Patent Publication Number: US-2023135989-A1

Title: Manufacturing methods and related structures, for example useful in airframes and other structures

Description:
FIELD OF THE DISCLOSURE 
     The present application generally relates to manufacturing methods and related structures which can be used in a large variety of applications, for example in a cost-effective manufacture and/or assembly of airframes or other structures, and in particular relates to manufacture and structures formed from assemblies of parts, for instance extruded parts, with a polymer or other lightweight (e.g., open cell or closed cell foam) core. 
     BACKGROUND 
     Description of the Related Art 
     There are various approaches currently employed in the manufacture and/or assembly of airframes and other structures. 
     One approach employs stamped sheet metal. Such typically requires a very large number of fasteners to physically couple various elements together. For example, a metal skin of a wing may be physically coupled by a large number of fasteners to ribs, spars and/or stringers or other underlying frame structures of the wing. Also for example, a skin of a fuselage (e.g., monocoque fuselage) may be physically coupled by a large number of fasteners to stringers or other underlying frame structure (e.g., frame) of the fuselage. These fasteners are typically installed by drilling a large numbers of holes in the sheet metal, than individually manually fixing a fastener in each hole, for example using a pneumatic puller. The cost of labor, as well as the cost the large number of fasteners and associated fixtures that are typically required for a given assembly adds significantly to the overall cost of manufacture. 
     Another approach employs manufacture of a shaped foam core. Such may employ post-shaping of a foam layup after application of composites. The resulting rough and unfinished surfaces require considerable time and labor to produce an acceptable finished surface. 
     Yet another approach employs mandrel wound composites. In such an approach, composite (e.g., pre-preg or fiberglass reinforced polymer matrix, for instance an epoxy or phenolic resin) is wound around a mandrel, and is typically cured in a large autoclave. The tooling involved in this approach can be complicated and/or costly and can require lengthy periods for design and procurement. The cycle time required for completion of finished structures using this approach preclude high volume production and is generally not well suited for mass production. 
     Another possible approach is additive manufacturing (e.g., three-dimensional (3D) printing). Additive manufacturing is not particularly suitable for manufacture of large structures, for instance structures typically associated with airframes (e.g., wing skins, fuselage skins). Additive manufacturing also typically suffers from high material costs, rendering such uneconomically and not particularly suited to mass production. 
     BRIEF SUMMARY 
     Described herein are unique manufacturing methods or processes and resulting structures that allow for the low cost production for finished goods, with minimal added labor. The cost of production may, for example, approach the cost of the raw materials. The described manufacturing methods or processes can, for example, advantageously avoid subtraction of material typically associated with stamping, machining or other removal techniques. The described manufacturing methods or processes can, for example, advantageously allow for the selection of a large range of physical characteristics, while advantageously employing long established materials (e.g., aluminum alloys such as 2024-T3, 6061-T6, 3003-H14, 7075-T6 and/or 5052-H32 aluminum alloys; titanium). 
     The described manufacturing methods or processes and resulting structures can, for example, include joining a number of parts (e.g., metal extrusions, plastic extrusions, other types of extrusions, non-extruded parts) in an assembly and a providing a polymer or other lightweight (e.g., open cell foam or closed cell foam) core in an interior of the assembly, for example as the assembly is held in a mold (e.g., injection molding). For example, one or more parts can be extruded. Also for example, one or more parts can be non-extruded, for instance rolled, stamped, bent and/or machined. The extrusions can, for example, be metal extrusions, plastic extrusions, a combination of metal and plastic extrusions, or other types of extrusions or combinations of various different types of extruded materials. For example, the parts or extrusions may each include respective portions of a skin with one or more integral or monolithic reinforcement structures or stiffeners (e.g., stringers, spars). The parts or extrusions may, for example, each include one or more joint features which matingly couple to complementary joint features on neighboring parts or extrusions in the structure (e.g., airframe structure). The joint features may, for example, lock neighboring parts or extrusions together. The parts may be assembled, for example via the joint features, to form an assembly. The assembly can, for example, be a partially closed structure, for example having a continuous or closed surface when viewed in profile, although the assembly may be open at one or both ends thereof. One or more main stiffeners or other support member can optionally be added to the assembly, for example one or more main spars or frames. The resulting structure can be located in a mold (e.g., between two or more portions of a mold) and a core material (e.g., polymer or other lightweight core material for instance an open cell or closed cell foam) injected or otherwise provided into a cavity. The core material (e.g., open cell or closed cell foam) may expand, forcing the skins of the parts or extrusions against an inner surface of the mold, providing precise alignment of each individual part or extrusion that forms the assembled structure. The external surface of the resulting structure being a fairly precise analog of the inside of the mold. The parts or extrusions may include one or more capture features that cause the expanding polymer or foam to become entrapped such that the assembled parts or extrusions and the polymer or expanded foam form a unitary or monolithic structure that cannot be separated without destruction of a least a portion of that structure. 
