Method for recycling scrap from thermoplastic composite materials

Abstract

The invention relates to a method for recycling scrap from parts made of composite material reinforced with continuous fibres in a thermoplastic polymer matrix, the method comprising the steps consisting in: i) obtaining a composite preform (110, 500) which is continuously reinforced and is suitable for obtaining a structural part; ii) obtaining the structural part (200, 400) from the composite preform which is continuously reinforced; iii) cutting out the structural part (200, 400); iv) recovering (310) the scrap (120, 220) produced in steps i) and iii); v) grinding (320) the scrap to obtain a ground material consisting of pieces of composites; vi) compounding (330) the ground material obtained in step v) to obtain a compound; vii) obtaining a second composite part (410, 600) by shaping the compound obtained in step vi).

Description

Process for the revaluation of offcuts of thermoplastic composite materials

[0001] The invention belongs to the field of the implementation of composite materials with a thermoplastic polymer matrix. More particularly, the invention belongs to the field of recycling, notably, but not exclusively, in the context of a circular economy.

[0002] Thermoplastic polymer matrix composite materials, particularly continuous fiber composites, offer numerous advantages in terms of processing and mechanical and chemical characteristics, particularly, but not exclusively, in aeronautical construction.

[0003] The ability to process these materials using techniques similar to those for processing metallic materials, in particular, but not exclusively, stamping, leads to material waste during initial processing resulting, for example, from the cutting of a range of blanks and the trimming of formed parts.

[0004] These scraps can represent up to 50% of the material used in a large-scale process, or even more when the production flow does not allow for optimization of the ranges.

[0005] While the thermoplastic polymer constituting the matrix is ​​generally considered recyclable, the same is not true for the composite, where the offcuts of said composite which mix polymer and fibers.

[0006] However, particularly in the aeronautical field, both the polymer constituting the matrix and the reinforcing fibers are high-performance and high-cost materials.

[0007] Furthermore, specifically in the aeronautical field, the material must be certified and to this end must meet quality assurance and traceability rules during its production, which further increases the value, or more precisely, the loss of value associated with the landfilling of these scraps, made up of material certified for the aeronautical field.

[0008] Generally speaking, processes aimed at separating the matrix from the fibres in order to direct them towards separate recycling channels are not economically or energetically viable to date.

[0009] In addition, the diversity of fiber rates, matrices and part thicknesses makes so-called open-loop recycling difficult.

[0010] Document WO 2021 / 259757 describes a process for recycling CF / PEKK composite scraps.

[0011] DAY R et al.: "Recycling of APC-2 offcuts", COMPOSITES MANUFACTURING, BUTTERWORTH SCIENTIFIC, GUILDFORD, SURREY, GB, vol. 5, no. 3, 1 September 1994 (1994-09-01), pages 187-193, describes a process for recycling CF / PEEK prepreg offcuts.

[0012] Document EP 0 643 093 describes the recycling of a composite reinforced with glass fibers in a polypropylene thermoplastic matrix.

[0013] The invention aims to improve the rate of use of the material by recovering the offcuts during implementation.

[0014] To this end, the invention relates to a method for manufacturing two composite parts comprising a structural part made of a composite reinforced by continuous fibers, according to a volume ratio of continuous fibers, in a matrix made of a first thermoplastic polymer with a first melting temperature, and a composite part comprising a fibrous reinforcement comprising sections comprising discontinuous fibers according to a volume ratio of discontinuous fibers and a thermoplastic matrix with a second melting temperature and comprising the first thermoplastic polymer, characterized in that it comprises steps consisting of:

[0015] i) obtain a composite preform with continuous reinforcement suitable for obtaining the structural part;

[0016] ii) obtaining the structural part from the continuously reinforced composite preform;

[0017] iii) cut out the structural part;

[0018] wherein steps i) and iii) produce falls, the method further comprising the steps of:

[0019] iv) recover the waste produced in steps i) and iii);

[0020] v) crushing the waste recovered in step iv) to obtain a ground material;

[0021] vi) compounding the ground material obtained in step v) to obtain a compound;

[0022] vii) obtaining the second composite part by shaping the compound obtained in step vi).

[0023] This process makes it possible to make the best use of the material, particularly high added value materials such as thermoplastic matrix composites and high-performance fibers.

