WO2007149547A2

WO2007149547A2 - Integrated composite structure

Info

Publication number: WO2007149547A2
Application number: PCT/US2007/014519
Authority: WO
Inventors: Larry Carver
Original assignee: Nova Tech Engineering Inc
Current assignee: Nova Tech Engineering Inc
Priority date: 2006-06-23
Filing date: 2007-06-22
Publication date: 2007-12-27
Anticipated expiration: 2008-12-23
Also published as: WO2007149547A3

Abstract

Composite structures for producing articles include a core encapsulated in a somewhat rigid material. Both the core and encapsulating material can comprise a temperature resistant material to limit or substantially prevent degradation of the composite material when exposed to relatively high temperatures, such as those typically experienced during autoclave curing processes. The rigid material can be a wear resistance material that forms durable external surfaces. The core is made, in whole or in part, of carbon foam and the encapsulating material can be made, in whole or in part, of carbon fibers in a matrix. The composite structures can form a mandrel assembly for fabricating at least a portion of a fuselage of an aircraft.

Description

INTEGRATED COMPOSITE STRUCTURE

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U. S. C. § 119(e) of U.S. Provisional Patent Application No. 60/816,289 filed June 23, 2006, which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Field

The present invention relates generally to composite structures.

Description of the Related Art Metal tooling is often used to fabricate a wide range of structures.

Metal mandrels are one type of tooling used to form structures made of composite materials. Because a metal mandrel may have a relatively high rotational inertia, it may be difficult to rapidly adjust the rotational speed of the mandrel, especially if the mandrel has relatively large radial dimensions. Additionally, it may be difficult to re-engineer the mandrel while maintaining tight tolerances often required for structural components of aircraft, such as the fuselage of an airplane.

BRIEF SUMMARY OF THE INVENTION

The embodiments disclosed herein generally relate to integrated composite structures that have various uses, such as forming ,at least a portion of a fabrication system (e.g., a mandrel, mold, and the like) or a product itself. The composite structures can be designed and optimized for desired physical properties, structural properties, thermal properties, and/or electrical properties. The composite structures in some embodiments comprise a core encapsulated in a somewhat rigid material. The core can comprise structural foam that enhances the overall structural properties of the composite structure. Both the core and encapsulating material can comprise a temperature resistant material (e.g., carbon) to limit or substantially prevent degradation of the composite material when exposed to relatively high temperatures, such as those typically experienced during autoclave curing processes. The rigid material can be a wear resistance material that forms durable external surfaces. In some embodiments, the core is made, in whole or in part, of carbon foam and the encapsulating material can be made, in whole or in part, of carbon fibers in a matrix.

The composite structures can form master source tooling, bond jig tooling, fixture devices (e.g., fixture devices used during a curing process), or other fabrication systems/components that may require dimensional stability. In some variations, the composite structures can form at least a portion of a male tool and/or female tool (e.g., a bond jig, cure tool, male/female mold systems, and the like). As noted above, the composite structures can have durable external surfaces for relatively high damage resistance. In some embodiments, the materials forming the composite structures have high resistance to environmental degradation, thereby improving the useful life of the structure, even in extreme operating conditions. If needed, the composite structures can provide dimensional stability for producing products with low tolerances. For example, the tolerances can be equal to or less than about +/- 0.01 inch.

The composite structures can be well suited for rapid thermal cyclic loading (e.g., fast heat up and cool down) to reduce fabrication times and costs. Mandrels formed from the composite structures have a small weight-to-strength ratio resulting in reduced rotational inertia for improved rotational control while also reducing wear on drive assemblies. The reduced rotational inertia also reduces winding time, which reduces the overall lay-up time. During the fabrication process, the mandrel can maintain tight tolerances by avoiding or reducing sagging and other problems associated with heavy mandrels.

Additionally, the composite structures can be incorporated into different articles, such as transportation vehicles (e.g., automobiles, aircraft, airplanes, watercraft, boats, etc.) or other end products. Thus, the composite structures can be used as fabrication tools or incorporated into various types of products. In some embodiments, a structure comprises an upper layer, a lower layer, and an intermediate layer. The upper layer comprises a first high density material. The lower layer comprises a second high density material. The intermediate layer is interposed between the upper and lower layers. The intermediate layer comprises a low density material (e.g., foam). In some variations, the intermediate layer is encapsulated by the upper and lower layers.

In some other embodiments, a mandrel comprises a generally tubular body. The body comprises a plurality of longitudinally-extending arcuate panels. Each panel comprises a foam core sandwiched between an inner layer and an outer layer. The inner and outer layers each comprise at least one laminate.

In spme embodiments, a structure comprises a first layer comprising a first high density material, a second layer comprising a second high density material, and a core encapsulated by the first and second layers. The core comprises a low density foam material. In some embodiments, the core comprises mostly foam (e.g., a low density foam material). In some variations, the first and second high density materials comprise fibers, such as carbon fibers, in a matrix.

