Numerical and experimental analysis of HIPS sheets in thermoforming process

In this study, two different thermoforming molds, i.e., male and female, were prepared and used to conduct different tests at various heating times and evacuation powers. High impact polystyrene sheets of 0.5 mm thick were used to produce the cups with two vacuum and drape forming process. The experimental results showed that a more uniform thickness distribution could be obtained by increasing the heating time for the female mold. However, for the male mold, the heating time must be decreased in order to achieve a more uniform thickness distribution. Our findings showed that biaxial stretching was dominant in the vacuum forming, while uniaxial stretching was dominant in the drape forming. A finite element simulation of the vacuum forming process was also conducted to present a simple and accurate study of the forming process. In this work, a hyperviscoelastic constitutive model was used for modeling the high impact polystyrene behavior at forming temperature. The thickness distribution obtained by the finite element analysis is in a good agreement with the experimental results. In addition, the effect of friction coefficient was investigated by finite element analysis on the thickness distribution of the cup.