Biaxial testing for the modeling of the thermoforming processes

Modeling techniques for thermoforming have become increasingly important in optimizing products and processes. Model accuracy is strongly dependent on the integrity of experimental data used to fit model parameters. For this reason, a custom-built biaxial forming machine capable of strain rate up to 32s ^-1 was constructed in order to obtain experimental data at conditions similar to those in thermoforming processes. The biaxial deformation behaviors of a wide range of thermoplastic materials such as PET, PS, PP, and LDPE have been analyzed in three different stretching modes (simultaneous equal biaxial, constant width, and sequential stretching). The results are presented in the paper.