FR3070625A1 - PROCESS FOR MAKING PREFORMS WITH APPLICATION OF A BINDER ON DRY FIBER FORMED OF SEVERAL INITIAL FIBERS - Google Patents

Abstract

The present invention relates in particular to a process for producing preforms comprising applying a binder to at least one continuous dry fiber (9), each fiber being formed from at least two distinct initial fibers, and the draping of said fiber provided with binder by means of a draping head to form a preform. The application of binder is carried out by means of a fiberization nozzle (50) comprising a discharge orifice (53) supplied with liquid or pasty binder, and one or more injection orifices (57) supplied with gas under pressure, so that said nozzle is able to deliver the binder in the form of a spiral filament (92), the filament turns being deposited on the fiber moving past a nozzle to obtain a fiber provided with filaments (93) of binder, said binder filaments providing a bond between the initial fibers.

Description

The present invention relates to a process for producing preforms by applying a binder to dry fibers and by draping said fibers. The present invention also relates to a process for producing parts made of composite material from such preforms.

Fiber application or draping machines are known for automatic draping on a draping tool, such as a male or female mold, of a wide strip formed of one or more fibers, in particular continuous fibers. flat ribbons, commonly called wicks, in particular carbon fibers made up of a multitude of carbon threads or filaments.

These machines conventionally comprise a fiber application head comprising guide means for guiding the fiber or fibers towards the layup surface. These machines further include fiber storage means such as a remote creel, and routing means for routing fibers from said storage means to the head, and optionally a system for moving the lay-up head. In the case of a strip formed of several fibers, the head guide means make it possible to bring the fibers towards the draping surface in the form of a strip, in which the fibers are arranged substantially edge to edge in parallel. For draping in contact with the fibers, these machines, conventionally called fiber placement machines, comprise a head fitted with a compacting roller intended to come into contact against the draping surface in order to apply the strip, the guide means guiding the fibers to the roller in the form of a strip.

The fibers applied can be fibers pre-impregnated with a thermoplastic or thermosetting polymer, or dry fibers provided with a binder, conventionally called "binder", to impart a tacky character to the fibers during draping.

In the case of draping of fibers pre-impregnated with polymer, the preform, known as pre-impregnated, obtained after draping, is subsequently hardened or polymerized by passing through an oven to obtain a part made of composite material.

In the case of dry fibers with binder, a polymer is injected or infused into the preform, called dry, before a hardening step. The dry preforms with binder comprise a small quantity of binder, generally less than 5% by weight, making it possible to maintain the cohesion of the preform, while allowing its subsequent impregnation.

For the layup of dry fibers provided with a binder, a first technique consists in using fibers already coated with a binder by the supplier of the raw material. To date, such fibers, known as powdered and / or veiled, are proposed in coils, in which the binders are in the form of powder and / or a veil on one surface or on each surface of the fibers. The binder is applied to a wide strip of fibers, the strip is then split into several fibers calibrated to the desired width for use in an automatic draping machine. This technique has the drawback of using an expensive product which is difficult to use for certain applications, in particular in the automotive field. Furthermore, during the slitting, filaments are cut on the edges of the fiber, which causes significant fouling of the machines.

A second solution consists in coating the binder in line on a dry fiber by means of a nozzle, in particular a lip nozzle, for example at the level of the head as described in patent document FR2882681, or at the level of the creel as described in document FR3016827. In patent document FR2999973, it has been proposed to apply the binder in the form of a wire to the fibers, in particular at the level of the creel.

It has also been proposed in patent application FRI6 / 70088 filed by the applicant on March 7, 2016, to apply the binder to a fiber by means of at least one fiberizing nozzle capable of delivering the binder in the form of a spiral filament.

The object of the present invention is to propose an alternative solution to that proposed previously.

To this end, the present invention provides a process for producing preforms, by draping fibers on a draping surface, comprising the application of a liquid or pasty binder on at least one continuous dry fiber, and the draping of said fiber. provided with binder by means of a lay-up head to form a preform, characterized in that the application of binder to a fiber is carried out by means of at least one fiberizing nozzle comprising a discharge orifice supplied with liquid binder or pasty under pressure, and one or more injection ports supplied with pressurized gas, for example compressed air, so that said nozzle is capable of delivering the binder in the form of a spiral filament, the filament turns settling on the fiber running opposite the nozzle to obtain a fiber provided with binder filaments, said binder filaments ensuring a connection between the initial fibers, and thus the cohesion of the fiber.