In some embodiments, a mandrel assembly for fabricating at least a portion of a fuselage of an aircraft is provided. The mandrel assembly comprises a fuselage molding main body. The main body comprises an outer layer, inner layer, and intermediate layer. The outer layer is formed mostly of a first high density material. The first high density material has a first average density. The inner layer is formed mostly of a second high density material. The second high density material has a second average density. The intermediate layer is interposed between the outer layer and the inner layer. The outer layer defines a fuselage molding surface. The intermediate layer includes a foam material having a third average density that is less than at least one of the first average density and the second average density. In some embodiments, the first average density and the second average density are equal to each other. In some embodiments, the first average density and the second average density are different than each other. m other embodiments, a mandrel assembly for forming a component of an aircraft is provided. The mandrel assembly is coupleable to a mandrel holder for retaining the mandrel. The mandrel assembly comprises a tubular body having a plurality of separable, longitudinally-extending panels adjacent to one another. At least one of the panels comprises a foam core sandwiched between an inner layer and an outer layer. At least one of the inner layer and the outer layer includes a non-foam material. The longitudinally-extending panels, in some embodiments, are configured to be separated from one another when the mandrel assembly is decoupled from a mandrel holder. In some embodiments, a method of fabricating at least a portion of a molding mandrel used to mold tubular structures is provided. The method comprises forming a panel having a plurality of separate blocks integrated together. The panel comprises a low density material. The panel is processed to form a convex first surface and an opposing second surface. The convex first surface and the second surface define a thickness of the panel and extend between opposing lateral sides of the panel. A first layer and a second layer are applied to the convex first surface and second surface, respectively. At least one of the first layer and the second layer has an average density greater than an average density of the low density material. The first layer defines at least a portion of an outer molding surface of the molding mandrel.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Figure 1A is a perspective view of a fabrication system having a mandrel system and a pair of opposing holders, according to one illustrated embodiment. Figure 1B is a perspective view of an outer mold for surrounding a mandrel main body of the mandrel system of Figure 1 A.

Figure 2 is an axial cross-sectional view of the mandrel system of

Figure 1A.

Figure 3 is a perspective view of an elongate panel of the mandrel system of Figure 1 A, according to one illustrated embodiment. Figure 4 is an enlarged isometric view of one end of the elongate panel of Figure 3.

Figure 5 is an enlarged isometric cross-sectional view of the elongate panel of Figure 3. Figure 6 is an enlarged isometric cross-sectional view of one side of the elongate panel of Figure 3.

Figure 7 is an isometric view of a channel of an elongate panel, according to one illustrated embodiment.

Figure 8 is a perspective view of the elongate panel of Figure 3. Figure 9 is an isometric view of a series of blocks coupled together, according to one illustrated embodiment.

Figure 10 is an isometric view of the series of blocks of Figure 9 after performing a material removal process to remove unwanted material.

Figure 11 A is an elevational view of a core for forming an elongate panel, according to one illustrated embodiment.

Figure 11B is an elevational view of a pair of flanges coupled to the core of Figure 11A.

Figure 11 C is an elevational view of an upper layer and a lower layer disposed on the core of Figure 11 B. Figure 11 D is an elevational view of a curing set-up for thermally setting the upper and lower layers of Figure 11 C.

Figure 12A is a schematic cross-section of a portion of an elongate panel for forming a mandrel, wherein the portion has a channel, according to one illustrated embodiment. Figure 12B is a schematic cross-section of the portion of the elongate panel of Figure 12A after the channel has been removed, by forming a trench.

Figure 12C is a schematic cross-section of the portion of the elongate panel of Figure 12A, wherein the trench is filled with material.

Figure 12D is a schematic cross-section of the portion of the elongate panel of Figure 12C after applying a layer of material across the filled trench. Figure 12E is a schematic cross-section of the portion of the elongate panel after the applied layer of Figure 12D has been machined down.

Figure 13A is a schematic cross-section of a portion of an elongate panel in which forming a channel is desired. Figure 13B is a schematic cross-section of a portion of the elongate panel, illustrating a trench with sloped sidewalls.

Figure 13C of the elongate illustrates a layer on the trench of Figure 13B.

Figure 13D illustrates the applied layer of Figure 13C after a trimming process.

Figure 14A is a schematic cross-section of a portion of an elongate panel with a preformed trench.

Figure 14B is a schematic cross-section of the portion of the elongate panel of Figure 14A with an insert disposed in the trench. Figure 14C is a schematic cross-section of the portion of the elongate panel of Figure 14B after a layer is applied over the insert.

Figure 15 is a schematic cross-section of an insert embedded in an upper layer of a multilayer composite structure.

Figure 16 is a cross-sectional view of an elongate panel with a coupling system.

Figure 17 is a side elevational view of a mandrel system, according to one illustrated embodiment

Figure 18 is a perspective view of one end of the mandrel system of Figure 17. Figure 19 is an enlarged perspective view of one end of the mandrel system of Figure 17.

Figure 20 is a perspective view of one of the elongate panels of the mandrel system of Figure 17.

Figure 21 is a perspective view of an elongate panel having a pair of end fittings, according to one illustrated embodiment. Figure 22 is another perspective view of the elongate panel of Figure 21.

Figure 23 is an enlarged perspective view of a coupling arrangement of the elongate panel of Figure 21. Figure 24 is a perspective view of the elongate panel, wherein the end fittings have been removed.

Figures 25-28 illustrate one method for using a composite structure to form a part of an aircraft.

DETAILED DESCRIPTION OF THE INVENTION Figure 1 shows a fabrication system 90 including a mandrel system

100 rotatably supported by a pair of mandrel holders 110, 112. Generally, the mandrel system 100 can be used to lay-up and cure various types of materials, such as pre-impregnated composite sheets. In the illustrated embodiment, the mandrel holders 110, 112 are positioned at opposing ends of the mandrel system 100. The mandrel system 100 thus extends between the mandrel holders 110, 112.

A lay-up process can involve winding material(s) onto the mandrel system 100. During the lay-up process, the mandrel holders 110, 112 cooperate to rotate the mandrel system 100 about an axis of rotation 125. The axis of rotation 125 can be substantially collinear with a longitudinal axis 130 of the mandrel system 100. One or more pre-impregnated composite sheets can be wound onto the rotating mandrel system 100. After applying the sheets to the mandrel system 100, the laid-up sheets and mandrel system 100 can be subjected to a curing process to set the impregnated sheets. A female mold can be disposed over the laid-up material during the curing process. Figure 1 B shows a female mold system 135 having mold halves 137, 139 that can receive and surround the laid-up material and mandrel system 100. Once the mandrel system 100 is encapsulated by the mold system 135, heat and pressure can be applied until the wound material has been sufficiently processed. With reference again to Figure 1A, each of the mandrel holders 110,

112 can have at least one drive motor that drivably engages the mandrel system

100. The drive motors can be energized to rotate the mandrel system 100 at various selected rotational speeds for improved tolerances as compared to traditional all metal mandrels.

