Manufacturing a part made of thermoplastic composite material having a cylindrical shape

Abstract

Manufacturing a part made of thermoplastic composite material having a cylindrical shape. The invention relates to a method for manufacturing a cylindrical thermoplastic composite part, comprising: - positioning a cylinder (3) made of pre-impregnated thermoplastic fibrous material in a vacuum molding tool (10), at least one vacuum bag (12) being located opposite the cylinder, and - consolidating the cylinder in the vacuum molding tool, during which a vacuum is drawn to apply a shaping pressure on the cylinder by said at least one bag, the cylinder being subjected to a heat treatment comprising (i) a sweep (B) of its circumference by localized heating, of extent (E24) limited to a sector of the cylinder, in relative motion with respect to the cylinder around its axis, and (ii) cooling, after this localized heating, to fix the shape of the cylinder. Fig. 1.

Description

Title of the invention: Manufacturing of a part made of thermoplastic composite material having a cylindrical shape. Technical field

[0001] The present description relates to a method for manufacturing a part made of thermoplastic matrix composite material, as well as an associated installation. The invention is of particular interest for the manufacture of cylindrical parts, known as shells, intended to be integral parts of space launch vehicles, but is not limited to this application. Previous technique

[0002] Composite materials provide a mass saving compared to metallic materials, which is of particular interest in aerospace and aeronautical applications with a view to improving performance.

[0003] The use of a thermoplastic composite can, in particular, be considered to form a shell forming an integral part of a stage of a space launcher which may have substantial dimensions, for example several meters in diameter.

[0004] The prior art offers methods, such as ovens or autoclaves, for shaping thermoplastic composites using a hot-forming technique known as consolidation. This involves heating the entire prepreg composite to melt or soften the resin(s) present, while applying a forming pressure. However, most of these hot-forming methods are not large enough to accommodate a monolithic (one-piece) launcher shell. The largest available methods that could accommodate such a structure may, in turn, exhibit temperature inhomogeneities between different areas of the part, resulting in suboptimal processing.

[0005] It is therefore desirable to have a hot forming process for thermoplastic composites that is more suitable for processing large cylindrical parts.

[0006] Furthermore, when using metal tooling, it may be desirable to control the stresses and deformations resulting from differential expansion between the metal and the composite in order to improve the material integrity of the resulting part. One solution is to use Invar tooling, which has a coefficient of expansion close to that of the composite. However, while not to be ruled out, this solution has the disadvantage of being much more expensive than steel tooling, which leads to significantly greater differential expansion.

[0007] It is therefore also desirable to have a hot forming process for thermoplastic composites which makes it possible to improve the material health of the part in the case where a metal tooling is used, while keeping a controlled cost.

[0008] The invention aims to address all or part of the drawbacks of the prior art. Description of the invention

[0009] The present description relates to a method for manufacturing a part made of thermoplastic composite material having a cylindrical shape, the method comprising: - positioning a cylinder made of pre-impregnated thermoplastic fibrous material in a vacuum molding tool, the cylinder extending around an axis and at least one vacuum bag being located opposite the cylinder, and - consolidating the cylinder in the vacuum molding tool, during which a vacuum is drawn to apply a shaping pressure on the cylinder by said at least one bag, the cylinder being subjected to a heat treatment comprising (i) sweeping its circumference by localized heating, limited to a circumferential sector of the cylinder, moving relative to the cylinder around the axis, the localized heating allowing the thermoplastic resin(s) in the heated zone to be selectively melted or softened, and (ii) cooling,after this local heating, to solidify the shape of the cylinder.

[0010] The present invention proposes a method for shaping a thermoplastic composite cylinder by consolidation, during which the cylinder is shaped under vacuum and subjected to heat treatment. Instead of performing the heat treatment of the entire cylinder in a hot vessel that would contain the whole structure, the invention proposes to perform the consolidation locally by moving the heated zone relative to the cylinder. The process is thus particularly suited to the hot shaping of large thermoplastic composites, offering an "out-of-oven" solution. The invention therefore eliminates the need for a hot vessel of sufficient volume to accommodate the cylinder to be treated, or for maintaining a homogeneous temperature within that vessel.The invention also has the advantage of reducing energy consumption because it avoids heating a large volume inside the hot medium containing the structure.

