FR3026979A1 - - Google Patents

Abstract

A method for making a fiber reinforced composite member which is formed of a fiber material infused with a matrix material. Fiber-based material is introduced into a gap formed between forming tools. The fiber material comprises a first portion (6a) of fiber material and a second portion (6b) of fiber material. The first portion of fiber material has a higher degree of compaction than the second portion of fiber material.

Description

The invention relates to a method for manufacturing a fiber-reinforced composite part which is formed by a fiber-based material infused with a matrix material. Structural parts made of a fiber-reinforced composite material, called fiber-reinforced composite parts, are today essential in the aeronautical and aerospace field, but the use of such constituent materials is also more and more popular in the automotive field. . Particularly critical structural elements made of fiber reinforced plastics are produced with minimal weight because of their high specific strength and stiffness for a given weight. Thanks to the anisotropic properties resulting from the fiber orientation of the fiber-reinforced composite materials, the parts can be adapted to local loads or constraints, thus allowing an optimal exploitation of the material in the optics of a lightened construction. The current aspirations for the development of airframe airliners made of fiber-reinforced composite materials with a greater degree of integration compared to the state of the art require new and innovative manufacturing processes. Thus, for example, according to DE 10 2010 109 231 A1, a method is known for producing integrally reinforced wing shells, according to which, for the compaction and shaping of the reinforcing elements. in relief on the surface of the skin of the wing, the thermal expansion of the tool cores is used to obtain the necessary compaction of the reinforcing elements during the heating of the shaping tool and thus fiber-based material infused with matrix material.

The closing movement that the tool cores can reach during the manufacturing process to ensure the necessary compaction of the stiffeners, due to the thermal expansion during the temperature increase, is however limited by project specifications and physical constants. However, since a reinforcement element to be shaped is, before the beginning of the actual process, less compacted and thus thicker than in the final state, the closing displacement of the core must be at least sufficiently large for the element stiffener finds, during the process of the establishment of the preform, sufficient space between two neighboring tool cores. From a number of layers, namely a certain set thickness of the stiffener, the preform becomes too thick, so that said condition can no longer be met. Thus, for a particular tooling core material and a determined fiber-based composite semi-product, a maximum possible thickness of the integrally formed stiffening elements, which can be manufactured with the respective manufacturing method, is possible. DE 10 2005 026 010 A1 discloses a method for manufacturing reinforced shells for producing partial components of aircraft, according to which the reinforcing elements consist of composite parts reinforced with already hardened fibers, which are then fixed to the skin of the hull using connecting elements not yet hardened. Then, the connecting elements and the shell are hardened together. The purpose of the method is to overcome the need for massive forming tooling parts for shaping and supporting slats or stiffeners during the autoclave process. The object of the present invention is to indicate an improved process for manufacturing a fiber reinforced composite part, according to which, by exploiting the thermal expansion, in particular reinforcing elements can be compacted during the curing, to thereby achieve highly integrated parts. The desired object is achieved according to the invention by a method of the type mentioned in the introduction and comprising the following steps: a. providing and preparing a tooling or shaping having a plurality of shaping cores, which can be arranged, forming a predetermined gap between two neighboring shaping cores, such that when the temperature is set to the forming tool, at least one forming core is thermally expanded in the direction of at least one gap, b. introducing fiber material and forming cores into the forming tool, the fiber material being placed in at least one gap formed by the forming cores, and c. curing the matrix material having been infused into the fiber-based material by heating the forming tool to produce the fiber reinforced composite member characterized by d. introducing and arranging at least two portions of fiber material in at least one gap formed by the shaping cores, the first fiber material portion having as a preform a greater degree of compaction high than the at least second part of fiber-based material.

According to the method, a shaping tool having a plurality of shaping cores, which can be arranged in the shaping tool, is first provided and prepared by forming a predetermined gap between neighboring shaping cores. such that when the forming tool is set to temperature, at least one forming core is thermally expanded towards at least one interstice. Such forming tooling may for example be a forming tool such as that known from DE 10 2012 109 231 A1. For the purposes of the present invention, shaping cores are shaping elements belonging to the forming tool, and making it possible to form at least part of the geometry of the future composite fiber-reinforced part, and which are adapted to make a gap. A shaping core can here be an element that can be removably connected to the shaping tool. But it is also contemplated that a forming core is a fixed integral part of the forming tool, for example a fixed peripheral edge.

