Method and device for transferring and stamping a thermoplastic composite blank

Abstract

The invention relates to a device for conveying a laminated composite blank (100) with a thermoplastic polymer matrix for heating and stamping, comprising: a conveyor including a pair of opposing jaws (130) and a tensioning mechanism configured to bring the pair of jaws (130) closer together and further apart; a laminated composite blank (100) comprising at least one ply of continuous fibrous reinforcements in a thermoplastic polymer matrix; a plurality of strips (140) made of pre-impregnated unidirectional fibers and extending over a width greater than one width of the laminated composite blank; wherein: the ends of the plurality of strips (140) are pinched in the pair of jaws (130), the plurality of strips being tensioned by the tensioning mechanism and the pair of jaws (130) being separated from each other by a width equal to one conveying width (115);and a weight of the laminated composite blank (100) is supported between the pair of jaws (130) by the plurality of tensioned bands (140). Figure to be published with the abbreviation [Fig.1];

Description

Title of the invention: Method and device for transferring and stamping a thermoplastic composite blank. Technical field

[0001] The invention belongs to the field of implementation of thermoplastic polymer matrix composite materials.

[0002] More particularly, the device and method of the invention relate to the transfer of a thermoplastic composite blank for the purpose of stamping it. Previous technique

[0003] A stamping process for a continuous fiber-reinforced thermoplastic composite blank is described for example in document EP 1 543 942.

[0004] According to the teaching of this document, a blank of suitable shape is cut from a consolidated or partially consolidated composite plate, then the blank is brought to a temperature on the order of the melting temperature of the thermoplastic polymer constituting the matrix, the blank thus deconsolidated is then stamped between a punch and a stamping die before being cooled and reconsolidated in shape between said punch and said stamping die.

[0005] Indeed, insofar as continuous fibrous reinforcements, such as carbon fibers, do not exhibit plasticity, including at the melting temperature of the thermoplastic polymer, the deformation of the blank during stamping is achieved by interlaminar sliding, which requires a reduced viscosity of the thermoplastic polymer matrix.

[0006] One of the difficulties of this process lies in the ability to transfer the blank into a heating zone, then, once it has been brought to a temperature suitable for its forming, to transfer it to the stamping station while ensuring precise positioning of said blank in relation to the stamping tooling.

[0007] Since the heating temperature of the blank before stamping is on the order of the melting temperature of the thermoplastic polymer constituting the matrix of the composite, after this heating, the blank exhibits very little cohesion, and is likely to collapse under the effect of its own weight.

[0008] According to a prior art technique, the blank is placed on a high-temperature resistant polyimide film.

[0009] To this end, a conveyor adapted for moving the blank from the heating station to the stamping station comprises a pair of parallel jaws capable of pinching the edges of a polyimide film format and stretching this polyimide film between the jaws. Thus the A stretched polyimide film serves as a support for the blank and its transfer from one implementation station to another.

[0010] Thus, in a first station, the blank, placed on the polyimide film, is heated, in particular by radiant panels, in order to bring the thermoplastic polymer constituting the matrix of said blank to a temperature equal to or greater than its melting temperature.

[0011] At this temperature, the blank is deconsolidated and exhibits very low rigidity. Since the polymer constituting the matrix is ​​in a near-liquid state, it does not impede the relative movement of the composite's reinforcing fibers.

[0012] The unconsolidated blank is brought, still placed on the stretched polyimide film, above a tool, in this case a stamping die of a punch die tool, then the blank, still on the polyimide film, is stamped by a punch pushing the blank and the polyimide film against the walls of the stamping die while the tension of the polyimide film is relaxed.

[0013] The blank and the polyimide film are then contained within a gap defined by the walls of the stamping die and the walls of the punch. A cooling cycle allows the part to reconsolidate into shape, while controlling the gap between the punch and the stamping die ensures the calibration of the finished part's thickness.

[0014] This prior art process has several drawbacks, notably that of the polyimide film, which is stamped simultaneously with the blank and is susceptible to wrinkling during this operation. The resulting creases are imprinted in the polymer constituting the matrix of the composite part and can constitute undesirable defects, particularly for demanding applications such as aeronautical applications.

