Additive manufacturing process for high-performance composite pressure vessels and structures

Abstract

The disclosed systems and methods optimize the manufacturing of composite pressure vessels and structures by streamlining the fabrication of tooling and internal structures through the use of additive manufacturing processes such as vat photopolymerization, material or binder jetting, material extrusion, and powder bed fusion to improve quality, scalability, extensibility, and cost-effectiveness. In embodiments, a computer readable medium has computer readable instructions stored thereon that, when executed by a 3D printer, cause the 3D printer to print a composite pressure vessel mandrel (10), the mandrel having a predetermined size, shape, and interior volume (10b) and including at least one end (13) having an opening (17) to the interior volume.

Description

Technical Field

[0001]

[0001] This disclosure is in the field of composite pressure vessels and, more particularly, is directed to a method of forming a pressure vessel using a gas-impermeable composite material that includes carbon fibers and is intended for use in high-pressure and low-pressure applications.

Background Art

[0002]

[0002] For decades, expendable tooling made using a casting process or a removal process has been used to manufacture composite pressure vessels and structures. Currently, polyvinyl alcohol (“PVA”) and other similar water-soluble tooling are utilized. A typical block is fabricated and then machined to its final dimensions. This method is widely used but is costly and time-consuming. Other methods include investment casting with a lost mold that melts or combusts and vaporizes wax or other materials.

Summary of the Invention

Problems to be Solved by the Invention

[0003]

[0003] All of those casting methods require a high initial cost for investing in tooling. Each tool is specific to the use of one geometry, typically one application. The types of complex geometries that can be formed using these methods are limited.

Means for Solving the Problems

[0004]

[0004] Embodiments of the composite pressure vessels of this disclosure include a 3D printed mandrel rather than utilizing a casting process or a removal process. The mandrel can be 3D printed using an additive manufacturing process such as the vat photopolymerization method, the material or binder jetting method, the material extrusion method, the powder bed fusion method.

[0005]

[0005] In some embodiments, a non-temporary medium or a computer-readable medium stores computer-readable instructions that, when executed by the 3D printer, cause the 3D printer to print a mandrel of a composite pressure vessel, the mandrel having a predetermined size, shape, and internal volume, and including at least one end having an opening to the internal volume of the mandrel. The computer-readable instructions may further cause the 3D printer to print one or more fluid management devices that are integrated into and contained within the mandrel. The computer-readable instructions may be in a slicing file. A digital representation of the mandrel to be 3D printed may be stored and displayed.

[0006]

[0006] The mandrel may be 3D printed as a single unit, or its components may be printed. For example, the first end section, the second end section, and the intermediate section of the mandrel may be printed individually and then assembled. The intermediate section or body of the mandrel may be a single printed part, or two or more printed parts may be joined together. One or more fluid management devices may be printed as part of the first end, the second end, or the intermediate section (or any combination thereof). The first and second ends may be dome-shaped, and the intermediate section may be cylindrical. One or both ends may include a boss that provides an opening to the internal volume. The boss may be 3D printed. Fittings or valves may be connected to the boss or end. Fittings or valves may be 3D printed.

[0007]

[0007] The fluid control device may be a baffle. The baffle may be arranged coaxially with the longitudinal centerline of the mandrel. The baffle may extend radially with respect to the longitudinal centerline of the mandrel. The baffle may include a plurality of through holes.

[0008]

[0008] In some embodiments, the fluid management device is a cylinder positioned coaxially with the longitudinal centerline of the mandrel. The cylinder may include a plurality of through holes. The cylinder may be connected to a boss.

[0009]

[0009] The fluid management device can be a wall that divides the internal volume into at least two chambers. The chambers may be in fluid communication with each other. In other embodiments, the fluid management device may be a channel, such as a cooling channel, but is not limited to this. In other embodiments, the fluid management device is a diaphragm.

