Provisional Application Serial No. 62/915,144, filed on October 15, 2019, entitled “Hybrid Foam Mandrel (HFM) Trapped Tooling Technique for Conformal Composite Tanks and Tubes,” the entire contents of each of which are hereby incorporated by this reference.

FIELD OF THE DISCLOSURE

[0002] The field of this disclosure relates to a hybrid mandrel that can be used for filament winding a composite pressure vessel, tank, or tube. The hybrid mandrel is formed of at least two components, an inner component and an outer component. The inner component may be a foam material that can be extracted from the formed tank. This portion is generally not reusable and is removed via a chemical solvent or via raised temperature, causing the component to shrink or otherwise reduce to a size that allows it to be removed from an opening of the tank. The outer component is generally formed of a different material and may either be reusable or non-reusable. If reusable, the outer component may be formed in a jigsaw configuration that allows it to be disassembled and removed through the tank opening.

BACKGROUND

[0003] Commonly, fluid tanks or pressure tanks are manufactured via filament winding. Filament winding is a fabrication technique that can be used for manufacturing open structures, such as cylinders, or closed end structures, such as pressure vessels or tanks. The process involves winding filaments under tension over a rotating mandrel. The mandrel rotates around a spindle or shaft that has an axis. A delivery eye on a carriage traverses horizontally (usually in line with the axis of the rotating mandrel), and lays down fibers onto the mandrel in a desired pattern or angle. Common filaments used are glass or carbon, impregnated in a bath with resin as they are wound onto the mandrel. Once the mandrel has been wound and is completely covered to the desired thickness, the resin is allowed to cure. Depending upon the resin system that is used and its cure characteristics, the rotating mandrel may be placed in an oven or under radiant heaters until the wound material is cured.

[0004] Once the resin has cured, the mandrel may be removed or extracted, leaving the hollow final product. Removal of the mandrel can create certain challenges. For example, during manufacturing of aircraft water and waste composite tanks, the industry’s current trapped tooling design uses a solid mandrel that requires a complete washout procedure to remove the mandrel from the cured composite tank.

[0005] For example, the mandrel may be formed via a silica/sand material with binders, with the mandrel cured to shape. Once the tank or vessel has been formed, the internal mandrel is dissolved and washed out. This means that the mandrel is not re-usable. The washable mandrel can be made of ceramic tooling material that is heavy in weight and has high a material cost, rendering it impractical for large parts and high volume production for conformal or irregular composite tanks and tubes.

[0006] Presently known trapped tooling mandrel techniques for conformal tank or irregular shape composite parts typically utilize a solid ceramic material applicable for small parts and low volume production or prototype. Other options are to use collapsible metal tooling for low production. Other options are to use a 3D printed mandrel. If the tank to be formed is symmetrical, an inflatable bladder may be used. However, the use of inflatable bladders is limited only to symmetrically shaped tanks inflatable bladders. Inflatable bladders cannot be used in an autoclave for the curing process without an exterior clamshell to maintain the shape of the conformal, non-symmetrical composite tank and tube. Other industry techniques use blow molded or rotomolded thermoplastic mandrels either as a stay- in tank/tube liner or a one-time use. Most, if not all, of these options are more expensive than the disclosed hybrid foam mandrel.

[0007] Accordingly, improvements to mandrels that allow the mandrel to be removable are desirable. It is also desirable to lower costs and mandrel weight. The disclosed hybrid mandrel design helps solve some of these challenges.

SUMMARY

[0008] Accordingly, the present inventors have designed a hybrid mandrel that may be used in manufacturing vehicle water and waste composite tanks. The hybrid mandrel is provided with two components, an inner component and an outer component. The inner component is generally a foam that can be reduced in size and extracted from the tank opening. The outer component is generally formed of a different material and may either be reusable or non-reusable. If reusable, the outer component may be formed in a jigsaw configuration that allows it to be disassembled after formation and removed through the tank opening. [0009] The terms “invention,” “the invention,” “this invention” “the present invention,” “disclosure,” “the disclosure,” and “the present disclosure,” used in this patent are intended to refer broadly to all of the subject matter of this patent and the patent claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the patent claims below. Embodiments of the invention covered by this patent are defined by the claims below, not this summary. This summary is a high-level overview of various aspects of the invention and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this patent, any or all drawings and each claim.

