Method for creating a first-pleat attachment in thermoplastic composite draping

Abstract

The invention relates to a method for preparing a deposition surface (110) of a draping tool (100) configured for draping a prepreg comprising a thermoplastic polymer matrix, the method comprising the steps of: preparing the deposition surface (110); depositing a thin layer (320) of a thermoplastic polymer onto at least a portion of the prepared deposition surface (110); wherein a melting temperature of the thermoplastic polymer in the thin layer is equal to or greater than a melting temperature of the thermoplastic polymer matrix. The invention also relates to a tool obtained by such a method.

Description

Title of the invention: Method for achieving a first-pleat attachment in thermoplastic composite draping. Technical field

[0001] The invention relates to the methods for implementing thermoplastic polymer matrix composite materials.

[0002] More particularly the process is aimed at the deposition of thermoplastic matrix prepregs by draping or automatic placement of fibers, and more particularly at the preparation of a surface of a tooling used during such an operation. Previous technique

[0003] Draping is an operation consisting of producing a composite preform comprising a layering of folds deposited on a tool comprising a depositing surface reproducing the shape of a preform of the final part.

[0004] The plies are made of a pre-impregnated material comprising fibers and the polymer constituting the matrix of the composite.

[0005] The preform thus obtained is then baked or consolidated by subjecting it to a cycle of pressure and temperature so as to give it the final shape and characteristics of the part.

[0006] Unlike prepregs comprising a thermosetting matrix, prepregs comprising fibers and a thermoplastic polymer matrix do not exhibit stickiness at room temperature.

[0007] The adhesion of a new ply deposited on a previously made lamination is obtained by localized heating in the deposit zone of both the deposited ply and at least of the exposed surface of the underlying lamination, to a sufficient temperature, as well as by the application of pressure, to achieve the adhesion of the new ply on the preform being draped.

[0008] Document EP 4 349 576 Al describes such a localized heating process using a laser beam for draping a thermoplastic prepreg.

[0009] Throughout this text, the term draping refers to the application of a prepreg in the form of sheets or in the form of fibers or strands, the latter variant being commonly referred to as automatic fiber placement, or by the Anglo-Saxon acronym AFP for "Automatic Fiber Placement". These application methods are known in the prior art.

[0010] Thus, during the draping of a thermoplastic prepreg, the adhesion of the ply deposited on the preform being made depends on the underlying presence of a thermoplastic polymer contained in the previously deposited plies.

[0011] During the deposition of the first ply onto the tooling, the tooling is made of a material (metallic or ceramic) that does not allow chemical bonding with the prepreg polymer when the layup is performed at high speed, as described, for example, in US patent 10,773,470, without melting the impregnating polymer. Consequently, there is a problem with the adhesion of the deposited first ply to the tooling's dispensing surface, which is particularly pronounced when the layup is performed at high speed.

[0012] If the draping conditions of the first ply are such that it is possible to hang the first ply directly on the surface of the tooling, then the problem of demolding the preform following draping arises.

[0013] This technical difficulty is currently resolved by coating the tooling surface with a high-temperature resistant polyimide film commonly referred to as thermalimide. This thermalimide film, attached to the tooling with adhesive tapes, ensures sufficient adhesion of the first ply to the film, allowing the preform to be demolded while the film remains bonded to it. The thermalimide film can then be removed from the preform without damaging it.

[0014] Thus, before each draping operation, the draping tooling must be covered with a new thermalimide film.

[0015] Such a thermalimide film is not deformable, so that when the tooling is of complex shape, non-developable or exhibiting silking and other local variations in shape, the covering of the surface of the tooling is made with small portions of thermalimide film, individually glued with adhesive tape, according to a "scrapbooking" type method, so as to avoid the formation of wrinkles or creases in the film, which would be reproduced on the preform and would lead in particular to local undulations of fibers potentially affecting the mechanical characteristics of the final part.

[0016] This manual operation is meticulous, tedious and time-consuming and associated with the cost of the non-reusable thermalimide film, affects the cost of parts and the overall productivity of the draping operation. Summary of the invention

[0017] The resolution of the drawbacks of the prior art lies in a method for preparing a deposit surface for a draping tool configured for draping a prepreg comprising a thermoplastic polymer matrix, the method comprising the steps of:

[0018] prepare the depositing surface;

[0019] deposit a thin layer of a thermoplastic polymer on at least part of the depositing surface thus prepared;

[0020] in which a melting temperature of the thermoplastic polymer of the thin layer is equal to or greater than a melting temperature of the thermoplastic polymer matrix.

[0021] Thus the thin layer of polymer adheres strongly to the deposited surface due to the surface preparation and allows the first ply to catch during a subsequent draping operation.

[0022] The process can be implemented according to the embodiments and variants set out below, which are to be considered individually or according to any technically feasible combination.

