FR2689809A1 - Forming thick, non-developable composite profiles - by placing blank between two sealed deformable bags creating vacuum between them, then applying pressure difference to form assembly to forming tool, without profile deformations - Google Patents

Abstract

Method of forming a composite material profile consists of placing a flat blank between two sealed deformable bags between which a vacuum is drawn before applying to that assembly a press. difference that forms the assembly over the forming tool. The pressure difference on the bags exerts a longitudinal tension to the blank due to tensioning devices fitted to the bag ends. USE/ADVANTAGE - Forming of composite material profiles partic. thick profiles or non-developable profiles for many inndustry sectors. The method elliminates large deformations in the profile such as creases or stretches.

Description

METHOD AND TOOLS FOR FORMING A THICK PROFILE
AND / OR NOT DEVELOPABLE IN COMPOSITE MATERIAL.

DESCRIPTION
The invention relates to a method for forming a profile of composite material, usable in particular for the forming of a thick and / or non-developable profile. The invention also relates to a tool for implementing this method.

 In many industrial sectors, the share taken by metal elements is gradually decreasing, in favor of the share taken by elements made of composite materials. This development is very noticeable, particularly in the aeronautical industry. It is mainly explained by the gain in weight which the use of composite materials provides for a given mechanical strength and by the possibility offered by these materials of producing structures having mechanical characteristics which differ from one direction to another. .

Another advantage provided by structures made of composite materials relates to the possibility of producing structures having non-planar shapes, without loss of material. Indeed, such shapes can be obtained directly by draping sheets of unidirectional fibers pre-impregnated with resin on a tool having a shape complementary to the shape to be produced. In addition, when the structure to be produced is not too thick and has a developable shape, it is possible to produce a planar blank by draping, then to give the final shape by applying the blank against a forming matrix. using a sealed and deformable bladder, on either side of which a pressure difference is created ensuring the desired deformation. The latter technique is illustrated, for example, by the document
US-A-4,664,737.

However, the techniques for manufacturing structures made of composite materials currently used are not satisfactory when these structures have large angulation zones preventing their direct manufacture by draping and when they are very thick and / or when they have a shape. not developable. In fact, if such a structure is manufactured using a technique of the type described in the document US
At 4,664,737, the forming of the blank on the die results in deformations which make the part unacceptable.

 Thus, FIG. 1 shows a profile 1 with an L-shaped section, of large thickness and of non-developable shape, manufactured using the forming technique described in document US-A4 664 737. The defects observed have been voluntarily accentuated to facilitate the explanation.

 The profile 1 has a substantially flat outer surface on the two parts of the L formed by the profile, and a stepped inner surface giving the profile a greater thickness in the two end parts la than in the central part 1b. The parts 1a and 1b are connected by transition zones lc, in which the thickness varies gradually. This configuration is the same in the main part 1D of the profile as in the part 1E folded down during forming. The shape thus defined is not developable. In addition, the profile has a relatively large thickness (for example about 30 mm in the end portions la).

 Under the effect of forming, it can be seen in FIG. 1 that two kinds of folds have formed in the sheets of fibers situated outside the profile.

The first of these folds, designated by the reference 2 2 in Figure 1, are located on the folded part 1E of the profile, and extend parallel to the folding angle 1F of the profile, near this angle, in the thicker end parts. Other folds, designated by the reference 3 in FIG. 1, are also formed on the folded part 1E of the profile, perpendicular to the folding angle 1F, along the zones of thickness change of the profile, these folds being the more marked the further away from the angle 1F.

 As also illustrated in FIG. 1, the forming of the profile has also led to a narrowing of the folded part 1E in the direction of the length of the profile, the more sensitive the further away from the folding angle 1F.

 As described in document US-A4 784 920, it is possible to remedy the drawbacks posed by the forming of a very thick profile by separately forming complementary thin profiles, then by assembling them so as to obtain the thick profile to be produced. However, this technique has the major drawback of being very long to implement, which makes it practically unusable industrially.

 The subject of the invention is precisely a forming process allowing the industrial manufacture of profiles made of composite materials which may have a large thickness and / or an undevelopable shape, without this forming causing significant deformations such as folds making the profile obtained unusable.

 In accordance with the invention, this result is obtained by means of a process for forming a profile of composite material, according to which a planar blank is placed on a forming matrix extending along a longitudinal axis of the profile to be formed, a first sealed and deformable bladder is placed on this blank, and this bladder is subjected to a pressure difference, so as to apply the blank to the matrix, characterized in that a second sealed bladder is placed and deformable between the blank and the die, a pressure below the atmospheric pressure and below the pressure prevailing on either side of the bladders is established between the first and the second bladder, and the said pressure difference is applied to on either side of the bladders, while exerting a tension on the blank along said longitudinal axis.