[0010]

[0010] Embodiments of the method of the present disclosure for manufacturing a composite pressure vessel include the following steps: a step of 3D printing a mandrel, the mandrel having a predetermined size, shape and internal volume, and the mandrel including at least one end having an opening to the internal volume; a step of smoothing surface defects, filling surface voids, or smoothing surface defects and filling surface voids after the 3D printing step; a step of assembling at least one fitting to the mandrel after the smoothing step or the filling step or the smoothing and filling step; a step of applying an impermeable film to at least one fitting and the mandrel after the assembling step; a step of sealing the impermeable film by applying carbon fiber roving and resin to the mandrel at a pre-programmed angle after the applying step; and a step of curing the composite pressure vessel after the sealing step.

[0011]

[0011] The smoothing and filling processes are performed because there are layer lines on the outer surface of the printed mandrel. The mandrel can be used as is, but these lines may be transferred to the fiber shell, potentially affecting its performance. The smoothing and filling processes are performed using the same material that was used to print the mandrel. These are also additional processes.

[0012]

[0012] In some embodiments, the method includes the step of 3D printing a fluid management device to be integrated into and enclosed by a mandrel. The mandrel may include at least two 3D printed parts that will later be assembled together. The fluid management device may be printed as a component of one or both of the two 3D printed mandrel parts. If the mandrel is soluble, i.e., soluble because a liner-free composite pressure vessel is desired, the method further includes, after the curing step, rinsing the pressure vessel with water to break down or remove the mandrel. [Brief explanation of the drawing]

[0013] [Figure 1] This is a process flow of the parts of the mandrel produced by this disclosure, which are decomposed after the composite packaging material has hardened. [Figure 2] This is a process flow of the parts of the printed mandrel produced by this disclosure that remain inside the tank after manufacturing. [Figure 3] This is one embodiment of a printed mandrel portion (end cap) having an integrated fluid management device (through-hole). During winding, the spokes provide strength to the portion. If printed as soluble, the device can be removed from the final composite pressure vessel. [Figure 4] This is one embodiment of a printed mandrel portion (central section or body) having an integrated slosh baffle (perforated radial structure). The slosh baffle provides strength and, if printed as soluble, can be removed from the final composite pressure vessel. [Figure 5] This is a cutaway view of one embodiment of a finished tank of the present disclosure having a sealed tank / fluid volume inside, manufactured by additive manufacturing. For example, the tank may be 3D printed and then used as a substructure for 3D printing a soluble mandrel. When the mandrel is removed by rinsing, an annular space remains between the tank and the composite fiber shell of the pressure vessel. [Figure 6]This is a partial break section of the inner surface of another embodiment of a printed mandrel. The inner surface may include an isogrid, i.e., a hexagonal or triangular grid structure facing perpendicular to the surface. The isogrid provides strength that helps withstand the load of fiber winding and allows for a thinner printed structure. In this embodiment and other embodiments, the mandrel may be printed as a single piece or as multiple pieces joined together. [Figure 7] Figure 6 is an enlarged view of the isogrid. The printed mandrel may include annular snap-fit ​​arrangements, as shown for assembling the sections of the printed mandrel. Other means for connecting the printed end caps to the body or to the connection sections of the body may include joint arrangements and cone-and-cup arrangements. [Modes for carrying out the invention]

[0014]

[0021] The systems and methods of this disclosure optimize the manufacture of composite pressure vessels and structures, and optimize manufacturing by streamlining the production of tooling and internal structures through the use of additive manufacturing processes such as vat photopolymerization, material or binder injection, material extrusion, and powder bed fusion, in order to improve quality, scalability, expandability, and cost-effectiveness.

