Patent Description:
Restrictions on the use of certain cluster-type munitions have led militaries to pursue other armaments which may achieve similar net results without running foul of international agreements. Various types of munitions have been proposed as substitutes and while each of these munitions has tangible benefits to their use, they each have associated drawbacks as well.

For example, smart munitions or munitions which are directed by GPS, are one recent development which has been touted as a substitute for cluster-type munitions. Smart munitions provide greater accuracy thereby potentially reducing the number or size of munitions required to neutralize a given target. However, these munitions are limited in the amount of targets that may be engaged by a single munition. Additionally, the GPS module and associated components which provide the guidance to the munition add increased expense and complexity to the munition.

Fragmentation warheads are another type of armament which may be employed in place of cluster munitions. Fragmentation warheads allow for the engagement of multiple targets with a single warhead. Large caliber gun launched munitions ranging from <NUM> mortars up through <NUM> artillery projectiles typically uses fragmentation as its primary target defeat mechanism. Although blast wave effects also contribute to lethality, it is generally a secondary mechanism of defeat.

The fragments produced by the munitions are very specific to the type of explosive, quantity of explosive and the steel thickness. Each munition will generally produce a normal distribution of fragments based on test data. A normal distribution allows the munition to defeat a wider range of targets but is not optimized for any specific targets. Target defeat is a function of number of each specific sized fragments produced, fragment velocity, fragment shape, and total number of fragments. However, current methods to produce these warheads are not ideal.

One approach involves the insertion of perforated flexible metal sheet liners into the warhead to reliably create patterned fragments out of the metal shell casing. However, this method is not easily compatible with current manufacturing methods and many munition warhead designs such as common artillery munitions. In artillery munitions such as <NUM> artillery munitions, the diameter of the fuze well opening at the top of a metal artillery warhead shell casing is much smaller than the internal diameter of the main portion of the shell casing. Additionally, the liner cannot conform to the tapered end of the shell casing without significant gaps and spaces between the sheet and the internal metal surface. When explosive fill is added into the shell casing from the top fuze well hole, the potential for voids and cracks in these gaps becomes very high. Such voids and cracks in the explosive fill create a safety hazard for both personnel and material. The probability of the explosive fill pre-detonating in the gun tube becomes extremely high due to the abrupt high speed movement of the explosive fill into these voids and cracks due to the extreme setback G-forces experienced during gun-launch.

As an alternative to metal liners, warhead cases may be scored with a fragmentation pattern by mechanical means. However, this process is time consuming, machine intensive, and limited in the type of patterns that can be produced. Additionally, it is impractical to score internal surfaces of the artillery munitions due to dimensional limitations of the fuze well opening described above.

Finally, another approach has been to score warhead cases with a fragmentation pattern by electron beam welding. Again, this process is time consuming, machine intensive, and limited in the type and location of patterns. Electron beam welding has the additional disadvantage of being ineffective in reliably producing patterned fragments.

Accordingly, there is a need for a cost-effective and timely method of manufacturing fragmentation warheads, especially those optimized against specific targets. <CIT> relates to annealing treatment for controlling warhead fragmentation size distribution. It discloses a method for controlling the size and shape of fragments produced by a steel warhead casing having the nominal composition <NUM>% C, <NUM>% Mn, <NUM>% P, <NUM>% Si, <NUM>% S, <NUM>% Al and a balance of Fe wherein the percentages are by weight, said method comprising the steps of:.

<CIT> relates to Charge Case fragmentation Control for Gun Survival. It claims a shaped charge comprising an outer case, an inner liner and an explosive material retained between the outer case and the inner liner, wherein the outer case comprises one or more predefined fracture lanes.

<CIT> relates to an incendiary projectile, and a method of introducing the incendiary composition into the projectile. The projectile is to have a structured coating of an incendiary composition on its inner surface and an explosive material filler for defined fragmentation disintegration of its wall structure, the explosive material filler extending to the structured coating and the coating defining a grid-shaped channel structure, the method comprising the steps of:.

<CIT> relates to a system and method for explosively stamping a selective fragmentation pattern. According to this specification a selective fragmentation pattern of explosive material is applied to the inside surface of a munition arranged so that none, some or all of that explosive material may be detonated thus to etch a preselected fragmentation pattern, this explosive material application being followed by completing assembly of the munition.

<CIT> relates to a warhead in which aspects such as a fragmentation pattern are created by forming the warhead itself with different deposited metal layers.

<CIT> relates to a projectile in which a fragmentation pattern comprising intersecting helical grooves are formed on the exterior or the interior by machining or laser cutting.

According to the present invention there is provided a method according to appended claim <NUM>.

The method may comprise a further step of depositing a stress protection material evenly over both the exposed portion of the interior surface and the portion covered by the protective material. This stress protection material may also be applied with a <NUM>-D printer.

The <NUM>-D printer may be inserted into the cavity interior via a fuze well opening thereto. Whether or not a stress protection layer is deposited the method then comprises filling the warhead casing with explosive.

According to a feature of the invention the method may comprise as a precursor step at least one of:.

The depth differential between a stress raiser or raised surface and the warhead interior surface may be between <NUM> and <NUM>.

The method may be arranged to provide a rectangular, bow tie, helix, triangular or diamond shaped fragmentation pattern with a maximum dimension of <NUM> to <NUM>.

Preferably the warhead (<NUM>) casing comprises HF-<NUM> Steel.

The accompanying figures further illustrate the present invention.

The components in the drawings are not necessarily drawn to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. In the drawings, like reference numerals designate corresponding parts throughout the several views.

