Method for manufacturing a hollow part made of composite material by hydroforming, and corresponding manufacturing device and equipment

Abstract

The present invention relates to a method and a device for manufacturing a hollow part made of composite material, based on a step of shaping the hollow part from the draped preform (PD) by injecting a pressurised heat-transfer fluid (F) into the draped preform, which has been placed in a hermetically sealed mould (M) beforehand, so as to force the draped preform to expand radially towards the walls of the mould until the shape of the prepreg ply of the preform matches the walls of the mould.

Description

[0001] Manufacturing process by hydroforming of a hollow part made of composite material, corresponding manufacturing device and equipment.

[0002] Technical field

[0003] The invention falls within the field of materials science, and more particularly, the shaping of composite materials.

[0004] The invention finds numerous applications, notably, but not exclusively, in the cycle sector (e.g., frame elements, handlebars, stems, rims), the automobile and aeronautics sectors (e.g., chassis, steering tubes, axles, passenger compartment parts, tubing), in the industrial logistics sector (robot arms, portable power tools) or in the sports and leisure goods manufacturing industry (e.g., rackets, paddles, sailing masts).

[0005] Technological background

[0006] In the remainder of this document, we will focus more specifically on describing the problem existing in the field of cycling with which the inventor was confronted. The invention is of course not limited to this particular context of application, but is of interest for any technique for manufacturing hollow composite parts having to deal with a similar or similar problem.

[0007] Since the end of the Covid-19 pandemic, the cycling sector has seen strong growth, driven in particular by an increase in sales volumes of electrically assisted bicycles. Practical, beneficial for the environment and health, the bicycle or "bike" is becoming an increasingly popular mode of transport, constituting an economically and ecologically attractive alternative to purchasing a motorized vehicle.

[0008] Faced with this strong dynamic, the bicycle industry is struggling to absorb all global demands and is now looking for new technical solutions to meet current demand.

[0009] The bicycle frame, for example, is the fundamental element that allows the wheels, saddle, handlebars and pedals to be interconnected. It is the subject of numerous constructive proposals, based on a set of tubular elements whose shape and the material(s) that compose it give it its main technical characteristics (rigidity, weight, impact resistance, etc.). The main materials used are metals such as steel, titanium or aluminum), polymer-based materials or composite materials. The tubular elements that make up the frame can be obtained in a single piece or assembled by welding, gluing or other methods.

[0010] Thermosetting polymer composites are increasingly used materials in the cycling industry, as they allow the development of composite parts with more or less complex geometry and high performance. These materials offer multiple advantages, such as easy shaping thanks to their malleability and increased properties on the finished product (mechanical resistance, lightness, non-perishability over time, etc.). Carbon fiber, for example, is now one of the most widely used composite materials in the conventional manufacture of bicycle frames.

[0011] A technique for manufacturing hollow composite parts well known to those skilled in the art is based on the use of a flexible sealing bladder (typically made of silicone).This known technique is based on the following steps: draping a flexible sealing bladder (typically silicone) with a prepreg ply (typically a composite material of the polymerizable fiber-resin type); placing the draped assembly in a mold whose impression is conformed to the shape and dimensions of the part to be manufactured; forming a molded part by applying isostatic air pressure inside the sealing bladder (process also known as "blow molding") so as to make it swell and thus force the prepreg ply to extend towards the walls of the mold; once the part is formed, demolding the molded part and removing the inflation bladder; heat treatment in an autoclave oven of the molded part to activate the polymerization of the prepreg ply; and obtaining the hollow part after cooling and removing the preform.

[0012] However, such a manufacturing technique is relatively complex and expensive to implement. Indeed, it requires the use of a specific sealing bladder and heat treatment in an autoclave oven. Furthermore, the recycling of thermosetting resins, which is interesting due to their physicochemical properties, remains technically delicate and economically unattractive. Finally, such a technique remains reserved for the production of hollow parts in small series. There is therefore a real need to provide a manufacturing technique for hollow composite parts that is simpler and less expensive to implement, thus offering prospects for industrializable production for this type of part. In other words, there is a need to provide a manufacturing technique for hollow composite parts suitable for industrial volume production.

[0013] Statement of the invention

[0014] In a particular embodiment of the invention, a method is proposed for manufacturing a hollow part made of composite material, the method comprising a step of obtaining a draped preform, said draped preform comprising a plastically deformable hollow base preform covered, at least partially, with a ply of composite material. The method is such that it comprises a step of shaping the hollow part from said draped preform by injecting a heat transfer fluid under pressure inside said draped preform, previously placed in a hermetically sealed mold, so as to force said draped preform to deform plastically and to expand radially towards the walls of the mold until the ply of composite material conforms to the walls of the mold.