The illustrated mandrel system 100 of Figure 1A has a main body 150. The body 150 is a multilayer composite structure comprising foam encapsulated in a laminate. The mandrel system 100 can weigh substantially less than similarly sized all metal mandrels, thus resulting in reduced rotational inertia. This leads to improved angular acceleration/deceleration of the mandrel system 100, which in. turn leads to reduced fabrication times and fabrication costs.

As shown in Figure 2, the mandrel main body 150 comprises a plurality of curved panels 160a-f held together, at least in part, by the end fittings 140, 142 of Figure 1A. In the illustrated embodiment of Figures 1A and 2, the mandrel main body 150 is a generally tubular body (preferably a generally cylindrical body) formed by the juxtaposed longitudinally-extending panels 160a-f. In some embodiments, the tubular mandrel main body 150 has a substantially circular axial cross-sectional profile, elliptical cross-sectional profile, polygonal cross-sectional profile (including rounded polygonal), combinations thereof, and the like. The panels 160a-f can be generally similar to each other and, accordingly, the description herein of one of the panels applies equally to the others, unless indicated otherwise.

The panels 160a-f of Figure 2 cooperate to form an outer tool surface 170 for engaging the wound material and an inner surface 180. The illustrated main body 150 has six curved panels 160a-f, each subtending an angle of about 60 degrees. However, any number of panels can be used to form the main body 150. For example, more than six panels can be used if the size of the main body 150 is increased to improve handling of the panels.

Figures 1 A and 2 show the main body 150 having a generally circular axial cross-section. In other embodiments, the mandrel main body 150 can have a non-circular cross-section, such as a polygonal cross-section (including rounded polygonal), elliptical, or any other suitable shaped cross-section. The shape and configuration of the main body 150 can be selected based on the desired shape and configuration of the manufactured product.

Figures 3 and 4 show the panel 160a having a pattern 190 that may aid the fabrication process. The illustrated pattern 190 includes a plurality of longitudinally-extending channels 200 (see Figure 7) that can be evenly or unevenly spaced between opposing longitudinal sides 210, 220 of the panel 160a. Each of the illustrated U-shaped channels 200 extends along the length of the panel 160a. In other embodiments, the channels 200 can be V-shaped, W- shaped, or any other suitable shape based on the fabrication process, desired production time, lay-up material, and/or other criteria known in the art. For example, the channels 200 can be suitable for drawing a vacuum to promote proper contact between the panel 160a and a moldable sheet applied to the panel 160a. Although not illustrated, the panel 160a can have other types of patterns, contours, grooves, protrusions, or surface treatments.

With respect to Figures 5 and 6, the panel 160a has a multilayer construction and includes a first flange 240, a second flange 242, and a panel main body 250 extending between the first and second flanges 240, 242. The illustrated main body 250 includes an upper layer 260, a lower layer 262, and a core or intermediate layer 270 therebetween. The panel main body 250 can thus be a composite structure comprising materials having different physical properties.

The core 270 can comprise, in whole or in part, structural foam that is encapsulated by the upper layer 260, lower layer 262, and flanges 240, 242. In some embodiments, the upper layer 260 and lower layer 262 comprise a somewhat high density material {e.g., a carbon fiber laminate with a density greater than 35 Ib/ft³). In such embodiments, the main body 250 can be a lightweight and strong structure that generally maintains its shape throughout the fabrication process (e.g., before, during, and/or after lay-up and/or curing processes). Advantageously, the main body 250 can weigh substantially less than traditional metal mandrels (e.g., mandrels formed of invar) while providing very tight tolerances. The first and second flanges 240, 242 (see Figure 8) extend inwardly towards one another. The flanges 240, 242 can therefore mate with corresponding flanges of adjacent panels when the panels 160a-f are assembled, as shown in Figure 2. Pins, fasteners, mechanical assemblies (e.g., nut and bolt assemblies), adhesives, bonding agents, and the like can temporarily or permanently couple adjacent flanges together. When the main body 150 is assembled, the flanges 240, 242 preferably extend inwardly in the radial direction towards the longitudinal axis 130. Of course, the flanges 240, 242 can be at other orientations.

As used herein, the term "foam" is a broad term that may include, without limitation, a cellular material and/or material having voids. Foam may include a foaming agent, binder, carrier materials, fibers, expandable cellular materials, and the like. The foam can be a high density foam or low density foam as desired. To lower the overall weight of the main body 150, for example, the foam can be a low density foam having rather large voids. In some non-limiting embodiments, the foam can be in the form of structural carbon foam with a closed or open cell structure. To reduce or substantially eliminate heat transfer and fluid flow (e.g., to maintain a proper vacuum during curing) through the foam, the foam can have a mostly closed cell structure that also provides a stable coefficient thermal expansion (CTE). These types of foams have a relatively high compressive strength-to-density ratio while also providing low gas permeability, as noted above. Various types of carbon or graphite foams can be used to form the core 170. For example, GRAFOAM™ (e.g., with a density less than about 5 Ib/ft³, 10 Ib/ft³, or 35 Ib/ft³) from GraphTech International Limited is one type of foam that can be used to form the core 170. The type, density, and structural properties of the foam can be selected based on operating parameters (e.g., thermal loads, structural loads, cycle time, and the like). In some embodiments, for example, the foam density of the core 170 can be in the range of about 0.03 grams/cm³ to about 0.6 grams/cm³. The density of the foam can be decreased or increased to decrease or increase, respectively, the total weight of the mandrel system 100. . As noted above, the upper layer 260 and lower layer 262 each can be a laminate. As used herein, the term "laminate" is a broad term that may include, but is not limited to, a material having one or more layers or plies of material united by an adhesive or other means. For example, a laminate can be a multilayer fiber reinforced composite material.

