Investigation of Creases

Abstract

One of the main concepts that made Tetra Pak a world leading company in producing
packages for liquids, is the idea of folding paperboards. To get a good and precise
fold it is necessary to crease the paper before the folding process takes part. By using
creasing, the package can get more precise, stronger folds and can be produced at
high speed. The creasing tool consists of a male plate and a female plate. The male
plate presses the paperboard into the female plate to weaken the paper in the desired
area. Since the creasing process consists of a male die pressing the paperboard into a
female die, the position of the male die affects the crease properties. To get the
ultimate result, the male die should be positioned exactly in the middle of the female
die.
The purpose of this master thesis is in general to determine how a displacement of the
dies affects the actual crease. Since cracks are fatal for the creasing procedure it is
necessary to investigate how the displacement influences the ease of crack initiation
and if it is possible to somehow prevent it. This subject has hardly been explored. Due
to the lack of information about displaced creasing tools, it is not possible to scale
down the problem by using already know facts. Instead, several studies and tests had
to be undertaken where many parameters were observed.
The different tests involved an experimental part and a simulation part. The
experimental part is divided into three different parts. The main part is when making
straight creases by using a flat bed creasing machine. MODDE has been used to
obtain information about which factors may be significant. MODDE is software that
employs Design of Experiments. The second part of the laboratory tests also
comprised use of a flat bed creasing machine, but with a tool consisting of a bottom
pattern of a straight crease. The third and last experimental part was in Tetra Pak’s
pilot plant, were analyses of the process in full scale were done.
The simulation part was done in ABAQUS/CAE. The simulation is important since it
is of particular interest to compare simulations with the real tests that were made. The
simulation makes it easy to get graphs that can be compared between the different
experimental parts.
From the experimental tests on the straight creases the significant factors was picked
out and insignificant factors was discard from interest.
In the second experimental part on the bottom crease pattern, tests on both MD
(machine direction) and CD (cross direction) were made, and the goal was to crease
as close to the crack limit as possible and with different displacements.
The same thought was when creasing in the pilot plant i.e. as close to the crack limit
as possible. Form these different tests, results were plotted and information could be
read out.
It is determined that it is possible to crease different depths depending on what type of
paperboard is used. The crease depth is also affected by the displacement of the die
since it is not possible to crease as deep with a displaced die as with a centered one.
The distortion does completely changes with displaced dies. Two curves were plotted
to see when the displacement is significant and when it is insignificant, one curve for the thick paperboard and one for the thin paperboard. Curves were also plotted to
make it easy for the operator to use the RCSp (see page 39) to foresee if there will be
cracks in the paperboard or not.

• author: Alberius, David and Gerstner, Fredrik
• supervisor: Giorgos Nikoleris
• organization: Innovation
• course: MMK820 20112
• year: 2011
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Distortion, uncentering, displacement, creasing, RCS
• language: English
• id: 1939973
• date added to LUP: 2011-05-04 15:43:29
• date last changed: 2011-05-04 16:01:41