[0011] As will be described in the following paragraphs, the vacuum molding tooling may include one or more metallic parts, but the invention is not limited to this embodiment insofar as, according to a variant, two vacuum bags, respectively internal and external to the cylinder and sealed together, can be used to apply the shaping pressure, without any metallic part in the tooling.

[0012] In certain embodiments, the vacuum molding tooling further comprises a metal forming mandrel, annular in shape, inside the cylinder to which the vacuum bag is hermetically sealed, the cylinder conforming to the mandrel during consolidation. In a particular case, for example associated with a non-segmented (one-piece) mandrel, the mandrel and the cylinder may be separated by a non-zero gap before the initiation of local heating.

[0013] In these embodiments, the cylinder is formed between the mandrel and the vacuum bag during the vacuum application. The embodiment just described makes it possible to use a material with a high coefficient of thermal expansion, such as steel, for the mandrel, thus significantly reducing tooling costs compared to the use of Invar mentioned above, while preserving the material integrity of the resulting part. The mandrel's temperature rise fills any gap between the mandrel and the cylinder, along its entire circumference, through local expansion of the mandrel in the heated zone, which produces a mechanical deformation of the mandrel in the unheated zone. The local heating generates a slight increase in the mandrel's perimeter, which in turn generates a slight increase in the mandrel's diameter, thus filling any gap between the mandrel and the cylinder around its entire periphery.The low expansion rate also allows for very low stress on the cylinder, permitting the use of materials such as steel for the mandrel. Furthermore, the mandrel's shape remains unchanged during the localized heating process. Thus, after localized heating of a zone on the cylinder, this zone is cooled on a mandrel with iso-geometry, thereby eliminating the detrimental effects of differential expansion in the circumferential direction, which is the most problematic. Indeed, thermoplastic resins stiffen during cooling, which can generate significant deformations, wrinkling, and rippling in the case of a cylindrical part and a uniformly heated metal mandrel.With local heating, the shape of the chuck is not altered during cooling and therefore does not generate these deformations, creases, and undulations during cooling, allowing the use of a metallic material such as steel for the manufacture of the chuck.

[0014] Alternatively, the vacuum molding tooling further comprises annular retaining flanges arranged at each axial end of the cylinder, an internal vacuum bag for the cylinder and an external vacuum bag for the cylinder being sealed together on these flanges.

[0015] This feature advantageously simplifies tooling by eliminating the need for a mandrel. The flanges ensure the cylinder's circularity at its axial ends and maintain it in the correct position in the lower zone if its axis is oriented vertically during processing.

[0016] The simplification of tooling through the use of flanges is made possible by the implementation of localized heating, which produces localized softening or melting without affecting the structural integrity, which remains ensured by the rigid, unheated area and the vacuum bags. The use of flanges in combination with the localized heating also helps to preserve the material integrity of the resulting part, even when steel flanges are used.

[0017] In some embodiments, local heating is achieved by a first heating wall internal to the cylinder and a second heating wall external to the cylinder in circumferential overlap, total or partial, with the first wall, the first and second walls being in joint relative motion with respect to the cylinder around the axis.

[0018] Such a feature further contributes to improving the homogeneity of cylinder heating. It should be noted that various devices can be implemented to achieve localized heating, as will be described later, and that the invention is not limited to the implementation of a specific heating method.

[0019] In some embodiments, the local heating is continuously moved relative to the cylinder around the axis.

[0020] In this case, the local heating element is always kept in relative motion with respect to the cylinder. In other words, there is no heating phase during which the local heating element is stationary with respect to the cylinder. This characteristic further improves the homogeneity of the cylinder heating, and therefore its consolidation, and can allow for better control, if desired, of the thermoplastic's cooling rate to promote a microstructure of interest in the matrix. However, a variant where the cylinder is heated sector by sector sequentially does not depart from the scope of the invention.

[0021] In some embodiments, the cylinder, positioned in the vacuum molding tooling, has its axis oriented in a vertical direction and a lower axial end resting on a positioning surface transverse to the vertical direction.

[0022] In this case the cylinder is placed on its lower axial end, which advantageously simplifies maintaining the cylinder in position during treatment.