[0024] According to a surprising effect, the process makes it possible to produce the part reinforced by discontinuous fibers with a fiber content higher than what is possible to obtain with the processes of the prior art and the commercially available compounds.

[0025] The invention is implemented according to the embodiments and variants set out below, which are to be considered individually or in any technically effective combination.

[0026] According to an example of implementation the first polymer is a PPS, the volume rate of continuous fibers is greater than 40% and the volume rate of discontinuous fibers is greater than 40%.

[0027] Preferably, a greater length of the composite sections obtained in step v) is between 2 mm and 15 mm, preferably between 4 mm and 10 mm and more preferably between 6 mm and 10 mm.

[0028] Advantageously, step v) comprises grinding by a knife mill in which a cutting angle γ of the knives is between 30° and 40°, a clearance angle α is between 20° and 30° and a cutting angle β is at least 30° with α+β+γ = 90°.

[0029] This type of knife allows for clean cutting of scraps and greatly reduces the risk of jamming.

[0030] According to one embodiment, step vi) comprises the addition, during compounding, of a second polymer having a third melting temperature and alloyable with the first polymer, to the crushed scraps. This addition makes it possible to control both the fiber content in the aggregate and the melting temperature of the aggregate.

[0031] Thus, the third melting temperature of the second polymer may be lower, higher or equal to that of the first polymer.

[0032] According to one embodiment, the compounding step vi) is carried out in an extrusion device comprising an assembly of a plurality of screw lengths, a screw length comprising a heating sleeve and a screw comprising a feed zone, a heating zone and a mixing zone, said extrusion device comprising at least two lengths downstream of a ground material feed point in a direction of progression of the material in the extrusion device.

[0033] According to an exemplary embodiment, the first polymer is chosen from PEEK, PEK and PAEK and in which the second polymer is chosen from PEEK, PEK, PAEK and LMPAEK, the volume rate of continuous fibers is greater than 50% and the volume rate of discontinuous fibers is greater than 40%.

[0034] Advantageously, during step vi) the feed point of the ground material into the extrusion device is located at least two lengths downstream of the feed point of the second polymer in the direction of progression of the material.

[0035] According to one embodiment, the compound obtained in step vi) is a wound wire and step vii) is carried out by an additive manufacturing process involving the melting of the wire.

[0036] According to another embodiment, the compound in step vi) is a granule and step vii) is carried out by plastic injection.

[0037] Thus, the method of the invention offers several alternatives for the production of the part reinforced by discontinuous fibers.

[0038] According to a particular embodiment, the method comprises, after step vii), a step consisting of:

[0039] (viii) bonding the second composite part to the structural part.

[0040] According to this latter embodiment, steps vii) and viii) are carried out by overmolding the added part onto the structural part.

[0041] According to another variant, step viii) is carried out by welding the added part onto the structural part.

[0042] According to yet another variant, step viii) is carried out by co-consolidation of the added part and the structural part.

[0043] Of course, two or more of these variants can be combined when making the same structural part.

[0044] Thus, according to one embodiment, the result of adding a virgin polymer to the ground material has the effect that the second melting temperature is higher than the first melting temperature. This embodiment is for example suitable for producing an assembly of the second part on the structural part by overmolding or by co-consolidation.

[0045] Alternatively, the result of this addition of virgin polymer is also to obtain a second melting temperature lower than the first melting temperature. This method of implementation is, for example, suitable for producing the second part by plastic injection molding.

[0046] According to an exemplary implementation, the first polymer is a LMPEAK and the second polymer is selected from PEEK and PEKK.

[0047] According to another exemplary embodiment, the first polymer is a PEI and the second polymer is chosen from PEEK, PEKK and LMPAEK.

[0048] These two examples of implementation lead to a compound having a melting temperature higher than that of the polymer constituting the matrix of the structural part, these methods of implementation being more suited to overmolding and co-consolidation.

[0049] Alternatively, inverse combinations produce a compound whose melting temperature is lower than that of the matrix polymer of the structural part.

