PEO Ammunition and ARDEC have a patent-pending and cost-effective way to LFT the 155 mm high-explosive round for increased anti-materiel performance
by Mr. Paul Manz
In an attempt to partially mitigate the capability gap resulting from DOD’s policy on cluster munitions—which mandates a significant reduction in the amount of potential unexploded ordnance they leave on the battlefield by 2019—a trio of technical professionals at Picatinny Arsenal, New Jersey, faced the challenge of eking out increased performance from existing 155 mm high-explosive unitary munitions without breaking the bank. The policy-driven loss of most U.S. cluster munitions impacts all Army and Marine Corps dual-purpose improved conventional munitions (DPICMs) used by the Army and Marine Corps.
LFT, or lithographic fragmentation technology, is a new, patent-pending processing technique developed by the government to cost-effectively pattern and generate pre-formed fragments for optimized target effects. LFT, pronounced “lift,” can be used to force unitary high explosive (HE) munitions to produce larger specific fragment sizes and shapes when increased anti-materiel performance is required versus the multitude of smaller-sized anti-personnel fragments produced by most current fragmentation warhead products.
The current DOD cluster munitions policy was established on June 19, 2008 during then-President George W. Bush’s Administration. This policy is focused on minimizing the potential unintended harm to civilians and civilian infrastructure to the extent possible when employing U.S. cluster munitions while recognizing cluster munitions can be the most effective/efficient weapons for engaging massed formation of enemy forces, individual targets dispersed over a defined area, targets whose precise location are not known, and time-sensitive or moving targets. The policy defines cluster munitions as munitions composed of a non-reusable canister or delivery body containing multiple, conventional explosive submunitions but excludes nuclear, chemical, or biological weapons; obscurants, pyrotechnics, nonlethal systems (e.g., leaflets); nonexplosive kinetic submunitions (e.g., flechettes or rods); electronic effects; and landmines. The policy applies to systems delivered by aircraft, cruise missiles, artillery, mortars, missiles, tanks, rocket launchers, or naval guns that deploy payloads of explosive submunitions that detonate via target acquisition, impact or altitude, or that self-destruct (or a combination of both). The policy states that after Dec. 31, 2018, DOD can no longer use cluster munitions that, after arming, result in more than 1 percent unexploded ordinance across the range of intended operational environments.
PATTERNING FRAGMENTS
The pattern imprinted on the inside of a warhead casing causes it to fragment along those lines when it detonates. Using this lithographic fragmentation technique can increase the anti-materiel lethality of unitary explosives, helping to partially close the capability gap created by the loss of cluster munitions from DOD’s arsenal. (Photos courtesy of Paul Manz, PEO Ammunition)
Without DPICMs, some target sets may require development of new and relatively expensive advanced sensor-fuzed munitions (SFMs). SFMs are expensive for a reason: they are basically intelligent munitions that use multiple sensors and onboard processing to autonomously engage and defeat targets independent of terrain and weather conditions. Many of the remaining target sets can be reasonably engaged through a combination of precision guidance, programmable height-of-burst fuzing or enhanced lethality capabilities. LFT is focused on addressing the latter capability and leverages current 155 mm cannon HE unitary (i.e., a single explosive, as opposed to a cluster of smaller ones) solutions, including well-known materials, explosive fragmentation principles, established manufacturing methods and industrial base sunk-cost investments.
THE USES OF FRAGMENTATION
Fragmentation warheads allow for the engagement of multiple targets with a single warhead. Large caliber gun-launched munitions, such as 155 mm cannon HE unitary projectiles, typically use fragmentation as their primary target-defeat mechanism. Although blast wave effects also contribute to lethality, it is generally a secondary mechanism of defeat.
The fragments produced by these munitions are very specific to the type of explosive, quantity of explosive, steel wall material and the thickness of the steel wall of the projectile. Each munition will generally produce a natural distribution of many small and some larger sized fragments based on test data. This natural distribution allows these munitions to defeat a wider range of targets but is not optimized for specific target sets. Target defeat is a function of the number of each specific sized fragments produced, fragment velocity, fragment shape and total number of fragments.
THE PATH TO LFT
Affordable enhanced lethality is a recurring imperative across DOD’s large, diverse conventional munitions portfolio, which is managed by the Program Executive Office (PEO) for Ammunition. The U.S. Army Armament Research Development and Engineering Center (ARDEC), co-located with PEO Ammunition at Picatinny Arsenal, investigated several potential innovative approaches to enhance cannon HE unitary lethality.
One approach looked at using flexible, perforated metal sheets as liners in an attempt to reliably create patterned fragments out of the metal shell casing. While cost-effective, this method was not easily compatible with current manufacturing methods and many munition warhead designs such as one-piece artillery shell bodies.
