Abstract:
Warhead structures and features are fabricated using direct manufacturing technologies, a method for fabricating bulk warhead structures by sequential and additive deposition of melted feedstock layers. Suitable energy sources for melting the feedstock can be various high energy density technologies including laser, electron beam, plasma arc deposition, and the like. The high energy density in combination with high cooling rates results in structures with homogeneous microstructures. The feedstock can be in the form of wire or powder and is applied to a substrate by introduction to a molten pool on the substrate, accumulating to additively combine with the substrate. The approach provides for warhead structures with singular and combined unique features to include: integral constructions, tailored fragmentation patterns, use of dissimilar materials for special effects, and variable material property constructions for enhanced performance.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     Warheads and warhead structures are used in many various conditions and circumstances including air to air ordnance, ground to air ordnance, air to ground ordnance, ground to ground ordnance, and structural demolition charges. Design of an effective warhead or other penetrating projectile involves analysis of several considerations including penetration, blast, and fragmentation performance. Pertinent design parameters include shape, size, mass, material composition, enhanced or combined effect features (combinations of fragmentation, incendiary, and explosive effects), and others.  
         [0002]     Warhead shape, size, and material composition are selected according to functional considerations. Some warheads have an aerodynamic shape that facilitates delivery through the air while others are shaped to assist penetration or to affect a particular explosive signature upon impact/detonation. Some warheads are shaped and integrated into higher order assemblies such as missile systems. Warhead size and mass are examples of design parameters that support and enable the ultimate performance of the warhead.  
         [0003]     Various existing techniques are used to attain enhanced/combined effects. For example, several techniques have been used to attain enhanced fragmentation capabilities. These include prefabricated fragments molded into a shell constructed from metal or other suitable materials, and machining (scribing) of a fragmentation pattern into a continuous wall surface of a shell body. Combined effects have been achieved through the incorporation of warhead sub-assemblies using specialized reactive or dissimilar materials that are “attached” to the basic warhead.  
         [0004]     Conventional warhead manufacturing methods typically use casting or forging technologies to construct core components. Warhead material selections and designs are generally restricted to those capable of casting or forging, limiting allowable shapes, sizes, material compositions, capabilities, and effects. Multiple part subassembly constructions (particularly for combined effects features) are typically used. These increase touch labor, parts count, and design/development/production costs while reducing design options.  
         [0005]     Conventioinal warhead manufacturing methods involve design and fabrication of molds and other overhead that hinder development of new warhead design concepts. This tooling requirement lengthens both design and fabrication cycles, necessitates significant upfront and specialized infrastructure expenses, and fails to efficiently support rapid prototyping activities.  
       SUMMARY OF THE INVENTION  
       [0006]     Warheads and warhead structures (warhead structures include bombs, munitions, cluster bomblets, bullets, nose-caps, missiles, and other projectiles) are fabricated using direct manufacturing technologies, a method for fabricating bulk warhead structures by sequential and additive deposition of thin melted feedstock layers. The feedstock can be in the form of wire or powder and is applied to a substrate by introduction to a molten pool on the substrate caused by a high density energy source.  
         [0007]     Suitable energy sources for melting the feedstock can be various high energy density technologies including laser, electron beam, plasma arc deposition, and the like. The high energy density in combination with high cooling/solidification rates results in structures with homogeneous microstructures and high structural integrity. The process metallurgically bonds deposited layers, promoting a continuous grain structure and epitaxial growth between layers. The technique produces a gradual accumulation (“growing”) of material by repetitive deposition of uniform beads of material that quickly solidify due to efficient heat conduction into the substrate material.  
         [0008]     Direct manufacturing techniques of additive fabrication enable design and fabrication of specialized warheads using unique shaping, materials, and structures that have conventionally been difficult or impossible to use. Special warhead shapes may include nose cones, walls of controlled thickness, fragmentation patterns, and the like. Unique and previously unused materials include new material alloys, non-homogeneous materials, deformable materials, variable hardness or density material mixes, and others.  