According to the invention, the binder is applied to dry fibers by means of a fiberizing nozzle, the filament turns are deposited on the fiber arranged opposite the nozzle, in particular in the form of loops more or less regular overlapping. The method according to the invention makes it possible to drape dry fibers with binder starting from an inexpensive raw material. The use of fiberizing nozzles allows a simple and precise application of binder. The binder filaments form a kind of veil allowing subsequent infusion of the preform. The application of binder according to the invention also makes it possible to ensure an assembly between the two initial fibers forming the fiber, and thus makes it possible to easily form fibers with the desired properties by combining different initial fibers.

Preferably, at least one of the initial fibers is a continuous unidirectional continuous fiber, for example a carbon fiber, a glass fiber, an aramid fiber, a polyethylene fiber, and / or a natural fiber, such as for example a flax fiber, formed from a multitude of threads or filaments, for example a fiber from 12 to 50 K in the case of carbon, or a fiber from 1200 to 9600 Tex for glass. These initial unidirectional continuous fibers can have widths of an eighth of an inch, a quarter of an inch or a half-inch (1/8, 1/4 or 1/2), or larger widths, greater than half an inch .

According to one embodiment, each fiber is formed from two initial fibers of the same kind, for example identical.

The initial fibers can be of the same nature, the method according to the invention then makes it possible to obtain a fiber of high titre from initial fibers of low titre. For example, each fiber is formed from two, three or four initial glass fibers of 2400 Tex or 4800 Tex.

According to other embodiments, each fiber can be formed of initial fibers of different natures, having different properties.

Each fiber can be formed from unidirectional continuous initial fibers of different natures, for example one or more initial glass fibers and one or more initial carbon fibers.

One or more second initial fibers may be added to one or more first fibers, in particular unidirectional continuous fibers, to modify one or more properties of the resulting preform, for example to increase its conductivity, or to increase its permeability, the second fiber or fibers initials used as draining.

One or more second initial fibers, for example of polymer material, preferably thermoplastic, can be added to one or more first fibers, in particular continuous unidirectional fibers, the said second initial fiber or fibers serving as filler in the final composite material, for example for confer volume in the final part, the said second initial fiber or fibers being lighter and / or less expensive than the first initial fiber or fibers.

One or more second initial fibers of polymer material, preferably thermoplastic, can be added to one or more first fibers, in particular continuous unidirectional fibers, the said second initial fiber or fibers being intended to form at least partially the polymer matrix of the final part made of composite material.

The binder used can comprise one or more thermosetting polymers, for example an epoxy, polyester, vinyl ester, phenolic, polyimide, or bismaleimide polymer, or one or more thermoplastic polymers, for example a polyamide, thermoplastic polyester, polyethersulfone, polyetheretherketone, thermoplastic polyurethane, thermoplastic epoxy, or polyolefin. According to one embodiment, the binder is a thermoplastic copolyester.

According to one embodiment, each fiber comprises initial fibers from spools of fibers unwound from the center of the spool or from outside the spool, without rotation of the spool, preferably unwound from the center of the spool. Obtaining fibers from initial fibers unwound allows us to offer a simple creel of design. Each initial fiber coming from a spool of unwound fiber turns around itself for each turn wound from the spool, the initial fiber thus having twisted filaments. Each initial fiber can make a turn on itself on less than one length of turn or on more than one length of turn. Thus, the resulting fiber passing at the level of the nozzle may have a constant or non-constant section, in particular when each initial fiber makes a turn on itself over a short length of fiber. The resulting fiber may have a flat or flattened shape, with two opposite main faces, flat or non-planar, in particular concave, or a generally circular section.

According to one embodiment, each fiber is formed from initial fibers from spools of fibers unwound in different directions, so that the initial fibers overlap, the fiber being formed from twisted initial fibers. The resulting fiber formed from twisted initial fibers has an elliptical or circular section. The presence of twisted filaments in each initial fiber, and of twisted initial fibers, combined with the presence of a binder guaranteeing the maintenance of the initial fibers, makes it possible to obtain fibers of substantial strength having good cohesion, from which it is possible to drape plies of heavy grammage and / or drape plies of fibers with spacings between fibers.

According to one embodiment, during the application of binder, the filament turns are deposited on the fiber and go around the fiber so that the fiber is coated with binder filaments, ensuring good retention of the initial fibers and different filaments constituting the fiber, facilitating the draping operations and making it possible to obtain a good quality of draping. The use of a dry fiber thus provided with a binder facilitates bonding between two plies of the preform and ultimately improves the cohesion of the resulting preform. Furthermore, the method according to the invention makes it possible to apply the binder by means of a single nozzle, and thus simplifies and limits the size of the binder application device.

