A method of forming a composite pressure vessel

Abstract

This invention relates to a method for molding a composite pressure vessel. A front and rear connector are rigidly connected to both ends of a positioning shaft to form a support frame. The support frame is vertically fixed, and a 3D printer is driven to extrude fiber-reinforced thermoplastic composite filaments circumferentially along the positioning shaft, forming a printed layer between the front and rear connectors. The support frame with the printed layer is horizontally installed onto a horizontal rotating support, and the positioning shaft is driven to rotate and wrap pre-impregnated fibers around the outer surface of the printed layer, forming a fiber-wound layer. After installing the front and rear skirts, the process is cured to form an integral structure. Finally, the horizontal rotating support and positioning shaft are removed. This invention first utilizes 3D printing technology to construct the printed layer, then wraps pre-impregnated fibers around the outer surface of the printed layer, ensuring the design accuracy, molding efficiency, and burst pressure of the vessel. Finally, the pre-impregnated fibers are cured on the printed layer, ensuring the interfacial shear strength between the two, and eliminating the need for demolding.

Description

Technical Field

[0001] This invention relates to the field of composite material pressure vessel molding technology, and more specifically to a composite material pressure vessel molding method. Background Technology

[0002] As lightweight load-bearing components, the dimensions of composite pressure vessels directly affect their load-bearing capacity. The materials used in composite wound pressure vessels are primarily thermosetting resin-based continuous fiber-reinforced composites, which are wound onto a mandrel and then cured. After curing, the mandrel needs to be separated from the composite material for demolding. This demolding process is not only time-consuming but also carries the risk of damaging the composite material. Currently, air-filled mandrels are mainly used to shorten demolding time. However, air-filled mandrels rely on internal pressure to support the shape, resulting in lower surface accuracy. Summary of the Invention

[0003] To address the problems of long demolding time, easy damage to composite materials, and low surface accuracy in existing winding molding technologies, this invention provides the following technical solution:

[0004] This invention provides a method for molding a composite material pressure vessel, comprising:

[0005] The front and rear connectors are rigidly connected to both ends of the positioning shaft to form a support frame.

[0006] A vertically fixed support frame is used to drive the 3D printer to extrude fiber-reinforced thermoplastic composite filaments circumferentially along the positioning axis, forming a printing layer between the front and rear joints;

[0007] The support frame with the printed layer is horizontally installed onto the horizontal rotating bracket, and the positioning shaft is driven to rotate and wrap pre-impregnated fibers around the outer surface of the printed layer to form a winding layer.

[0008] Before and after the skirt is installed, it is cured to form an integral structure. Finally, the horizontal rotating bracket and positioning shaft are removed.

[0009] This invention provides a method for molding a composite material pressure vessel, comprising:

[0010] The front and rear connectors are rigidly connected to both ends of the positioning shaft to form a support frame.

[0011] A vertically fixed support frame is used to drive the 3D printer to extrude fiber-reinforced thermoplastic composite filaments circumferentially along the positioning axis, forming a printing layer between the front and rear joints;

[0012] The support frame with the printed layer is horizontally installed onto the horizontal rotating bracket, and the positioning shaft is driven to rotate and wrap pre-impregnated fibers around the outer surface of the printed layer to form a winding layer.

[0013] Before and after the skirt is installed, it is cured to form an integral structure. Finally, the horizontal rotating bracket and positioning shaft are removed.

[0014] According to certain embodiments of the present invention, the fiber-reinforced thermoplastic composite filament is a filament composed of a first fiber and a first thermoplastic resin; wherein:

[0015] The first fiber is one or more blended fibers selected from carbon fiber, modified carbon fiber, quartz fiber, boron fiber, glass fiber, ceramic fiber, basalt fiber, and alloy fiber; and / or,

[0016] The carbon fiber is a blend of two or more of T700 and T800 fibers; and / or,

[0017] The first thermoplastic resin is one of PA, PP, PEEK, PEKK, PPS, PEI, PEEK-HT, PA12, PBT, PET, TPU, and PCL.

[0018] According to certain embodiments of the present invention, the printed layer is a spiral layup; and / or,

[0019] The porosity of the printed layer is 0.5%–0.75%; and / or,

[0020] The compressive strength of the printed layer is greater than the winding pressure of the pre-impregnated fiber.