[0023] According to one embodiment, the thermoplastic polymer of the thin layer is the same as the thermoplastic polymer matrix.

[0024] According to one embodiment, the thermoplastic polymer of the thin layer and the thermoplastic polymer matrix are polymers from the polyaryletherketone family.

[0025] According to one embodiment, the step of preparing the depositing surface includes sandblasting the depositing surface.

[0026] Advantageously, the surface roughness after the surface preparation step is Ra greater than or equal to 6.3 micrometers over the entire surface. This roughness ensures strong adhesion of the thin polymer layer to the surface and the ability to demold the draped preform without tearing the thin polymer layer from the draping tooling.

[0027] According to another embodiment, compatible with the previous one, the step of preparing the deposition surface includes texturing the deposition surface by a process chosen from laser texturing, chemical etching and electrochemical machining.

[0028] According to one embodiment, a strip with a width between 1 mm and 10 mm extending from at least one edge of the application surface differs from the rest of the application surface by a portion of the strip selected from: being uncovered by the thin polymer layer and being covered by a high-temperature resistant adhesive tape. These features prevent the thin polymer layer from being degraded in the areas where the fibers are rerouted and cut during draping.

[0029] The invention also relates to tooling adapted for draping a thermoplastic matrix composite preform, the tooling comprising a deposition surface having a roughness Ra of at least 6.3 micrometers and in which at least a portion of the deposition surface is covered by a layer of a thickness of between 120 micrometers and 400 micrometers of a thermoplastic polymer adhering at all points to the deposited surface.

[0030] According to one embodiment, the tooling includes a heating device for the depositing surface integrated into the tooling. Brief description of the drawings

[0031] The process is implemented according to the preferred, non-limiting embodiments described below with reference to [Fig. 1] to [Fig. 3], in which: Fig. 1

[0032] [Fig.1] shows, in a perspective and exploded view, an example of implementation of the process; Fig. 2

[0033] [Fig.2] shows, in perspective view, an example of the realization of a composite preform obtained from the tooling shown [Fig.1]; Fig.3

[0034] [Fig.3] shows, in perspective view, the example of the tooling of [Fig.1] covered with a thin layer of polymer on part of its depositing surface. Description of the implementation methods

[0035] [Fig.1] According to an example of an embodiment, a draping tool (100) includes a deposition surface (110) of complex non-developable shape and / or including localized shape changes such as silking (not shown).

[0036] Such tooling is commonly produced by machining a tool steel, which can be a low coefficient of thermal expansion steel of the INVAR® type for the implementation of a composite comprising carbon fibers in a draping operation including direct consolidation to draping.

[0037] The process is however adapted to other types of tooling, depending on the application and the technical field of the parts concerned, in particular tooling made of aluminium alloy, copper alloy or ceramic.

[0038] [Fig.2] This tooling is intended to produce a composite preform (200) of a part comprising continuous fibers (210) i.e. extending without discontinuity from one edge to the other of the part and of the preform (200), in a thermoplastic polymer matrix.

[0039] By way of non-limiting examples, the fibers are carbon fibers, aramid glass fibers or any combination thereof; the thermoplastic polymer matrix is ​​made of a polymer from the polyaryletherketone (PAEK) family such as PEEK (polyetheretherketone), PEK (polyetherketone), PEKK (polyetherketoneketone), LMPAEK® (a low-melting-point polyaryletherketone copolymer), or even polyphenylene sulfide (PPS) for aeronautical applications, but the process is suitable for other types of polymer matrices and other types of fibers.

[0040] The part is obtained by means of a preform (200) comprising a layering of composite plies, the fibers being of different orientation according to the plies.

[0041] The preform (200) is thus obtained by a first draping operation, in particular by automatic placement of fibers (AFP).

[0042] This first operation is advantageously carried out without direct consolidation to the draping, that is to say, the fiber strands are deposited at a high deposition speed. According to this example, the deposited fibers adhere to the previously deposited ply by the action of localized heating and the application of pressure at the deposition site.

[0043] According to this non-limiting embodiment, the deposition speed combined with the control of heating conditions at the deposition site makes it possible to obtain, at the end of the draping operation, a rigid but not totally consolidated preform (200), i.e. that the plies are firmly linked to each other without the molecular chains of the polymer constituting the matrix passing through the plies.

[0044] Also, according to this embodiment, the preform (200) undergoes an additional consolidation step, consisting of subjecting it to a pressure-temperature cycle, for example by heating it beyond its melting temperature in a sealed, shaped and vacuum-drawn tool.

[0045] At the end of this consolidation stage, the part takes its final shape and thickness and is possibly machined to carry out drilling, contouring and other finishing.