[0015] Moreover, the high-temperature resistant polyimide film is for single use only; it is therefore a consumable, of relatively high cost, which directly affects the cost of a part obtained by such a process.

[0016] Document EP 3 065 931 describes an improvement to the process shown above, in which the blank is transported from the heating station to the stamping station on a support frame, which support frame includes means for precisely positioning the blank on the support frame and means for precisely positioning the support frame relative to the stamping tooling.

[0017] This embodiment thus avoids the use of a polyimide film, however it requires specific tooling which must be adapted to the conveyor.

[0018] While this embodiment is satisfactory, it remains limited to blanks with relatively low mass. Indeed, as the thickness and mass of the blank increase, the heating times under the radiant panels also increase, and the modifications to the transfer frame are no longer sufficient to support the blank.

[0019] Document EP 4 349 560 describes a transfer frame adapted to a thick and heavy thermoplastic composite blank. This device must also be adapted to the conveyor and requires more extensive preparation of the blank. Summary of the invention

[0020] These drawbacks of the prior art can be overcome by a device for conveying a thermoplastic polymer matrix laminated composite blank for heating and stamping, comprising:

[0021] a conveyor comprising a pair of opposing jaws and a tensioning mechanism configured to maintain the jaws of the pair at a conveying distance from each other;

[0022] a laminated composite blank comprising at least one ply of fibrous reinforcements in a thermoplastic polymer matrix;

[0023] a plurality of strips made of pre-impregnated unidirectional fibers and extending over a width greater than a width of the laminated composite blank;

[0024] in which:

[0025] the ends of the plurality of strips are pinched in the pair of jaws (130), the jaws of the pair being separated from each other by the conveying width; and

[0026] a weight of the laminated composite blank (100) is supported between the pair of jaws by the plurality of tensioned strips (140).

[0027] Thus, the composite blank is laminated and conveyed on stretched fiber strips. These fibers retain their rigidity at the heating temperature of the laminated composite blank without the use of a polyimide film or a special transfer frame. The rigidity of the strips allows them to support heavy and thick blanks requiring prolonged heating.

[0028] The device can be implemented according to the embodiments and variants set out below, which are to be considered individually or according to any technically operative combination.

[0029] Advantageously, a thermoplastic polymer for impregnating the pre-impregnated unidirectional fibers of the strips is chosen from the same polymer as the thermoplastic matrix polymer and a polymer miscible in the thermoplastic matrix polymer.

[0030] Thus, during stamping, the polymer impregnating the strips, being of the same nature as the polymer of the matrix of the laminated composite blank, the strips become integrated into the part.

[0031] Advantageously, the pre-impregnated unidirectional fibers of the strips are of the same nature as the fibrous reinforcements of the laminated composite blank.

[0032] Thus, according to one embodiment, the plurality of strips can be integrated into a fold of the laminated composite blank.

[0033] In one embodiment, the device includes a mechanism configured to bring the pair of jaws closer together after they have been moved apart by the conveying width.

[0034] Such a mechanism makes it possible to control the deformation of the strips during stamping.

[0035] According to one embodiment, the device comprises at least two cables extending between the pair of jaws, with a cable length configured so that at least two cables are under tension when the pair of jaws is moved away from the conveying width

[0036] Thus, in a stamping system comprising such a conveying device, and:

[0037] a stamping tool comprising a matched punch and stamping die;

[0038] a press suitable for receiving the stamping tooling, configured to move the punch relative to the stamping die between an open position and a closed position;

[0039] the open position allowing the passage of the laminated composite blank held between the pair of jaws by the plurality of tensioned bands, between the punch and the stamping die; and

[0040] This system includes at least two pads attached to the punch and configured to come into contact with the at least two cables when the punch moves from the open position to the closed position before the punch comes into contact with the laminated composite blank placed between the punch and the stamping die.