[0050] The invention is implemented according to the preferred embodiments and examples, which are in no way limiting, set out below with reference to figures 1 to 8 in which: Fig. 1

[0051] is a top view of an example of blanks cut into a panoply from a consolidated plate reinforced with continuous fibers; Fig.2

[0052] shows in a perspective view simplified examples of cutouts made on a structural part obtained by stamping one of the blanks of the; Fig.3

[0053] is a flowchart summarizing the method of the invention; Fig.4

[0054] is a perspective and exploded view of an exemplary embodiment of a spar implementing the method of the invention; Fig.5

[0055] shows in a perspective and exploded view an example of tooling for the production of the spar of the; Fig.6

[0056] shows in two perspective views from above and below an example of the embodiment of a rudder pedal by implementing the method of the invention; Fig.7

[0057] shows a front view of an example of a shredder knife suitable for shredding composite waste with a detailed view of the cutting area showing characteristic angles; Fig.8

[0058] is a schematic sectional view of a screw length of an injection device.

[0059] according to an exemplary embodiment, a composite part with a thermoplastic matrix is ​​obtained from a blank (110), that is to say an essentially flat blank cut out according to an appropriate contour, which blank is stamped between a punch and a die after said blank has been heated to a temperature of the order of the melting temperature of the polymer matrix.

[0060] According to an exemplary embodiment, the blank (110) is for example cut from a consolidated composite plate (100) reinforced by fibers comprising continuous fibers (101), that is to say fibers extending continuously from one edge to another of the consolidated plate (100) and which, after cutting the blank, extend from one edge to another of the blank (110).

[0061] By way of non-limiting examples, the plate (100) is made of a thermoplastic polymer PEEK (polyetheretherketone), PEKK (polyetherketoneketone), PAEK (polyaryletherketone), PEI (polyetherimide), PPS (polyphenylene sulfide) or any other thermoplastic polymer.

[0062] Fiber reinforcements are carbon, glass or aramid fibers, but these examples are not exhaustive.

[0063] The blank is cut, for example, using a high-pressure abrasive water jet.

[0064] Several blanks, organized in a panoply, are cut from such a plate (100). However, even by optimizing the nesting of the blanks cut from the plate, there remains a waste in the form of a skeleton (120, filled in dotted lines in the figure) which represents a significant part of the initial plate, typically between 30% and 50% of the volume of the consolidated plate before cutting out the panoply,

[0065] after stamping, the part obtained is trimmed on its edges to eliminate an unconsolidated part inherent in the stamping process and is also trimmed in current section according to various trajectories (211, 212), in particular to create lights there.

[0066] These cutouts are for example carried out by milling and also produce offcuts (220) made of the same material as the structural part (200).

[0067] According to the prior art, these offcuts, both the skeletons of the panoply and those resulting from the cutting of the raw stamping part, are discarded and must be treated according to a specific process in a waste disposal center, which results in additional costs.

[0068] To date, there is no industrial recycling channel for scraps of these composite materials reinforced with continuous fibres.

[0069] At best, these scraps are burned in a process known as energy recovery, which emits greenhouse gases.

[0070] The difficulties in recycling are due in particular to the fact of mixing the polymer constituting the matrix with fibrous reinforcements and, on the other hand, on the scale of an industrial production installation, to the diversity of the materials processed both from the point of view of the matrices and the reinforcing fibres and the thicknesses.

[0071] Given the sorting operations that would be necessary, the difficulty of visually differentiating the nature of the waste and the low value of the waste as such, such recycling operations using traditional industrial channels have too significant an impact on production costs, to the point that, to date, it remains more profitable to pay for special waste treatment than to set up processes allowing external recycling.

[0072] Furthermore, the methods for obtaining composite parts with a thermoplastic matrix and continuous fiber reinforcement are not limited to the stamping of blanks taken from consolidated plates but can implement other methods such as partially consolidated blanks obtained by placing fibers, consolidation in the form of unconsolidated folds, etc. without these examples being either exhaustive or limiting.

[0073] However, whatever the process, scraps are produced, these scraps being made up of materials having undergone different thermal histories with equivalent composition, depending on the process implemented for the production of the part reinforced by continuous fibers, thermal histories which result in cohesion and in particular different porosity rates, even if these remain within strict acceptable limits.

[0074] The invention relates to recycling, described as internal, in which the offcuts are used, after appropriate treatment as set out below, as material for the production of parts with non-continuous reinforcement.

