A Numerical/Experimental Approach to Software Development for Thermoforming Simulations (Survey Paper)

Abstract

This paper describes a combined numerical and experimental approach to the development of a software package for simulating the thermoforming process. In this process thin polymer sheets are forced under pressure into a mold cavity. During the forming process the polymer is subjected to large deformations, which result in severe nonuniform thinning. The development of the simulation software was facilitated by a close interaction between numerical modeling and experiment. On the one hand, experimental results guided the development of the software, and on the other hand, numerical developments have been used to suggest new experiments to be performed and critical quantities to be measured. The numerical software is based on the finite element method and the hot polymer is modeled as a nonlinear elastic membrane. Because of the very large deformations occurring in this process, a rigorous large deformation theory has been employed. The numerical formulation also contains contact capabilities for contact between the polymer and the mold and for contact between different parts of the polymer itself. Since very little was known about the physical processes before the program was started, especially about the material behavior and temperatures involved, carefully planned experiments were carried out to guide the selection of the material models used in the software. Since there also was a widespread misconception about the nature of some of the process parameters involved, numerical calculations were used to suggest measurements to be performed on some of these critical parameters. Excellent correlation between calculations and experiment have been obtained and are presented in the paper.