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CAD Data Import and Export OverviewThe ability to import geometrical CAD data from other systems plays an increasingly important role in the operation of modern CAE tools. Reducing the need for re-modeling structures (which have already been drawn in a CAD system) for electromagnetic analysis can significantly reduce the cost for computer simulations.ContentsInspect and Repair the Imported Model Manual Repair of Imported Models Parameterize the Imported Model IntroductionCST STUDIO SUITE offers powerful import options for geometrical data in both two and three dimensions. This chapter will provide an introduction on how import options should be used without focusing on the actual dialog boxes. Refer to the online documentation for more information. The structural import process usually consists of two steps:
The first step can be seen as a pure geometric language translation step. All inaccuracies in the imported models remain during this stage. The second step then repairs the data so that valid ACIS models are obtained. In general, problems during the import and healing process arise from different accuracy levels of the CAD system and the ACIS kernel used in CST STUDIO SUITE. The accuracy of a CAD system is usually the distance for which the system considers two points to be identical. The ACIS kernel uses an accuracy of 1e-6 whereas some other CAD systems operate at accuracies of 1e-3 only. Assuming that the CAD data have been created on a system with an accuracy level of 1e-3, it may easily contain gaps of this size (which the CAD system would still consider to be closed). Importing such a model into the ACIS kernel afterward would keep these gaps. However, in contrast to the less accurate CAD system, ACIS would not consider these gaps to be closed which may consequently cause failures in creating solids. To circumvent these problems, sophisticated automatic healing technology can be used to close the gaps in the imported model.
The following picture illustrates this step in the case of a 3D part:
The healing modifies the imported model so that it forms a valid solid shape. The following section discusses the import process in 2D and 3D in more detail. Import CAD DataA variety of files can be imported using Drag and Drop. Import 2D FilesCST STUDIO SUITETM currently supports the following 2D data file formats:
We recommend using the DXF file format whenever possible because this is the most flexible and robust choice for 2D data transfer.
By default (if the option "Import as curves only" is NOT used), the imported 2D elements (lines, arcs, polygons, etc.) will be connected automatically so that they form closed profiles. Additionally a healing option is available which tries to close small gaps in the resulting profiles. Once a closed profile is obtained, it will automatically
be covered and extruded by the height specified for the corresponding
DXF layer. If no height has been specified, CST STUDIO SUITE will import
the DXF data as an infinitely thin double-sided face. You can use this
face as a basis for further construction. You may, for instance, use the
Modeling:
Tools The following picture shows a typical yet simple model imported from a DXF file:
If you zoom into the structure, you can check the finite thickness of the imported metallization layer:
Please note: Due to the PBA technique, these thin layers do not slow down the solution process for solvers based on hexahedral grids. Even though the import of 2D files is usually much less critical than the import of 3D models, problems may sometimes occur. The following hints should help to make the import as robust as possible:
Following these rules will usually yield successful import results. However, if you experience problems, read the Inspect and Repair the Imported Model section later in this chapter to get information on how defects in the model can be resolved. Import 3D FilesCST STUDIO SUITE offers import filters for various 3D geometrical CAD formats:
The SAT file format is the native data format of the ACIS kernel and should therefore be used whenever possible. The STL data format contains only facet information. Importing these kinds of data usually becomes problematic when more than one shape of this type is imported and the shapes touch each other. The following picture illustrates this problem:
Since the two-faceted representations of the cylindrical hole and the cylinder are not identical, the assembly contains holes and overlapping rather than a cylinder that perfectly fits into the hole. Please note: The STL import is often most useful in combination with the staircase meshing option. Refer to the online documentation for more information. The IGES, STEP and VDA-FS data formats are based on standardized file format specifications, in contrast to proprietary file formats such as Pro/E, Autodesk Inventor, CATIA V4 and CATIA V5. The data translation process consists of two stages. First the CAD system converts and exports its data into a certain file format. Afterwards CST STUDIO SUITE reads the file and converts it into its own internal data structures. It is usually preferable to import the native data format of the CAD system in order to avoid the first data translation step. Since every translation step may entail a loss of accuracy, it is advantageous to avoid unnecessary translation steps. With regard to standardized CAD data formats, the STEP format is preferable to the IGES or VDA-FS formats because it also contains topology information about the relationship of neighbored faces. This important information must be recreated from pure geometry data if IGES or VDA-FS files are imported. Therefore, the guidelines as to which data format should be used for which CAD system are as follows:
