Modeling of the thermoforming process of high impact polystyrene

Thermoforming process is one of the common and low cost methods of forming thermoplastic polymers and producing high quality products. This method is used for producing industrial products and packaging products such as food storage containers. In this research¡ finite element modeling of the thermoforming process is carried out and the effects of process parameters on the quality of final product are investigated. In this research¡ Maxwell viscoelastic constitutive equation is adopted and simulation of a high impact polystyrene (HIPS) polymeric specimen with rectangular shape is carried out in ABAQUS finite element software. Constitutive equations of material behavior are implemented in a user defined material subroutine (UMAT). User subroutine verification is carried out by simulation of pure shear test in constant strain rate loading. Considering uniform thickness of the final product as criteria of product quality¡ the effects of four parameters namely¡ friction coefficient¡ plug velocity¡ sheet dimension and temperature on the quality of the final product are investigated. The results of process simulation shows that the friction coefficient between die and work piece has the most significant effects on the uniform thickness distribution of the final product.