According to one embodiment, during the application of binder, portions of filament turns are pressed against the fiber by overlapping, thus improving the retention of the initial fibers, and therefore of the different filaments of the fiber.

According to one embodiment, after passing through the fiberizing nozzle, the fiber passes through a calibration and / or calendering system to calibrate the fiber in width, and / or compress the fiber in thickness, the fiber being subjected to pressure on each main face. During this calendering, the binder filaments applied to the fiber, are crushed against the fiber and bind to the filaments constituting the fiber, thus guaranteeing good bonding of the binder to the fiber. This calibration and calendering immediately after application of the binder makes it possible to obtain a calibrated dry fiber, facilitating the routing of the fibers to the lay-up head, with little fouling and ensures good lay-up quality.

According to one embodiment, after application of the binder, the fiber is provided with binder filaments having a diameter between 0.02 mm to 0.10 mm, preferably between 0.04 and 0.06 mm.

According to one embodiment, after application of the binder, the fiber provided with binder filaments comprises 2 to 10% by weight of binder, the preform obtained after draping being able to be subjected to an operation of adding polymer.

According to one embodiment, the application of binder is carried out online, the method comprising the routing of at least one dry fiber from a storage and distribution system to the lay-up head for draping said fiber over a layup surface, the formation of a fiber from initial fibers from fiber reels and the application of binder on the fiber are carried out during the layup, the application of binder on the fiber being carried out in the storage system and distribution or when routing the fiber between the storage system and the head. The lay-up is carried out from dry fibers and a binder application is carried out online, as the lay-up takes place, by means of one or more nozzles actuated as a function of the speed as a function of the fibers. Preferably, the application of binder on the fiber or fibers is carried out at the level of the fiber storage and distribution system, said process comprising the routing of the fiber or fibers provided with binder to the lay-up head. Surprisingly, the inventors have noticed that the draping of fibers provided with a binder applied in line makes it possible to perform the draping without requiring the binder to be heated at the head, the binder having just been applied retaining a tacky character. which is sufficient to allow adhesion of said fiber to the layup surface and / or to one or more fibers provided with a binder previously draped over said layup surface.

According to one embodiment, the routing is carried out by means of a flexible tube, in the interior passage through which the fiber passes. Surprisingly, the inventors have noticed that the fibers which have just been covered with binder in the creel could be conveyed in tubes, without being damaged and without fouling the tubes, while allowing draping without heating of the binder at the level of the head.

According to another embodiment, the fiber provided with the binder is rewound into a reel which will then be loaded into the storage and distribution system of a draping machine to perform the draping operation.

In the case of an on-line application, the method comprises draping strips formed of one or more fibers by means of a draping head, preferably provided with an application roller for draping in contact with said strip against the draping surface, the application of binder being carried out by several fiberizing nozzles, each nozzle applying the binder independently on a single fiber, said nozzles being able to be supplied with binder by a common feeding system, each nozzle being actuated as a function of the speed of travel of the fiber traveling under said nozzle.

According to one embodiment, the fiber provided with the binder passes through a tension limiting system just before its application on contact with the application surface by means of an application roller, or compacting roller, in order to limit the tension. of fiber at the level of the application roller, said tension limiting system comprises at least one cylinder on which the fiber is able to come to be partially wound, and drive means for driving said cylinder in rotation, said means drive being controlled by the machine control unit, so that the peripheral speed of the cylinder is greater than the speed of travel of the fiber at the application roller.

The use of a tension limiting system just before the layup of the fiber makes it possible to limit, or even eliminate, the compaction effort during draping and thus to reduce the risks of displacement of the previously draped fibers, in particular in the case draping a dry preform.

According to one embodiment, the layup comprises the production of plies of fibers superimposed in different orientations, plies comprising adjacent fibers, not edge to edge, with a spacing defined between them, in order to facilitate the subsequent infusion of the preform , the gaps between the fibers of the plies being arranged so as to form infusion channels in the thickness of the preform for infusion. This spacing between adjacent fibers can be obtained when draping a strip of fibers, by means of an appropriate head and / or an appropriate calibration and calendering system, and / or obtained between two strips of adjacent fibers, by programming this spacing in the software before draping. This spacing is for example between 0.5 and 4 mm, preferably between 1 and 3 mm.