     The near raw material cost for extrusion is the lowest practical manufacturing approach for metals, for instance metal alloys typically used in aviation, and provide know characteristics using long established materials. The parts or extrusions can be pre-finished, for example via anodizing, painting, power painting, powder coated, prior to being assembled into the assembly or molded into a finished structure, advantageously further reducing labor costs and time. Internal structures, for example conduits for transportation or containment of fluids, are readily manufactured using the same or similar techniques as described herein. Similarly, structures which can be used for electrical wiring, hydraulics, actuators (e.g., push rods, control cables) along with various other types of structures can be readily manufactured using the same or similar techniques as described herein. 
     The described manufacturing methods or processes and resulting structures can, for example, be particularly useful for aircraft and airframes, and can, for instance, be used to manufacture relative large structures (e.g., wings, vertical stabilizers, horizontal stabilizers, other airfoils, fuselages and empennages), control surfaces (e.g., rudder, ailerons, flaps, slats, spoilers, trim tabs), and/or internal structures (e.g., load bearing floors, conduits for fluids, conduits for control cables, power lines, electrical wiring). The described manufacturing methods or processes and resulting structures can, for example, be particularly usefully applied to various other structures, for example surface and subsurface watercraft, surface vessels or vehicles, storage containers, intermodal shipping containers, enclosures, buildings, and a multitude of other fabricated structures. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG.  1    is a side isometric view of a part or extrusion in the form of a leading edge extrusion according to at least one illustrated implementation. 
         FIG.  2    is an isometric view of a part or extrusion being extruded from an extruder according to at least one illustrated implementation. 
         FIG.  3    is a side isometric view of two parts or extrusions joined together via complementary joint portions or features to form a portion of an assembly according to at least one illustrated implementation, the parts or extrusions including a leading edge extrusion and a lower leading edge skin extrusion. 
         FIG.  4    is an enlarged side isometric view of the two parts or extrusions joined together via complementary joints of  FIG.  3    to better illustrate the complementary joint portions or features thereof. 
         FIG.  5    is a side isometric view of three parts or extrusions joined together via complementary joint portions or features to form a portion of an assembly according to at least one illustrated implementation, the parts or extrusions including a leading edge extrusion, a lower leading edge skin extrusion, and an upper leading edge skin extrusion. 
         FIG.  6    is a side isometric view of four parts or extrusions joined together via complementary joint portions or features to form a portion of an assembly according to at least one illustrated implementation, the parts or extrusions including a leading edge extrusion, a lower leading edge skin extrusion, an upper leading edge skin extrusion, and a lower trailing edge skin extrusion. 
         FIG.  7    is a side isometric view of five parts or extrusions joined together via complementary joint portions or features to form an assembly according to at least one illustrated implementation, the parts or extrusions including a leading edge extrusion, a lower leading edge skin extrusion, an upper leading edge skin extrusion, a lower trailing edge skin extrusion, and an upper trailing edge skin extrusion. 
         FIG.  8    is a side isometric view of six parts or extrusions joined together via complementary joint portions or features to form an assembly according to at least one illustrated implementation, the parts or extrusions including a leading edge extrusion, a lower leading edge skin extrusion, an upper leading edge skin extrusion, a lower trailing edge skin extrusion, an upper trailing edge skin extrusion, and a trailing edge skin extrusion. 
         FIG.  9    is a side isometric view of the assembly of  FIG.  8    with a main support structure added, in the form of a main spar, according to at least one illustrated implementation. 
         FIG.  10    is a top, side isometric view of the assembled structure of  FIG.  9    with the main spar extending outwardly from an interior of the assembly of  FIG.  8   , according to at least one illustrated implementation. 