The present invention relates to a system and method for removing or depositing material on a warhead casing to create a fragmentation pattern. Lithographic and other techniques are employed to create a fragmentation pattern on a surface of a warhead casing thereby enabling the creation of a desired pattern of fragments upon detonation of the warhead. A reductive (i.e. etching) or additive (i.e. deposition) process creates a thickness differential in the warhead casing which produces a natural stress raiser in the presence of an explosive blast wave. The stress raiser causes the warhead casing to fragment in a predictable and desired manner based on the fragmentation pattern. Patterned fragmentation for munitions is more desirable than natural fragmentation since it provides more consistent efficient target engagement efficiency on a per round basis for more "stowed kills" before a weapon system needs to supplied with more munitions. "Stowed kills" provides a measure of the lethality of a weapon system, that is, if a weapon such as an artillery shell has a potential lethality of <NUM> targets and <NUM> artillery shells can be carried, then the stowed kills is <NUM> targets.

Advantageously, the method for creating the fragmentation patterns described herein allows for efficient and effective manufacture of warhead casings patterned with fragmentation patterns. The fragmentation pattern creation process is adaptable to current processes in the manufacturing of warhead casings. Further, by employing the processes described below, the rate of creating fragmentation patterned warhead casings is increased over current technologies relying on electron beam welding or mechanical etching processes.

Additionally, the methods described herein allow for a variety of complex patterns to be created thereby increasing the versatility of certain ammunitions. Complex patterns may be created on warhead casings to create fragments with desired properties such as increased lethality against specific targets or unique aeroballistic properties.

The below methods also allow for the use of both high grade high fragmentation steel (i.e. HF-<NUM> steel) as well as other more commonly available forms of steel. For example, more commonly available types of carbon steel types, alloy steel, stainless steel or tool steel produced in a variety of means may be used in place of HF-<NUM> steel to produce similar results. Initial tests performed indicate that desired fragment patterns are produced by employing the methods described herein on both HF-<NUM> steel and more commonly available steel. By applying the method for creating fragmentation patterns described herein, the industrial base of suppliers for warhead casings is greatly increased.

While the methods described below may be used to create a fragmentation pattern on a variety of munitions and surfaces, they are particularly suited for the creating fragmentation patterns on an interior surface of artillery and mortar warhead cases. It is difficult to produce fragmentation patterns on artillery and mortar warhead cases with prior art methods due to their unique construction and dimensions. The one piece construction of the warhead casing and relatively narrow opening on the top of the warhead compared to their internal diameter are not conducive to the insertion of liners or other mechanical or electronic machinery. However, the below methods may be employed to create complex fragmentation patterns on an interior surface of the warhead casing without altering the warhead casing or its methods of manufacture.

<FIG> shows an artillery casing with a cutaway section exposing an interior surface <NUM> of the casing etched with a fragmentation pattern, in accordance with an illustrative embodiment of the invention. The artillery casing <NUM> is part of an artillery warhead suitable for use with an artillery weapon system. For example, the artillery casing <NUM> may be a casing <NUM> for an M795 <NUM> warhead employed by the United States Army for use in an artillery piece such as the M777 howitzer.

While an artillery casing <NUM> is shown in <FIG> and an artillery casing <NUM> is used throughout this specification to illustrate the system and method of creating a fragmentation pattern on an interior surface <NUM> of a warhead casing <NUM>, the system and methods for creating a fragmentation pattern are not limited to an artillery or mortar shell. The system and method described herein are suitable for any munition which may comprise a fragmentation pattern such as missile propelled warheads or medium caliber fragmentation grenades. Additionally, the system and method may be employed for etching or depositing materials on a surface other than a fragmentation pattern. The methods of selectively etching or depositing material on a surface may be employed on a wide variety of devices such as handguns, bullets or any other surface on which a portion of the material is desired to be etched or covered with additive material.

The artillery casing <NUM> is an integral unit having a cylindrical bottom or breech section topped by a conical section at the muzzle or fuze end of the warhead. The warhead casing <NUM> is hollow thereby forming an interior cavity. The interior cavity is accessed via a single fuze weld opening <NUM> at the top or muzzle end of the warhead.

In an embodiment of the invention, the artillery casing <NUM> is composed of high fragmentation (HF1) steel. In other embodiments, the artillery casing <NUM> may be comprised of other variants of steel or any another material suitable for use in a fragmentation warhead casing.

The interior surface <NUM> of the artillery casing <NUM> includes a fragmentation pattern etched into the surface. While the fragmentation pattern shown in <FIG> and <FIG> is a grid-like pattern, the fragmentation pattern is not limited to a grid-like pattern. Other fragmentation shapes are also easily produced based on the pattern of the source image being replicated. The function of the warhead will dictate the fragmentation pattern with the shape of the positive image being designed to optimize the shape and velocity of the resultant warhead fragments. Advantageously, the system and method for etching the fragmentation pattern is adaptable to a wide variety of fragmentation patterns including fragmentation patterns which are impractical to mechanically score on artillery casing <NUM> using known techniques. It is an advantage of the methods described below that these processes allow for a variety of patterns to be created depending on the desired effect of the warhead.

For example, <FIG> and <FIG> show alternate fragmentation patterns which are particularly suited for being created using the below described methods. <FIG> is an artillery casing with a cutaway exposing an interior surface of the casing etched with a bow-tie fragmentation pattern, in accordance with an illustrative embodiment of the invention and <FIG> is an artillery casing with a cutaway exposing an interior surface of the casing etched with a helix fragmentation pattern, in accordance with an illustrative embodiment of the invention. The warhead casing <NUM> of <FIG> is configured for producing warhead fragments having a bow-tie shape upon detonation and the warhead casing of <FIG> is configured for producing warhead fragments having a diamond shape upon detonation. Whereas, the creation of these patterns using existing methods, such as mechanical scoring, would be difficult, each of these patterns is particularly suited for being created using the methods described herein.