[0015] Thus, the invention is based on a new and inventive approach to shaping hollow composite parts by hydroforming from a composite draped preform. This approach consists of injecting a heat transfer fluid under pressure inside the draped preform so as to inflate the draped preform, "like a balloon", inside a mold shaped to the desired shape, until the composite material ply conforms to the walls thereof. The composite material ply may be a ply of pre-impregnated fibers or a ply of dry fibers.

[0016] According to a particularly advantageous characteristic, the shaping step is preceded by the following steps: securing at least one nozzle to said draped preform so as to form a nozzle-preform assembly; placing the nozzle-preform assembly in the mold, said at least one nozzle being housed in a housing provided for this purpose with a sliding ability such that during said shaping step, said at least one nozzle moves by sliding in translation inside its housing under the effect of the expansion of said draped preform. Thus, when the draped preform is subjected to pressurized heat transfer fluid, the nozzle(s) mounted to move in translation inside the mold make it possible to effectively accompany the expansion of said draped preform during the hydroforming of the part.This approach is all the more clever because the nozzle-preform assembly thus formed also greatly facilitates the gripping of the draped preform before its placement in the mold. This therefore makes it easier to drape the basic preform, place it inside the mold, and more generally handle it.

[0017] According to a particular implementation, the nozzle-preform assembly is provided with a single nozzle (for example a tubular preform with a bottom having a single opening through which the heat transfer fluid is injected and ejected).

[0018] According to an alternative implementation, the nozzle-preform assembly is provided with a plurality of nozzles (for example a tubular preform with two openings, each being secured to a nozzle).

[0019] According to a particular aspect, the positioning step comprises a step of holding said draped preform in position inside the mold, the holding in position being ensured by means of said at least one nozzle of the nozzle-preform assembly.

[0020] The use of such a nozzle-preform assembly according to the invention is particularly advantageous. It gives said at least one nozzle two functions: a basic function of injecting / ejecting a fluid into / from a receptacle, and a complementary function of holding the preform in the mold. No additional equipment is therefore necessary to ensure that the preform is held in the mold, making the part manufacturing process simpler and less expensive to implement.

[0021] According to a particular implementation, the vacuum step belongs to the group comprising: vacuuming a filling space of said draped preform via said at least one nozzle; vacuuming an expansion space of the mold via at least one hole made in the mold.

[0022] The vacuuming of these two spaces facilitates the hydroforming of the hollow part, and is particularly well suited to the large-scale production of hollow composite parts where it provides a productivity gain by facilitating the forming of this type of part. The vacuuming of the mold expansion space ensures, on the one hand, a watertight closure of the mold, and on the other hand helps to accelerate the pressurized injection of the fluid inside the preform. The vacuuming of the filling space also helps to facilitate the injection of the pressurized fluid inside the preform.

[0023] According to a particular implementation, the method comprises a step of heating the mold before the shaping step and / or during the shaping step.

[0024] This makes it possible to reduce the appearance of residual manufacturing defects and to promote the deformability of the draped preform during hydroforming. Such heating also improves the surface quality of the parts produced. Finally, heating is well suited to large-scale production where it provides a productivity gain by facilitating the forming of the hollow part.

[0025] In another embodiment of the invention, a device is proposed for manufacturing a hollow part made of composite material from a draped preform, said draped preform comprising a plastically deformable hollow base preform and a ply of composite material covering, at least partially, said hollow preform. Such a device comprises means for shaping the hollow part from said draped preform, comprising a mold intended to receive said draped preform, means for injecting a heat transfer fluid under pressure and said draped preform.The shaping means are configured so that when the injection means are activated, the heat transfer fluid is injected under pressure inside said draped preform previously placed in the mold, so as to force said draped preform to deform plastically and to expand radially towards the walls of the mold until the ply of composite material conforms to the walls of the mold.

[0026] The invention therefore also relates to a device for hydroforming hollow parts made of composite material, suitable for industrial volume production.

[0027] Advantageously, the device comprises means for implementing the steps that it carries out in the method as described previously, in any one of its different embodiments.

[0028] According to a particularly advantageous aspect, at least one nozzle is secured to said draped preform to form a nozzle-preform assembly intended to be placed inside the mold, the draped preform being held in position inside the mold by said at least one nozzle, said at least one nozzle being housed in a housing provided for this purpose with a sliding ability such that, when the injection means are activated, said at least one nozzle moves by sliding in translation inside its housing under the effect of the expansion of said draped preform. The translational movement of the nozzle(s) inside the mold makes it possible to effectively accompany the expansion of the preform during the shaping of the part, which facilitates the hydroforming step.

[0029] According to a particular implementation, the securing of said at least one nozzle to said draped preform is ensured by means of a collar formed on the wall of said draped preform.

