Chapter 3 Computer simulation of thermoforming

This chapter provides a description of the application of the finite element method to the simulation of the thermoforming process. The objective of thermoforming simulation is the provision of a rational means of mold design and to also allow for the design of “optimal” final parts using the minimum amount of material. This can be achieved by comparing the simulated behavior using various materials and mold configurations with varying process conditions. This eliminates the need to perform inefficient and expensive “trial-and-error” procedures. A “state-of-the-art” review of the finite element method in the simulation of thermoforming is given. The review covers the details of the membrane and thick sheet finite element formulations as well as non-linear elastic (Ogden, Mooney-Rivlin) and visco-elastic (K-BKZ) material constitutive relationships. Some examples, giving comparisons between simulation results and experimental values are also included. Good agreement was obtained between the predicted and measured thickness distributions. The results also indicate that the choice of mateiral model (non-linear elastic versus visco-elastic) must be done carefully if reliable predictions of the thickness distribution are to be achieved. For straight thermoforming into shallow molds a non-linear elastic model is suitable. However, when deep drawn forming, complex mold geometry or plugassistance is involved, a visco-elastic model is required to obtain accurate predictions.