Similarly, while the fragmentation pattern shown in <FIG> and <FIG> encompasses the entire inner surface, the fragmentation pattern may cover only a portion of the surface of the warhead depending on the desired effect. While the warhead casings <NUM> shown in <FIG> and <FIG> show a warhead casing <NUM> with a fragmentation pattern created on an interior surface <NUM> of the warhead casing <NUM>, it will be appreciated that the fragmentation may be formed on an outer surface of the casing <NUM> (though this may not be within the scope of the claims) or on a combination of both the outer and inner surfaces.

The artillery casings shown in <FIG> shows the etched portion of the fragmentation pattern forming a cut-out in the artillery casing having a triangular cross section. However, the etched portion of the fragmentation pattern may form a cut-out having a different cross-section depending on the method of manufacture and intended use. <FIG> shows a portion of an interior surface of an artillery casing etched with a negative image of a grid fragmentation pattern, in accordance with an illustrative embodiment of the invention. The artillery casing shown in <FIG> shows the etched portion of the fragmentation pattern forming a cut-out in the artillery casing having a rectangular cross-section.

Similarly, the artillery casing in <FIG> shows the protruding portion of the fragmentation pattern having a triangular cross section. The artillery casing in <FIG> shows the protruding portion of the fragmentation pattern having a rectangular cross-section.

The grid-like fragmentation pattern shown in <FIG> corresponds to a positive image of the fragmentation pattern in which the pattern is formed of the desired fragment shapes being thicker in depth than the lines delineating those shapes. The rectangular fragment regions <NUM> of the fragmentation pattern are delineated by a negative image of the pattern, intersecting recesses or grooves <NUM> etched into the warhead casing <NUM>. As will be described below, this differential is created through either a reductive or additive process. For example, the negative image <NUM> of the fragmentation pattern may be etched or the positive image <NUM> may be increased in thickness or some combination of the two may be employed to achieve the desired result. The differential between the positive and negative regions of the fragmentation pattern is of a sufficient depth to create a natural tension raiser in the presence of a detonation blast wave but not of a depth to affect the structural integrity of the casing <NUM>.

In an embodiment of the invention in which the warhead casing is a <NUM> warhead casing such as an M795 <NUM> high explosive projectile, the differential between the positive and negative regions of the fragmentation pattern is approximately <NUM> (<NUM> inches). Initial testing of similar munitions with patterns created using the below described inventions have shown that a <NUM> (<NUM> inch) groove of a pre-defined pattern have yielded fragment pattern similar to the pre-defined pattern. In other embodiments and depending on the desired performance, the differential may be greater than or less than <NUM> (<NUM> inches) for example <NUM> to <NUM>.

In embodiments of the invention, a negative image of the fragmentation pattern may be created on the warhead casing <NUM>. <FIG> shows an artillery casing <NUM> with a cutaway section exposing an interior surface <NUM> of the casing <NUM> etched with a negative image of the fragmentation pattern, in accordance with an illustrative embodiment of the invention. In the negative image of the fragmentation pattern, the rectangular shapes <NUM> corresponding to the desired fragments is of a reduced thickness while the lines <NUM> delineating those shapes is at an increased thickness.

Initially, the warhead casing <NUM> is provided without a fragmentation pattern. The warhead casing <NUM> may be provided from a manufacturing line, either integrated or separate, or may be an existing warhead casing that is being retrofitted to create a fragmentation pattern. The fragmentation pattern is created through either a reductive or additive process through the methods described herein. Subsequent to creation of the fragmentation pattern, the interior cavity of the warhead is filled with an explosive fill and outfitted with a fuze or similar device to facilitate detonation of the warhead by a weapon system. In operation, the material thickness differential of the fragmentation pattern in the warhead casing <NUM> is configured for creating a natural stress raiser across the pattern when hit by a detonation wave of the warhead's explosive fill. Accordingly, the warhead casing <NUM> fragments in known areas and produces predictably sized fragments corresponding to the positive image of the fragmentation pattern. Patterned fragmentation for munitions is more desirable than natural fragmentation since it provides more consistent efficient target engagement efficiency on a per round basis for more "stowed kills" before a weapon system needs to supplied with more munitions.

In an embodiment, the fragmentation pattern of the warhead casing <NUM> is created through a lithographic process. A warhead casing <NUM> is provided without a fragmentation pattern. The warhead casing <NUM> may be patterned as a set of steps during initial manufacture of the warhead casing <NUM> or warhead casings <NUM> may be provided subsequent to manufacture at a separate facility. Advantageously, the method for creating the fragmentation pattern is compatible with current manufacturing practice and the warhead casing <NUM> can be manufactured according to currently employed manufacturing techniques. The unpatterned warhead casing <NUM> undergoes the lithographic process to create the fragmentation pattern on a surface of the casing <NUM>. As will be described below, the lithographic process may be reductive, additive or a combination of the two.

<FIG> is a is a flowchart illustrating steps for a method of etching a fragmentation pattern into a warhead with a lithographic process, in accordance with one illustrative embodiment of the invention. <FIG> illustrates the warhead casing <NUM> undergoing the method of etching a fragmentation pattern into the warhead casing <NUM> with a lithographic process, in accordance with an illustrative embodiment of the invention.

