EP0162097A1

EP0162097A1 - Process for fabricating hollow rigid structures made of fibers impregnated with resin, device for implementing such process and structure obtained thereby

Info

Publication number: EP0162097A1
Application number: EP19850900127
Authority: EP
Inventors: Georges Boitelle
Original assignee: SEPTEM SA
Current assignee: SEPTEM SA
Priority date: 1983-11-28
Filing date: 1984-11-22
Publication date: 1985-11-27
Also published as: WO1985002365A1; FR2555501A1

Abstract

Procédé de fabrication de structures creuses caissonées (figure 1B) réalisées en une seule opération de polymérisation et renforcée de mèches de fibres (27). Le procédé utilise des mandrins rigides recouverts de gaines gonflables que l'on drape de nappes de fibres et que l'on dispose en même temps que les mêches de fibre dans un moule (figure 4) au profil externe de la pièce finie à l'intérieur duquel s'effectue la polymérisation après gonflage des gaines élastiques. La réalisation en série de telles structures par le procédé décrit ne nécessite pas d'étuve ou d'autoclave.Method for manufacturing boxed hollow structures (FIG. 1B) produced in a single polymerization operation and reinforced with wicks of fibers (27). The process uses rigid mandrels covered with inflatable sheaths which are draped with sheets of fibers and which are placed at the same time as the fiber wicks in a mold (FIG. 4) with the external profile of the finished part. inside of which polymerization takes place after inflation of the elastic sheaths. The serial production of such structures by the method described does not require an oven or autoclave.

Description

Method for manufacturing hollow rigid structures made of resin-impregnated fibers, device for its implementation and structure obtained.

The present invention relates to a method for manufacturing hollow rigid structures produced from sheet material of fibers impregnated with resin, as well as to a device for carrying out the method. It also relates, as an industrial product, to the structures obtained according to the process. Although the invention can be the subject of various applications in various fields of industry, it has very particular advantages in aeronautics in particular for the constitution of structures of complex shapes which must combine perfect mechanical resistance with lightness as well. great as possible. This is the reason why the invention will be exposed by reasoning from structures used in aeronautics without this being a desire to limit the invention.

In general, rigid hollow structures, such as aircraft wings for example, currently consist of an outer skin defining two walls spaced from one another and stiffened by a series of ribs and internal beams. This organization is characteristic of metal construction where the skins, ribs and beams are linked most of the time by riveting. When the coverings, the ribs and the side members are made of fibers impregnated with resin, the structure remains the same and the riveting is replaced by bonding of the elements. This known process for producing rigid hollow structures made of resin-impregnated fibers is long to implement, requires numerous and delicate operations to be carried out as much as to control, sophisticated equipment (autoclave) and requires a very long manufacturing cycle qyi is not compatible with mass production. However, this method has drawbacks with regard to the final product obtained. Indeed, the forces applied during the use of the parts often cause detachments at the points of connection of the elements. Gluing cannot be carried out in complete safety whatever the shape of the part, so that it is often necessary to add metal parts to reinforce the connections. The present invention provides a new method for manufacturing rigid hollow structures which makes it possible to obtain a one-piece structure, produced in a single polymerization operation and entirely made of fiber materials impregnated with resin.

To this end, the invention, in its most general aspect, relates to a new process for the manufacture of hollow rigid structures produced from materials in sheets of fibers impregnated with polymerizable resins, characterized in that

- Preparing a rigid mandrel equipped on its periphery with an elastically deformable flexible envelope

- The plies of fibers are placed on the flexible envelope in such a way that the said plies can slide over one another.

- We enclose the assembly thus formed in a mold whose rigid walls are spaced from the sheets of fiber beforehand. completely impregnated with resin.

- After heating, the flexible envelope is caused to expand until the layers of fibers come into contact with the walls of the mold and the resin is polymerized.

- Then what causes the flexible envelope to be retracted and the entire mandrel-polymerized structure that is separated from one another is extracted from the mold, the mandrel being able to be recovered for other operations. For the production of large rigid hollow structures of complex shape which must have a continuous external wall and multiple internal cavities separated by partitions stiffening the external wall as is the case in particular for aircraft wings, the method according to invention is characterized in that:

- Preparing several mandrels of section adapted respectively to each part of the desired final shape, mandrels equipped with a flexible envelope and each coated with sheets of fibers capable of moving relative to each other.

- These coated mandrels are placed side by side in a mold, taking care that the plies of fibers impregnated with resins coating each mandrel are separated from the other plies and from the wall of the mold. - It covers all the mandrels coated with a second series of layers of fibers.

- the mold is closed and, after heating, the flexible envelopes are caused to expand in order to press the sheets of fibers previously impregnated with resin against each other others and against the walls of the mold then which ensures the polymerization of the resin.

- Then the flexible envelopes are retracted to extract the final structure from the mold, which is separated from the mandrels.