         FIG.  11    is a top, side isometric view of a mold according to at least one illustrated implementation, which can be employed in manufacturing a finished structure comprising one or more parts or extrusions, for example employing the assembled structure of  FIGS.  9  and  10   . 
         FIG.  12    is a top, side isometric view of the mold of  FIG.  11    with the assembled structure of  FIG.  10    inserted or received in a cavity of the mold, according to at least one illustrated implementation. 
         FIG.  13    is an isometric view of an injection system operable to inject core material into the cavity of the mold of  FIG.  11    and into an interior of the assembled structure of  FIG.  10    while the assembled structure is received in the cavity of the mold, according to at least one illustrated implementation. 
         FIG.  14    is a top, side isometric view of the mold of  FIG.  11    with the assembled structure of  FIG.  10    received in a cavity of the mold and a core injected into the interior of the assembled structure of  FIG.  10   , according to at least one illustrated implementation. 
         FIG.  15    is a top, side isometric view of a resulting or finished structure removed from the mold of  FIG.  11   , comprising the assembly of  FIG.  8    with the main spar and the core, according to at least one illustrated implementation. 
         FIG.  16    is a flow diagram of a method of manufacture, according to at least one illustrated implementation. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that implementations and embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, certain structures associated with extrusion, co-extrusion, molding, injection molding and various extrusions, assemblies, and/or structures have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the various implementations and embodiments. 
     Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense, that is as “including, but not limited to.” 
     Reference throughout this specification to “one implementation” or “an implementation” or “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one implementation or at least one embodiment. Thus, the appearances of the phrases “one implementation” or “an implementation” or “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same implementation or the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more implementations or in one or more embodiments. 
     As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content 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. 
     The headings and Abstract of the Disclosure provided herein are for convenience only and do not interpret the scope or meaning of the implementations or embodiments. 
       FIG.  1    shows a portion  100  of an assembly as one part or extrusion in the form of a leading edge extrusion  102 , according to at least one illustrated implementation. The leading edge extrusion  102  includes a skin  104  and a plurality of reinforcement structures or stiffeners, for example in the form of stringers  106   a ,  106   b  (only two called out). The skin  104  typically provides a closed surface between a set of perimeter edges. The stringers  106   a ,  106   b  may extend along a length or longest dimension of the leading edge extrusion  102 , and arrayed about a primary axis  108 . The leading edge extrusion  102  can, for example, form a leading edge of an airfoil. 
     The leading edge extrusion  102  include one or more complementary joint portions or features  110   a ,  110   b . The complementary joint portions or features  110   a ,  110   b  allow the leading edge extrusion  102  to be physically coupled or joined to one or more other parts or extrusions, as described below. 
     The leading edge extrusion  102  can include one or more retainers or structural features  112  (five shown, only one called out in  FIG.  1   ) that are shaped and position to capture and/or hold onto a core (e.g., polymer, open cell or closed cell foam) when inserted and/or expanded and/or cured. The retainers or structural features  112  can, for example, take the form of a head or widen area with a capture region  113 , for example formed at a distal end of the stringers  106   a ,  106   b . The retainers or structural features  112  can, for example, resemble arrowheads, and be positioned at the end of the retainers or structural features  112  which resemble shafts of arrows. Notable, each retainers or structural features  112  can, for example, have a recess (e.g., where arrowhead interfaces to shaft). The retainers or structural features  112  can, for example, be distributed to be in direct opposition or in partial opposition to one another. The skin  104  and the retainers or structural features  112  can, for example, are advantageously an integral, monolithic structure formed via extrusion. 
     The parts of an assembly can include one or more metal parts, plastic parts, composite parts, or parts formed of materials other than or in addition to metal and/or plastic. Where the part is flat or has a relatively simple geometry, it may be advantageous for the part to be formed via any variety of manufacturing operations, for example stamping, rolling, bending, and/or machining. Where the part has a relatively complex geometry or profile, an extrusion may be preferred. Extrusions can take the form of metal extrusions, plastic extrusions or combinations of metal and plastic extrusions, or even extrusions of other materials or other combinations of materials. While some implementations are described with respect to an assembly of extrusions or even metal extrusions, such is not intended to be limiting unless expressly recited as extrusions or even metal extrusions in the claims. 
