Additively manufactured metal casing

Abstract

One embodiment of the bomb casing (1) defines a generally conical nose portion (2) and a cylindrical body portion (3). At least one, and more preferably both, of the generally conical nose portion (2) and / or the cylindrical body portion (3) are preferably formed from an additive manufacturing process that is cryogenic gas kinetic spraying of metal particles onto a support member. In one embodiment, the generally conical nose portion and the cylindrical body portion are integrally formed.

Description

[Technical field]

[0001] The present invention relates to a device and associated methods for additively manufactured metal casings. Embodiments of the invention find application in the fields of ammunition, weapons, and in particular bomb casings, although not exclusively. [Background technology]

[0002] Any discussion of documents, acts, materials, devices, articles or the like which has been included in this specification is solely for the purpose of providing a context for the present invention and is not to be construed as an admission that any or all of those matters form part of the prior art or were general knowledge in the fields relevant to the invention existing in Australia or elsewhere prior to the priority date of this application.

[0003] Warhead casings have different characteristics that depend on the specific proposed use of the warhead, such as air-to-air, surface-to-air, air-to-ground, surface-to-ground, and structural demolition charge applications. To ensure a warhead is effective, the ability of the casing to penetrate and fragment the intended target must be considered. Design parameters that contribute to the performance of the casing include shape, mass, material composition, mechanical properties, and fragmentation performance.

[0004] The choice of warhead casing design is based on functional considerations which may include aerodynamic efficiency, penetration performance or fragmentation pattern. In the case of the BLU (i.e. Bomb Live Unit, aka Bunker Buster Bomb), the casing plays a key role in the penetration capability of the system.

[0005] The BLU warhead typically consists of three core components: the nose cone, the cylindrical body, and the tail. Conventional warhead manufacturing methods typically use casting or forging techniques to construct these core components separately before being joined in the final assembly process. The separate sub-structure of the BLU is dictated by the need to achieve higher hardness in the nose section of the casing to ensure adequate penetration performance. Material selection and design are generally limited to what can be cast or forged, limiting the permissible shapes, sizes, material compositions, capabilities, and effects. Multiple part sub-assembly structures (especially for mixed effect features) are typically used. These increase labor costs, part count, design, development, and production costs while reducing design options.

[0006] Conventional warhead manufacturing methods involve the design and fabrication of molds and other overhead that impedes the development of new warhead design concepts. This tooling requirement extends both the design and fabrication cycles, requires significant upfront and specialized infrastructure costs, and cannot efficiently support rapid prototyping activities.

[0007] The casting or forging techniques typically used to form bomb casings also require significant energy input to melt the material. Investments in forging plants can be prohibitively expensive and tend to limit suppliers to only a few manufacturers worldwide.

[0008] In pursuit of design freedom, Lockheed Martin has patented an additive manufacturing method for warhead casings that uses directed energy deposition of material. However, this method suffers from thermal distortion resulting from the concentrated application of heat to parts of the part, which can cause distortion and affect the recrystallization of the metal as it solidifies from the molten pool.

[0009] Other examples of the prior art include US 2410813A, Method of Forming Casings, Walter Dillon, 08 / 05 / 1942, which describes the basic casing manufacturing process. Instead of forging or casting the casing, the inventor describes a method in which heat is applied to and rolling a seamless steel tube to form the nose cone of the casing.

[0010] Another example of the prior art is US5305505A, Process of Making a Multi-Section Bomb Casing, Ellwood National Investment Corp, 12 / 03 / 1990, which describes a process for making a multi-section bomb casing that has the strength and spallation characteristics of a single piece casing. The casing is constructed from two or more alloy steel sections by friction welding techniques. Summary of the Invention [Problem to be solved by the invention]

[0011] It is an object of the present invention to overcome or substantially ameliorate one or more of the disadvantages of the prior art, or to provide a useful alternative. [Means for solving the problem]

[0012] In one aspect of the invention, a bomb casing is provided defining a generally conical nose portion and a cylindrical body portion, where at least one of the generally conical nose portion and / or the cylindrical body portion is formed from an additive manufacturing process.

[0013] Preferably, the additive manufacturing process is cold gas kinetic spraying of metal particles onto a support member.

