## 3 Results and Discussion
### Dimensional Accuracy
This disagreement can be put down to the different materials used, PLA in this study and ABS in the study by [PERSON] et al. ABS is subject to greater shrinkage than PLA [3]. They also found that a larger air gap (corresponding to a lower infill percentage) decreases percentage change, which is in accordance to the findings of this study. To obtain the optimal values for each response, the prediction plots generated by MATLAB are used. Hence, the vertical dashed lines in Figures 6 and 8, Figures 11, 13 and 15 were moved along the trends to the corresponding parameter values in order to acquire the desired optimal response value, which should be either the minimum or maximum. For optimization of dimensional accuracy (10 mm in X direction) three parameters were set to minimize the percentage error using a regression model created by MATLAB; layer thickness was set to 0.11 mm, printing speed to 40.7 mm/s, and printing temperature to 216 \({}^{\circ}\)C. The infill percentage and the surface inclination angle stayed at the medium values of 35% and 45\({}^{\circ}\), respectively. These values were applied in an experimental test to validate the predictions. With these settings, the model predicted a percentage error of 0.02%, but the validation test print produced an even smaller value of 0.01%. In comparison to the effects of the predictors on the dimensional accuracy in X and Y directions, the effects in the Z direction differ. Equation (7) presents the regression model for the percentage error of dimensional accuracy for 10 mm in the Z direction (termed \(Error_{Z}\) [%])  
\[ \begin{array}{c}Error_{Z}\ [\%]=1.139-0.061*x_{1}-0.129*x_{2}+0.12*x_{3}-0.076*x _{4}-0.192*x_{5}+\\ 0.083*x_{1}x_{2}-0.067*x_{1}x_{3}-0.057*x_{1}x_{4}+0.428*x_{1}x_{5}+0.409*x_{2 }x_{3}-0.044*x_{2}x_{5}-\\ 0.021*x_{3}x_{4}+0.036*x_{3}x_{5}-0.731*x_{2}{}^{2}-0.011*x_{3}{}^{2}-0.227*x_{ 4}{}^{2}+0.167x_{5}{}^{2}\end{array}  \tag{4}\]  
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 8 shows the effects regarding printing speed, printing temperature, and infill percentage. These were less extreme than for the X and Y directions. To achieve a lower value of percentage error, either low or high values of layer thickness should be used. The higher accuracy of thin layers (0.1 mm) can be put down to the fact that thinner layers do not accumulate errors as the thicker ones do. However, the higher accuracy of the thickest layer (0.3 mm) cannot be explained yet, but further investigations will be carried out. Hot printing temperature and slower printing speed give better accuracy because of the lower viscosity of the material and because the material is not under so great a tension, and therefore, bonds better with the previous layer and reduces inaccuracies in the Z direction. A slight, but recognizable, effect shows that higher percentages of infill reduce measured error since the denser the infill, the less sagging of the top layers. Again, ANOVA was used to identify the three most significant parameters: first was the interaction of layer thickness and printing speed (\(p\)-value = 0.00077), second, the interaction of infill percentage and surface inclination angle (\(p\)-value = 0.00239), and third, the interaction of printing speed and printing temperature (\(p\)-value = 0.00912). The importance of these parameter interactions is also shown in Figure 9. The greatest error occurs with 0.2 mm layer thickness, independent of the printing speed or temperature, whereas the outcome, when employing 0.1 or 0.3 mm, depends on the printing speed and temperature.