         [0009]     Direct manufacturing techniques expand available capabilities in warhead design and fabrication, enabling shapes and material compositions that have heretofore been unavailable in warhead manufacture. In accordance with some embodiments, a warhead comprises a casing formed of a plurality of additively-deposited, direct-manufactured layers.  
         [0010]     According to other embodiments, a warhead comprises an integral casing having regions of controlled and varied structural parameters in additively-deposited, direct-manufactured layers.  
         [0011]     In further embodiments, a warhead comprises a casing and a structural feature coupled to the casing. The casing and the structural feature are integrally formed in a plurality of additively-deposited, direct-manufactured layers.  
         [0012]     According to other embodiments, a method of fabricating a warhead comprises additively depositing a plurality of direct-manufactured layers of a selected material type, and controlling positioning of the deposition of layers to build a structure of a selected geometry. The method further comprises varying at least one controlled structural parameter during deposition of the additively-deposited, direct-manufactured layers.  
         [0013]     In some embodiments and applications, direct manufacturing techniques can be used to “scribe” materials for tailored and optimized fragmentation. In some embodiments, non-homogeneous constructions, based on deposition of varying materials or variable deposition of a single material, can be obtained for specialized performance. In some embodiments, non-homogeneous materials can be combined to affect a time varying (deformable) warhead capability that facilitates steering performance, optimized penetration, and other desired functionality.  
         [0014]     Usage of direct manufacturing techniques also enables a faster and more flexible warhead development process, from design through early fabrication phases, increasing innovation and productivity in comparison to conventional methods.  
         [0015]     Through the various embodiments, the illustrative direct manufacturing techniques enable and facilitate rapid and innovative warhead design capabilities from conception through design and fabrication. Direct manufacturing techniques applied to warhead design and manufacture enables and facilitates an expanded breadth of useful warhead materials, material combinations, shaping techniques, and construction approaches. The illustrative direct manufacturing techniques enable reduction in touch labor during sub-munitions and combined effects warhead fabrication and facilitate increased capabilities to tailor warhead performance to application requirements. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     Embodiments of the invention relating to both structure and method of operation, may best be understood by referring to the following description and accompanying drawings.  
         [0017]      FIG. 1  is a schematic pictorial diagram illustrating an example of a suitable high energy density direct manufacturing device for usage in fabricating warheads and special warhead structures.  
         [0018]      FIG. 2  is a schematic pictorial diagram that illustrates a view of the substrate, feedstock, and high energy density source during deposition of molten material.  
         [0019]      FIG. 3  is a pictorial diagram that shows an example of a casing for a warhead with a deposited variable wall thickness.  
         [0020]      FIG. 4  is a three-dimensional pictorial diagram showing an example of a warhead segment with a fragmentation pattern formed by selective material placement during the deposition process.  
         [0021]      FIG. 5  is a three-dimensional pictorial diagram showing a warhead segment with a fragmentation pattern formed by controlling and varying material density during the deposition process.  
         [0022]      FIG. 6  is a three-dimensional pictorial diagram that illustrates an example of a warhead segment containing internally fabricated special material elements formed by controlling and varying material type during the deposition process.  
         [0023]      FIGS. 7A and 7B  show illustrative warhead segments that include metal casings with internal slugs formed integral to the casing by controlling and varying material type during the deposition process.  
         [0024]      FIG. 8  is a cross-sectional pictorial diagram showing an embodiment of a warhead segment that improves penetration by deposition of a hard and dense material tip on the end of a less hard and dense material body.  
         [0025]      FIG. 9  is a cross-sectional pictorial showing an embodiment of a warhead segment that improves penetration by deposition of a softer material blunt nose cone over a harder material internal penetrator body.  
         [0026]      FIG. 10  is a three-dimensional pictorial diagram of an integrally formed structural feature, illustratively a suspension lug, which is formed by controlled deposition directly on the warhead casing.  
         [0027]      FIG. 11  is a three-dimensional pictorial diagram of a cylindrical-type warhead structure with internal compartments separated by integral walls formed by controlled deposition of material.  