The following list of rules applies to all types of file formats and should help you get the best results for importing CAD data:
Copy file to projectIn general, the option 'Copy file to project' should be activated for the import. When 'Copy file to project' is activated, the original import file will be copied to the Model/3D sub folder of the project. For the import, the copied file will be converted to a sat file, and will be saved to the Model/3D sub folder of the project, too. During a rebuild, the sat file is usually read except when the copied import file in the Model/3D sub folder is newer. When 'Copy file to project' is not activated, only the converted sat file will be saved to the project. During a rebuild, the sat file is usually read except when a newer file of the import exists. This option is available for the following imports: SAT, STL, IGES, VDAFS, STEP, Autodesk Inventor, PROE (Part), CATIA4, CATIA5 (Catpart), Nastran, Microstripes, Conventor, Mecadtron, HFSS, DXF, GDSII, Gerber. Please note: For CATIA5 Catproduct files and ProE Assembly files this option is always deactivated, and these imports behave like explained above. Inspect and Repair the Imported ModelAs outlined above, an automated healing step is necessary after importing a model from foreign CAD data. Therefore you should always use the option Healing in the CAD data import dialog boxes. After importing and healing the data, a message box will appear informing you of the status of the model. The following picture shows such a message box as it appears for a STEP file import:
Some shapes have been imported and healed without any problems (100% OK). However, some other shapes show minor defects indicated by a percentage of 98-99%. Clicking on the shape default:import_3 and selecting Healing Details would, in this example, provide a text output window. In order to understand the healing process better, it is advantageous to know the meaning of this output. Thus we will provide some explanations of the most important information in this text step by step. The first section gives some statistics about the solid after the import and before the actual healing process starts:
SIMPLIFICATION ANALYSIS : ========================= INPUT STATISTICS : 296 Splines, 0 Planes, 0 Spheres, 0 Cylinders, 0 Cones, 0 Tori 0 Straights, 0 Circles, 0 Ellipses, 757 Intcurves, Simplification tolerance set to 0.0001 Planes-Only option set OFF
In the case investigated here, the imported shape consists of spline faces only. However, the healing technology tries to reduce the complexity of the imported data by converting as much of the imported spline faces to analytical trimmed surfaces as possible (simplification). The result of this stage is shown in the next section:
SIMPLIFICATION CALCULATION RESULTS : ==================================== CALCULATED AT TOLERANCE = 0.0001 : Expected spline conversions 116 Planes, 2 Spheres, 114 Cylinders, 8 Cones, 48 Tori
SIMPLIFICATION FIX RESULTS : ============================ Simplification tolerance = 0.0001 no. of initial splines = 296 no. of final splines = 8 Number of analytics made from splines: 116 Planes, 2 Spheres, 114 Cylinders, 8 Cones, 48 Tori 757 Intcurves, 115 Intcurves, 408 Straights, 234 Circles, 0 Ellipses,
The simplification step is able to simplify 288 of the originally 296 spline faces to analytic geometry (e.g. planes, spheres, cylinders, etc.). The next section in the text files gives information on the original status of the model’s geometry:
GEOMBUILD ANALYSIS : ==================== geom build tol = 10 analytic solver tol = 0.0101 no. of edges = 757 no. of bad edges = 177 no. of coedges = 1514 no. of bad coedges = 360 no. of vertices = 471 no. of bad vertices = 51 no. of bad tangent edges = 44 no. of bad tangent edges analytic = 37 no. of G1 bad tangent edges analytic = 39 no. of bad tangent edges uv_uv = 1 no. of bad tangent edges boundary uv_uv = 1 no. of bad tangent edges uv_nonuv = 6 no. of bad tangent edges nonuv_nonuv = 0 no. of bad tangent edges 3_4_sided = 7 no. of surfaces = 296 no. of discontinuous surfaces = 0 percentage of good geom = 92
A lot of elements (171 edges and 51 vertices) have somehow invalid geometry data indicating that this model clearly needs healing. The next sections in the text file give more involved information which is not addressed in this introduction. However, the final section in the text file shows the result of the healing process:
GEOMBUILD FIX RESULTS : ======================= Statistics of the healed body after geombuild fix : no. of edges = 757 no. of bad edges = 2 no. of coedges = 1514 no. of bad coedges = 29 no. of vertices = 471 no. of bad vertices = 2 no. of bad tangent edges = 0 no. of bad tangent edges analytic = 0 no. of G1 bad tangent edges analytic = 7 no. of bad tangent edges uv_uv = 0 no. of bad tangent edges boundary uv_uv = 0 no. of bad tangent edges uv_nonuv = 0 no. of bad tangent edges nonuv_nonuv = 0 no. of bad tangent edges 3_4_sided = 0 no. of surfaces = 296 no. of discontinuous surfaces = 0 percentage of good geom = 99
Automatic healing is quite successful in this case. Only two edges and two vertices are still invalid. After getting the general information that there
are still some defects in the model, it is important to localize the problems.
