# Optimization of Shape Design of Grommet through Analysis of Physical Properties of EPDM Materials
## 2 Experimental Analysis Based on Molding Process Conditions  
### Analysis of Physical Properties Based on Molding Process Conditions  
The physical properties of EPDM rubber, which is a raw material for making grommet, were analyzed according to the conditions of the injection process. The controllable factors that were expected to affect the physical properties were set, and specimens were fabricated according to the KS M 6518 [13] standard for each experimental condition. The physical properties were set as tensile strength and elongation, which were measured using a universal testing machine. Table 1 shows the main process parameters for injection molding. The experiment was conducted 16 times. The table shows the experimental conditions for each process value.  
Figure 1 shows the main effects and interactions of the factors that affect tensile strength. Temperature and time affect tensile strength, while degassing does not. Additionally, interactions occur according to time and temperature and no interactions occur, owing to degassing.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & **Tem.** & **Time** & \multirow{2}{*}{**Degassing**} & **Strength** & **Elongation** & \multirow{2}{*}{**No**} & **Tem** & **Time** & \multirow{2}{*}{**Degassing**} & **Strength** & **Elongation** \\  & **(°C)** & **(s)** & & & & & & & & **(°C)** & **(s)** \\ \hline
1 & 160 & 200 & \(\bigcirc\) & 11.2 & 969.0 & 9 & 160 & 200 & X & 10.5 & 968.3 \\
2 & 160 & 200 & \(\bigcirc\) & 11.1 & 960.4 & 10 & 160 & 200 & X & 10.8 & 944.8 \\
3 & 160 & 600 & \(\bigcirc\) & 13.4 & 853.9 & 11 & 160 & 600 & X & 13.5 & 851.5 \\
4 & 160 & 600 & \(\bigcirc\) & 12.9 & 815.2 & 12 & 160 & 600 & X & 13.0 & 821.2 \\
5 & 180 & 200 & \(\bigcirc\) & 13.2 & 840.5 & 13 & 180 & 200 & X & 12.8 & 838.7 \\
6 & 180 & 200 & \(\bigcirc\) & 13.1 & 836.0 & 14 & 180 & 200 & X & 13.2 & 844.8 \\
7 & 180 & 600 & \(\bigcirc\) & 13.4 & 775.0 & 15 & 180 & 600 & X & 13.0 & 749.7 \\
8 & 180 & 600 & \(\bigcirc\) & 13.7 & 792.3 & 16 & 180 & 600 & X & 13.3 & 767.1 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Experimental conditions for different process values (DOE).  
Table 2 shows the analysis of variance (ANOVA) result for the factors that affect tensile strength. ANOVA is a collection of statistical models and their associated estimation procedures (such as the \"variation\" among and between groups) used to analyze the differences among group means in a sample. 'Adj. SS' represents the sum of squares, 'Adj. MS' is the mean squares, and '\(F\)-Value' is the value of the adj. The SS of each factor divided by the mean squares error. '\(p\)-value' was derived based on \(F\) value. \(p\) values larger than 0.05 are pooled as error terms, and only significant factors are shown. The regression Equation (1) was derived through ANOVA analysis. The R\({}^{2}\) value of the regression equation is 94.59% and the adj. R\({}^{2}\) value is 93.24%.  
\[\textit{tensile strength}=\ -15.59+0.1585\textit{Temp}+0.04592\textit{Time}-0.00 025\textit{Temp}\times\textit{Time} \tag{1}\]