Patent Application
20080305701
The invention relates to the field of the manufacture of composite parts, by resin injection or infusion moulding processes.
The invention relates more precisely to the textile complexes used for the manufacture of these composite parts, and more specifically a complex suitable for producing three-dimensional parts requiring the use of a preformed reinforcement.
It is a particular object of the invention to facilitate the operations associated with the manufacture of these preforms, particularly to facilitate their transport and storage, and to limit the handling operations during the manufacture of the composite part.
In general, the manufacture of composite parts by moulding processes, whether by injection or infusion, requires the placement of a reinforcing textile structure which is then impregnated with a resin. After this resin is cured, the reinforcement imparts a certain stiffness and strength to the composite part. In the case of three-dimensional parts having complex shapes, a number of operations are necessary to ensure that the textile reinforcing layers perfectly match the outer shape of the part to be manufactured. It is in fact important, for reasons of mechanical performance, for the reinforcing layer to be as close as possible to the future outer face of the composite part.
Thus, one widely used technique for placing the reinforcement consists in cutting out a textile complex in the shape of the three-dimensional part and then manually placing the cutout complex in the injection mould. It is clear that this technique is more suitable for almost flat parts than for three-dimensional parts. This is because the textile complex is obviously manufactured in the flat state, and it is necessary to perform cutouts, folds, and other draping operations to ensure that the reinforcement matches the shape of the part to be manufactured, with the minimum possible stretching. In the case of complex shapes, this technique may prove to be problematic, insofar as the pieces of cutout reinforcement have a natural tendency to sag.
Another known technique consists in spraying reinforcing fibres and a binder of these fibres directly into the injection mould, of which typical examples are processes having the trade name “P4” and “RimFire”. The reinforcement thus being produced directly in the mould, it is clear that it has the exact shape desired. However, the production of the reinforcement of these conditions, directly in the injection mould, does not guarantee an homogeneous, uniform thickness of the reinforcement, insofar as, before fixation of the binder, the fibres will naturally tend to move under the effect of gravity. Nor is the addition of a large quantity of binder more satisfactorily insofar as this binder may then hinder the drainage and flow of the resin, and above all, degrade the surface appearance of the composite part.
This is why it has already been proposed to use preformed reinforcements, that is almost having the final shape of the mould. Such reinforcements are thus produced by weaving and stitching operations to the shape of the desired part. It is clear that this type of operation is relatively long and must be repeated according to a pattern defined for each mould. This technique is therefore difficult to apply on an industrial scale, at least at reduced production cost.
Other types of preforms are produced from reinforcements combined with a binder which gives them a certain stiffness. Such reinforcements have the advantage of being producible independently of the manufacture of the injected part. However, the production of preforms, in particular rigid preforms, has drawbacks in terms of size, particularly for storage and transport. Furthermore and above all, these reinforcements are produced by hot pressing, which does not allow the exact production of the geometry of the final part, and requires costly moulds and presses.
It is therefore an object of the invention to produce preformed reinforcements offering great ease of transport, while being easy to produce, that is without requiring large scale investment. A further object of the invention is to produce reinforcements which impart optimal mechanical properties to the parts on which they are mounted, that is which have a weight and uniformity of thickness adapted to the composite parts that they reinforce, without any deterioration in the final mechanical performance by the preforming operation.
The invention therefore relates to a textile complex intended to be used as reinforcing layer for the manufacture of three-dimensional composite parts, by resin injection or infusion processes. Conventionally, such a complex therefore includes a reinforcing layer based on reinforcing fibres, which may be highly varied, particularly based on glass, carbon, aramide or other synthetic fibres.
According to the invention, this complex is characterized in that it comprises, on one of its faces, a thermoplastic-based fixing layer, which has an almost zero cold elongation. This material has a melting point which is lower than the melting point of the other materials of the complex, so as to melt at least partially, before the materials of the textile layer are degraded. Complementarily, the said fixing layer is apertured to allow the passage of the injected or infused resin during the manufacture of the composite part.
In other words, the complex according to the invention comprises a layer which is combined loosely with the textile reinforcing layer. This layer may be joined to the textile layer when the complex is placed in a preformed mould, and then heated sufficiently so that the said fixing layer softens and adheres to the reinforcement. After cooling, this fixing layer is joined at a large number of points to the textile reinforcing layer, so that at the fold zones, for example, this fixing layer maintains a sort of surface tension in the textile reinforcement.
The fact that the thermoplastic is not cold-extensible serves to impose a dimensional stability of the complex when the fixing layer is cooled. The non-extensible character, or the almost zero elongation, applies under normal stresses observed in the manufacture of preformed reinforcements.
The complex can thus be deformed, and particularly folded for its transport, and then recover its original shape when unfolded. In other words, this type of complex serves to obtain flexible or predraped preformed reinforcements, which can therefore be handled and folded without necessarily losing the geometry which had been imparted to them initially. The preformed reinforcement thus has a sort of shape memory which enables it to undergo easy handling and particularly a very compact size for its transport and storage.
It is clear that the addition of this fixing layer can be advantageous for many types of reinforcement, insofar as the fixing layer has a capacity to adhere to the textile layer, and a compatibility with the resin to be employed in the manufacture of the composite parts.
Thus, the complex according to the invention can integrate various types of reinforcing layer, whether woven, uni- or multidirectional textiles, or even textile reinforcements including several superimposed fibre layers, and for example superimpositions of laps of yarns oriented in different directions, of the “cross-ply” type. Mention can also be made of the textile reinforcements including a central layer performing a drainage function, acting as a spacer between two reinforcing layers, in order to permit the resin to flow during the injection or infusion process. Combinations of various reinforcing layers can also be employed, in association with the characteristic fixing layer.
