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

Abstract

The invention relates to a method for manufacturing a cylindrical, thermoplastic composite part, the method comprising: - positioning a cylinder (3) made of thermoplastic pre-impregnated fibrous material in a vacuum moulding tooling (10), at least one vacuum bag (12) being situated facing the cylinder, and - consolidating the cylinder in the vacuum moulding tooling, during which a vacuum is drawn so that the at least one bag applies a shaping pressure to the cylinder, the cylinder being subjected to a heat treatment comprising (i) sweeping (B) its circumference with a local heating, of extent (E24) limited to a sector of the cylinder, in a relative movement in relation to the cylinder about its axis, and (ii) cooling, after this local heating, so as to fix the shape of the cylinder. Fig. 1

Description

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

[0001] This document describes a method for manufacturing a part from a 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 components of space launch vehicles, but is not limited to this application. Previous technique

[0002] Composite materials offer a weight 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 that is an integral part of a stage of a space launcher which can have substantial dimensions, for example several meters in diameter.

[0004] State-of-the-art methods, such as ovens or autoclaves, are used to heat-form thermoplastic composites using a technique called 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 heating methods are not large enough to accommodate a monolithic (one-piece) launcher shell. Even the largest available methods capable of accommodating such a structure can exhibit temperature inconsistencies 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 better suited to the processing of large cylindrical parts.

[0006] Furthermore, in cases where metal tooling is used, it may be desirable to control the stresses and deformations resulting from differential expansions between the metal and the composite in order to improve the material health of the part obtained. One solution to do this is to use Invar tooling which has a coefficient of expansion close to that of the composite, but this solution, without wanting to exclude it, has the disadvantage of presenting a much higher cost compared to steel tooling which leads, in turn, to much greater differential expansions.

[0007] It is therefore also desirable to have a hot forming process for thermoplastic composites that improves the material health of the part when metal tooling is used, while keeping costs under control.

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

[0009] This presentation concerns a manufacturing process for a part made of thermoplastic composite material having a cylindrical shape, the process comprising: - the positioning of 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 - the consolidation of the cylinder in the vacuum molding tooling, during which a vacuum is drawn to apply a conforming pressure on the cylinder by said at least one sheet, the cylinder being subjected to a heat treatment comprising (i) a sweep of its circumference by local heating, limited in extent 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.

[0010] The present invention proposes a method for shaping thermoplastic composite cylinders 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 forming pressure, without any metallic part in the tooling.

[0012] In some embodiments, the vacuum molding tooling further includes 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 local heating begins.

[0013] In these embodiments, the cylinder is formed between the mandrel and the vacuum bag during the vacuum process. The embodiment just described allows the use of 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 compensates for 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 localized heating generates a slight increase in the mandrel's perimeter, which in turn slightly increases its diameter, thus compensating for 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 modified during cooling and therefore does not generate these deformations, creases, undulations during cooling, allowing the use of a metallic material such as steel for the making of the chuck.

[0014] Alternatively, the vacuum molding tooling further includes 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 chuck. The flanges ensure the cylinder's circularity at its axial ends and maintain its 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 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] This feature further contributes to improving the uniformity 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 displaced 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 relative 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 within 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 not divided into juxtaposed panels or into locally overlapping panels. This corresponds to a full-barrel configuration where the fibers extend continuously around the entire axis of the cylinder. The invention is of particular interest for this type of structure, especially since the continuity of the circumferential fibers can lead to high stresses if the entire structure is heated on a steel tool (and not locally as in the invention). However, the use of a divided cylinder is also envisaged within the scope of the present invention, particularly with panels assembled by overlapping before consolidation.Indeed, if for example the automated draping means do not allow draping a cylinder several meters in diameter but only sectors of a cylinder, then this sectorized option can prove to be very interesting from an industrial point of view.

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

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

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

[0028] The use of an automated fiber placement (AFP) technique allows the fiber orientation of the stack to be configured according to requirements, thus optimizing the mechanical properties of the resulting part. 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 the vacuum, and the temperature increase allows them to become fluid to guarantee the Good contact of the stiffening elements on the cylinder, and therefore good mechanical strength of the welded joint. The part is, in this case, obtained by an operation called co-consolidation of the cylinder and the stiffening elements which produces a weld, after cooling, due to the interpenetration of the polymer chains which took place, 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 interposing a polymer film, in particular polyetherimide (PEI), and heating the whole.

