Open CAD Files

Work Locally

Save models on a local drive not a network location. If the CAD model is on a network drive, transfer the model to Autodesk Simulation. Then use the Save As command to save the FEA model to the local computer.

CAD models are solid models with surface information or wire frame models. The CAD solid models can be automatically meshed using the capabilities of the Autodesk Simulation user interface. Wire frame models cannot be meshed automatically (except for flat, 2D models) and are typically used for line elements or as edges of hand meshed models.

Limitations

If any of the following conditions apply, a CAD model cannot be opened in, or transferred from the CAD package into, Simulation Mechanical:

• If a legacy .DMIT file exists at the destination import location having the same file name.
• If a legacy .ESX file exists at the destination import location having the same file name.
• If a legacy .FEM file exists at the destination import location having the same file name.

If any of the preceding conditions are true, the model import operation is aborted. In some cases, you are informed that you first need to convert the legacy model by opening it. After the old model is converted, the new CAD model can be imported.

Parameters You Might Need to Define when Opening a CAD File

• Application-Specific Prompts: Depending upon the type of CAD model being opened, you may be presented with option prompts. For example, when you open an Autodesk Inventor model, you are asked whether you want to import Inventor data points into the simulation model.
• Simulation Mechanical Color Palette: This prompt asks if you want to use the default Simulation Mechanical color palette for incoming CAD parts. Otherwise, the colors defined within the CAD model are used. Choose Yes or No. Activate the Do not ask this question again checkbox to set the answer you give as a default. This action also prevents the prompt from appearing when you open future CAD models.
• CAD Part Names: This prompt asks if you want to import the names assigned to parts within a CAD model. Choose Yes or No. Activate the Do not ask this question again checkbox to set the answer you give as a default. This action prevents the prompt from appearing when you open future CAD models. If you do not import the names, the parts within Simulation Mechanical are numbered and indicated as <unnamed> in the browser.
  Note: If you are reimporting a model, and you previously edited part names within Simulation Mechanical, choose No when this prompt appears. This choice prevents your changes from being overwritten.
• Existing Material Properties Found: This prompt asks if you want materials defined within the CAD model to overwrite materials specified within Simulation Mechanical (when reimporting a previously opened CAD model). Choose Yes or No. There are two options checkboxes you can activate to prevent future prompts:
  • Do not ask this question again for this model only.
  • Do not ask this question again for any new models.
• Analysis Type: If you have not defined a default analysis type, you are prompted to choose the analysis type while opening the CAD file. Activate the Use as default analysis type checkbox to set the default analysis type. This action prevents the Choose Analysis Type prompt from appearing when you open future CAD models or create new simulation models.
  Note: If you are reimporting a previously opened model, the previously defined analysis type is retained. A prompt to choose the analysis type does not appear (regardless of whether you have specified a default type).

Tip: If you have deactivated any of the applicable prompts above, you can re-enable them from the application Options dialog box. Click Tools Options Application Options CAD Import Global CAD Import Options. You can set the various defaults to Yes, No, or Ask. You can also define the desired actions separately for first-time CAD model importing and CAD model reimporting operations. In addition, if you have set a default analysis type and later want to change it or restore the prompt, click Tools Options Analysis. Then, either check the Ask each time option, or click Set Analysis Type and choose a different default.

Guidelines

When dealing with CAD solid models, follow these guidelines to avoid FEA modeling issues.

Guideline	Notes
Use the proper element type.	CAD solid models are typically used to generate brick elements, but parts with thin walls do not always give the best results with brick elements. Thin-walled models may give more accurate results when used to generate plate elements (midplane mesh).
Remove parts that are not relevant to the stress calculations.	Simplify complicated assemblies by eliminating some parts. The only reason some parts are in an assembly is to prevent other parts from moving in a particular direction. Replace them by properly constraining the model. Other parts are included solely to connect two parts together, such as screws and pins. These types of connections can be simulated more efficiently by directly connecting the nodes of the parts together (replacing a screw). Another method is to use other element types, like beam and truss elements (replacing a pin, for example).
Remove unnecessary details.	Many assemblies have small features such as fillets or holes that do not affect the results. To accurately represent such features, a finer mesh size is required in those areas, which could result in significantly more elements. Remove these features to reduce the analysis time. Most complex features can be suppressed in the CAD software by selecting the Simplify Model command. You can suppress features individually or globally in the model by using sliders.
Split surfaces	Many loads in Autodesk Simulation are applied to surfaces of a model. If a load applies to only a portion of a large face, split the surface in the CAD software. It places the region to be loaded on a unique face which remains a unique surface. (Check the documentation for your CAD software. See split lines, imprint, split face, split part, and project geometry.) Another use of splitting a surface would be to control how the surfaces are created along a cylindrical hole. Most CAD packages create two semicircular surfaces. and rotate them 90 degrees from how you would need them to properly apply a load.