The laminate can comprise a fiber woven laminate. In some embodiments, the laminate can comprise a quasi-isotropic material for enhanced structural properties. The quasi-isotropic material can be a sheet of layered strips (e.g., randomly oriented layered strips of unidirectional fiber). For example, HEXTOOL™ from Hexcel Composites Limited is one type of quasi-isotropic material that can be used to form the upper and lower layers 260, 262, but other types of quasi-isotropic materials can also be used. These materials may be readily machined for producing a durable working surface that is resistant to fluid migration to maintain vacuum integrity. The randomly oriented fibers serve to limit fluid travel along the fibers. The upper layer 260 and lower layer 262 can be formed of other types of materials, including non-laminate materials. Any one of several different processes can be used to enclose the core 270. Preferably, the core 270 is shaped prior to being covered with the layers 260, 262. A material removal process can shape a plurality of structural foam blocks into the core 170. The blocks may or may not be coupled together before performing the material removal process. The blocks can have various axial cross-sections, including, but not limited to, rectangular cross-sections, square cross-sections, triangular cross-sections, and the like. As used herein, the term "material removal process" is a broad term that may include, but is not limited to, machining, etchings, grinding, cutting, or other processes for removing material. The machining processes can be milling processes, for example. Alternatively, the core 270 can be monolithically formed from a single block. In other embodiments, however, the core 270 is formed by injecting expanding foam (e.g., expanding urethane foam) into a mold corresponding to the desired shape of the core.

Figure 9 illustrates a plurality of blocks that are used to form the core 270 of Figure 10. In the illustrated embodiment, a plurality of blocks 300a-f are coupled together. Any suitable coupling means can couple the blocks together. For example, adhesive strips or films, bonding materials, epoxies, polyamides, bismaleimide (BMI), and other suitable adhesives can be utilized. The illustrated blocks 300a-f form a single layer. A material removal process can be performed to cut away unwanted material to form the core 270. Because the blocks 300a-f are securely coupled together, material can be quickly and efficiently removed to form the curved core 270. If desired, each of the blocks 300a-f can be separately cut and then assembled to form the core 270.

Different types of machines can cut the blocks 300a-f into the desired shape. Waterjet cutting systems, for example, can accurately cut away unwanted material. Various types of multi-axis waterjet cutting systems (e.g., a five-axis waterjet system from Flow International Corporation of Kent, Washington), milling machines (such as CNC milling machines), and the like can also be utilized.

Figures 11 A-11 D illustrate one method of forming the panel 160a of

Figure 5. As shown in Figure 11 A, the core 270 is the starting material. The flanges 240, 242 are attached to opposing longitudinal extending sides 210, 220 respectively, of the core 270. Fasteners, adhesives, couplers, and the like can couple the flanges 240, 242 to the core 170. Alternatively or additionally, the flanges 240, 242 can be embedded in the core 270. The lengths of the embedded portions of the flanges 240, 242 can be selected based on the physical properties of the flanges 240, 242 and the core 170.

Each of the flanges 240, 242 can be formed of a somewhat rigid material, such as hardboard, metal, plastic, composites (e.g., carbon fiber woven laminates), and the like. After the flanges 240, 242 are indirectly or directly coupled to the core 270 (see Figure 11B), one or more sheets (e.g., pre- impregnated sheets) can be applied to an upper surface 330 of the core 270. Similarly, one or more pre-impregnated sheets can be applied to the lower surface 332 of the core 270. To promote adhesion between the sheets and core 170, adhesives can be disposed between the sheets and core 170. As used herein, the term "adhesive" is a broad term and may include, without limitation, bonding agents, adhesive sheets or films, film adhesives, epoxies, or other materials suitable for coupling two structures together. The type of adhesive can be selected based on the materials forming the core 270 and sheets applied thereto, service temperatures, and working environment. In some embodiments, the adhesive is a film adhesive that has a coefficient of thermal expansion (CTE) similar to or substantially the same as the CTE of the core 170. The core 170 and adhesive may have a CTE of about °F-1 = 1.3x10-6. This minimizes stresses due to thermal loading, thus improving the working lifetime of the bonded components.

The illustrated upper and lower layers 260, 262 (Figure 11C) can be formed by multiple pre-impregnated carbon fiber plies, to achieve a desired thickness. For example, six plies may be used to create the upper layer 260 with a thickness of about 0.5 inch. The upper layer 260 can taper towards the periphery of the core 170. By way of example, the lower layer 262 can be formed by three pre-impregnated plies forming a layer with a thickness of about 0.21 inches. The plies of the upper layer 260 and lower layer 262 may or may not wrap around the sidewalls of the core 170. Any number of plies can be stacked onto the core 170 until reaching a desired thickness.

As shown in Figure 11C, the applied sheets can form the upper layer 260 and lower layer 262. The layers 260, 262 can then undergo a subsequent process, such as a thermal process or curing process (preferably an autoclave curing process to ensure proper curing and bonding). Figure 11 D shows one envelope curing process for thermally setting the upper layer 260 and lower layer 262. The upper layer 260 is disposed between the cover 280 and core 170. The lower layer 262 is disposed between a second cover 282 and the core 170. The second cover 282 is attached to and extends between the flanges 240, 242. A vacuum can be pulled so that the covers 280, 282 press the layers 260, 262, respectively, against the core 170, preferably while the assembly is cured. Once the curing process is completed, the coverings 280, 282 can be removed.