 By placing the workpiece blank between two bladders between which a vacuum is established and by exerting a longitudinal tension on the blank, the profile is formed in such a way that the folds and the necking which normally tend to form in the folded part of the profile, as described above with reference to Figure 1, essentially disappear.

 According to a preferred embodiment of the invention, the pressure difference is applied by creating between the second bladder and the matrix a pressure less than atmospheric pressure and greater than the pressure established between the bladders.

 Advantageously, the longitudinal tension is exerted on the blank by associating with the bladders organs that are substantially non-deformable along the longitudinal axis of the profile, at least in the first areas of the bladders located beyond the blank, along this longitudinal axis, and called to deform when the pressure difference is applied on both sides of the bladders.

 Preferably, the vies are also associated with bodies that are substantially non-deformable in second zones of these bladders adjacent to the first zones and with end parts of the blank, these second zones being located beyond a lateral edge of these end parts.

 The substantially non-deformable members may in particular consist of strips placed between the first and second bladders, these strips being made of a material capable of not sliding on the bladders when the pressure difference is applied on either side of these. Advantageously, this material can be the same as that in which the bladders are made.

 The invention also relates to a tool for forming profiles of composite materials, comprising a forming matrix extending along a longitudinal axis of the profile to be formed and on which can be placed a planar blank, a first waterproof and deformable bladder suitable to be placed on the blank, and first means for subjecting the bladder to a pressure difference, so as to apply the blank to the matrix, characterized in that it comprises a second sealed and deformable bladder, capable of be placed between the blank and the matrix, second means for establishing between the first and the second bladder a pressure lower than atmospheric pressure and the pressure established by the first means on either side of the bladders, and means of longitudinal tensioning of the blank, associated with the bladders to exert a tension on the blank along said longitudinal axis, during actuation of the first ers means.

A preferred embodiment of the invention will now be described, by way of non-limiting example, with reference to the accompanying drawings, in which
- Figure 1, already described, is a perspective view showing a profile of composite material, thick and non-developable, manufactured according to a conventional forming technique
- Figure 2 is a cross-sectional view showing a tool for forming a profile of composite material produced in accordance with the invention; and
- Figure 3 is a top view of the tool of Figure 2, after removal of the upper sealed bladder.

 Firstly, with reference to FIGS. 2 and 3, a forming tool will be described, making it possible, in accordance with the invention, to directly produce a profile of composite material which may have a relatively large thickness and an undevelopable shape, without this profile has unacceptable defects.

 In FIG. 2, the reference 10 designates a marble on which a forming matrix 12 is fixed, the upper part of which has a shape complementary to the interior shape of the profile to be formed.

The marble 10 also seals supports a frame 14 placed around the forming die 12, at a certain distance from the latter. The thickness of the frame 14 is substantially the same as that of the matrix 12, so that the upper faces 14a and 12a of the frame 14 and of the matrix 12 are located substantially in the same horizontal plane.

 The assembly formed by the marble 10, the matrix 12 and the frame 14 constitutes the fixed part of the forming tool, the latter further comprising mobile parts which will now be described with reference to FIGS. 2 and 3.

 These moving parts of the forming tool firstly comprise an outer bladder 16, sealed and deformable, mounted on a rigid frame 18 whose shape and dimensions are close to those of the frame 14.

 The movable elements of the forming tool also include an inner bladder 20, waterproof and deformable, also mounted on a rigid frame 22 whose shapes and dimensions are the same as those of the rigid frame 18. This rigid frame 22 is provided for be interposed in a sealed manner between the frame 18 and the frame 14, so that the frames 18 and 22 can be assembled and disassembled separately.

 More specifically, the frame 22 carrying the inner bladder 20 is provided on its face facing the frame 14 with sealing means allowing it to be applied in a sealed manner to the upper face of this frame 14. In a comparable manner, the frame 18 carrying the outer bladder 16 is provided on its face facing the frame 22 with sealing means allowing it to be applied in a sealed manner to the upper face of this frame 22.

 As shown schematically in FIG. 2, the bladders 16 and 20 are provided to be placed on either side of a blank of part 24, of planar shape, obtained by a prior draping operation, made for example using a draping machine. Thus, the blank for parts 24 is formed from a number of layers of unidirectional fibers preimpregnated with resin, the fibers of the adjacent layers being arranged in different directions. When the forming process according to the invention is used, the number of these layers can be greater than 100.

 Usually, separator films 26 are interposed between the blank of part 24 and each of the bladders 16 and 20. These separator films 26 have the function of facilitating the disassembly of the bladders and of the part in the presence of the resin impregnating the fibers. in draft 24.

 By way of example, the impervious and deformable material in which the bladders 16 and 20 are made can, for example, be latex, a polyamide or an elastomer. In the case where the composite material comprises a thermoplastic resin, the bladders can also be made of polyimide, or of super plastic aluminum.