In step <NUM>, a photosensitive material coating <NUM> is applied to the interior surface <NUM> of the warhead casing <NUM>. The photosensitive material coating <NUM> may be any material which hardens in the presence of light radiation. For example, in an embodiment of the invention, the photosensitive material <NUM> is a photoresist material. In another embodiment of the invention, the photosensitive material <NUM> is a light cure resin based polymer composite such as those commonly used in the dental health field.

In an embodiment, the photosensitive material coating <NUM> is applied via a photosensitive material applicator which is inserted into the interior cavity of the warhead casing <NUM>, such as via the fuze weld opening <NUM>. The photosensitive material applicator sprays a coating of photosensitive material <NUM> on the interior surface <NUM> of the warhead casing <NUM>. Alternatively, the applicator may paint the coating onto the interior surface <NUM> of the warhead casing <NUM>. In alternative embodiments in which a photosensitive material applicator is not employed, the photosensitive material <NUM> may be applied via a vapor deposition process or in the alternative, the warhead casing <NUM> may be dipped in photosensitive material <NUM> to coat the inner surface.

In embodiments of the invention, prior to applying the photosensitive material <NUM>, the interior surface <NUM> of the warhead casing <NUM> is conditioned for receiving the photosensitive material <NUM>. In such an embodiment, one or more of the following steps may be performed on the interior surface <NUM> of the warhead casing <NUM>: cleaning the interior surface <NUM> of the warhead; dehydrating the interior surface <NUM> of the warhead; and applying an adhesive promoter to the interior surface <NUM> of the warhead.

In embodiments of the invention, the warhead casing <NUM> is then spun about an axis, such as a longitudinal axis, to ensure an even distribution of photoresistive material coating on the interior surface <NUM> of the casing <NUM>. For example, the warhead casing <NUM> may be secured to a base configured for spinning the casing <NUM> around a longitudinal axis running through the fuze weld opening <NUM>. Alternatively, the warhead casing <NUM> may be suspended by a spinning arm to evenly distribute the material within the casing <NUM>.

In step <NUM>, a portion <NUM> of the photosensitive material coating <NUM> is exposed to light radiation thereby curing that exposed portion <NUM>. In a preferred embodiment, a positive image of the fragmentation pattern is projected onto the interior surface <NUM> of the warhead casing <NUM> thereby exposing the desired fragment shapes <NUM> to light radiation. However, in an alternative embodiment, a negative image of the fragmentation pattern is projected onto the interior surface <NUM> of the warhead casing <NUM>, thereby exposing the lines <NUM> delineating the fragment shapes <NUM> to light radiation.

<FIG> shows a light source projecting a light image of the fragmentation pattern onto an interior surface <NUM> of a warhead casing <NUM>, in accordance with an embodiment of the invention. In this embodiment, a photomasked light source assembly <NUM> is inserted into the internal cavity of the warhead casing <NUM>. The light source assembly <NUM> comprises a support <NUM>, a light source <NUM> and a mask <NUM>. The light source <NUM> further comprises a bulb emitting selected to produce light radiation at a frequency tuned to cure the photosensitive material <NUM>. For example, the light radiation may be at an ultraviolet frequency for photosensitive materials which cure when exposed to light radiation at an ultraviolet frequency.

To project the positive image of the fragmentation pattern onto the interior surface <NUM>, the light source is surrounded by a mask <NUM> of the negative image of the fragmentation pattern. The mask <NUM> is offset from the light source <NUM> a predetermined distance and the openings in the mask <NUM> are sized and dimensioned to produce, in conjunction with the light source <NUM>, a positive image of light of the fragmentation pattern at a desired size on the interior surface <NUM> of the warhead casing <NUM>. In the embodiment shown in <FIG>, the openings in the mask may be longer or angled to compensate for their increased distance from the warhead casing <NUM>. In other embodiments, the light source assembly may extend the entire depth of the warhead casing <NUM>.

As shown in <FIG>, the positive image of the fragmentation pattern is projected onto the inner surface of the warhead casing <NUM>. Rectangular fragments <NUM> are projected in light and the grid lines <NUM> delineating those fragments are in shadow.

The entire interior surface <NUM> may be simultaneously exposed to the positive image of the fragmentation pattern such as by a light source emitting light in three hundred and sixty degrees. Alternatively, the light source, mask or both may be rotated around the interior cavity of the warhead casing <NUM> to incrementally expose the interior surface <NUM>.

After a length of time dependent on the material properties and thickness of photosensitive material <NUM>, the intensity of the light source and other environmental factors, such as temperature, the portion of the photosensitive material <NUM> exposed to the light radiation (i.e. the positive image of the fragmentation pattern) is cured by the light radiation.

In alternative embodiments, the light source is not masked but rather a mask is inserted into the internal cavity of the warhead such that an outer surface of the mask is in contact with the photosensitive material <NUM> or the inner surface of the warhead casing <NUM>. For example, the mask diameter may be compressed to fit through the fuze weld opening <NUM> of the warhead casing <NUM> and then once inserted, expanded to cover the interior surface <NUM> of the warhead casing <NUM>.

In step <NUM>, the unexposed portion <NUM> of the photosensitive material <NUM> coating is removed, such as via a chemical wash or an ionic process. The chemical wash removes the uncured unexposed portion <NUM> of the photosensitive material <NUM>, however, due to the curing process, the exposed positive image <NUM> of the fragmentation pattern remains on the interior surface <NUM> of the warhead casing <NUM>. In the embodiment of the invention in which a positive image of the fragmentation pattern is projected onto the interior surface <NUM>, the removed photosensitive material <NUM> corresponds to the negative image of the fragmentation pattern (i.e. the lines delineating the shapes).