[0030] In another embodiment of the invention, a draped preform is provided for implementing the method as described above, in any of its various embodiments. Such a preform comprises a hollow base preform and a ply of composite material covering, at least partially, the surface of the base preform, the hollow preform being made from a plastically deformable material and said ply of composite material consisting of at least one layer of pre-impregnated composite material or at least one layer of dry fiber-based composite material.

[0031] The prepreg ply may consist of a single layer of prepreg composite material or of a plurality of superimposed layers, the nature and thickness of which are chosen according to the technical characteristics desired for the part to be manufactured. The layup of the hollow preform consists of manual or automatic (via machine control) deposition of the prepreg ply on the surface of the base preform. To facilitate the layup operation, at least one nozzle secured to the base preform may be provided to form a nozzle-preform assembly (i.e. a sort of “preform holder”) that is easily handled.

[0032] According to a particular aspect, the draped preform comprises an internal cavity opening onto at least one collar intended to be secured to a nozzle. This is an inexpensive shaping process.

[0033] In another embodiment of the invention, a nozzle is provided intended to be secured to a draped preform to constitute a nozzle-preform assembly for implementing the method as described above, in any one of its different embodiments. Such a nozzle comprises means for fixing to a collar belonging to the group comprising: fixing by screwing, fixing by fitting, fixing by snap-fastening, fixing by gluing, fixing by riveting.

[0034] Thus, several types of fixation, reversible or non-reversible, are possible.

[0035] List of figures Other characteristics and advantages of the invention will appear on reading the following description, given as an indicative and non-limiting example, and the appended drawings, in which:

[0036] [fig. 1] represents a block diagram of a manufacturing device for which the invention is implemented according to a particular embodiment;

[0037] [fig. 2] presents a flowchart of a particular embodiment of the method according to the invention;

[0038] [fig. 3] illustrates the main stages of manufacturing a hollow composite part, in accordance with the method of the invention;

[0039] [fig. 4] represents the simplified structure of a control unit implementing the method according to a particular embodiment of the invention;

[0040] [fig. 5], [fig. 6], [fig. 7], [fig. 8], [fig. 9], [fig. 10] illustrate, in the form of truncated and sectional views, the structural detail of the part at its different stages of manufacture;

[0041] [fig. 11] illustrates, in the form of perspective views, another example of the embodiment of a hollow composite part according to the invention;

[0042] [fig. 12] schematically illustrates the principle of vacuuming the device before forming according to a particular implementation of the invention;

[0043] [fig. 13] schematically illustrates the principle of vacuuming according to a particular implementation of the invention, after forming.

[0044] Detailed description of the invention

[0045] In all figures of this document, identical elements and steps are designated by the same numerical reference.

[0046] The general principle of the invention is based on obtaining a hollow part made of composite material by hydroforming a preform draped with a ply of prepreg, making it possible to form the part and at the same time give it its mechanical properties.

[0047] In the remainder of the description, an example of implementation of the invention is considered in the context of the manufacture of tubular structures for bicycle frames. Indeed, it turns out that the construction of high-quality bicycle frames in large series represents a considerable challenge for the bicycle industry. The invention is of course not limited to this particular field of application, but is applicable to any sector or application requiring the shaping of hollow part(s) made of composite material.

[0048] Figure 1 is a block diagram illustrating a HYD manufacturing device for a hollow part according to a particular embodiment of the invention. The HYD device is configured to allow the shaping by hydroforming of a tubular part with a circular section, constituting a bicycle frame.

[0049] The HYD device includes a shaping mold M, a heat transfer liquid injection unit Ul, a UV vacuum unit and a control unit UC.

[0050] The mold M is shaped in this implementation example to carry out the vacuum molding of a tubular part made of composite material from a draped preform. The mold M comprises an enclosure whose walls define the final shape and dimensions of the part to be manufactured. In this example, the mold M is composed of two parts: a fixed lower part PF and a movable upper part PM forming, after assembly, the mold M shaped to accommodate a nozzle-preform assembly E-BP. It may comprise in the lower part and / or in the upper part heating means (in the form of hoses or resistors for example) to facilitate shaping.

[0051] The nozzle-preform assembly E-BP according to the invention is composed of a draped preform PD and two nozzles BI-BO each secured to one end of the draped preform PD. The nozzle Bl constitutes the liquid injection nozzle (inlet nozzle) and the nozzle BO constitutes the liquid ejection nozzle (outlet nozzle), both ensuring that the draped preform is held in position inside the mold M in the closed state.