 As shown schematically in Figure 2, the forming tool further comprises a pipe 28 for depressurizing the space 30 formed between the fixed part of the tool and the inner bladder 20. This pipe 28 is connected to a vacuum installation (not shown) making it possible to establish in space 30 a maximum pressure of the order of 0.1 atmosphere. The pipeline 28 crosses the plate 10 and opens onto the upper face of the latter between the forming die 12 and the frame 14.

 Furthermore, the end of a pipe 32 for depressurizing the space 34 formed between the bladders 16 and 20 is tightly fixed on the outer bladder 16. The opposite end of this pipe 32 is connected to a vacuum installation (not shown) making it possible to establish, in space 34, a pressure which can be controlled at any time. For example, the pressure prevailing in the space 34 may be between approximately 0.1 atmosphere and approximately 0.2 atmosphere.

 The strong depression established in the space 34 makes it possible, throughout the forming time, to keep the blank 24 tightly between the bladders 16 and 20. The depression created in the space 30 makes it possible to establish a difference in pressure between the atmospheric pressure prevailing outside the tool and the pressure prevailing in this space 30. This pressure difference acts on either side of the two bladders 16 and 20 between which is trapped the blank part 24 It has the effect of deforming the assembly thus formed, so as to make it conform to the shape of the forming matrix 12 as regards the part of this assembly situated above the matrix. One or two folded-down parts are thus produced, as the case may be, leading to the formation of an L-shaped or U-shaped section profile.

 As illustrated more precisely in FIG. 3, the forming tool further comprises complementary elements making it possible to ensure longitudinal tensioning of the workpiece blank 24 during forming, in order to oppose the formation of folds on the folded part (s) and at the longitudinal constriction of these parts.

 To obtain this longitudinal tensioning, there are placed between the bladders 16 and 20, at locations which will be specified later, members that are substantially non-deformable along the longitudinal axis of the blank. In the embodiment illustrated in FIG. 3r, these substantially non-deformable members consist of strips 36a and 36b arranged side by side along the longitudinal axis of the part and made of a material capable of not sliding on the bladders 16 and 20 when these are deformed during forming. It will be understood that these bands 36a and 36b then have the effect, in the zones in which they are located, of preventing or significantly reducing the elongation of the bladders 16 and 20 in the longitudinal direction of the part, which is reflected by applying a longitudinal tensile force to the blank during forming. In order to avoid any slippage between the strips 36a and 36b and the bladders 16 and 20, a material is chosen to produce the strips whose coefficient of friction with the material constituting the bladders is very high. Such a result can advantageously be obtained by producing the strips 36a and 36b in the same material as the bladders 16 and 20.

 As illustrated more precisely in FIG. 3, the strips 36a are oriented along the longitudinal axis of the blank and placed in two first zones situated beyond the longitudinal ends of a part 24E of the blank 24 intended to be folded down during forming. These bands 36a, which are for example three in number in each of the zones considered, prevent or greatly limit the deformation of the bladders 16 and 20 in these zones during forming, which then results in the application of a tension on the blank 24, in the longitudinal direction thereof, on the folded portion 24E.

 The strips 36b are also oriented along the longitudinal axis of the blank. In addition, they are placed in second zones adjacent to the first zones in which the strips 36a are located.

More precisely, these second zones are situated beyond the lateral edge 25 of the part 24E of the blank 24 folded down during forming and they are adjacent to the strips 36a as well as to the longitudinal end parts of the blank 24. The strips 36a may for example be two in number in each of the second zones considered, as shown in FIG. 3.

 By being placed beyond the lateral edge 25, the strips 36a exert a tension oriented obliquely on the blank 24. More precisely, this tension has a longitudinal component comparable to the tension exerted by the strips 36a, as well as a component transverse, oriented towards the outside of the blank, applied to the ends of the folded-down portion 24E of the blank, during the forming thereof.

 As shown in FIG. 3, the quality of the forming can be further improved by doubling, on the side of the blank 24, each of the bladders 16 and 20 by means of a reinforcing plate 38, advantageously made of the same material as the bladders 16 and 20, and by placing on each of the longitudinal ends of this reinforcing plate 38 a reinforcing tape 40 on which the strips 36a and 36b are placed. The reinforcing tapes 40 are also advantageously made of the same material as the bladders 16 and 20. In addition, they thus have the reinforcing plate 38, substantially the same thickness as the bladders. Finally, the strips 36a and 36b have a thickness such that the total thickness of the stack in line with these strips is substantially the same as the thickness of the stack in line with the blank 24.

 Furthermore, edging strips 42 are advantageously placed on the longitudinal ends of the blank 24 as well as along the longitudinal edge opposite the part 24E folded down during forming.