       FIG.  2    shows an extruder  200  extruding a part or extrusion  202 , according to at least one illustrated implementation. The extruder  200  may take the form of an extruder or co-extruder that is operable to extrude materials (also referred to herein as core material) such as metals and/or polymers in a specified shape. 
       FIG.  3    shows a portion  300  of an assembly of two parts or extrusions in the form of the leading edge extrusion  102  ( FIG.  1   ) and a lower leading edge skin extrusion  302 , according to at least one illustrated implementation. The lower leading edge skin extrusion  302  includes a skin  104  and a plurality of reinforcement structures or stiffeners, for example in the form of stringers  106   a ,  106   b  (only two called out). The leading edge extrusion  102  and the lower leading edge skin extrusion  302  each include complementary joint portions or features  110   a ,  110   b ,  310   a ,  310   b . The complementary joint portions or features  110   a ,  110   b ,  310   a ,  310   b  physically coupled or join the leading edge extrusion  102  and the lower leading edge skin extrusion  302  together at joints to form the portion of the assembly  300 . The complementary joint portions or features  110   a   110   b ,  310   a ,  310   b  can take the form of locking joint portions or features with lock together when physically engaged with one another. 
     The lower leading edge skin extrusion  302  can include one or more retainers or structural features  112  (only one called out in  FIG.  3   ) that are shaped and position to capture and/or hold onto a core (e.g., polymer, open cell or closed cell foam) when inserted and/or expanded and/or cured. The retainers or structural features  312  can, for example, take the form of a head or widen area, for example formed at a distal end of the stringers  106   a ,  106   b . 
       FIG.  4    shows an enlarged view of the leading edge extrusion  102  and the lower leading edge skin extrusion  302  joined together via the joints formed by joint portions or features  110   a ,  110   b ,  310   a ,  310   b  of  FIG.  3   , better illustrating the complementary joint portions or features  110   a ,  110   b ,  310   a ,  310   b  thereof. 
       FIG.  5    shows a portion  500  of an assembly of three parts or extrusions in the form of the leading edge extrusion  102 , the lower leading edge skin extrusion  302 , and an upper leading edge skin extrusion  502 , according to at least one illustrated implementation. The upper leading edge skin extrusion  502  includes a skin  104  and a plurality of reinforcement structures or stiffeners, for example in the form of stringers  106   a ,  106   b  (only two called out). The lower leading edge skin extrusion  302  and the upper leading edge skin extrusion  502  each include complementary joint portions or features  310   a ,  310   b ,  510   a ,  510   b . The lower leading edge skin extrusion  302  and the upper leading edge skin extrusion  502  are each physically coupled or joined to the leading edge extrusion  102  at joints formed via complementary joint portions or features  310   a ,  310   b ,  510   a ,  510   b ,  110   a ,  110   b  to form the portion  500  of an assembly. 
     The upper leading edge skin extrusion  502  can include one or more retainers or structural features  112  (only one called out in  FIG.  4   ) that are shaped and position to capture and/or hold onto a core (e.g., polymer, open cell or closed cell foam) when inserted and/or expanded and/or cured. The retainers or structural features  112  can, for example, take the form of a head or widen area, for example formed at a distal end of the stringers  106   a ,  106   b . 
       FIG.  6    shows a portion  600  of an assembly of four parts or extrusions in the form of the leading edge extrusion  102 , the lower leading edge skin extrusion  302 , the upper leading edge skin extrusion  502 , and a lower trailing edge skin extrusion  602 , according to at least one illustrated implementation. The lower trailing edge skin extrusion  602  includes a skin  104  and a plurality of reinforcement structures or stiffeners, for example in the form of stringers  106   a ,  106   b  (only two called out). The leading edge extrusion  102 , the lower leading edge skin extrusion  302 , the upper leading edge skin extrusion  502 , and the lower trailing edge skin extrusion  602  each include complementary joint portions or features  110   a ,  110   b ,  310   a ,  310   b ,  510   a ,  510   b ,  610   a ,  610   b . The lower leading edge skin extrusion  302  and the upper leading edge skin extrusion  502  are each physically coupled or joined to the leading edge extrusion  102  at joints formed via complementary joint portions or features  310   a ,  10   a ,  310   a ,  10   b ,  510   a ,  510   b ,  110   a ,  110   b  and the lower trailing edge skin extrusion  602  is physically coupled or joined to the lower leading edge skin extrusion  302  at joints formed via complementary joint portions or features  610   a ,  610   b ,  310   a ,  310   b  to form the portion  600  of the assembly. 
