Removing Unwanted Features

The defeature function in 3D-CAD allows you to remove unwanted features from a geometry. Unwanted features can include faces, holes, protrusions, chamfers, and fillets. The defeature function can also merge split surfaces into a single surface.

Two modes are available—one that operates by selecting bodies, and another that operates by selecting faces.

All automatic and manual defeature functions can complete with partial success, provided that the defeature function was able to perform some of the operation. For example, if you are defeaturing holes, and some of the holes have cutouts in them, the feature removes all holes without the cutouts and retains those holes that have cutouts. A symbol appears next to the partially successful feature in the 3D-CAD feature tree.

For selected bodies and faces, you access the defeature function from the Repair Tools sub-menu within the right-click menu.

To defeature a body using the automatic defeature mode:
1. Right-click anywhere on a body in the 3D-CAD View scene and select Repair Tools > Defeature Bodies.
2. Retain the Defeature Mode setting as Automatic.
  The Manual mode is designed only for faces.
3. To operate on all bodies in the model, set Bodies to All.
4. To operate on chosen bodies only, retain Bodies as Selected. You can select additional bodies by clicking within the Select Bodies box and then selecting bodies in the 3D-CAD View scene.
5. Activate one or more of the options, Fillets, Chamfers, and Holes. For each one, specify a characteristic size that governs the defeature, and the option by which to apply the size.
  For more details on these options, see Defeature Panel.
6. While making changes in the dialog, observe the preview shown in the 3D-CAD View scene. This preview updates to show what will change when you apply the action, depending on which choice you make for Mode.
7. After setting all properties, click OK.
To defeature a body through face selection:
1. Right-click on a face in the 3D-CAD View scene and select Repair Tools > Defeature Faces.
2. Retain the Defeature Mode as Manual.
  The Automatic mode only applies to selected bodies.
3. To add further faces, click in the Select Faces box then select them in the 3D-CAD View scene.
4. For manual defeaturing, you have two options:
  - ( Delete Selected Faces)
  - ( Delete Interior Faces)
  For more information, see Defeature Panel.

The Delete Interior Faces mode allows you to choose faces that surround the interior faces that you want to remove.

To use the Delete Interior Faces method:
1. In the Defeature panel, select the Delete Interior Faces option.
  
  While making changes in the panel, observe the preview shown in the 3D-CAD View scene. This preview updates to show what will change when you apply the action. However, if what you see in the preview is not correct, then use the Faces to Retain and Faces to Delete options to guide the defeature tool.
2. To add faces that you want to defeature, click in the Select Faces box then select them in the graphics window.
  In the following example, the main goal of defeaturing is to remove the inner channel. The image below shows a selection of faces that surround the inner channel, highlighted in purple.
3. In the 3D-CAD View scene, examine the preview to discover which wetted surfaces are targeted for removal based on the initial selection.
  The example below shows the preview in the 3D-CAD View scene based on the initial selection above. The edges of the inner loops that belong to the selected faces are highlighted in purple.
  
  Based on the initial selection the defeaturing is operating on the outer faces instead of the inner channel. Because of this, further selection is required in the panel to identify faces to retain and faces to delete.
4. To identify faces that you want to retain from the defeaturing process:
  1. Click inside the Faces to Retain box.
  2. In the Graphics window, select the faces that should remain after the defeaturing process.
  The example below shows a face that must remain after defeaturing—highlighted in blue.
  
  At this stage of selection, the preview no longer shows any yellow faces in the 3D-CAD View scene, so you know that further selections are required.
5. To identify faces that you want to delete:
  1. Click inside the Faces to Delete box.
  2. In the Graphics window, select the faces that you want to delete.
  The inner channel is selected for deletion—highlighted in red. With these additional selections of faces to retain and faces to delete, the defeaturing operation identifies the inner channel for removal.
Click OK to perform the defeature.
After the defeature, the inner channel is removed while preserving the faces of the main body.

When the defeature operation completes, Simcenter STAR-CCM+ adds a Defeature node to the feature tree.

In the following example, the Automatic defeature mode is used to remove holes that are above 0.001m from the geometry:

In the following example, the Manual defeature mode is used to remove an embossed feature from the geometry:

Outer face of embossed surface is selected.
On the Defeature panel, the option, Delete Interior Faces, is activated
Final result removes the interior faces

As another example, the Manual defeature mode with Delete Interior Faces activated is used in the following geometry to remove faces which are connected to the inner loop of the selected faces: