The Initial Graphics Exchange Specification (IGES) is a vendor-neutral standard format used to exchange geometric models between various CAD and CAE systems. The filter can import partial files, so you can generally import at least part of your file. You can also import multiple files into the same model.
Mechanical APDL provides the SMOOTH method (NURBS-based or RV52) for importing IGES files. This method uses the standard Mechanical APDL geometry database and has no capabilities for automatically creating volumes.
The SMOOTH method provides robust features for importing the model and preparing it for analysis. The method is also ideal for exporting your model to an IGES file or creating new modeling entities on top of the imported model.
To import an IGES file using the SMOOTH method, issue the IOPTN,IGES,SMOOTH command.
To select the IGES file, issue the IGESIN command. This command should be executed after the IOPTN command.
When importing the IGES model, adhere to the following guidelines.
Observe solid modeling procedures with regard to planning, symmetry, and the amount of detail needed for a finite element analysis. For example, for axisymmetric models, the program requires that the global Y axis be the axis of rotation. Refer to Planning Your Approach.
Avoid creating closed curves (that is, a line that starts and ends at the same point and closed surfaces (such as a surface that starts and ends at the same edge). The program cannot store closed curves or closed surfaces. (At least two keypoints are required.) If a closed curve, closed surface, or "trimmed" closed surface--defined by IGES entities 120 and 144 or 128 and 144--is encountered while reading an IGES file, the program will attempt to split it into two or more entities.
As much as possible, write to the IGES file using data that the program supports. (See the description of the IOPTN command.)
Transfer only the portion of the geometry required for the analysis. A finite element analysis may not need as much detail as a CAD model requires.
For trimmed surface transfer, include global XYZ data along with UV data in the IGES file.
If the model to be analyzed is very large, use the CAD program's selection capabilities to create several IGES files, each containing a portion of the model. The Mechanical APDL program will use the next available entity number as each file is read. You can then use the PREP7 merge feature (NUMMRG command) to merge coincident entities.
Write the IGES file in ASCII format, with 80 characters per record.
For the Pro/ENGINEER program, use these additional guidelines:
Set the Config.pro option "iges_out_trim_xyz" to "yes."
Set the accuracy to 1E-6 and regenerate the model.
Pay attention to the messages issued by the Mechanical APDL program. Warning messages give details such as IGES entities not transferred and the corresponding Mechanical APDL entity numbers.
If any IGES entities were not transferred, reconstruct them using Mechanical APDL solid modeling commands. The SMOOTH IGES filter is capable of reading in any rational B-spline curve entity (type 126), or rational B-spline surface entity (type 128) with a degree less than or equal to 20. Attempts to read in B-spline curve or surface entities of degree higher than 20 may result in error messages.
Duplicate lines and keypoints are possible when transferring a model in from an IGES file. This often happens with CAD models due to the tolerances and practices that they were created with. You sometimes need to "clean up" these solid models with Mechanical APDL commands that merge duplicate entities together (NUMMRG command).
Merging is done automatically when an IGES file is read into Mechanical APDL (IGESIN) in AUX15. Default tolerances are used to determine if keypoints should be merged together into a single keypoint. Sometimes the default tolerances are not adequate and must be adjusted.
Set the system of units (/UNITS) before writing the IGES file. This information is captured on the IGES file and is read by many programs that read IGES files. (You cannot access the /UNITS command directly in the GUI.)
Select all lower level solid modeling entities before writing the file (ALLSEL,BELOW,ALL).
If you wish to write out a portion of your model, select only those entities (areas) to be written and all corresponding lower level entities (lines and keypoints). Then unselect any higher level entities (volumes) before writing the file.