[0075] The method of the invention also has the advantage of being able to combine scraps of the same material but from different implementation processes by eliminating the thermal histories associated with these processes and providing a homogeneous material.

[0076] However, surprisingly, the process of the invention takes advantage of the prior implementation of the material by making it possible to achieve reinforcement rates higher than what is possible to obtain with a raw material not derived from the process of the invention.

[0077] In industrial fields where the material must be pre-qualified, particularly in the aeronautical field, the material resulting from the process of the invention benefits, at least partially, from the qualification of the material from which the offcuts come, thus facilitating this process.

[0078] In certain embodiments, for the manufacture of parts comprising a structural part (200) reinforced by continuous fibers on which other parts such as supports or cleats are attached, these attached parts, obtained from scraps from the manufacture of the structural part, are particularly suitable for being integrated into said structural part, or into a structural part from the same batch, in an integral manner, without fixing, by processes such as welding, co-consolidation or overmolding, with perfect bonding of the polymers present.

[0079] Also, the parts obtained from recycled material from scraps are generally parts with high added value, due to their high reinforcement rate and the nature of their polymer matrix, and directing the scraps towards a perfectly identified use in a production unit greatly increases the profitability of the operation.

[0080] , to this end, the invention relates to a method comprising a first step of collecting the scraps (310).

[0081] According to a particular, non-limiting embodiment, the offcuts are assigned to the same production process as that of the structural part so that they remain, for example, referenced in the ERP in the same general range.

[0082] Grinding

[0083] According to a grinding step (320) the offcuts are ground, so as to constitute sections of appropriate length.

[0084] According to one embodiment, the grinding comprises a first crushing step, aimed at breaking the scraps into sections whose greatest length is between 10 mm and 100 mm, preferably between 10 mm and 50 mm.

[0085] Alternatively, the offcuts can be cut into such sections on the blank trimmer.

[0086] Following the crushing operation, screening is carried out to eliminate sections less than 10 mm long.

[0087] Grinding is preferably carried out by a slow-speed knife mill, producing clean cuts of the sections without crushing and without delamination away from the edges of the sections.

[0088] To this end, the crusher preferably uses knives (700) adapted to the composite, avoiding excessive cutting forces and blockages.

[0089] According to an exemplary embodiment, a knife comprises 2 teeth (701, 702) thus providing a high clearance (703) compared to traditional knives used in particular in the grinding of injection cores of unfilled plastic material.

[0090] According to this embodiment, each of the two teeth has a cutting angle γ (711) of between 30° and 40°, preferably between 35° and 40°, so as to reduce cutting forces, a clearance angle α (712) of between 20° and 30° to limit jamming and a cutting angle β (713) of at least 30° so as to provide a sufficient resistant section to the tooth, with α+β+γ = 90°.

[0091] In addition, the very positive cutting angle promotes clean cutting of the scraps while maintaining cohesion between the polymer constituting the matrix and the fibers.

[0092] Following the grinding operation, the ground material is sieved so as to eliminate sections less than 2 mm in length; according to a preferred embodiment, the ground material is sieved to eliminate sections less than 6 mm in length.

[0093] The ground material is washed, in particular to eliminate any presence of abrasive when the offcuts come from water jet cutting, lubricant or any other pollution to which the material was exposed during these cutting or processing stages, any metal particles present in the ground material are removed by a magnetic filter, then the ground material is dried in an oven, for example at 150°C for 6 hours.

[0094] Thus, the shredded material is made up of sections whose greatest average length is statistically between 2 mm and 15 mm, preferably 4 mm and 10 mm and more preferably between 6 mm and 10 mm at + / - 3 standard deviations from the average. The shredded material comprises both polymer and sections of fibers from the continuous fibers of the structural part, the polymer being at least partially bonded to the fibers.

[0095] The creation of the scraps results from cutting or trimming of consolidated plates for the ranges of blanks or semi-finished parts which have been subject to consolidation for example during stamping, consolidation in shape or at least partial consolidation during draping by high-speed fiber placement, or even pre-impregnated plies. In fact, the material included in the scraps has, in most cases, already undergone a thermomechanical cycle of melting of the polymer constituting the matrix, including in particular compression and degassing for impregnation and intimate bonding of the reinforcements and the matrix and porosity rates of less than 5% or commonly less than 2%.