In step <NUM>, an etchant material <NUM> is applied to the interior surface <NUM> of the warhead casing <NUM>. The etchant material <NUM> is a material chosen such that the bare portion of the interior surface <NUM> in which the photosensitive material <NUM> has been removed is etched by the material whereas the portion of the warhead casing <NUM> covered by the cured photosensitive material <NUM> remains untouched by the etchant material. The etchant material may be a chemical etchant. The chemical etchant may be acidic or basic such Nital (i.e. alcohol and nitric acid). In other embodiments, the etchant material <NUM> may be an etchant for use in an electrochemical process.

In step <NUM>, after an amount of time suitable for the etchant material to etch the interior surface <NUM> to a depth sufficient to create a differential which will result in a natural stress raiser in the presence of an explosive blast wave, the etchant material <NUM> and the cured photosensitive material <NUM> are removed from the interior surface <NUM> of the warhead casing <NUM>. The negative image of the fragmentation pattern has been etched into the interior surface <NUM> of the warhead casing <NUM>.

An additive lithographic process may also be employed to create the thickness differential in the warhead casing <NUM>. <FIG> is a flowchart illustrating steps for a method of creating a fragmentation pattern onto a warhead casing <NUM>, according to an illustrative embodiment of the invention. <FIG> illustrates the warhead casing <NUM> undergoing the method of creating a fragmentation pattern into the warhead casing <NUM>, in accordance with an illustrative embodiment of the invention.

In step <NUM>, the photosensitive material coating <NUM> is applied to the interior surface <NUM> of the warhead casing <NUM>. The photosensitive material coating <NUM> is applied in a similar manner as described in step <NUM> of <FIG>.

In step <NUM>, a portion <NUM> of the photosensitive material coating <NUM> is exposed to light radiation thereby curing that exposed portion <NUM>. In a preferred embodiment, a portion <NUM> corresponding to the positive image of the fragmentation pattern is exposed (i.e. the desired fragmentation shapes <NUM>). However, in an alternate embodiment, the portion exposed to the light radiation corresponds to the negative image of the fragmentation pattern (i.e. the lines <NUM> delineating the fragmentation shapes). The step of exposing the portion of the photosensitive material coating <NUM> to light radiation is performed in a similar manner as described in step <NUM> of <FIG>.

In step <NUM>, the unexposed portion <NUM> of the photosensitive material coating <NUM> is removed, such as via a chemical wash. The chemical wash removes the uncured unexposed portion <NUM> of the photosensitive material <NUM>. However, due to the curing process, the exposed positive image <NUM> of the fragmentation pattern remains on the interior surface <NUM> of the warhead casing <NUM>.

In certain embodiments in which an additive lithographic process is used to create the fragmentation pattern, the photosensitive material <NUM> is chosen with material properties which when cured, provides stress protection sufficient for further manufacture of the warhead and to create natural stress raiser in the presence of an explosive blast wave.

In other embodiments in which an additive lithographic process is used to create the fragmentation pattern, in step <NUM>, a protective coating <NUM> is deposited onto the interior surface <NUM> of the warhead casing <NUM>. The protective coating <NUM> is deposited with a uniform thickness over both the exposed portion of the interior surface <NUM> and the portion covered by the photoresistant material <NUM> thereby preserving the thickness differential between the formed by the exposed portion and unexposed portion <NUM>. The thickness differential in the protective coating <NUM> is sufficient to cause a natural stress raiser in the presence of an explosive blast wave.

In an embodiment of the invention, the protective coating <NUM> is a metal coating applied via a laser powder forming or cold spray process. In one embodiment, the protective coating <NUM> is a steel coating.

The method of creating a fragmentation pattern on a warhead is not limited to a lithographic process and can be achieved through other means. A stencil or silk screen may be employed to apply an additive protective material over a portion of the interior surface <NUM> corresponding to the positive image of the fragmentation pattern during etching. An etchant material is then employed to remove a portion of the interior surface <NUM> corresponding to the negative image of the fragmentation pattern. Alternatively, the negative image of the fragmentation pattern may be protected by the additive protective material and the positive image etched from the interior surface <NUM> by the etchant.

<FIG> is a flowchart illustrating steps etching a fragmentation pattern onto a warhead casing <NUM>, according to an illustrative embodiment of the invention. <FIG> illustrates the warhead casing <NUM> undergoing the method of creating a fragmentation pattern into the warhead casing <NUM>, in accordance with an illustrative embodiment of the invention.

In step <NUM>, a stencil comprising the fragmentation pattern is inserted into the interior cavity of the warhead casing <NUM>. While the stencil will be described throughout this embodiment as comprising a negative image of the fragmentation pattern, thereby creating a positive image of the fragmentation pattern on the interior surface <NUM> of the warhead casing <NUM>, it is understood that the stencil may comprises either a positive image or a negative image of the fragmentation pattern depending on which image is desired to be etched into the interior surface <NUM>. The stencil is inserted through an opening <NUM> in the internal cavity and then positioned so that it is in contact with the interior surface <NUM>. In embodiments in which the warhead casing <NUM> is a single piece artillery casing <NUM>, the stencil may be compressed to a diameter sufficient to allow insertion through a fuze weld opening <NUM> in the top of the casing <NUM>. The stencil diameter may then be expanded such that it is in contact with the interior surface <NUM> of the warhead casing <NUM>.