         [0028]      FIG. 12  is a three-dimensional pictorial diagram of a warhead segment including integrally formed closeout and fuze housing formed by controlled deposition of material.  
         [0029]      FIG. 13  is a schematic pictorial cross-sectional diagram showing an example of a metallic-foam deposition construction, illustratively a solid metallic outer layer and an internal metallic foam region. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0030]     Referring to  FIG. 1 , a schematic pictorial diagram illustrates an example of a suitable high energy density direct manufacturing device  100  for use in fabricating warheads and warhead structures. The illustrative high energy density direct manufacturing device  100  is a precision controlled moving-gun electron beam welding system although other devices can also be used, for example laser beam devices, plasma arc deposition devices, and others. The direct manufacturing process or method is similar to welding using a high energy heat source to create a molten pool on a substrate and adding wire or powder material to the molten pool to create a deposited bead of material. These deposited beads can be combined to create a layer of deposited material, and many layers can be combined to create a large deposited structure.  
         [0031]     The direct manufacturing device  100  includes an electron beam gun  102  that produces an energy beam  104 , illustratively an electron beam, used to melt the substrate and feedstock  106  and to accumulate deposited material on the substrate  108 . The substrate  108  and the electron beam gun  102  are positioned within a chamber  110  with relative movement between the two enabling continuous and proper positioning of the deposition pool. The electron beam gun  102  generates the energy beam  104 , focused so that energy density at a point  112  at which the energy beam  104  intersects with the surface of the substrate  108  is sufficient to locally melt the substrate. Electron beam energy transforms into heat at the substrate surface. An electron beam system  100  can commonly include a vacuum chamber  110  to fabricate articles from any electrically conductive substance, typically metals, capable of melting upon application of a high-energy source. In some embodiments using laser or plasma arc energy sources the chamber  110  is filled with an inerting gas for improved deposition performance. In some embodiments alloying elements in gaseous form are introduced into the atmosphere around the molten pool and these become incorporated into the resulting deposited material.  
         [0032]     The energy beam  104  moves relative to the substrate surface, resulting in an absorbed energy rate sufficient to melt the substrate  108  to a shallow depth. The energy beam  104  melts additional material from the feedstock  106  and this material accumulates into the molten pool forming a bead on the substrate  108 . The electron beam gun  102  and/or the substrate target move under power of motion control robotics, moving the molten pool along the substrate  108 , leaving behind a bead of material formed in a continuous path.  
         [0033]     Various warhead structures can be designed and fabricated by varying feedstock materials, varying density patterns on the substrate, and programming the controllers of the robotic electron beam gun to form different shapes, including highly complex shapes. Particular heat sources may be more effective or better suited to fabrication using particular feedstock materials. In various applications different energy sources may be appropriate for particular metal substrates.  
         [0034]     Referring to  FIG. 2 , a schematic pictorial diagram illustrates a view of the substrate  108  during deposition of molten material. The feedstock  106  is introduced to the molten pool at the intersection  112  of the energy beam  104  and the substrate surface  108   
         [0035]     In various embodiments, the feedstock  106  can be a wire fed through a feeding apparatus conventional to welding processes. A wide variety of wire feedstock options exist with this approach.  
         [0036]     In other embodiments, the feedstock  106  can be in powder form and be supplied through a nozzle. Appropriate conventional powder feedstock delivery devices supply a constant mass flow of powder in a uniform stream or streams. Powder feedstock composition can be varied during operations to enable a continuously changing alloy or non-homogeneous material composition during the deposition process.  