Because the upper layer 260 and lower layer 262 are cured in a one- step process, the production time of the panel 160a can advantageously be reduced. In other embodiments, however, the upper layer 260 and lower layer 262 are formed in a multi-step process. In the multi-step process, the upper layer 260 can be placed upon the core 270 and then subjected to a curing process. Next, the lower layer 262 can be placed upon the core 270 and then subjected to a curing process. Thus, a multi-step curing process can set the upper and lower layers 260, 262. The panel 160a can be autoclave cured at 375 degrees Fahrenheit and post-cured at 420 degrees Fahrenheit to produce tooling surfaces capable of being used for more than about 500 cycles at a maximum temperature of about 400 degrees Fahrenheit at about 100 psi, for example. For example, the panel 160a can withstand a temperature greater than about 400 degrees Fahrenheit when at least one sheet or other material applied to the panel 160a is cured. Thus, the panel 160a is reusable and can maintain its shape within desired manufacturing tolerances.

After the curing process, the panel 160a can be machined into a desired shape. Various types of machines, such as a CNC machine using 3D model digital data, can accurately shape the panel 160a. For minimizing manufacturing tolerances, the panel 160a can be built up with excess material. This excess material can be removed with a high degree of accuracy (e.g., a material removal process may have a higher degree of accuracy than a molding process alone) resulting in low tolerances. For example, the upper layer 260 can be machined down to a thickness in the range of about 0.25 inches to about 0.38 inches. The lower layer 262 can be machined down to about 0.14 inches. In this manner, mold line surfaces having complex or simple geometries can be rapidly formed with a high degree of accuracy.

To ensure proper tolerancing, a machining process can be used to form the outer surfaces of the upper layer 260 within +/- 0.01 inch. This ensures that the molded part formed by the mandrel system 100 will have the proper dimensions. A quality control machine (e.g., a laser tracker device) can analyze and determine whether the upper layer 260 is properly formed. If needed, the upper layer 260 can be reshaped any number of times. Preferably, the outer surface 361 (Figure 5) of the upper layer 260 has a surface finish equal to or less than about 63 RMS. The mandrel system 100 of Figure 1 can be a fuselage molding mandrel system used to fabricate the fuselage barrel section of an airplane. In such embodiments, the mandrel system 100 can have an average diameter (e.g., inner or outer diameter) of about 19 feet and an axial length of about 50 feet. Such a mandrel system 100 can weigh less than about 1/3 of a traditional metal mandrel system. In some embodiments, the mandrel system 100 can weigh less than about 1/5 of a traditional metal mandrel system. The upper layer 260 forms a tool surface that engages the inner surface of the laid-up material. In such embodiments, the upper layer 260 can have a thickness in the range of about 0.25 to about 0.38 inches. The lower layer 262 can have a thickness that is less than the thickness of the upper layer 260. For example, the lower layer 262 can have a thickness of about 0.14 inches. The panel 160a can have a thickness of about 3.5 inches.

The mandrel body 150 itself can also be incorporated into a final product. For example, the mandrel body 150 can be incorporated into at least a portion of an aircraft, such as a portion of the fuselage of the airplane. Of course, the dimensions and shape of the mandrel body 150 can be varied depending on the design of the product to be produced.

To enhance seating between adjacent panels 160a-f, the flanges 240, 242 can have one or more inserts for engaging corresponding inserts of the adjacent panels. These inserts mate to limit, inhibit, or substantially prevent relative movement between adjacent panels 160a-f, thereby ensuring proper positioning of each panel. Similarly, the end fittings 140, 142 can be configured to engage inserts or fittings at the ends of the panels 160a-f. As such, the fittings 140, 142 can be securely coupled to the panels 160a-f for a generally rigid mandrel system 100.

^" The inserts can be formed of a hardened and/or high wear material. If the inserts contact metal tooling or jigs, the inserts are preferably formed of a hard metal, such as tool steel, for a prolonged useful life. The inserts can function as alignment aids, keying members, assembly locating jigs, and the like. Indicia can be located along the surface of the mandrel system 100 to indicate the location of any embedded inserts. The indicia can be printing, embossing, markers, or other type of indicator that is preferably readily recognizable.

If the panels 160a-f need to be transported, each of the panels 160a-f can have one or more handling features. For example, each of the panels 160a-f can have one or more handles so that the panels can be easily carried and maneuvered relative to one another. This facilitates assembling and disassembling of the mandrel system 100. If the panels 160a-f are incorporated into a product, they may not have any handling features.

Traditional metal mandrels for molding may be unsuitable for retooling because of the working surface requirements. The working surfaces of the tools may have to be both vacuum tight and ground flush with a tool. Thus, if a metal mandrel is retooled via a welding process, leaks may form through the mandrel resulting in a non-vacuum tight seal. Additionally, welds may result in pitting that is often unsuitable for contacting molded parts. Accordingly, metal mandrels may be unsatisfactory for building-up features, thereby limiting retooling options.