[0023] In some embodiments, the cylinder is in one piece.

[0024] In this case, the cylinder is in particular not divided into juxtaposed panels or divided into locally overlapping panels. This corresponds to a full-barrel configuration where the fibers extend continuously around the axis of the cylinder. The invention is of particular interest for this type of structure, notably because of the continuity of the circumferential fibers This can lead to significant stresses if the entire structure is heated on steel tooling (and not locally as in the invention). However, the use of a segmented cylinder is also considered within the framework of the present invention, particularly with panels assembled by overlapping before consolidation. Indeed, if, for example, the automated draping equipment does not allow for draping a cylinder several meters in diameter but only segments of a cylinder, then this segmented option can prove very advantageous from an industrial perspective.

[0025] Thus, according to one variant, the cylinder is sectorized and formed by an assembly of panels around the axis with overlap between neighboring panels. In particular, the neighboring panels may have a thinning of thickness in their overlap area towards their edges.

[0026] Such a characteristic helps to further minimize outcrops and stress concentrations in the resulting part.

[0027] In certain embodiments, the process further comprises a formation of the cylinder by automatic fiber placement technique by stacking of pre-impregnated thermoplastic fibrous layers.

[0028] The use of an automated fiber placement (AFP) technique allows the fiber orientation of the stack to be parameterized according to the need, thus optimizing the mechanical properties of the part to be obtained. However, the invention is not limited to this method of cylinder formation, as will be detailed below.

[0029] In some embodiments, the cylinder includes, on an internal or external surface, stiffening elements made of a second pre-impregnated thermoplastic fibrous material, identical or different from the material of the cylinder, and the stiffening elements are bonded to the cylinder by co-consolidation during heat treatment.

[0030] In this case, the stiffening elements are pressed onto the cylinder by vacuum, and the temperature increase allows them to become fluid, ensuring proper contact between the stiffening elements and the cylinder, and therefore the mechanical strength of the welded joint. The part is thus obtained through a process called co-consolidation of the cylinder and the stiffening elements, which produces a weld after cooling, due to the interpenetration of the polymer chains that occurred during local heating on both sides of the welded interfaces.

[0031] According to one variant, the stiffening elements can be welded to the cylinder after its consolidation, for example by interposition of a polymer film, in particular of polyetherimide (PEI), and heating of the assembly.

[0032] In some embodiments, a smoothing plate is interposed between the cylinder and each vacuum bag.

[0033] The smoothing plate (or "caul plate") is thin, for example, on the order of 1 mm thick, and allows for even better control of the geometry and surface finish of the workpiece. Each smoothing plate can be metallic. They can be used without a mandrel, or in addition to the mandrel (on the outside). If the mandrel is omitted, this can have the advantage of only requiring heating a thin sheet of metal on the inside of the cylinder. Of course, each plate can be segmented and formed from several juxtaposed segments around the axis.

[0034] In some embodiments, the part is a ferrule of a space launcher stage.

[0035] The invention is of particular interest for this type of structure which has a significant dimension, for example of at least two meters, or even at least three meters, in diameter.

[0036] The present description also relates to an installation for manufacturing a part made of thermoplastic composite material having a cylindrical shape, comprising: - a cylindrical vacuum molding tool extending around an axis, comprising at least one vacuum bag delimiting an internal volume intended to receive a cylinder of pre-impregnated thermoplastic fibrous material and configured to apply a shaping pressure to it during a vacuum draw in the internal volume, - a local heating device comprising at least one heating wall configured to melt or soften one or more thermoplastic resins impregnating the cylinder, said at least one heating wall having an extent limited to a circumferential sector of the molding tool, and - a displacement device configured to set said at least one heating wall in relative motion with respect to the molding tooling around the axis. The installation can allow the implementation of the process described above.

[0037] In some embodiments, the vacuum molding tooling further includes a metallic forming mandrel, of annular shape, on which the vacuum bag is securely attached in a sealed manner, the internal volume being defined between the forming mandrel and the vacuum bag.

[0038] Alternatively, the vacuum molding tooling further comprises annular retaining flanges arranged at each axial end of the molding tooling, an internal radial vacuum bag and an external radial vacuum bag being sealed together on these flanges.