[0021] According to certain embodiments of the present invention, the winding layer, after curing, forms a fiber-reinforced layer with the printed layer.

[0022] According to certain embodiments of the present invention, the pre-impregnated fiber is a second fiber impregnated with a second resin; and / or,

[0023] The second resin is a thermoplastic or thermosetting resin, and its peak curing temperature is at least 30°C lower than the melting point of the first thermoplastic resin; and / or,

[0024] The thickness of the printed layer accounts for 1% to 5% of the fiber reinforcement layer.

[0025] According to certain embodiments of the present invention, the second resin is a thermosetting resin; and / or,

[0026] The thermosetting resin is one of epoxy resin, bismaleimide, or phenolic resin; and / or,

[0027] The curing temperature of thermosetting resins is 60–160℃.

[0028] According to certain embodiments of the present invention, the front connector and the rear connector are fastened to the positioning shaft to achieve axial fixation and circumferential limiting connection.

[0029] According to certain embodiments of the present invention, the horizontal rotating support is provided with two sets of horizontal rotating shafts, which are coaxially connected to both ends of the positioning shaft and are synchronously driven by a servo motor to rotate around its axis.

[0030] According to certain embodiments of the present invention, the working pressure of the composite material pressure vessel is 35-70 MPa.

[0031] According to certain embodiments of the present invention, the outer surface of the printed layer is subjected to plasma treatment before the prepreg fiber is wound.

[0032] The beneficial effects of the technical solutions provided in this application include at least the following:

[0033] This invention first uses 3D printing technology to construct a high-precision, rigid support printing layer, ensuring the accuracy of the inner surface; then, pre-impregnated fibers are wound around the outer surface of the printing layer, ensuring molding efficiency and the burst pressure of the container; finally, the pre-impregnated fibers and the printing layer are solidified into a whole, ensuring the interfacial shear strength between the pre-impregnated fibers and the printing layer, and completely eliminating the traditional mold demolding process. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a flowchart of a composite material pressure vessel molding method according to certain embodiments of the present invention.

[0036] Figure 2 This is a schematic diagram showing the formation of a printed layer during the molding process of a composite material pressure vessel in some embodiments of the present invention.

[0037] Figure 3 This is a schematic diagram of the composite material pressure vessel after the winding layer is formed during the molding process in some embodiments of the present invention.

[0038] Figure 4 This is a schematic diagram of the composite material pressure vessel after molding and removal of the horizontal rotating support and positioning shaft in some embodiments of the present invention. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0040] For simplicity, this invention only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated; similarly, any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0041] It should be noted that, in the description of this invention, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more. Relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0042] In the description of this invention, the terms "any embodiment / mode," "one embodiment / mode," "some embodiments / modes," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment / mode or example, which are included in at least one embodiment / mode or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples. Furthermore, without contradiction, those skilled in the art can combine and integrate the different embodiments / modes or examples described in this specification, as well as the features of different embodiments / modes or examples.

[0043] The above description of the invention is not intended to describe every disclosed embodiment or implementation of the invention. Exemplary embodiments are described in more detail below. These embodiments can be used in various combinations. In each example, the listing is merely representative and should not be construed as exhaustive.

[0044] As mentioned earlier, the winding molding technology requires mandrel support, which has high cost, low surface accuracy, long demolding time, and is prone to damaging the cured layer.

[0045] Although 3D printing technology can print high-precision shapes, it has low printing efficiency and the printed profiles cannot meet the design requirements for the burst pressure of pressure vessels.

[0046] In view of this, the present invention first uses 3D printing technology to construct a high-precision, rigid support printing layer to ensure the accuracy of the inner surface; then, pre-impregnated fibers are wound around the outer surface of the printing layer to ensure molding efficiency and the burst pressure of the container; finally, the pre-impregnated fibers and the printing layer are solidified into a whole to ensure the interfacial shear strength between the pre-impregnated fibers and the printing layer, and completely eliminates the traditional mold demolding process.

[0047] Figure 1 This is a flowchart of a composite material pressure vessel molding method according to certain embodiments of the present invention. Figure 2 This is a schematic diagram showing the formation of a printed layer during the molding process of a composite material pressure vessel in some embodiments of the present invention. Figure 3 This is a schematic diagram of the composite material pressure vessel after the winding layer is formed during the molding process in some embodiments of the present invention. Figure 4 This is a schematic diagram of the composite material pressure vessel after molding and removal of the horizontal rotating support and positioning shaft in some embodiments of the present invention.

