Optimisation of deep drawn paperboard structures by adaptation of the blank holder force trajectory

The deep drawing process of paperboard has proven to be comparable to deep drawing of sheet metal in only a few aspects due to the nature and completely different behaviour of the material. However the blank holder also plays a key role with regard to quality and rupture prevention at 3D-structures. The aim of this paper is to describe the capabilities of variable blank holder force trajectories to improve the distribution of wrinkles and the quality of 3D-structures. The results show that the blank holder force should be adapted to the punch position keeping the highest possible force level. The force can be increased during the drawing process and needs to be strongly reduced short before the blank is drawn out of the blank holder completely. The introduced force trajectories lead to a significantly improved visual quality increasing the initial height where wrinkles occur encouraging fibre to fibre movement at the beginning of the process. The results furthermore contribute to a better understanding of the rupture behaviour. The increase of the circumference towards the border of the blank can be used to generate a blank holder force design that does not lead to ruptures but is able to make more intensively use of the capability the material exhibits to avoid wrinkles or distribute them as uniform as possible over the wall.