# Geometric Benchmarking of Metal Material Extrusion Technology: A Preliminary Study
## 2 Materials and Methods
### Equipment and Material  
All the proposed GBTAs were fabricated using an Ultrafuse 316L filament with a diameter of 2.85 mm, provided by BASP SE, Heidelberg, Germany. The filament could be handled safely and easily due to the AISI 316L powder (90 wt%) being immobilized in a binder matrix made up of polyoxymethylene (POM) and polyolefin (PO). Green parts were produced using an Ultimaker S5 MEX machine (Ultimaker, Utrecht, The Netherlands), whose direct drive extruder was equipped with a CC0.6 high wear resistance hardened steel nozzle (0.6 mm diameter) to avoid clogging and abrasion during extrusion. Support structures were introduced to sustain the beams of bridge features during printing. Such  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Geometry**} & \multirow{2}{*}{**Feature**} & \multirow{2}{*}{**Thickness (mm)**} & \multirow{2}{*}{**Height (mm)**} & \multicolumn{2}{c}{**Height-to-Thickness**} \\  & & & & **Ratios** \\ \hline \multirow{8}{*}{Thin wall} & W1 & 0.6 & 25 & 41.60 \\  & W2 & 2 & 25 & 12.50 \\  & W3 & 0.6 & 20 & 33.30 \\  & W4 & 2 & 20 & 10.00 \\  & W5 & 0.6 & 15 & 25.00 \\  & W6 & 2 & 15 & 7.50 \\  & W7 & 4 & 25 & 6.25 \\  & W8 & 6 & 25 & 4.16 \\  & W9 & 4 & 20 & 5.00 \\  & W10 & 6 & 20 & 3.33 \\  & W11 & 4 & 15 & 3.75 \\  & W12 & 6 & 15 & 2.50 \\ \hline \multirow{8}{*}{Pillar} & P1 & 10 & 30 & 3.00 \\  & P2 & 5 & 30 & 6.00 \\  & P3 & 2 & 30 & 15.00 \\  & P4 & 10 & 20 & 2.00 \\  & P5 & 5 & 20 & 4.00 \\  & P6 & 2 & 20 & 10.00 \\  & P7 & 10 & 10 & 1.00 \\  & P8 & 5 & 10 & 2.00 \\  & P9 & 2 & 10 & 5.00 \\ \hline \multirow{8}{*}{Hollow cylinder} & HC1 & 1 & 36 & 36.00 \\  & HC2 & 3 & 36 & 12.00 \\ \cline{1-1}  & HC3 & 5 & 36 & 7.20 \\ \cline{1-1}  & HC4 & 1 & 24 & 24.00 \\ \cline{1-1}  & HC5 & 3 & 24 & 8.00 \\ \cline{1-1}  & HC6 & 5 & 24 & 4.80 \\ \cline{1-1}  & HC7 & 1 & 12 & 12.00 \\ \cline{1-1}  & HC8 & 3 & 12 & 4.00 \\ \cline{1-1}  & HC9 & 5 & 12 & 2.40 \\ \hline \multirow{8}{*}{Bridge} & B1 & 6 & 6 & 1.00 \\ \cline{1-1}  & B2 & 6 & 12 & 2.00 \\ \cline{1-1}  & B3 & 6 & 18 & 3.00 \\ \cline{1-1}  & B4 & 6 & 24 & 4.00 \\ \cline{1-1}  & B5 & 6 & 30 & 5.00 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Nominal dimensional ratios of the designed features.  
supports were realized using BASF Ultrafuse Support Layer, a ceramic-based filament specifically developed to be used in combination with metal filaments and easily removable at the end of the shaping-debinding-sintering process. Figure 2 shows the printing equipment and the filament used for the experiments. All the proposed artifacts were realized according to the printing parameters suggested by the Ultrafuse user guidelines [33] and are summarized in Table 2.  
The green part was characterized by a composite material; specifically, the parts were composed of a polymeric matrix containing stainless steel powder. To obtain real metal parts (white part), the green parts must be subjected to debinding and sintering processes, which remove polymer components and consolidate the bonding of the powder grains. These treatments were conducted by an external company that applied the guidelines defined directly by BASF. The first treatment was the catalytic rebinding, and the thermal debinding process was performed at 393.15 K in an HNO\({}_{3}\) environment (98% concentration) to remove the main polymer content. The resulting brown parts were equal in volume to the initial green parts, but a loss of mass was experienced due to the decay of the polymer component. The sintering cycle, necessary for secondary binder removal and metal particle coalescence (white part), took place in an argon atmosphere and involved three thermal ramps. First, the temperature increased at a rate of 5 K/min from room temperature up to 873.15 K, which was held for 1 h. The temperature was then increased again at a rate of 5 K/min until it reached 1653.15 K. After being held for 3 h, the temperature decreased to room temperature through furnace cooling.