## 4 Results
### Optimal Parameter Settings for the Individual Performance Measurements  
#### 4.1.1 Printing Time  
For all the design types, the printing time is significantly affected by each process parameter itself along with its interactions with other process parameters (see Table 6). Figure 5 shows the main significant effects on printing time for each design case. The dotted line in Figure 5 represents the population mean of the printing time. The slope of each plot of the main effects indicates the impact of each parameter change; the steeper slope indicates the greater difference in the effect on the printing time. The greatest difference in printing time is observed in layer thickness for all the design cases; the 0.3 mm layer thickness leads to much a shorter mean printing time than the 0.2 mm layer thickness. In addition, printing time decreases when the build orientation is 0\({}^{\circ}\) regardless of the design cases; however, the impact of build orientation in the ASTM D695 case is relatively smaller than other design cases. Moreover, the fastest printing speed (i.e., at 1400 mm/min) results in the shortest mean printing time among the printing speed levels for all the design cases. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
** ASTM D638** & **DF (Degrees of Freedom)** & **Sum of Square** & **Mean Square** & **F-Value** & \(p\)**-Value** \\ \hline Layer Thickness (L) & 1 & 584.03 & 584.0280 & 3003.57 & 0.000 \({}^{\star}\) \\ Build Orientation (O) & 1 & 210.25 & 210.2500 & 1081.29 & 0.000 \({}^{\star}\) \\ Printing Speed (P) & 2 & 229.56 & 114.7780 & 590.29 & 0.000 \({}^{\star}\) \\ L \(\times\) O & 1 & 20.25 & 20.2500 & 104.14 & 0.000 \({}^{\star}\) \\ L \(\times\) P & 2 & 10.89 & 5.4440 & 28.00 & 0.000 \({}^{\star}\) \\ O \(\times\) P & 2 & 8.67 & 4.3330 & 22.29 & 0.000 \({}^{\star}\) \\ L \(\times\) O \(\times\) P & 2 & 0.67 & 0.3330 & 1.71 & 0.201 \\ Error & 24 & 4.67 & 0.1940 & - & - \\ Total & 35 & 1068.97 & - & - & - \\ \hline
** ASTM D695** & **DF** & **Sum of Square** & **Mean Square** & **F-Value** & \(p\)**-Value** \\ \hline Layer Thickness (L) & 1 & 5852.25 & 5852.2500 & 35,113.50 & 0.000 \({}^{\star}\) \\ Build Orientation (O) & 1 & 476.69 & 476.6900 & 286.17 & 0.000 \({}^{\star}\) \\ Printing Speed (P) & 2 & 2355.50 & 1177.7500 & 7066.50 & 0.000 \({}^{\star}\) \\ L \(\times\) O & 1 & 12.25 & 12.500 & 73.50 & 0.000 \({}^{\star}\) \\ L \(\times\) P & 2 & 108.50 & 54.2500 & 325.50 & 0.000 \({}^{\star}\) \\ O \(\times\) P & 2 & 9.39 & 4.6900 & 28.17 & 0.000 \({}^{\star}\) \\ L \(\times\) O \(\times\) P & 2 & 0.17 & 0.0800 & 0.50 & 0.613 \\ Error & 24 & 4.00 & 0.1700 & - & - \\ Total & 35 & 8818.75 & - & - & - \\ \hline
** ASTM D3039** & **DF** & **Sum of Square** & **Mean Square** & **F -Value** & \(p\)**-Value** \\ \hline Layer Thickness (L) & 1 & 2635.11 & 2635.11 & 18,972.80 & 0.000 \({}^{\star}\) \\ Build Orientation (O) & 1 & 2025.00 & 2025.00 & 14,580.00 & 0.000 \({}^{\star}\) \\ Printing Speed (P) & 2 & 992.39 & 496.19 & 3572.60 & 0.000 \({}^{\star}\) \\ L \(\times\) O & 1 & 196.00 & 196.00 & 1411.20 & 0.000 \({}^{\star}\) \\ L \(\times\) P & 2 & 51.39 & 25.69 & 185.00 & 0.000 \({}^{\star}\) \\ O \(\times\) P & 2 & 45.50 & 22.75 & 163.80 & 0.000 \({}^{\star}\) \\ L \(\times\) O \(\times\) P & 2 & 3.17 & 1.58 & 11.40 & 0.000 \({}^{\star}\) \\ Error & 24 & 3.33 & 0.14 & - & - \\ Total & 35 & 5951.89 & - & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 6: ANOVA results for the printing time (\({}^{\star}\)\(\alpha<0.05\)). The non-parallel lines in Figure 6 indicate that all the design cases have similar interaction effects. For layer thickness, the 0\({}^{\circ}\) of build orientation and the 1400 mm/min of printing speed are associated with the shortest mean printing time if the 0.3 mm layer thickness is used. Similarly, the 0\({}^{\circ}\) build orientation is associated with the 0.3 mm layer thickness and the 1400 mm/min printing speed results in the shortest mean printing time for each case.