[0096] Compounding

[0097] According to a compounding step (330) the ground material is placed in an extruder, in order to carry out compounding.

[0098] Compounding is a process known from the prior art consisting of passing the ground material through an extrusion device, such as a screw extruder, in order to extrude a substantially cylindrical wire through a die.

[0099] Said yarn is a composite yarn comprising a thermoplastic polymer and discontinuous fibers corresponding to the portions of reinforcing fibers initially continuous and included in the structural part then present in the sections of the shred.

[0100] Discontinuous fibers can be short fibers with an aspect ratio l / d less than 500 where l is the fiber length and d is the fiber diameter or long fibers with an aspect ratio l / d greater than 500. The fiber length depends on the dimensions of the sections in the regrind as well as the conditions under which the compounding operation is carried out.

[0101] However, the compounding implemented for the revaluation of offcuts differs from conventional compounding by at least two characteristics:

[0102] - the reinforcements are already present in the ground material whereas for conventional compounding the reinforcements are added as filler to the molten polymer at the screw level during extrusion;

[0103] - the reinforcement rate in the shred and in the extruded yarn are much higher than what is conventionally used in compounding where the fiber rate very rarely reaches 40% while the process of recycling scraps makes it possible to achieve reinforcement rates higher than 40% or even higher than 50% by volume.

[0104] These differences have consequences on the conditions for implementing the compounding stage.

[0105] Thus, unlike conventional compounding where the reinforcing filler is introduced either in the form of filler alone or in the form of pre-compounded pellets comprising the filler and calibrated in shape, the reinforcement is here introduced in the form of ground material, in an uncalibrated form, comprising a high level of fibres bound to the polymer.

[0106] The extruder is a single-screw or twin-screw extruder but whose L / D ratio of the total length of the screw in relation to the diameter of the cut part is preferably greater than 30 or even greater than 40. This configuration allows for better homogenization of the material.

[0107] according to a schematic embodiment, the extrusion device comprises a sleeve (810) in which one or two screws (820) rotate depending on whether it is a single-screw or twin-screw extruder.

[0108] The entire extrusion device is made up of the assembly of several successive lengths (800) as shown.

[0109] Schematically over such a length (800), the screw (820) comprises a feed zone (821), a heating zone (822) where the material is subjected to intense mechanical stress which causes it to melt, and a mixing zone (823) to homogenize the material. The length of the different zones varies depending on the extruders. The pitch of the worm screw and the depth of the threads reduce when passing from the feed zone (821) to the end of the heating zone (823) in the direction of progression of the material (850).

[0110] Advantageously, the barrel of the extrusion screw or screws is preheated to a temperature of the order of 0.8 to 0.9 Tf where Tf is the melting temperature of the polymer constituting the matrix of the ground material expressed in Celsius. This preheating of the barrel allows the temperature of the material to rise more quickly than under the sole effect of the compression and shear imposed on it by the screw (8200).

[0111] During extrusion, under the effect of mechanical stress, the temperature in the barrel reaches at least Tf.

[0112] The ground material is introduced into a feed zone (821) and the extrusion device comprises at least 2 successive lengths (800) between the feed point, where the ground material is introduced, and a third length leading to a die from which the extruded wire emerges.

[0113] Thus, in the case of direct compounding of the ground material without adding material, for example in the case of falling PPS carbon composite, the extrusion device comprises at least 3 lengths (800): two lengths following the ground material feed and one length leading to the die.

[0114] In the case of a material addition, either to modify the melting temperature and / or to modify the fiber content, the material addition is introduced first into the extrusion device in the direction of progression of the material and the point of introduction of the ground material is made at least one length and preferably two lengths (800) downstream of the point of introduction of the material addition in the direction of progression of the material. Then, in the direction of progression of the material, two lengths (800) are necessary before a last length leading to the die. Also, in this configuration the extrusion device comprises at least 4 lengths and preferably 5 lengths (800).

[0115] Preheating, carried out along the length of the extrusion device, as well as the minimum of two lengths following the introduction of the ground material until the final length leading to extrusion, are necessary to obtain good homogeneity of the material. It is possible to consider more than 2 lengths between the introduction of the ground material and the last length leading to extrusion, however in this case the length of the fibers in the extruded yarn is reduced.