[0041] This system enables the implementation of a process for manufacturing a part by stamping a laminated composite blank comprising at least one continuous fibrous reinforcement ply in a thermoplastic polymer matrix comprising the steps of:

[0042] drape a laminated composite blank comprising a ply in which pre-impregnated fiber strips extend outside a blank width in the form of pre-impregnated unidirectional fiber strips;

[0043] install the blank thus obtained in a conveying device in such a system;

[0044] move the laminated composite blank on the tensioned strips under a device heating and bringing the laminated composite blank to a temperature suitable for its stamping;

[0045] move the blank, held in the conveying device, between the punch and the stamping die of the system;

[0046] stamp the laminated composite blank between the punch and the stamping die to obtain the part;

[0047] to trim the part to eliminate a portion of the strips extending outside a width of the part. Brief description of the drawings

[0048] The device is implemented according to non-limiting embodiments set out below with reference to Figures [Fig. 1] to [Fig. 9] in which: Fig. 1

[0049] [Fig.1] shows in top view a simplified representation of the device for conveying a composite blank; Fig. 2

[0050] [Fig.2] shows, according to a simplified cross-sectional view AA defined [Fig.1], the device at a stamping station before blank stamping; Fig.3

[0051] [Fig.3] represents the device during the stamping of the blank according to the same view that [Fig.2]; Fig. 4

[0052] [Fig.4] shows, in perspective view, an example of a part obtained after demolding following stamping shown [Fig.2] and [Fig.3]; Fig. 5

[0053] [Fig. 5] shows an embodiment of the device at the stamping station according to a view from the right; Fig. 6

[0054] [Fig. 6] shows a simplified view of the device of [Fig. 5] according to a defined BB section [Fig.l]; Fig. 7

[0055] [Fig.7] shows, according to a simplified cross-sectional view AA, the device of [Fig.6] in progress stamping; Fig. 8

[0056] [Fig.8] represents, in perspective view, an example of a part obtained by a composite flan in which the strips are integrated into a fold just after demolding. Fig. 9

[0057] [Fig.9] shows in top view an example of a laminated composite blank adapted to obtaining a part as shown [Fig.8]. Description of the implementation methods

[0058] [Fig.1] According to a schematic embodiment, the device for conveying a composite blank (100) for stamping is mounted on rails (111, 112) of a conveyor capable of moving the device in translation to bring it successively to a heating station and then to a stamping station.

[0059] The conveyor includes a tensioning mechanism configured to move the rails (111, 112) closer together or further apart so as to define a conveying width (115).

[0060] According to this embodiment, the device comprises a pair of mounting bars (120) fixed to the conveyor rails.

[0061] The tensioning device is here symbolized by hydraulic cylinders (150) acting on the rails (111, 112) of the conveyor according to a force, symbolized by arrows (151), tending to move the rails (111, 112) apart from each other.

[0062] The person skilled in the art understands that [Fig.1] is a simplified representation and that the conveyor may include intermediate connecting pieces between the conveyor rails and the mounting bars, and that the conveying width can be adjusted by acting on these intermediate connecting pieces, the rail spacing remaining fixed.

[0063] A pair of jaws (130) is mounted on the mounting bars (120), one jaw on each of the mounting bars.

[0064] The blank (100) is a contoured flat plate made up of a layering of fibrous plies in a thermoplastic polymer matrix which may include continuous fibers (101), i.e. fibers extending without interruption from one edge to the other of the blank.

[0065] The blank can for example be obtained by draping or by automatic placement of fibers, or by manual stacking of folds, it can be fully consolidated or partially consolidated.

[0066] The implementation of the process and device described below is not, however, limited to stamping a blank comprising continuous reinforcing fibers.

[0067] According to non-limiting embodiment examples, the reinforcing fibers are carbon, glass, aramid fibers or a combination thereof, the thermoplastic polymer matrix can be from the family of polyaryleterketones, polyetherimide, polyphenylene sulfide, polyethylene terephthalate.

[0068] According to examples of implementation, these reinforcing fibers are integrated into the composite in the form of continuous fibers, included in unidirectional plies deposited by automatic fiber placement, in the form of fabric or non-woven, long fibers or short fibers oriented or not.

[0069] The fibrous reinforcements are not plastically deformable and retain their rigidity at a temperature corresponding to a temperature suitable for stamping the laminated composite blank, i.e. generally a temperature close to the melting temperature of the thermoplastic polymer matrix.