[0039] In some embodiments, the local heating device comprises a first heating wall configured to be positioned inside the cylinder, and a second heating wall configured to be positioned outside the cylinder in circumferential overlap, total or partial, with the first wall, and the displacement device is configured to put the first and second walls in joint relative motion with respect to the molding tooling around the axis.

[0040] The aforementioned features and advantages, as well as others, will become apparent from the following detailed description and non-limiting examples of embodiments of the invention. This detailed description refers to the accompanying drawings. Brief description of the drawings

[0041] The attached drawings are schematic and are intended primarily to illustrate the principles of the exposition.

[0042] [Fig-1] Fig. 1 represents in perspective, schematically and partially, a example of an installation according to the invention.

[0043] [Fig.2] The [Fig.2] represents, schematically and partially, a cross-sectional view along II-II of the installation of the [Fig.1] during the consolidation of the cylinder.

[0044] [Fig.3] Fig.3 represents, schematically and partially, an example of a sectored cylinder.

[0045] [Fig.4] Fig.4 represents, schematically and partially, the relative movement of the local heating with respect to the cylinder in the context of an example according to the invention.

[0046] [Fig.5] Fig.5 represents, schematically and partially, a detail of a heating wall that can be implemented within the framework of the invention.

[0047] [Fig.6] Fig.6 represents, schematically and partially, a cross-sectional view in a plane containing the axis of the cylinder of a variant of vacuum molding tooling that can be implemented within the framework of the invention.

[0048] [Fig.7] The [Fig.7] represents, schematically and partially, a cross-sectional view in a plane containing the axis of the cylinder of a variant allowing the cylinder to be co-consolidated with stiffening elements.

[0049] [Fig. 8] [Fig. 8] schematically and partially represents an example of a shell of a space launcher stage that can be obtained within the scope of the invention. Description of embodiments

[0050] Fig. 1 illustrates an example of an installation 1 according to the invention for manufacturing a part made of thermoplastic composite material having a cylindrical shape.

[0051] The installation 1 comprises a cylindrical vacuum molding tool 10 extending about an axis X. In the example of [Fig. 1], the tool 10 comprises a metallic mandrel 14 of annular shape, to which a vacuum bag 12 is securely attached. The mandrel 14 may be made of steel. The mandrel 14 may be a single piece, or detachable, being formed from a plurality of The segments are removably linked. The cover 12 may be made of polyimide or elastomeric material, reinforced or unreinforced, and is a known element in itself. The mandrel 14 and the cover 12 each extend around the X-axis.

[0052] Fig. 1 illustrates the installation 1 during the hot and vacuum consolidation of a cylinder 3 made of pre-impregnated thermoplastic fibrous material, precursor of the composite material part to be obtained.

[0053] Cylinder 3 is advantageously manufactured by automated fiber placement, a technique known per se. Cylinder 3 comprises a fibrous reinforcement pre-impregnated with a thermoplastic resin. The choice of the reinforcement material and the resin depends on the intended application. For example, the fibrous reinforcement may include carbon fibers, glass fibers, aramid fibers, or a mixture of such fibers. For example, the resin may be PAEK (polyaryletherketone), PEEK (polyetheretherketone), PEKK (polyetherketoneketone), PES (polyethersulfone), PPS (poly(phenylene sulfide)), or PEI (polyetherimide). For example, cylinder 3 may be formed from sheets or strands of fibers pre-impregnated with a polyaryletherketone resin, for example, marketed under the reference LMPAEK® by Victrex.

[0054] In the illustrated example, cylinder 3 is made of a single piece, but this does not depart from the scope of the invention if the cylinder is sectorized, formed by juxtaposition or local overlapping of panels along its circumference. In the case of a sectorized cylinder, the same resin is advantageously used in the different panels, or failing that, compatible resins.

