Numerical modeling of injection/compression molding for center‐gated disk: Part II. Effect of compression stage

Abstract

In the accompanying paper, Part I, we have presented a physical modeling and the associated numerical analysis of the injection molding process with a compressible viscoelastic fluid model. In Part II, effects of the compression stage in the injection/compression molding process are presented. Numerical results showed that the injection/compression molding process reduced birefringence as compared with the injection molding process. In this respect, the injection/compression molding process seems to be more suitable for manufacturing precise optical products of good optical quality than the injection molding process. Effects of the packing stage on the birefringence distribution in the injection/compression molding process were found to be similar to those in the injection molding process. Our numerical results show that the birefringence becomes smaller as the melt temperature gets higher and the closing velocity of the mold gets smaller with the flow rate and the mold temperature affecting the birefringence insignificantly. As far as the density distribution is concerned, the flow rate, melt temperature, and mold closing velocity have insignificant effects on the density distribution in comparison with the mold temperature.

Birefringence in injection‐compression molding of amorphous polymers: Simulation and experiment

“…6b. Similar velocity profiles are also obtained by Kim et al [26], Chen et al [31], and Lee and Isayev [57]. The velocity behavior can be explained by considering the mass balance.…”

“…In particular, the birefringence of ICM PC disk increases and then decrease slightly with the radial position, whereas that of CIM PC disk continues to decrease significantly with the radial position. This trend in ICM and CIM disks is explained in detail [26, 57]. A reduction of birefringence in ICM PC disk at a radial position of 2.948 cm compared with that at a radial position of 3.704 cm is due to the fact that the velocity and shear rate increase with the radial position during the compression stage.…”

“…Park et al [25] presented a numerical simulation for ICM of a center‐gated disk using finite difference (FD) method using Leonov compressible viscoelastic model and the Tait equation of state. Kim et al [26] and Lee et al [27] developed a numerical analysis using FD for the solution of governing equations of the radial flow and studied the distribution of birefringence in CIM and ICM center‐gated disk using the Leonov model. Chen et al developed a numerical algorithm to simulate the filling stage of the stamping type of ICM using an inelastic [28–30] and viscoelastic [31] flow.…”

“…Friedrichs et al [32] used an incompressible viscous flow model to simulate the birefringence in ICM of the stamping type. Kim et al [26, 33] carried out a numerical analysis to investigate the effects of the compression stage on the birefringence in ICM of the stamping type using a viscoelastic model. They found that, in comparison with CIM, ICM reduced the birefringence and the mold temperature had a significant effect on the density distribution in comparison with other processing conditions.…”

Numerical simulation for flow‐induced stress in injection/compression molding

“…Although Hele‐Shaw model can describe some characters of compressing flow , it only performs well for thin part with uniform thickness because flow change on thickness direction is neglected. To fully characterize the flow behavior in nonuniform or complex mold cavity, one has to use three‐dimensional (3D) method even it involves great deal of computation.…”