RELATED CASES

The present application is a National Phase entry of PCT Application No. PCT/FR2018/000245, filed Nov. 9, 2018, which claims priority from FR Patent Application No. 1701172, filed Nov. 13, 2017, which applications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates to a fiber application head for a fiber application machine for producing composite material parts, and more particularly to a so-called fiber placement head equipped with a particular application roller. The present invention also relates to a method for manufacturing parts made of composite material by means of a corresponding application head.

BACKGROUND

There are known fiber application machines, commonly called fiber placement machines, for the application by contact onto a layup tool, such as a male or female mold, of a wide band formed of several continuous flat fibers, of ribbon type, dry or impregnated with thermosetting or thermoplastic resin, in particular carbon fibers consisting of a multitude of carbon threads or filaments.

These machines are used to produce preforms formed of several superposed plies, each ply being formed by laying up onto the mold of one or more bands side by side. In the case of a layup of fibers pre-impregnated with thermoplastic or thermosetting resin, typically of a quantity of at least 40% in weight, the pre-impregnated preform obtained after laying up is hardened or polymerized by passing it through an oven to obtain a composite material part. In the case of so-called dry fibers, which are not pre-impregnated with resins, the fibers comprise a reduced quantity of so-called bonding resin, also called a binder, generally a thermoplastic resin, in a quantity of less than or equal to 5% in weight, to give a tackiness to the fibers during the layup. After layup, the so-called dry preform is subjected to a resin injection or infusion operation before the curing step.

These machines, such as described in the patent document WO2006/092514, typically comprise a fiber application head, a system for moving said head, fiber storage means, and fiber conveying means for conveying the fibers from said storage means to the head. The head typically comprises an application roller, also called a compacting roller, intended to come into contact with the mold for applying the band, and means for guiding the fibers on said application roller.

The head generally further comprises a heating system for heating the fibers. The compacting roller presses the band of fibers against the application surface of the mold, or against the band(s) of fibers previously applied, in order to facilitate the adhesion of the applied bands to each other, as well as to progressively discharge the air trapped between the laid bands. The heating system ensures the heating of the bands of fibers to be applied, and/or of the mold or bands already applied upstream of the compacting roller, just before the compacting of the band, in order to at least soften the pre-impregnation resin or bonding resin, and thus promote adhesion of the bands to one another.

In the case of thermosetting resins, the pre-impregnated fibers are simply heated to soften them, typically at temperatures of about 40° C. The heating system typically comprises an infrared heating system comprising one or more infrared lamps.

In the case of thermoplastic resins, the fibers pre-impregnated or having a binder must be heated at higher temperatures, at least up to the resin melting temperature, being of about 200° C. for nylon type resins, and up to about 400° C. for PEEK type resins.

To achieve these higher temperatures, hot air torch systems have been proposed, and more recently laser type heating systems to achieve accurate and concentrated heating. Due to the higher heating temperatures, the fiber placement heads are typically equipped with metallic compacting rollers, resistant to heat, which can furthermore be cooled by the interior via a water circuit. To be able to adapt itself to the profile of the application surface, segmented metallic compacting rollers have been proposed, comprising several roller segments independently mounted side by side on a same axle, each segment being radially moveable and in an independent manner, and being elastically biased against the application surface. These segmented metallic rollers have proven however to be complex in structure and implementation.

Flexible rollers formed from a so-called high temperature elastomer, including a thermal stabilizer, are also used. These rollers generally comprise an anti-adherent sheath heat-shrunk and glued to the cylinder made of elastomeric material, as described in patent documents FR 2948058 and FR 3009512. To cool them, it has been proposed to equip the placement heads with a cooling system capable of delivering an air flow to cool the roller from the outside or from the inside, as described in the patent document FR 2948058. Despite these cooling systems, flexible rollers can have a tendency to deteriorate when using thermoplastic resins. Depending on the heating temperatures used, the anti-adherent sheath may tend to degrade quickly. Laser heating can tend to deteriorate the glue used for gluing the sheath and lead to a disassembling of the sheath and the cylinder of flexible material. Furthermore, the deteriorated adhesive layer absorbs laser radiation and can rise to high temperatures which can deteriorate the sheath.