[0055] Generally, the cylinder 3 can be formed from a stack of pre-impregnated thermoplastic fibrous layers, as illustrated in [Fig. 2], for example. The use of an automated fiber placement technique is advantageous for obtaining a fiber orientation finely adapted to the requirements. However, those skilled in the art will recognize that the cylinder 3 can be formed differently, for example, by draping superimposed fibrous layers of pre-defined orientation, by winding a pre-impregnated woven strip in several layers, or even by a single woven layer of pre-impregnated thermoplastic fibrous material with overlapping or juxtaposed edges. [Fig. 3] illustrates, for its part, a possible example of a sectored cylinder 3s formed by local overlaps of panels 3p along its circumference. The panels 3p are arranged around the axis of the cylinder.In the illustrated example, the cylinder 3s is formed by overlapping all the 3p panels, meaning that each panel has a first edge 3pb overlapping (above) a first neighboring panel, and a second edge 3pa, opposite the first edge 3pb, overlapped (below) by a second neighboring panel, opposite the first neighboring panel. Note in particular the thinning of the neighboring 3p panels in their ZR zone. overlapping towards their edges 3pa, 3pb. A person skilled in the art will recognize that other panel assembly variations are possible.

[0056] The cylinder 3 is positioned in the tooling 10 with the axis of the cylinder 3 corresponding to the X-axis of the tooling 10. The X-axis may correspond to an axis of revolution of the cylinder 3 or to an axis of revolution of the tooling. In the illustrated example, the X-axis corresponds to a vertical direction DV, that is, the direction along the height relative to the ground. In other words, the cylinder 3 is positioned in the tooling 10 so that its X-axis is directed substantially along the DV direction, extending between a lower axial end 31 (at the bottom) and an upper axial end 32 (at the top). More specifically and as illustrated in [Fig.2], the tooling 10 includes, in its lower part, a positioning flange 16 on which rest the chuck 14 and the end 31 of the cylinder 3. The flange 16 defines a positioning surface SP which is transverse, or even perpendicular, to the direction DV.In the illustrated example, the flange 16 is a separate element from the mandrel 14, but this does not, of course, depart from the scope of the invention if the flange is a single unit with the mandrel. The tarpaulin 12 is securely attached to the mandrel 14 and the flange 16 by sealing gaskets, for example formed by a sealing compound 11.

[0057] In the illustrated example, the axis of the cylinder 3 is oriented along the vertical direction DV, but those skilled in the art will recognize that this feature is not essential to the invention, as the cylinder can, for example, be oriented horizontally by being supported by suitable tooling such as a mandrel or support flanges at the ends. According to one embodiment, the cylinder is draped directly onto the mandrel 14 (the latter in this case also corresponding to the draping tooling), but it is also possible for the cylinder to be draped onto a draping support separate from the mandrel and then positioned on the mandrel once the draping is complete.

[0058] The cylinder 3 positioned in the tooling 10 is interposed between the mandrel 14 and the tarpaulin 12. The mandrel 14 and the tarpaulin 12 together delimit an internal volume of the tooling 10 in which the cylinder 3 is present. The mandrel 14 is located inside the cylinder 3, and the tarpaulin 12 is located outside the cylinder 3. The cylinder 3 is located around the mandrel 14, and the tarpaulin 12 is located around the cylinder 3. The tarpaulin 12 is located opposite an external surface SE of the cylinder 3, and the mandrel 14 is located opposite an internal surface SI of the cylinder 3. The mandrel 14 extends over the entire internal circumference of the cylinder 3, and the tarpaulin 12 extends over the entire external circumference of the cylinder 3. It should be noted that a smoothing plate 13 is interposed between the tarpaulin 12 and the cylinder 3 in the illustrated example, but the invention remains within the scope of the invention if this plate 13 is omitted.

[0059] Cylinder 3 is hot-welded by drawing a vacuum into the internal volume of tooling 10. This vacuuming leads to the plating of the tarpaulin 12 onto cylinder 3. The cylinder 3 is shaped between the mandrel 14 and the sheet 12 by applying a shaping pressure PC. During consolidation, the cylinder 3 undergoes heat treatment by sweeping its circumference with localized heating to selectively melt or soften the thermoplastic resin(s) in the heated area. Following the application of the PC pressure and the heat treatment, the cylinder's thickness e3 can be reduced by at least 5%, for example, by at least 10%, specifically by 5% to 15% or by 10% to 15%.

[0060] Figures 1 and 2 illustrate a non-limiting example of a local heating device 20 that can be implemented within the framework of the invention.