[0010] According to certain embodiments of this disclosure, there may be provided a hybrid mandrel for use with filament winding a tank or tube, comprising: an inner component formed of a one-time use material that is dissolvable or shrinkable; and an outer component positioned around the inner component. In the preceding of any subsequent example, the tank or tube is formed on the hybrid mandrel, and the inner component and the outer components are removed from an opening in the tank or tube. In any of the preceding of any subsequent examples, the inner component may be a dissolvable or shrinkable material. In any of the preceding of any subsequent examples, the inner component may be expanded polystyrene (EPS) foam. In any of the preceding of any subsequent examples, the outer component is re-usable. In any of the preceding of any subsequent examples, the outer component may be a rigid urethane foam. In any of the preceding of any subsequent examples, the outer component may be cork. In any of the preceding of any subsequent examples, the outer component is not re-usable, but is removed after removal of the inner component. In any of the preceding of any subsequent examples, wherein the outer component comprises a plurality of pieces, wherein at least one piece comprises one or more handles for removal. The outer component plurality of pieces may be secured to one another via a plurality of magnets, a locking system, or any combination thereof.

[0011] In a further example, there is provided a method for using a hybrid mandrel for use with filament winding a tank or tube, wherein the hybrid mandrel comprises an inner component and an outer component, the method comprising: filament winding a tank or tube on the hybrid mandrel; removing the inner component from the tank or tube via chemical solvent or via raised temperature such that the inner component shrinks to a size that allows a user to remove the inner component from an opening in the tank or tube; and removing the outer component. Removing the outer component may include removing the outer component piece by piece.

BRIEF DESCRIPTION OF THE DRAWINGS [0012] Figure 1 is a side plan view of a hybrid mandrel.

[0013] Figure 2 is a side plan cross-sectional view of the hybrid mandrel of Figure 1.

[0014] Figure 3 is a side perspective cross-sectional view of a hybrid mandrel with a plurality of jigsawed pieces forming the outer component.

[0015] Figure 4 is a front view of one embodiment of a locking system for a jigsawed outer component.

[0016] Figure 5 is a side perspective view of the locking system of Figure 4.

[0017] Figure 6 is a side perspective view of a hybrid mandrel with at least one of the outer component pieces comprising a handle for ease of removal.

[0018] Figure 7 is a schematic view illustrating the process of filament winding to create a pressure vessel using a mandrel.

DETAILED DESCRIPTION

[0019] The described embodiments provide a hybrid mandrel 10. This new trapped tooling mandrel technique utilizes common, low cost, lightweight materials. The hybrid mandrel is provided in at least two components, an inner component 12 that forms a core of the mandrel and an outer component 14 that forms an external shell of the mandrel. As shown by Figure 1, the inner component can also support a shaft 16, which is used to rotate the mandrel 10 during filament winding.

[0020] The inner component 12 may be a one-time use material. After the tank has been formed, the inner component 12 is removed from the tank. One specific example of a material that may be used for the inner component 12 is an expandable polystyrene (EPS) foam material. (Other examples of lightweight foam-like materials that can be removed from the tank are provided in a material list below.) One benefit of using foam, such as an EPS foam, as the inner component 12 is that it may be extracted from the formed mandrel. One extraction method is via use of a chemical solvent. The solvent applied may be acetone, citric acid, D-limonene dissolution, or any solvent that can dissolve or otherwise cause the EPS foam to shrink to a size that allows it to be removed from the tank opening. Alternatively, the inner component 12 may be removed via application of heat at a certain temperature. This may be referred to as thermal deformation. For example, EPS foam can be caused to shrink at temperatures of about 70°C or higher. EPS has a wide density range that corresponds to compressive strength needed for any cure pressure requirements.

[0021] Because the mandrel 10 is intended to be used for filament winding and must support a certain amount of pressure (due to winding) and heat (due to autoclaving or finishing of the tank), an outer component 14 of the mandrel 10 can be provided in order to help protect the integrity of the inner component 12. For example, the presence of the inner component 12 is useful to provide a support for the shaft 16, which is necessary for the winding process. Once the winding process is complete, the inner component 12 may be removed. (However, it is also possible for the inner component 12 to remain in place during finishing of the tank.) The outer component 14 is generally intended to remain in place during finishing (e.g., autoclaving, curing, etc.) of the tank in order to provide structural support. Because of the necessity of using heat during the finishing process and the application of pressure during the winding process, the outer component 14 should generally be of a more rigid and heat-resistant material.

[0022] In one example, the outer component 14 may be a high density urethane rigid foam or a natural or synthetic cork material. (Other examples of alternative materials that can be used to form the outer component are provided in a material list below.) These materials can provide an outer component 14 that forms an external shell and that functions as a heat shield to protect the inner component/EPS foam. Urethane rigid foam and cork have been found particularly useful. They have a low specific heat capacity, high heat resistance, and high compressive strength. The outer component 14 can accordingly be designed to the appropriate grade and thickness and material to delay the heat transfer during autoclave or oven cure to the EPS foam core (inner component 12) and to support and sustain the shape of the composite part during cure cycle.