In this forming tool is then introduced fiber material, and the shaping cores are arranged therein so far as they are not yet connected to the shaping tool. On this occasion, fiber-based material is also disposed in at least one gap formed by the shaping cores. Due to the thermal expansion of the shaping cores, the fiber-based material in the gap is compacted upon warming up during curing of the matrix material having been infused into the fiber material. In the sense of the present invention, the heat-up means in particular a temperature setting suitable for causing the hardening of the matrix material having been infused in the fiber-based material, so as to be able to manufacture a fiber-reinforced composite part. As a general rule, a warming up here consists of an increase of the temperature with respect to the ambient temperature, up to the necessary process temperature, for example at 180 ° C. The fiber-based material introduced into the shaping tool can here be dry or pre-impregnated fiber material (prepregs). In the case of preimpregnated fiber material, the fiber material is already infiltrated by the matrix material. According to the invention, it is now proposed to introduce and arrange at least two parts of fiber-based material in the at least one gap formed by the shaping cores, the first portion of 40-fiber base having as a preform a higher degree of compaction than the at least second portion of fiber-based material. In accordance with the invention, the first portion of fiber material made as a preform has been pre-compacted and optionally deformed prior to introduction into the interstice, so that the first portion of The fiber base has a higher degree of compaction than the second portion of fiber material. It is also conceivable that the second portion of fiber-based material is pre-compacted, however with a lesser degree of compaction than that of the first portion of fiber-based material. Due to the placement of two different fiber-based material parts, one of which has a higher degree of compaction than the other, the natural limit of the maximum thickness or width of one can be increased. reinforcement element achievable by the fiber-based material in the gap, without having to change the fundamental geometry of the workpiece. On the contrary, the inventors have found that, thanks to a fiber-based material which is at least partially more compacted, occupying at least part of the gap between the shaping cores, it was possible to increase the thickness of the maximum achievable setting for the reinforcing elements, without modifying the parameters of the part or the physical properties of the shaping tools to be used.

For the purposes of the present invention, the degree of compaction is a measure for compaction of the fiber-based material. Such a measure may for example be the volume fraction of fibers or the volume content of the fibers. The volume content of the fibers here indicates the proportion of the volume of the fibers relative to the overall volume of the preform or the subsequent part. The larger the volume content of the fibers, the greater the degree of compaction of the fiber-based material. The lower the thickness of the fiber-based material for a constant number of layers of compressed fibers, the lower the compaction measurement or the degree of compaction. Ultimately, any proportion that directly or indirectly indicates the volume of the fibers in relation to the overall volume of the preform can be considered for compaction measurement or degree of compaction. The preform is here the shape of the fiber-based materials, which is made in the gap by introduction of fiber-based material. The higher the degree of compaction of the fiber-based materials, the higher the proportion of fibers participating in the overall volume of the preform, which is formed for example by the first part of fiber-based materials in the gap. . According to an advantageous embodiment, said at least two parts of fiber-based material are introduced and arranged in said at least one interstice so that the first portion of fiber-based material is partially or completely enclosed by the at least second portion of fiber-based material in the interstice formed by the shaping cores. The fiber-based material portion having a higher degree of compaction than the other portion of fiber-based material is thus arranged between the fiber-based materials having a lower degree of compaction, and is enclosed in the 'gap. The second fiber material portion here can be arranged in this L-shaped region on the first portion of fiber-based material as well as on a base structure on which is formed the first portion of the fiber material. fiber base. This arrangement is particularly advantageous when the first portion of fiber material having the high degree of compaction is made of already hardened or consolidated fiber material in the form of a preform, namely a fiber reinforced composite preform. so that during the entire manufacturing process, the preform with the high degree of compaction is embedded between uncured fiber material, thus being integrally connected to the overall structure.

