Paper Technology International 2024 - Journal - Page 45
PAPERTECHNOLOGYINTERNATIONAL
[5]
[4]
[6]
Figure 4: Out-of-plane shear test rig to determine the shear modulus and shear strength across the material thickness
Figure 5: Curvature Resistance Test (CRT) to determine the thickness-independent bending properties of natural 昀椀bre materials
Figure 6: FEM analysis of hydroforming during compression in the thickness direction and representation of different stressed
areas of the mould pattern
Furthermore, test scenarios and test conditions (nearprocess conditions) were identi昀椀ed, which provide information about
the formability of materials. Quality parameters agreed with the
industry were used to assess the forming process. These could be
divided into several categories and in昀氀uence each other. An example
of this for deep drawing is the question of the degree of forming
(drawing depth) in relation to the resulting number of folds (see Fig.
7). In hydroforming, the focus was particularly on mould 昀椀lling in the
two spatial directions MD and CD.
The targeted combination of input and output variables was
then used to predict the forming limits. Finally, the test methodology
for the different 3D forming process variants of deep drawing and
hydroforming was harmonized so that a standard was created that
then characterizes a paper material in terms of its forming ability.
The correlation analysis has shown that in some cases there are
very high correlations between the material parameters and the
forming quality. This is particularly evident in the characteristic
values determined from the cupping test and the tensile test. Models
created from parameters assigned to these two methods have
already shown good (preliminary) calculations for new combinations
of material and forming quality. If this parameter set is speci昀椀cally
extended with test results from the methods of splitting strength,
CRT, the above-mentioned shear methods and 2-point bending, the
models can make even more detailed predictions.
The project results will enable users to estimate the forming
quality of a material for deep drawing and hydroforming in the future
without the need to carry out extensive test series. This means that
papers can be tested for their suitability before they are used in 3D
forming and a targeted selection can be made for practical trials.
Scienti昀椀cally based Predictions about the Creasing Behavior of
Corrugated Board
The functionality of corrugated board packaging depends
to a large extent on the design of the box edges created by
creasing and bending or folding. Various aspects have to be taken
into account, such as the perfect appearance, strength-relevant
packaging properties and the desired hinge effect of the creasing.
The industry’s lack of knowledge about creasing corrugated board
in light of the ever-increasing demands on high-quality corrugated
board packaging, the trend towards lower grammages and
increased productivity requirements leads to increased rejects due
to product quality defects and system downtimes. The defects on
the product side relate to the cracking of the creasing directly during
creasing and after the folding process, an inadequate reduction in
bending stiffness and deviations from the internal dimensions of the
erected carton. This leads to machine downtimes, especially during
further processing in automatic raising machines if the deviations
are too large. However, the direct causes of creasing errors are
usually unclear, making a targeted solution to the problem dif昀椀cult or
even impossible. At present, it is not possible to estimate potential
problems that may occur during creasing in advance and thus avoid
them.
The Papiertechnische Stiftung Heidenau (PTS), together
with the Leipzig University of Applied Sciences (HTWK), has been
working on this topic since June 2021 as part of a research project
(“Creasing of corrugated board” IGF 21804 BR). The project, which
was completed in July 2023, focused on developing a applicable
knowledge base on the mechanical-physical relationships in the
process of creasing corrugated board.
Figure 7: Different results of deep drawing in terms of the degree of deformation and number of folds
due to the use of different materials.
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