# Optimisation of Shrinkage and Strength on Thick Plate Part Using Recycled LDPE Materials
## 2 Methods and Materials
### Response Surface Methodology (RSM)
#### 2.1.1 Full Factorial Design  
Mould temperature, melt temperature, packing pressure and cooling time were selected as the input parameters due to their influence on the shrinkage and tensile strength, as stated in the literature [13; 17; 32; 35; 36; 37]. An AMI 2012 simulation software was used to determine the input parameters, as shown in Table 2. The software can also determine the maximum and minimum range of the input parameters, as seen in Table 3. Packing pressure and cooling time min and max range were determined based on the Fill+Pack analysis and cool (FEM) analysis in the AMI software. The maximum value for packing pressure and cooling time (output) were determined when all of other processing settings (input) in Table 3 were set to the maximum values. Meanwhile, the minimum value for packing pressure and cooling time (output) were determined when all other parameter settings (input) in Table 3 were set to the minimum values. Table 1 shows the mould and melt temperatures obtained from the material properties. The mould temperature was in the range between 20-60 \({}^{\circ}\)C, as recommended by the supplier. It was also recommended that melt temperatures remain between 160-180 \({}^{\circ}\)C.  
For design of experiments (DOE) analysis, Design Expert software was employed to assist the computation of the full factorial. In the full factorial, a set of 20 combination settings of processing parameters with four centre points was formed. The set of processing parameters was formed based on the range of processing parameters shown in Table 3 as the input parameter. The ANOVA in FFD evaluates the model as well as eliminating the insignificant input parameters that have probability values more than 0.05 (\(p\)-value \(>\) 0.05) and are considered to influence the shrinkage and tensile strength of the thick plate part. The presence of curvature in the ANOVA shows that the quadratic model is a more suitable fit in comparison to the linear model [38]. Hence, augmentation of FFD adds another 10 settings of processing parameters into the prior 20 settings of processing parameters. This is called the face centred central composite design (CCD), with a total of 30 combinations of parameters, as tabulated in Table 4. The additional 10 settings of processing parameters are to add points to the quadratic shaped graph and provide a better representation of the interaction between parameters and responses.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Filling Time (s)** & **5.5** \\ \hline Mould Temperature (\({}^{\circ}\)C) & 50 \\ Melt Temperature (\({}^{\circ}\)C) & 170 \\ V/P switch-over (mm) & 22.50 \\ Packing time (s) & 18.03 \\ Packing pressure (MPa) & 15.15 \\ Cooling Time (s) & 22.32 \\ Shear Rate (1/s) & 1437.0 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Recommended setting of input parameters (Reproduced from [33], with the permission of AIP publishing).  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Factor** & **Levels** & \\
**Factor** & **Low** & **High** \\ \hline Mould Temperature (\({}^{\circ}\)C) & 40 & 60 \\ Melt Temperature (\({}^{\circ}\)C) & 160 & 180 \\ Packing pressure (MPa) & 12.20 & 18.56 \\ Cooling time (s) & 19.42 & 26.54 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Input parameters of the thick plate part.