SHRINKAGE OF THE AMORPHOUS AND SEMI CRYSTALLINE THERMOPLASTICS IN INJECTION MOLDING PROCESS AT CONSTRAINED STATE

Existence of molds constraints exerts noticeable effect on the final dimensions (shrinkage) of molded parts due to the viscoelastic characteristics of polymeric materials. In the present study, an analytical approach is introduced to predict constrained shrinkage of both semi-crystalline and amorphous thermoplastics and then experimentally examined using a case study. A mold was constructed to produce a plate featured by holes (as constraints) and injected to produce experimental data. The results indicated that there is a good agreement between the prediction and the experimental data, especially at longer cooling time.

Keywords:

Shrinkage , Injection molding , Viscoelastic , Constraint , Cooling times