Experimental and numerical investigation of the effects of sheet material, plug-assist tool material, and process conditions on the mechanical pre-stretching stage of plug-assist thermoforming.

Plug-assist thermoforming is a complex process with numerous parameters influencing the quality of the manufactured product. The pre-stretching stage is the most important step in plug-assist thermoforming. Mechanical pre-stretching is used to redistribute material from thicker regions to thinner ones with a plug-assist tool. Experimental tests do not assess all potentially relevant influences. Numerical simulations are therefore useful to achieve a deeper understanding of the process and the mutual interactions between the input parameters. In this paper, we develop thermoelastoviscoplastic polymer behavior and thermomechanical friction finite element models to simulate the plug-assist pre-stretching of high-impact polystyrene, amorphous polyethylene terephthalate, and lightweight polystyrene sheets. The effects of plug-assist tool materials and process conditions are experimentally and numerically analyzed. Plug pre-stretching force and thickness distribution of the simulated test match well with the measured results. The proposed models accounting for the main thermomechanical aspects of the plug-assist thermoforming process provide a way to predict the quality of thermoformed parts. [ABSTRACT FROM AUTHOR]