The main mandrel body 150 of Figure 1A, however, can be conveniently re-engineered to accommodate various types of engineering and processing changes. The re-engineered body 150 can still have a durable, high wear outer surface with low tolerances {e.g., metallic surface profile tolerances), while still maintaining its vacuum integrity. One or more layers of material can be rapidly added to the mandrel main body 150 to build-up a desired portion of the tool surface. If needed, the built-up portion(s) of the mandrel main body 150 can be processed (e.g., machined) to form the molding surfaces. To form new molding surfaces on the mandrel main body 150, a thin layer of the upper layer 260 can be removed. Material can be deposited on or otherwise applied to the upper layer 260 to create new molding surfaces. As such, the main body 150 is a very stable and machinable structure capable of maintaining tight tolerances under extreme loading conditions. Figures 12A-E illustrate one method of reworking a portion of the mandrel main body 150. Generally, the illustrated method shows howto remove a feature in the form of a channel 400 (Figure 12A). A molding surface 420 (Figure 12E) can replace the channel 400. The molding surface 420 can be a continuous, smooth surface. Other types of molding surfaces 420 are also possible.

With respect to Figure 12A, the channel 400 can be removed by cutting away a portion of the upper layer 260 and the core 270. In the illustrated embodiment, a trench 406 (Figure 12B) is formed to remove the channel 400. The term "trench" can include, without limitation, one or more recesses, channels, or other structures suitable for receiving material or inserts. After forming the trench 406, material 410 (e.g., foam material) can be positioned within the trench 406. - The material 410 can be foam material adhered to the surfaces 411 of the trench 406. Thus, a lightweight material can at least partially fill the trench 406.

As shown in Figure 12C, an upper surface 412 of the material 410 can be subjacent the upper surface 415 of the upper layer 260. A layer 413 (Figure 12D) can be formed over the material 410 and a portion of the upper layer 260 surrounding an opening 416. In one embodiment, a coupling means used to couple the Iayer413 tothe upper layer 260 and the material410. For example, an adhesive sheet can be interposed between the layer 413 and both the material 410 and upper layer 260. The layer 413 can be subjected to a curing process for improved bonding. Afterthe Iayer413 and adhesive are cured, a material removal process can be used to form a suitable tooling surface 420, as shown in Figure 12E.

A similar process can be used to install an insert or fitting. For example, an insert can be positioned within the trench 406 of Figure 12B. The layer 413 is then disposed over the embedded insert and the upper layer 260. A material removal process can then be used to form a suitable tooling surface. In this manner, any number of inserts, devices, and/or components can be embedded within the panel 160a with or without removing a feature.

Figures 13A-D illustrate one method of forming a feature in a portion of the panel 160a. A material removal process forms a trench 460, as shown in Figure 13B. The trench 460 is subjacent the upper layer 260 and extends at least partially through the core 270. A layer 470 of material (e.g., HEXTOOL™) is then formed on an upper surface 471 of the trench 460 and the portion of the upper layer 260 surrounding the trench 460. After forming the layer 470, a material removal process can be used to remove the excess material 480, 482 so that the layer 470 is generally flush with the layer 260. Using the methods described herein, any number of contours, features, or components can be formed on or removed from a panel. A single mandrel main body 150 can be modified repeatedly and reused for a wide variety of fabrication processes.

Figures 14A-C illustrate another method of embedding a component, such as an insert, into the panel 160a. This method is similar to the method illustrated in Figures 13A-D, except as detailed below. As shown in Figure 14A, a trench 500 can be formed in the core 270. An insert 502 (Figure 14B) can be placed in the trench 500. The upper layer 260 and lower layer 262 can then be applied to the core 270. In such embodiments, the upper layer 260 extends continuously across the embedded insert 502 to define a continuous and uninterrupted molding surface. If needed, however, the insert 502 can be accessed by forming an access opening in the upper layer 260. The access opening can be formed by, for example, drilling a hole through the upper layer 260.

The inserts described herein can be metal inserts that have one or more internally threaded holes to receive externally threaded pins or fasteners. Various types of features can be formed in the inserts after the embedding process. In some embodiments, at least a portion of each insert extends outwardly through the upper layer 260. For example, the insert 502 can comprise one or more pins that extend outwardly through the layer 260. The one or more pins can be used as locators, couplers, and the like. Figure 15 shows an embedded insert 560 positioned within the upper layer 260. To embed the insert 560, a trench 570 having angled sidewalls 572, 574 can be formed in the core 270. Material, such as HEXTOOL™, can be deposited in the trench 570 and along the surfaces of the core 270 to form the upper layer 260. A recess 580 corresponding to the shape of the insert 560 is formed in the upper layer 260. The insert 560 can be easily inserted into the recess 580 for convenient assembly. As explained in connection with Figures 9 and 10, the core 270 can comprise a plurality of separate members, such as blocks, that are coupled together. Different types of coupling arrangements can ensure that the members are securely coupled together. Figure 16 illustrates one coupling system 600 used to compress the core 270. The illustrated coupling system 600 comprises a plurality of through holes 610 formed in the core 270. The illustrated holes 610 are each a longitudinally-extending hole that is generally centrally located between the upper layer 260 and lower layer 262. The holes 610 can also be at other suitable locations and/or orientations. A plurality of rods 620 are provided in corresponding holes 610.

Each of the rods 620 can be generally similar to one another. Thus, the description of one of the rods applies equally to the other rod, unless indicated otherwise. Each rod 620 extends through a corresponding hole 610, preferably between the fittings 140, 142 of Figure 1A. One end of the rod 620 can be configured to couple to the fitting 140. The other end of the rod 620 can be configured to couple to the fitting 142. In some embodiments, the ends of the rod 620 can be externally threaded. The fittings 140, 142 can have internally threaded nuts suitable for receiving the threaded ends of the rod 620. When the rods 620 are coupled to the fittings 140, 142, the rods 620 can be tensioned to compress the mandrel main body 150 sandwiched between the fittings 140, 142. For high temperature applications, the rod 620 can comprise invar, carbon, steel alloys, or other suitable high temperature materials.

