Outside vs. inside creasing - A parameter study

Abstract: Creasing of paperboard is an essential operation to obtain a well defined shape and strength of a package. The creasing tool consists of one male and one female creasing plate. The male plate presses the paperboard into the female plate and introduces damage in the creasing zone. Today the standard creasing operation at Tetra Pak is that the male creasing plate presses the top ply (print side) of the paperboard, and female is pressed against bottom ply (back side). This is called outside creasing, and the opposite is called inside creasing. This master's thesis has the purpose of studying the differences between inside and outside creasing with respect to how the paperboard behaves during bending and creasing. Since this area is hardly explored the purpose is to make a broad study about the differences of inside versus outside creasing. Many parameters will be measured and computer simulations will be used to get a better understanding of the parameters involved. The experimental tests are divided into three different parts: 1) Straight creases are made using a flat bed laboratory creasing tool, 2) A bottom crease pattern is made using a flat bed laboratory creasing tool, 3) The pattern of a Tetra Brik 250ml Base package is made in pilot plant and tested on paperboard and packaging material. MODDE, software using the method Design of Experiments, is used during two of the experimental parts in order to reduce the number of experiments. Straight creases are simulated using Abaqus built in material models for the continuum model and cohesive interface model for delamination. The creasing operation is simulated with rigid creasing plates while the folding operation is simulated using constraints and boundary conditions. In the experimental part, for straight creases, there is a significant difference between inside and outside creasing on a few of the responses investigated, but all tests show that change of paperboard, crease tool and crease depth have a bigger impact on the responses than the crease side. However cracks occur on inside creasing at a lower crease depth than outside creasing. From the other two experimental parts, no significant difference between inside and outside creasing could be found, and also here change of paperboard, crease tool and crease depth have a bigger influence on the responses and crack propagation. The simulations do not give a univocal result since they are all too similar independent of crease depth and web tension something that do not correspond with the experimental results. However the delamination behavior in the simulations and the experimental tests are similar, the delamination behavior is very different in the inside and outside creasing but this fact is not shown in the investigated responses.