 When the tool which has just been described is used, by applying in the space 34 a vacuum between approximately 0.1 atmosphere and 0.3 atmosphere and by applying in space 30 a vacuum between approximately 0.5 atmosphere and about 0.6 atmosphere, one or two folded-down parts are produced on the blank 24, depending on the shape of the forming die 12. In addition, the initially planar shape of the blank 24 may become non-developable if the forming surface defined by the matrix 12 is non-developable.

 However, thanks to the maintenance of the blank 24 between the bladders 16 and 20 throughout the forming and thanks to the application on this blank of a longitudinal tension thanks to the strips 36a and 36b, the part obtained is practically devoid of folds. and shrinking, even if it is a thick profile and / or having an undevelopable shape.

 Of course, the invention is not limited to the embodiment which has just been described by way of example, but covers all its variants. In particular, the invention applies to the forming of any type of profile in composite material having a relatively small thickness compared to the other dimensions, whatever the application concerned and the nature of the composite material. Thus, in the particular case of the manufacture of the profiles used in the composition of aircraft, the method and the tool according to the invention can be used, for example, for the forming of the wing spars, of the panel elements. autoraidis and fuselage frames. Furthermore, the composite material in which the profile is made can be an organic, ceramic or metallic type material, comprising, as the case may be, a thermoplastic, thermosetting or metallic matrix and reinforcing fibers which can be continuous, long or short. Finally, it should be noted that the longitudinal tensioning of the blank can be obtained by different means, which can for example be an integral part of the bladders.

Claims (11)

 1. A method of forming a profile of composite material, according to which a flat blank (24) is placed on a forming die (12) extending along a longitudinal axis of the profile to be formed, a first sealed bladder is placed and deformable (16) on this blank, and this bladder is subjected to a pressure difference, so as to apply the blank to the matrix, characterized in that a second sealed and deformable bladder (20) is placed between the blank and the matrix, a pressure is established between the first and the second bladders (16,20) lower than atmospheric pressure and lower at all times than the pressure prevailing on either side of the bladders, and the applying said pressure difference on either side of the bladders, while exerting tension on the blank along said longitudinal axis.  2. Method according to claim 1, characterized in that the said pressure difference is applied by creating between the second bladder (20) and the matrix (12) a pressure below atmospheric pressure and greater than the pressure established between the bladders (16,20).  3. Method according to any one of claims 1 and 2, characterized in that one exerts said tension on the blank by associating with the bladders (16,20) organs (36a) substantially non-deformable along said longitudinal axis, at less in first zones of said bladders located beyond the blank (24), along said longitudinal axis, and called to deform when the pressure difference is applied on either side of the bladders.  4. Method according to claim 3, characterized in that also associated with the bladders organs (36b) substantially non-deformable in second zones of the bladders adjacent to the first zones and to end portions of the blank, and located beyond a side edge (25) of these end portions.  5. Tooling for forming profiles in composite materials, comprising a forming matrix (12) extending along a longitudinal axis of the profile to be formed and on which can be placed a planar blank (24), a first waterproof and deformable bladder ( 16) able to be placed on the blank, and first means (28) for subjecting the bladder to a pressure difference, so as to apply the blank to the matrix, characterized in that it comprises a second bladder waterproof and deformable (20), suitable for being placed between the blank and the die, second means (32) for establishing between the first and the second bladders (16,20) a pressure below atmospheric pressure and under pressure established by the first means on either side of the bladders, and longitudinal tensioning means (36a, 36b) of the blank, associated with the bladders to exert a tension on the blank along said longitudinal axis, during 'an actio first means.  6. Tool according to claim 5, characterized in that the first means (28) are means for establishing between the second bladder (20) and the matrix (12) a pressure below atmospheric pressure and above the established pressure between the bladders by the second means (32).  7. Tool according to any one of claims 5 and 6, characterized in that the longitudinal tensioning means comprise members (36a) substantially non-deformable along said longitudinal axis, associated with the bladders (16,20) at least in first zones thereof located beyond the blank, along said longitudinal axis, and called to be deformed upon actuation of the first means.  8. Tool according to claim 7, characterized in that it also comprises members (36b) substantially non-deformable, associated with the bladders in second zones adjacent to the first zones and with end parts of the blank, and located beyond a side edge (25) of these end portions.  9. Tool according to any one of claims 7 and 8, characterized in that said substantially non-deformable members are strips (36a, 36b) placed between the first and second bladders (16,20), in said areas, and made of a material capable of not sliding on the bladders during actuation of the first and second means (28,32).  10. Tool according to claim 9, characterized in that the strips (36a, 36b) and the bladders (16,20) are made of the same material.  11. Tool according to any one of claims 5 to 10, characterized in that the bladders (16,20) are mounted on two frames (18,22) removable separately.