[0116] At the die outlet, the extruded wire is cooled with water. According to one embodiment, to avoid excessively abrupt cooling leading to the creation of stresses in the wire, which then deforms under the effect of these stresses, the cooling bath can be preheated to a temperature between 70°C and 95°C.

[0117] Finishing

[0118] According to embodiments, the composite wire thus extruded is wound for subsequent use, for example in a wire fusion additive manufacturing process.

[0119] In this case the process is adjusted, particularly at the compounding stage, to obtain a rate and length of discontinuous fibers in the compound compatible with the additive manufacturing process.

[0120] According to another embodiment, the extruded wire is cut into sections, for example of a length of the order of 2 mm, in order to constitute granules or pellets suitable for plastic injection, said granules comprising short fibers.

[0121] Plastic injection can then be used for the production of molded parts, as shown in an example, or for the extrusion of profiles, tubes or plates.

[0122] Adjustment

[0123] The achievable fiber content depends on the viscosity of the polymer at the compounding temperature and the ability of the polymer to impregnate the fibers so that the extruded yarn is cohesive.

[0124] Without being bound by any theory, it seems that the impregnation of the fibers by the polymer and the cohesion of the composite in them is, at least in part, inherited in the extruded wire from the operations of implementing the material constituting the offcut during the production of the structural part.

[0125] The process thus allows the yarn to maintain its cohesion up to volume rates of fibers in the yarn or granule of up to 60%.

[0126] Such volume rates of discontinuous fibers are far beyond those obtained in commercially available pellets which are not produced by the process of the invention.

[0127] The fiber content in the extruded yarn can be controlled by adding polymer pellets or chips during compounding, so as to achieve a fiber content lower than that included in the scrap.

[0128] The polymer added during compounding can be the same as that constituting the matrix of the scraps, or be of a different nature, provided that it is alloyable with the original polymer, or even a combination of the two.

[0129] Adding a different, alloyable polymer to the first also allows the melting point of the wire or pellet to be adjusted.

[0130] Thus if (325), after grinding, the fiber rate x of the ground material is equal to the fiber rate X targeted in the granule and if the melting temperature Tf of the ground material is equal to the melting temperature tf targeted for the granule, then the compounding is carried out directly from the ground material. Otherwise, during an adjustment step (335), a polymer is added during the compounding.

[0131] The polymer added during the adjustment step must be alloyable with the first polymer constituting the matrix of the scraps. It can be the same polymer, in which case only the fiber content of the extruded yarn is modified, or it can be another polymer, in which case both the fiber content and the melting temperature of the yarn are modified compared to that of the matrix of the composite constituting the structural part.

[0132] As explained above, this filler polymer is preferably introduced into the extrusion device upstream of the introduction of the ground material in the direction of progression of the material.

[0133] According to implementation examples, the polymer constituting the matrix of the scraps is from the poly(aryletherketone) PAEK family and the polymer added during the adjustment step is also from the PAEK family or a PEI.

[0134] PAEKs are a family of thermoplastic polymers with high stability at high temperatures and high mechanical characteristics, making them particularly suitable for aeronautical structural applications.

[0135] The PAEK family includes low melting point PEK, PEEK, PEKK, PEEKK, PEKEKK, PEEEK, PDEK and LMPAEK®.

[0136] Thus, the second melting temperature of the polymer included in the composition of the second part is a function of a third melting temperature of the filler polymer.

[0137] For example, if the scrap matrix is ​​made of a low melting temperature PAEK (LMPAEK®), adding PEEK or PEKK to the ground material during compounding increases the melting temperature of the granule.

[0138] Conversely, if the polymer constituting the matrix of the scraps is, for example, PEEK, the addition of LMPAEK or PEI to the ground material during the compounding operation makes it possible to lower the melting temperature of the granule in comparison with the melting temperature of the polymer constituting the matrix of the scraps.

[0139] Extruded yarn or pellet is used to make a part reinforced with discontinuous fibers during a manufacturing step (340), by additive manufacturing or by a plastic injection molding process.