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

[0033] The smoothing plate (or "caul plate") is thin, approximately 1 mm thick, allowing for even better control of the workpiece's geometry and surface finish. Each smoothing plate can be made of metal. They can be used without a mandrel, or in conjunction with one (on the outside). When the mandrel is omitted, the advantage is that only a thin sheet of metal needs to be heated on the inside of the cylinder. Of course, each plate can be segmented and formed from several adjacent 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 at least two meters, or even at least three meters, in diameter.

[0036] This presentation also concerns an installation for manufacturing a part made of thermoplastic composite material having a cylindrical shape, comprising: - a vacuum molding tool of cylindrical shape 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 tooling, and - a displacement device configured to put 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 an annular metallic forming mandrel to which the vacuum bag is securely attached, the internal volume being defined between the forming mandrel and the vacuum bag.

[0038] Alternatively, the vacuum molding tooling further includes annular retaining flanges arranged at each axial end of the molding tooling, with an internal radial vacuum bag and an external radial vacuum bag being hermetically secured to these flanges.

[0039] In some embodiments, the local heating device includes 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 primarily intended to illustrate the principles of the presentation.

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

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

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

[0045] [Fig. 4] Figure 4 schematically and partially represents 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] Figure 5 schematically and partially represents a detail of a heating wall that can be implemented within the framework of the invention.

[0047] [Fig. 6] Figure 6 schematically and partially represents 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] Figure 7 schematically and partially represents 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] Figure 8 represents, schematically and partially, an example of a ferrule of a space launcher stage that can be obtained within the framework of the invention. Description of the implementation methods

[0050] Figure 1 illustrates an example of 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 shown in Figure 1, the tool 10 includes a metal mandrel 14 with an 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, consisting of a plurality of removably connected segments. The bag 12 may be made of, but is not limited to, a polyimide or elastomeric material, reinforced or unreinforced, and is a known component in itself. Both the mandrel 14 and the bag 12 extend about the axis X.

[0052] Figure 1 illustrates 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 well-established technique. Cylinder 3 comprises a fibrous reinforcement pre-impregnated with a thermoplastic resin. The choice of reinforcement material and 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). As an example, Cylinder 3 is formed from sheets or strands of fibers pre-impregnated with a polyaryletherketone resin, such as the one marketed under the reference LM PAEK® by Victrex.

[0054] In the illustrated example, cylinder 3 is made of a single piece, but the invention remains within the scope of the invention if the cylinder is segmented, formed by juxtaposition or local overlapping of panels along its circumference. In the case of a segmented cylinder, the same resin is advantageously used in the different panels, or failing that, compatible resins.

[0055] In general, the cylinder 3 can be formed from a stack of pre-impregnated thermoplastic fiber layers, as illustrated in Figure 2, for example. The use of an automated fiber placement technique is advantageous for achieving a fiber orientation precisely tailored to the requirements. However, those skilled in the art will recognize that the cylinder 3 can be formed in different ways, for example, by draping superimposed fiber layers with a predefined orientation, by winding a pre-impregnated woven strip in several layers, or even by a single woven layer of pre-impregnated thermoplastic fiber material with overlapping or juxtaposed edges. Figure 3 illustrates 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. This means 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 adjacent 3p panels in their overlapping ZR zone towards their 3pa and 3pb edges. Those skilled in the art will recognize that other panel assembly variations are possible.

[0056] Cylinder 3 is positioned in tooling 10 with its axis aligned with the X-axis of tooling 10. The X-axis can be either an axis of revolution of cylinder 3 or 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, cylinder 3 is positioned in tooling 10 so that its X-axis is oriented 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 particularly and as illustrated in Figure 2, the tooling 10 includes, in its lower part, a positioning flange 16 on which rest the mandrel 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 integral 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 sealant 11.

[0057] In the illustrated example, the axis of cylinder 3 is oriented along the vertical direction DV, but a person 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 variant, the cylinder is draped directly onto the mandrel 14 (the latter in this case also corresponds to the draping tooling) but it is not excluded that the cylinder is draped onto a draping support separate from the mandrel and then positioned on the mandrel, once the draping is completed.