The first portion of fiber material arranged between the second fiber material portion may here be partially or completely enclosed by the second fiber material portion. The first portion of enclosed fiber material may be larger in its vertical extent than the second portion of fiber material, or vice versa. According to another embodiment, however, it is also possible to envisage that said at least two parts of fiber-based material are introduced and arranged in said at least one interstice in such a way that the first part 30 of fiber-based material is press against one of the forming cores constituting the gap, while the second portion of fiber material rests against the opposite forming core constituting the interstice. It is obvious that such an arrangement of the fiber-based materials is provided for each interstice formed by placing the shaping cores in the shaping tool. Thus, in the case of a large number of shaping cores, accordingly, there is formed between the neighboring individual shaping cores a large number of interstices between which is then introduced in accordance with the present invention. , a fiber-based material of which a portion of fiber-based material has a higher degree of compaction than the other portion of fiber-based material. As already mentioned, it is advantageous that the first portion of fiber material, as a preform, is a fiber reinforced composite preform partially or fully cured. The first portion of fiber material is thus a fiber-based material infused with a matrix material which has subsequently been cured, whereby a fiber-reinforced composite part made of matrix material and material is obtained. based on 5 fibers. This fiber-reinforced composite part consequently has dimensions which make it possible to introduce into one of the interstices said fiber-reinforced composite part as the first part of fiber-based material, so that it is precisely still possible. to add other parts of fiber-based material into the gap. The first portion of fiber-based material is here pre-compacted in the manner of a preform before introduction into the corresponding gap, which occurs during the manufacture of the preform.

It is particularly advantageous in this regard that the first portion of fiber-based material, including a partially or fully cured fiber-reinforced composite part, is made in advance by producing, by heating, curing. partially or completely of a matrix material having been infused into a fiber-based material prior to the introduction and arrangement of the first portion of fiber-based material into the interstice or gaps of the tooling formatting. It is thus possible to manufacture, for example reinforcing elements, industrially and in series, which makes it possible to prepare such reinforcing elements with a quality that remains constant, in particular for critical structural parts. During the manufacture of the overall structure, it is then possible to use prepared and prefabricated reinforcing elements. It has furthermore been found to be advantageous for the first part of fiber material to occupy at least 10%, preferably at least 30%, and particularly preferably at least 50% of the width or volume of the piece. to make, in the interstice. The percentage indication refers here only to the part of the room which is arranged in the gap.

The present process is particularly advantageous for the manufacture of wing hulls for which the reinforcement elements formed by the interstices represent the necessary stiffeners or stiffeners. However, one can also consider the manufacture of other bearing structures, such as vertical fins or empennages and horizontal empennages. The invention will be explained by way of example, with reference to the appended figures which show FIG. 1a, 1b, a manufacturing method known from the state of the art, using tooling cores. FIG. a schematic representation of an embodiment of the invention; Figure 3 is a schematic representation of an alternative embodiment. FIGS. 1a and 1b show the manufacture of a fiber-reinforced composite part by means of tool cores, as known for example from DE 10 2012 109 231 A1. The figure shows it here the state where the shaping tools and shaping cores are not put in temperature, while Figure 1b shows the state when put in temperature.

FIGS. 1a and 1b show two shaping cores 1a, 1b of not shown shaping tooling. Between the two forming cores 1a, 1b is formed a gap 2 in which are introduced and arranged portions of fiber-based material 3 of a composite fiber-reinforced component 4 to be manufactured. As shown in FIG. 1a, the gap 2 has a gap size S greater than the uncompacted thickness t 1 of the fiber material introduced into the gap in the non-heat-up state. 2. In the example of FIG. 1a and 1b, the two shaping cores 1a, 1b are connected to the shaping tool via fixed supports 5a, 5b, where results a spacing of fixed supports L between the two cores 1 a, 1 b. From the spacing of fixed supports L of the two cores 1a, 1b, when the cores 1a, 1b are heated from the temperature difference ΔT from room temperature to the maximum process temperature during the manufacturing process, the gap dimension S of the gap 2 will then decrease as a result of the coefficient of thermal expansion a, so that the setpoint thickness t2 of the fiber material 3 in 2. This is shown schematically in Figure 1b. The effective length of the nuclei 1a, 1b, which elongates and contributes to the closing of the gap S, is the spacing of fixed supports L from the two cores 1a, 1b. The gap dimension S between the two cores 1a, 1b does not constitute a freely adjustable parameter, but results directly from the spacing of the reinforcing elements, which must be formed by the fiber-based material 3 in FIG. the gap 2 over the entire length of the part, as well as the thermal expansion of the material of the cores and the prescribed thickness t2 prescribed.