In step <NUM>, an etchant resistant material <NUM> is applied to the exposed portions of the interior surface <NUM>. The etchant resistant material <NUM> may be applied via an additive material applicator inserted through the opening <NUM> of the warhead casing <NUM>. Such an applicator applies the etchant resistant material <NUM> in a liquid or solid phase via a spray or paint process. In alternative embodiments, the etchant resistant material <NUM> is coated onto the inner surface with a vapor deposition process. Alternatively, the warhead casing <NUM> may be dipped into a liquid volume of additive material.

In an embodiment, the etchant resistant material is a plastic polymer based material such as a thermoplastic. For example, the etchant resistant material may be Halar ECTFE applied in an electrostatic deposition process or fused deposition modeling process. Halar ECTFE, available from Solvay Group of Brussels, Belgium is a copolymer of ethylene and chlorotrifluoroethylene and is a semi-crystalline melt processable partially fluorinated polymer with anti-corrosive properties suited for such an application.

In step <NUM>, the stencil is removed from the interior cavity of the warhead casing <NUM> thereby leaving behind a pattern of etchant resistant material <NUM> corresponding to the positive image of the fragmentation pattern. In embodiments in which the warhead casing <NUM> is a single piece artillery casing <NUM>, the stencil may be compressed to a diameter sufficient to allow removal through a fuze weld opening <NUM> in the top of the casing <NUM>. The stencil diameter may then be expanded such that it is in contact with the interior surface <NUM> of the warhead casing <NUM>.

In step <NUM>, an etchant material <NUM> is applied to the interior surface <NUM> of the warhead casing <NUM>. The etchant material is an acidic or basic chemical wash chosen such that the bare portion of the interior surface <NUM> in which there is no protective etchant resistant material <NUM> applied is etched while the portion of the warhead casing <NUM> covered by the etchant resistant material <NUM> remains untouched by the etchant material <NUM>.

In step <NUM>, after an amount of time suitable for the etchant material <NUM> to etch the interior surface <NUM> to a depth sufficient to create a differential which will result in a natural stress raiser in the presence of an explosive blast wave, the etchant material <NUM> and the etchant resistant material <NUM> are removed from the interior surface <NUM> of the warhead casing <NUM>. The negative image of the fragmentation pattern has been etched into the interior surface <NUM> of the warhead casing <NUM>.

An additive process may be utilized with the stencil to create the fragmentation pattern as well. <FIG> is a flowchart illustrating steps creating a fragmentation pattern onto a warhead casing <NUM> with a stencil, according to an illustrative embodiment of the invention. <FIG> illustrates the warhead casing <NUM> undergoing the method of creating a fragmentation pattern into the warhead casing <NUM> with a stencil, in accordance with an illustrative embodiment of the invention.

In step <NUM>, a stencil <NUM> comprising the fragmentation pattern is inserted into the interior cavity of the warhead casing <NUM>. While the stencil <NUM> will be described throughout this embodiment as comprising a negative image of the fragmentation pattern, thereby creating a positive image of the fragmentation pattern on the interior surface <NUM> of the warhead casing <NUM>, it is understood that the stencil <NUM> may comprises either a positive image or a negative image of the fragmentation pattern depending on which image is desired to be etched into the interior surface <NUM>. The stencil <NUM> is inserted through an opening <NUM> in the internal cavity and then positioned so that it is in contact with the interior surface <NUM>. In embodiments in which the warhead casing <NUM> is a single piece artillery casing <NUM>, the stencil <NUM> may be compressed into a smaller diameter and then inserted through a fuze weld opening <NUM> in the top of the casing <NUM>. The stencil <NUM> diameter may then be expanded such that it is in contact with the interior surface <NUM> of the warhead casing <NUM>.

In step <NUM>, an additive material <NUM> may be applied to the exposed portions of the interior surface <NUM>. The additive material <NUM> may be applied via an additive material applicator inserted through the opening <NUM> of the warhead casing <NUM>. The applicator may spray or paint the etchant resistant material in a liquid or solid phase onto the warhead casing <NUM>. In alternative embodiments, the additive material <NUM> is coated onto the inner surface with a vapor deposition process or the warhead casing <NUM> may be dipped into a volume of liquid additive material <NUM>.

In step <NUM>, the stencil <NUM> is removed from the interior cavity of the warhead casing <NUM> thereby leaving behind a pattern of additive material <NUM> corresponding to the positive image of the fragmentation pattern. In embodiments in which the additive material <NUM> provides sufficient stress protection to create natural stress raisers in the presence of an explosive blast wave, the warhead casing <NUM> is now in a state to be filled with explosive fill, and have a fuze and other components installed prior to operation.

For other embodiments in which an additional stress protection is desired, in step <NUM>, a protective coating <NUM> is deposited onto the interior surface <NUM> of the warhead casing <NUM>. The protective coating <NUM> is deposited evenly over both the exposed portion of the interior surface <NUM> and the portion covered by the additive protective material thereby preserving the thickness differential formed between the inner surface and the additive material <NUM>. The differential in thickness is sufficient to cause a natural stress raiser in the presence of an explosive blast wave. The warhead casing <NUM> may now be filled with explosive and have a fuze and other components installed prior to operation.

In other embodiments, a stencil <NUM> may be selected which provides sufficient protective properties to negate the need for an additional etchant resistant material <NUM>. In these embodiments, the stencil <NUM> may be an adhesive film configured for adhering to the interior surface <NUM> of the warhead casing <NUM>. While the stencil <NUM> will be described throughout this embodiment as comprising a negative image of the fragmentation pattern, thereby creating a positive image of the fragmentation pattern on the interior surface <NUM> of the warhead casing <NUM>, it is understood that the stencil <NUM> may comprises either a positive image or a negative image of the fragmentation pattern depending on which image is desired to be etched into the interior surface <NUM>.