[0061] In the illustrated example, the device 20 comprises a first heating wall 22 internal to the cylinder 3 and a second heating wall 24 external to the cylinder 3. More specifically, the first wall 22 is here inside the space internal to the annular mandrel 14, and the tarpaulin 12 is here located between the cylinder 3 and the wall 24.

[0062] Each wall 22, 24, or more generally the local heating, has an extent limited to a circumferential sector of the cylinder 3, or of the tooling 10. In other words, the local heating extends only over a part of the circumference of the cylinder 3, or of the tooling 10. The local heating, or the walls 22, 24, can otherwise extend over the entire axial dimension of the cylinder 3, or of the tooling 10, that is to say here over its entire height.

[0063] This limited extent of local heating is materialized, in figures 1 and 2 in particular, by the relative reference E24 corresponding to the arc length of the wall 24.

[0064] Generally, the area heated by the local heating system can have an angular coverage α, measured in a transverse plane, for example perpendicular to the X-axis, for example less than or equal to 120°, for example less than or equal to 90°, or less than or equal to 25°. This angular coverage α can be between 5° and 120°, for example between 5° and 90° or between 5° and 25°, or it can be between 10° and 120°, for example between 10° and 90° or between 10° and 25° (see [Fig. 4]). In the illustrated example, the walls 22, 24 have full circumferential overlap, that is, they each cover the same angular sector when viewed in a transverse plane, for example perpendicular to the X-axis. However, this does not depart from the scope of the invention if this overlap is only partial.

[0065] The first 22 and the second 24 walls are here connected by a junction wall 26 which allows for the joint movement of these walls 22, 24 during the movement of the device 20 and also allows for better thermal confinement by minimizing heat loss by convection into the air. The walls 22, 24 and 26 thus move as a unit. The junction wall 26 can, as illustrated, be located above the cylinder 3. The walls 22, 24 and 26 can, as illustrated, together define a housing in which the tooling 10 and, in particular, the cylinder 3 are located. In the illustrated example, the wall 26 includes a removable portion 262 allowing the passage of the cylinder 3.

[0066] The device 20 includes a displacement device, here in the form of wheels 30, which allows it to be set in relative motion with respect to the cylinder 3 around the X-axis. The local heating element is thus set in rotational motion around the X-axis during consolidation. The device 20 sweeps the circumference of the cylinder along the circumferential direction DC.

[0067] Figures 1 and 2 illustrate a specific device 20, but those skilled in the art will recognize that other variations are possible. In particular, it is possible to use a single heating panel (internal or external), or a different movement device. As an alternative, a heating device comprising at least one robotic arm on which at least one heating panel is mounted can be used. A movement device guided by rails, rather than wheels 30, can also be used. The case where the heating device is moved around the X-axis and the cylinder 3 is fixed has also been described, but this does not, of course, depart from the scope of the invention when this device is fixed and the cylinder is rotated around its axis so as to produce localized heating around the circumference of the cylinder.

[0068] An example of heat treatment applied to cylinder 3 during consolidation will now be described in more detail with reference to [Fig. 4]. Generally speaking, the vacuum is maintained during the heat treatment, i.e. during the local heating sweep, as well as during the cooling after this local heating.

[0069] At room temperature, the mandrel 14 is separated from the cylinder 3 by a non-zero clearance J (which can be very small, for example less than or equal to 1 mm). This is the situation at a time denoted T0, once the cylinder 3 has been positioned in the tooling 10 but before the consolidation process begins.

[0070] The consolidation is then initiated by local heating of a first zone ZC1 (situation at time T1). As indicated above, the temperature rise of the mandrel 14 closes the gap J between the mandrel 14 and the cylinder 3, over its entire circumference, by a local expansion of the mandrel 14 in zone ZC1, which produces a mechanical deformation of the mandrel in the unheated zone ZNC1. The mandrel 14 can advantageously have a relatively thin thickness el4, for example, of no more than 1.5 cm, to facilitate this deformation. In addition, a limited thickness for the mandrel also has the advantage of making the heating of the cylinder 3 from the inside more efficient.

[0071] Local heating allows the thermoplastic resin(s) in the ZC1 zone to be selectively melted or softened (the resin(s) in the ZNC1 zone are substantially not softened or melted).

[0072] The local heating then sweeps around the circumference of the cylinder, for example by moving it continuously around the X axis (along the DC direction).

