CAD wireframe models do not contain the surface information that a CAD solid model has; therefore, a CAD wireframe model cannot be imported and meshed with the direct transfer technology. Instead, the wireframe model consists of pure lines, circles, arcs, and so on. These objects are ideal for creating beam and truss models. The wireframe models can also be imported as constructions objects and used as the edges of a hand-built mesh, such as meshes between two objects. If the geometry is planar and encloses one or more regions, it can be automatically meshed with the 2D mesh generator. (See Mesh Hand-built Models.)
Autodesk Inventor files are a special case in which you can mix solid, surface, and 3D sketch geometry. Furthermore, Simulation Mechanical can import this mixed geometry. 3D sketches are imported as wireframes along with the surface and solid geometry. The wireframe geometry is suitable for use as construction lines or line-type elements (such as beams and trusses).
Import AutoCAD DXF/DWG Wireframe Files
AutoCAD DXF/DWG files can be imported using the 
Open command and selecting either AutoCAD DXF (*.dxf) or AutoCAD DWG (*.dwg) in the Files of type: drop-down box. There are several options that can be used to import DXF/DWG files. These options are selected by pressing the Options button on the Open dialog.
When opening a drawing, the software detects if the drawing contains only wireframe entities or only surface/solids and uses the appropriate import settings. The import setting If both exists, import As: determines what entities import if both are present in the drawing.
See CAD Import Tab for the surface/solid import options. The options for importing wireframe drawings are as follows:
- If all the entities in the files lie in a single plane, the file can be imported into a sketch by selecting the Drawing is 2-D drawn in check box, then selecting the plane in which the DXF drawing was made. Only objects drawn in the chosen plane will be imported into the model, and placed in the corresponding sketch plane.
If the model will be analyzed using 2D elements, it must be imported into the YZ plane. Activate the Transform to YZ Plane (for 2-D elements) check box.
If the DXF represents a 3D model, the entities can be imported directly into the display area by deactivating the Drawing is 2-D drawn in check box.
All objects can be imported as either construction objects or as regular mesh lines.
- If the check box Import lines/arcs/curves as mesh lines is not activated, all objects will be imported as construction objects and have an entry under a sketch plane (if the Drawing is 2-D drawn in is activated) or the 3D Objects branch (if the Drawing is 2-D drawn in is not activated) under the appropriate part.
- If the check box Import lines/arcs/curves as mesh lines is activated, all objects import as regular mesh lines. Arcs and circles are split into the number of lines specified in the Arc Divisions: field. Entries for each object also appear under the 3D Objects branch under the appropriate part. This enables the number of divisions on circles and arcs to be changed, and so on. (Right-click the entry for the 3D object and choose Edit.)
AutoCAD properties are translated as follows. The part number applies to construction objects and regular mesh lines.
- AutoCAD layer number becomes the part number
- AutoCAD color number becomes the surface number
- AutoCAD line type number becomes the layer number
If the ID of an entity in the DXF file cannot be used in Autodesk Simulation, the entity will be placed with the number specified in the Replace Invalid _ IDs with: field. One common example of this is Layer 0 in AutoCAD. Entities cannot be placed in Part 0 in Simulation Mechanical.
If some entities are not connected properly in the sketch or 3D model, you can loosen the tolerance value. This can be done by activating the Use Tolerance check box and specifying a value in the adjacent field. All values beyond the decimal point specified will be truncated. For example, using the default tolerance of 1E-4, all digits at five decimal points or more will be truncated. The tolerance should only be used if initial import does not succeed.
DXF Entities Supported:
| 2D Sketches* | 3D Models* |
|---|---|
| ARC | ARC |
| CIRCLE | CIRCLE |
| LINE | LINE |
| POINT | POLYLINE |
| SPLINE | LWPOLYLINE |
| POLYLINE | |
| LWPOLYLINE |
* Files with entities not listed will still be imported. The non-supported entities will be ignored.
If your DXF/DWG file contains blocks, you have the option to Import Blocks As Separate Parts.
Import Wireframe IGES Files
Wireframe IGES files can be imported using the Open command and selecting the Wireframe IGES (*.igs, *.iges) option in the Files of type: drop-down box. There are different methods that can be used to wireframe files. These methods can be set by pressing the Options button on the Open dialog.
If all the entities in each part lie in a single plane, the entities in the part can be imported into a sketch by selecting the Import as 2D objects check box. (Each part is treated separately.) If the model will be analyzed using 2D elements, it must be imported into the YZ plane. Activating the Import into YZ plane check box will translate the positive X axis in the IGES file to the positive Y axis in the sketch and the positive Y axis in the IGES file to the positive Z axis in the sketch.