[0014] In one embodiment, the generally conical nose portion and the cylindrical body portion are integrally formed, hi another embodiment, the bomb casing is of unitary construction.

[0015] In one embodiment, the generally conical nose portion and / or the cylindrical body portion may have a substantially uniform metallurgical property along its length, hi another embodiment, the generally conical nose portion and / or the cylindrical body portion may have a substantially uniform metallurgical property across each cross-section taken along its length.

[0016] Preferably, the support members are configured to mirror the intended configuration of the interior surfaces of the bomb casing.

[0017] The support member may be retained within the bomb casing after cryogenic gas kinetic spraying is completed. Alternatively, the support member may be retained within the bomb casing in one or more locations and removed from others after cryogenic gas kinetic spraying is completed. In other embodiments, the support member is removed in its entirety after cryogenic gas kinetic spraying is completed.

[0018] Preferably, the casing has metallic features along its axial location that define a rupture mechanism and / or rupture seam. In one embodiment, the rupture mechanism and / or rupture seam is defined by a geometric feature on the scaffolding and / or combines with a geometric feature on the final contour of the bomb casing. In one embodiment, the rupture mechanism and / or rupture seam is a line of weakness that extends axially and / or laterally along the cylindrical body portion.

[0019] In one embodiment, the metal particles sprayed to form the generally conical nose portion include a high density refractory metal or alloy.

[0020] In one embodiment, the generally conical nose section has the following characteristics: Ultimate tensile strength of over 1320MPa, Tensile strength at yield of over 1200MPa, Minimum elongation at break of 11% Penetration hardness of over 44 Rockwell C scale, and It has a density of greater than 7.86 g / cc.

[0021] Preferably, the metal particles deposited on the support member form an interlaced layer. In one embodiment, the interlaced layer extends in a circumferential direction. Preferably, the interlaced layer forming the cylindrical body portion has an elongated dimension extending parallel to the longitudinal axis of the cylindrical body portion.

[0022] The features and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments, given by way of example only, in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic diagram illustrating the major components of a cryogenic gas kinetic spray device. [Diagram 2] FIG. 2 is a side view of a robotic nozzle handling assembly. [Diagram 3] 1 is a partial cross-sectional side view of cryogenic gas kinetic spraying of material to form an embodiment of a casing. [Figure 4] FIG. 2 is a cross-sectional partial view of one embodiment of a casing. [Diagram 5] FIG. 13 is a cross-sectional partial view of another embodiment of a casing. [Figure 6] FIG. 13 is an isometric view showing hidden details of another embodiment of the casing. [Figure 7] FIG. 7 is a cross-sectional view of the embodiment depicted in FIG. [Figure 8] FIG. 13 is a side view showing hidden details of another embodiment of the casing. [Figure 9] FIG. 2 is a schematic cross-sectional close-up view of a portion of a casing sidewall depicting an interlaced grain formation created by the deposition of successive beads. [Figure 10] FIG. 13 is a schematic cross-sectional close-up view showing overlapping bead formation contributing to a smoother outer finish. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] For example, as shown in Figures 3-8, the illustrated embodiments of bomb casing 1 each define a generally conical nose portion 2 and a cylindrical body portion 3. At least one or the other of the generally conical nose portion 2 or the cylindrical body portion 3 is additively manufactured using additive manufacturing equipment. In the embodiment illustrated in Figure 5, it is only the generally conical nose portion 2 that is additively manufactured and then connected to the conventionally manufactured cylindrical body portion 3. More preferably, however, both the generally conical nose portion 2 and the cylindrical body portion 3 are additively manufactured. The latter is the type of manufacturing process that is primarily discussed below.

[0025] Some examples of additive manufacturing equipment use a heat source, such as a laser, electron beam, etc., to heat metal powder or wire. The heated metal then bonds to generate the desired three-dimensional object. The additive manufacturing equipment 4 used in a preferred embodiment of the process is configured for cold gas kinetic spraying of metal particles 5 contained within a gas stream emitted from at least one nozzle 6. In some embodiments of the manufacturing process, two or more nozzles 6 may be utilized to increase the manufacturing production rate. In one embodiment, the cold gas kinetic sprayed metal particles 5 are high strength steel. In another embodiment, the metal particles 5 sprayed to form the conical nose portion 2 are steel alloys, such as nickel-chromium-molybdenum alloy steel (SAE4340).

[0026] As best shown in Figures 1 and 2, the additive manufacturing equipment 4 includes a rotatable mandrel shaped to mate with a support member 8 (which may also be referred to as a substrate or scaffolding). A drive, such as an electric motor, is configured to rotate the mandrel, which in turn rotates the support member 8. This arrangement is suitable for producing casings with axial symmetry and is believed to be applicable to most bomb casing designs. This allows the support member 8 to rotate as material is deposited thereon, while the nozzle remains stationary or only moves slowly relative to it. This is more efficient compared to having to repeatedly displace the nozzle around the support member 8 while the support member 8 is stationary and material is deposited on the support member 8.

[0027] As best seen in Figures 3 and 4, the support member 8 is axially symmetrical and has a pre-machined outer surface that corresponds to the desired shape of the bomb casing to be manufactured. In one embodiment, the support member 8 is made from aluminum, preferably grade 6061 aluminum. In another embodiment, the support member 8 is made from copper.

[0028] As best shown in FIG. 1, the cold gas kinetic spraying apparatus includes an enclosure 11 into which high pressure process gas from a gas source 12 is supplied via a pair of circuits 13 and 14. It is desirable for the process gas to be relatively inert since it is undesirable for the process gas to react with the metal. Nitrogen is used as the process gas in the preferred embodiment because it is relatively inert and widely available at a relatively low cost. However, other embodiments use other inert gases such as, for example, helium and / or argon. The first circuit 13 supplies the high pressure process gas to a powder feed hopper 15 containing the metal particles 5. The second circuit 14 supplies the high pressure process gas to a heater 16. The two circuits converge to a nozzle 6 which has an on-board electric heater 17.

[0029] Two heaters 16 and 17 are used to ensure that the process gas stream has a temperature of 600°C to 800°C, most preferably 700°C, when it exits the nozzle 6. A process gas stream temperature below about 600°C may inhibit deformation of the metal particles upon impact with the part being formed by the cryogenic gas kinetic spraying equipment. A process gas stream temperature above about 800°C may lead to melting or excessive softening of the metal particles 5, which may lead to the particles breaking apart upon impact with the part, adversely affecting the spraying efficiency and the mechanical integrity of the part.

[0030] The arrangement of FIG. 1 can eject metal particles 5 from nozzle 6 at supersonic speeds typically exceeding 1000 m / sec. This provides the particles with sufficient kinetic energy to fuse with the support member upon impact. Importantly, the cold gas kinetic spraying process does not heat metal particles 5 beyond their melting point. Thus, the original structure and properties of metal particles 5 can be preserved without changes that may otherwise be caused by phase changes inherent in techniques that melt metals, such as forging and casting. Further details regarding cold gas kinetic spraying equipment are available in U.S. Pat. No. 5,302,414, the contents of which are incorporated herein by reference in their entirety.

[0031] As best shown in FIG. 2, the additive manufacturing equipment 4 also includes a robotic assembly in the form of a robotic arm 9 configured to position and orient the nozzle 6 to direct a spray of metal particles 6 onto the support member as it rotates. A programmable controller, which may be a suitably programmed general-purpose computing system or may be a dedicated control system, is configured to drive the robotic arm 9. That is, the programmable controller transmits command signals that are received by the robotic arm 9. These command signals define the configuration that the robotic arm 9 assumes, which ultimately defines the position and orientation of the nozzle 6. This in turn defines the trajectory of the metal particles 5 that are ejected from the nozzle 6 at very high speeds to impact and thereby bond to the support member 8. Over time, this deposition process builds up an outer layer of material that surrounds and is bonded to the support member 8, as shown, for example, in FIGS. 3 and 4.

[0032] As the nozzle 6 from which the metal particles 5 are discharged passes against the support member 8, beads 18 of material are deposited. The programmable controller may be configured to position and orient the nozzle 6 to drive the robotic arm 9 to deposit the beads 18 of metal particles 5 on the rotating support member 8 in the form of interlaced layers. As illustrated in FIG. 9, the interlacing effect is achieved by aligning the centers of the beads 18 forming the underlying layer with the edges of the beads 18 forming the layer immediately above. This is similar to the well-known manner in which bricks may be layered and interlaced to form a wall. Interlacing the layers of beads 18 effectively forms a granular structure, contributing improved directional strength properties to the finished casing. For casings intended to provide strong penetration performance, the interlaced layers of beads 18 extend in the circumferential direction because this contributes to increased tensile strength in the axial and circumferential directions. In other words, the interlaced layers of beads 18 forming the cylindrical body portion 3 have an elongated dimension extending parallel to the longitudinal axis of the cylindrical body portion 3 .