According to a particular aspect of the invention, it is possible to avoid the use of large-sized heating enclosures necessary in conventional processes by ensuring polymerization by the addition of heat in the zone situated on the internal side of the deformable envelope. That is to say either in the chamber formed between the mandrel and the deformable envelope or by circulation inside the mandrel of a heat fluid. This technique has the following advantages: the amount of energy required to the polymerization is less than that used in the heating chambers, the temperature distribution is more homogeneous since the thermal inertia of the external mold is neutralized, finally, the time required for the temperature rise and cooling are considerably reduced. In addition, the deformations of the external mold during the rise in temperature are reduced, thus allowing better precision.

Likewise, after polymerization, the cooling of the part can be improved by ensuring the forced circulation of a cooling fluid either between the deformable envelope and the mandrel or preferably inside the mandrel itself.

The device that is the subject of the invention therefore makes it possible, among other things, to significantly reduce the times necessary for temperature stabilization of the mold and cooling of the assembly to shorten the manufacturing cycles.

The device for implementing the method is characterized in that it comprises at least one hollow rigid mandrel on which is threaded an elastically deformable envelope, a means for at least locally expanding the deformable envelope to separate it from the hollow mandrels , means for mounting and immobilizing the envelope mandrel assembly in a mold so that the periphery of the envelope is spaced from the walls of the mold before the expansion phase

Finally, the invention relates, as a new industrial product, to a hollow rigid structure comprising a continuous peripheral surface forming the upper and lower faces of the cells extending over the entire length of the structure and of the partitions connecting the upper and lower faces over the entire length of the structure and separating the cells from each other, the said structure being produced in a single block from materials in layers of fibers impregnated with resin.

The advantages of the present invention are manifold, but we will especially mention the following: - 1 - simultaneous polymerization (or baking) of the outer skins of the structure and the internal stiffeners, which results in the elimination of any sticking and a reduction in the overall mass of the structure with equal mechanical characteristics. - 2 - cortrôlable evacuation of air and resin contained in the sheets of fibers during the polymerization by acting on the inflation pressure of the deformable envelope which allows to obtain a product of the required quality. - 3 - manufacture of rigid structures of great lengths with local resistances perfectly mastered and adapted to needs thanks to an internal distribution of stiffenings according to the profile cut and thanks to the possibility of modulating the thickness of the layers of fibers according to the locations.

- 4 - removal of large autoclaves required in known processes.

- 5 - possibility of introducing wicks of fibers under the outer skin to improve the mechanical characteristics of the structure in tension or compression.

An embodiment of the invention will now be described, by way of nonlimiting example, with reference to the appended drawings in which:

- Figure 1a shows schematically, with partial cutaway, an airplane wing structure produced according to known techniques;

- Figure 1b schematically shows a wing obtained by the method according to the invention;

- Figure 2 is a longitudinal section of a mandrel used to implement the method of the invention;

- Figure 3 is a cross section of the mandrel of Figure 2;

- Figure 4 shows a half mold being fitted with mandrels; - Figure 5 is an elevational view of the closed mold;

- F igure 6 is a section of the mold along line 6-6 of Figure 5 containing the structure obtained according to the invention; - Figure 7 shows a drain; and FIGS. 8 to 8d show different configurations of structures which can be obtained according to the method of the invention.

As can be seen in FIG. 1a, the current conventional process for manufacturing a hollow structure such as an airplane wing consists in placing a series of perforated ribs N in the transverse direction of the wing, these ribs having the profile of the section of the wing and being spaced from each other and rigidly held together by the longitudinal P-beams. The whole is covered with a skin E which completely envelops ribs and beams. FIG. 1b shows in comparison the structure of a similar wing obtained according to the method of the invention and in which all the elements are made of fibers impregnated with resin forming a single block consisting of a surface skin S stiffened by internal walls I constituting a series of non-deformable related hollow boxes.

The basic method of the invention will now be described with reference to FIGS. 2 and 3. In order to obtain a hollow structure with a single box, a hollow mandrel 1 is used, the section of which may be any, but preferably has a polygonal shape which approaches the final shape of the Turkish structure as shown in FIG. 3 comprising two lateral faces 2, two sides 3 upper and lower and four inclined faces 4.

The mandrel must be very rigid to withstand radial crushing forces during the pressurization and therefore, preferably, must be made of metal with internal reinforcing ribs 5 stiffening each face. The inner chamber 6 of the mandrel is obstructed at its end by cheeks 7. Inside the chamber 6 are provided ducts 8 of pressurized air inlet which are connected to orifices 9 formed in the wall of the mandrel. The pipes 8 pass through the cheeks 7 at the end of the mandrel and are connected on the one hand to a source of pressurized air not shown and on the other hand to a suction system not shown. The mandrel 1 is covered on its periphery with an envelope 10 or sheath made of elastically deformable flexible material, the ends of which are forcefully clamped (in a leaktight manner) between flanges 11 of the mandrel and sealing flanges 12 fixed on the mandrel. A sealed chamber 13 is thus provided between the mandrel and the sheath, a chamber into which the pipes 8 for the arrival of air flow under pressure, thereby ensuring the expansion of the envelope or its retraction at will.

