As America marks 250 years of nationhood, we must recognize that we stand on the shoulders of giants and reflect on the legacies they’ve built that enable us to live our lives today. We’ve fought hard and continue to fight to preserve the things that define us as Americans — from our national parks to our engineering feats — because we collectively understand that some legacies are too important to lose. We must also reflect on the legacies that have been lost to time and on those that are at risk of slipping away. In the foundries that sustain America’s aerospace and defense fleets, a different kind of legacy is under threat. The legacy parts that power the aircraft, engines, and weapons systems that have protected this nation for generations and are becoming harder and harder to source. Fortunately, ceramic additive manufacturing technology is transforming the architecture of investment casting, the process that many legacy parts rely on to be produced, to provide a more robust production pathway for these endangered parts.
250 Years’ Worth of Legacy Parts
On August 25th, 1916, President Woodrow Wilson signed the Organic Act, creating the National Park Service and enshrining the radical idea that some things are worth protecting, not because they are profitable, but because they are scientifically, historically, or recreationally irreplaceable.
Legacy parts are recreations of discontinued components of systems that are still in use that have been reverse engineered and manufactured via small-batch production for sustainment purposes. The average age of the U.S. Air Force’s aircraft fleet now exceeds 30 years, which is the oldest it has ever been. The B-52 has been in continuous service since 1955 and is expected to fly past 2050, meaning individual airframes will approach a century of operational life. The KC-135 tanker fleet averages roughly 60 years in service. For these and similar platforms, fleet managers need to find, procure, and deliver components whose original manufacturers no longer exist, rendering legacy part production critical for the sustainment of a not insignificant portion of America’s aerospace and defense (A&D) fleet. And right now, the manufacturing infrastructure that upholds legacy part production is disappearing.
Investment casting has been one of the pillars of A&D manufacturing for more than a century. It is the process by which molten metal (typically an alloy or superalloy) is poured into ceramic molds to produce complex, high-tolerance components that cannot be machined from solid stock Turbine blades with internal cooling channels and structural airframe components with organic geometries are examples that have been historically produced via this method. Investment casting supply chains, however, have been contracting for decades due to foundry consolidation, offshoring, and the economics of low-volume production. Conventional investment casting tooling (i.e., the dies, cores, and shells required to produce a complex cast) can take greater than a year — sometimes up to 2 years — assuming a qualified supplier can be found at all. Under these lead times, aircrafts become grounded, missions get deferred, and readiness deteriorates. Because legacy programs might need to procure dozens of parts at a time, rather than thousands, the economics rarely justify the investment required to stand up new tooling through conventional means. Without a new approach to legacy part production, America risks losing the ability to sustain the very systems that have projected its power and protected its people for generations.
Ceramic Additive Manufacturing: A Shifting Paradigm in Investment Casting
President Eisenhower didn’t condemn the early roads to their demise; In 1956, he ordered the Interstate Highway System to be built on top of them, thereby transforming the economics of American commerce. The existing transportation system remained, albeit with a newfound capacity to support transnational industry.
Ceramic additive manufacturing (AM) technology is transforming investment casting without fundamentally altering the process. It does not replace the foundry, nor does it obsolete the metallurgist or the qualification standards that the A&D industry demands. Rather, it reduces the traditional dependency on hard tooling. In conventional investment casting, tooling represents a fixed cost that must be amortized across a production run, making low-volume orders economically punishing. And when it’s gone, it’s gone. Reproducing legacy tooling requires original engineering drawings, material specifications, and process knowledge, as well as a qualified supplier that is willing to take on the work, all of which are growing scarcer with each passing year.
Ceramic additive manufacturing processes, like vat photopolymerization, allow disposable ceramic cores, shells, and molds to be printed directly from digital design files. The geometry of the legacy part lives in a CAD model, rather than in the physical tooling that can be lost in a foundry closure or gradually degraded upon use. In this distributed manufacturing model, legacy part production is decoupled from the fragile network of highly specialized suppliers, and a “digital parts library” can be maintained. If a qualified ceramic 3D printer or fleet of ceramic 3D printers exists at a domestic foundry or an associated OEM, production of turbine blades designed in 1978 or impellers with tooling that was scrapped in 2005 can be reproduced at-scale and on-demand with nothing more than the appropriate digital design file, additive expertise, and material(s).
The performance case is equally compelling. Shells, cores, and molds printed via ceramic additive manufacturing can achieve dimensional tolerances that are competitive with those produced using conventional tooling, meeting the most stringent geometric requirements for A&D castings. Also, because there is no tooling cost to amortize, the standard economics of low-volume production are flouted. Dozens of parts become reasonable cost-friendly to produce using ceramic additive manufacturing, while the same order would be conventionally untenable. Lead times compress from years or months to just weeks. This is not speculation. Ceramic additive manufacturing is being qualified and adopted today by OEMs and foundries that support A&D sustainment. It integrates well into existing investment casting workflows and quality control programs.