The non-compacted thickness of the fiber-based materials 3 here differs from the desired target thickness t 2 by a compaction factor X so that the following relationship = tex. For low thicknesses, in the untemperature state, the fiber-based material 3 between adjacent cores 1a, 1b is thinner than the gap size S and the recesses on the neighboring cores. If the thicknesses become larger, by construction, as is necessarily the case for airliners because of the long wing lengths and the consequent increasing load in the inner zone of the wing, the Thermal expansion of tool cores runs up against a natural limit. The limit case is reached when the difference in thickness to be compacted by thermal expansion during the process reaches the absolute value of the thermal expansion of the tool cores, that is to say when ti = S. In this case , the tooling can just yet be closed and fiber material 3 to be introduced into the gap. For the maximum target thickness that can be obtained in the hardened state, the following equation can then be used: ## EQU1 ## where L is the spacing distance of fixed supports L two cores 1a, 1b, which determines the maximum displacement of the thermal expansion, where a is the coefficient of thermal expansion of the material used and AT is the temperature difference between the ambient temperature or the preforming temperature and the process temperature. The parameter x is here the compaction factor, as mentioned above. Apart from the compaction factor, all parameters of the equation are subject to imposed conditions. The temperature difference ΔT is determined by the cure temperature of the matrix system of the fiber-reinforced composite semi-product and is constant throughout the room.

For conventional epoxy matrix systems of fiber-reinforced composite structures, the curing temperature is 180 ° C, so that an AT of 160 ° C results when the fiber-based material is introduced at ambient temperature and arranged in the shaping tool. The spacing of the fixed supports L is fixed by the project of the part to be manufactured and 3026979 corresponds as a rule to the spacing of the individual reinforcing elements which must be formed by the gap 2. In the context of a mounting test with spacing of fixed supports L = 210 mm, temperature difference AT = 160 ° C, as well as aluminum tools with coefficient of thermal expansion a = 2.38 E-5 mm / K * mm , and a compaction factor x = 1.13, a maximum setpoint thickness t2 = 5.954 mm is obtained. In this case, the non-compacted fiber material 3 in the gap 2 is 13% thicker than the target thickness 10 t2 referred to the cured fiber reinforced composite part, in the gap 2. In the case more pre-compaction of the laminate during the preforming process to a thickness which is only 5% greater, the maximum possible setpoint thickness would be t2 = 14.809 mm. Elements to be made by the gap 2 of the cores 1a, 1b, and which must have a greater thickness, can no longer, for the same compaction, be manufactured, because the tool could no longer close and the fiber-based material 3 could no longer be introduced into the tool gap 2 available.

When defining the parameters necessary for the process, the maximum target thickness that can be obtained thus has a natural limit. According to the invention, it is therefore proposed to introduce into the tool gap 2 two pieces of fiber material 6a, 6b, the first part of fiber material 6a having a degree of compaction higher than the second portion of fiber-based material 6b. This is schematically shown in FIG. 2. The fiber-based material placed in gap 2 can thus be made up of 30 parts of more heavily pre-compacted, or fully hardened fiber-based materials, so that the natural limitation for the maximum setpoint thickness can be shifted to larger thicknesses. The global setpoint thickness T is here formally subdivided into two parts: t * pl and rp2, with pi + p2 equal to 1 and 0 <pi, p2 <1. The two parts of fiber-based material 6a, 6b therefore have two different degrees of compaction x 1 and x 2, which leads to completing the equation mentioned above in the following manner: ## EQU1 ## AT (p1x1 P2X2) The parameter xi here refers to the compaction factor of the partial fiber material 6a having the higher degree of compaction, while the parameter x2 refers to the second portion of the fiber material 6b to the material. fiber-based compacted weaker or uncompressed. The parameter p1 here designates the portion or fraction of thickness of the first portion of fiber-based material 6a with the higher degree of compaction, while pz denotes the portion or fraction of thickness of the second portion of material. fiber-based 6b with the compacted fiber material more weakly or uncompressed.

With the use of partially pre-compressed, partly or fully cured fiber materials 6a, the total thickness of the fiber reinforced composite member member to be formed by the tool gap can be increased. 2, without having to make any conceptual modifications to the tooling or changes in the position of the reinforcing element on the workpiece. Keeping the parameter values L, a and AT as described above and fixing xi = 1 and x2 = 1.13, this results in a 50% thickness of the first part of the material. fiber base 6a, i.e. pi = 0.5, a maximum attainable target thickness of t2, max. = 11.580 mm. This is almost a doubling compared to the conventional method. The first part of the fiber-based material used may for example be a separately manufactured preform which is introduced into the gap 2 of the tooling cores 1a, 1b. The first portion of fiber-based material is generally of a flat configuration and is adapted to the higher pre-compaction described, for example of a rail or a stiffener.