At the center of the cheeks 7 of the mandrel are fixed two hollow supports 13 intended to ensure the seat of the mandrel in a mold as will be seen with reference to FIG. 4. These supports are connected to pipes 14 - 15. The pipe 14 provides the introduction of a heat fluid or a cooling fluid inside the chamber of the mandrel while the tube 15 ensures the evacuation of these fluids. For this purpose the pipes 14 and 15 are selectively connected to sources of hot or cold fluids (water or gas for example) not shown

The mold intended to receive a series of mandrels like that of FIG. 3 is shown in FIGS. 4 to 6. The lower part 16 of the mold has an imprint 17 on the lower face of the final structure to be obtained and the upper plate 18 has a imprint 19 of the upper face of the structure. The junction plane of the mold comprises a number of seats 20 in which are intended to rest the supports 13 of the mandrels which will therefore protrude from the mold. The mold also has passages for the pipe 8 for supplying pressurized fluid. An orifice 21 is also provided to create a slight depression inside the mold, this orifice being connected by a pipe 22 to a suction device not shown.

The implementation of the process is carried out in the following manner: the sheath 10 not being inflated, a series of fiber layers 23-24 is draped first of all on the mandrels 1 so that the layers can follow the expansion of the sheath 10. Preferably, as shown in FIG. 3, one or more plies 23 covering a little more than the upper half of the mandrel will be used alternately with one or more plies 24 covering a little more than the lower half of the mandrel so that the edges of the plies overlap, however allowing their relative free movement. The lower part 16 of the mold is prepared by covering the imprint 17 with one (or more) ply 25 then the mandrels coated with the fiber plies are placed in the mold. We cover all of the mandrels with one (or more) ply, upper matching the imprint 19 of the upper plate of the mold and the mold is closed. Naturally, all the layers of fibers are impregnated with resin as is well known. It will be noted that in this position, the layers of fibers draping the mandrels are spaced from the mold cavities and they are spaced from one mandrel to the other in order to allow the expansion of the inflatable sheaths 10.

Furthermore, it is possible preferably to place in the areas left free between the inclined faces 4 of two successive mandrels of the wicks or drains 27 as shown in FIGS. 7 and 4. These drains which can for example have the shape of a half cylinders as in the drawings comprise a hollow hollow core 28 and porous (for example pierced with a multitude of holes) coated with a sleeve 29 of fibrous material impregnated or not with resin. The purpose of this drain is to capture air bubbles and excess resin discharged from the mold holes where the fiber sheets are subjected to significant pressure during the polymerization. These drains are intended to remain embedded in the final structure by making an accessory reinforcement. The drains are placed in the mold before closing by inserting them into the housings 30 provided in the mold (see FIG. 4). It will be noted that these drains can possibly protrude horidu from the mold in order to connect them, to a suction device for create a slight aspiration and strengthen their drainage role. Note that it is possible to improve (for very precise parts) the relative prior positioning of the draped mandrels and the drains by exerting traction on the ends protruding from the mold of the mandrels and drains, whether the assembly is in a horizontal position or in a vertical position.

When the mold is closed, the assembly begins to heat by circulating a hot fluid in the interior chamber of the mandrel through the pipes 14-15. It will be noted that, as a variant, the heating could advantageously be obtained by a series of electrical resistors (heating cords) 32 fixed to the wall of the mandrel in the space reserved between the latter and the deformable sheath 10 as shown in the figures. 6 and 3.

When the desired viscosity of the resin is reached, the sheaths 10 are inflated by admitting the fluid under pressure through the pipes 8. The sheets of impregnated fibers are then pressed against each other, an inflation control being able to be provided to ensure spontaneous and correct placement of the tablecloths.

When the polymerization is complete, the assembly is cooled from the inside of the beams by circulating a cooling fluid either through the pipes 8 or through the pipes 14-15.

When the cooling is sufficient, the sheaths 10 are deflated, the mold is opened and the mandrels are extracted from the final structure. It will be noted that the progressive inflation of the sheaths 10 ensures progressive contacting of the layers of excess fibers in the direction of the spaces occupied by the drains.

The triangular cavities that remain between the plies of the boxes and the outer buckets are therefore filled with resin and the drain so that the external skin is supported even in this place which is not directly in contact with the fiber sheets of the boxes. Depending on the composition of the rigid core of the drain, the latter may be used to improve the mechanical characteristics of the structure in tension and / or in compression. Finally, it should be noted that the (non-descriptive) examination of the additional resin accumulated in the drain provides a useful indication of the forces undergone by the structure during its operational use; security is thus improved.