     The lower trailing edge extrusion  602  can include one or more retainers or structural features  112  (only one called out in  FIG.  6   ) that are shaped and position to capture and/or hold onto a core (e.g., polymer, open cell or closed cell foam) when inserted and/or expanded and/or cured. The retainers or structural features  112  can, for example, take the form of a head or widen area, for example formed at a distal end of the stringers  106   a ,  106   b . 
       FIG.  7    shows a portion  700  of an assembly of five parts or extrusions in the form of the leading edge extrusion  102 , the lower leading edge skin extrusion  302 , the upper leading edge skin extrusion  502 , the lower trailing edge skin extrusion  602 , and an upper trailing edge skin extrusion  702 , according to at least one illustrated implementation. The upper trailing edge skin extrusion  702  includes a skin  104  and a plurality of reinforcement structures or stiffeners, for example in the form of stringers  106   a ,  106   b  (only two called out). The leading edge extrusion  102 , the lower leading edge skin extrusion  302 , the upper leading edge skin extrusion  502 , the lower trailing edge skin extrusion  602 , and the upper trailing edge skin extrusion  702  each include complementary joint portions or features  110   a ,  110   b ,  310   a ,  310   b ,  510   a ,  510   b ,  610   a ,  610   b ,  710   a ,  710   b . The lower leading edge skin extrusion  302  and the upper leading edge skin extrusion  502  are each physically coupled or joined to the leading edge extrusion  102  at joints formed via complementary joint portions or features  310   a ,  310   b ,  510   a ,  510   b ,  110   a ,  110   b , the lower trailing edge skin extrusion  602  is physically coupled or joined to the lower leading edge skin extrusion  302  at joints formed via complementary joint portions or features  610   a ,  610   b ,  310   a ,  310   a ,  10   b , and the upper trailing edge skin extrusion  702  is physically coupled or joined to the upper leading edge skin extrusion  502  at joints via complementary joint portions or features  710   a ,  710   b ,  710   a ,  710   b  to form the portion  700  of the assembly. 
     The upper trailing edge extrusion  702  can include one or more retainers or structural features  112  (only once called out in  FIG.  7   ) that are shaped and position to capture and/or hold onto a core (e.g., polymer, open cell or closed cell foam) when inserted and/or expanded and/or cured. The retainers or structural features  112  can, for example, take the form of a head or widen area, for example formed at a distal end of the stringers  106   a ,  106   b . 
       FIG.  8    shows an assembly  800  of six parts or extrusions in the form of the leading edge extrusion  102 , the lower leading edge skin extrusion  302 , the upper leading edge skin extrusion  502 , the lower trailing edge skin extrusion  602 , the upper trailing edge skin extrusion  702 , and a trailing edge skin extrusion  802 , according to at least one illustrated implementation. The trailing edge skin extrusion  302  includes a skin  104  and a plurality of reinforcement structures or stiffeners, for example in the form of stringers  106   a ,  106   b  (only two called out). The leading edge extrusion  102 , the lower leading edge skin extrusion  302 , the upper leading edge skin extrusion  502 , the lower trailing edge skin extrusion  602 , the upper trailing edge skin extrusion  702 , and trailing edge skin extrusion  802  each include complementary joint portions or features  110   a ,  110   b ,  310   a ,  310   b ,  510   a ,  510   b ,  610   a ,  610   b ,  710   a ,  710   b ,  810   a ,  810   b . The lower leading edge skin extrusion  302  and the upper leading edge skin extrusion  502  are each physically coupled or joined to the leading edge extrusion  102  at joints formed via complementary joint portions or features  310   a ,  10   a ,  310   a ,  10   b ,  510   a ,  510   b ,  110   a ,  110   b , the lower trailing edge skin extrusion  602  is physically coupled or joined to the lower leading edge skin extrusion  302  at joints formed via complementary joint portions or features  610   a ,  610   b ,  310   a ,  310   b , the upper trailing edge skin extrusion  702  is physically coupled or joined to the upper leading edge skin extrusion  502  at joints via complementary joint portions or features  710   a ,  710   b ,  710   a ,  710   b , and the lower trailing edge skin extrusion  602  and the upper trailing edge skin extrusion  702  are each coupled or jointed to the trailing edge skin extrusion  802  via complementary joint portions or features  610   a ,  610   b ,  710   a ,  710   b ,  810   a ,  810   b  to form the assembly  800 . 
