Examination of Modeling for Computer Simulation of Thermoforming Process

The deformation patterns and the thickness distribution of the products in a thermoforming process with blowing, stretching and vacuuming was simulated. A simple material model (Mooney-Rivlin model) was employed in this simulation. The visco-plastic behavior and the effect of the temperatare distribution of the specimen sheet in the observed thermoforming process were taken into consideration in the value of the Mooney constant for each element of the modeled sheet in the finite element analysis. For axisymmetric forming, the calculated results with uniform temperature in the specimen sheet had a fairly good agreement with the experimental results. On the other hand, for non-axisymmetric forming to make a 3-D rectangular box, the calculated results with uniform temperature in the specimen sheet had some differences from the experimental result, but those with distributed temperatures were in good agreement with the experimental results. In conclusion, it is confirmed that consideration of the distributed temperature in a specimen sheet for the simulation of the thermoforming process is most important. The strain rate of the specimen sheet in the thermoforming process or the anistropy of the specimen sheet had little effect on the precision of the calculated results.