Plug materials for thermoforming: The effects of non-isothermal plug contact

The plug-assisted thermoforming process is the largest and most important industrial thermoforming process. The main aim of this study was to investigate the interaction between the properties of the plug and the polymer sheet in thermoforming. Non-isothermal plug only thermoforming tests were carried out using identical plug designs for various combinations of plug and sheet materials. It was hoped that this study would help to improve the understanding of friction and heat transfer effects during the thermoforming process. The plug materials used included: Hytac-BlX (thermoplastic syntactic foam), Hytac-WFT (epoxy syntactic foam with added Teflon), Blue Nylon, and POM (polyoxymethylene). The sheet materials included aPET and polystyrene (HIPS). It was found that the magnitude of slip during plug contact was much higher with aPET than with HIPS and that this reduced as the temperature of the plug was increased. Different plug materials produced significantly different wall thickness distributions in the preforms. It was concluded that friction was the dominant effect during contact.