[0033] The composition of the metal particles 5 sprayed from the nozzle 6 may be altered as the positioning of the nozzle 6 changes relative to the support member 8. This may be accomplished by varying the composition of the material contained in the process gas stream as the position of the nozzle 6 changes relative to the support member 8. This technique may be used to vary the density of the material deposited between different parts of the bomb casing. This technique may also be used to vary the chemical properties of the material deposited between different parts of the bomb casing. For example, one embodiment utilizes multiple powder feed hoppers 15, with the composition of the contained metal particles 5 varying between the different hoppers 15. In this embodiment, the programmable controller is configured to issue command signals to define and change the particular hopper 15 to which the metal particles 5 are supplied for use in the cryogenic gas kinetic spray process. In an exemplary implementation of this embodiment, the first hopper 15 contains metal particles 5 with little or no high density refractory metal or alloy. The second hopper 15 contains metal particles 5 with a substantial proportion of high density refractory metal or alloy, such as any one of the following: 20% to 30% by weight of tungsten metal or alloys such as WC or WC_Ni14, 2% to 10% by weight of nickel metal or alloy, 3% to 4% by weight of vanadium metal or alloy, or 3% to 4% by weight of manganese metal or alloy.

[0034] These additives can improve the properties of the deposited material, such as ductility, elongation, density, strength and hardness. When programming the programmable controller, an operator can select the ratios of the various additives to tune for a particular desired property. This may require balancing or trade-offs between things, such as hardness versus ductility.

[0035] In this example, the programmable controller is programmed to send command signals to ensure that the metal particles 5 are fed from the first hopper 15, while the nozzle 6 is positioned and oriented relative to the support member 8 to deposit material forming the cylindrical body 3. However, when the nozzle 6 moves to a position and orientation relative to the support member 8 to deposit material forming the conical nose portion 2, the programmable controller issues command signals to the multiple powder feed hoppers 15 to feed the metal particles 5 from the second hopper 15. This ensures that the deposited material forming the conical nose portion 2 includes a high density refractory metal or alloy, and therefore has enhanced penetration properties. However, the cylindrical body 3 typically does not require such enhanced penetration properties, and therefore the material deposited to form the cylindrical body 3 does not need to include a high density refractory metal or alloy. In a slight variation, the programmable controller can be programmed to ensure that the deposited material forming the portion of the cylindrical body 3 adjacent to the generally conical nose portion 2 also includes a high density refractory metal or alloy. This allows the portion of the cylindrical body 3 adjacent the generally conical nose portion 2 to support the conical nose portion 2 .

[0036] In one embodiment of the bomb casing 1, the generally conical nose section 2 has the following desirable characteristics for penetration performance: Ultimate tensile strength of over 1320MPa; -Yield tensile strength of over 1200MPa, Minimum elongation at break of 11% -Penetration hardness of over 44 Rockwell C scale, and Has a density of over 7.86g / cc.

[0037] The programmable controller may also be programmed to vary various spray parameters depending on the positioning of the at least one nozzle 3 relative to the support member 8. Such parameters may include spray standoff distance, spray path linear velocity, and / or spray offset distance. For example, the programmable controller may be programmed to increase one or more of these parameters by 1% to 50%, inclusive, when the nozzle 6 is depositing material to form the cylindrical body portion 3. The increase is relative to the normal amount of the associated parameter when the nozzle 6 is depositing material to form the conical nose portion 2. Such variations to the spray parameters may be used to tailor properties such as decreasing the elongation at break of the deposited material forming the cylindrical body portion 3. This may enable the cylindrical body portion 3 to provide improved fragmentation performance, such as decreasing fragmentation from 10% to 15% to 7% to 8%, resulting in smaller, more uniform fragments.