[0015]

[0022] The additive manufacturing process may be a vat photopolymerization method in which a mandrel tool is fabricated in a vat containing a liquid photopolymer resin. Infrared (UV) light may be used to cure or solidify the resin as needed, and the build platform is indexed to accept the next layer as each new layer hardens. In another embodiment, the additive manufacturing process is a binder spraying method in which a print head selectively deposits a liquid binder onto a thin layer of metal, sand, ceramic, or composite powder particles to construct the mandrel. This process is repeated layer by layer until the mandrel is printed. In yet another embodiment, the additive manufacturing process may be a material extrusion method in which a continuous filament of a thermoplastic or composite material in the form of a plastic filament is fed through a heated nozzle and then deposited onto a build platform to form the mandrel layer by layer. Alternatively, the additive manufacturing medium may be a powder or pellet bed fusion bonding method, in which a hopper provides the medium material for the mandrel, and each layer of the mandrel is sequentially bonded onto preceding adjacent layers. The mandrel may be fabricated as a single structure or as individual components joined together to form an assembly. Joining can be done by adhesive made from the same material used to print the mandrel, by a welding process (heat and melt), or by annular snap-fit ​​(male and female tabs). The mandrel may also contain a mixture of soluble and insoluble mandrel components, such mixtures are useful for creating integrated features of structures such as segmented chambers, anti-slosh baffles, diaphragms, and other fluid management devices.

[0016]

[0023] The pressure vessels of the present disclosure may be lineless or liner-free pressure vessels, i.e., vessels having no metal or plastic liner inside the innermost composite material layer of the vessel in its final manufactured configuration. That is, the mandrel is washed away or disassembled, and the composite shell formed around the mandrel remains. During intended use, since there is no inner liner, there is no barrier between the gas, liquid, or powder contained in the vessel and anything other than the surface of the shell that faces the innermost side. The mandrel tool can be removed by immersing the vessel in water or other suitable solvents (which may be agitated) or washing it away with water or such solvents.

[0017]

[0024] In other embodiments, non-soluble metal or polymer mandrels may be used. Such mandrels remain with the vessel and form a liner or internal structure. However, by eliminating the need for a metal or plastic gas barrier, the possibility of liner defects is excluded.

[0018]

[0025] The embodiments of the present disclosure can be used for gas storage applications at any pressure range. The vessel may be a Type III, Type IV, or Type V pressure vessel. The vessel may be used to store gas, liquid, or powder. The vessel may include cooling channels, baffles, diaphragms, valves, regulators, or other fluid management devices designed and formed to be integrated into the vessel. The shape of the vessel may be any predetermined shape suitable for storage applications. The shape of the vessel may be spherical or cylindrical, or may be non-spherical or non-cylindrical. The vessel may have the same or substantially similar geometry as an INFINITE COMPOSITES® composite pressure vessel (Tulsa, Oklahoma).

[0019]

[0026] The pressure vessels of the present disclosure may be composite overwrapped pressure vessels that utilize a 3D printed mandrel to serve as its liner and as a permeation barrier or gas barrier. Alternatively, the pressure vessels may be those using a removable mandrel process. The 3D printed mandrel provides the shape of the container but does not continue to be part of the container, leaving only the composite material and resin to serve as strength and permeation barrier.

[0020]

[0027] The containers of the present disclosure can be used in applications such as, but not limited to, lightweight mobile CNG fueling, launch system components, propulsion system components, nitrogen accumulator vessels, adsorbed natural gas storage vessels that require non-cylindrical composite pressure vessels, high-pressure flow test vessels, satellite propellant pressure vessels, cryogenic gas storage vessels, satellite propulsion pressure vessels, medical oxygen containers, and pressurant containers.

[0021]

[0028] Embodiments of the present disclosure include an additive manufacturing system for fabricating composite pressure vessels and structures using a combination of a decomposable or permanent additive manufacturing mandrel and a composite overwrap shell. The containers can be fabricated using filament winding, automated fiber placement, continuous fiber printing, or a combination thereof. The containers may also be fabricated by a multi-axis robotic printer / filament winding arm oriented around a rotating substrate. Using the methods of the present disclosure, high-performance composite pressure vessels and structures can be fabricated with enhanced performance, manufacturability, and scalability compared to traditional methods.

[0022]

[0029] In some embodiments, the mandrel is 3D printed using a soluble material such as polyvinyl alcohol ("PVA") and then encased with a fibrous reinforcement impregnated with a polymer resin to create a composite pressure vessel. The resin-encased vessel is then cured. Once fully cured, water is used to decompose the mandrel. See Figure 1. In other embodiments, a non-soluble metal or polymer mandrel may be printed, and the mandrel remains trapped within the shell after the composite shell has cured. See Figure 2.