The present invention also relates to a process for manufacturing parts made of composite material, characterized in that it comprises

- making a preform by draping fibers as described above;

- a polymer impregnation step in the preform, said impregnation step comprising

- in the case of a dry preform, the addition of one or more polymers by infusion or injection,

- or in the case of a preform with an amount of binder intended to form the final matrix, heating the preform to impregnate in the whole of the preform the polymer or polymers forming the binder and / or one or more initial fibers ; and eventually

- a hardening step.

According to a first embodiment, the method according to the invention comprises the production of dry preforms, comprising the application of a binder on dry fibers, to form a dry preform comprising less than 10% by weight of binder, preferably less than 5% by weight of binder, said dry preform being subsequently subjected to a polymer impregnation operation to form a part made of composite material.

According to a second embodiment, the method is a method for producing pre-impregnated type preforms, comprising the application of a binder formed from one or more polymers to form a pre-impregnated preform comprising at least 30% in weight of binder, preferably at least 40% by weight of binder, the pre-impregnated preform being subsequently subjected to an impregnation operation, for impregnation at the heart of the binder in the fibers, then a curing operation.

According to a third embodiment, the preform is formed from fibers each comprising one or more first initial fibers, in particular continuous unidirectional fibers, and one or more second initial fibers made of polymeric material, preferably thermoplastic, said second initial fiber or fibers being intended to form at least partially the polymer matrix of the final part made of composite material.

The preforms will preferably be draped flat at high speeds, and subjected to a forming step to form the preforms in their desired final shape.

The present invention also relates to a fiber draping machine comprising

a draping head comprising guide means for guiding one or more fibers towards a draping surface and preferably an application roller intended to come into contact against the draping surface,

- a storage and distribution system for storing and distributing at least one continuous fiber,

routing means for routing the fiber or fibers from said storage and distribution system to the lay-up head, and

application means for applying a binder to the dry fiber or fibers, characterized in that the binder application means comprise at least one fiberizing nozzle comprising a discharge orifice supplied with liquid or pasty binder under pressure and a or several injection ports supplied with gas under pressure, so that said nozzle is capable of delivering the binder in the form of a spiral filament, said nozzle being controlled by a control system as a function of the running speed of the fiber facing the nozzle, said nozzle being arranged upstream of the lay-up head, preferably in the fiber storage and distribution system, said storage and distribution means being capable of storing fibers initials, identical or different, and in delivering said initial fibers so as to form at least one fiber from at least two initial fibers.

The nozzle comprises, for example, a chamber supplied with binder under pressure via a supply orifice and provided with a discharge orifice and a valve mounted movably in the chamber and actuated by actuation means between a closed position to close the discharge port and an open position for delivering the binder under pressure through its discharge port.

According to one embodiment, the machine comprises a system for calibrating and / or calendering the fibers arranged downstream of the application means, for calibrating the fiber in width and / or compressing the fiber in thickness.

According to one embodiment, the lay-up head is equipped with a tension limiting system, upstream of the guide system, capable of limiting the tension of the fiber or fibers.

The machine according to the invention can be:

- a fiber placement machine for application in contact with a single fiber or a wide strip formed of several fibers, or

- a machine for contactless application, for example a filament winding machine for the application of a fiber or a strip formed of one or more fibers.

In the case of a fiber placement machine, the head comprises an application roller for draping in contact with the fibers, said machine being able to further comprise a system for moving the draping head. According to one embodiment, the storage and distribution system is arranged at a distance from the lay-up head, for example placed on the ground or is mounted on one of the elements of the head displacement system.

The invention will be better understood, and other objects, details, characteristics and advantages will appear more clearly during the detailed explanatory description which will follow of particular embodiments of the invention, with reference to the appended schematic drawings, in which :

- Figure 1 is a schematic side view of a fiber draping machine according to one embodiment;

- Figure 2 is an enlarged partial schematic view of the creel of the machine of Figure 1, illustrating the means of applying binder on a fiber formed from three initial fibers;

- Figure 3 is a schematic partial view of the fiberizing nozzle of Figure 2;

- Figure 4 is a schematic sectional view of the fiber after application of the binder;

- Figure 5 is a schematic view of the fiber after calibration and calendering;

- Figure 6 is a view similar to Figure 3 illustrating the application of binder on a fiber formed of two identical initial fibers superimposed;

- Figure 7 is a schematic sectional view of a fiber formed of a first initial fiber and two second initial fibers, before application of the binder; and,

- Figure 8 is a schematic view of a fiber application head according to an alternative embodiment.