     The trailing edge extrusion  802  can include one or more retainers or structural features  112  (only one called out in  FIG.  8   ) that are shaped and position to capture and/or hold onto a core (e.g., polymer, open cell or closed cell foam) when inserted and/or expanded and/or cured. The retainers or structural features  112  can, for example, take the form of a head or widen area, for example formed at a distal end of the stringers  106   a ,  106   b . 
     Notably, the assembly  800  has a closed surface  814  (at least when viewed in profile) formed by the skin, with an interior or cavity  816  delineated by the closed surface of the assembly. The assembly  800  can be open at one or both ends  818  of the closed surface  814 . 
       FIGS.  9  and  10    show an assembled structure  900  formed by the assembly  800  of  FIG.  8    with a main support structure added, in the form of a main spar  902 , according to at least one illustrated implementation. The main spar  902  can, for example, extend outwardly from the interior or cavity  816  of the assembly  800  of  FIG.  8   , according to at least one illustrated implementation. The main spar  902  may or may not be an extrusion. 
       FIG.  11    shows a mold  1100  according to at least one illustrated implementation. The mold  1100  can have two or more portions  1100   a ,  1100   b  (two shown) and a mold cavity  1102  with an inner surface, the mold cavity  1102  sized to be employed in manufacturing a structure comprising one or more extrusions, for example employing the assembled structure  900  of  FIGS.  9  and  10   . The portions  1100   a ,  1100   b  may, for example be separable from one another to allow the assembled structure  900  to be positioned into the mold cavity, then the portions  1100   a ,  1100   b  fastened to one another to prevent movement of the assembled structure  900 . One end of the mold  1100  can be sealed, while the other end has at least one aperture or opening to allow the ingress of a fluid or colloidal suspension (e.g., core material in fluid or colloidal suspension form). 
       FIG.  12    shows the mold of  FIG.  11    with the assembled structure  900  ( FIGS.  9  and  10   ) inserted or received in the mold cavity  1102  of the mold  1100 , according to at least one illustrated implementation. The mold  1100  retains the various parts or extrusions (e.g.,  102 ,  302 ,  502 ,  602 ,  702 ,  802 ) in a relatively fixed relationship, particularly as a core is provided or formed in the interior of the assembly  800  or assembled structure  900 , as explained herein. 
       FIG.  13    shows an injection system  1300  operable to inject core material into the cavity of the mold of  FIG.  11    and into an interior of the structure of  FIG.  10    while the structure is received in the cavity of the mold, according to at least one illustrated implementation. The injection system  1300  may include one or more reservoirs  1302   a ,  1302   b  (two shown) that contain one or more materials  1304   a ,  1304   b  (e.g., one material for each of two or more reservoirs). The core material may for example take the form of a polymer, an epoxy, or preferably a lightweight per volume foam, for example an open cell or closed cell foam (e.g., polyurethane foam, isocyanate and polyol resin, foam rubber). The core material is preferably flowable, at least under pressure, for example from a pump  1306 , and is preferably self-expandable or expandable under pressure once injected to a cavity (e.g., interior or cavity  816  of assembly  800 , and/or mold cavity  1102 ). 
       FIG.  14    shows the mold  1100  with the assembled structure  900  ( FIGS.  9  and  10   ) received in the cavity  1102  of the mold  1100  and a core in the form of an expanded foam core  1400  injected into the interior or cavity  816  of the assembly  800  or the assembled structure  900  ( FIGS.  9  and  10   ), according to at least one illustrated implementation. 
     The core material can advantageously be self-expandable or expandable under pressure when injected or otherwise provided into a cavity, for example taking the form of an expandable foam which advantageously has a low weight to volume ratio. Various open cell or closed cell foams can be employed, for instance polyurethane foam. The expansion of the core material can apply a radially outward force the parts or extrusions, which parts or extrusions are physically constrained in place by the inner surface of the cavity of the mold and/or by the various joints. In at least some implementations, the radially outwardly applied force can cause the outer surface of the assembled structure  900  to conform to the inner surface of the cavity  1102  of the mold  1100 , and thus may closely resemble at least in overall shape the inner surface of the cavity  1102  of the mold  1100 . 