<FIG> is a flowchart illustrating steps creating a fragmentation pattern onto a warhead casing <NUM> with a stencil, according to an illustrative embodiment of the invention. <FIG> illustrates the warhead casing <NUM> undergoing the method of creating a fragmentation pattern into the warhead casing <NUM> with a stencil, in accordance with an illustrative embodiment of the invention.

In step <NUM>, a stencil <NUM> comprising the fragmentation pattern is inserted into the interior cavity of the warhead casing <NUM>.

In step <NUM>, an etchant coating is applied to the interior surface <NUM> of the warhead casing <NUM>. The etchant material <NUM> is a chemical etchant chosen such that the exposed interior surface <NUM> is etched an amount based on the volume of etchant and time of exposure while the adhesive stencil <NUM> protects the covered portion from being etched.

In step <NUM>, after a sufficient length of time for the etchant to etch the interior surface <NUM> to a desired depth, the etchant material <NUM> is removed from the interior surface <NUM> of the warhead casing <NUM>.

In step <NUM>, the stencil <NUM> is removed from the interior surface <NUM> of the warhead casing <NUM>. In embodiments of the invention in which the stencil <NUM> does not cause issues with the explosive fill to be filled into the interior cavity, the stencil <NUM> need not be removed from the interior casing <NUM> of the warhead casing <NUM>.

In other embodiments, an additive process may be utilized over the adhesive stencil <NUM> to create the thickness differential in the warhead casing <NUM>. <FIG> is a flowchart illustrating steps creating a fragmentation pattern onto a warhead casing <NUM> with a stencil, according to an illustrative embodiment of the invention. <FIG> illustrates the warhead casing <NUM> undergoing the method of creating a fragmentation pattern into the warhead casing <NUM> with a stencil, in accordance with an illustrative embodiment of the invention.

In step <NUM>, a stencil <NUM> comprising the fragmentation pattern is inserted into the interior cavity of the warhead casing <NUM>. While the stencil <NUM> will be described throughout this embodiment as comprising a negative image of the fragmentation pattern, thereby creating a positive image of the fragmentation pattern on the interior surface <NUM> of the warhead casing <NUM>, it is understood that the stencil <NUM> may comprises either a positive image or a negative image of the fragmentation pattern depending on which image is desired to be etched into the interior surface <NUM>.

In step <NUM>, a protective coating <NUM> is deposited onto the interior surface <NUM> of the warhead casing <NUM>. The protective coating <NUM> is deposited evenly over both the exposed portion of the interior surface <NUM> and the portion covered by the adhesive stencil <NUM> thereby preserving the thickness differential between the portions. In this embodiment, it is understood that a stencil <NUM> of sufficient thickness is selected to create the desired thickness differential in the warhead casing <NUM>. The differential in thickness is sufficient to cause a natural stress raiser in the presence of an explosive blast wave. The warhead casing <NUM> may now be filled with explosive and have a fuze and other components installed prior to operation.

In embodiments of the invention, controlled deposition of protective material by an additive manufacturing machine, otherwise known as a <NUM>-D printer, may be utilized in place of a mask or stencil <NUM> in both additive and reductive processes. The <NUM>-D printer or other similar print head capable of controllably depositing material on a surface, deposits an etchant resistant material <NUM> to a portion of the interior surface <NUM> to protect that portion of the surface from the etchant material <NUM>. In an embodiment, the etchant resistant material is a plastic polymer based material such as a thermoplastic. For example, the etchant resistant material may be Halar ECTFE applied in a fused deposition modeling process. Halar ECTFE, available from Solvay Group of Brussels, Belgium is a copolymer of ethylene and chlorotrifluoroethylene and is a semi-crystalline melt processable partially fluorinated polymer with anti-corrosive properties suited for such an application.

Alternatively, the <NUM>-D printer may deposit an additive material to a portion of the interior surface <NUM> to create a thickness differential with the exposed portions of the interior surface <NUM>. Depending on the stress tolerance of the additive material, an additional coating of additive material may be applied over the protected and unprotected portions of the interior surface <NUM>. While the <NUM>-D printer will be described throughout this embodiment as depositing material over a positive sections of the fragmentation pattern, thereby creating a positive image of the fragmentation pattern on the interior surface <NUM> of the warhead casing <NUM>, it is understood that the <NUM>-D printer may deposit material over either a positive image or a negative image of the fragmentation pattern depending on which image is desired to be etched into the interior surface <NUM>.

In step <NUM>, a <NUM>-D printer or other controllable printer device capable of selectively depositing material is inserted through an opening <NUM> of an interior cavity of the warhead casing <NUM>.

In step <NUM>, an etchant resistant material is selectively applied to portions of the interior surface <NUM> corresponding to the positive portions of the fragmentation pattern.

In step <NUM>, an etchant material <NUM> is applied to the interior surface <NUM> of the warhead casing <NUM>. The etchant material <NUM> is an acidic or basic chemical wash chosen such that the bare portion of the interior surface <NUM> in which there is no protective coating applied is etched by the material whereas the portion of the warhead casing <NUM> covered by the protective coating material remains untouched by the etchant material <NUM>. After an amount of time suitable for the etchant material <NUM> to etch the interior surface <NUM> to a depth sufficient to create a differential which will result in a natural stress raiser in the presence of an explosive blast wave.

In step <NUM>, the etchant material <NUM> and the protective material are removed from the interior surface <NUM> of the warhead casing <NUM>. The negative image of the fragmentation pattern has been etched into the interior surface <NUM> of the warhead casing <NUM>. The warhead casing <NUM> may now be filled with explosive fill, and have a fuze and other components installed prior to operation.