[0070] The laminated composite blank is held together by a plurality of pre-impregnated unidirectional fiber strips (140), preferably the same fibers as the fibrous reinforcements of the laminated composite blank, pre-impregnated with the same polymer than that constituting the thermoplastic polymer matrix of the flan, or a thermoplastic polymer miscible with the polymer constituting the thermoplastic polymer matrix of the flan.

[0071] The continuous unidirectional fibers of these strips are not plastically deformable and retain their rigidity at a temperature corresponding to a temperature suitable for stamping the laminated composite blank, i.e. generally a temperature close to the melting temperature of the thermoplastic polymer matrix.

[0072] The ends of the pre-impregnated unidirectional fiber strips (140) are pinched at their ends in the pair of jaws (130), and the strips are tensioned with the conveyor tensioning mechanism.

[0073] According to one embodiment, the laminated composite blank (100) is placed on the pre-impregnated unidirectional fiber strips (140), optionally held thereon by a limited number of sections of high-temperature resistant adhesive tape such as a polyimide adhesive tape.

[0074] The rigidity of the strips (140) made of pre-impregnated unidirectional fibers is high; for example, the elastic modulus of the fibers is, depending on their nature, greater than the elastic modulus of steel or aluminum. Thus, the tensioned strips support the weight of the laminated composite blank even if the latter is heavy and thick.

[0075] According to another embodiment, the pre-impregnated unidirectional strips (140) are integrated into a fold of the blank lamination during the production of this blank.

[0076] For example, if the blank is obtained by automatic placement of fibers, some of the fiber strips thus placed can be extended outside the contours of the blank constituting the future part, so as to constitute the unidirectional retaining strips in the stamping tooling.

[0077] Tensioned and made of unidirectional fibers, the strips are very rigid. The number of strips depends in particular on the weight of the laminated composite blank (100).

[0078] Thus held by the pre-impregnated unidirectional fiber strips, the laminated composite blank is brought by the conveyor to a heating station.

[0079] The heating station consists, for example, of infrared radiant panels, adapted to heat the blank and at least part of the pre-impregnated unidirectional fiber strips to a temperature suitable for its stamping, on the order of the melting temperature of the thermoplastic polymer constituting the matrix of the laminated composite blank when the latter includes continuous fiber plies.

[0080] When brought to this temperature, the blank deconsolidates and the reduced viscosity of the thermoplastic polymer matrix at this temperature allows interlaminar sliding and the forming of the laminated composite blank by stamping.

[0081] The pre-impregnated unidirectional strips retain their rigidity, conferred by the fibers, even when heated to this temperature, and continue to support the weight of the laminated composite blank (100) and to hold it in position between the pair of jaws (130).

[0082] [Fig.2] After the heating station, the conveyor carries the laminated composite blank (100) held by the bands (140) towards a stamping station.

[0083] The stamping station includes a punch (202) and a stamping die (201) comprising an impression (203) whose shape is matched with an external shape of the punch (202).

[0084] This punch-stamping die assembly is for example placed in a press (not shown), the stamping die (201) on a plate of the press and the punch linked to a slide allowing the punch to be maneuvered in a movement of approach (200) of the punch (202) towards the stamping die (201) between an open position, as shown [Fig.2], where the blank carried by the conveyor can be brought between the punch and the stamping die, and a closed position (not shown) where the external shape of the punch (202) is distant from the impression (203) of the stamping die (201) by a gap corresponding to the thickness of the final part.

[0085] As the device is brought to the stamping station, the conveyor tensioning mechanism is relaxed. For example, if this mechanism is implemented by hydraulic cylinders (150), these are no longer supplied with pressure and one of their chambers is vented so that the force (151) opposing the closing of the jaws (130) corresponds only to the viscous forces of the hydraulic fluid evacuated from the vented chamber.

[0086] Thus, while maintaining support of the blank on the strips, the jaws can be moved substantially perpendicular to the approaching movement (200) of the punch when the latter begins to act on the blank.

[0087] [Fig.3] Stamping occurs through the approach movement (200) of the punch (202) towards the closed position, movement during which the laminated composite blank (100), deconsolidated because it has been previously brought to a temperature suitable for its stamping, is pushed by the punch (202) into the impression (203) of the stamping die (201), thus forcing the laminated composite blank to conform to a shape of the finished part with a thickness calibrated by the gap between the external shape of the punch and the impression in the closed position.

