# Optimization Parameters for PLA Through Additive Manufacturing: Taking Mixed Shapes as an Example
## 3 Results and Discussion
### Rsm
#### 3.3.2. RSM of Tensile Strength
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Exp.** & **A. Nozzle Gap Height** & **B. Fill Spacing** & **C. Infill Pattern** & **Tensile Strength** \\  & **(mm)** & **(mm)** & **(N/mm\({}^{2}\))** \\ \hline
1 & 0.1 & 0.5 & Straight line & 43.4533 \\ \hline
2 & 0.15 & 0.8 & Grid & 48.5224 \\ \hline
3 & 0.18 & 0.5 & Triangle & 49.6351 \\ \hline
4 & 0.1 & 0.5 & Triangle & 51.6311 \\ \hline
5 & 0.1 & 0.5 & Grid & 49.5632 \\ \hline
6 & 0.1 & 0.5 & Triangle & 49.9983 \\ \hline
7 & 0.02 & 0.5 & Triangle & 56.6987 \\ \hline
8 & 0.15 & 0.2 & Grid & 46.1568 \\ \hline
9 & 0.15 & 0.8 & Straight line & 40.6982 \\ \hline
10 & 0.1 & 0.1 & Triangle & 53.9872 \\ \hline
11 & 0.15 & 0.2 & Straight line & 47.3352 \\ \hline
12 & 0.1 & 0.5 & Triangle & 48.3649 \\ \hline
13 & 0.05 & 0.8 & Straight line & 44.9336 \\ \hline
14 & 0.1 & 0.5 & Triangle & 48.3949 \\ \hline
15 & 0.05 & 0.8 & Grid & 40.6354 \\ \hline
16 & 0.05 & 0.2 & Grid & 49.6879 \\ \hline
17 & 0.1 & 0.5 & Triangle & 51.4619 \\ \hline
18 & 0.1 & 1.0 & Triangle & 53.0964 \\ \hline
19 & 0.05 & 0.2 & Straight line & 48.9745 \\ \hline
20 & 0.1 & 0.5 & Triangle & 49.7815 \\ \hline \hline \end{tabular}
\end{table} 
Table 19: Design results of Response Surface Method (Tensile strength). and larger fill spacing, the tensile strength is higher. According to Figure 9b, the tensile strength is higher at fixed fill spacing and Infill pattern and a smaller nozzle gap height. When the fill spacing and nozzle gap height are fixed, and the Infill pattern is closer to the straight line, tensile strength is higher. In Figure 9c, the tensile strength is higher when the nozzle gap height and Infill pattern are fixed with a smaller fill spacing. The tensile strength is higher at a fixed nozzle gap height and fill spacing with closer Infill pattern and straight line. A single-factor experiment is used for analysis to verify the existence of an optimal combination of printing parameters for the maximum tensile strength. A total of 25 experimental groups were designed. A single factor/parameter is changed at a time. The relationships of the factors are analyzed. The optimal parameters of various groups were compared, and then five parameters were combined. These are verified optimal process parameters for printing. The parameters are designed according to the Taguchi and the response surface methods, as shown in Table 21. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Item** & **Effect** & **Coefficient** & **Coefficient Standard Deviation** & **T Value** & _p Value_ \\ \hline Constant & & 48.41 & 3.45 & 14.02 & 0.000 \\ \hline X1 & \(-8.91\) & \(-4.45\) & 2.29 & \(-1.94\) & 0.000 \\ \hline X2 & 6.00 & 3.00 & 2.29 & 1.31 & 0.035 \\ \hline X3 & \(-6.90\) & \(-3.45\) & 2.29 & \(-1.51\) & 0.001 \\ \hline X1 \(\times\) X1 & \(-0.40\) & \(-0.20\) & 2.23 & \(-0.09\) & 0.931 \\ \hline X2 \(\times\) X2 & \(-3.19\) & \(-1.59\) & 2.23 & \(-0.71\) & 0.491 \\ \hline X3 \(\times\) X3 & \(-0.97\) & \(-0.49\) & 2.23 & \(-0.22\) & 0.831 \\ \hline X1 \(\times\) X2 & 11.94 & 5.97 & 2.99 & 1.99 & 0.034 \\ \hline X1 \(\times\) X3 & \(-10.57\) & \(-5.29\) & 2.99 & \(-1.77\) & 0.108 \\ \hline X2 \(\times\) X3 & 12.26 & 6.13 & 2.99 & 2.05 & 0.068 \\ \hline \end{tabular} S = 8.46488, R-sq = 66.21%, R-sq (adj) = 93.22%, R-sq (pred) = 84.83%.  
\end{table} 
Table 20: Regression model coefficients (Tensile strength). \begin{table}
\begin{tabular}{c c c c c c c c} \hline  & **Experimental Factors** & **Unit** & **Level 1** & **Level 2** & **Level 3** & **Level 4** & **Level 5** \\ \hline A. & Nozzle gap height & mm & 0.10 & 0.15 & 0.20 & 0.25 & 0.30 \\ \hline B. & Fill spacing & mm & 0.4 & 0.5 & 0.6 & 0.7 & 0.8 \\ \hline C. & Infill pattern & straight line & straight line & triangle & grid & grid \\ \hline D. & Infill print head & mm/s & 25 & 30 & 35 & 40 & 45 \\ velocity & & & & & & \\ \hline E. & Extruder & \({}^{\circ}\)C & 200 & 205 & 210 & 215 & 220 \\ temperature & & & & & & \\ \hline \end{tabular}
\end{table} 
Table 21: Single-factor experiment control levels (Tensile strength).