a jet engine, comprising: a) manufacturing a first element comprising a continuous or long fiber that is impregnated with a thermoplastic or thermosetting resin; b) manufacturing a series of second elements comprising a series of discontinuous fibers that are impregnated with a thermoplastic or thermosetting resin, either after or together with step a), wherein step b) is performed such that the second elements are arranged transversely with respect to the longitudinal direction of the first element on one side thereof and spaced apart from each other along the longitudinal direction on the other side thereof to form a comb-like structure, and said second elements are integrated into the first element. Claim 2 A method according to claim 1, wherein the first element manufactured during step a) comprises a series of notches, each notch accommodating a second element. Claim 3 A method according to claim 1, wherein the first element has a first side and a second side opposite to the first side, and step b) further comprises fixing a second element to the first element on the second side of the related first element. Claim 4 A method according to claim 1, further comprising: c) a step of repeating steps a) and b) at least once to obtain at least one other comb-shaped structure, wherein the second element is integrated into the first element; d) a step of placing the previously obtained comb-shaped structure on a frame configured to be attached to a jet engine; and e) a step of fixing the comb-shaped structure to the frame. Claim 5 In claim 4, the two second elements of the two different comb-shaped structures obtained in step c) are welded and / or joined and / or fixed to each other in a complementary shape. Claim 6 In claim 4, the method wherein the frame comprises, depending on the case of a notch or lug accommodating each comb-shaped structure. Claim 7 In claim 4, the method comprises four sides, each of which is secured in pairs by removable fastening means. Claim 8 In claim 4, the method comprises a frame comprising continuous fibers or long fibers that are pre-impregnated with a thermoplastic or thermosetting resin. Claim 9 A method according to any one of claims 1 to 8, wherein step a) comprises: a1) a substep of providing at least one sheet made of continuous fibers that are impregnated with a thermoplastic or thermosetting resin; a2) a substep of placing said at least one sheet in a mold; and a3) a substep of compression molding said at least one sheet in the mold to obtain said first element. Claim 10 In claim 9, step b) comprises: b1) a substep of providing at least one second sheet made of continuous fibers that are impregnated with a thermoplastic or thermosetting resin; b2) a substep of cutting the second sheet to produce a shaving formed of discontinuous fibers that are impregnated with a thermoplastic or thermosetting resin; and b3) a substep of placing the shaving in a mold; and b4) a substep of compression molding the shaving in the mold to obtain the second element. Claim 11 In claim 10, sub-steps a2) and b3) are performed in the same mold, sub-steps a3) and b4) are performed together, and steps a) and b) are performed together, method. Claim 12 In claim 10, substep b3) is performed in a mold in the presence of the first element obtained in substep a3), so that steps a) and b) are performed in succession to each other, method Claim 13 A method according to any one of claims 1 to 8, wherein step a) comprises: a'1) a substep of providing a sheet made of continuous fibers that are impregnated with a thermoplastic or thermosetting resin; a'2) a substep of cutting the sheet to produce a shaving formed of long fibers that are impregnated with a thermoplastic or thermosetting resin; a'3) a substep of placing the shaving in a mold; and a'4) a substep of compression molding the shaving in the mold to obtain the first element. Claim 14 In claim 13, step b) comprises: b'1) a substep of providing at least one second sheet made of continuous fibers that are pre-impregnated with a thermoplastic or thermosetting resin; b'2) a substep of cutting the second sheet to produce a shaving formed of long fibers that are pre-impregnated with a thermoplastic or thermosetting resin; b'3) a substep of placing the shaving in a mold; and b'4) a substep of compression molding the shaving in the mold to obtain the second element. Claim 15 In claim 14, sub-steps a'3) and b'3) are performed in the same mold, sub-steps a'4) and b'4) are performed together, so steps a) and b) are performed together, method. Claim 16 A method according to any one of claims 1 to 8, wherein step a) is performed by drawing, and then step b) is performed by injection overmolding for the first element. Claim 17 In claim 16, the injection overmolding step b) is performed with short fibers that are pre-impregnated with a thermoplastic or thermosetting resin, i.e., discontinuous fibers having a length of less than 100 microns that is not zero, a method.

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