## 2 Materials and Methods
### Fabrication
After fabrication, parts undergo a preliminary dimension check before proceeding with the heat treatment. The heat-induced laser melting process causes considerable residual stress and, as a result, dimensionally unstable parts [55]. A stress relieving heat treatment in a Nabertherm LH120/14 (Nabertherm GmbH, Lilienthal, Germany) controlled atmosphere haven was applied according to the following characteristics. The building platform with the parts still attached was subjected to heat treatment to minimize possible distortion due to the variation of internal stresses in the material. The parts were slowly heated at a 5 \({}^{\circ}\)C/min rate up to the soaking temperature of 300 \({}^{\circ}\)C and maintained for 2 h; after, cooling at a 5 \({}^{\circ}\)C/min rate was performed. \begin{table}
\begin{tabular}{c c c} \hline  & **EOS M290** & **EOS M400** \\ \hline Laser type & Ytterbium fiber continuum & Ytterbium fiber continuum \\ Laser number & \(1\) & \(1\) \\ Laser max power & 400 W & 1000 W \\ Working volume & 250 \(\times\) 250 \(\times\) 325 mm\({}^{3}\) & 400 \(\times\) 400 \(\times\) 400 mm\({}^{3}\) \\ Volume rate & 5.1 mm\({}^{3}\)/s (with 30 \(\upmu\)m layer) & 27.8 mm\({}^{3}\)/s (with 90 \(\upmu\)m layer) \\ \hline \multicolumn{3}{c}{Exposure parameters} \\ \hline Laser Power & 370 W & 600 W \\ Hatch distance & 0.19 mm & 0.1 mm \\ Scanning speed & 1300 mm/s & 1450 mm/s \\ Layer thickness & 30 \(\upmu\)m & 90 \(\upmu\)m \\ Volumetric Energy Density & 49.93 J/mm\({}^{3}\) & 45.98 J/mm\({}^{3}\) \\ \hline \end{tabular}
\end{table} 
Table 2: Summary of machines characteristics and exposure parameters used for fabrication. Detachment from the building platform was carried out through wire Electrical Discharge Machining (EDM) technology using the U6 H.E.A.T. Extreme Wire (Makino, Japan) machine to reduce mechanical stress and to have a clean, flat surface in the underside of the parts. After parts detachment, a second preliminary dimension check was performed. Once part machinability is confirmed by adimension check, each part is CNC machined individually. The employed machine is a five-axis machining center S616 (C.B. Ferrari, Italy). Custom gripping equipment was designed and used to hold the part for the removal of 0.5 mm onto the wall skins. An assembly jig was developed for finishing the junction points and the screw inserts to guarantee overall dimensions and perform assembly operations. It is made of tempered steel, machined into two plates each one with a 5 mm-deep groove with a tolerance of 0.04 mm from edge to edge to facilitate assembly while ensuring tolerance compliance (Figure 2a). The plates are aligned and connected by vertical rods and also have rectangular openings for each junction point to allow for final CNC milling operations and a set of inserts and positioning pins (Figure 2b). The configuration during the real assembly operations is shown in Figure 2.  
As part of quality assurance, a tensile test was carried out to validate the AM process on the specimen printed in the same building platform of the parts. A 50 kN Zwick Z050 TN (ZwickRoell GmbH & Co. KG, Ulm, Germany) universal testing machine was employed under quasi-static loading conditions, imposing a ramped displacement at 0.05 mm/min speed. The sample geometry was a dog bone, with a square cross-section of \(5.72\times 4.00\) mm\({}^{2}\) and a nominal gauge length of 25.40 mm in accordance with the standard ASTM E8/E8M [56].