Ctime —0.013322 0.004902 —2.72 0.013

S = 0.1040 R-Sq(pred) = R-Sq(adj) = Regression 4 5.3280 1.3320 124.45 0.000

93.90% 94.9% Residual error 22 0.2355 0.0107

PRESS = 0.339428 R-Sq = 95.9% Total 26 5.5634

The first-order regression model is developed to obtain the values obtained from the FE analyses when compared to the simulated values. By utilizing the first-order regression  model

First-order model

5 10 15 20 25 30

Experiment number

Fig. 3 Comparison of the values of FE analyses with the simulated values

Second-order model

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Experiment number

Fig. 4 Comparison of the values of FE analyses with the simulated values

for the shrinkage, the maximum error (ME) and the average absolute percentage error (APE %) are found to be 3.895 and 0.678%, respectively. Figure 3 displays the comparison of the values of FE analyses with the simulated values obtained from the first-order regression model for the shrinkage. It can be observed that the values of the FE analyses agree with the simulated values.

The second-order regression model is developed to obtain the values obtained from FE analyses versus the simulated values. By employing the second-order regression model for the shrinkage, the ME and the APE (%) are found to be 3.994 and 0.705%, respectively. Figure 4 illustrates the comparison of the values of the FE analyses with the simulated values obtained from the second-order regression model for the shrinkage. It can also be observed that the values of FE analyses agree with the simulated values.

4.2 Simulation (Mold Flow) Results

The simulation results obtained from FE analyses run in Moldflow during the plastic injection molding of the plastic part of the DVD-ROM cover consisted of the variation of the volumetric shrinkage values under different process parameters and the other graphs (Fig. 6, 7) that relate to machine   setups.

From the results of Table 2, it can be postulated that the shrinkage is highly influenced by the plastic injection param- eters such as Ctime and Itime when compared with the other parameters of Tmold, Tmelt, and Pinj. The values of the shrinkage generally decrease as the Ctime parameter increases at the injection times of 1, 2, 3 s. Further, the values of the shrinkage tend to decrease to the mold temperature from 40 to 60 °C at the first value of the injection time (1 s). After that point, they follow an irregular pattern.