     In at least some implementations, the core material may be allowed to harden or cure, for example naturally when exposed to air over a sufficient time period, or in response to a stimulus (e.g., exposure to selected wavelengths of electromagnetic energy for instance ultraviolet light), or in response to a chemical reaction between two or more chemicals (e.g., two-part epoxy), or in a combination of the aforesaid. Once hardened or cured, the resulting structure  1500   
       FIG.  15    shows a resulting structure  1500 , also denominated as a finished structure, removed from the mold  1100  ( FIG.  11   ), comprising the assembled structure  900  ( FIGS.  9  and  10   ) formed from the assembly  800  ( FIG.  8   ) with the main spar  902  and the expanded foam core  1400  ( FIG.  14   ), according to at least one illustrated implementation. In the resulting structure  1500  the expanded foam core  1400  ( FIG.  14   ) may be hardened or cured as discussed above. The parts or extrusions of the resulting structure  1500  are securely bound together via the complementary joint portions or features  110   a ,  110   b  and the expanded foam core  1400  ( FIG.  14   ), and/or via the physical interaction of the retainers or structural features  112  with the expanded foam core  1400 . The expanded foam core  1400  provides added structural rigidity while adding little weight to the overall structure  1500 . In at least some implementations, when the expanded foam core  1400  ( FIG.  14   ) is hardened or cured, the resulting structure  1500  cannot be disassembled without destruction of one or more portions (e.g., destruction of the expanded foam core  1400 ). 
       FIG.  16    shows a method  1600  of manufacturing, according to at least one illustrated implementation. 
     At  1602 , one or more extruders extrude one or more parts or extrusions. 
     Optionally at  1604 , one or more parts or extrusions are treated. For example, one or more parts or extrusions may be anodized, painted, powder coated using conventional techniques. Treatment can alternatively or additionally occur after the parts or extrusions are assembled into an assembly. 
     At  1606 , the parts or extrusions are assembled into an assembly. For example, the parts may be physically coupled to one another (e.g., physically coupled to immediately adjacent parts or extrusions) via one or more joint portions or features, which can be integral to the respective part or extrusion. 
     Optionally at  1608 , one or more additional components (e.g., main spar) or structures can be added to the assembly. 
     At  1610 , the assembled structure is placed into a mold. 
     At  1612 , core material is injected into a cavity in assembled structure while the assembled structure is held or retained by the mold. 
     Optionally at  1614 , core material is cured or allowed to harden into a cured or hardened core. 
     At  1616 , the resulting structure (e.g., finished structure) is removed from mold. 
     EXAMPLES 
     Example 1. A method of manufacturing, comprising:
     assembling two or more parts or extrusions into an assembly;   placing the assembly into a mold;   injecting a core material into an interior or cavity of the assembly while the assembly is retained in the mold; and   removing a resulting structure from the mold.   

     Example 2. The method of example 1, further comprising: extruding the two or more parts or extrusions before assembling the two or more parts or extrusions into the assembly. 
     Example 3. The method of example 1, further comprising: extruding the two or more parts or extrusions as metal extrusions before assembling the two or more parts or extrusions into the assembly. 
     Example 4. The method of example 1, further comprising: extruding the two or more parts or extrusions as plastic extrusions before assembling the two or more parts or extrusions into the assembly. 
     Example 5. The method of example 1 wherein assembling two or more parts or extrusions into an assembly comprises assembling two or more extrusions into the assembly. 
     Example 6. The method of example 1 wherein assembling two or more parts or extrusions into an assembly comprises assembling at least one stamped part and at least one other part or extrusion into the assembly. 
     Example 7. The method of any of examples 2 through 6, further comprising: treating at least one of the two or more parts or extrusions before assembling two or more parts or extrusions into the assembly. 
     Example 8. The method of any of examples 2 through 6, further comprising: treating at least one of the two or more parts or extrusions after assembling two or more parts or extrusions into the assembly. 
     Example 9. The method of any of examples 1 through 8, further comprising: adding one or more additional components (e.g., main spar) or structures to the assembly before placing the assembly into the mold. 
     Example 10. The method of any of examples 1 through 9, further comprising: adding one or more additional components (e.g., main spar) or structures to the assembly after placing the assembly into the mold. 