         [0037]     Referring to  FIG. 3 , a pictorial diagram shows an example of a casing  302  for a warhead  300  with varying wall thickness. The warhead  300  has a relatively thick casing portion  304  in the vicinity of the warhead nose cone  306  that changes to a thin casing portion  308  anterior to the nose cone  306  at the cylindrical walls  310 . One technique for fabricating the warhead casing  302  comprises accumulation of multiple beads  311  formed in a circular configuration to build the cylindrical walls  310 . The nose cone  306  is formed by gradually reducing the radius of the circular configuration at increasing heights and, in some embodiments, increasing wall thickness. Once the fundamental structure of the warhead  300  is complete, including cylindrical walls  310  and nose cone  306 , inner walls  312  and/or outer walls  314  of the warhead  300  can be machined to desired surface characteristics. A closeout piece  316  can be constructed separately or integral to the warhead  300  using the disclosed direct manufacturing process or using an alternative construction technique. A separate closeout piece  316  can be fastened to the nose cone  302  by welding using the energy beam  104  as a heat source. In an alternative embodiment, closeout piece  316  is formed by inverting the nose cone  306  and accumulating layers that close the open circle at the warhead base.  
         [0038]     Referring to  FIG. 4 , a three-dimensional pictorial diagram shows an example of a warhead segment  400  with a fragmentation capability. The warhead segment  400  can be formed in an appropriate configuration, such as a cylinder, by direct manufacturing techniques through accumulation of multiple layers in a circular form. The warhead segment  400  is a preformed fragmentable block  402  that can be fabricated into a warhead casing. The fragmentable block  402  is capable of fragmenting consistently in a specified, predictable pattern upon explosion or impact. In some embodiments, the fragmentation pattern is produced by accumulating layers in the direct manufacturing process so that notches  404  are formed in a preselected pattern. The notches  404  form lines of weakness having increased susceptibility to fracture. The notches  404  can be precisely controlled in position and depth, resulting in highly predictable fragmentation effects.  
         [0039]     Referring to  FIG. 5 , in other embodiments, fragmentation patterns can be inserted by controlling and varying density of the wall material  500 . One technique for producing reduced density areas  504  is to vary deposition temperature, time, or composition of deposited material. Reduced density areas  504  have lower strength, so that the casing  502  has greater susceptibility to fracture along predetermined lines  506 . The reduced density areas  504  can be precisely controlled in position, material composition, and hardness, leading to highly predictable fragmentation effects.  
         [0040]     Referring to  FIG. 6 , a three-dimensional pictorial diagram illustrates an example of a warhead segment  600  containing internally fabricated special material elements  602 . In an illustrative embodiment, the special material elements  602  are zirconium slugs. In Combined Effects Munitions (CEMs) and Combined Effects Bombs (CEBs), the warhead  600  can be a shaped charge with a scored steel casing  604  and special material elements  602  including zirconium slugs, aluminum particles, magnesium particles, tungsten slugs, and other materials to introduce fragmentation, incendiary, and anti-armor capabilities. The warhead segment  600  is fabricated by introducing various selected materials during the deposition process to provide the special material elements and controlling and varying the deposition to create individual fragmentation zones about these elements. For example, zirconium slugs can be positioned on the substrate during layering at selected positions or in selected densities. Special material elements can be positioned on the top layer of substrate during fabrication and combined with the molten material as the energy beam passes over the segment of substrate. Molten feedstock encases the material elements  602  as layers accumulate. The material elements  602  can be combined with various metals including new material alloys.  
         [0041]     Referring to  FIG. 7A and 7B , pictorial diagrams illustrate warhead designs including multiple integrally formed metal components. Referring to  FIG. 7A , a warhead segment  700  includes a steel casing  702  with a cylindrical body  704  tapering to a nose cone  706 , and a tungsten slug  708  formed integral to the casing  702 . Integral layers of steel casing  702  and tungsten slugs  708  are fabricated by exchanging feedstock materials during layering of molten material.  FIG. 7B  shows a three-dimensional view of the warhead segment  700  including the steel casing  702  and tungsten slugs or pellets  708  integrally formed into the casing (akin to the CEM and CEB embodiments described above). In the illustrative embodiment of the warhead segment  700 , the steel casing  702  has reduced density/deposition lines  710  to generate predetermined fragmentation effects. In various embodiments, casing, slug, and other particle materials can be varied to facilitate penetration and to produce variable properties such as strength, ductility, hardness, density, and the like.  