During layup, combustion of the impregnation resin of the fibers may occur. The combustion fumes tend to form deposits on the sheath. In addition to the problem of fouling the sheath, these deposits absorb laser radiation and can lead to the destruction of the sheath.

In document FR 3009510, it has been proposed to provide blowing nozzles to diffuse an inert gas previously heated, such as nitrogen, to locally form a protective atmosphere and to avoid oxidation of the resins. This diffusion of nitrogen represents a significant cost. Furthermore, this diffusion of nitrogen does not allow the presence of an operator in the layup cell during layup, and requires a renewal of the air in the cell before access is allowed.

The aim of the present invention is to propose a solution to overcome at least one of the aforementioned drawbacks, which in particular enables the use of a wide variety of resins, both thermosetting and thermoplastic, with a substantially uniform compaction of the applied band, and which is simple in design and construction.

To this end, embodiments of the present invention provide a fiber application head for producing composite material parts, comprisinga compacting system comprising a compacting roller, also called an application roller, for applying one or more fibers, in particular a band formed of one or more flat fibers, onto an application surface, the compacting roller comprising a rigid central tube by which the roller is rotationally mounted on a support structure of the head and at least one cylindrical part made of a flexible material, elastically deformable, assembled coaxially, directly or indirectly, on the central tube, and an anti-adherent sheath covering the cylindrical part, anda heating system capable of emitting theral radiation in the direction of the fiber or fibers in the direction of the band, preferably just before the application by the application roller,

characterized in that the anti-adherent sheath has lateral portions extending beyond the cylindrical surface of the cylindrical part in the direction of the rotation axis of the roller, the assembly of the anti-adherent sheath to the cylindrical part being carried out by the lateral portions, said lateral portions effecting a translational and rotational blocking of the sheath in relation to the cylindrical part.

According to an embodiment of the invention, the protective sheath is assembled by lateral portions outside the heating zone. This assembly allows to avoid a gluing of the sheath in the heating zone and therefore to avoid any risk of deterioration of the sheath due to a deterioration of the glue due to the radiation.

The use of a roller provided with such a sheath according to an embodiment of the invention makes it possible to obtain a flexible thermally stable compacting roller usable for the application of fibers at high temperatures, in particular above 400° C., in particular for the application of fibers impregnated with thermoplastic resins. The head according to an embodiment of the invention, which comprises a compacting roller of simple design, offers the possibility of using a wide variety of thermosetting or thermoplastic resins combined with a wide variety of fibers, synthetic or natural, hybrid or not, in particular fibers commonly used in the field of composites, such as glass fibers, carbon, quartz, and aramid fibers.

According to one embodiment, the compacting roller comprises a cylindrical part made of an elastomeric material, preferably unexpanded, for example a silicone or a polyurethane, preferably made of silicone, preferably having a hardness of between 25 Shore A and 80 Shore A, preferably at least 40 Shore A, in order to guarantee a good resistance of the sheath over time.

According to one embodiment, the compacting roller comprises a cylindrical part of foam, for example an expanded elastomer such as a polyurethane foam, preferably having a density between 200 kg/m3and 500 kg/m3.

The anti-adherent sheath is advantageously formed from a fluoropolymer, preferably a fluoropolymer chosen from the group consisting of a polytetrafluoroethylene (PTFE), a perfluoroalkoxy (PFA), a fluorinated ethylene propylene (FEP), an ethylene tetrafluoroethylene (ETFE), preferably a PFA or FEP, and a fluoroelastomer, for example an FPM, FFPM or FEPM or a polyimide.