[0140] According to an exemplary embodiment, the part produced during this manufacturing step (340) is assembled to a structural part during an integration step (350), preferably by a method without fixing.

[0141] Non-limiting examples of such methods include:

[0142] - overmolding, during which the added part is injected directly onto the structural part, in this case the adjustment step (335) preferably aims to obtain a granule having a melting temperature higher than that of the polymer constituting the matrix of the structural part;

[0143] – co-consolidation in this case the adjustment step (335) preferably aims to obtain a granule having a melting temperature higher than that of the polymer constituting the matrix of the structural part;

[0144] – Welding, in this case the adjustment step (335) aims to possibly lower the rate of discontinuous fibers in the granule without modifying the melting temperature.

[0145] According to an exemplary embodiment, the structural part is an aircraft frame and the added part is an accessory support ("bracket") or a cleat linked to this frame.

[0146] Compounding subjects the ground material to severe thermo-mechanical stress bringing the material to a state of fusion. This stress eliminates cohesion defects, even slight ones, present in the scraps due to the processing methods including trimming, eliminating, for example, porosities and delaminations, although surprisingly the process of the invention takes advantage of the impregnation of the fibers and the homogeneity of the material obtained during previous processing of the structural part such as consolidation, stamping, etc.

[0147] according to another example, the structural part is a spar (400) made of a low melting temperature PAEK thermoplastic matrix composite (LMPAEK®) and comprising a continuous fibrous reinforcement of carbon fibers corresponding to 60% by volume of fibers (66% by mass).

[0148] Said spar comprises a plurality of ribs (4101…4105). According to an exemplary embodiment, said ribs are produced by plastic injection molding with a granule obtained from trimming offcuts of said spar (400), in practice, from one or more similar spars produced and trimmed previously.

[0149] Said scraps are ground and added with a PEEK or PEKK type polymer, alloyable in LMPAEK®, so as to increase the melting temperature of the polymer matrix and to reduce the fiber content in the granule to a rate of between 40% and 55% by mass. The high fiber content achievable by the process of the invention makes it possible to achieve the mechanical characteristics targeted for the ribs.

[0150] according to an exemplary embodiment, the ribs (4101…4105) are placed in a mandrel tool (590), assembled, such that the soles of said ribs to be assembled with wings of the spar are flush with the surface of the mandrel tool.

[0151] A preform (500) of the spar is draped over the mandrel tool (590), for example by automatic placement of fibers or by manual draping of non-woven plies. The plies produced come into contact with the soles of the ribs placed in the mandrel tool (590).

[0152] The assembly is then bagged tightly, evacuated and heated to a temperature equal to or greater than the melting temperature of the preform matrix (500).

[0153] This temperature is lower than the melting temperature of the polymer (modified during compounding) constituting the matrix of the ribs, but remains sufficient to activate self-hesion and welding phenomena at the interfaces between said preform (500) and the ribs (4101…4105) without the latter losing their cohesion and deforming excessively.

[0154] The preform (500) thus undergoes a pressure-temperature cycle capable of consolidating the spar and integrating the ribs.

[0155] After demolding, the spar is trimmed to give it its final profile. The offcuts from this trimming are used to make a granule suitable for plastic injection molding of the ribs.

[0156] It should be noted that they represent a composite spar demonstrator. The person skilled in the art understands that the length of the wing is nearly 2 orders of magnitude greater than the width of the ribs, and that consequently the volume of scrap collected during the final trimming is sufficient to produce one or more of these ribs.

[0157] according to another example of embodiment, scraps of a PPS matrix composite reinforced with continuous carbon fibers with a volume rate of 50% (57% by mass) are ground then formed into granules without adding virgin polymer during compounding.

[0158] These granules are used, for example, to obtain by injection molding a rudder pedal for an aircraft. This part is traditionally made of aluminum alloy, the shape of this part makes its production in composite with continuous reinforcement difficult or even impossible, and its production by plastic injection from a commercially available granule on the one hand does not allow sufficient reinforcement rates to be achieved and would require qualification of the material. The use of a granule obtained from scrap aeronautical parts makes it possible to solve these two problems, with an injected part (600) comprising 57% fibers by mass (50% by volume) and made of an already qualified material.