         [0042]     Referring to  FIG. 8 , a cross-sectional pictorial diagram shows an embodiment of a warhead segment  800  that improves penetration by fabricating a higher strength tip  802  on the end of a lighter weight/lower strength tube  808 . The high strength tip  802  is layered onto the end cap  810  of a lighter weight/lower strength tube  808  using the direct manufacturing processes. The direct manufacturing approach enables the controlled tapering and wall thickness of the tube  808  to the end cap  810 .  
         [0043]     Similarly, referring to  FIG. 9 , a cross-sectional pictorial diagram shows a warhead nose cone  900  with tailored properties. This embodiment provides for the creation of nose cones that undergo erosion/shape change during penetration. Materials can be selected from among many appropriate materials such as alloys of steel, tungsten, titanium, zirconium, rhenium, aluminum and others, including various similar metal materials that are appropriate for warhead manufacture, and are deposited in a planned arrangement to affect desired variations in nose cone strength and ductility. The nose cone  900  is constructed (conventional or deposition method) as a cylinder  902  that transitions into a shaped tip  904  using a strong and hard material. The nose cone  900  is then filled out using a more ductile, soft material deposition  906  resulting in varying and shaped hardness characteristics for penetration performance enhancements.  
         [0044]     Referring to  FIGS. 10, 11 , and  12 , several three-dimensional pictorial diagrams illustrate examples of integral shapes, structures, and geometries that are enabled using direct manufacturing techniques in warhead manufacture, in lieu of conventional multipart assembly approaches.  FIG. 10  depicts an integrally formed suspension lug  1002  that can be formed on a warhead casing  1000 . The suspension lug  1002  is formed by building multiple layers of material on a portion of the casing  1000 , typically followed by machining the casing  1000  and lug  1002  to form a smooth structure. In another example, a tab can be formed on a casing by layering material and machining.  
         [0045]      FIG. 11  shows a cylindrical-type warhead structure  1100  with internal compartments  1102  separated by integral direct manufactured walls  1104  or stiffeners. The compartments  1102  can be filled with special materials such as explosives, or other materials, or left vacant as desired.  
         [0046]      FIG. 12  shows a warhead segment  1200  with an integrally formed closeout fuze housing. The fuze housing has a cylindrical casing  1204  enclosing an interior region  1206 , and an end piece  1208 . A cylindrical vesicle  1210  interior to and axial with the cylindrical casing  1204  extends inward from the end piece  1208  and is capable of holding a fuze. The vesicle  1210  is separated from the interior region  1206  by a wall  1212 . In other embodiments, various integrally formed features can include attachment features, electronics attachment features, nose or tail structures, fins, kit attachments, integral nose and/or tail features, and other structures.  
         [0047]     Referring to  FIG. 13 , a schematic pictorial cross-sectional diagram shows an example of a metallic-foam construction  1300  including a solid metallic outer layer  1302  and an internal metallic foam region  1304 . Metallic foam  1304  is useful in application such as lightweight bomb or bomblet devices. The metallic foam  1304  is open-celled and enables the potential for tailored filling of interstitial volumes  1306  with materials such as explosives, or other materials, or may be left vacant to reduce weight. The metallic foam  1304  provides multiple load paths for high strength and stiffness. The metallic foam  1304  forms by incorporating a gas-generating material, for example a titanium hydride powder, into the feedstock. The incorporated foaming agent thermally decomposes in the melt and generated gas converts the melt into porous metal.  
         [0048]     While the invention has been described with reference to various embodiments, it will be understood that these embodiments are illustrative and that the scope of the invention is not limited to them. Many variations, modifications, additions combinations, and improvements of the embodiments described are possible. For example, those having ordinary skill in the art will readily implement the steps necessary to provide the structures and methods disclosed herein, and will understand that the process parameters, materials, and dimensions are given by way of example only. The parameters, materials, and dimensions can be varied to achieve the desired structure as well as modifications, which are within the scope of the invention. Variations and modifications of the embodiments disclosed herein may be made based on the description set forth herein, without departing from the scope and spirit of the invention as set forth in the following claims. For example, although the examples discuss particular deposited materials and combinations of materials, other materials can be formed into the described structures and be used to produce warheads having desired properties.