Additive Friction Stir Deposition of Aluminum Alloys and Functionally Graded Structures

State-of-the-art additive manufacturing technologies for metal parts have evolved primarily around powder metallurgy and fusion welding-based processes. These processing methodologies yield parts with inferior mechanical and physical properties as compared to wrought metal of the same composition. Additionally, the production rates for even the fastest processes are relatively low, the part envelopes are limited to a few cubic feet, and often the process must be conducted in an atmospherically controlled chamber. Aeroprobe's additive friction stir (AFS) process is a novel high-speed, large-volume wrought metal additive manufacturing technology that will enable affordable, full-density, near net-shape component manufacturing from a wide range of alloys, including aerospace aluminum alloys, nickel-based super alloys, and metal matrix composites. The ability to rapidly fabricate large-scale, complex wrought and functionally graded aluminum components from three-dimensional models will be an enabling manufacturing advancement in exploration launch vehicle fabrication, for parts such as those on the Orion Crew Module. A scaled representation of the window frame structure proposed for the Orion Crew Module was fabricated from 6061 Al using Aeroprobe's additive friction stir process during the Phase I program. To move AFS up the TRL ladder to full-scale demonstration and deployment, two major technical objectives must be met: (1) develop process/structure/property relationships for AFS deposition of aluminum aerospace alloys, such as 2219, which can be used for process control and material property optimization; and (2) demonstrate net-shape, large-scale aluminum launch vehicle and aerospace components (including a functionally graded structure) with mechanical properties comparable to traditional wrought metals.

Additive manufacturing via AFS has the potential to lower the cost and improve the performance of NASA exploration launch vehicles, such as the Orion Crew Module. Additionally, AFS also offers a means of fabricating advanced aluminum airframe structures such as bulk heads and stiffened panels. AFS offers the ability to locally control composition, which can be used to impart functional gradients in components, thus improving part performance. High buy-to-fly ratios are often attributed to subtractive manufacturing of webbed and ribbed components to reduce the structural weight while maintaining required stiffness. Manufacturing such components using additive manufacturing could drastically reduce the machining operations, material requirement, energy consumption, and part specific tooling. Using AFS to additively manufacture components on NASA exploration launch vehicles and airframes has the potential to reduce total system costs while maintaining wrought metal performance of traditionally fabricated parts and the design flexibility of additive manufacturing.

The primary applications for early adoption of AFS are high-value propositions for which AFS enables some performance that is not achievable by traditional processing methods. One of the key benefits of AFS is that consolidation and deposition occur in the solid-state, thus highly engineered microstructures can be retained throughout processing. For, example AFS is being applied to large-plate and component manufacturing using ultra-fine-grained (UFG) Mg. Fabrication of UFG Mg components at a large-scale is currently not feasible and AFS is proving to make this possible. Aeroprobe is currently working with commercial defense and aerospace primes on proprietary AFS demonstration projects with commercial applications. Other commercial applications of AFS under development include coating of shaft journals for use in extreme wear and corrosion applications.

This is a mature technology (TRL 7) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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