According to one embodiment, the anti-adherent sheath is thermoformed on the cylindrical part, preferably heat-shrunk, the thermoformed lateral portions ensuring at least partially the blocking of the sheath in rotation and in translation. The use of a heat-shrinkable sheath enables a simple and rapid assembly of the sheath starting from a sheath in the form of a tube which is subsequently heat-shrunk on the cylindrical part.

According to one embodiment, the central tube is provided with radial holes, the cylindrical part of flexible material having fluid communication means capable of putting the radial holes in fluid communication with the external cylindrical surface of the cylindrical part, the head comprising thermal regulation means capable of injecting a thermal regulation gas flow, advantageously a gas at room temperature or cooled, particularly air, in the internal passage of the central tube, the roller comprising an draining the cylindrical part, the intermediate layer ensuring intermediate layer interposed between the anti-adherent sheath and the evacuation of the thermal regulation fluid by the lateral faces of the roller. The use of such a draining layer combined with aby-inside cooling system makes it possible to effectively maintain the sheath and the cylindrical part at reasonable temperatures, below the deterioration temperatures of the materials used.

The intermediate layer is preferably formed from glass fibers, carbon fibers, metallic fibers or threads, for example copper or stainless steel, or polymer fibers, preferably thermoplastic fibers, for example PAN or PEEK fibers, the layer may be in the form of a non-woven fiber felt and/or in the form of a fabric. The thickness and the grammage of the intermediate layer are defined so as to ensure a passage of the gas flow sufficient to remove the calories. In the case of glass fibers, the intermediate layer forms an insulating barrier, limiting the rise in temperature by conduction of the cylindrical part made of flexible material. In the case of metallic fibers, the intermediate layer forms a barrier to the radiation emitted by the heating system.

Preferably, the fluid communication means comprises radial channels, each radial channel opening onto a radial hole in the central tube and onto the external cylindrical surface of the cylindrical part. The radial holes are distributed over the cylindrical wall of the central tube. The central tube has for example several sets of holes offset longitudinally along the axis of the compacting roller, each set comprising a plurality of holes made at regular angular intervals.

According to one embodiment, the head further comprises thermal regulation means capable of delivering a flow of thermal regulation fluid, in particular air, in the direction of the compacting roller, in order to cool the compacting roller from the exterior.

According to one embodiment, the intermediate layer comprises glass fibers preferably in the form of a fabric, for example in the form of a sleeve or braid.

According to one embodiment, the intermediate layer has end portions extending beyond the cylindrical surface of the cylindrical part, so as to guarantee the evacuation of injected gas.

According to one embodiment, each lateral portion of the sheath is assembled by its annular end section to the mechanical assembly means.

According to one embodiment, each lateral portion of the intermediate layer is assembled by its annular end section to the mechanical assembly means. Mechanical means can be used alone or in combination with thermoforming of the sheath, to assemble the sheath and/or the draining intermediate layer. According to one embodiment, the sheath is thermoformed and only the intermediate layer is assembled via mechanical means. Separate mechanical means can be used for the sheath and for the intermediate layer.

According to another embodiment, the intermediate layer is glued to the cylindrical part, on the cylindrical surface and/or on the lateral faces.

According to one embodiment, the mechanical means comprises two washers, assembled to each other by assembly means, such as screws, and between which the end section of the sheath and/or of the layer intermediate is enclosed.

According to one embodiment, the roller has at each end a portion defining a curved or inclined surface arranged in the extension of the cylindrical surface, in order to obtain a progressive folding of the sheath, this portion being formed of a part added to the cylindrical part or being integral with the cylindrical portion of the cylindrical part.

According to one embodiment, the head constitutes a fiber placement head comprising cutting means and feeding means, and possibly fiber blocking means. According to one embodiment, the head is used to perform a filament winding type application.