[0088] With the tensioning mechanism relaxed, under the effect of this thrust the jaws (130) move in a following motion (300) towards the imprint, so that the distance between the jaws is less than the conveying width and decreases with the progression of the punch in the approach motion (200). The strips (140) are constrained to follow the shape imposed on the laminated composite blank (100) by the punch-stamping die assembly.

[0089] Having reached the end of the approach movement, in the closed position, the blank, being caught in the gap between the punch and the impression, cools and reconsolidates into shape, to the shape and thickness of the desired part which can then be demolded.

[0090] [Fig.4] under the stamping conditions described above, the strips (140) are welded and co-consolidated with the part on its convex surface (401), the thickness of the strips being largely exaggerated on [Fig.4].

[0091] Sections of strips extending beyond the contour of the part are eliminated, for example by trimming.

[0092] This result is obtained, for example, when the laminated composite blank is placed on the strips. Depending on the intended application, it may be acceptable.

[0093] When the strips are integrated into a ply of the laminated composite blank, the same process can be applied. However, depending in particular on the depth of the stamping, there is then a risk of delamination or breakage of the strips during stamping, as shown by the delamination of the strips on the edges of the blank [Fig.3].

[0094] To this end, according to an exemplary embodiment [Fig. 1], the device comprises at least one cable (190) stretched parallel to the belts (140) when the pair of jaws (130) are separated from each other by the conveying width (115). At least one cable (190) is installed outside an area subject to stamping between the punch and the stamping die.

[0095] [Fig. 5] at least one pad (500), one opposite each cable, is fixed to the punch (202) outside an area delimited by the stamping die (201), so that the pads (500) move with the punch during the approach movement (200).

[0096] [Fig.6] the tensioning mechanism being relaxed, during the approach movement (200), the pad (500) linked to the punch (202) presses on the cable (190) causing the jaws (130) to move closer together according to the follow-through movement (300) even before the punch comes into contact with the laminated composite blank (100).

[0097] Advantageously, a pulley mechanism (601, 602) fixed relative to the punch and which can be fixed on one face of the stamping die or on any other support, allows better control of the amplitude of movement of the jaws (130) under this effect of the pad (500).

[0098] This embodiment is easily adaptable to an existing conveyor and stamping system. Alternatively, a motorized jaw movement device following the tracking motion (300) would achieve the same result.

[0099] [Fig.7] under the effect of the following movement (300) triggered by the pressure of the buffer on the cable, the strips (140) are subjected to a compressive stress which induces a buckling of them between the jaws and the side.

[0100] This initial buckling (700) then facilitates the accompaniment by the bands (140) of the deformation of the laminated composite blank (100) during stamping thus avoiding fiber breaks or delaminations in the ply including the bands (140).

[0101] Also, this embodiment is particularly suitable for the case where the strips are integrated into a fold of the laminated composite blank while also being applicable in the case where the laminated composite blank is simply placed on the strips.

[0102] [Fig-7] represents the bands (140) integrated into a ply on the surface of the composite blank laminated but these can be integrated into any fold in the thickness of the lamination.

[0103] [Fig.8] according to this embodiment where the strips are draped with a fold of the laminated composite blank, after stamping, the strips (140) are co-consolidated with the part (800) for their part in the layering of folds, the ends of the strips protruding from the contour of the part (800) are eliminated for example by trimming.

[0104] [Fig.8] the composite part (800) may comprise several plies whose fibers are oriented according to predefined directions.

[0105] Thus, [Fig.9] a laminated composite blank suitable for making such a part can comprise one or more plies of fibers (901) oriented at 0°, one or more plies of fibers (902) oriented at any angle, for example at 45°, and one or more plies of fibers (903) oriented at 90°.

[0106] Such a flan is obtained for example by automatic placement of fibers.

[0107] According to one embodiment example, the strips (140) are obtained by extending outside the contour of the blank forming the future part, the deposit of fibers in a fold of fibers oriented at 90°.

[0108] Thus draped, the blank is stamped by the implementation of the device as described above.

