Thermoforming shrinkage prediction

Most thermoforming product development processes rely on costly and time-co nsuming forming trials to determine the adequacy of the mold and process. I n this paper, an analytical method is developed for shrinkage predictions o n the basis of a visco-elastic constitutive material model with initial con ditions from a commercial thermoforming simulation. The theoretical analysi s has been developed to accommodate different sets of materials, process co nditions, and mold geometry. The shrinkage model consists of a transient th ermal analysis for temperature solution; a stretching phase analysis for in flation-induced stress estimation; a post-contact analysis for thermal stre ss and relaxation; and a post-molding strain analysis based on stress solut ion. The shrinkage prediction analysis has been developed and validated wit h a complex geometry thermoforming application. The results indicate that t he shrinkage estimates provided by the analysis were within the objective t olerances of 0.1%, as measured in terms of absolute prediction error of par t dimensions.