Usually the automatic healing will convert the incorrect elements to tolerant
objects. By applying tolerances, the modeler is able to perform a limited
set of structural modifications on the model even if it is not 100% valid.
Thus all erroneous elements become tolerant elements in the final stage
of automatic healing. These tolerant elements can easily be visualized
by selecting Modeling:
Tools
In this example, the problems arise mainly due to the imported blends’ faces. Whenever you encounter such problems in the healing process, we recommend contacting your CAD drawing department first. On many occasions a careful inspection of the CAD model at these locations may show some minor defects or inaccuracies in the original model. After revising the drawing and re-importing the structure, you should check whether the problem disappeared. If improving the quality of the CAD data is not possible, or if the problem still persists, you may need to manually repair the model. In the example shown here, it is sufficient to delete
the inaccurate blend using the Face Modifications tool. If you plan to
re-apply the blend later and do not know its radius, you should measure
it before its removal. Afterward you only need to select the blend’s face
using the face pick tools and use Modeling:
Tools
The blend can then be re-applied by selecting the
edge and using Modeling:Tools
The procedure above is typical for the manual healing of invalid blends. However, in many cases it is advantageous to avoid these blends before exporting the model from the original CAD system. Quite often, the blends have little or no effect on the electromagnetic behavior of the structure, so there may be no need to re-apply them. Remember the best rule for CAD data exchange: Keep it simple! In the second example, the following steps explain how unnecessary details can be simply removed from the model. Let us assume that the pin shown in the picture below does not affect the electromagnetic properties and should thus be removed from the model:
The easiest way to achieve this is to use the Remove
Feature tool after selecting all faces of the unwanted structure detail.
To easily obtain this face selection, activate Modeling:
Picks
After properly selecting this edge, activate Modeling: Picks
Now all faces connected to the currently picked
one will be selected. However, the face selection will stop at previously
picked edges. By properly selecting the picked edges, you can advise the
tool to select the faces of the unnecessary structure detail only. Finally
the Face
Modifications dialog in Modeling:
Tools
Manual Repair of Imported ModelsAfter importing the CAD models, a warning message will be shown if the automatic healing procedure could not fix all problems. There exist a variety of different problems that may not all be explained here. Please contact the technical support for assistance. Apply Modeling:
Tools
The affected elements will be highlighted. Dangling edges belong only to one face, junction edges belong to more than two faces, spline elements result from various spline evaluation processes, bad elements have no proper association to the selected shape, and tolerant elements possess a certain tolerance range regarding their dimensions due to repair procedures concerning the overall shape structure. If tolerant elements occur, the maximum tolerance
of the associated shape is given by Modeling:
Tools Furthermore, Modeling: Tools Iit is possible to remove faces using Modeling:
Tools Another solution in many cases is to cut away
the problem parts using boolean operations. Afterwards, you should invoke
the automatic healing operation again by selecting the particular shape
and then choosing Modeling: Tools Finally, we recommend that you repeat the steps above until the automatic healing operation no longer shows any errors. If you frequently deal with CAD import from less accurate CAD systems, we recommend you to attend a training class to obtain more up-to-date information about repairing models from your particular CAD system. Heal faces Imported shapes
from DXF, GDSII files may have self-intersecting faces. Select only the
shape with the self-intersecting face and use Modeling:
Tools Circumventing problems with imported models In some cases, boolean operations with imported models will fail with an error message such as ”inconsistent face/face intersections.” This will usually happen when the boolean operation attempts to intersect almost coplanar faces that contain a tiny offset between them (this offset typically arises either from inaccurate CAD models). A simple way to circumvent this problem is to
offset the faces or adjusting the radius by using Face
Modifications dialog and the Face
Constraints dialog in Modeling:
Tools Consider the following situation: We have imported a brick and a cylinder where the cylinder just fits into a hole in the brick.