Figure 3 schematically shows a preferred arrangement, according to which the first portion of fiber material 6a of higher degree of compaction is arranged between the second portion of fiber material 6b, so that with respect to Since the forming cores 1a, 1b form the gap, the first portion of fiber material does not come into contact with the flanks of the shaping cores. This makes it possible, in particular, to obtain that preforms already made separately can, as first part of fiber-based material 6a, be fixedly connected to the overall structure of the part, and are then surrounded by connecting elements in the form of L in this area and consisting of the second portion of fiber material 6b.

The first portion of fiber material 6a may be provided for example with a film of glue on the joint surfaces so that the fiber material portions 6a and 6b can be attached to each other. the other. The treatment of the reinforcing layers as a first part of fiber-based material with a higher degree of compaction is carried out in a manner connected to the manufacturing in a partially closed tool under a vacuum film in an autoclave, for manufacture in closed tooling in an autoclave or press, respectively according to a pure prepregs process, a SQRTM (Same Qualified Resin Transfer Molding) process or a Liquid Composite Molding (LCM) process.

3026979 12 Nomenclature of marks: la, lb - forming or tooling cores 2 - gap 5 3 - fiber material in gap 4 - fiber reinforced composite part 5a, 5b - fixed supports 6a - first part of fiber material 6b - second part of fiber material 10 L - distance of fixed supports AT - temperature difference a - coefficient of thermal expansion t1 - uncompacted thickness ti of fiber material t2 - thickness set point 15 S - gap size from the first part of fiber material p2 - thickness share of the second part of fiber material x - compaction factor - compaction factor of the first portion of fiber material X2 - compaction factor of the second portion of fiber material

Claims (9)

Claims 1. A method for making a fiber reinforced composite member which is formed of a fiber material infused with a matrix material, the method comprising the steps of: a. providing and preparing a forming tool having a plurality of forming cores (1a, 1b), which can be arranged in the forming tool, forming a predetermined gap (2) between two setting cores in the form of neighbors, such that during the heating of the forming tool, at least one forming core is thermally expanded towards at least one gap, b. introducing fiber-based material and forming cores into the forming tool, the fiber-based material being placed in at least one interstice formed by the shaping cores, and c. curing the matrix material having been infused into the fiber material by heating the forming tool to manufacture the fiber reinforced composite member, characterized by d. introducing and arranging at least two portions (6a, 6b) of fiber-based material into at least one gap (2) formed by the shaping cores (1a, 1b), the first portion of the base material of fibers (6a) having as a preform a degree of compaction higher than the at least second portion (6b) of fiber-based material. 2. Method according to claim 1, characterized in that the at least two parts of material. fiber base are introduced and arranged in the at least one gap so that the first portion of fiber-based material is partially or completely enclosed by the at least second portion of fiber-based material in the interstice formed by the shaping nuclei. 3. Method according to claim 1, characterized in that the at least two parts of fiber-based material are introduced and arranged in the at least one gap in such a way that the first part (6a) of The fibers rest against one of the forming cores constituting the interstiye, and the second portion (6b) of fiber-based material rests against the other shaping cores constituting the interstice. 4. Method according to one of the preceding claims, characterized in that the first part (6a) of fiber-based material is a fiber reinforced composite preform partially or completely hardened. 3026979 14 5. Method according to claim 4, characterized in that the first part (6a) of fiber-based material is manufactured as fiber-reinforced composite preform by producing, by heating, the partial or complete hardening of a matrix material having been injected or infused into a compacted fiber-based material prior to introduction and arrangement of the first portion of fiber-based material into the gap or interstices of the dispensing tool; form. 6. Method according to one of the preceding claims, characterized in that the first part of fiber-based material and / or second part of fiber-based material is provided with glue prior to introduction into the gap. 7. Method according to one of the preceding claims, characterized in that the first part of fiber-based material occupies at least 10%, preferably at least 30%, and particularly preferably at least 50% of the width. or the volume of the part to be made, in the gap. The method according to one of the preceding claims, characterized in that the fiber reinforced composite part to be manufactured has one or more reinforcing elements, which is or are formed by the fiber-based material in the interstices. 9. A method according to claim 8, characterized in that the composite fiber-reinforced component to be manufactured is a wing shell, having one or more stiffeners or smooth as reinforcing elements.