[0048] In an exemplary embodiment, such as Figures 1-4 As shown, the composite material pressure vessel molding method includes the following steps:

[0049] S1. Rigidly connect the front and rear connectors to both ends of the positioning shaft to form a support frame;

[0050] S2. The vertically fixed support frame is used to drive the 3D printer to extrude fiber-reinforced thermoplastic composite filaments circumferentially along the positioning axis, forming a printing layer between the front and rear joints;

[0051] S3. Horizontally install the support frame with the printed layer onto the horizontal rotating bracket, drive the positioning shaft to rotate and wrap pre-impregnated fibers around the outer surface of the printed layer to form a winding layer;

[0052] S4. After installation and curing of the skirt to form an integral structure, finally remove the horizontal rotating bracket and positioning shaft.

[0053] This invention first constructs a support frame as the basic structure for container forming, and uses the positioning axis as the central axis to provide a reference for printing and winding, ensuring the coaxiality of the printed layer and the winding layer.

[0054] This invention utilizes 3D printing to construct a single-piece mandrel from the printed layers and front and rear joints. This mandrel can be directly used as the internal surface of a pressure vessel and solidifies into a single unit with the winding layers during the subsequent curing process, eliminating the need for demolding. The invention first places the support frame vertically, making it the primary load-bearing component during printing and reducing stress on the printed layers. During printing, the 3D printer's print head rotates circumferentially along the support frame, printing and building up the filament layer in concentric circles, ultimately forming a spiral or annular printed layer between the front and rear joints. Because it avoids curing deformation, the resulting printed layer has high surface precision, meeting the accuracy requirements of the internal surface of composite pressure vessels. The 3D printer employs fused deposition modeling (FDM) or continuous fiber-reinforced extrusion technology. Preferably, the 3D printer completes the process between the front and rear joints in a single pass, saving time and preventing layer separation.

[0055] This invention winds pre-impregnated fibers around the outer surface of the printed layer to form a winding layer, aiming to accelerate the container molding process. While 3D printing technology can precisely construct complex shapes, its molding efficiency is a significant bottleneck due to the layer-by-layer stacking principle. This invention employs automated fiber winding technology to wind pre-impregnated fibers around the outer surface of the printed layer, ensuring the accuracy of the container's internal shape while significantly improving the container molding rate. Furthermore, from the perspective of material mechanical properties, the thermoplastic resins used in conventional 3D printing have an inherent defect of low compressive modulus, making it difficult to meet the stringent design requirements of pressure vessel burst pressure. This invention selects thermosetting resin as the winding matrix material, whose compressive modulus is significantly higher than that of thermoplastic resins. Combined with the prestressed structure formed by the oriented fiber arrangement, this significantly improves the explosion resistance of the pressure vessel.

[0056] The front and rear skirts installed in this invention can be used for subsequent system integration. The curing step allows the resin on the pre-impregnated fibers to crosslink and diffuse into the pores of the printed layer, improving the bonding strength between the printed layer and the winding layer. After removing the horizontal rotating support and precision positioning shaft system, a completely formed pressure vessel with independent structural stability can be obtained.

[0057] In an exemplary embodiment, the fiber-reinforced thermoplastic composite filament is a filament composed of a first fiber and a first thermoplastic resin. The first fiber accounts for 20% to 50% of the total weight of the filament; too high a percentage will cause printing blockage, while too low a percentage will result in insufficient reinforcement. The first fiber needs to withstand the printing temperature (above the melting point of the first thermoplastic resin) to avoid breakage or carbonization at high temperatures. Exemplarily, the first fiber is one or more of the following: carbon fiber, quartz fiber, boron fiber, glass fiber, ceramic fiber, basalt fiber, and alloy fiber; to enhance the interfacial bonding with the first thermoplastic resin, the surface of the first fiber is treated with a coupling agent. To ensure lightweight, the first fiber is preferably a blend of one or two of T700 and T800. The melting point range of the first thermoplastic resin needs to be compatible with the print head of the 3D printer, have good compatibility with the first fiber, and exhibit small deformation and high impact strength after cooling. For example, the first thermoplastic resin is one of PA, PP, PEEK, PEKK, PPS, PEI, PEEK-HT, PA12, PBT, PET, TPU, and PCL. To meet the burst pressure design requirements of the pressure vessel, the first thermoplastic resin is preferably PEEK or PEKK.