However, due to some inaccuracy problems, the cylinder does not fit exactly into the brick, thereby causing an overlapping shapes error during the mesh generation. The typical method for solving the problem of again inserting the cylinder into the brick will fail with an inconsistent face/face intersections error. In this case,
you may simply make the hole a bit smaller by picking the cylindrical
face of the hole and using the Set Radius
feature of the Face
Constraints (Modeling:
Tools Afterwards, the
insert operation will still fail because of the small offset between the
planar faces of the cylinder and the brick. This problem may be circumvented
by offsetting either the cylinder’s face or the brick’s face by a small
amount (e.g. 1e-4) using the Face
Modifications dialog in Modeling:
Tools The insert operation will now work properly. In general, users who work with imported models require training to become efficient. The quality of the automatic CAD repair operations will be improved continuously, but there will always be a few cases where manual interaction will become necessary.
This section only provides some ideas on how imported models can be healed manually if the automatic healing is unable to fix all problems. However, there are many more options available. Optimal strategies may also differ according to your structure and the originating CAD system. We strongly recommend that you attend a specialized training class on this topic in order to obtain best results. Please contact your support center for more details. Parameterize the Imported ModelQuite often, the aim of the electromagnetic analysis is not just to know the given structure’s behavior but also to optimize it according to various goals. Such optimizations require the ability to modify the model even if it was obtained by importing a CAD data file. CST STUDIO SUITE offers the outstanding possibility of parameterizing shapes for which no construction history exists by using Local Modifications. The Getting Started manuals contain a section explaining how these tools are generally applied. You should familiarize yourself with this functionality before you proceed to the next sections since they focus on the application of these operations to imported solids. For the following explanations, let's assume you wish to change the radius of the cylinder’s outer face shown in the picture below:
You could simply start the Face Constraints mode
(Modeling:
Tools
In order to close the resulting gaps, the chamfer’s face automatically extends up to its intersection with the modified cylindrical face. This results in an enlargement of the chamfer which is probably not what is required. This problem can be circumvented by removing the chamfer, changing the face’s radius, and finally re-applying the chamfer. If you don’t know the size of the chamfer, you will need to measure it first by picking two points and checking the distance:
In this example, you will find the chamfer has a
width of 0.2. Now you can pick the chamfer’s face and remove it with the
Face Modifications
mode in Modeling:
Tools
The next step is to change the radius of the face and to re-apply the chamfer as shown in the picture below:
You can use a variable to specify the new radius of the face (by entering it in the edit field or by pressing the Parametrize... button in the dialog). This will allow you to fully parameterize (and thus later optimize) the model even though it has been imported from CAD data. The example outlined above should provide you with some idea as to how imported models can be parameterized by using local modifications. Since many different (more or less efficient) solutions exist to achieve such a parameterization, we recommend that you visit a specialized training class on this topic. Please contact your support center for more information. Export CAD Data3D Export
2D Export
Graphics ExportThese export options allow the export of graphical data to files or Windows clipboard.
Results ExportThese export options allow the export of results data for usage in external post-processing. See alsoExporting Results Overview, Export BMP File, Export POV File, Drag and Drop,Import Problem Handling
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Import
operation to create a solid from the face.
) presenting a window frame to see if the
shape contains any errors. Use 
) points out any bounding-box problems of
the shape.
). If this healing still fails, you may convert the shape to
its 
)).
) to repair this shape.
