Finite element modelling of low temperature forming of polymer films with application in in-mould decoration

This paper explores the development and use of finite element simulations of forming processes used for printed polymer films as part of the in-mould decoration (IMD) process. Material models developed from tensile test data were used in the simulation of matched metal and high pressure forming of a simple single element of a keypad.Consideré stress and logarithmic strain were appropriate for converting engineering stress–strain data into an elastic–plastic form suitable for finite element simulations, and were capable of capturing differences in behaviour in polymer films.Friction between tooling and film prevented key face deformation for both forming methods. Upon unloading, significant spring back occurred due to elastic recovery in the film. Formed geometry was dependent on the process, film type and temperature. The potential draw depth of the high pressure forming was higher than for matched metal due to the increased film area available for deformation and higher film elongation at elevated temperature. Polyester blended films were capable of higher draw depths than polycarbonate film, particularly at elevated temperature where they softened to a greater extent and had greater maximum elongation. Blended films also required lower forming pressures than polycarbonate film due to the lower stresses required for a given strain.