[0058] In an exemplary embodiment, the printed layer is a helical layup with a winding angle controlled within the range of 30°-85°, and the fiber spacing is precisely positioned to ±0.2mm using a CNC winding device. This helical layup adopts an equal tension variable angle design, gradually transitioning to circumferential winding in the pressure vessel head region to form a closed-loop reinforcing structure composed of continuous fibers.

[0059] In an exemplary embodiment, the porosity of the printed layer is controlled within the range of 0.5% to 0.75%, aiming to achieve interfacial reinforcement with the fiber-wound layer through its microporous structure. When the pre-impregnated fibers are wound onto the surface of the printed layer, the resin matrix can penetrate into the pores via capillary action, forming a mechanically interlocking structure that runs through both phases during subsequent curing. This cross-scale bonding mechanism not only significantly improves the interlayer bonding strength (by 30% to 50% compared to non-porous structures), but also optimizes the interfacial stress transfer efficiency through the chemical bonding of the resin-skeleton, thereby ensuring the structural integrity of the composite pressure vessel under high-pressure conditions.

[0060] In an exemplary embodiment, the compressive strength of the printed layer is greater than the winding pressure of the pre-impregnated fibers (typically 0.5-3 MPa). This mechanical property ensures that during the fiber winding stage, the printed layer can stably bear the winding tension and lateral stress generated by resin curing shrinkage, avoiding plastic deformation or structural collapse, thereby guaranteeing the geometric accuracy and interfacial bonding quality of the wound layer. The compressive strength of the printed layer can be optimized through material design and process to make its compressive strength threshold significantly higher than the winding pressure of the pre-impregnated fibers. For example, axial compressive strength can be improved by orienting the fibers along the principal stress direction through 3D printing path planning. The thickness of the printed layer, accounting for 1% to 5% of the fiber reinforcement layer, is sufficient to meet the requirements.

[0061] In an exemplary embodiment, the pre-impregnated fiber is a second fiber impregnated with a second resin. The second fiber may be the same as or different from the first fiber. The second resin may be a thermoplastic resin or a thermosetting resin, and its curing peak temperature must be at least 30°C lower than the melting point of the first thermoplastic resin to ensure that the accuracy of the printed layer is not affected by the molten state of the second resin. Preferably, the second resin is a thermosetting resin. Thermosetting resins have a higher elastic modulus and a lower coefficient of thermal expansion, and do not undergo a phase change after curing. Compared with thermoplastic resins, they are more suitable for scenarios requiring high temperature and high pressure, long-term load, and high-precision dimensions. Exemplarily, the thermosetting resin is one of epoxy resin, bismaleimide, and phenolic resin. Preferably, it is an epoxy resin with a high elastic modulus.

[0062] In an exemplary embodiment, the printing layer is T700 carbon fiber + PP resin, and the winding layer is T700 carbon fiber + epoxy resin.

[0063] In an exemplary embodiment, the winding layer is cured and then combined with the printed layer to form a fiber-reinforced structure, wherein the thickness of the printed layer is controlled within the range of 1% to 5% of the total thickness of the fiber-reinforced structure. The curing process adopts a gradient temperature rise mode, the hot pressing temperature is controlled within the range of 20-30°C above the resin melting point, and the holding pressure is maintained within the range of 0.5-2.0 MPa.

[0064] In an exemplary embodiment, the front and rear connectors are fastened to the positioning shaft to achieve axial fixation and circumferential limiting connection. For example... Figure 2 As shown, the positioning shaft is I-shaped, consisting of two parallel flanges and a long shaft located between them and perpendicular to them. The front / rear connector is integrally formed from a neck and a shoulder: the neck is cylindrical; the shoulder is disc-shaped with an arc-shaped outer surface; the inner cavity has a stepped surface. The stepped surface of the inner cavity of the front / rear connector abuts against the inner end faces of the two flanges and is fixed by positioning bolts (not shown). Multiple positioning bolts parallel to the long shaft penetrate the flanges and are inserted into the stepped surface of the front or rear connector, achieving a tight connection between the front and rear connectors and the flanges, thereby achieving axial fixation and circumferential limiting of the front and rear connectors.