[0023] One way to identify the appropriate grade and thickness of the outer component

14 is to use Fourier’s Law of Heat Conduction q=-kA dt/dx, to delay the heat transfer during autoclave or oven cure to the EPS Foam core (inner component 12) in order to support and sustain the shape of the composite part during cure cycle. An EPS foam core alone would not be compatible for a high temperature composite cure above 75°C (167°F). The resulting hybrid mandrel 10 trapped tooling technique thus does not need an additional clamshell or outer mold tool to control the shape of the part, as laminate pressure is uniformly applied by the autoclave onto the mandrel surface.

[0024] This outer component 14 material can be designed/machined or molded into a plurality of jigsaw pieces 18 that allow each piece 18 to be extracted from the composite tank 20 after the inner component 12 has been removed. One example configuration is illustrated by Figure 3. In this example, each piece 18 has a length “L” dimension that is the desired length of the interior of the tank. Each piece 18 has a width “W” dimension that is less than the width dimension of the resulting opening 22 formed in the tank 20. In the specific example shown, the width W of the piece 18 is about 1/6 of the interior diameter of the tank, such that the outer component 14 can be formed into six pieces 18 for individual removal.

[0025] Removal of the pieces 18 can be assisted by providing one or more finger holds on an interior-facing surface 24 of one or more pieces 18. A user can reach into the tank through opening 22 and use the finger hold(s) as a support to pull the piece 18 away from its neighboring pieces. Neighboring pieces may be secured to one another in any appropriate manner. One non limiting example of how pieces 18 may be connected to one another may be via magnetic force. This can allow a user to apply enough force to one of the pieces in order to overcome the magnetic force of the neighboring piece 18 and allow one the pieces to disengage from the remainder of the body of the outer component 14.

[0026] Additionally or alternatively, the pieces 18 of the outer component 14 may be secured to one another via a locking system 28. In one example illustrated by Figures 4 and 5, the locking system 28 may be a tongue and groove or dovetail system. Figure 5 illustrates cooperation between a tongue 30 and a groove 32. As shown, at least one of the pieces has a protruding tongue 30 that is received by a corresponding indented groove 32. Although these examples are shown, it should be understood that any type of sliding cooperation between the pieces as possible. For example, sliding cooperation may be achieved via a T and slot configuration, a J/slot configuration, a track configuration, or any other appropriate sliding cooperation.

[0027] Referring back to Figure 4, one of the pieces may be a key piece 40. The key piece 40 is provided without a locking system 28 component on its sides. This allows the key piece 40 to be removed first. Because it does not have a locking system 28, the key piece 40 may be held in place via friction, so it can be pulled out of place/separated from the adjacent pieces 18 in any direction. Once key piece 40 has been removed through the opening 22, the adjacent pieces 18 may be slidably disconnected and similarly removed.

[0028] Another way to assist removal is to provide a handle 26 on an interior-facing surface 24 of one or more of the pieces 18. One example is illustrated by Figure 6. The handle 26 may be hinged such that it can fold into an indentation on the surface 24 and reached once the inner component 12 has been removed. In one example, the handle 26 may be provided on the key piece 40. This allows the key piece to be pulled downwardly and removed.

[0029] In order to ease removal of the outer component 14, each piece 18 can be wrapped or coated or otherwise associated with a form of release paper, release sheet, or release coating (such as polytetrafluoroethylene PTFE, also referred to as Teflon™). In a specific example, each piece 18 can be wrapped with PTFE release tape or painted with a layer of PTFE in order to protect the piece 18 from adjacent pieces or the tank opening during handling and operation. This may help prolong the lifetime of the mandrel 10. In a specific example, PTFE coating can help achieve 20-100 uses of the outer component 14. Replacement or repair can be accomplished per piece, without the need to rebuild the entire component 14. Urethane rigid foam can also be fabricated using liquid foam grade to fill-in the exterior heat shield of the mandrel.

[0030] In some examples, the outer component 14 can be non-reusable, such that once the inner component 12 has been removed, the outer component 14 can be chipped or broken away in pieces using tools or manually. Use of cork material can be successful as a non-reusable outer component 14 due to the fact that it is inexpensive, and can be easily broken down. Additionally or alternatively, a cork outer component 14 may be extracted manually or with the application of low household vacuum to collapse the remaining interior mandrel and remove it from the tank opening 22. It is also possible to remove a cork outer component 14 via chemical degradation or breakdown. This method takes advantage of cork’s low fracture toughness. The environmental impact of using cork can be positive; cork is natural, organic, recyclable, renewable, and sustainable, lending to an eco-design principle. Cork can also withstand high heat, such that it can stay in place during finishing of the tank.