Figures 17-20 illustrate a pattern 149 (shown in phantom) formed by the lower layer 262 of the mandrel main body 150. The pattern 149 can effectively stiffen the mandrel main body 150 thereby eliminating the need for an underlying support structure. The size and configuration of the pattern 149 can be selected to achieve a desired amount of structural rigidity for improved dimensional stability. The illustrated pattern 149 is a somewhat "eggcrate" shaped or lattice pattern that significantly improves the structural properties and dimensional stability of the mandrel main body 150 for improved manufacturing tolerances. Stiffeners can also be incorporated into the mandrel main body 150, if desired. Alternatively, the pattern 149 can be suitable for engaging an underlying support structure that can further enhance the structural properties of the mandrel main body 150. The illustrated pattern 149 can be configured to mate with an inner support frame structure. The support frame structure can help maintain the dimensional stability of the mandrel main body 150 during fabrication processes, for example. One skilled in the relevant art can select the pattern formed on the inner surface of lower layer 262 based on the configuration and shape of the support structure.

The lattice pattern 149 hat-stiffened back-up structure can be used for large tools with a working surface having an area that is equal to or greater than 100 ft². Advantageously, the composite structures described above may provide sufficient dimensional stability without a back-up structure and/or strengthening pattern. Tools having working surfaces equal to or less than about 100 ft² may not benefit significantly from the lattice hat-stiffened pattern or an underlying support structure, as noted above.

Figures 21-24 illustrate one panel assembly 299 that forms a portion of a mandrel main body. The illustrated panel assembly 299 has a pair of opposing end plates 310, 312 and a panel 301 extending therebetween. The end plates 310, 312 can be interlocked with the flanges 320, 322. As shown in Figure 23, a tongue and groove arrangement 350 can be used to secure the end plates 310, 312 to the flanges 320, 322. The end plates 310, 312 can then be conveniently installed with the fittings 140, 142 of Figure 1 A. In this manner, the elongate panel assembly 299 can be quickly and conveniently assembled to form the mandrel main body 150. Figures 25-28 illustrate one method for using composite structures to form a part of an aircraft, such as the nose cone of the airplane. As shown in Figure 25, a core 400 can be formed by stacking separate blocks together. The illustrated blocks are interlocked together by self-jigging interlocks. Alternatively or additionally, one or more dowels 431 can extend through one or more of the stacked blocks. The dowels 431 can comprise a material suitable for engaging the blocks. For high temperature uses, the dowels 431 can comprise carbon, including carbon fibers. The blocks can be carbon foam blocks that are bonded together via adhesives. Figures 26-28 illustrate a nose cone assembly 460 that comprises the core 400 and a unitary section 462. The unitary section 462 can be formed of foam material, composites, or other suitable materials. The unitary section 462 can be coupled to the core 400 using dowels 431 or other coupling devices. A measurement system can determine whether the geometry of the assembled blocks is within acceptable tolerances at any time during the fabrication process. A material removal process can shape the stacked blocks before the encapsulation process. To encapsulate the stacked blocks, layers of material (e.g., laminates, HEXTOOL™, and the like) can be applied to the outer surfaces of the stacked blocks. In this manner, the blocks can be rapidly encapsulated. Oven vacuum bag curing can be used to cure the applied layers. To cure the outer layers, separate curing bags can isolate the outer and inner applied layers. As shown in Figure 26, the nose cap can have sub-assemblies that are then assembled together. Optionally, after applying outer materials, the exterior surface can be machined within desired tolerances.

It should be noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. It should also be noted that the term "or" is generally employed in its sense including "and/or" unless the content clearly dictates otherwise. For example, the phrase "a layer" includes a single layer and multiple layers. For example, an outer layer of a mandrel assembly can be formed by the outer surfaces of a plurality of panels. The various methods and techniques described above provide a number of ways to carryout the invention. Of course, it is to be understood that not necessarily all objectives or advantages described may be achieved in accordance with any particular embodiment described herein. Thus, for example, those skilled in the art will recognize that the methods may be performed in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objectives or advantages as may be taught or suggested herein.

Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments disclosed herein. Similarly, the various features and steps discussed above, as well as other known equivalents for each such feature or step, can be mixed and matched by one of ordinary skill in this art to perform methods in accordance with principles described herein. Additionally, the methods which are described and illustrated herein are not limited to the exact sequence of acts described, nor are they necessarily limited to the practice of all of the acts set forth. Other sequences of events or acts, or less than all of the events, or simultaneous occurrence of the events, may be utilized in practiding the embodiments of the invention.

Although the invention has been disclosed in the context of certain embodiments and examples, it will be understood by those skilled in the art that the invention extends beyond the specifically disclosed embodiments to other alternative embodiments and/or uses and obvious modifications and equivalents thereof. The materials, methods, ranges, and embodiments disclosed herein are given by way of example only and are not intended to limit the scope of the disclosure in any way. Accordingly, the invention is not intended to be limited by the specific disclosures of preferred embodiments disclosed herein.

Claims

CLAIMSWhat is claimed is:

1. A mandrel assembly for fabricating at least a portion of a fuselage of an aircraft, the mandrel assembly comprising: a fuselage molding main body having an outer layer defining a fuselage molding surface, the outer layer formed mostly of a first high density material having a first average density, an inner layer formed mostly of a second high density material having a second average density, and an intermediate layer interposed between the outer layer and the inner layer, the intermediate layer including a foam material having a third average density that is less than at least one of the first average density and the second average density.

2. The mandrel assembly of claim 1, wherein the fuselage molding main body is tubular and comprises a plurality of longitudinally-extending panels forming the outer layer, the inner layer, and the intermediate layer.