[0065] In an exemplary embodiment, forming a printed layer between the front and rear connectors specifically includes: as follows Figure 2 As shown, fiber-reinforced thermoplastic composite filaments are welded to the connection between the neck and shoulder of the front / rear connector. After printing is completed on the outer surface of the shoulder, the printing of the part between the front / rear connector shoulders is continued.

[0066] In an exemplary embodiment, such as Figure 3 As shown, the horizontal rotating support has two sets of horizontal rotating shafts, which are coaxially connected to both ends of the positioning shaft and synchronously driven by a servo motor to rotate the positioning shaft around its axis. The rotating shaft and the positioning shaft can be positioned and limited by positioning bolts or keyways (not shown).

[0067] In an exemplary embodiment, the working pressure of the composite material pressure vessel is >5 MPa. Exemplarily, the composite material pressure vessel is a high-pressure hydrogen storage tank for a hydrogen fuel cell vehicle, a rocket propellant tank, a satellite pressure vessel, a high-pressure gas storage and transportation container, etc.

[0068] In an exemplary embodiment, the outer surface of the printed layer is subjected to plasma treatment before winding the prepreg fibers. The prepreg fiber winding process must be completed within 2 hours after plasma treatment, and maintained for 10 hours using a vacuum degassing device. -3 ~10 -2 Interface activation is maintained in a vacuum environment of Pa.

[0069] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method of forming a composite pressure vessel, characterized by, include: The front and rear connectors are rigidly connected to both ends of the positioning shaft to form a support frame. A vertically fixed support frame is used to drive the 3D printer to extrude fiber-reinforced thermoplastic composite filaments circumferentially along the positioning axis, forming a printed layer between the front and rear joints; the porosity of the printed layer is 0.5%~0.75%; The support frame with the printed layer is horizontally installed onto the horizontal rotating bracket, and the positioning shaft is driven to rotate and wrap pre-impregnated fibers around the outer surface of the printed layer to form a winding layer. Before and after the skirt is installed, it is cured to form an integral structure. Finally, the horizontal rotating bracket and positioning shaft are removed.

2. The composite material pressure vessel molding method according to claim 1, characterized in that: The fiber-reinforced thermoplastic composite filament is a filament composed of a first fiber and a first thermoplastic resin; wherein: The first fiber is one or more of the following: carbon fiber, quartz fiber, boron fiber, glass fiber, ceramic fiber, basalt fiber, and alloy fiber. The carbon fiber is a blend of two or more of T700 and T800 fibers; The first thermoplastic resin is one of PA, PP, PEEK, PEKK, PPS, PEI, PEEK-HT, PA12, PBT, PET, TPU, and PCL.

3. The method for molding a composite pressure vessel according to claim 1, characterized in that: The printed layer is a spiral layup; and / or, The compressive strength of the printed layer is greater than the winding pressure of the prepreg fiber.

4. The method for molding a composite material pressure vessel according to claim 1, characterized in that: After the winding layer is cured, it forms a fiber-reinforced layer with the printed layer.

5. The composite material pressure vessel molding method according to claim 4, characterized in that: The thickness of the printed layer accounts for 1% to 5% of the thickness of the fiber reinforcement layer.

6. The method for molding a composite material pressure vessel according to claim 2, characterized in that: The pre-impregnated fiber is a second fiber impregnated with a second resin; The second resin is a thermoplastic resin or a thermosetting resin, and its curing peak temperature is at least 30°C lower than the melting point of the first thermoplastic resin. The thermosetting resin is one of epoxy resin, bismaleimide, and phenolic resin; The curing temperature of the thermosetting resin is 60~160℃.

7. The method for molding a composite material pressure vessel according to claim 1, characterized in that: The front and rear connectors are fastened to the positioning shaft to achieve axial fixation and circumferential limiting connection.

8. The method for molding a composite material pressure vessel according to claim 1, characterized in that: The horizontal rotating support is provided with two sets of horizontal rotating shafts, which are coaxially connected to both ends of the positioning shaft and synchronously driven by a servo motor to rotate the positioning shaft around its axis.

9. The method for molding a composite material pressure vessel according to claim 1, characterized in that: The working pressure of the composite material pressure vessel is >5MPa.

10. The method for molding a composite pressure vessel according to claim 1, characterized in that: Before winding the prepreg fiber, the outer surface of the printed layer is subjected to plasma treatment.

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