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ACHIEVING THE BEST ACCURACY IN SHELL PRODUCTION WITH ELONGATION REPORTS
1.
What is an elongation report and why is it important?
A proper bending process will give the shell plate its final shape and size. It is important to
note that the bending process does not only change the shape of the plate but also affects
the size of the plate depending on the bending method and the material used. A cold
bending process will enlarge the plate size, while a line heating bending process will shrink
the plate.
Elongation is used to compensate for the size of the shell plate due to the bending process.
An elongation report contains all the necessary information for production about how much
deformation is needed to give a 2D plate its final 3D shape.
Please note that the standard norm in our examples does not comply with the very
specific values appropriate for your production.
The Hull system will calculate every plate regardless of its bending abilities. The system will
use this as input to create an elongation report for each plate.
Without reviewing this information, production can produce unacceptable results, which
might lead to material wasting, high production times or inaccuracies.
These reports should be customized to make sure that the plates can be properly bent
by production.
The information below will assist you in creating these reports to achieve the best results in
the production phase of your shell plates.
2.
What you need to know to create your own reports
In the case of a completely flat, a cone or a cylinder shell plate it’s not necessary to add
elongation. However, most shell plates are double curved, and for this reason, elongation is
required to bend the plate to its final accurate shape and contour.
A spherical shaped plate gets its highest elongation in the middle section of the part while a
saddle shaped plate will get the highest elongation at the sides. Plates that contain both of
these peculiarities in shape are the most difficult to bend and should be avoided.
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The bending process is mostly done by the human workforce and requires professional skills.
The insight of these experts is very important to achieve a good result; it can reduce time
spent on the bending process to a minimum while choosing the wrong bending process can
result in wasting the plate. The highly qualified professionals use templates generated by the
engineers to understand the curvature and torsion of the plate. The templates also help
them to find the almost cylindrical or conical directions. In some cases, the roller line can
help, but the bending process for 3D curved shapes is mainly a handicraft process.
There is a correlation between the level of professional skills and maximum elongation value
that can be handled at the production site. The professionals involved in production should
inform the system manager which maximum values they are able to handle. The engineer
should always take into consideration the competence level and the limitations indicated by
production when designing the shell plates. The material type and thickness also affects the
limit of the acceptable deformation.
When the elongation has exceeded the maximum values, the engineer must double-check
his plate boundaries or shell plate shape. Shell plates with shorter width are usually easier to
handle. The elongation grows significantly when the width of the shell plate is increased.
Last but not least, the elongation report also allows you to control results. Plates with high
elongations values have to be checked and considered as unacceptable for production.
The following sections will help you to define your own rules and create your own reports.
In case you have questions or need further assistance don’t hesitate to contact CADMATIC
Support.
3.
Parts of the elongation report
A good elongation report is a combination of five important input parameters:
1.
2.
3.
4.
5.
3.1.
The shell plate.
The template set.
The elongation layout.
The color rules.
The extremity rules.
The shell plate
The boundaries of the shell plate are created by the engineer; the system is not limiting the
size or shape. While the engineer can create all kind of shapes, the production has to
consider many limitations such as the plate size of the raw material, the type of the bend
tool or even the size of the production area. This means that even if a part is defined as a
simple cone by the engineer, in case the production has no tools to bend it as one it has to
be split into smaller parts.
3.2.
The template set
A 3D image of the plate and the templates are presented in the elongation list to provide
production with a better understanding of its complexity.
3.3.
The elongation layout
The elongationreport.xls is the template layout for all elongation reports. This file
can be edited by using Microsoft Excel. The system manager has the freedom to define
general shell plate information such as size, weight, work breakdown data, legend, color map
of the plate, a 3D picture of the plate and templates, company name, etc. The system will
use this template to create an informative excel report for each plate. The name and location
of the report can be defined in the system management application.
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3.4.
The color rules
This is a spherical shaped plate with a thickness of 24mm that has been created to
demonstrate the color based bending information. In the elongation, report values are
colored based on thickness and material type.
In our example, the colors are defined by inverse rainbow colors that range from blue
(lowest values) to red (highest values). Minimum and maximum values are defined by the
extremities. All values larger than the acceptable range will be marked with black color. You
can create your own rules and color settings for your elongation report.
Just as the user would expect, the elongation of this shell plate is lowest at the sides and the
highest in the middle section.
The rule should always be set up based on the feedback of the skilled professionals working
on the production site. In this specific example production indicated that they could handle
plates with a maximum elongation of 16mm per meter in length direction. The colors show
clearly that this plate oversteps the indicated maximum limit by having a maximum of
21.5mm per meter elongation in the middle section.
Below you will find the rule definition:
Elongation color for plate thicknesses > 10.0
elo_type==ELO_TYPE_X and elo>=elo_min_x and elo<=elo_max_x $
INV_RAINBOW(elo_min_x,elo_max_x,elo,11)
elo_type==ELO_TYPE_Y and elo>=elo_min_y and elo<=elo_max_y $
INV_RAINBOW(elo_min_y,elo_max_y,elo,11)
rgb(0,0,0)
Variable elo is the elongation of each point on the plate; this value will be used to give the
plate the color. When this value is low it will use blue, when it is almost 16 it will use red. All
values larger than 16 will show up in black color.
The color black is defined by the function rgb() and will be used when the first two
conditions in the rule are false. This could be a negative elongation or an elongation bigger
the 16mm/meter. Normally a negative elongation is not possible.
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In the example above we use the elocol0003.cfg rule because our example plate is
thicker than 10mm. The system manager is free to define multiple rules and conditions.
3.5.
The extremity rules
With the extremity rules, the system manager can define the minimum and maximum limits
for elongation. These values will be expressed in the color map of the plate.
The first rule file eloext0001.cfg uses the thickness to select one of the other rule file
2,3 or 4.
Elongation extrema
thickness<10 $ eloext0002
thickness>=10 and thickness<18 $ eloext0003
thickness>=18 $ eloext0004
-1
The below rule file eloext0004.cfg defines the minimum and maximum extremity in
x(0-16) and y(0-8) direction.
Elongation extrema
elo_extremum==elo_min_x
elo_extremum==elo_max_x
elo_extremum==elo_min_y
elo_extremum==elo_max_y
-1.0
$
$
$
$
0.0
16.0
0.0
8.0
The xy extremum not mentioned here can be used to define a third picture which expresses
the enfolding deformation. This deformation value expresses how extreme the deformation
is (f.i. from rectangle to diamond shape).
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