- Open the IGES file and use the Import as 2D objects. The file will be imported and placed into a sketch plane.
- Right-click the resulting sketch plane and choose Change Plane.
- Choose the YZ-Right plane as the target. The objects in the selected sketch will be transformed to the YZ plane. (See Drawing Planes for more details.)
If the wireframe file is in a plane other than the XY or YZ plane and you need to create 2D elements, it can still be transformed to the YZ plane as follows:
If the Import as 2D objects check box is not activated, then the file will be imported as 3D construction objects. If the Import as 2D objects check box is activated and the entities within the part do not lie in the same plane, the entities within that part will be imported as 3D construction objects.
If the part number of an entity in the IGES file cannot be used, the entity will be placed with the number specified in the Replace Invalid Part IDs with: field.
IGES Entities Supported:
| Type | Description |
|---|---|
| 100 | Circles and Arcs |
| 104 | Conic Arc |
| 106 | Copious data read in as individual lines |
| 110 | Line |
| 112 | Parametric Spline Curve |
| 126 | Rational B-Spline Curve |
Import 3D Sketches from Autodesk Inventor Files.
Inventor files can be imported using the Open command and selecting the Autodesk Inventor Files (*.ipt, *.iam) option in the Files of type: drop-down box. You can also push models from Inventor directly into Simulation Mechanical using the Launch Active Model command in the Inventor ribbon. Lastly, you can drag Inventor files into the Simulation Mechanical user interface.
Solid and surface geometry is always imported from Inventor models. Importing 3D sketches from Inventor is optional. There are four ways to access the import options for Inventor files:
- Click the Options button in the lower left corner on the Open dialog box (when the Files of type field specifies Autodesk Inventor Files (*.ipt, *.iam).
- Access the Options dialog box from the Application Menu ( Options CAD Import, select CAD Import: Autodesk Inventor files in the list of CAD plugins, and click Options.
- Access the Options dialog box from the ribbon (Tools Options Application Options CAD Import, select CAD Import: Autodesk Inventor files in the list of CAD plugins, and click Options.
Choose one of the following Import 3D sketches options:
- Yes: Import 3D sketches in addition to surface and solid geometry.
- No: Do not import 3D sketches.
- Ask each time: Present a prompt each time an Inventor file is opened. So, you can conveniently choose whether to include the 3D sketches on a per-model basis.
Inventor 3D Sketch Entities that are Supported:
- Lines
- Arcs
- Circles
How to use imported 3D sketch geometry as line elements:
The Inventor 3D sketch entities will come into Simulation Mechanical as construction objects. You can only use straight, non-construction line segments for line-type elements. Convert construction lines to regular lines to use as elements. Additionally, you can convert circles and arcs into a number of straight line segments for use as line-type elements too.
To use construction objects as elements, complete the following steps:
- Select the straight construction lines that you wish to use for line-type elements. (Use the Selection Select Construction Objects selection mode.)
- ClickDraw Modify Attributes, or right-click in the display area and choose Edit Attributes from the context menu.
- Deactivate the Construction Objects checkbox.
- Specify the desired Part, Surface, and Layer numbers for the lines. For example, you can place beam elements of a common material but differing cross sections in one part but in differing layers. Similarly, surface numbers control beam element orientation. So, you can specify the appropriate surface numbers for the applicable lines.
- Click OK to convert the construction lines to regular lines, suitable for use as line-type elements.
- Optionally, select a circle that you want to convert into line-type elements.
- Right-click and choose Divide from the context menu.
- In the Number of Lines field, specify the number of arc segments into which you want to divide the circle.
- Click OK. The circle is divided into the specified number of arc segments
- Right-click and choose Divide from the context menu.
- Optionally, to convert an arc into a number of straight line segments, suitable for use as line-type elements, click Mesh Structured Divide 1 Object. The appears Object Mesh Setup dialog box appears.
- Click an arc in the display area.
- Specify the number of divisions in the AA' field.
- Optionally, click the ellipsis button (…) to change the mesh spacing setup. Click OK or Cancel to return to the Object Mesh Setup dialog box.
- Specify the desired Part, Surface, and Layer numbers for the new lines.
- Click OK to produce the straight line segments. Note that the original construction arc remains.
- Optionally, select and delete the construction arc if you no longer need it. You can also choose to hide construction objects rather than delete them (View Visibility Construction Objects). Of course, wait until you converted all construction objects to the necessary straight line segments before making them all invisible.
- Repeat the above steps until all needed construction objects are converted to FEA lines.
- Define the element type, cross section properties, and materials for your line elements.