[0052] The injection unit Ul is configured to generate a pressurized heat transfer fluid F, for example a water-oil mixture having a predefined temperature and flow rate. The injection unit Ul is connected, on the one hand, to the inlet nozzle Bl by a first connection guide Cl (inlet channel) and, on the other hand, to the outlet nozzle BO by a second connection guide CO (outlet channel). By way of example, this injection unit Ul comprises a high-pressure injection pump PI and a heating element EC cooperating with the injection pump so as to produce the pressurized heat transfer fluid F at the outlet of the unit. The injection unit Ul and the connection guides CI-CO form a hydraulic circuit in fluid communication with the interior of the draped preform PD.The interior of the preform PD can be isolated from the hydraulic circuit by means of a valve V which can take two positions: an open position allowing the injection of the heat transfer liquid F into the preform and a closed position preventing the injection of the heat transfer liquid F.

[0053] The injection unit Ul and the valve V form the means for injecting the heat transfer liquid F under pressure. They are controlled by the control unit UC. The mold M, the injection unit Ul and the nozzle-preform assembly E-BP form the forming means according to the invention. The vacuum unit UV (for example a primary or secondary vacuum pump) is connected to the mold M via a suitable connection guide so as to apply a predefined vacuum within the enclosure of the mold M, by means of a hole made in the thickness thereof. This unit makes it possible to implement a vacuum-assisted hydroforming technique.

[0054] The control unit UC is electrically connected to the injection unit Ul on the one hand and to the UV vacuum unit on the other hand to control the injection of the heat transfer fluid F and the UV vacuum of the mold enclosure. The control unit UC can also be electrically connected to the mold M to control the opening and closing of the mold, and / or to temperature sensors and / or to pressure sensors with which the mold could be equipped, typically to record and monitor the temperature and / or the pressure of the heat transfer fluid during the hydroforming operation, and / or the activation of the heating means and / or the activation of the pressurizing means and the means for moving the fluid. The control of these different elements by the control unit UC is carried out by means of pilot commands (the principle of which is described later in relation to Figure 4).This unit provides the programming and control interface for the HYD device, via a human / machine interface (not shown). This human / machine interface allows the machine programming instructions to be entered into a given numerical control, using a programming language adapted to the machine, as well as feedback to the operator during its use.

[0055] The method according to a particular embodiment of the invention is now presented in relation to Figures 2 and 3. The method is implemented using the HYD manufacturing device presented above in relation to Figure 1.

[0056] Production of the draped preform

[0057] In step 100 (referenced “OBT_PD”), a draped preform PD is produced comprising a hollow base preform PC and a prepreg ply PR covering the surface of the base preform PC. The hollow preform PC is made from a plastically deformable material that is impervious to the pressurized heat transfer fluid F, for example a thermoplastic polymer. The prepreg ply PR is made up of one or more prepreg composite material layers, for example a thermoplastic resin-based matrix impregnating reinforcing fibers, also sometimes called a fiber-resin composite. It may be a fiber fabric ply or a ply based on non-woven fibers. Thus, the prepreg ply can consist of a single layer of prepreg composite material or of a plurality of superimposed layers, the nature and thickness of which are chosen according to the technical characteristics desired for the part to be manufactured.

[0058] Examples of thermoplastic polymer-based resins include polypropylene, polyamide, and polyethylene. Examples of thermosetting polymer-based resins include epoxy and polyester, but are not exhaustive. Examples of reinforcing fibers include carbon fiber, glass fiber, Kevlar, and aramid, but are not exhaustive. The prepreg ply can be in the form of a fiber fabric or a non-woven fiber film.

[0059] Laying up the PC base preform consists of either manual or automatic deposition (via machine control) of the prepreg ply on the surface of the PC base preform (single-layer or multi-layer deposition).

[0060] As illustrated in Figure 3, the basic preform PC in this example comprises a main body of revolution, hollow, of generally tubular shape, defining an internal cavity which opens onto two projecting CI-CO collars, each collar being intended to be secured to a nozzle. The overall shape chosen for the basic preform depends on the desired shape for the part to be manufactured.

[0061] According to a particular implementation (not illustrated in the figures), it is possible to provide for fixing at least one nozzle beforehand to one of the ends of the basic preform so as to facilitate gripping thereof and thereby make the draping operation easier.

[0062] Obtaining the nozzle-preform assembly

[0063] After obtaining the draped preform PD, step 200 (referenced “SOL_BU”) is carried out to secure the injection nozzle Bl to the collar Cl and the ejection nozzle BO to the collar CO, so as to form a nozzle-preform assembly E-BP intended to be introduced inside the mold M. The principle of securing the nozzle to the collar can be done in a reversible or non-reversible manner depending on the chosen implementation method. Several examples are illustrated later in the description.

