Development of a Hybrid Additive Manufacturing Process for Aerospace Hardware

Fusion-based Additive Manufacturing (AM) technologies such as Selective Laser Melting (SLM) face operational hurdles that prevent their widespread adoption within the manufacturing sector. If a hybrid manufacturing approach is adopted, the advantages of each discrete technique can be exploited synergistically thus expanding the areas of implementation. However, current hybrid methods involving AM techniques target dimensional accuracy and surface finish by incorporating subtractive processes; still, production rates and solidification-related issues remain unresolved. Additive Friction Stir (AFS), a patented solid-state, near net shape, AM process, offers complementary capabilities to fusion-based additive technologies. This process is capable of producing monolithic and/or bimetallic structures, at a superb production rate, in an ambient atmosphere. Consequently, the overarching goal of the proposed work is to develop a hybrid manufacturing program, targeted to an external customer base, which can yield mid and long-term funding opportunities for the Center. The Research and Development (R&D) endeavor proposed here is a strategic partnership between Marshall Space Flight Center (MSFC), and Solid-State Solutions Inc. (SolidRTD). In order to ensure a successful collaboration, the team will implement an innovative Benefits of Realization (BR) Project Management Methodology (PMM) tailored to consider the heterogeneity of stakeholders and assure Return of Investment (ROI), technology infusion, and future partnerships.

AM is center stage as the Agency seek to realize its potential innovation, financial and efficiency benefits. At a Center level, MSFC is heavily vested in fusion-based AM processes, specifically SLM, with an aim towards reducing lead times, component weight, and production costs. Despite its game-changing potential, limitation to homogeneous feedstock powder, spatially restrictive deposition chambers, low production rates and solidification defects are operational hurdles fusion-based AM technologies face as these processes look for implementation in manufacturing environments. As a result, while experimentation and early adoption have garnered attention, the reality is that the industrial manufacturing sector is still slowly finding their way. For instance, according to a recent study by Boston Consulting Group, only 34% of U.S.-based manufacturing executives have implemented AM within their companies.

While the reasons for the low adoption rates are multiple, varying by industry, company size and product type, there is a production concept that manifest itself as the only feasible solution to overcome fusion-based AM shortcomings. Often referred to as “hybrid manufacturing”, it combines two or more established manufacturing processes into a new combined set-up whereby the advantages of each discrete technique can be exploited synergistically thus expanding the areas of implementation. Unfortunately, the aforementioned operational hurdles associated to fusion-based AM processes neglect, in most cases, any advantage offered by a potential hybrid approach. Whenever successful, where production volumes or rates are not a metric, engineering design and/or sequential thermal post-processing has to compensate for the anisotropic performance and the material distortion caused by the complex thermal history during the deposition process. In the light of this a question arises: By adopting a hybrid manufacturing concept, is there an established production technique that could supplement fusion-based AM processes? If so, how does its performance over production cost ratio compare against isolated conventional and novel production technologies? AFS, a patented solid-state, near net shape, AM process, offers complementary capabilities to fusion-based additive technologies. This process is capable of producing monolithic and/or bimetallic structures, at a superb production rate, in an ambient atmosphere. Unlike fusion-based processes, where material feedstock is melted, AFS plasticizes the feedstock (solid or powder) to consolidate, thereby avoiding solidification-related issues (volumetric porosity, microstructural anisotropy) noted in traditional metallic AM techniques. AFS excels in the production of large, high strength components. By first producing the basic volume of the structure with AFS (essentially replacing forming and other transformative manufacturing techniques), this volume could then be used as the substrate for powder bed fusion or direct energy deposition processes to produce more detailed geometries on top of the base shape. Therefore, this proposal describes a pilot research program designed to accelerate the widespread adoption of an AFS + fusion-based hybrid metal AM process by establishing preliminary process-microstructure-mechanical properties interplays for bimetallic testing articles. Considering MSFC capabilities and expertise in developing and implementing manufacturing solutions, the establishment of the aforementioned program not only will position the Center at the forefront of the hybrid manufacturing research arena but also will diversify the funding stream by offering advanced manufacturing and certification services to the Nation’s industrial sector.

Analogous to joining, coating, and repairing operations, a significant effort of the proposed method will be the characterization of the bi-metallic interface. Leveraging MSFC expertise on advanced materials intended for propulsion applications, GRCop-42 and IN718 were selected for this pilot program. Similarly, by exploiting the advantages of the AFS deposition technique, a gradient transition, from GRCop-42 to IN718 could be attain thus assuring bonding compatibility at the AFS-SLM juncture. The applied R&D endeavor proposed here represents a strategic partnership between MSFC and SolidRTD. Outside its sister company, MELD Manufacturing, SolidRTD, located in Tuscaloosa AL, is the sole-provider of AFS consultation and manufacturing services. On the other hand, fusion-based AM (SLM) synthesis activities as well as the microstructural, mechanical and thermal post-processing programs will be performed using exiting MSFC infrastructure.

The proposed innovation represents a low-risk, high-return investment opportunity for the Center since the individual manufacturing processes (AFS and SLM) had been tested in a laboratory or at a relevant environment thus owning TRL classifications between 4 and 5. On the contrary, the AFS+SLM hybrid process is at its concept level (TLR level 3). With the knowledge that will be obtained from the proposed research activities (refer to the Management Approach section), the hybrid process will be classified as a TRL 5 at the end of its performance period. Moreover, MSFC has extensive expertise on propulsion-related materials (GRCop-42 and IN718) and novel manufacturing techniques (SLM). In addition, the Center has the required capabilities to perform a comprehensive material characterization program. Lastly, unlocking AM technologies for an industrial production setting could translate in unlimited ROI potential in the form of development of manufacturing solutions, production and assembly, workforce training and material certification programs. More details on this concept will be offered in the Business Case section.

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