## 2 Materials and Methods  
The material often used for a wide range of 3D printing applications is PLA, a biodegradable material which is easy to print and has fewer printing problems than other polymers in terms of adhesion to the printing platform and resulting warping of the part, a print issue at which the corners of the printed part bend up and detach from the build platform due to a lack of adhesion between the printed part and the platform. In this study, the effects and interactions of five process parameters (infill percentage, layer thickness, printing speed, printing temperature, and surface inclination angle) on generated surface roughness, dimensional accuracy, productivity, and energy consumption are examined. Figure 1 shows the test structure (H \(\times\) W \(\times\) D 10 mm \(\times\) 46 mm \(\times\) 46 mm). It was designed to allow assessment of dimensional accuracies of 5, 10, and 20 mm long features in the X and Y directions, a 10 mm long feature in the Z direction, and surface roughness at surface inclination angles of 0\({}^{\circ}\), 45\({}^{\circ}\), 60\({}^{\circ}\), 75\({}^{\circ}\), and 90\({}^{\circ}\). Note that the effect of the surface inclination angle will be analyzed only in relation to surface roughness, since it has no reasonable influence on the other three responses. To convert the 3D model of the test structure shown in Figure 2 into printable files, the slicing software Simplify3D was used, and subsequently, the test samples were printed using the Zmorph 2.0 SX, Figure 3, under the different printing conditions. Table 1 lists the printing parameters maintained constant for the experimental trials. Figure 2: CAD model of a test sample (10 mm \(\times\) 46 mm \(\times\) 46 mm). It was decided to use a Taguchi orthogonal array (OA), rather than a central composite design, since in this investigation, all levels are equally important and only values commonly found in FFF printing are used. Moreover, it was expected that the values of the outer levels have a higher influence on the output parameters, and therefore, a more detailed investigation of those is necessary. Next, it was decided which OA to use. Taguchi (OA) designs offer the possibility of investigating five factors at five levels, starting with the Taguchi (OA) L25 (5'6), continuing with the Taguchi (OA) L50 (2'1 \(\times\) 5'11) and the Taguchi L125 (5'31). The L25 was not detailed enough, whereas the L125 was too extensive. Therefore, the L50 was selected because it was sufficiently detailed while relatively time saving. The L50 is a mixed orthogonal array (2'1 \(\times\) 5'11), meaning one factor, in comparison to the others, is varied on only two levels instead of five. It was decided to set the infill percentage as the factor with only two levels due to its anticipated linearity, and its predominant influence was expected to be on build time and material consumption. The detailed allocation of levels and normalized values can be found in Table 2. \begin{table}
\begin{tabular}{c c c} \hline
**Constant Parameter** & **Unit** & **Value** \\ \hline Bed temperature & \({}^{\circ}\)C & 60 \\ Top solid layers & - & 5 \\ Bottom solid layers & - & 3 \\ Outline shells & - & 2 \\ Infill outline overlap & \% & 25 \\ First layer speed & \% & 50 \\ (in relation to set printing speed) & \% & 100 \\ (in relation to set layer height) & \% & 100 \\ Infill pattern & Rectilinear & 45 \\ Nozzle diameter & mm & 0.2 \\ \hline \end{tabular}
\end{table} 
Table 1: Printing parameters maintained constant during trials.