Printed Silica Cores: An Overview
America’s greatest engineering feats, like the construction of the Hoover Dam, the redirection of the Chicago River, and the Moon Landing, share a common characteristic: they were solutions to problems that most people had decided were simply too hard to solve.
In investment casting for A&D sustainment, the primary technical constraint has been the design and conventional manufacture of the ceramic core, which is the element that defines the internal geometry of the final part. It must withstand the extreme heat and mechanical stresses that are incurred by the investment casting process, and it must be removed from the solidified part without damaging it.
Ceramic cores are conventionally produced via injection molding, a process by which ceramic slurry forced through a precision die under high pressure until a desired geometry is achieved. This process works for legacy parts from a functional perspective, but it is constrained by cost (i.e., tooling is expensive) and limits to achievable complexity. Cores also take months to produce; each iteration of a core design requires new tooling, new qualification, and new lead time.
Printed silica cores eliminate these constraints. Silica is the material of choice for investment casting cores because it is (1) thermally stable and (2) dissolvable. Silica-based ceramics can withstand temperatures up to 1550C, allowing cores to maintain their geometry in the presence of intense temperature differentials as molten metal is poured and cools. Second, although ceramics are typically known to be chemically durable, silica can be dissolved using a strong base (e.g., sodium hydroxide or potassium hydroxide) without corroding the casted alloy. Once the silica core is dissolved, a clean internal cavity that replicates its geometry to tight dimensional specification is left behind.
Vat photopolymerization and other ceramic additive manufacturing processes bypass the geometric constraints of injection molding and enable unparalleled design freedom with comparable dimensional accuracies for silica cores. For example, turbine blades containing serpentine cooling channels with sub-millimeter wall thicknesses that would be impossible or prohibitively costly to manufacture using conventional tooling become feasible when using printed silica cores. If the cooling channel design needs to change, whether it’s because the thermal analysis has been updated or because a new alloy is being qualified, the digital design file may be revised, and a new core can be printed based on the new configuration. No new tooling. No new qualification. No new lead time.
The general value chain for a legacy turbine blade program using printed silica cores is structured as follows: (1) the original core geometry, if the drawings still exist, is converted into a CAD model and stored in an OEM’s digital parts library. (2) When a casting order is placed, the core file is retrieved and validated, and (3) it is sent to a qualified ceramic additive manufacturing system to be printed. (4) Following printing, the green parts must be cleaned of residual slurry and thermally post-processed to achieve the final, usable cores. (5) The cores are inspected for dimensional accuracy and for material properties. (6) The OEM then ships the cores to a foundry, where they are incorporated into the investment casting process exactly as conventionally produced cores would be. (7) Investment casting occurs. (8) After casting and solidification, the cores are chemically dissolved. (9) The castings are inspected, and (10) the finished turbine blades proceed through the standard qualification pathway. The only other difference from conventional practice is that the first article can be delivered in weeks to months rather than years, at a cost that does not require a multi-year program commitment to justify.
There are many A&D sustainment opportunities beyond turbine blades for printed silica cores. Turbine vanes with similar geometric complexity and thermal performance demands as turbine blades, combustion components with internal features that govern complex mixing and cooling processes, and structural castings with several distinct internal features like weight-saving pockets and internal conduits may be rescued from conventional tooling-based processes that make legacy part production cost-prohibitive in low volumes. Anywhere that a hollow legacy casting is part of an aging A&D platform’s sustainment challenge, printed silica cores offer a path of affordable reproducibility and potential design optimization that conventional tooling cannot accommodate.
Ultimately, there is a vision among the investment casting community for an A&D manufacturing ecosystem in which no legacy part is ever lost to history. The ongoing transition from physical tooling to tool-less, CAD-driven manufacturing schemes will allow part geometries to live on in digital parts libraries and be printed on-demand. The legacy part production pathway of the future will be powered by ceramic additive manufacturing, a technology that does not depend on the survival of any foundry, toolmaker, or single supply chain node.
A Legacy Worth Casting
250 years ago, America’s founding fathers committed to an idea that was audacious to the point of recklessness: that a people could govern themselves, that the institutions they built could endure, that the work they began would be worth preserving for generations to come. They were right, not because the work was easy, but because each generation found the will and the tools to carry it forward.
The A&D platforms that have protected this nation are a different kind of legacy, but they deserve to be sustained with the same reverence. The parts they need, including all the turbine blades, the structural castings, and the precision components that keep aging systems operational, deserve a production pathway that is as resilient as the platforms themselves.
Ceramic additive manufacturing, and printed silica cores in particular, provide that pathway. They promise innovation — a better way to do a hard thing that needs doing. For the foundries, program managers, and sustainment engineers who carry the responsibility of keeping America’s legacy fleets operational, that is not a small promise. It is, in the truest sense of the word, a casting of new legacies to preserve what matters