[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] The cylinder 3 is hot-formed by drawing a vacuum from the internal volume of the tooling 10. This vacuum forces the sheet 12 onto the cylinder 3, conforming it between the mandrel 14 and the sheet 12 by applying a conforming pressure PC. During the consolidation process, 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 scope of the invention.

[0061] In the illustrated example, the device 20 includes a first heating wall 22 internal to the cylinder 3 and a second heating wall 24 external to the cylinder 3. More precisely, 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 portion of the circumference of the cylinder 3, or of the tooling 10. The local heating, or the walls 22, 24, can also 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, of, for example, less than or equal to 120°, 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 Figure 4). In the illustrated example, the walls 22 and 24 have full circumferential overlap, meaning that 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 second 24 walls are connected by a connecting wall 26, which allows for the simultaneous movement of these walls 22 and 24 during the movement of the device 20. This also provides better thermal insulation by minimizing heat loss through convection into the air. The walls 22, 24, and 26 thus move as a single unit. The connecting 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 mechanism, 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. For example, a heating device comprising at least one robotic arm on which at least one heating panel is mounted can be used. Alternatively, a movement device guided by rails, rather than wheels 30, can 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, of course, remains within the scope of the design. of the invention when this device is fixed and the cylinder is rotated around its axis so as to produce the sweep of local heating over the circumference of the cylinder.

[0068] An example of heat treatment applied to cylinder 3 during consolidation will now be described in more detail in relation to Figure 4. In general, the vacuum is maintained during the heat treatment, i.e. during the sweep by local heating, 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 process is then initiated by local heating of a first zone ZC1 (the current state, denoted T1). As mentioned above, the temperature rise of the mandrel 14 closes the gap J between the mandrel 14 and the cylinder 3, along its entire circumference, through a local expansion of the mandrel 14 in zone ZC1. This expansion 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, no more than 1.5 cm, to facilitate this deformation. Furthermore, a limited mandrel thickness also has the advantage of making the internal heating of the cylinder 3 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 not substantially 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 not substantially 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 performed continuously around the circumference of the cylinder, thus allowing for homogeneous consolidation. In general, each zone heated ZC1, ZC2 by the 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 which includes 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 Figure 6 shows another tooling 10a which includes annular retaining flanges 17 arranged at each axial end 31, 32 of the cylinder 3, an internal vacuum bag 12a and an external vacuum bag 12b being sealed to these flanges 17 by sealants 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 another variant not shown, the annular flanges can be omitted, and a sealed connection can be made directly between the internal and external vacuum bags.

[0077] The example in Figure 7 concerns the case where the cylinder 3 has, on its internal surface SI, stiffening elements 40 made of a second pre-impregnated thermoplastic fibrous material, identical or different from the cylinder material, and where the stiffening elements are bonded to the cylinder by co-consolidation during heat treatment. Local heating, while maintaining the vacuum, leads to melting or softening of the thermoplastic resin(s) present. The fluidization of the resin(s) promotes the shaping 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 can 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 can 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 components 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 Its sole purpose is to position the elements 40 on the cylinder 3, but not to produce a robust bonding of the latter to the cylinder 3, which is obtained after co-consolidation

[0080] The part may be a ferrule for a space launcher stage, as illustrated in Figure 8, but the scope of the invention is not limited to this application. Alternatively, the part may find application in the aeronautical field or, more generally, in any application requiring a ferrule. The ferrule 100 in Figure 8 comprises a composite portion 50 obtained by implementing the process described above. This portion 50 is fitted with stiffeners 400a and 400b, which have, for example, been welded by co-consolidation as described in connection with Figure 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 boundaries.

Claims

Demands

1. A method for manufacturing a part (100) of thermoplastic composite material having a cylindrical shape, the method comprising: - the positioning of a cylinder (3) made of pre-impregnated thermoplastic fibrous material in a vacuum molding tool (10; 10a), the cylinder extending around an axis (X) and at least one vacuum bag (12; 12a; 12b) being located opposite the cylinder, and - the 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 pre-impregnated thermoplastic 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. 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 around 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 tooling, the local heating extending only over a portion of the circumference of the tooling, 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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