## 3 Results and Discussion
### Energy Consumption  
Equation (6) presents the quadratic regression model for the predicted energy consumption. \[ \begin{split}&\text{\emph{Energy Consumption}}=0.193+0.036*x_{1}-0.105*x_{2}-0.173*x_{3}+0.014*x_{4}-\\ & 0.002*x_{5}-0.014*x_{1}x_{2}-0.027*x_{1}x_{3}+0.009*x_{1}x_{4}+0.007*x_{1} x_{5}+0.032*x_{2}x_{3}-\\ & 0.006*x_{2}x_{5}-0.004*x_{3}x_{4}+0.016*x_{3}x_{5}+0.008*x_{4}x_{5}+0.0 43*x_{2}+0.133*x_{3}{}^{2}-\\ & 0.014*x_{4}{}^{2}-0.011*x_{5}{}^{2}\end{split}  \tag{6}\]  
Figure 12: Effects of interaction of parameters on measured R\({}_{\text{a}}\) in X direction. where \"\(x_{1}\)\" is the normalized value for infill percentage, \"\(x_{2}\)\" refers to the normalized value of layer thickness, \"\(x_{3}\)\" denotes the normalized value of printing speed, \"\(x_{4}\)\" is the normalized value for printing temperature, and \"\(x_{5}\)\" represents the normalized value for the surface inclination angle. Figure 13 shows the influence of the five factors on energy consumption. The longer the duration of the printing process, the greater the amount of energy consumed, which is also a function of infill percentage, the printing speed, and the layer thickness. This finding is supported by ANOVA were the three most important terms were found to be: first, printing speed (\(p\)-value = \(2.81\times 10^{-12}\)), second, layer thickness (\(p\)-value = \(5.98\times 10^{-8}\)), and third, interaction of layer thickness and printing temperature (\(p\)-value = \(7.45\times 10^{-5}\)). As expected, the energy consumed is linearly related to infill percentage. With increase in printing temperature, the energy consumed rises until the temperature reaches 210 \({}^{\circ}\)C and then remains constant until 230 \({}^{\circ}\)C. However, the difference is only marginal and therefore not significant. It is also interesting to note that the energy consumed generally decreased with increased printing speed, however, the curve is not linear and has its minimum at roughly 86 mm/s. This suggests that at printing speeds higher than 86 mm/s, energy saved due to saved production time is exceeded by the energy expended on the printing head motors. The interaction effects related to energy consumption are shown in Figure 14. Looking at the interaction of printing speed and layer thickness, it is not difficult to see that lower printing speeds and thinner layers result in higher energy consumption. A 0.1 mm layer thickness results in a big gap between the plotted lines, but the separation gets smaller, the thicker the layers. An inverse trend can be observed with the printing temperature, i.e., the influence of printing temperature is only recognizable at low speed or thin layers, meaning it is only visible in interaction with other parameters as indicated by ANOVA. In this study, layer thickness was the second most important parameter after printing speed, but [PERSON] et al. [PERSON] et al. (2016) found that layer thickness had the greatest effect on energy consumption because they did not investigate the latter. They also examined the infill percentage and found no effect worth mentioning, but a trend was observed which was similar to the one seen in our study. [PERSON] et al. [PERSON] et al. (2016) agreed with the statement that energy consumption depends very much on the build time, and this has also been confirmed by studies of [PERSON] et al. [PERSON] et al. (2017) and [PERSON] et al. [PERSON] et al. (2017). The latter also found a correlation between increasing printing speed, layer thickness, and reduction of build time regarding the energy consumption, which fits with the importance of those two parameters found in our study. Because the energy consumption is determined mainly by build time, it was important to reduce this to a minimum when optimizing the parameters. Thus, layer thickness was set to 0.3 mm, printing speed to 74 mm/s, and infill percentage to 20%.