Static Special Factors for Metal Additive Manufacturing

Additive manufactured parts have seen a significant increase in use for aviation applications in recent years. The term additive manufacturing (AM) encompasses an ever-growing list of technologies that can themselves be used with an ever-growing list of materials. This means that, within the scope of AM, engineers have an extensive choice of ways to design and make parts that may not have been available just a few years ago.

For structural aviation applications, material design data for any manufacturing process, AM included, must be in compliance with FAA regulations § 2x.603, § 2x.605 and § 2x.613 and the Part 23 counterparts. The unique feature of AM materials is that their final mechanical properties are established during the entire fabrication process, including post-processing steps. As such, the data used to design AM structure must account for not only the typical variability of the as-purchased material, but also for the variability imparted by the manufacturing process and the unique part design. The manufacturing variability for AM can be substantial and has been reported to be an order of magnitude greater compared to other conventional manufacturing processes. This creates a challenge for industry to develop material design data that have wide applicability.

Regulations currently exist for the application of static special factors that are intended to account for uncertain variabilities in a manufacturing process. This paper/presentation will provide the AeroMat community an overview of an effort by the FAA and NIAR to evaluate the feasibility of applying a static special factor to metal AM applications. Most notably, a literature review was completed that compiled published data from over 250 research programs that evaluated various metal AM processes and build orientations, all using the Ti-6Al-4V alloy. Conclusions on combinability of the data and feasibility of developing a static special factor will be presented.