[0023]

[0030] Whether the mandrel is soluble or remains a permanent component of the vessel, the composite pressure vessels of this disclosure can be manufactured with optimal performance characteristics and significantly reduced manufacturing time compared to conventional methods. 3D printing processes can be used to manufacture composite pressure vessels with complex geometric and integral features, such as cooling channels, baffles, diaphragms, valves, regulators, or other fluid management devices.

[0024]

[0031] As an example, a water-soluble tool to be 3D printed may use PVA converted into a 3D printable filament. Any commercially available fused deposition modeling (FDM) 3D printer has the capability to print PVA filaments. In 3D printing, PVA is typically used as a support material for dual extruder printers. Here, the purpose of PVA printing is to assist in the fabrication of composite pressure vessels. With a low glass transition temperature, almost all PVA filaments are printed at extrusion temperatures of 200-220°C. The bed or substrate temperature is 50-60°C. This allows for proper bed adhesion and viscosity of the polymer. PVA can undergo thermal decomposition if exposed to high temperatures for extended periods.

[0025]

[0032] When printing a mandrel, a CAD file is generated during the initial design phase. This CAD file is then loaded into a slicing software application that converts it into a language called ".gcode," which is used to control the CNC machine. This slicer file determines most of the parameters that determine the manufacturing process and the quality of the product.

[0026]

[0033] Embodiments of the composite pressure vessels of this disclosure include a 3D printed mandrel and a shell wrapped around the mandrel, wherein the mandrel is made of a soluble printed material, and the shell comprises at least two layers of composite material, the mandrel being decomposed after the composite material of the shell has hardened, and as a result, the storage space of the composite vessel is defined by the innermost surface of the shell. The soluble printed material may be PVA or an equivalent.

[0027]