According to one embodiment, the head further comprises a blowing system comprising an air blowing nozzle connected to an air supply system, the nozzle being positioned upstream of the roller relative to the movement direction, and is capable of forming an air knife, preferably parallel to the axis of the roller, in the direction of the nip point between the compacting roller and the layup surface.

The head comprises a blowing nozzle delivering an air knife in the direction of the nip zone, also called the contact zone, so as to limit or even eliminate any deposit of combustion fumes on the external surface of the roller. The air knife enables the combustion flames to be extinguished by being blown out, or even to eliminate the emergence of any combustion flames by blowing them out. It is possible to blow out the flames with an air knife while guaranteeing, despite the high air flow rate, a satisfactory fiber layup quality, and efficient heating of the laid fiber(s), in particular with a laser type heating system, without the need to heat the air beforehand to form the air knife. This assembly of the sheath combined with the blowing nozzle guarantees a good stability of the sheath.

According to one embodiment, the blowing nozzle comprises a longitudinal discharge slot arranged parallel to the axis of the roller, or a plurality of outlets arranged along a line parallel to the axis of the roller. This parallel arrangement makes it possible to ensure an air knife at a high flow rate, sufficient to blow out the flames, without altering the fiber layup quality, in particular without displacing the fibers at the end of the trajectory.

According to embodiments,the blowing system is capable of forming an air knife having a length at least equal to half the length of the roller, preferably close to the length of the fiber or the bands of fibers laid by the head, the air knife preferably being centered relative to the roller;the blowing system is capable of delivering an air knife at a flow rate of at least 300 Nl/min, preferably at least 500 Nl/min, more preferably at least 600 Nl/min, for example about 700 Nl/min;the blowing system is capable of delivering an air knife at a flow rate of at least 50 Nl/min per centimeter of air knife lengthwise, preferably at least 100 Nl/min, more preferably at least 120 Nl/min; and/orthe air blowing nozzle is connected to a supply source formed by a compressed air source or to a turbine, preferably mounted on the head, delivering pulsed air.

According to one embodiment, the head comprises a laser type heating system, in particular laser diodes, a YAG laser or a fiber laser, capable of emitting a laser beam in the direction of the contact zone between the roller and a layup surface. Alternatively, the heating system may include one or more infrared lamps.

The present invention also relates to a method for manufacturing a composite material part comprising the application of continuous fibers onto an application surface, characterized in that the application of fibers is carried out by means of a fiber application head as described previously, by relative displacement of the application head in relation to the layup surface along layup trajectories, the fiber being compacted during their application by means of said application roller.

The fibers conventionally used are continuous flat fibers, also called tows, generally unidirectional, and comprising a multitude of filaments. The laid fibers can be dry fibers or fibers pre-impregnated with thermosetting or thermoplastic resin. The fibers typically have widths of ⅛, ¼ or ½ inch. As used herein, the term “fibers” also refers to fibers of greater width, greater than ½ inch, conventionally called band in placement technology.

The method according to the invention is particularly advantageous in the case of the production of dry preforms produced from dry fiber provided with a binder and/or thermoplastic preforms produced from fibers pre-impregnated with thermoplastic resin, requiring high heating temperatures during layup to at least reach the melting point of the binder and/or the thermoplastic resins.

In the case of a dry preform, the method further comprises a step of impregnating resin into the dry preform, by adding one or more impregnating resins by infusion or injection to the dry preform, and a curing step to obtain a composite material part. In the case of a thermoplastic preform, the preform may possibly be subjected to an additional consolidation step to obtain a final composite material part. In situ consolidation can also be obtained during the application of the fibers.

The application of fibers can be carried out on the application surface of a tool to form a preform, such as described previously, by fiber placement, band placement, and/or winding. According to another embodiment, the application of fibers is carried out directly on the application surface of a prefabricated part, to reinforce this part with unidirectional fiber reinforcements, the prefabricated part being for example a part obtained by injection, molding or additive manufacturing, from one or more thermoplastic and/or thermosetting resins.

