In-mould graining of 3D-shaped parts with micro-structured surfaces

To make functional surface effects on plastic components usable on an industrial scale, new processes have to be developed. The in-mould graining (IMG) process is a variant of the thermoforming enabling the manufacture of micro-structures. One advantage of the IMG process is that the surface structure is formed to the final shape of the part. Recent investigations show that the forming accuracy of a flat mould can be extended by applying a variothermal mould heating in the IMG process. As high mould temperatures lead to high forming accuracies but also increase the cycle time of the process, a conflict of interests follows. In this paper, it is investigated to what extent high moulding accuracies can be achieved to form three-dimensional parts by using the IMG process extended by a variothermal mould heating. The results show that forming accuracies of micro-scaled structures of >90% can be reached on the bottom and the side walls of a cup-shaped mould. To address the conflict of interests between high moulding accuracy and long cycle times, the influence of the mould temperature is investigated in detail. To analyse the micro-forming behaviour of the processed material, analyses of the rheological behaviour with a rotational rheometer are carried out.