CAD Data Import and Export Overview

The 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.

Contents

Introduction

Import CAD Data

Import 2D Files

Import 3D Files

EDA Imports

Copy File to Project

Inspect and Repair the Imported Model

Manual Repair of Imported Models

Biological Data

Parameterize the Imported Model

Export CAD Data

See also

Introduction

CST 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:

  1. Import of the geometrical data and its conversion into ACIS models. Note that the origin of the imported CAD model will automatically be adjusted to the origin of the currently active coordinate system.

  2. Healing of the newly created ACIS models in order to obtain valid geometry.

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 Data

A variety of files can be imported using Drag and Drop.

Import 2D Files

CST STUDIO SUITE™ 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: ToolsShape ToolsShell Solid or Thicken Sheet operation to create a solid from the face.

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:

  1. Organize your structure into layers. Always put the structural drawing and additional data (such as hatchings, measure lines, text, etc.) on different layers, and only import the structural layers.

  2. Only import those parts you are actually interested in. Since CST STUDIO SUITE needs to build 3D objects from the 2D input data, the complexity of the model is heavily increased during the import process. The deletion of unwanted objects after importing the complete structure is unnecessarily inefficient.

  3. Try to use polygons in the drawing of the 2D files as opposed to a collection of independent lines. Due to some accuracy constraints or a less accurate drawing, independent lines may have gaps, which must be closed with much effort during the import process.

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 Files

 CST 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:

  1. Keep the complexity reasonably low: Bear in mind that you are going to run an electromagnetic analysis with your models. Importing an entire car including details, such as the door locks for instance, will exceed today’s computational resources. Please import only the most relevant parts for highly complex models (e.g. the car’s body).

  2. Avoid unnecessary blends in the CAD model: Excessive application of blends will also increase the complexity in the data. You should always try to avoid unnecessary blends and other complex shape details (e.g. embossed text) in the exported files whenever possible.

  3. Avoid tiny model sizes: Due to the limited numerical precision in the file formats, you should use units in which the model has reasonably large absolute dimensions. If your model has a bounding box diagonal of 0.1 m, for instance, you should export it in mm in order to get a larger absolute diagonal of 100 (mm).

  4. Avoid Boolean operations before exporting the model: Whenever possible, you should try to avoid Boolean operations between parts before exporting the model to a file. In the example of the STL import shown earlier, the problem is due to the insertion of a cylinder into a plate, which then contains a hole. If the insertion were omitted in this case, inserting the imported and healed shapes within CST STUDIO SUITE would not cause any problems. This issue is most critical when faceted CAD data are used (e.g. STL) but still should be considered for the other more accurate data formats as well.

  5. Try different export options: Whenever you experience problems in any of the data translation steps, you should try to use different export options for your CAD system. You may need to experiment a bit in order to find the combination which works best for your system and your type of models.

Copy file to project

In 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 Model

As 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: ToolsShape Tools Healing Tools Model AnalysisShow Tolerant Edges, respectively.

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 Modify LocallyModify Face to remove the face.

The blend can then be re-applied by selecting the edge and using Modeling:ToolsBlendBlend Edges.

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: PicksPicksPick Edge Chain (Shift+E) and double-click on the edge that connects the detail with the rest of the model:

After properly selecting this edge, activate Modeling: PicksPicksPick Face Chain (Shift+F) and double-click on one of the detail’s faces:

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 Modify LocallyModify Face can be used to remove the shape and automatically close the gaps:

Manual Repair of Imported Models

After 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: ToolsShape ToolsHealing ToolsModel AnalysisCheck Shape () presenting a window frame to see if the shape contains any errors. Use Modeling: ToolsShape ToolsHealing ToolsModel AnalysisCheck Level  to vary the accuracy of the check between quick, normal and intensive. To receive more detailed information of the current state of its faces, edges and/or vertices, use the following properties:

 

Modeling: ToolsShape ToolsHealing ToolsModel AnalysisShow Spline Faces

Modeling: ToolsShape ToolsHealing ToolsModel AnalysisShow Spline Edges

Modeling: ToolsShape ToolsHealing ToolsModel AnalysisShow Tolerant Vertices

Modeling: ToolsShape ToolsHealing ToolsModel AnalysisShow Tolerant Edges

 

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: ToolsShape ToolsHealing ToolsModel AnalysisShow Maximum Tolerance.

Furthermore, Modeling: ToolsShape ToolsHealing ToolsModel AnalysisShow Bounding Box Problems () points out any bounding-box problems of the shape.

Iit is possible to remove faces using Modeling: ToolsShape ToolsHealing ToolsModel HealingDelete Zero Faces or Delete Faces for Selected Edges.

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: ToolsShape ToolsHeal Shape (). If this healing still fails, you may convert the shape to its faceted representation (Modeling: ToolsShape ToolsHealing ToolsModel HealingFaceted Shape Representation ()).

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: ToolsShape ToolsHealing ToolsModel HealingHeal Self Intersecting Shape () to repair this shape.

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: ToolsModify Locally to circumvent this accuracy problem.

Consider the following situation: We have imported a brick and a cylinder where the cylinder just fits into a hole in the brick.

image\heal_import.gif

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: ToolsModify LocallyDefine Face Constraints) mode.

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: ToolsModify LocallyModify Face (either in Move face or in Offset face mode).

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 Model

Quite 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: ToolsModify LocallyDefine Face Constraints), select the corresponding face and apply the set the radius to yield the following result:

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: ToolsModify LocallyModify Face:

 

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 Data

3D Export
2D Export
Graphics Export

These export options allow the export of graphical data to files or Windows clipboard.

Results Export

These export options allow the export of results data for usage in external post-processing.

See also

Exporting Results Overview, Export BMP File, Export POV File, Drag and Drop,Import Problem Handling