## 2 Materials and Methods
### Adaptable Fan Casing Design
The most significant impact on the longevity of the inserts would be the fan blade rubbing against the surface. If the blade were to rub the surface of the inserts, all six would need to be replaced with new prints. Aluminum fan casings typically have an abradable layer to protect the blade tips. If a rub occurred, this abradable layer would need to be reapplied, which is nontrivial and costly. Furthermore, depending on the required flowpath geometry, it may be impractical to implement this abradable layer. Thus, an aluminum insert would likely need to be replaced if a rub occurred as well and offers no additional benefit in the event of a rub compared to the PerFORM. Leaks are prevented between components using O-rings and room temperature vulcanizing (RTV) silicon. The AM inserts were designed with a jagged interface where they meet in the assembly to discourage air leaks from the flowpath. The outer diameter where the inserts meet is sealed with a layer of RTV silicon. Furthermore, O-rings span the axial length of each insert in the middle of the jagged interface. Splitting the annulus presents a unique advantage of the assembly. Individual inserts can be exchanged depending on requirements for instrumentation or part-circumference flowpath changes. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Manufacturing Method** & **Lead Time** & **Cost** & **Available Treatments** \\ \hline
3D Printing (Plastic) & Weeks & USD 15,000–20,000 & High Complexity \\
3D Printing (Metal) & Months & USD 30,000–40,000 & High Complexity \\ Precision Machining & Months & USD 50,000+ & Low Complexity \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Cost, lead time, and complexity comparison for three manufacturing techniques. A major advantage of AM techniques lies in the instrumentation capabilities. Fan casings typically have extensive instrumentation required for measuring various quantities through the rotor. Some of the measurements involve light probes for tip deflections, capacitance probes for tip clearance, and static pressure taps to measure the pressure rise. Each piece requires specific features and they can quickly take up valuable space in machined hardware. Traditionally machined parts would require individual callouts on detailed engineering drawings for the different features, which can add significant costs and time to the development process as well as the overall machining process. Furthermore, more complicated features can be implemented in AM components that would have otherwise been impossible to machine. [PERSON] and [PERSON] made extensive use of SLA printing to include static pressure taps in previously unavailable locations in a centrifugal compressor diffusion section [5; 11]. Additionally, designers for AM components do not need to take into account traditional tooling requirements that might interfere with the resolution or spacing. Static pressure taps and light probes often have optimal circumferential placements around the annulus. With traditional machining, the final layout may not be optimal after taking into account the manufacturing and tooling processes. The workflow is summarized in Figure 3. The flowpath instrumentation is simpler in the fan compared to the centrifugal compressor. Figure 4 shows the layout of the static pressure taps surrounding the fan rotor. The axial resolution of the taps was increased compared to the aluminum configuration. Additionally, time was saved by using the CAD models for the printing process compared to engineering drawings.