Figure 1 schematically illustrates a fiber placement machine according to the invention, allowing draping in contact on a mold of a strip formed of several fibers. The machine comprises a displacement system 1 which is formed here of a poly-articulated arm 11, of the poly-articulated robot type six axes, known per se, mounted movably on a linear rail 12 fixed to the ground. The poly-articulated arm 11 is fixed by its base 112 on a carriage 13 slidably mounted on the rail 12. A placement head 2 is mounted on the end wrist 11a of the poly-articulated arm. The head comprises, in a manner known per se, guide means for guiding several fibers in the form of a strip towards an application roller or compacting roller 21, the compacting roller being able to come into contact with a mold to apply the tape. The head further comprises cutting means for individually cutting each fiber, re-routing means for re-routing each fiber which has just been cut, so as to be able to stop and resume the application of a fiber at any time, as well as to choose the width of the strip, and blocking means in order to block a fiber which has just been cut. By way of example, the machine comprises a lay-up head as described in patent document WO2008 / 132299.

In the present embodiment, the machine is provided for draping dry fibers 9, each fiber being formed from three initial fibers, for example of the glass fiber type, packaged in spools 8a, 8b, 8c. The storage and distribution system comprises a creel 3, for receiving coils of initial dry fibers, and delivering said fibers independently of each other. Each initial fiber spool 8a, 8b, 8c is arranged on a horizontal support 31 so that it can be unwound from the center of the spool.

The creel is also mounted on a follower carriage 32, placed on the rail 12 and mechanically connected to the carriage 13 carrying the robot. In the illustrated embodiment, the machine is provided for draping a strip of four fibers 9, the creel comprising twelve spools of initial fiber.

The routing means for routing the fibers from the creel to the placement head are formed here of flexible tubes, as described for example in patent document WO2012 / 160270. The tubes are gathered in a bundle, represented schematically under the reference 40, and are placed in the internal passage of a flexible sheath 41, possibly cooled to cool the fibers.

According to the invention, the machine is equipped with means 5 for applying binder, here arranged at the level of creel 3, and provided for applying by spraying a binder in liquid or pasty form onto each dry fiber formed from three initial fibers 81a, 81b, 81c. With reference to FIGS. 2 and 3, the initial fibers intended to form a fiber 9 are unwound by the center of the spools, and the spools are here arranged one above the other, so that an initial fiber unwound by the center a lower coil passes through the center of the upper coil (s), the horizontal supports 31 having openings to allow these passages. The coils are arranged on the supports 31 so that they are unwound in opposite directions, the first reel 8a and the third reel 8c being unwound, for example clockwise, while the second central reel 8b is unwound in the direction counterclockwise. The initial fibers unwound from the spools pass over a first pulley 33 disposed above the three superimposed spools, then over a second pulley 34 disposed below the first pulley in order to guide a fiber 9 formed of said fibers towards the application means 5 initial fibers.

Upstream of the application means, each fiber passes through a first calibration system 61, making it possible to calibrate the fiber at a given section before the application of binder. In this embodiment, as shown diagrammatically in FIG. 3, the calibration system makes it possible to form a fiber 9 of generally circular section. This calibration system comprises for example for each fiber a frustoconical tube with a circular section which decreases from upstream to downstream, the diameter of the section of the tube at its downstream end corresponding to the desired fiber diameter.

The application means comprise for each fiber 9 a nozzle 50 for fiberizing, the nozzle being connected to a supply system 71 supplying several nozzles by binding under pressure.

A nozzle is disposed above each fiber 9 formed of three initial fibers. Each fiberizing nozzle 5, known per se, comprises a chamber 51 with a supply port 52 for its connection to the supply system 71 via a supply line 72, and a discharge port 53. A valve 54 is movably mounted in the chamber and is movable between a closed position in which the valve cooperates with the lower part of the chamber, shaped as a seat, to close the discharge orifice, and an open position in which the valve is away from the seat to open the discharge port. This valve is controlled in opening and closing by an actuation system comprising a rod 55 which extends substantially axially in the chamber and which carries at its free end the valve 54. This rod is able to be operated in translation by actuating means 56 for moving the valve between its two positions. These actuation means, for example of the electrical or pneumatic type, are controlled by a control system 73, as illustrated by the control line shown diagrammatically under the reference 74. The supply system 71 makes it possible to supply each nozzle by binder under pressure, at a temperature at which the binder has a viscosity suitable for its application by means of the nozzle.