3. The mandrel assembly of claim 2, further comprising: a first end fitting coupled to a first end of the fuselage molding main body; and a second end fitting coupled to a second end of the fuselage molding main body, the plurality of longitudinally-extending panels extend between the first and second ends of the fuselage molding main body such that the first and second end fittings hold the plurality of longitudinally-extending panels in a selected arrangement.

4. The mandrel assembly of claim 1, wherein the first high density material and the second high density material each comprise a carbon fiber laminate.

5. The mandrel assembly of claim 1 , wherein the first high density material and the second high density material comprise graphite fibers embedded in a resin.

6. The mandrel assembly of claim 5, wherein the intermediate layer comprises foam.

7. The mandrel assembly of claim 1 , wherein the intermediate layer comprises mostly carbon foam.

8. The mandrel assembly of claim 7, wherein the intermediate layer has an average thickness that is greater than a combined average thickness of the inner layer and the outer layer.

9. The mandrel assembly of claim 1 , wherein the intermediate layer has an upper surface and a lower surface, the upper surface is bonded to the outer layer of the fuselage molding main body, and the lower surface is bonded to the inner layer of the fuselage molding main body.

10. The mandrel assembly of claim 1 , wherein the outer layer and the inner layer at least partially encapsulate the intermediate layer.

11. The mandrel assembly of claim 1 , wherein the first high density material, the second high density material, and the foam material each withstand a temperature greater than about 204 degrees Celsius when at least one formable composite sheet applied to the fuselage molding main body is cured.

12. The mandrel assembly of claim 1 , wherein the fuselage molding surface is substantially impermeable to air.

13. A mandrel assembly for forming a component of an aircraft, the mandrel assembly coupleable to a mandrel holder for retaining the mandrel assembly, the mandrel assembly comprising: a tubular body comprising a plurality of longitudinally-extending panels adjacent to one another, at least one of the longitudinally-extending panels comprising an inner layer, an outer layer, and a foam core sandwiched between the inner layer and the outer layer, at least one of the inner layer and the outer layer including a non-foam material.

14. The mandrel assembly of claim 13, wherein the at least one of the longitudinally-extending panels further comprises a first sidewall and a second sidewall; the first and second sidewalls extending between the inner layer and the outer layer such that the foam core is encapsulated, at least in part, by the first sidewall, the second sidewall, the inner layer, and the outer layer.

15. The mandrel assembly of claim 13, wherein the foam core comprises a high temperature resistant foam.

16. The mandrel assembly of claim 13, wherein the foam core comprises carbon foam.

17. The mandrel assembly of claim 16, wherein the foam core has an average thickness that is greater than a combined average thickness of the inner layer and the outer layer.

18. The mandrel assembly of claim 13, wherein the inner and outer layers comprise carbon fibers embedded in a matrix.

19. The mandrel assembly of claim 13, wherein at least one of the inner layer and outer layer comprises a high-temperature resistant fiber laminate.

20. A method of fabricating at least a portion of a molding mandrel used to fabricate tubular structures, the method comprising: forming a panel comprising a plurality of separate blocks integrated together, the panel comprising a low density material; processing the panel to form a convex first surface and an opposing second surface, the convex first surface and the second surface defining a thickness of the panel and extending between opposing lateral sides of the panel; and applying a first layer and a second layer to the convex first surface and the second surface, respectively, at least one of the first layer and the second layer having an average density greater than an average density of the low density material, the first layer defining at least a portion of an outer molding surface of the molding mandrel.

21. The method of claim 20, wherein forming the panel comprises coupling together the plurality of separate blocks, at least one of the blocks being made of foam.

22. The method of claim 21, wherein coupling together the plurality of separate blocks comprises: adhering adjacent blocks together with a high temperature resistant adhesive.

23. A structure comprising: an upper layer comprising a first high density material; a lower layer comprising a second high density material; and an intermediate layer interposed between the upper layer and the lower layer, the intermediate layer comprising a low density foam material.

24. The structure of claim 23, wherein the first and second high density material each comprise at least one carbon fiber laminate.

25. The structure of claim 23, wherein the first and second high density materials comprise graphite fibers embedded in a resin.

26. The structure of claim 23, wherein the intermediate layer comprises carbon foam.

27. The structure of claim 23, wherein the intermediate layer has an upper surface and a lower surface, the upper surface is bonded to the upper layer, and the lower surface is bonded to the lower layer.

28. The structure of claim 23, wherein the upper layer and the lower layer encapsulate the intermediate layer such that a vacuum can be maintained when applied to the upper layer.

29. A mandrel comprising: a tubular body comprising a plurality of longitudinally-extending arcuate panels, each panel comprising a foam core sandwiched between an inner layer and an outer layer, the inner and outer layers each comprising at least one laminate.

30. The mandrel of claim 29 wherein each panel comprises a first sidewall and a second sidewall, the first and second sidewalls extending between the inner layer and the outer layer, the foam core disposed between the first and second sidewalls.

31. The mandrel of claim 29, wherein the foam core comprises foamed carbon.

32. The mandrel of claim 29, wherein the inner and outer layers comprise carbon fibers embedded in bismaleimide.

33. A structure comprising: a lower layer comprising a first high density material; an upper layer comprising a second high density material; and a core encapsulated by the upper layer and the lower layer, the core comprising a foam material.

34. The structure of claim 33 wherein the first and second high density materials comprise fibers in a matrix.

35. A structural assembly for aircraft comprising: a first structural section including a sidewall formed by a plurality of separate composite members integrated together, at least one of the composite members including a first layer made of a non-foam material, a second layer comprising a non-foam material, and a foam core encapsulated by the first layer and the second layer.

36. The structural assembly of claim 35, further comprising: a second structural section coupled to the first structural section, the second structural section forming at least a portion of a nose cone of the aircraft, and the first structural member forms at least a portion of a fuselage of the aircraft.