# Optimization of Shape Design of Grommet through Analysis of Physical Properties of EPDM Materials
## 2 Experimental Analysis Based on Molding Process Conditions
### Measurement of Grommet Mounting Performance according to Molding Process Parameters  
We derived the process parameters that increase mounting performance by measuring mounting performance according to grommet shape. Based on the results described in the previous section, temperature and time were set as the process parameters because they affect tensile strength and elongation. We set the maximum and minimum values for each factor according to grommet shape and fabricated the grommet. Here, degassing was applied in the fabrication of all products. The mounting performance of the products was analyzed by measuring the insertion force required for fastening the grommet and the required separation force. Insertion force and separation force were measured using a universal tensile tester when the grommet was inserted into or removed from a panel fixing jig. The experimental speed was set as 50 mm/min, and the experiment was repeated twice. We employed three widely used types of shapes for the grommet. The temperature and time parameters for molding the grommet of each shape in the initial test are shown in Table 4. Figure 3 shows the types of grommet shape.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Type**} & \multicolumn{2}{c}{**Temp. (\({}^{\circ}\)C)**} & \multicolumn{2}{c}{**Time (s)**} \\ \cline{2-5}  & **Min(\(-\)1)** & **Max(1)** & **Min(\(-\)1)** & **Max(1)** \\ \hline Bellows & 160 & 180 & 200 & 600 \\ Cable & 170 & 190 & 400 & 800 \\ Blank & 180 & 200 & 300 & 900 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Experimental conditions.  
Figure 2: Main effects plot and interaction plot for elongation. (**a**) Main effects plot for elongation; and (**b**) Interaction plot for elongation.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source** & **DF** & **Adj SS** & **Adj MS** & **F-Value** & **\(p\)-Value** \\ \hline Model & 3 & 75,096.2 & 25,032.1 & 116.87 & 0.000 \\ Linear & 2 & 71,937.7 & 35,968.9 & 167.93 & 0.000 \\ Temp. (\({}^{\circ}\)C) & 1 & 34,243.5 & 34,243.5 & 159.88 & 0.000 \\ Time (s) & 1 & 37,694.2 & 37,694.2 & 175.99 & 0.000 \\
2-way interactions & 1 & 3158.4 & 3158.4 & 14.75 & 0.034 \\ T (\({}^{\circ}\)C) \(\times\) Time (s) & 1 & 3158.4 & 3158.4 & 14.75 & 0.002 \\ Error & 12 & 2570.2 & 214.2 & & \\ Total & 15 & 77,666.4 & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: ANOVA result for elongation.  
The insertion force and separation force for different grommet shape types are given in Table 5. ANOVA was used to analyze the insertion force and separation force for each type of shape, and it was confirmed that there was no difference between insertion force and separation force according to grommet process parameters. As shown in Figure 4, even though there is no difference between insertion force and separation force according to process parameters, the times at which the maximum insertion force and maximum separation force occur vary depending on process parameters. This appears to be because the elongation rate changes according to process parameters. Moreover, it was confirmed that the change in insertion force and separation force was more influenced by the changes in the shape of the grommet.