HOW LFT BREAKS DOWN
Because LFT causes munitions to fragment in a predefined pattern, it improves those munitions’ effectiveness against a specific target set. Where a munition without LFT might break into a natural distribution of some large fragments and some small, a LFT-enabled munition can force the creation of larger fragments in higher quantities that would not otherwise occur naturally.
In these one-piece 155 mm artillery shells, the only opening is a small hole at the top that is about one-third the diameter of the main portion of the shell casing. This opening is used to pour in explosive fill; it then serves as a threaded well for attaching a fuze. Unfortunately, the aforementioned metal liner cannot be rolled up, inserted through this hole, and then unrolled to conform to the tapered end of the shell casing without creating potential significant gaps and spaces between the sheet and the internal metal surface. When hot, liquefied explosive fill is subsequently poured into the shell, the potential for voids and cracks to form in the explosive fill as it cools around these gaps becomes very high. Those potential voids and cracks create a probability of premature detonation in a gun tube because of the abrupt, high-speed movement of the explosive fill into these voids and cracks during high-G gun-launch setback.
As an alternative to metal liners, ARDEC has long understood that warhead cases may also be scored with a fragmentation pattern by mechanical means, a process that would be, unfortunately, more costly and time-consuming for artillery shells.
MUNITIONS GET A LFT
Enter LFT, which combines the positive aspects of these known approaches for creating pre-formed fragments with high-volume, low-cost, repeatable lithographic techniques. One such technique is commonly used across the semiconductor industry to enable manufacturing of affordable products for the commercial consumer marketplace. After conceiving the idea of LFT, the three U.S. government inventors from PEO Ammunition and ARDEC have since prototyped, tested and demonstrated the application of LFT for increased anti-materiel performance.
The method can be employed on currently produced, otherwise naturally fragmenting, metal shell bodies from the government-owned, contractor-operated Scranton Army Ammunition Plant in Pennsylvania. The performance results to date, along with the predicted low manufacturing costs, have been impressive enough that Army leadership has recently directed the use of LFT on a new, extended-range, artillery projectile being developed by ARDEC and PEO Ammunition for accelerated Army production.
This extended-range round will have a small payload (i.e., less HE fill) than its existing shorter-range naturally fragmenting counterpart in the U.S. munitions stockpile. LFT will help make up the difference in anti-materiel lethality to cost-effectively get the same or better performance at longer ranges.
CROSS-SECTION VIEW
LFT is patterned inside munitions like the 155 mm HE artillery shell shown here. LFT can be used on current, otherwise naturally fragmenting, shells without raising costs excessively.
LFTING THE JOINT WARFIGHTER AND INDUSTRY
As DOD’s official single manager for conventional munitions, PEO Ammunition also considers the requirements and products it provides to the Air Force, Navy, Marines, Special Forces and Coast Guard in addition to those it provides to the Army. Many of these other military customers also use larger unitary HE munitions that rely upon fragmentation for lethality. These stakeholders are also facing the policy-driven loss of most of their cluster munitions after Dec. 31, 2018. Communicating through its on-site Air Force, Navy and Marine Corps liaisons co-located at Picatinny Arsenal, PEO Ammunition and ARDEC are ensuring these other customer applications are also being considered. Proactive collaborative engagement of the appropriate service stakeholders upfront will maximize joint warfighter “goodness” down the line as LFT is being matured and further optimized for initial use in cannon artillery munitions.
CONCLUSION
As a U.S. government patent-pending technology, it is envisioned that LFT could be modestly licensed to U.S. industry to allow it to potentially win back previously-lost NATO or allied munition customers by providing improved products at equal or lower cost than offerings from international industry competitors. This could also enable U.S. taxpayers to recoup some of LFT’s development investment.
LFT is just one example of the many good ideas that continue to be delivered from Joint Center Picatinny Arsenal and is a result of their institutionalized culture that continuously considers all aspects of materiel development and acquisition starting from technology inception and throughout the product life cycle to ensure maximum benefit to the joint warfighter, U.S. taxpayers, and industry partners.
For more information, visit Picatinny Arsenal’s website at www.pica.army.mil.
This article is scheduled to be published in the April – June 2017 issue of Army AL&T Magazine.
MR. PAUL MANZ currently serves as chief scientist for PEO Ammunition at Picatinny Arsenal, the Joint Center for Weapons and Ammunition. He is a multiple-certified senior member of the Army Acquisition Corps and certified Lean Six Sigma Black Belt with more than three decades of experience spanning the entire materiel development life cycle from science and technology through production and deployment. He recently won the 2016 Undersecretary of Defense for Acquisition, Technology and Logistics Workforce Individual Achievement Award in Engineering.
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