[0109] Regardless of the embodiment of the conveyor described above, the unidirectional fiber strips supporting and holding the composite blank during all the operations necessary for stamping forming, whether these strips are independent of the lamination of the blank or whether they are made at the same time as this lamination, the strips advantageously replace the polyimide film used by the prior art, limiting the supplies of such a film, which is poorly reusable and non-recyclable, and thus reducing the cost of the parts thus produced, as well as the consumption of resources and the generation of waste.

[0110] As the device replaces the polyimide film, the device can be very easily implemented on an existing installation, without modification of that installation.

[0111] The ends of strips removed from the part by trimming, unlike polyimide film, are recyclable, for example in the process described in document EP 4 410 512.

[0112] The rigidity of the unidirectional strips makes it possible to support thick and heavy blanks that a polyimide film could not support.

[0113] Finally, the absence of polyimide film avoids the problems related to the formation of puckers which are created in the film during stamping and which can be printed on the surface of the part, potentially leading to the disposal of the latter.

[0114] Thus the conveying device on unidirectional fiber belts also solves, at least in part, some of the problems addressed in document EP 4 349 560.

Claims

Demands

1. Device for conveying a thermoplastic polymer matrix laminated composite blank (100) for heating and stamping, comprising: a conveyor including a pair of opposing jaws (130) and a tensioning mechanism (150) configured to maintain the jaws of the pair at a conveying distance (115) from each other; a laminated composite blank (100) comprising at least one ply of fibrous reinforcement in a thermoplastic polymer matrix; a plurality of strips (140) made of pre-impregnated unidirectional fibers and extending over a width greater than one width of the laminated composite blank; wherein: the ends of the plurality of strips (140) are pinched in the pair of jaws (130), the jaws of the pair being separated from each other by the conveying width (115);and a weight of the laminated composite blank (100) is supported between the pair of jaws (130) by the plurality of tensioned bands (140).

2. Device according to claim 1, wherein a thermoplastic polymer for impregnating the pre-impregnated unidirectional fibers of the strips (140) is selected from the same polymer as the thermoplastic matrix polymer and a polymer miscible in the thermoplastic matrix polymer.

3. Device according to claim 2, wherein the pre-impregnated unidirectional fibers of the strips (140) are of the same nature as the fibrous reinforcements of the laminated composite blank.

4. Device according to claim 3, wherein the plurality of strips (140) is integrated into a fold of the laminated composite blank (100).

5. Device according to claim 1, comprising a mechanism configured to bring the pair of jaws (130) closer together after they have been moved apart from each other by the conveying width (115).

6. Device according to claim 5, comprising at least two cables (190) extending between the pair of jaws (130) of which a cable length is configured such that the at least two cables (190) are tensed when the pair of jaws (130) is moved away from the conveying width (115).

7. Stamping system comprising a conveying device according to claim 6, and: a stamping tool comprising a matched punch (202) and stamping die (201); a press, suitable for receiving the stamping tool, configured to move the punch (202) relative to the stamping die between an open position and a closed position; the open position allowing the passage of the laminated composite blank (130) held between the pair of jaws (130) by the plurality of tensioned strips (140), between the punch and the stamping die; and comprising at least two pads (500) attached to the punch (202) and configured to come into contact with the at least two cables (190) when the punch (202) moves from the open position to the closed position before the punch (202) comes into contact with the laminated composite blank (100) placed between the punch and the stamping die (201).

8. A method for manufacturing a part (800) by stamping a laminated composite blank (100) comprising at least one continuous fibrous reinforcement ply in a thermoplastic polymer matrix comprising the steps of: draping a laminated composite blank comprising a ply in which pre-impregnated fiber strips (140) (903) extend beyond a blank width in the form of pre-impregnated unidirectional fiber strips (140); installing the blank thus obtained in a conveying device of a system according to claim 7; moving the laminated composite blank over the stretched strips (140) under a heating device and bringing the laminated composite blank to a temperature suitable for its stamping; moving the blank, held in the conveying device, between the punch (202) and the stamping die (101) of the system according to claim 7;stamp the laminated composite blank (100) between the punch (202) and the stamping die (201) to obtain the part (800); trim the part to remove a portion of the strips (140) extending outside one width of the part.

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