Metal additive manufacturing (AM) encapsulates the myriad of manufacturing processes available to meet industrial needs. Determining which of these AM processes is best for a specific aerospace application can be overwhelming. Based on the application, each of these AM processes has advantages and challenges. The most common metal AM methods in use include Powder Bed Fusion, Directed Energy Deposition, and various solid-state processes. Within each of these processes, there are different energy sources and feedstock requirements. Component requirements heavily affect the process determination, despite existing literature on these AM processes (often inclusive of input parameters and material properties). This article provides an overview of the considerations taken for metal AM process selection for aerospace components based on various attributes. These attributes include geometric considerations, metallurgical characteristics and properties, cost basis, post-processing, and industrialization supply chain maturity. To provide information for trade studies and selection, data on these attributes were compiled through literature reviews, internal NASA studies, as well as academic and industry partner studies and data. These studies include multiple AM components and sample build experiments to evaluate (1) material and geometric variations and constraints within the processes, (2) alloy characterization and mechanical testing, (3) pathfinder component development and hot-fire evaluations, and (4) qualification approaches. This article summarizes these results and is meant to introduce various considerations when designing a metal AM component.
Improved technical and programmatic performance demonstrations have bolstered the justification for metal additive manufacturing (AM) adoption in the aerospace industry. Technical advantages of AM span from reduced mass, complex geometry (not feasible with traditional manufacturing), enhanced heat transfer, part consolidation, and use of novel high-performance alloys (Ref 1). Programmatic cost savings from utilizing AM appropriately is evident because of reduction in part lead times and cost, expansion of the supply chain (addressing obsolescent methods and eliminating programmatic risks of limited supply chains), rapid design-fail-fix cycles, faster time to market, reduced scrap material waste, and lower buy-to-fly ratio (Ref 2,3,4). These advantages are not universal, and investigation of AM process selection is warranted.
To narrow the AM process for a given application, one must trade the technical advantages and constraints between the part design, material properties, and process (Ref 5, 6). Unique requirements of part performance, metallurgical considerations, post-processing methods, certification and qualification approaches further complicate the AM process trade for aerospace components (Ref 7). High-strength or high-conductivity applications may limit the material selection, which consequently limits the AM processes available. A large-scale design may require an AM process with a large build volume but has lower feature resolution. Novelty and lack of material certifications for some AM materials may dissuade selection regardless of potential technical benefits (Ref 8, 9). These nuances lead to the crux of the designer’s dilemma. How to determine the optimal AM process for a candidate part is neither well documented nor naturally intuitive. At best, the designer will be guided through the AM process selection by trades of unique component requirements (e.g., complexity, feature resolution, part size, material properties) and manufacturing processes (e.g., material availability, build volumes).