## 2 Materials and Methods
### Fabrication  
For the fabrication, two EOS machines based on Direct Metal Laser Sintering (DMLS) technology were selected: an EOS M290 (EOS GmbH-EOS Additive Manufacturing, Krailling, Germany) was used for preliminary testing and an EOS M400 (EOS GmbH-EOS Additive Manufacturing, Germany) was employed for prototype fabrication. EOS M290 is equipped with a 400 W ytterbium fiber continuum laser characterized by a beam spot diameter of 100 \(\upmu\)m and a building volume of 250 \(\times\) 250 \(\times\) 325 mm\({}^{3}\); using a typical layer thickness of 30 \(\upmu\)m, the max volume rate is 5.1 mm\({}^{3}\)/s. The process was carried out in an argon inert atmosphere with less than 0.1% oxygen and the building platform was preheated at 200 \({}^{\circ}\)C to reduce residual stresses. EOS M400 is equipped with a 1000 W ytterbium fiber continuum laser characterized by a beam spot diameter of 90 \(\upmu\)m and a building volume of 400 \(\times\) 400 \(\times\) 400 mm\({}^{3}\); with the layer thickness set to 90 \(\upmu\)m, the max volume rate is 27.8 mm\({}^{3}\)/s. The process was carried out in an argon inert atmosphere with less than 0.2% oxygen and the building platform was preheated at 165 \({}^{\circ}\)C to reduce residual stresses. The processing parameters have a direct effect on the final component behavior creating unique micro- and macro-structures due to the repeated extremely fast melting and cooling of the material. Optimized combinations of the laser power, the hatch distance, the layer thickness, the scanning speed and scanning strategies can lead to desired outcomes concerning the final microstructures, the corrosion resistance, the residual porosity, the mechanical properties, and the stress \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline
**Si** & **Fe** & **Cu** & **Mn** & **Mg** & **Ni** & **Zn** & **Pb** & **Sn** & **Ti** & **Al** \\ \hline
9–11 & \(\leq\)0.55 & \(\leq\)0.05 & \(\leq\)0.45 & 0.20–0.45 & \(\leq\)0.05 & \(\leq\)0.10 & \(\leq\)0.05 & \(\leq\)0.05 & \(\leq\)0.15 & Bal. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of the employed powder. induced distortions [43]. Many authors evaluated the combined effect of the exposure parameters by using a factor called Volumetric Energy Density (VED) defined as:  
\[VED=P/(V_{s}.h_{d}.L_{T}) \tag{1}\]  
where \(P\) is the laser power, \(V_{s}\) is the scanning speed, \(h_{d}\) is the hatch distance, and \(L_{T}\) is the layer thickness. At low layer thickness, a VED of about 50 J/mm\({}^{3}\) leads to high density, good surface roughness and mechanical performance [52; 53]. At high layer thickness, typically chosen for high productivity, the employment of a high laser power corresponds to the selection of lower hatch distance resulting in a comparable VED [54]. In Table 2 the main characteristics of the two employed machines are summarized together with the exposure parameters. Since large walls with a small thickness of 0.5 mm are difficult to achieve with PBF-LB/M systems and surface roughness could compromise mechanical performance, additional material was provided. The required roughness and thickness were assured by CNC machining. Hence, the machining allowances are:  
* +0.5 mm additional material on skins
* +1.0 mm additional material on all junction point planes
* +1.0 mm additional material on upper junction point teeth
* holes for module connection and screw inserts are closed. PBF-LB/M manufacturing preprocessing was performed using Materialise Magics 23.01 (Materialise, Leuven, Belgium). The part orientation was dictated by the wide thin walls and was vertically positioned. The support structures were generated and, together with the model, were uploaded in EOSPRINT 2.4 (EOS GmbH-EOS Additive Manufacturing, Krailling, Germany) software in the required formats. Here, the exposure parameters were assigned, and the laser path was simulated and checked before the build phase. Specific calibration operations were performed to ensure the best performance in producing the design geometries.