## 4 Results
### Optimal Parameter Settings for the Individual Performance Measurements
#### 4.1.3 Material Cost  
The ANOVA results in Table 10 show that the main terms for layer thickness and build orientation are only statistically significant to estimate the material cost in all the design cases. Since the same amount of the CFR-PEEK filament is used for the same parameter settings, it is noted that the calculated filament costs are the same for all the experimental replicates of the same parameter combination. Thus, the ANOVA table cannot calculate the statistics of interaction effects due to the lack of enough degrees of freedom for residual error, and the main effects are only presented in the result table in Table 10.  
The main effect plots in Figure 10 support that the material cost for CFR-PEEK depends on layer thickness and build orientation. The optimal settings that minimize the mean material cost are consistent across the design cases in which the 0.2 mm layer thickness and the 0\({}^{\circ}\) build orientation are optimal. However, the cost reduction effect of each process parameter is different depending on the design types; the cost reduction becomes the biggest at the 0.2 mm layer thickness for the ASTM D638 case, the 0\({}^{\circ}\) build orientation for the ASTM D695 case, and both factor levels for the ASTM D3039 case. The material cost is related to the amount of the CFR-PEEK filament used for the fabrication of a final output. The average filament volumes consumed for the design cases fabricated at the 0.2 mm layer thickness are 19.99 cm\({}^{3}\) for ASTM D638, 67.03 cm\({}^{3}\) for ASTM D695, and 41.63 cm\({}^{3}\) for ASTM D3039. The amount of each filament volume increases to 21.90 cm\({}^{3}\) for ASTM D638, 67.67 cm\({}^{3}\) for ASTM D695, and 44.01 cm\({}^{3}\) for ASTM D3039 at the 0.3 mm layer thickness, respectively. The fact that the 0.2 mm layer thickness is associated with the lowest dimensional error indicates that the 0.2 mm layer thickness reduces the material cost due to its more precise fabrication. Moreover, it seems that the designs with a relatively thin dimension such as ASTM D638 and ASTM D3039 have a large impact of layer thickness on filament consumption and their material cost (see Figure 10a,c) since a lower \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
** ASTM D638** & **DF** & **Sum of Square** & **Mean Square** & **F-Value** & \(p\)**-Value** \\ \hline Layer Thickness (L) & 1 & 0.499142 & 0.499142 & 908.58 & 0.000 * \\ Build Orientation (O) & 1 & 0.017030 & 0.017030 & 31.00 & 0.000 * \\ Printing Speed (P) & 2 & 0.000000 & 0.00000 & 0.00 & 1.000 \\ Error & 31 & 0.017030 & 0.000549 & - & - \\ Total & 35 & 0.533203 & - & - & - \\ \hline
** ASTM D695** & **DF** & **Sum of Square** & **Mean Square** & **F-Value** & \(p\)**-Value** \\ \hline Layer Thickness (L) & 1 & 0.056882 & 0.056882 & 39.42 & 0.000 * \\ Build Orientation (O) & 1 & 0.723350 & 0.723350 & 501.29 & 0.000 * \\ Printing Speed (P) & 2 & 0.000000 & 0.00000 & 0.00 & 1.000 \\ Error & 31 & 0.044732 & 0.001443 & - & - \\ Total & 35 & 0.824965 & - & - & - \\ \hline
** ASTM D3039** & **DF** & **Sum of Square** & **Mean Square** & **F -Value** & \(p\)**-Value** \\ \hline Layer Thickness (L) & 1 & 0.801920 & 0.801920 & 196.70 & 0.000 * \\ Build Orientation (O) & 1 & 0.770010 & 0.770060 & 188.88 & 0.000 * \\ Printing Speed (P) & 2 & 0.00000 & 0.0000 & 0.000 & 1.000 \\ Error & 31 & 0.126380 & 0.004077 & - & - \\ Total & 35 & 1.698310 & - & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 10: ANOVA results for the material cost (* \(\alpha<0.05\)).