[0064] Placement in the mold

[0065] After securing the nozzles, step 300 (referenced “MEP_PB”) is used to place the nozzle-preform assembly E-BP inside the mold M. The nozzle-preform assembly E-BP is first placed in the lower part of the mold M via housings L1-L2 provided for this purpose, then the upper part of the mold is attached to the lower part thereof so as to allow hermetic closure of the mold when it is locked. The draped preform PD is held in position inside the mold M by the nozzles BI-BO, each housed in a housing provided for this purpose: the nozzle Bl is housed in the housing L1 and the nozzle BO is housed in the housing L2, thus forming the support points for the preform PD. Each of the nozzles Bl and BO is mounted to move in translation in its respective housing with the ability to slide axially along the X axis.The free ends of the BI-BO nozzles (shown here protruding from the mold surface) are then connected to the hydraulic circuit before vacuuming the system.

[0066] Once the nozzle-preform assembly E_BP is in place in the hermetically sealed mold and connected to the hydraulic circuit, the internal cavity of the draped preform PD defines a filling space (referenced “ER”) which is in fluid communication with the hydraulic circuit and ready to receive the heat transfer fluid F. The filling space ER is shaped to be sealed against the pressurized heat transfer liquid F. As for the volume remaining in the mold enclosure (i.e. the volume delimited by the internal walls of the mold M and the external walls of the nozzle-preform assembly E_BP), it defines the expansion space of the draped preform (referenced “EE”) which is in communication with the vacuum pump.

[0067] This example of a two-part mold facilitates the installation of the preform. Of course, other mold configurations can be envisaged without departing from the scope of the invention.

[0068] Vacuuming the device

[0069] We then proceed to step 400 (referenced “MEP_PB”) in which the expansion space EE and the filling space ER are subjected to a vacuum in order to place the device HYD under a controlled atmosphere. We first ensure that the valve V is in the closed position so that the hydraulic circuit is isolated from the mold M. The vacuuming of the expansion space EE is carried out via the purge hole P made in the wall of the mold and which is connected to the UV pump and which makes it possible to create a vacuum in this space. As for the vacuuming of the filling space ER, it must be carried out with a level identical to that of the space EE in order to avoid a differential which could lead to a collapse of the preform or to premature inflation.

[0070] According to a particular implementation, a first level of vacuum in the space EE is achieved to ensure the closure of the mold before injection, then a second level of vacuum is achieved during the injection to facilitate the expansion of the draped preform PD. The vacuuming of the expansion space EE is obtained by activating the UV vacuum pump of the device HYD. It facilitates the hydroforming of the tubular part during step 500.

[0071] When all gases have been expelled from the EE expansion and ER filling spaces, vacuum pumping of the ER filling space is stopped.

[0072] Forming the tubular part

[0073] Step 500 (referenced “MEF_PC”) consists of hydroforming the tubular part P using an incompressible heat transfer liquid, typically an oil or a mixture of oils capable of withstanding temperatures above 150°C (for example, oils used in solar installations, or laboratory water bath oils). The injection unit LU is first activated and the valve V placed in the open position in order to allow the injection of the heat transfer liquid F into the filling space ER of the preform PD (fluid communication between the unit LU and the interior of the preform PD). The liquid F is heated by the heating element EC, then set in motion by the injection pump PI and thanks to the vacuum previously established in the filling space ER.The thrust effect of the injection unit Ul combined with the depression existing in the filling space ER makes it possible to effectively set the pressurized heat transfer fluid in motion in the direction of the arrows F shown in the figures, via the inlet and outlet nozzles. The heat transfer fluid F is continuously injected under pressure (typically of the order of 30 to 100 Bars) inside said draped preform so as to force the draped preform PD to deform plastically and expand radially towards the walls of the mold until the prepreg ply PR hugs the walls. This results in an increase in the volume of the filling space ER to the detriment of the volume of the expansion space EE.

[0074] The temperature and pressure conditions are determined so that, under the effect of heat, the preform PD has sufficient flexibility to be plastically deformed and that, under the effect of the force applied to the internal surface of the preform PD by the liquid F, the preform PD extends by centrifugal radial expansion (arrows E) towards the walls of the mold M, like a balloon. The vacuum effect in the expansion space EE promotes the radial expansion of the preform towards the walls of the mold M, while minimizing the appearance of undesirable residual gases. These temperature and pressure conditions allow efficient shaping of the part, while simultaneously giving it its mechanical properties (no need for subsequent autoclave heat treatment as for the techniques of the prior art).According to a particular implementation, in order to promote the deformability of the draped preform, the mold is heated and maintained at temperature by activating the aforementioned heating means before and / or during step 500 (typically from 200 to 400°C). This has the effect of making the hydroforming step more efficient. To provide uniform mechanical properties, the presence and activation of heating means in the upper and lower parts of the mold are preferred. It is noted that such an operation avoids the formation of micro-void zones, air bubbles or other point defects, which improves the quality of the molding. These defects can appear in the case of insufficient fluidity, due to an insufficient temperature in contact with the mold, hence the interest of the aforementioned heating means.