[0038] In the context of bomb casing construction, it has been understood by the inventors of the present application that the median size of the metal particles 5 is preferably between 15 μm and 55 μm inclusive, with 53 μm being considered optimal for some embodiments of the process. Particles below 15 μm typically do not have enough energy to deform and adhere on impact with the support member 8. This is due to their low mass which translates to low kinetic energy after acceleration in the process gas stream. Particles above 55 μm typically are not accelerated to sufficient velocity due to their higher mass and therefore may not have enough energy to deform and adhere on impact with the part. Whether the particles are very large or very small, the undesirable effects of poor adhesion to the part are as follows: - Integrity of the lower part, porosity due to improperly fused particles, - Reduced spray efficiency due to powder not adhering to the part, and -Increased amount of waste powder treated by pollution control systems.

[0039] In the context of bomb casing construction, it has been understood by the inventors of the present application that it is preferred that the median hardness of the metal particles 5 be less than 30 Rockwell C. Powder hardness has been identified as a critical process variable in the cryogenic gas kinetic spraying of high strength ferrous alloys during empirical testing. The cryogenic gas kinetic spraying process relies on the particles flattening and adhering to the support member 8 upon impact, and the hardness of the particles directly impacts how efficiently this is accomplished. Excessive hardness of the metal particles may inhibit the particles from adhering to the part being formed. Instead, excessively hard particles may bounce off the surface, reducing process efficiency and increasing powder waste. Alternatively, excessive hardness may cause the particles to adhere but not flatten properly. This results in very high porosity and unacceptably low part strength. It has been empirically found that due to high hardness, the problem of particles not adhering is dramatically exacerbated as the spray jet impinges on the part at an angle away from the vertical. Metal powders with softer particles can be successfully sprayed at much shallower impact angles than harder powders. Hard powders result in a limiting impact angle at which particle adhesion appears to completely cease, which imposes constraints on the part geometry that can be built.

[0040] In the context of bomb casing construction, it has been understood by the inventors herein that a flow rate of metal particles 5 emitted from a single nozzle is preferred between 16 kg / hr and 35 kg / hr, with an optimal flow rate for some embodiments of the process being approximately 25-30 kg / hr. Below approximately 16 kg / hr, production rates are so low that it becomes uneconomical to use the cryogenic gas dynamic spray process for the manufacture of airborne bomb casings. Financial analysis has shown that the process is cost-competitive with conventional manufacturing methods above approximately 16 kg / hr per spray head. When powder flow rates exceed 35 kg / hr per spray head, problems may arise with managing the formation heat of the parts being manufactured by the cryogenic gas dynamic spray process. The formation process results in localized heat where the spray jet impinges on the part and this heat is distributed through the part by thermal conduction. Heat is removed from the part primarily by natural and forced convection. It is currently theorized that flow rates higher than 35 kg / hr per spray head of powder may be achieved by managing the heat buildup within the part through cooling methods.

[0041] In the bomb casing construction context, it has been understood by the inventors of the present application that the spray standoff distance between the nozzle exit and the substrate is preferably between 15 mm and 50 mm inclusive, with the optimum distance being approximately 15 mm to 25 mm. As the distance from the nozzle 6 increases, the diameter of the spray jet increases due to the divergence of the jet. Due to this effect, the width of the bead 18 of deposited material increases and the maximum thickness of the bead 18 decreases as the offset distance increases. The velocity of the spray jet also decreases with increasing offset distance. An offset distance of less than approximately 15 mm may result in the bead 18 being deposited being very thick and narrow, resulting in insufficient localized heat dissipation. Excessive localized heat in the formation of the bead 18 may adversely affect the metallurgy of the part being formed by the cryogenic gas dynamic spray process. An offset distance of more than approximately 50 mm may result in very low impact velocities, especially for particles on the outer layer of the beam. This may adversely affect the spray efficiency and may lead to increased porosity and reduced mechanical integrity of the part.