[0046] The draping tooling preparation process is particularly suited to the manufacturing process as described above but is also applicable to a draping process implementing total consolidation at the time of application, directly during draping, in which the reduced application speed and the conditions of application of the fibers at application (pressure, temperature) allow the consolidation of the folds, the elimination of porosity and the development of the molecular chains of the polymer matrix through stratification during application.

[0047] Returning to [Fig. 1], the preparation process aims to prepare a deposition surface (110) so that it allows the first ply deposited on this surface to adhere while ensuring the ability to remove the preform from the tooling after the draping operation without degrading either the preform or the tooling.

[0048] To this end, a surface preparation is applied to the deposition surface (110) and following this surface preparation, a polymer film (120) is applied to the surface thus prepared.

[0049] The surface preparation aims to strengthen the adhesion of the polymer film (120) to the deposition surface (110) so that when the preform is removed from the tooling the polymer film remains bound to the deposition surface.

[0050] By way of example, the preparation of the deposit surface (110) is carried out by sandblasting aimed at obtaining a roughness Ra of the order of or slightly greater than 6.3 micrometers.

[0051] Sandblasting produces a surface whose roughness is said to be ergodic, resulting in stochastic reliefs.

[0052] A similar result of enhanced adhesion to the deposited surface can be achieved by texturing the deposited surface according to defined patterns, in particular by laser engraving, chemical or electrochemical etching, or even directly during machining with a cutting tool. In these cases, the desired roughness depends on the texture, especially in the case of laser engraving, which allows for the creation of complex patterns such as "adhesion wells" or the superposition of coarser and finer patterns, so that the appropriate texturing conditions can be determined by testing. These tests can be carried out economically by draping tests on flat sheets prepared in this way.

[0053] It is also possible to combine several surface preparation methods, for example sandblasting and laser engraving.

[0054] The draping tooling (100) with the polymer film (120) covering all or part of the depositing surface (110) are bagged in a vacuum bag, drawn under vacuum, and the assembly is heated to a temperature at least equal to the melting temperature of the thermoplastic polymer constituting the polymer film (120).

[0055] Thus, the polymer film perfectly conforms to the shape of the deposited surface, including its texture and roughness, adhering strongly to it in the form of a thin layer of polymer.

[0056] [Fig.3] the thickness of the polymer film is typically between 120 micrometers and 400 micrometers, so that after this heat treatment a thin layer (320) of thermoplastic polymer, whose thickness is of the same order of magnitude, covers at least part of the deposited surface (110) and adheres strongly to it.

[0057] The depositing surface (110) can be machined to take into account this additional thickness, more particularly when the draping operation includes direct consolidation during draping.

[0058] This thin layer (320) of thermoplastic polymer will allow the adhesion of a thermoplastic prepreg deposited during a subsequent draping operation.

[0059] In order that the adhesion of the first ply to the thin polymer layer is less strong than that of the thin polymer layer to the tooling deposition surface, the the melting temperature of the polymer constituting the thin layer must be greater than or equal to the melting temperature of the impregnation polymer of the prepreg.

[0060] According to a first embodiment, the polymer constituting the thin layer is selected as the same as the thermoplastic polymer for impregnating the prepreg.

[0061] By way of examples of this first embodiment, if the draped prepreg is a carbon-PEEK the thin polymer layer (320) is made of PEEK, if the prepreg is a carbon-PPS, the thin polymer layer (320) is made of PPS.

[0062] The high-speed draping conditions as described above ensure that an adhesion force of the thin polymer layer (320) to the deposition surface (110) is greater than an adhesion force of the thin polymer layer to the first ply, which makes it possible to demold the preform after draping without tearing off the thin polymer layer and to immediately reuse the tooling (100).

[0063] According to another embodiment, the thermoplastic polymer constituting the thin layer is of the same family as the pre-impregnating polymer but has a higher melting temperature.

[0064] For example, according to this second embodiment, if the draped prepreg is a carbon-PEEK, the thin polymer layer can be made of PEKK. If the prepreg is a carbon-LMPAEK®, then the thin layer can be chosen from PEEK and PEKK.

[0065] This configuration ensures strong adhesion of the first ply including in high-speed draping while ensuring that the adhesion force of the thin layer of polymer to the deposited surface is greater than the adhesion force between the thin layer of thermoplastic polymer and the first ply due to the difference in melting temperature.

[0066] According to these two embodiments, the miscibility of the polymer constituting the thin layer and that of the impregnation of the prepreg, either because they are of the same nature or because they are of the same family, means that if a small portion (chip) of the thin layer of polymer adheres to the preform and is torn from the tooling during the demolding of the preform, this portion of polymer will be integrated into the part during the subsequent consolidation without degrading the quality of the part.