[0075] According to a particularly interesting characteristic of the invention, the BIBO nozzles are housed in the housings L1-L2 provided for this purpose with a capacity for axial sliding along the X axis, such that during the shaping step, the nozzles move by sliding in translation inside their housing under the effect of the centrifugal expansion of the draped preform. This makes it possible to cleverly accompany the expansion of the draped preform PD so that the part P can take the desired shape, without constraint in all directions, despite the presence of the nozzles forming supports.

[0076] Obtaining the tubular part

[0077] Once the mold cavity is completely filled with the prepreg ply and the thermosetting resin has solidified (polymerization complete), the injection of the heat transfer fluid F and the vacuum pumping of the expansion space EE are stopped. The heating of the mold is also stopped if necessary, and the part can be finalized as illustrated in step 600 (referenced “OBT_P”).

[0078] The mold is first opened to extract the molded part Pm (step 600a). Since the nozzles Bl and BO are still secured to the molded part, the latter are removed by manual removal or by cutting depending on the nature of the means of attachment to the collars (step 600b). Once the nozzles have been removed, the remaining excess parts, such as the collars for example, are then trimmed in order to obtain the finalized part P (step 600c).

[0079] The basic preform PB contained in the part P can be left in place or, alternatively, can be destroyed, for example by chemical dissolution with a suitable solution. Figure 4 shows the simplified structure of a control unit 10 implementing part of the method of the invention, for example according to the particular embodiment described above in relation to Figures 1 to 3 (the control unit being referenced “UC”). This control unit 10 comprises a random access memory 13 (for example a RAM memory), a processing module 11, equipped for example with a processor, and controlled by a computer program stored in a read-only memory 12 (for example a ROM memory or a hard disk). At initialization, the code instructions of the computer program are for example loaded into the random access memory 13 before being executed by the processor of the processing module 11.The processing module 11 receives as input an initialization command 14 of the manufacturing process, processes the command and generates as output the control commands 15 intended for the different elements of the manufacturing device, according to the instructions of the computer program.

[0080] For example, after placing the nozzle-preform assembly E-BP inside the mold M and closing it, the operator starts the process of shaping the part P via the human / machine interface (command 14). The control module 10 transmits to the injection units Ul, vacuum UV and to the mold M the corresponding commands to activate and deactivate the vacuum, the heating of the mold, and the injection of the heat transfer liquid under pressure in accordance with the steps 400 and 500 necessary for forming the part P according to the method of the invention. This is a purely illustrative example, simplified to understand the concept of the invention. Of course, other implementation examples are possible.For example, as a supplement, without being exhaustive, the manufacturing device according to the invention can be configured so that: the control unit 10 automatically controls the opening and closing of the mold M, the control unit 10 controls temperature sensors and / or pressure sensors included in the mold M to take readings (one-off or systematic) and monitor the temperature and / or pressure level of the heat transfer fluid during the hydroforming of the part, for the purposes of monitoring the manufacturing and regulation parameters; the control unit 10 controls the activation and deactivation of the heating means of the mold M so as to apply predefined heating ramps and / or cooling ramps within the mold, for the purposes of optimizing the shaping process of the part; etc.

[0081] It could also be envisaged, as an alternative, to make the aforementioned steps 100, 200 and 300 of the method automatic, by means of a robotic system integrated into the HYD device in order to make the manufacturing method according to the invention fully automated and controllable by the control unit 10 (thus offering industrializable production possibilities compatible with the concept of the invention).

[0082] This figure 4 illustrates only one particular way, among several possible ones, of carrying out the different algorithms detailed above, in relation to figures 2 and 3. In fact, the technique of the invention is carried out indifferently:

[0083] - on a reprogrammable computing machine (a PC computer, a DSP processor or a microcontroller) executing a program comprising a sequence of instructions; or

[0084] - on a dedicated computing machine (for example a set of logic gates such as an FPGA or an ASIC, or any other hardware module).

[0085] In the case where the invention is implemented on a reprogrammable computing machine, the corresponding program (i.e. the sequence of instructions) may be stored in a removable storage medium (such as for example a floppy disk, a CD-ROM or a DVD-ROM) or not, this storage medium being partially or totally readable by a computer or a processor.

[0086] Figures 5 to 10 represent sectional and truncated views of a composite part illustrated at different stages of its manufacture.

[0087] Figure 5 shows schematically the draped preform PD obtained in step 100 of the process, just before the nozzles are installed. As illustrated, the base preform PC comprises a hollow internal cavity (intended to receive the heat transfer liquid) opening onto a collar C1 intended to receive an injection nozzle. In this implementation example, the prepreg ply PR covers the entire base preform PC except at the collars.