[0042] In the context of bomb casing construction, it has been understood by the inventors of the present application that a spray path linear velocity between 0.5 m / s and 1.5 m / s is preferred, with an optimal velocity for some embodiments being approximately 1.0 m / s. In the context described above where the support member rotates while spraying occurs, the spray path linear velocity can be calculated from the rotational speed and diameter of the part being formed at the location where the bead 18 is being deposited. If the spray path linear velocity is less than 0.5 m / s, the deposited bead 18 can become too thick. Additionally, localized heating can become excessive at the location of impact. At spray path linear velocities greater than 1.5 m / s, the bead 18 can become too thin and porosity at the outer edge of the bead 18 can increase unacceptably. As shown in FIG. 3, when spraying a conical nose section 2 at a location toward the tip of the casing, the rotational speed required to achieve a linear path velocity greater than 0.5 m / s can be excessive due to the small diameter of the tip. To compensate for this, it may be necessary to program the robotic arm 9 to displace the nozzle 6 around the tip of the conical nose portion 2 in a rotational direction opposite to the direction in which the support member 9 is rotating.

[0043] In the context of bomb casing construction, it has been realized by the inventors herein that it is preferable for the spray path overlap between adjacent beads 18 to be between 30% and 60% of the spray path overlap, which may result in minimal overlap of two adjacent beads 18. This helps to create a smoother finish on the exterior surface, for example, as illustrated in Figure 10. The objective is for adjacent beads 18 to overlap such that the combined thickness of their shallow sections adds up to a thickness approaching the maximum thickness of a single bead 18.

[0044] The cold gas dynamic spray process continues until deposition creates the desired sidewall thickness, shape, and overall casing properties, as illustrated in Figure 3. Some examples of the resulting casings are shown in Figures 4-8.

[0045] An embodiment of the manufacturing process includes heat treating the bomb casing once the cryogenic gas kinetic spraying is completed. This heat treatment is generally very similar to the heat treating steps used in conventional bomb casing manufacturing processes, however, it is anticipated that substantially less total energy may be required when heat treating an embodiment of the present invention. This is primarily due to the desirable properties discussed above that result from the lack of melting of the metal particles 5 during the cryogenic gas kinetic spraying process.

[0046] After heat treatment of the bomb casing, at least one further layer of metal, ceramic, energetic material, or any combination thereof may be applied to at least a portion of the outer surface of the bomb casing by cryogenic gas kinetic spraying. The composition of this final layer may be selected to increase the bomb casing's potential lethality, improve its shelf life, and / or create radiation shielding.

[0047] The final step in the process of manufacturing the bomb casing is the machining of the exterior and / or interior surfaces of the bomb casing. Such machining steps are very similar to those performed in conventional casing manufacturing methods. In some embodiments, this machining may remove some or all of the material that originally comprised the support member 8. In other embodiments of the method, the support member 8 is retained entirely within the bomb casing, for example, as illustrated in FIG. 3.

[0048] In some embodiments, the generally conical nose portion 2 and the cylindrical body portion 3 are integrally formed, for example as shown in Figures 3, 4, 6, 7, and 8. Thus, in some embodiments, the resulting bomb casing may be considered to be a unitary structure.

[0049] It will be appreciated that if the same metal particles 5 are used throughout, and if all other spray parameters are held constant, the generally conical nose portion 2 and the cylindrical body portion 3 may each have substantially uniform metallurgical properties along their lengths. Alternatively, the metal particles utilized and / or other spray parameters may be adjusted to create a bomb casing in which the generally conical nose portion 2 and / or the cylindrical body portion 3 have substantially uniform metallurgical properties across each cross-section taken along their lengths.

[0050] The casing embodiments may be designed with metallurgical properties that define the rupture mechanism and / or rupture seam. In one embodiment, the rupture mechanism and / or rupture seam are defined by geometric features, such as channels, provided on the scaffolding and / or combined with geometric features on the final profile of the bomb casing. In another embodiment, the rupture mechanism and / or rupture seam are lines of weakness that extend axially and / or laterally along the cylindrical body portion. These lines of weakness are established during the cryogenic gas kinetic spray process by programming the programmable controller to change one or more spray parameters when depositing material within the proposed areas of weakness. This may involve establishing changes in any spray parameters that affect the strength of the deposit, such as changes in metal particle composition, deposit density, bead deposit geometry, etc.

[0051] It will be appreciated by those skilled in the art that the present invention provides a number of important practical advantages over conventional bomb casing manufacturing methods that rely on casting or forging. As previously discussed, conventional casting or forging manufacturing methods limit design freedom. In comparison, the additional methods of the present invention allow the freedom to customize manufacturing parameters without requiring extensive and expensive retooling of a production line or access to a foundry. The additional methods of the present invention allow for easy and economical experimentation and prototype development. Additionally, embodiments of the present invention provide a mass production method that offers cost advantages over conventional methods.