The nozzle further comprises injection channels 57 supplied with compressed air to form air flows towards the filament leaving the discharge orifice. The injection channels have injection orifices 57a distributed at regular angular space around the discharge orifice. The nozzle has for example eight injection channels. The injection channels open onto an annular chamber 58 connected to a source of compressed air 59 by a pipe 59a. The injection channels are arranged and oriented so that the binder filament leaving the discharge orifice is in a circular motion and is stretched and configured in a spiral, as illustrated in Figures 2 and 3 under the reference 92.

The nozzles apply by spraying, without contact between the nozzles and the fibers, the binder on the fibers in the form of filaments. Each nozzle is adjusted so that the filament turns turn around the fiber, said filament turns having end portions which overlap so that the binder filaments 93 form around the fiber a kind of sheath, such that illustrated schematically in Figure 4 ensuring the assembly of the initial fibers 8a, 8b, 8c and in particular the maintenance of the various constituent filaments of the fiber.

For example, the nozzle has a discharge port of about 0.3 mm in diameter. The filament coming out of the discharge port is stretched by the air flows from the injection channels, so that the fiber is provided with filaments of about 0.05 mm in diameter.

The control system 73 is connected to sensors to receive information representative of the running speed of each fiber. Each fiber passes for example on a roller 76 equipped with an encoder connected, via a line shown diagrammatically under the reference 77, to the control system to communicate the speed of travel of the fiber. For each fiber, the control system controls the opening and closing of the nozzle valve associated with the fiber, as a function of the speed of travel of said fiber, to apply the quantity of binder desired online as and when advancement of the fiber and its application by the lay-up head.

Downstream of the application means, each fiber passes through a calibration and calendering system 62 making it possible to calibrate the fiber in width and to compress the fiber in thickness. This system comprises for example for each fiber two calendering wheels between which the fiber passes. A first wheel 63 is provided with an annular groove of rectangular section, the width of which corresponds to the desired fiber width. A second wheel 64 is provided with a rib fitting into the groove of the first wheel. The rib inserted in the groove forming a passage whose cross section corresponds to the desired cross section of fiber. FIG. 5 schematically illustrates the section of fiber obtained at the outlet of the calibration and calendering system 62. The fiber has a flat or flattened shape, the section of the fiber being generally elliptical, with two opposite principal concave surfaces 91a, 91b . During the passage of the fiber between the two wheels, the binder filaments are crushed against the constituent filaments of the fiber, thus ensuring mechanical attachment of the binder filaments to those of the fiber. For example, the binder filaments of 0.05 mm in diameter applied by the nozzle, have, after calendering, a cross section of approximately 0.07 mm.

The presence of binder filaments coating the fiber, combined with this calendering step makes it possible to obtain a calibrated dry fiber, which facilitates the routing of the fiber up to the head and into the head, with little fouling, and ensures draping quality.

The creel can also be fitted with a tension limiting system 42 (Fig. 1), as described in patent document WO2006 / 092514, through which the fibers pass at the outlet of the application means, in order to limit the tension in fiber before entering the delivery tubes.

For example, the initial fibers placed in the creel are dry glass fibers, made up of a multitude of glass filaments and a small amount of sizing resin, of the order of 0.2% by weight, for example glass fibers of 2400 Tex or 4800 Tex.

The machine is used to make a dry preform, after application by spraying the binder in the form of filaments via the fiberization nozzles, each fiber comprises approximately 5% by weight of binder. The binder comprises, for example, a thermoplastic copolyester. The binder can also comprise one or more functional agents or charges, to give the preform different mechanical and / or electrical properties, for example agents or charges improving its electrical conduction, its permeability for infusion, its formability, and / or its shock resistance.

A dry preform can be obtained by draping several superposed plies by means of the draping head, the binder being applied to the fibers as the fibers are applied by the head. The draping being carried out with the binder freshly applied to the fibers, the binder has not completely crystallized, and retains a tacky character. Thus, it is not necessary to heat the binder at the head to guarantee the cohesion of the preform.

After making a dry preform, the dry preform can be subjected to an infusion or injection operation of an infusion or injection polymer, thermoplastic or thermosetting, then a curing operation to obtain a composite part . This hardening operation consisting of a so-called consolidation operation in the case of a thermoplastic polymer, and in a baking in the case of a thermosetting polymer.

A preform in the form of a plate with the desired dimensions can be obtained by draping several plies. The preform can then be subjected to a forming operation, preferably hot, the binder applied to the fibers allowing deformation of the preform and keeping it in shape. The preform can be placed in a forming tool corresponding to the final shape of the desired composite part in which the forming operation will then be carried out, followed by the polymer impregnation operation by injection or infusion.