[0088] Figure 6 shows schematically the nozzle-preform assembly E_BP obtained in step 200 of the process, intended to be introduced inside the mold M. As illustrated, the injection nozzle Bl is secured to the collar Cl by means of fixing means MF. The principle of securing the nozzle to the collar can be done in a reversible or non-reversible manner depending on the chosen implementation method. To ensure this function, each nozzle is provided with fixing means shaped to allow fixing of the nozzle to the collar by screwing for example, or by fitting, snap-fastening, gluing or riveting. Figures 7 and 8 illustrate the principle of shaping by hydroforming of the composite part, before (figure 7) and after (figure 8) injection of the heat transfer liquid F under pressure, in accordance with step 500 of the process.During the expansion of the draped preform PD, the pressure of the heat transfer liquid F exerted on the internal walls of the draped preform forces the nozzles to move along the longitudinal axis X of the part. Housings are therefore provided at the level of the mold, the profile of each of which is adapted to accommodate a nozzle with an axial sliding capacity allowing the nozzle to move in translation inside its housing under the effect of the expansion of the draped preform. Typically, as illustrated in Figures 7 and 8, once the mold M is closed, the housing L1 has, before hydroforming, a first portion with clearance (defining a space El left between the nozzle and the internal wall of the housing L1) and a second adjusted portion E2 (according to which the nozzle is in contact with the internal wall of the housing L1).During hydroforming, the pressure generated on the walls of the preform PD pushes the nozzle Bl towards the bottom of its housing (i.e. gradually occupying the space El until it stops) so as to be able to accompany the “inflation” of the preform PD until the end of the shaping step (figure 8). The movement of the nozzle Bl in its housing is represented in the figure by the arrow Y. After forming, the housing Ll no longer has any mechanical play.

[0089] Finally, figures 9 and 10 show diagrammatically the phases of finalization of the part P, in accordance with step 600, namely the trimming of the undesirable excess parts (removal of the nozzles and collars from the part obtained after hydroforming).

[0090] The particular embodiment presented above is based on the manufacture of a rectilinear tubular part with a circular section. Of course, this is a particular example of an embodiment and many other types of parts, of various dimensions and shapes, are possible without departing from the scope of the invention. Thus, one could envisage the manufacture of a hollow part with a more complex shape, such as for example a hollow part with a curved shape, a hollow part with a section of variable thickness, a hollow part opening onto a single or multiple openings. One could envisage manufacturing a hollow part in the shape of a U or a T, for example, whose section is circular, square, triangular, oval or oblong, or more simply a hollow part with a single bottom having only one opening.The overall shape of the part, its dimensions and the number of its openings can be adapted on a case-by-case basis, depending in particular on the type of part desired and the targeted mechanical performance. More generally, the technique of the invention applies to any type of hollow part made of composite material that can undergo hydroforming.

[0091] Figure 11 shows another particular embodiment in which a T-shaped tubular part is obtained by the method of the invention. The aim here is to show that the principle of the invention applies to other types of mechanical parts. The different steps of the method are referenced 11-A to 11-G, but are not detailed again here, the principle of the method mentioned above in relation to Figures 2 and 3 being transposable to this example.

[0092] A draped preform PD' (diagram 11-B) is produced from a hollow T-shaped base preform PB' representative of the part to be manufactured (but with smaller dimensions), comprising three openings each opening onto a collar (diagram 11-A). The prepreg ply PR' covers the base preform PB' over its entire surface except on the collars C1, C2, C3 which remain exposed. A nozzle is then assembled on each of the collars (nozzles B1, B2, B3 on collars C1, C2, C3 respectively) using the fixing means provided for this purpose, so as to constitute the nozzle-preform assembly E-BP' (diagram 11-C). The nozzle-preform assembly E-BP' is then placed inside the mold M' via the housings provided for this purpose (diagram 11-D). For the sake of legibility of the figures, only the lower part of the mold is shown.It is noted that the mold M' has a cavity shaped according to the desired shape and dimensions for the part, a T-shape in this case. Once the mold M' is hermetically closed, the nozzle-preform assembly E-BP' is subjected to the hydroforming process according to the principle of the invention: injection of a heat transfer fluid under pressure so as to force the draped preform to expand towards the walls of the mold until the prepreg ply conforms to the walls of the mold (diagram 11-E). The use of a pressurized fluid makes it possible to apply a uniform force in all directions and in areas that might be inaccessible by other means. The method according to the invention therefore makes it possible to obtain parts with various geometries (in particular asymmetrical hollow bodies). Once the part has been extracted from the mold M, the nozzles B1-B2-B3 are removed (diagram 11-F), then the collars C1-C2-C3 are trimmed to obtain the part P' (diagram 11-G).

[0093] The implementations described above are based on the use of a ply of composite material based on pre-impregnated layers. It is also possible, without departing from the scope of the invention, to use a ply of composite material based on dry fibers. In this case, the pressure injection of the resin is carried out during the step of shaping the hollow part and the injection of the heat transfer fluid.