In practice, the characteristic fixing layer can be prepared in various ways, according to the application and the type of textile reinforcement which it accompanies.
In a particularly advantageous embodiment, this fixing layer may consist of a thermoplastic film, compatible on the one hand with the textile reinforcement in terms of adhesion, and compatible on the other with the resin that is employed in the injection process.
Such a film has the advantage of having a surface that comes into contact with the textile reinforcement via many points which are defined at the time of the placement of the reinforcement in its final configuration.
Advantageously, this film can be stitched with the textile reinforcing layer, or at least, with part of the reinforcing layer when the latter comprises a plurality of superimposed layers. The points of passage of the stitching yarn constitute opening zones of the film when the latter has been heated to be joined to the reinforcement. In other words, the passage holes of the stitching yarn constitute openings allowing the passage of the resin during the injection process. Thus the characteristic film only marginally hinders the passage of the resin during the injection or infusion process.
The fixing layer may also be prepared of a grid itself composed of thermoplastic yarns, or a sticky film with an adhesive compatible with the textile reinforcement, and with the resin that will impregnate the said reinforcement.
In practice, the fixing layer may be combined with the textile reinforcing layer by a stitching or partial bonding operation, in order to form a complex that can be subsequently used to manufacture preformed reinforcements. The fixing layer may also be associated with a textile reinforcing layer at the actual time of production of the preform.
In this case, the procedure first consists in placing one or more textile fibre-based reinforcing layers in a preform mould. Then, the fixing layer is placed above the textile reinforcing layer or layers. The fixing layer, maintained in the preform mould, is then exposed to a heat source, in order to cause it to melt partially and be joined to the textile reinforcing layer.
Subsequently, when the fixing layer has cooled, it is joined at many points to the textile reinforcing layer, so that it maintains the latter in its configuration bent to the shape of the mould.
Various holding means can be employed to guarantee good contact between the fixing layer and the fibrous reinforcing layer. Among the means yielding good results, mention can be made of suction systems, which apply suction from the preform mould through the reinforcing layer, so that the fixing layer is pressed against the reinforcing layer before exposure to the heat source.
The characteristic fixing layer can be employed complementarily, to ensure the joining of the precut zones of the textile reinforcing layer. In other words, the fixing layer serves to join various widths of the reinforcement which face one another after folding inside the preform mould.
In the case of the use of an adhesive fixing layer, it can be placed cold, by bonding to the required locations.
The fixing layer may also serve to immobilise complementary members, such as foam or other inserts, inside the preform.
The manner of implementing the invention, and the advantages thereof, clearly appear from the description of the embodiments that follow, in conjunction with the appended figures in which:
As already stated, the invention relates to a complex that can be used to manufacture a flexible preformed reinforcement, usable in resin injection or infusion moulding processes.
Various textile reinforcing layers can be used, such as for example a warp and weft woven textile, as shown in
The fixing layer (3) is joined in the example in
In certain cases, the thermoplastic film (3) may integrate pre-prepared perforations, increasing the passage flow area of the resin. If a larger passage area is desired, the film (3) can be replaced by a network of yarns deposited in liquid form on the textile reinforcing layer (2), or even by the grid structure including thermoplastic yarns, of the same type as the film mentioned above.
In an alternative embodiment shown in
In the embodiment shown in
When the thermoplastic film (11) is exposed to a heat source, as shown in
The complex according to the invention can be used in a preform mould, to produce preform parts by placement inside the mould, followed by exposure to a heat source during its maintenance in the mould.
It is also possible, as shown in
In a first step, the textile reinforcement (36-38), regardless of its type, is cut out to drape the inside walls (34) of the preform mould Various cutouts can be made, optionally with superimpositions of the textile reinforcing layer. Certain zones (39) of the textile reinforcing layer are thereby bent either with outwardly or inwardly oriented angles. A suction is then created in order to pull the textile reinforcing layer (36-38) against the walls (34) of the mould.
In a subsequent step, shown in
In certain alternative embodiments not shown, additional pieces, such as foam or other inserts can be added, and kept in place by using additional particular portions of thermoplastic film.
When the thermoplastic film is correctly placed on the textile reinforcing layer, this film (40) is melted by a heating system adapted to the geometry of the part, the type of film and the type of reinforcement. For example, in the case of a reinforcement integrating a polypropylene-based drainage core, the heating is moderate to avoid degrading the core of the reinforcement. The suction applied to press the film is also useful at the time of heating thereof, because it enables the material of the melting film to penetrate into the reinforcement fibres. Once the heating is stopped, this suction participates in the cooling of the film material.
At the end of the process, the preform reinforcement (45) can be removed from the preform mould, to yield a directly usable part, as shown in
It appears from the above that the method according to the invention and the associated complex serve to produce preformed reinforcements having a capacity to be bent while preserving a shape memory, thereby considerably facilitating the storage and transport operations. The manufacturing process of the composite parts is therefore also improved, because it allows the use of preforms that are ready for use. It also has the substantial advantage of preserving the initial properties of the reinforcement, despite the preforming operation. It is also “clean” for the environment and the operators, because it does not require the spraying of resin or polluting product. A preform thus produced, thanks to its flexibility, can easily be placed in the mould, by comparison with the rigid preforms, without damaging the layers already present in the mould, and particularly the outer “gel coat” layers.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0553886 | Dec 2005 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2006/051308 | 12/7/2006 | WO | 00 | 6/16/2008 |