[0067] In the case where the draping operation includes direct consolidation during draping, the thermoplastic polymer selected to form the thin layer (320) is chosen with a melting point significantly higher than that of the thermoplastic polymer used to impregnate the prepreg; for example, the polymer film is a high-melting-point thermoplastic polyimide. This difference in melting point ensures a stronger difference in adhesion of the thin layer (320) to the deposited surface (110), and of the thin layer to the prepreg during the deposition, weaker as well as the absence of transfer between the thin layer and the preform, the thin layer not being brought to its melting temperature during deposition.

[0068] Unlike the prior art, according to this embodiment the thin layer (320) of thermoplastic polyimide perfectly conforms to the deposited surface due to the process involving the melting and application of the thermoplastic polymer film onto the deposited surface under pressure, and the thin layer of thermoplastic polyimide remains attached to the tooling, which can be reused immediately after demolding of the preform.

[0069] According to one embodiment, the tooling includes a heating device for the depositing surface which can be used during the draping operation.

[0070] According to examples of embodiments, this heating can be obtained by placing the tooling (100) on a heated platform during the draping operation, or, the tooling can have an autonomous heating device comprising conduits (350) adapted for the circulation of a heat transfer fluid, the routing of electrical resistances, inductors or any combination of these means.

[0071] Heating the deposited surface, particularly during the draping of the first ply, to a temperature significantly lower than the melting temperature of the thermoplastic polymer constituting the thin layer (320) allows a certain control of the adhesion force of the first ply on said thin layer, both during draping and demolding, thus offering an additional adjustment possibility.

[0072] Advantageously, at least one strip of the deposition surface at a distance of at least one edge (330) is prepared so that the thin polymer layer is not in contact with the prepreg during draping.

[0073] This width, ranging from 1 mm to 10 mm depending on the dimensions of the preform, corresponds to a cutting zone for the fibers in automatic fiber placement or for the strips in tape draping. This cutting and any laser flash phenomena in this zone are likely to degrade the thin polymer layer.

[0074] To this end, according to a first embodiment the thin polymer layer does not completely cover the deposited surface and leaves at least one uncovered border between the perimeter of the thin polymer layer and at least one edge (330) of the deposited surface (110).

[0075] According to another embodiment, the thin polymer layer covers the entire deposition surface (110) but at least one edge band is covered by a high-temperature resistant adhesive tape (335), such as a thermalimide adhesive tape.

[0076] These two embodiments can be combined, i.e., the thin layer (320) of thermoplastic polymer does not cover the entire deposited surface (110) and at least part of the surface not covered by the thin polymer edge layer is covered by a high-temperature resistant adhesive tape (335).

[0077] In all cases, the hooking of the first ply on the rest of the surface of the thin layer (320) is sufficient to ensure the stability of the first ply on the draping tooling.

Claims

Demands

1. A method for preparing a depositing surface (110) of a draping tool (100) configured for draping a prepreg comprising a thermoplastic polymer matrix, the method comprising the steps of: preparing the depositing surface (110); depositing a thin layer (320) of a thermoplastic polymer on at least a portion of the depositing surface (110) thus prepared; wherein a melting temperature of the thermoplastic polymer of the thin layer is equal to or greater than a melting temperature of the thermoplastic polymer matrix.

2. A method according to claim 1, wherein the thermoplastic polymer of the thin layer is the same as the thermoplastic polymer matrix.

3. A method according to claim 1, wherein the thermoplastic polymer of the thin film and the thermoplastic polymer matrix are polymers of the polyaryletherketone family.

4. A method according to claim 1, wherein the step of depositing a thin layer (330) of thermoplastic polymer comprises depositing a polymer film (120) on at least a portion of the depositing surface (110) and consolidating the polymer film (120) by heating the depositing surface (110) and the polymer film to a temperature equal to or greater than the melting temperature of the polymer film, under pressure.

5. Method according to claim 1, wherein the step of preparing the depositing surface (110) includes sandblasting the depositing surface (110).

6. A method according to claim 3, wherein a roughness of the deposited surface (110) after the step of preparing the deposited surface is an Ra greater than or equal to 6.3 micrometers over the entire deposited surface.

7. A method according to claim 1, wherein the step of preparing the deposit surface (110) includes texturing the deposit surface by a method selected from laser texturing, chemical etching and electrochemical machining.

8. Method according to claim 1, wherein a strip of a width between 1 mm and 10 mm from at least one edge (330) of the deposited surface differs from the rest of the deposited surface by a surface of the strip selected from: not covered by the thin polymer layer and a cover by a high temperature resistant adhesive tape (335).

9. Tooling (100) adapted for draping a thermoplastic matrix composite preform (200), the tooling comprising a deposition surface (110) having a roughness Ra of at least 6.3 micrometers and in which at least a part of the deposition surface is covered by a thin layer (320) of a thickness between 120 micrometers and 400 micrometers of a thermoplastic polymer adhering at all points to the deposition surface (110).

10. Tooling according to claim 9, comprising a heating device (350) for the depositing surface (110) integrated into the tooling.

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