[0094] We now present, in relation to figures 12 and 13, the operating principle of the vacuum system according to a particular implementation of the invention. To do this, a through hole T is provided in the thickness of the mold M at the level of the head of the injection nozzle Bl. This hole T forms a suction duct CA communicating with an air suction circuit placed outside the mold M (not illustrated here).

[0095] Before forming the part by injecting fluid into the filling space ER (Figure 12), air is expelled from the filling spaces ER and expansion spaces EE. Air is sucked out of the expansion zone using the suction duct CA. The shape of the injection nozzle head and the mold (at its ends) are designed to allow fluid communication between the expansion escape EE and the duct CA before forming, thus allowing the air flow to be sucked from the space EE via the duct CA into a suction circuit. The air flow is represented by dotted arrows.

[0096] During and after shaping of the part by expansion of the preform (figure 13), the injection nozzle Bl (then in free position) pushed by the pressure of the fluid slides in its housing until it reaches the stop. In this position (blocking position), the previously open air passage is obstructed by the specific shape of the head of the injection nozzle. This is represented by dotted crosses in the figure. Closing the passage prevents the flow of the preform material from the inside of the mold towards the suction duct CA. Such a device makes it possible to avoid the formation of a plug of plastic material in the duct CA, which would have the effect of rendering the suction system inoperative during subsequent use cycles.

Claims

CLAIMS 1. A method of manufacturing a hollow part made of composite material (P), the method comprising a step of obtaining (100) a draped preform (PD), said draped preform comprising a plastically deformable hollow base preform (PC) covered, at least partially, with a ply of composite material (PR), the method comprising a step of shaping (500) the hollow part from said draped preform by injecting a heat transfer fluid (F) under pressure inside said draped preform, previously placed in a hermetically sealed mold (M), so as to force said draped preform to deform plastically and to expand radially towards the walls of the mold until the ply of composite material fits the walls of the mold, the method being characterized in that the shaping step (500) is preceded by the following steps: securing (200) at least one nozzle (B1;BO) to said draped preform so as to form a nozzle-preform assembly (E-BP); placing (300) the nozzle-preform assembly in the mold, said at least one nozzle being housed in a housing provided for this purpose with a sliding ability such that during said shaping step, said at least one nozzle moves by sliding in translation inside its housing under the effect of the expansion of said draped preform.; 2. Method according to claim 1, in which the positioning step comprises a step of holding said draped preform in position inside the mold, the holding in position being ensured by means of said at least one nozzle of the nozzle-preform assembly.

3. Method according to claim 2, comprising at least one vacuum step belonging to the group comprising: vacuuming a filling space (ER) of said draped preform via said at least one nozzle; vacuuming an expansion space (EE) of the mold via at least one hole provided in the mold.

4. Method according to any one of claims 1 to 3, comprising a step of heating the mold before the shaping step and / or during the shaping step.

5. Device for manufacturing a hollow part made of composite material (P) from a draped preform (PD), said draped preform comprising a hollow base preform (PC) plastically deformable and a ply of composite material (PR) covering, at least partially, said hollow preform, the device comprising means for shaping the hollow part from said draped preform, comprising: a mold (M) intended to receive said draped preform; means for injecting under pressure a heat transfer fluid (F); said draped preform (PD); said shaping means being configured so that when the injection means are activated, the heat transfer fluid (F) is injected under pressure inside said draped preform previously placed in the mold, so as to force said draped preform to deform plastically and to expand radially towards the walls of the mold until the ply of composite material fits the walls of the mold, the device being characterized in that at least one nozzle (Bl;BE) is secured to said draped preform to form a nozzle-preform assembly (E-BP) intended to be placed inside the mold, the draped preform being held in position inside the mold by said at least one nozzle, said at least one nozzle being housed in a housing provided for this purpose with the ability to slide so that, when the injection means are activated, said at least one nozzle moves by sliding in translation inside its housing under the effect of the expansion of said draped preform.; 6. Draped preform (PD) for implementing the method defined according to any one of claims 1 to 4, characterized in that it comprises a hollow base preform (PC) and a ply of composite material (PR) covering, at least partially, the surface of the base preform, said hollow preform being made from a plastically deformable material and said ply of composite material consisting of at least one layer of pre-impregnated composite material or at least one layer of composite material based on dry fibers.

7. Draped preform according to claim 6, comprising an internal cavity opening onto at least one collar (Cl; CE) intended to be secured to a nozzle.

8. Nozzle intended to be secured to a draped preform to constitute a nozzle-preform assembly (E-BP) for implementing the method defined according to any one of claims 1 to 4, characterized in that it comprises means of fixing to a collar belonging to the group comprising: fixing by screwing, fixing by fitting, fixing by snap-fastening, fixing by gluing, fixing by riveting.

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