According to another example, the machine is used for producing pre-impregnated preforms comprising at least 40% by weight of binder, the binder then forming the polymer matrix of the final part. The preform obtained after draping can then be subjected to a heating and pressurizing operation to impregnate the polymer homogeneously throughout the preform, then a curing operation to obtain a composite part.

FIG. 6 illustrates another embodiment in which each fiber 109 is formed from two initial fibers 181a, 181b superposed, the initial fibers are for example unwound from spools of fiber mounted on mandrel mandrels, motorized or non-motorized, so that the two initial fibers come flat against each other.

Upstream of the application means, each dry fiber passes through a first calibration system, making it possible to calibrate the fibers to a desired width before the application of binder. This calibration system comprises for example for each fiber a frustoconical tube with a rectangular section which decreases from upstream to downstream, the width of the section of the tube at its downstream end corresponding to the desired width of fiber.

For the application of binder, each nozzle is adjusted so that the filament turns depositing on the first main face 109a opposite the nozzle has a width D2 greater than the width DI of the fiber, as illustrated in FIG. 6. The filament turns thus projected onto the first main face have portions of turn protruding from the longitudinal edges 109c of the fiber which fold around said edges and are pressed against the second main face 109b of the fiber. This application of binder on both sides is obtained by regulating in particular the flow of air injected, the pressure and the temperature of binder in the nozzle and the distance between the nozzle and the fiber. Preferably, the portions of filament turns coming from one longitudinal edge are superimposed with those coming from the other longitudinal edge. The fiber is thus provided on each main face with a binder in the form of filaments, the filaments of one main face extending on the other main face passing through the longitudinal edges. These binder filaments thus applied make it possible to assemble the two initial fibers and to maintain the different constituent filaments of the fiber.

For example, the initial fibers placed in the creel are dry carbon fibers, made up of a multitude of carbon filaments and a small quantity of sizing resin, of the order of 0.2% in weight.

FIG. 7 illustrates another embodiment in which each fiber 209 before application of binder is formed of a first fiber 281a having a flat shape, of generally elliptical section with two opposite concave surfaces, and two second fibers 281b, 281c. The first fiber 281a is for example a continuous unidirectional dry carbon fiber, and the two second initial fibers 281b, 281c are continuous fibers formed from discontinuous nonwoven filaments, the second initial fibers serving as a drain during the impregnation step of a preform obtained from such fibers 209. To form a fiber 209, the first initial fiber and / or the second fibers can be unwound or unwound from spools of fiber.

FIG. 8 illustrates a fiber placement head according to an alternative embodiment. The placement head 102 comprises an application roller 121, a guide system 122 for guiding the fibers in the direction of the roller in the form of two sheets of fibers 191a 191b arranged in two guide planes PI, P2, to form a strip of fibers in which the fibers are arranged substantially edge to edge. This guide system comprises for example guide channels, through which the fibers pass, formed at the assembly interface of a central part 122a, in the form of a wedge, and of two side plates (not shown). The guidance system is mounted on a support structure (not shown) by which the head is assembled to the wrist of the robot described above. As a variant, the head is fixed and the draping surface of the mold is able to be moved relative to the head to carry out the draping operations. The head further comprises, on either side of the guide system, cutting means 123, blocking means 124 and redirection means 125.

The head is equipped with a tension buzzer system 142 disposed upstream of the guide system 122 through which the fibers entering the head pass in order to limit, or even eliminate the tension in the fibers applied by the roller, and thus make it possible to reduce , or even eliminate the compaction force applied by the application roller. This tension limiting system is advantageously used in the case of thick preforms, comprising numerous plies and / or obtained from fibers having a high titer, in particular in the case of glass fiber. The tension in the fibers at the roller is for example between 0 and 100 g, and the compaction force is between 0 and 10 N / mm, preferably between 0 and 5 N / mm.

