THERMOFORMING SHRINKAGE PREDICTION SUBMITTED TO POLYMER ENGINEERING & SCIENCE REVISED 1-FEB-2001

Most thermoforming product development processes rely on costly and time consuming forming trials to determine adequacy of the mold and process. In this paper, an analytical method is developed for shrinkage predictions on the basis of a visco-elastic constitutive material model with initial conditions from a commercial thermoforming simulation. The theoretical analysis and transfer functions have been developed to accommodate different sets of materials, process conditions, and mold geometry. The shrinkage model consists of a transient thermal analysis for temperature solution; a stretching phase analysis for inflation-induced stress estimation; a post contact analysis for thermal stress and relaxation; and a post-molding strain analysis based on stress solution. The shrinkage prediction analysis has been developed and validated with a complex geometry thermoforming application. The results indicate that the shrinkage estimates provided by the analysis were within the objective tolerances of 0.1%, as measured in terms of absolute prediction error