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This task describes how to analyze flat regions. Contents: |
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Note:
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What is a flat region? |
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Car body parts need to have a certain minimum curvature. In surface areas that fail to meet this requirement, the sheet metal tends to spring back elastically after the forming process, so that the desired shape and aesthetics are not achieved in the manufacturing process. Exceedingly flat areas, therefore, need to be identified and adjusted before manufacturing the press tools. | ||||||||
Analysis interpretation |
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With this analysis, those critical areas can be graphically highlighted. Through suitable parameter settings you
can discover whether the flatness is in one direction, or if there are regions where the panel is flat in several or even in
all directions.
Using the subsequent manual deviation analysis you can additionally make a qualitative evaluation as this analysis also shows the actual curvature. |
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Definition of flatness |
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Experience has shown that the minimum curvature radius should be approximately 12500 mm. This corresponds to a minimum distance
from the geometry of 0.1 mm over a chord length of 100 mm. These are the default settings of the options
Length, Distance and Radius in the dialog box. The minimum curvature radius is defined by length and distance. |
Definition of the minimum curvature radius![]() |
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Flat region check in practice |
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The 'ruler/disk method' is used in the car body manufacturing. To concave parts applies: If you move a ruler with
a length of 100 mm across the car body surface, a minimum gap of 0.1 mm should remain between the surface and the middle of
the ruler, no matter where you place it. To convex parts applies: If you place the middle of the ruler tangentially on any surface
point, the gap remaining between the surface and the ends of the ruler should be at least the amount of 0.1 mm. See also figure Principle of the ruler/disk method. |
What are the verification methods used in the Flat Region Analysis? |
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The analysis offers the ruler/disk method, and additionally a method performing a local check (options under
Type), which are described in the following. In addition, you can execute a subsequent manual deviation analysis (see How is the subsequent deviation analysis used?) that enables an accurate assessment of the curvature situation at a specific surface point. |
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Ruler/disk method (Chord) |
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Local method (Local) |
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Comparison of the verification methods |
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The following figures illustrate the different results of both verification methods. They show a surface that
contains saddle points. The ruler/disk method does not find these areas, whereas the local method finds them. Analysis result with the ruler/disk method |
Which importance has the rotation angle? |
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Flat regions can be in one, or several and all directions. With the Rotation Angle
you can determine which type of flatness is considered to be a risk. Thus you are deciding which opening angle of the ruler
(sector) is the threshold at which sheet metal forming becomes problematic. Such a sector is identified by rotating the ruler
tangentially about its centre point where it touches the surface, starting at the minimum curvature direction and pivoting to
the left and right of this direction as far as exceedingly small curvatures are encountered. Only if this is the case at each
position of the ruler within the sector, the point will be displayed in red.![]() The following types of flat regions are distinguished: |
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Rotation Angle = 1°![]() |
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Rotation Angle = 15°![]() |
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Rotation Angle = 180°![]() |
How is the subsequent deviation analysis used? |
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The manual colored deviation analysis is an add-on to the Ruler/disk method (Chord). The
difference between a Bézier surface replacing the disk and the surface covered by the disk will be measured by comparing the
surfaces. This method enables a both qualitative and quantitative assessment of the curvature situation at the investigated
surface point. As the facetisation of the surface model is displayed (view mode 'Wireframe'), you may additionally assess whether the selected side length of the tessellation makes sense in relation to the disk. |
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Proceeding of the deviation analysis |
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Manual disk analysis![]() |
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Interpretation of the analysis result |
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The direction of the smallest curvature, the flat region, in the selected surface point (centre point of the disk)
is represented by a vector symbol (minimum curvature direction). It corresponds to the main direction of the red area. The shortest distance between disk and surface is measured and displayed in the following colors:
At the arrow tip, that means at the disk edge and in the direction of the minimum curvature, the amount of the deviation between the circular periphery and the corresponding surface point is determined and displayed as numerical value. Flatness becomes critical not until the red area touches the circular periphery, and the curvature values are below the minimum curvature in the entire sector. Detection of a critical area with the deviation analysis The critical rotation angle can be identified from the size of the red sector. If the disk radius is modified, the criterion for the minimum curvature changes as well leading to a different analysis result. Modification of the disk radius |
The Dialog box Flat Region Analysis |
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Open the FlatRegionAnalysis01.CATPart document. | |
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You can define the following options:
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Facet Length![]() Tolerance ![]() |
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Options
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