The voltage limiting system is for example of the type described in the aforementioned patent document WO2006 / 092514. For each fiber ply, the tension limiting system comprises one or more cylinders 1421 parallel to each other, for example four in number, on which the fibers of the ply are partially wound. The cylinders are positively driven in rotation by drive means. The tension limiting system is mounted on the head support structure. The fibers entering the head are oriented towards the cylinders via deflection pulleys 126. At the exit of the cylinders, the fibers enter the guide system 122. Said drive means are controlled by the machine control unit, so that the peripheral speeds of the rollers are greater than the running speeds of the fibers at the level of the application roller, in order to exert a tensile force on the fibers, and thus limit the tension in calling up the fibers at the level of the application roller. application at a substantially constant value, whatever the speed of the fibers. As described in the aforementioned document, belts can be mounted around each cylinder, so that a belt is interposed between each fiber and the cylinder, each belt being able to adhere to a fiber and to be driven more or less by the cylinder as a function of the pressure exerted by the fiber on the belt, said pressure being proportional to the inrush tension on the fiber. According to another embodiment, the tension limiting system comprises for each sheet, a single motorized cylinder, with or without a belt.

Although the invention has been described in connection with different particular embodiments, it is obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these these are within the scope of the invention.

Claims (14)

1. Method for producing preforms, by draping fibers on a draping surface, comprising - the application of a binder on at least one continuous dry fiber (9, 109, 209), and - the layup of said fiber provided with binder by means of a layup head to form a preform, characterized in that each fiber is formed from at least two separate initial fibers (81a, 81b, 81c; 181a, 181b ; 281a, 281b, 281c), the application of binder on a fiber is carried out by means of at least one fiberizing nozzle (50) comprising a discharge orifice (53) supplied with liquid or pasty binder, and one or more injection orifices (57) supplied with gas under pressure, so that said nozzle is capable of delivering the binder in the form of a spiral filament (92), the turns of filament being deposited on the fiber traveling in vis- with respect to a nozzle for obtaining a fiber provided with binder filaments (93), said binder filaments ensuring a connection between the initial fibers. 2. Method according to claim 1, characterized in that each fiber (9, 109) is formed from initial fibers (81a, 81b, 81c; 181a, 181b) of the same kind. 3. Method according to claim 1 or 2, characterized in that each fiber (9) comprises initial fibers (81a, 81b, 81c) from spools of fibers (8a, 8b, 8c) unwound. 4. Method according to claim 3, characterized in that each fiber (9) is formed from initial fibers (81a, 81b, 81c) from spools of fibers (8a, 8b, 8c) unwound in different directions. 5. Method according to claim 1 to 4, characterized in that during the application of binder, the filament turns depositing on the fiber (9) go around the fiber, so that the fiber (9) is coated with filaments. 6. Method according to claim 5, characterized in that during the application of binder, portions of filament turns are pressed against the fiber by overlapping. 7. Method according to one of claims 1 to 6, characterized in that the fiber, after passing through the fiberizing nozzle, passes through a calibration and / or calendering system (62) to calibrate the fiber in width and / or compressing the fiber in thickness. 8. Method according to one of claims 1 to 7, characterized in that after application of the binder, the fiber is provided with binder filaments having a diameter between 0.02 mm to 0.10 mm. 9. Method according to one of claims 1 to 8, characterized in that after application of the binder, the fiber provided with binder filaments comprises 2 to 10% by weight of binder. 10. Method according to one of claims 1 to 9, characterized in that the application of binder is carried out online, the method comprising the routing of at least one dry fiber (9) from a storage system and distribution (3) to the layup head (2) for draping said fiber over a layup surface, the formation of a fiber from initial fibers from fiber spools and the application of binder on the fiber are performed during layup, the application of binder being carried out in the storage and distribution system or during the routing of the fiber between the storage system and the layup head. 11. The method of claim 10, characterized in that it comprises draping strips formed of one or more fibers by means of a draping head, the application of binder being carried out by several fiberizing nozzles, each nozzle applying the binder independently on a single fiber. 12. Method according to one of claims 1 to 11, characterized in that the fiber provided with the binder passes through a tension limiting system (142) just before its application on the application surface by means of a roller. application (121), in order to limit the tension of the fiber at the level of the roller, said tension limiting system comprises at least one cylinder (1421) on which the fiber is able to come to be partially wound, and drive means to rotate said cylinder, said drive means being controlled by the machine control unit, so that the peripheral speed of the cylinder is greater than the speed of travel of the fiber at the application roller. 13. Method according to one of claims 1 to 12, characterized in that the layup comprises the production of plies of fibers superimposed in different orientations, plies comprising adjacent fibers, with a spacing defined between them. 14. Method for manufacturing parts of composite material, characterized in that it comprises - The production of a preform by draping fibers according to one of Claims 1 to 13; - a polymer impregnation step in the preform, said impregnation step comprising 5 - the addition of one or more polymers by infusion or injection, - Or the heating of the preform to impregnate throughout the preform the polymer or polymers forming the binder and / or one or more initial fibers.