# Optimization Parameters for PLA Through Additive Manufacturing: Taking Mixed Shapes as an Example
## 3 Results and Discussion
### Taguchi Method
#### 3.1.2 Taguchi Method of Tensile Strength  
Five control factors and four levels influencing the quality characteristics are selected. This study selected important parameters as the setting basis based on [9; 10; 11; 12]. These are nozzle gap height (mm), fill spacing (mm), infill pattern, infill print head velocity (mm/s), and extruder temperature (\({}^{\circ}\)C). The printing material used in this study is PLA. The processing parameters are determined based on material's characteristics, as shown in Table 6. After the model is printed, the universal tensile testing machine is used for the tensile strength experiment. The experimental data are recorded, and the S/N ratio of each group is calculated, as shown in Table 7. Five measurements were conducted, and the standard error of tensile strength is \(\pm 0.6\) MPa. \begin{table}
\begin{tabular}{c c c c c c} \hline  & **A.** & **B.** & **C.** & **D.** & **E.** \\ \hline Level 1 & **10.033** & **8.124** & 7.385 & 7.834 & 7.287 \\ \hline Level 2 & 8.065 & 7.863 & 7.301 & **8.082** & 7.483 \\ \hline Level 3 & 8.604 & 7.130 & 7.954 & 7.541 & **8.217** \\ \hline Level 4 & 4.346 & 7.959 & **8.408** & 7.591 & 8.062 \\ \hline Effect & 5.687 & 0.994 & 1.107 & 0.541 & 0.930 \\ \hline Rank & 1 & 3 & 2 & 5 & 4 \\ \hline \end{tabular}
\end{table} 
Table 5: Response table of factors to S/N ratio (Dimensional accuracy). Figure 6: Response diagram of factors to S/N ratio (Dimensional accuracy). Table 8 is the response table of the factors to the maximum tensile strength of the print and Figure 7 is the response graph of the factors to the maximum tensile strength of the print. Among them, experimental error in tensile strength is \(\pm\)10%, and this data is provided by the manufacturer. Regarding the latter-the-better quality characteristic, a larger S/N ratio represents a better quality characteristic. According to Table 8, the optimal factor level combination is A1 B1 C3 D2 E4. Specifically, the nozzle gap height of 0.1 mm, fill spacing of 0.6 mm, infill pattern triangle, infill print head velocity of 35 mm/s, and extruder temperature of 220 \({}^{\circ}\)C. \begin{table}
\begin{tabular}{l l l l l} \hline  & **Level 1** & **Level 2** & **Level 3** & **Level 4** \\ \hline A. Nozzle gap height (mm) & 0.1 & 0.15 & 0.2 & 0.25 \\ \hline B. Filling spacing (mm) & 0.6 & 0.8 & 1 & 1.2 \\ \hline C. Infill pattern & Grid & Straight line & Triangular & Spiral \\ \hline D. Infill print head velocity (mm/s) & 25 & 35 & 45 & 55 \\ \hline E. Extruder temperature (\({}^{\circ}\)C) & 190 & 200 & 210 & 220 \\ \hline \end{tabular}
\end{table} 
Table 6: Control factor level (Tensile strength). \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Exp.** & **A.** & **B.** & **C.** & **D.** & **E.** & **Tensile Strength (MPa)** & **S/N Ratio** \\ \hline
1 & 1 & 1 & 1 & 1 & 49.628 & 33.914 \\ \hline
2 & 1 & 2 & 2 & 2 & 2 & 44.566 & 32.980 \\ \hline
3 & 1 & 3 & 3 & 3 & 3 & 52.290 & 34.368 \\ \hline
4 & 1 & 4 & 4 & 4 & 4 & 37.166 & 31.403 \\ \hline
5 & 2 & 1 & 2 & 3 & 4 & 44.056 & 32.880 \\ \hline
6 & 2 & 2 & 1 & 4 & 3 & 48.537 & 33.721 \\ \hline
7 & 2 & 3 & 4 & 1 & 2 & 39.425 & 31.915 \\ \hline
8 & 2 & 4 & 3 & 2 & 1 & 43.970 & 32.863 \\ \hline
9 & 3 & 1 & 3 & 4 & 2 & 45.920 & 33.240 \\ \hline
10 & 3 & 2 & 4 & 3 & 1 & 33.883 & 30.600 \\ \hline
11 & 3 & 3 & 1 & 2 & 4 & 47.650 & 33.561 \\ \hline
12 & 3 & 4 & 2 & 1 & 3 & 34.800 & 30.832 \\ \hline
13 & 4 & 1 & 4 & 2 & 3 & 36.949 & 31.352 \\ \hline
14 & 4 & 2 & 3 & 1 & 4 & 46.559 & 33.360 \\ \hline
15 & 4 & 3 & 2 & 4 & 1 & 35.488 & 31.002 \\ \hline
16 & 4 & 4 & 1 & 3 & 2 & 40.507 & 32.151 \\ \hline \multicolumn{5}{c}{Average} & 42.587 & 32.509 \\ \hline \end{tabular}
\end{table} 
Table 7: Tensile strength and S/N ratio of each group (Tensile strength). The response factor table in Table 8 shows the effect of the factors on tensile strength. The greater the factorial effect, the greater the influence on the experimental results. According to the table, factor C (Infill pattern) has a greater effect on the maximum tensile strength of the print.