[0052] The low temperature spray deposition process allows for a variety of design flexibility, including: 1. Variation of deposition parameters to provide design flexibility with variations in metallurgical properties in various parts of the casing. This can assist in providing features such as rupture mechanisms and / or rupture seams. 2. Design flexibility with variation in metal powders used to form various parts of the casing. This may allow for mixing multiple pre-selected metal types in a pre-determined ratio to achieve required properties such as hardness. In one embodiment, the warhead is provided with additional hardness in the conical nose section 2 compared to the hardness of the bulk of the cylindrical body section 3. This may be achieved by spraying materials including high density refractory metals or alloys thereof, such as tungsten, WC, WC Ni14, etc., to form the conical nose section 2. It will be appreciated that high density refractory materials result in increased weight and increased kinetic energy when the bomb is in motion. 3. Flexibility in design in that the bomb casing 1 can be fabricated by depositing multiple beads 18 that form layers that impart granular directional strength characteristics.

[0053] While several preferred embodiments have been described, it will be understood by those skilled in the art that numerous variations and / or modifications may be made thereto without departing from the spirit or scope of the invention as broadly described. The present embodiments are therefore considered in all respects to be illustrative and not restrictive.

Claims

1. 1. A bomb casing defining a generally conical nose portion and a cylindrical body portion, wherein at least one of the generally conical nose portion and / or the cylindrical body portion is formed from an additive manufacturing process.

2. 10. The bomb casing of claim 1, wherein the additive manufacturing process is cryogenic gas kinetic spraying of metal particles onto a support member.

3. 2. A bomb casing as defined in claim 1, wherein said generally conical nose portion and said cylindrical body portion are integrally formed.

4. 2. A bomb casing as claimed in claim 1, wherein said bomb casing is of unitary construction.

5. 2. A bomb casing as claimed in claim 1, wherein said generally conical nose portion and / or said cylindrical body portion have substantially uniform metallurgical properties along their length.

6. 2. A bomb casing as claimed in claim 1, wherein said generally conical nose portion and / or said cylindrical body portion have substantially uniform metallurgical properties across each cross-section taken along its length.

7. 3. The bomb casing of claim 2, wherein said support members are configured to mirror the intended configuration of an interior surface of said bomb casing.

8. 10. A bomb casing as claimed in claim 2 or 7, wherein said support members are retained within said bomb casing after cryogenic gas kinetic spraying is completed.

9. 10. A bomb casing as claimed in claim 2 or 7, wherein the support members are retained within the bomb casing at one or more locations and removed from other locations after cryogenic gas kinetic spraying is completed.

10. 10. A bomb casing as claimed in claim 2 or 7, wherein said support members are completely removed after cryogenic gas kinetic spraying is completed.

11. 10. The bomb casing of claim 1, wherein said casing has metallic features that define a rupture mechanism and / or a rupture seam.

12. 12. A bomb casing according to claim 11, wherein the rupture mechanism and / or rupture seam are defined by geometric features on the scaffold and / or combined with geometric features on the final contour of the bomb casing.

13. 13. A bomb casing as claimed in claim 11 or 12, wherein the rupture mechanism and / or rupture seam is a line of weakness extending axially and / or laterally along the cylindrical body portion.

14. 3. The bomb casing of claim 2, wherein said metal particles sprayed to form said generally conical nose portion comprise a high density refractory metal or alloy.

15. A generally conical nose section having the following characteristics: Ultimate tensile strength of more than 1320 MPa; A yield tensile strength of more than 1200 MPa; Minimum elongation at break of 11%; A penetration hardness of greater than 44 Rockwell C scale, and 10. The bomb casing of claim 1 having a density greater than 7.86 g / cc.

16. 2. A bomb casing as claimed in claim 1, wherein said metal particles form interlaced layers as they are deposited on said support member.

17. 17. A bomb casing as claimed in claim 16, wherein said interlaced layers extend circumferentially.

18. 18. A bomb casing as claimed in claim 16 or 17, wherein the interlaced layers forming the cylindrical body portion have an elongated dimension extending parallel to a longitudinal axis of the cylindrical body portion.

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