[0073] At a later time, denoted T2, local heating is applied to a second zone ZC2, distinct from zone ZC1, to consolidate this zone ZC2. As with zone ZC1, the local heating then allows the thermoplastic resin(s) in zone ZC2 to be selectively melted or softened (the resin(s) in the unheated zone ZNC2 are substantially not softened or melted). The mandrel 14 retains its geometry relative to time T1, and the cooling of the previously heated zone ZC1 is advantageously carried out on a mandrel with iso-geometry. The local heating sweep continues in this manner until the entire circumference of the cylinder 3 is covered. As mentioned above, the local heating sweep can be carried out continuously around the circumference of the cylinder, thus allowing for homogeneous consolidation.In general, each zone heated ZC1, ZC2 by local heating can be brought to a temperature greater than or equal to 250°C, for example greater than or equal to 300°C, or even between 300°C and 400°C.

[0074] Figure 5 schematically shows an example of a usable wall 24 comprising a plurality of infrared lamps 243 attached to a frame 241. A person skilled in the art will recognize that other means are usable to produce the desired local heating.

[0075] Figures 6 and 7, which will now be described, illustrate variants that can be implemented within the scope of the invention. In these figures, the reference symbols are retained for the elements described previously.

[0076] The example in [Fig. 6] shows another tooling 10a which comprises annular retaining flanges 17 arranged at each axial end 31, 32 of the cylinder 3, a vacuum bag 12a internal to the cylinder and a vacuum bag 12b external to the cylinder being sealed tightly to these flanges 17 by sealing compounds 11. One or more relatively thin smoothing plates 13 ("caul plates"), which may be metallic, are positioned between the cylinder 3 and the bladders 12a and 12b. In a variant not shown, these smoothing plates can be omitted. In a variant not shown, the annular flanges can be omitted and a seal can be made directly between the internal vacuum bag and the external vacuum bag.

[0077] The example in [Fig. 7] relates to the case where the cylinder 3 comprises, on its internal surface SI, stiffening elements 40 made of a second thermoplastic prepreg fibrous material, identical or different from the material of the cylinder, and in The stiffening elements are bonded to the cylinder by co-consolidation during heat treatment. Local heating, while maintaining vacuum, leads to melting or softening of the thermoplastic resin(s) present. The fluidization of the resin(s) promotes the conformation of the parts to be welded and produces interpenetration of the polymer chains at the interfaces between the elements 40 and the cylinder 3.

[0078] The elements 40 are formed by conventional means known to those skilled in the art, for example by manual or automated draping, draping in a shaped mold, or press-forming flat plates. The elements 40 may have any cross-section, for example Omega, T, J, among other possible shapes. The elements 40 may or may not exhibit local variation in shape or cross-section. As illustrated, the elements 40 may be present over at least the majority (more than 50%), or even at least 80%, of the axial dimension of the cylinder 3.

[0079] The elements 40 are assembled onto the cylinder 3 using techniques known per se, such as spot welding, stapling, or the use of added fasteners. This assembly is simply intended to position the elements 40 on the cylinder 3, but not to produce a robust attachment of the latter to the cylinder 3, which is achieved after co-consolidation.

[0080] The part may be a ferrule for a space launcher stage as illustrated in [Fig. 8], but the scope of the invention is not limited to this application; alternatively, the part may find an application in the aeronautical field or, more generally, in any application requiring a ferrule. The ferrule 100 of [Fig. 8] comprises a composite portion 50 obtained by implementing the process described above. The portion 50 is provided with stiffeners 400a, 400b which have, for example, been welded by co-consolidation as described in connection with [Fig. 7]. Two axial flanges 52, for example made of metallic material, have been attached to the portion 50.

[0081] The expression "between ... and ..." should be understood as including the bounds.