     Example 11. The method of any of examples 1 through 10, further comprising: curing or hardening the core material into a cured or hardened core. 
     Example 12. The method of any of examples 1 through 11, further comprising: curing or hardening the core material into a cured or hardened core before removing the resulting structure from the mold. 
     Example 13. The method of any of examples 1 through 12 wherein assembling two or more parts or extrusions into the assembly comprises: physically coupled adjacent ones of the two or more parts to one another via one or more joint portions or features which are integral to the respective part or extrusion. 
     Example 14. The method of any of examples 1 through 13 wherein injecting a core material into an interior or cavity of the assembly while the assembly is retained in the mold comprises injecting an expandable foam into the interior or cavity of the assembly while the assembly is retained in the mold. 
     Example 15. An article of manufacture, comprising:
     an assembly of two or more parts or extrusions having an interior or cavity therein;   placing the assembly into a mold; and   a core of a cured or hardened core material in the interior or cavity of the assembly that provides structural rigidity to the assembly.   

     Example 16. The article of manufacture of example 15 wherein the cured or hardened a core material is an expandable foam material that has been allowed to hardened or cured. 
     Example 17. The article of manufacture of any of examples 15 or 16 wherein the two or more parts or extrusions each include one or more joint portions or features that complementary physically coupled to one or more joint portions or features of another one of the two or more parts or extrusions. 
     Example 18. The article of manufacture of example 17 wherein the one or more joint portions or features are integral to the two or more parts or extrusions. 
     Example 19. The article of manufacture of any of examples 15 through 18 wherein each of the two or more parts or extrusions includes a skin portion and the one or more joint portions or features are integral to skin portions of the two or more parts or extrusions. 
     Example 20. The article of manufacture of any of examples 15 through 19 wherein each of the two or more parts or extrusions includes a skin portion and a number of reinforcement structures or stiffeners, that are integral to the skin portion of the two or more parts or extrusions. 
     Example 21. The article of manufacture of example 17 wherein the reinforcement structures or stiffeners are stringers. 
     Example 22. The article of manufacture of any of examples 15 through 21 wherein each of the two or more parts or extrusions includes a skin portion and a number of retainers or structural features that are shaped and positioned to capture and/or hold onto the core. 
     23. The article of manufacture of any of examples 15 through 22 wherein each of the two or more parts or extrusions includes a skin portion, a number of reinforcement structures or stiffeners, and a number of retainers or structural features that are shaped and position to capture and/or hold onto the core, the retainers or structural features integral to respective ones of the reinforcement structures or stiffeners. 
     Example 24. The article of manufacture of any of examples 15 through 23 wherein at least one of the two or more parts or extrusions is a metal part or a metal extrusion. 
     Example 25. The article of manufacture of any of examples 15 through 23 wherein at least one of the two or more parts or extrusions is a plastic part or a plastic extrusion. 
     Example 26. The article of manufacture of any of examples 15 through 23 wherein at least one of the two or more parts or extrusions is a stamped part. 
     Example 27. The article of manufacture of any of examples 15 through 26 wherein article of manufacture is a component of an airframe. 
     Example 28. The article of manufacture of any of examples 15 through 26 wherein article of manufacture is a component of a vehicle. 
     Example 29. The article of manufacture of any of examples 15 through 26 wherein article of manufacture is a component of a building. 
     Example 30. The article of manufacture of any of examples 15 through 26 wherein article of manufacture is a component of a storage container or an intermodal shipping container. 
     Example 31. A method of manufacture as illustrated and described herein. 
     Example 32. An article of manufacture as illustrated and described herein. 
     The various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. All of the commonly assigned US patent application publications, US patent applications, foreign patents, and foreign patent applications referred to in this specification and/or listed in the Application Data Sheet, including but not limited to International Patent Application PCT/US2019/055687, published as WO 2020/077121; U.S. Provisional Pat. Application No. 63/178,948, filed Apr. 23, 2021; and U.S. Provisional Pat. Application No. 63/220,696, filed Jul. 12, 2021, are incorporated herein by reference in their entirety. In general, in the following claims, the terms used should not be construed to limit the claims to the specific implementations or embodiments disclosed in the specification and the claims, but should be construed to include all possible implementations or embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.