Furthermore, it will be understood that by using sheaths 10 not having a constant thickness, it will be possible to modulate the shape or the section of the final product or to obtain a differentiated evolution of the pressures from one zone to another.

The forms that can be obtained by the method are numerous and there are shown in Figures 8a, 8b, 8c, 8d some examples of possible embodiments.

For simplicity, the descriptions of the process which have been made assume that fibers impregnated with resins which polymerize under heat are treated. It is obvious that the same process, excluding the heating (and possibly cooling) means, applies to the treatment of fibers impregnated with resin which polymerize when cold.

Claims

CLAIMS 1 - Method for manufacturing hollow rigid structures of complex shapes made from materials in layers of fibers impregnated with polymerizable resins and which must have an outer wall continuous envelope stiffened by internal partitions forming with the outer wall multiple cavities characterized in that

- Several mandrels of section adapted respectively to each part of the desired final shape are prepared, mandrels equipped with the deformable envelope.

- The plies of fibers are placed on each of the mandrels equipped so that the said plies can slide over one another. - These coated mandrels are placed side by side in a mold.

- We cover all the mandrels coated with a second series of layers of fibers.

- The mold is closed, the controlled envelopes are caused to expand in order to press the sheets of fibers previously impregnated with resin against each other and against the walls of the mold, after which the pol yméri sati on of the resin is ensured.

- Then we cause the shrinkage of the flexible envelopes, we extract the final structure of the mold and we separate the mandrels which can be reused for other operations. 2 - A method according to claim 1 characterized in that it ensures the polymerization of the resin by supplying heat in the area located on the inner side of the deformable envelopes. 3 - Method according to any one of claims 1 to 2 characterized in that after polymerization is provided a forced cooling of the final structure by cooling the area located on the inner side of the defσrmable envelopes using a cooling. 4 - Method according to one of claims 1 to 3 characterized in that one clears spaces between the sheets of fibers carried by two successive mandrels and the outer skin so that the air bubbles and the resin contained in excess in the layers of fibers can be concentrated there during the expansion of the envelopes. 5 - Method according to claim 4 characterized in that it promotes the migration of air and excess resin to the free spaces by creating in them a slight depression. 6 - Process according to any one of claims 4 to 5 characterized in that the free spaces are filled with a clean drain to absorb the excess resin such as a wick of fibers. 7 - Salt process on which one conch of the sells cati ons 1 to 3 characterized in that, in the free spaces located between the mandrels previously coated with fibers impregnated with resin and the external skin, there are rigid drains extending over the entire length of the mandrels and consisting of a hollow core whose wall is perforated and of a peripheral sheath advantageously made of fibers intended to play the role of wick to capture the resin, the hollow core being able to be put under vacuum for promote the evacuation of air and excess resin.

8 - Process according to any one of the preceding claims, characterized in that the number of equipped mandrels is reduced to one. 9 - Device for implementing the method according to any one of the preceding claims, characterized in that it comprises at least one hollow rigid mandrel on which is threaded an elastically deformable envelope, means for at least locally expanding the envelope deformable in order to move it away from the hollow mandrels, means for mounting and immobilizing the mandrel-envelope assembly in a mold so that the periphery of the envelope is separated from the walls before the expansion phase of the envelope. 10 - Device according to claim 9 wherein the deformable envelope is fixed in sealed manner to the mandrel outside the sone to be deformed.

11 - Device according to any one of claims 9 to 10 characterized in that the means for expanding the deformable envelope are constituted by a series of tubes housed inside the mandrel, these tubes being connected to orifices practiced in the periphery of the mandrel and opening into the space between the mandrel and the deformable envelope, said tubes being connected to a source of pressurized fluid by their other end.

12 - Device according to any one of claims 9 to 11 characterized in that the mandrel-envelope assembly is equipped with heating and cooling means acting in the area located inside the deformable envelope.

13 - Device according to any one of claims 9 to 12 characterized in that the mandrels have the form of tubes of polygonal section.

14 - As an industrial product, a new hollow rigid structure comprising a continuous peripheral surface forming the upper and lower faces of the cells extending over the entire length of the structure and of the partitions connecting the upper and lower faces on the entire length of the structure and separating the cells from one another, the said structure being produced in a single block from materials in layers of fiber impregnated with resin. 15 - Structure according to claim 14 characterized in that each cell is delimited by a first internal series of layers of fibers and in that a second external series of layers of fibers surrounds all of the cells, the partitions being obtained by portions of the first internal series of tablecloths.

16 - Structure according to any one of claims 14 and 15 characterized in that wicks of fibers are inserted under the second external series of plies and in the extension of each partition, these wicks being embedded in the resin and extending in the length of the structure.