An additive process may be utilized with the <NUM>-D printer to create the fragmentation pattern as well. <FIG> is a flowchart illustrating steps creating a fragmentation pattern onto a warhead casing <NUM> with a <NUM>-D printer, according to an illustrative embodiment of the invention. <FIG> illustrates the warhead casing <NUM> undergoing the method of creating a fragmentation pattern into the warhead casing <NUM> with a <NUM>-D printer, in accordance with an illustrative embodiment of the invention.

In step <NUM>, an additive material <NUM> is selectively applied to portions of the interior surface <NUM> corresponding to the positive portions of the fragmentation pattern. In embodiments in which the protective material provides sufficient stress protection to create natural stress raisers in the presence of an explosive blast wave, the warhead casing <NUM> is now in a state to be filled with explosive and have a fuze and other components installed prior to operation.

For other embodiments in which an additional stress protection is desired, in step <NUM>, an additive stress protection material is deposited onto the interior surface <NUM> of the warhead casing <NUM>. The additive stress protection material is deposited evenly over both the exposed portion of the interior surface <NUM> and the portion covered by the additive protective material thereby preserving the thickness differential between the portions. The differential in thickness is sufficient to cause a natural stress raiser in the presence of an explosive blast wave. The warhead casing <NUM> may now be filled with explosive and have a fuze and other components installed prior to operation.

In an embodiment of the invention, a coating of additive protective material may be applied to the entire interior surface <NUM> and then portions may be selectively removed through directed energy, such as directed laser energy or directed energy from a jet of water. In an embodiment, the directed energy removes the additive protective material over a portion of the interior surface <NUM> corresponding to the negative image of the fragmentation pattern. The etchant then removes a portion of the interior surface <NUM> corresponding to the negative image of the fragmentation pattern. Alternatively, the negative image of the fragmentation pattern may be protected by the additive material and the positive image etched from the interior surface <NUM> by the etchant.

In step <NUM>, an etchant resistant material <NUM> is applied to the interior surface <NUM> of the warhead casing <NUM>. The etchant resistant material <NUM> may be applied via an additive material applicator inserted through the opening <NUM> of the warhead casing <NUM>. The applicator may spray or paint the additive material onto the warhead casing <NUM>. In alternative embodiments, the additive material is coated onto the inner surface with a vapor deposition process or the warhead casing <NUM> may be dipped into a volume of additive material.

In step <NUM>, portions of the etchant resistant material <NUM> are selectively removed through directed energy, such as directed laser energy or directed energy from a jet of water. In an embodiment, the directed energy removes the etchant resistant material <NUM> over a portion of the interior surface <NUM> corresponding to the negative image of the fragmentation pattern.

In step <NUM>, an etchant material <NUM> is applied to the interior surface <NUM> of the warhead casing <NUM>. The etchant material <NUM> is an acidic or basic chemical wash chosen such that the bare portion of the interior surface <NUM> in which there is no etchant resistant material <NUM> applied is etched by the material whereas the portion of the warhead casing <NUM> covered by the etchant resistant material <NUM> remains untouched by the etchant material <NUM>. After an amount of time suitable for the etchant material <NUM> to etch the interior surface <NUM> to a depth sufficient to create a differential which will result in a natural stress raiser in the presence of an explosive blast wave.

In step <NUM>, the etchant material <NUM> and the etchant resistant material are removed from the interior surface <NUM> of the warhead casing <NUM>. The negative image of the fragmentation pattern has been etched into the interior surface <NUM> of the warhead casing <NUM>. The warhead casing <NUM> may now be filled with explosive fill, and have a fuze and other components installed prior to operation.

An additive process may be utilized with the directed energy to create the fragmentation pattern as well. <FIG> is a flowchart illustrating steps creating a fragmentation pattern onto a warhead casing <NUM> with a directed energy stream, according to an illustrative embodiment of the invention. <FIG> illustrates the warhead casing <NUM> undergoing the method of creating a fragmentation pattern into the warhead casing <NUM> with a directed energy stream, in accordance with an illustrative embodiment of the invention.

In step <NUM>, an additive material <NUM> is applied to the interior surface <NUM> of the warhead casing <NUM>. The additive material <NUM> may be applied via an additive material applicator inserted through the opening <NUM> of the warhead casing <NUM>. The applicator may spray or paint the additive material <NUM> onto the warhead casing <NUM>. In alternative embodiments, the additive material <NUM> is coated onto the inner surface with a vapor deposition process or the warhead casing <NUM> may be dipped into a volume of additive material.

In step <NUM>, portions of the additive material <NUM> are selectively removed through directed energy, such as directed laser energy or directed energy from a jet of water. In an embodiment, the directed energy removes the additive material <NUM> over a portion of the interior surface <NUM> corresponding to the negative image of the fragmentation pattern.

In certain embodiments, an additive material <NUM> is chosen which provides stress protection sufficient to create natural stress raiser in the presence of an explosive blast wave. In this embodiment, the warhead casing <NUM> may now be filled with explosive and have a fuze and other components installed prior to operation.

Claim 1:
A method of creating a fragmentation pattern on the interior surface of a warhead (<NUM>), the method characterized by:
inserting a <NUM>-D printer through an opening (<NUM>) to an interior cavity of the warhead (<NUM>); and
with the <NUM>-D printer applying a protective material (<NUM>) selectively to portions of the interior surface (<NUM>) corresponding to positive portions of the fragmentation pattern, thus to create stress raisers in the presence of an explosive blast wave.