Athermalized lens prototype using additive manufacturing

Additive manufacturing (AM) can change the way we design opto-mechanics. One can realize complex structures with AM that are difficult or impossible to achieve with conventional fabrication techniques. In a recent project, the US Army attempted to demonstrate athermalization of an infrared lens using AM design and manufacturing techniques. The goal was to demonstrate these new techniques in a small-scale prototype lens for a missile application. U.S. Army Combat Capabilities Development Command, Aviation and Missile Center teamed with Materials Sciences LLC (MSC) to apply a previously-reported topology-optimization technique [1] to develop an additively manufactured multi-material, opto-mechanical structure. The composite structure was engineered to maintain the location of the detector focal plane at the focus of a lens as it changes with temperature. MSC initially fabricated several prototype lens housings of additively manufactured titanium and cast urethane which failed at the material interfaces during temperature cycling over the intended operational range. MSC is currently conducting fabrication trials with an injection molded thermoplastic polymer to replace the cast urethane. These unfinished prototype feedstocks are being evaluated for structural integrity under temperature cycling. Initial results are promising; but additional fabrication trials are required to produce fully dense feedstocks for finish machining. Composite structures allow tailoring of mechanics to react as designed to temperature and vibration. But it is nearly impossible to model all aspects of a composite structure. Prototyping and testing can quickly reveal limitations of materials and fabrication methods that can inform future optimization efforts. This effort documents these iterations and learned lessons, and presents evidence that this AM-composite technique is useful for designing robust opto-mechanics and that the current manufacturing method can be matured to deliver operational components.