## 2 Materials and Methods  
### Materials  
The punch geometry set for the experimental tests consisted of a hollow cylinder with a fillet radius on the face in contact with the blanks. The hollow geometry was designed to enable a mechanical connection by means of a screw between punch and press. To test the capability of the process, two geometries were used: a first, termed real geometry (RG), with an external diameter of 118 mm, similar to that found in real-world manufacturing applications; and a second, termed prototype geometry (PG), with an external diameter of 39 mm. Both geometries are depicted in Figure 1.  
Figure 1: Drafting of **(a)** real RG and **(b)** prototype PG geometries designed for the experimental tests.  
Table 1 lists the process parameters of the tool geometries tested. It can be seen that both had the same drawing ratio of 1:8. All other parameters were determined with reference to real-world industrial applications (RG) or to prototypes used in previous studies (PG).  
Table 1 shows that PG and RG had similar but not identical punch and matrix fillet radii, clearance distances, and blank thicknesses. The reason for this difference is that the author wished to compare the prototype geometry already tested in previous studies [12] with a geometry more comparable to that already used in industry for production purposes, but with steel punches.  
Fused filament fabrication (FFF) technology was used to produce punches. A full filling pattern was set with two layers for wall, and layer depth was set to 0.125 mm for both RG and PG. In each layer, wires were extruded parallel to the x-y plane with an orientation of 45\({}^{\circ}\) with respect to the \(x\)-axis; the orientation angle was then shifted by 90\({}^{\circ}\) in the next layer so that a sequence of angle orientations equal to \(\pm\) 45\({}^{\circ}\) was obtained. Samples were printed with the Mark Two 3D printer (Markforged, Watertown, MA, USA). Onyx, which is a Markforged commercial name for nylon reinforced with carbon microfibers (CF_Nylon), was used as the printing material. The forming die and blank holder were made of 45 NiCrMo 16 tool steel. AISI 304 was the material set for blanks. Table 2 lists the mechanical properties of the materials used.  
\begin{table}
\begin{tabular}{l l l} \hline \hline  & **Prototype Geometry (PG)** & **Real Geometry (RG)** \\ \hline Blank material & AISI 304 & AISI 304 \\ \hline Blank diameter [mm] & 70 & 210 \\ \hline Blank thickness [mm] & 1 & 0.7 \\ \hline Drawing ratio & 1:8 & 1:8 \\ \hline Drawing depth [mm] & 15 & 65 \\ \hline Punch material [mm] & CF\_Nylon & CF\_Nylon \\ \hline Punch diameter [mm] & 39 & 118 \\ \hline Punch fillet radius [mm] & 6 & 10 \\ \hline Punch speed [mm/s] & 10 & 10 \\ \hline Matrix material & 45 NiCrMo 16 & 45 NiCrMo 16 \\ \hline Matrix internal diameter [mm] & 41.2 & 120.16 \\ \hline Matrix fillet radius [mm] & 5 & 3.5 \\ \hline Clearance distance [mm] & 0.1 & 0.38 \\ \hline Blankholder load [kh] & 1 & 18.5 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Main blank and tool dimensions and process parameters.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline  & **CF Nylon** & **45 NiCrMo 16** & **AISI 304** \\ \hline Tensile modulus [GPa] & 2.4 & 284 & 193 \\ \hline Tensile stress at yield (Mpa) & 37 & 696 & 190 \\ \hline Tensile stress at break (Mpa) & 40 & 950 & 500–700 \\ \hline Tensile strain at break (\%) & 25 & 11 & 40 \\ \hline Density (g/cm\({}^{3}\)) & 1.2 & 7.84 & 8 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Mechanical properties of punches, forming dies and blanks.