[0031] If a cork outer component 14 is used and if it is desirable to it to be reused, there may be provided a chemical application, such as a coating or skin applied to (or soaked into) the cork, that allows it to be hardened and/or more rigid. This can prevent the cork outer component 14 from being flaked away during removal. Without such a treatment, cork is generally porous and may break relatively easily. [0032] Other materials may be used to form the inner component 12 and outer component 14 of the mandrel 10. It is generally desirable that the inner component 12 be made of a lightweight material that can be dissolved, shrunk, or otherwise reduced in size for removal. With those parameters in mind, additional exemplary potential materials for the inner component 12 include but are not limited to the EPS foam described above, polyurethane foam, carbon foam, polyetherimide foam, polyvinyl chloride foam, polymethyl methacrylate foam, styrene acrylonitrile foam, polystyrene foam, or any combination thereof.

[0033] It is generally desirable that the outer component 14 be made of a material that can withstand heat required to finish the completed tank and winding pressure. With those parameters in mind, additional exemplary potential materials for the outer component 14 include but are not limited to the rigid urethane or cork described above, thermoplastics, thermosets, polymer foams, fiberglass laminates, or any combination thereof. Exemplary plastic materials include but are not limited to polyetherimide, polysulfone, polybutylene terephthalate, polyimide, polybenzimidazole, polyamide imide, polyolefin, polyphenylene sulfide, polyether ether ketone, carbon foam, reticulated vitreous carbon, polyetherimide foam, polyvinyl chloride foam, polymethyl methacrylate foam, styrene acrylonitrile foam, or any combination thereof. Other materials that may be used include but are not limited to Airloy X103, Pyrogel HPS, a shape memory polymer, ceramics, or any combination thereof.

[0034] In order to manufacture the hybrid mandrel 10, the inner component 12 may be formed as a two-piece foam core with appropriately sized shaft-receiving indentations running an interior length of each piece; the indentations are generally shaped and configured to receive the shaft 16. The two pieces may be bonded to one another (and to the shaft) such that they enclose and support the shaft 16. In an alternate manufacturing method, it is possible to machine tubing with an inner diameter (ID) that matches outer diameter (OD) of shaft and bond the tubing through the center of the core. This results in a continuous, one-piece core, with the tubing containing the shaft 16 running therethrough. The shaft 16 may be formed integrally with the inner component 12, such that the EPS foam core is manufactured around the shaft 16.

[0035] Once the core/inner component 12 and shaft 16 are manufactured and secured, a rigid outer component 14 can be positioned over/around the inner component 12. For example, a foam core/inner component 12 may be molded. Then, a rigid outer component 14 can be bonded to the inner component 12 to form the hybrid mandrel. If the outer component 14 is provided in more than one piece, the pieces may be secured to another via magnetic force during assembly. For example, a magnet with one pole may be positioned on a first piece, and a magnetic with an opposite pole may be positioned in a corresponding location on a second piece. Additionally or alternatively, the pieces may be provided with a locking system 28. The locking system 28 may be used to assemble and secure the outer component 14 around the inner component 12.

[0036] Figure 7 shows use of a finished hybrid mandrel 10 on a filament winding machine. Filaments are wound around the mandrel 10 to form a finished tank. The hybrid mandrel may be used for filament winding or hand lay-up of conformal composite tanks and tubes. The tank or tubs is then finished (via heat finishing, curing, or any other appropriate finished methods to be used). Then, the hybrid mandrel is extracted from the formed tank 20 after cure.

[0037] The subject matter of certain embodiments of this disclosure is described with specificity to meet statutory requirements, but this description is not necessarily intended to limit the scope of the claims. The claimed subject matter may be embodied in other ways, may include different elements or steps, and may be used in conjunction with other existing or future technologies. This description should not be interpreted as implying any particular order or arrangement among or between various steps or elements except when the order of individual steps or arrangement of elements is explicitly described.

[0038] It should be understood that different arrangements of the components depicted in the drawings or described above, as well as components and steps not shown or described are possible. Similarly, some features and sub-combinations are useful and may be employed without reference to other features and sub-combinations. Embodiments of the invention have been described for illustrative and not restrictive purposes, and alternative embodiments will become apparent to readers of this patent. Accordingly, the present invention is not limited to the embodiments described above or depicted in the drawings, and various embodiments and modifications may be made without departing from the scope of the claims below.