[0034] Another embodiment of the composite pressure vessel of the present disclosure comprises a 3D printed mandrel and a shell wrapped around the mandrel, wherein the mandrel is made of an insoluble material and the shell comprises at least two layers of the composite material described above. The mandrel further comprises at least one 3D printed channel, baffle, diaphragm, valve, regulator, or sealed volume, such channel, baffle, diaphragm, valve, regulator, or sealed volume may be printed as part of the mandrel. See Figures 3–5. The storage capacity of the composite vessel is defined by the physical size of the mandrel. [Aspect 1] A computer-readable medium storing computer-readable instructions, wherein, when executed by a 3D printer, the instructions cause the 3D printer to print a mandrel (10) of a composite pressure vessel, the mandrel having a predetermined size, shape, and internal volume (10c), and including at least one end (13) having an opening (17) to the internal volume. [Aspect 2] A computer-readable instruction according to Embodiment 1, An instruction further comprising causing the 3D printer to print a fluid management device which, when executed by the 3D printer, is to be integrated into and enclosed by the mandrel. [Aspect 3] In the fluid management device described in Embodiment 2, The fluid management device is a baffle (31). [Aspect 4] In the baffle described in Embodiment 3, The baffle is positioned coaxially with the longitudinal center line (29) of the mandrel. [Aspect 5] In the baffle described in Embodiment 4, The baffle is a baffle that extends radially with respect to the longitudinal centerline of the mandrel. [Aspect 6] In the baffle described in Embodiment 3, The baffle includes a plurality of through holes (27). [Aspect 7] In the fluid management device described in Embodiment 2, The fluid management device is a cylinder (25) positioned coaxially with the longitudinal centerline of the mandrel, and the cylinder includes a plurality of through holes (27). [Aspect 8] In the fluid management device described in Embodiment 2, The fluid management device divides the internal volume into at least two chambers (41). [Aspect 9] In at least two chambers described in embodiment 8, A chamber in which at least two chambers are in fluid communication with one another. [Aspect 10] In the fluid management device described in Embodiment 2, The fluid management device is a channel (49). [Aspect 11] In the fluid management device described in Embodiment 2, The aforementioned fluid management device is a diaphragm. [Aspect 12] A computer-readable instruction according to Embodiment 1, A computer-readable instruction further comprising, when executed by the 3D printer, causing the 3D printer to print a valve that is partially enclosed by the opening. [Aspect 13] In the mandrel described in Embodiment 1, The mandrel further includes a boss (15), the opening of which is defined by the boss. [Aspect 14] In the computer-readable instruction described in Embodiment 1, The aforementioned computer-readable instructions are computer-readable instructions located within the slicing file. [Aspect 15] A mandrel according to Embodiment 1, A mandrel further comprising a first end section (13a), a second end section (13b), and an intermediate section (11). [Aspect 16] In the mandrel described in Embodiment 16, A mandrel in which the first and second end sections are dome-shaped ends, and the intermediate section is cylindrical. [Aspect 17] A mandrel according to Embodiment 1, A mandrel further comprising an inner surface (10c) of the mandrel containing an isogrid (43). [Aspect 18] A digital representation of a mandrel as described in any one of the embodiments 1 to 17. [Aspect 19] A method for manufacturing a composite pressure vessel, the method comprising the following steps, namely, A process for 3D printing a mandrel, wherein the mandrel has a predetermined size, shape, and internal volume, and the mandrel includes at least one end having an opening to the internal volume, After the 3D printing process, the process includes a step of smoothing surface defects, a step of filling surface voids, or a step of smoothing surface defects and filling surface voids. A step of assembling at least one joint to the mandrel after the smoothing step or the filling step or the smoothing and filling step, The assembly step is followed by the step of applying an opaque film to at least one joint and the mandrel, The process of sealing the opaque film by applying carbon fiber roving and resin to the mandrel at a pre-programmed angle after the above application process, After the sealing step, the process of hardening the composite pressure vessel is performed. A method that includes [a certain feature]. [Aspect 20] In the method described in aspect 19, A method wherein the mandrel comprises at least two 3D printed parts, and the assembly step includes the at least two 3D printed parts. [Aspect 21] In the method described in Embodiment 18, The mandrel is soluble, and the method further comprises, after the curing step, a step of rinsing the pressure vessel with water to decompose the mandrel. [Explanation of Symbols]

[0028] 10 3D printed mandrels 10a Outer surface of the mandrel 10b Internal volume 10C Mandrel Inner Surface 11. Central section or main body 11a First intermediate section 11b Second intermediate section 13 End section or end cap 13a First end section or first section or first end cap 13b Second end cap 15 Fittings or bosses 17 Passageway or opening 19 Opaque film 21 Carbon fiber roving and resin 21a Composite fiber shell for pressure vessel 23 spokes 25 Cylindrical Fluid Management Devices 27 Through hole 29. Central longitudinal axis of mandrel (and pressure vessel) 31 Baffles 33 Ribs 35 Internal Tank 37 Circular Space 41 Chamber 43 Isogrid 47 Snap-Fit 49 channels 50 Final pressure vessel

Claims

1. A method for manufacturing a composite pressure vessel, wherein the composite pressure vessel is a type V pressure vessel, and the method comprises the following steps, namely, A step of 3D printing a soluble mandrel, wherein the soluble mandrel has a predetermined size, shape, and internal volume, and the soluble mandrel includes at least one end having an opening to the internal volume, After the 3D printing process, the process includes a step of smoothing surface defects, a step of filling surface voids, or a step of smoothing surface defects and filling surface voids. A step of assembling at least one fitting to the soluble mandrel after the smoothing step or the filling step or the smoothing and filling step, The assembly step is followed by the step of applying an impermeable film to the at least one joint and the soluble mandrel, The process of sealing the impermeable film by applying carbon fiber roving and resin to the soluble mandrel at a pre-programmed angle, after the above application step, After the sealing step, the process of hardening the composite pressure vessel is performed. A method comprising the step of washing the composite pressure vessel with water after the curing step in order to decompose the soluble mandrel.

2. In the method according to claim 1, The 3D printing step is a 3D printing step performed by a material extrusion molding method, in this method.

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