Effects of rheological properties and processing parameters on ABS thermoforming

Understanding effects of material and processing parameters on the thermofo rming process is critical to the optimization of processing conditions and the development of better materials for high quality products. In this stud y we investigated the influence of both rheological properties and processi ng parameters on the part thickness distribution of a vacuum snap-back form ing process, Rheological properties included uniaxial and biaxial elongatio nal viscosity and strain hardening and/or softening while processing parame ters included friction coefficient, heat transfer coefficient, and sheet an d mold temperatures. The Wagner two parameter nonlinear viscoelastic consti tutive model was used to describe rheological behavior and was fit to shear and elongational experimental data. The linear viscoelastic properties alo ng with the Wagner model were utilized for numerical simulation of the ther moforming operation. Simulations of pre-stretched vacuum thermoforming with a relatively complex mold for a commercial refrigerator liner were conduct ed. The effects of nonlinear rheological behavior were determined by arbitr arily changing model parameters. This allows determination of which rheolog ical features (i.e., elongational mode, viscosity, and strain hardening and /or softening) are most critical to the vacuum snap-back thermoforming oper ation. We found that rheological and friction properties showed a predomina nt role over other processing parameters for uniform thickness distribution .