Claims

Demands

1. Method for manufacturing a part (100) of thermoplastic composite material having a cylindrical shape, the method comprising: - positioning a cylinder (3) of prepreg thermoplastic fibrous material in a vacuum molding tool (10; 10a), the cylinder extending around an axis (X) and at least one sheet (12; 12a;12b) vacuum being situated opposite the cylinder, and - consolidation of the cylinder in the vacuum molding tooling, during which a vacuum is drawn to apply a conforming pressure (PC) on the cylinder by said at least one sheet, the cylinder being subjected to a heat treatment comprising (i) a sweep (B) of its circumference by local heating, of extent (E24) limited to a circumferential sector of the cylinder, in relative motion with respect to the cylinder around the axis, the local heating allowing to selectively melt or soften the thermoplastic resin(s) in the heated area, and (ii) a cooling, after this local heating, to fix the shape of the cylinder.;

2. A method according to claim 1, wherein the vacuum molding tooling (10) further comprises a metallic mandrel (14) of annular shape, inside the cylinder (3) to which the vacuum bag (12) is hermetically sealed, the cylinder conforming to the mandrel during consolidation.

3. Method according to claim 1, wherein the vacuum molding tooling (10a) further comprises annular retaining flanges (17) disposed at each axial end of the cylinder, an internal vacuum bag (12a) of the cylinder and an external vacuum bag (12b) of the cylinder being hermetically secured to these flanges.

4. A method according to any one of claims 1 to 3, wherein the local heating is achieved by a first heating wall (22) internal to the cylinder (3) and a second heating wall (24) external to the cylinder in circumferential overlap, total or partial, with the first wall, the first and second walls being in joint relative motion with respect to the cylinder around the axis.

5. A method according to any one of claims 1 to 4, wherein the local heating is moved continuously relative to the cylinder (3) around the axis (X).

6. A method according to any one of claims 1 to 5, wherein the cylinder (3), positioned in the vacuum molding tooling (10; 10a), has its axis (X) oriented along a vertical direction (DV) and a lower axial end (31) bearing on a positioning surface (SP) transverse to the vertical direction.

7. A method according to any one of claims 1 to 6, wherein the cylinder (3) is in one piece.

8. A method according to any one of claims 1 to 6, wherein the cylinder (3s) is sectorized and formed by an assembly of panels (3p) around the axis (X) with overlap between neighboring panels.

9. A method according to any one of claims 1 to 8, wherein the cylinder (3) comprises, on an internal (SI) or external surface, stiffening elements (40) of a second thermoplastic prepreg fibrous material, identical or different from the material of the cylinder, and wherein the stiffening elements are bonded to the cylinder by co-consolidation during heat treatment.

10. A method according to any one of claims 1 to 9, wherein a smoothing plate (13) is intercalated between the cylinder (3) and each empty tarpaulin (12; 12a; 12b).

11. A method according to any one of claims 1 to 10, wherein the part (100) is a ferrule of a space launcher stage.

12. An installation (1) for manufacturing a part (100) of thermoplastic composite material having a cylindrical shape, comprising: - a vacuum molding tool (10; 10a) of cylindrical shape extending about an axis (X), comprising at least one vacuum bag (12; 12a; 12b) delimiting an internal volume intended to receive a cylinder (3) of pre-impregnated thermoplastic fibrous material and configured to apply a conforming pressure (PC) to it during a vacuum draw in the internal volume, - a local heating device (20) comprising at least one heating wall (24) configured to melt or soften one or more thermoplastic resins impregnating the cylinder, said at least one heating wall having an extent (E24) limited to a circumferential sector of the molding tool, and - a displacement device (30) configured to put said at least one heating wall in relative motion with respect to the molding tooling around the axis.

13. Installation according to claim 12, wherein the vacuum molding tooling (10) further comprises a metallic forming mandrel (14), annular in shape, on which the vacuum bag (12) is hermetically secured, the internal volume being defined between the forming mandrel and the vacuum bag.

14. Installation according to claim 12, wherein the vacuum molding tooling (10a) further comprises annular retaining flanges (17) disposed at each axial end of the molding tooling, an internal radial vacuum bag (12a) and an external radial vacuum bag (12b) being hermetically secured to these flanges.

15. An installation according to any one of claims 12 to 14, wherein the local heating device (20) comprises a first heated wall (22) configured to be positioned inside the cylinder (3), and a second heated wall (24) configured to be positioned outside the cylinder in circumferential overlap, total or partial, with the first wall, and wherein the displacement device (30) is configured to put the first and second walls in joint relative motion with respect to the molding tooling (10) around the axis (X).

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