[0159] The above examples show that the invention achieves the intended aim and makes it possible to recover, using a high added value process, composite manufacturing offcuts previously treated as ultimate waste.

Claims

Method for manufacturing two composite parts comprising a structural part (200, 400) made of a composite reinforced by continuous fibers, according to a volume ratio of continuous fibers, in a matrix made of a first thermoplastic polymer with a first melting temperature, and a composite part (410, 600) comprising a fibrous reinforcement comprising discontinuous fibers, sections of continuous fibers, according to a volume ratio of discontinuous fibers and a thermoplastic matrix with a second melting temperature and comprising the first thermoplastic polymer, characterized in that it comprises steps consisting in:i) obtaining a composite preform (110, 500) with continuous reinforcement suitable for obtaining the structural part;ii) obtaining the structural part (200, 400) from the composite preform with continuous reinforcement;iii) trimming the structural part (200, 400);in which steps i) and iii) produce scraps (120, 220) and which further comprises the steps of:iv) recovering (310) the scraps (120, 220) produced in steps i) and iii);v) grinding (320) the scraps recovered in step iv) to obtain a ground material consisting of composite sections;vi) carrying out a compounding (330) of the ground material obtained in step v) to obtain a compound;vii) obtaining the second composite part (410, 600) by shaping the compound obtained in step vi).; The method of claim 1, wherein the first polymer is a PPS, the volume content of continuous fibers is greater than 40% and the volume content of discontinuous fibers is greater than 40%. Method according to claim 1, in which the second composite part is obtained by plastic injection. Method according to claim 1, in which a greater length of the composite sections obtained in step v) is between 2 mm and 15 mm, preferably between 4 mm and 10 mm and more preferably between 6 mm and 10 mm. The method of claim 1, wherein step vi) comprises an adjustment step (335) comprising adding, during compounding, a second polymer having a third melting temperature and alloyable with the first polymer, to the ground scraps. Method according to claim 1, wherein step v) comprises grinding by a knife mill in which a cutting angle γ (711) of the knives is between 30° and 40°, a clearance angle α (712) is between 20° and 30° and a cutting angle β (713) is at least 30° with α+β+γ = 90°. Method according to claim 1, in which step vi) is carried out in an extrusion device comprising an assembly of a plurality of screw lengths (800), a screw length (800) comprising a heating sleeve (810) and a screw (820) comprising a feed zone (821), a heating zone (822) and a mixing zone (823), in a direction of progression of the material (850), the extrusion device comprising at least two lengths (800) downstream of a ground material feed point in the direction of progression of the material (850). Method according to claim 7, wherein, during step vi), the sheath (810) is preheated to a temperature between 0.8 and 0.9 Tf where Tf is the first melting temperature expressed in Celsius. The method of claim 5, wherein the first polymer and the second polymer are poly(aryletherketone), the volume content of continuous fibers is greater than 50% and the volume content of discontinuous fibers is greater than 40%. A method according to claim 9, wherein the first polymer and the second polymer are poly(aryletherketone), the volume ratio of continuous fibers is greater than 50% and the volume ratio of discontinuous fibers is greater than 40%, and wherein during step vi) the point of feeding of the ground material into the extrusion device is located at least two lengths (800) downstream of the point of feeding of the second polymer in the direction of progression of the material (850). The method of claim 9, wherein the first and second polymers are selected from LMPAEK, PEEK and PEK. The method of claim 5, wherein the second melting temperature is higher than the first melting temperature. The method of claim 5, wherein the second melting temperature is lower than the first melting temperature. The method of claim 13, wherein the first polymer is a poly(aryletherketone) and the second polymer is a PEI. Method according to claim 1, comprising after step vii) a step viii) comprising: bonding the second composite part to the structural part. Method according to claim 15, in which the compound obtained in step vi) is a wound wire and step vii) is carried out by an additive manufacturing process implementing the melting of the wire. Method according to claim 15, in which the compound obtained in step vi) is a granule and step vii) is carried out by plastic injection. Method according to claim 15, in which steps vii) and viii) are carried out by overmolding the second composite part onto the structural part (200). The method of claim 145, wherein step viii) is performed by welding the second composite part to the structural part (200). The method of claim 15, wherein step viii) is performed by co-consolidation of the second composite part and the structural part (400).

Images