# Optimization of Shape Design of Grommet through Analysis of Physical Properties of EPDM Materials
## 5 Conclusions  
This study conducted optimization to improve the mounting performance of a grommet using EPDM materials. The physical properties of the main molding materials were investigated according to process parameters. A grommet was fabricated according to the process parameters of fabrication. Insertion force and separation force were examined through experiments. Nonlinear material constants were determined through uniaxial and biaxial tensile tests. The nonlinear analysis of the grommet was conducted, and a compound design that incorporated the shape parameters for the minimum load of each part was derived. Then, additional nonlinear analysis was performed. This was followed by a comparative analysis of the actual model through experimental evaluation.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Classification** & **Predicted Value (N)** & **Simulated Value (N)** & **Experimental Value (N)** \\ \hline Insertion force & 62.5 & 62.8 & 50.0 \\ Separation force & 77.0 & 77.1 & 85.3 \\ \hline \hline \end{tabular}
\end{table}
Table 10: Predicted and measured insertion force and separation force.  
Figure 10: Comparison of simulated and experimental values. (**a**) Insertion force measurement; and (**b**) comparison of insertion and separation forces.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Classification** & **Predicted Value (N)** & **Analysis Value (N)** & **Difference (N)** \\ \hline Insertion force & 62.46 & 62.76 & 0.29 \\ Separation force & 76.98 & 77.08 & 0.10 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Comparison of predicted and analysis values.  
1. The physical properties of EPDM materials were analyzed according to molding parameters. Tensile strength and elongation were measured. Tensile strength increased with temperature and time.
2. A grommet was fabricated by applying the process parameters that affected the properties of specimens. Experiments were conducted to measure the insertion force and separation force of the fabricated grommet. We confirmed that the maximum load did not change with tensile strength and elongation. Moreover, differences in insertion time occurred owing to differences in elongation.
3. Uniaxial and biaxial elongation tests of the EPDM materials were conducted to perform the nonlinear analysis of the grommet, and physical property data were derived through the Ogden model. The grommet model was set for each shape parameter and analyzed for various cases. The influence of insertion force and separation force was confirmed through the set shape parameters, and the dimensions for minimizing insertion force and maximizing separation force were derived.
4. Additional analysis was performed for comparing the results of the optimization and experiments to verify the feasibility of the derived dimensions.  
Y.S.K., E.S.H. and E.S.J. conceived and designed the experiments; Y.S.K., E.S.H. and E.S.J. performed the experiments; Y.S.K., E.S.H. and E.S.J. analyzed the data; Y.S.K., E.S.H. and E.S.J. contributed reagents/materials/analysis tools; Y.S.K., E.S.H. and E.S.J. wrote the paper.  
This research was financially supported by the Ministry of SMEs and Startups (MSS), Korea, under the \"Convergence and Integration R&D(P0005112)\" supervised by the Korea Institute for Advancement of Technology (KIAT).  
The authors declare no conflict of interest.