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Additive Manufacturing for Protective Eyewear

Description:

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials

 

OBJECTIVE: Develop materials and an approach to manufacturing ballistic protection eyewear lenses with integrated prescription correction that is also suitable for point-of-need additive manufacturing.

 

DESCRIPTION: Combat eye protection is a ubiquitous need for all deployed Soldiers. The eyewear provides the wearer protection against ballistic-fragmentation and environmental concerns, like blowing sand, while remaining transparent to retain situational awareness. Protective eyewear lenses are currently made via injection molding and are not easily customized to provide vision correction. Any needed prescription vision correction is currently achieved with the Universal Prescription Lens Carrier (UPLC).[1] The UPLC sits behind the primary protective lens and contains a separate set of corrective lenses specific to the User’s vision correction needs mounted into the UPLC frame. This creates integration issues for equipment worn on the face and eyes and limited field-of-view through the prescription lenses in addition to adding substantial logistical burden. The Army product manager for Soldier Protective Equipment (PdM SPE) has an ongoing initiative to identify technologies that would allow the elimination of a separate vision corrective lens (I.e. an integrated vision correction / ballistic protection lens). These lenses are expected to have a life cycle of less than six months since ballistic eye protection lenses are often rapidly degraded in combat environments due to scratching and abrasion.[2] Therefore, it is also desirable to have rapid turnaround on individually customized corrective lenses and to limit the logistics burden by providing manufacturing capability that is close to the point-of-need as well as being customizable to an individual wearer. An additive manufacturing (AM) method is most likely to meet these requirements. As AM technology has progressed, printing resolution and material development have improved to the point where optically clear samples are now achievable.[3] The cost of this technology has also decreased to being a commercially viable approach to manufacturing custom lenses. Companies in this space are continuously developing new materials for their 3D printers to impart performance that has only previously been attainable with conventional manufacturing methods. Significantly, the expanded use of augmented reality (AR) in both military and civilian sectors has spurred advances in optically clear and durable eyewear manufactured with AM.  

 

The goal of this topic is to develop materials and processes to rapidly manufacture a customized (“one off”) optical lens that meets all requirements of MIL-PRF-32432A for ballistic protection lenses as well as providing excellent optical quality, dimensional tolerances, and stability in all environments sufficient to provide vision correction.

 

PHASE I: Develop the materials and additive manufacturing processes needed to fabricate flat plaques that are optically transparent (>89% luminous transmittance, with less than 3% haze and minimal optical distortion) yet provide ballistic protection as outlined in MIL-PRF-32432A.[4] It should also be demonstrated that the cured plaques remain optically transparent and maintain impact resistance across a range of humidity (35-95% ± 5%), temperature (-60 °F - +160 °F), exposure to solar radiation and common military chemicals to include: 6.0 % by weight sodium hypochlorite, insect repellent-controlled release diethyl toluamide (30% concentration DEET), fire resistant hydraulic fluid (MIL-PRF-46170), hydraulic fluid, petroleum base (MIL-PRF-6083), gasoline (87% octane), motor oil (SAW 10W-30) and F24 fuel (NATO Standard AFLP 3747), as well as resistant to scratching/abrasion, and be resistant to fogging, as required by MIL-PRF-32432A for currently fielded protective eyewear. Some possible candidate materials to achieve this balance include acrylics, urethanes and polycarbonates. Companies making and selling 3D printers and resins may not fully specify the formulation of their products due to proprietary restrictions so in-house resin development may be necessary.

 

PHASE II: Optimize materials and processes that allow for AM of optical quality structures that meet minimum MIL-PRF-32432A requirements for luminous transmittance, optical clarity and ballistic performance as outlined in MIL-PRF-32432A for military eyewear. The materials should be compatible with standard commercial-off-the-shelf AM systems (dynamic light projection, stereolithography, etc.) without needing customization. Printing of eyewear lens prototypes should be achievable in less than three hours with sub-100 µm printing resolution and allow for printing of a “one-off” lens that demonstrates custom vision correction. Demonstrate the optical transparency and ballistic protection of the resulting cured eyewear prototypes and the fidelity of the printed, cured part to the original design. Parts should be printed to demonstrate the utility of this approach by printing a range of lenses with incorporated vision correction covering a range of –10.00 to +8.00 diopters with up to -3.25 diopters of cylinder. Example lenses shall at a minimum include prescriptions at +8, -10, +5, -5, +1.5,-1.5 diopters as well as a non-prescription optically corrected variant for comparison.  Prescriptions shall be reasonably accurate (within 0.25 diopter) as measured on a lensometer.  Lens designs shall maximize field of view through the lens, and offer peripheral protection.  It is highly encouraged that offerors partner with a protective eyewear supplier early on in the effort. [5]

 

PHASE III DUAL USE APPLICATIONS: The development and maturation of this technology will allow for integrated sensory protection and vision correction for the wearer. This advancement will enhance situational awareness of the wearer by enabling customization for optimal vision correction not currently available in fielded products. It also reduces the logistical burden and timeframe needed for replacement lens to reach point-of-need, and supports the DoD’s National Defense S&T strategy to create and field capabilities at speed and scale through innovation of industrial processes.[6] With this technology, there is significant benefit to the civilian sector for not only protective eyewear, but eyewear in general. The customization achievable with this approach would ensure wearers of every head size, shape and prescription could obtain the best vision correction possible. [7] Specifically the safety, sports and augmented reality areas would benefit from this technology development.

 

REFERENCES:

  1. Auvil, J. R., Evolution of military combat eye protection. U.S. Army Medical Department Journal 2016 April-September, 2016, p 135+.;
  2. Program Executive Office Soldier FAQ. https://www.peosoldier.army.mil/Resources/Frequently-Asked-Questions/ (accessed 10/19/2023);
  3. MIL-PRF-32432A, Performance Specification Military Combat Eye Protection (MCEP) System, January 2013;
  4. Program Executive Office Soldier Authorized Protective Eyewear List (APEL). https://www.peosoldier.army.mil/Equipment/Approved-Eyewear-QPL/;
  5. 2023 National Defense Science and Technology Strategy, United States Department of Defense, May 2023;
  6. Lee, L.; Burnett, A. M.; Panos, J. G.; Paudel, P.; Keys, D.; Ansari, H. M.; Yu, M., 3‐D printed spectacles: potential, challenges and the future. Clinical and Experimental Optometry 2020, 103 (5), 590-596

 

KEYWORDS: Additive manufacturing; Ballistic protection; Eyewear; Optically transparent; Vision correction; Multifunctional; Integrated protective eyewear; Combat eye protection; Authorized protective eyewear list (APEL)

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