Creating an overhang control restriction

You can specify a geometric restriction for overhang control in a topology optimization.

An overhang control geometric restriction forces the optimized model to satisfy specified additive manufacturing requirements. The restriction can prevent overhanging features in a model that exceed a critical angle. In general, an overhanging feature with an angle greater than 45º is difficult to print and usually requires the addition of support structures.

The base plane defines the printing bed. Only parts of the model situated above the base plane need support. By default, the overhang restriction tries to remove all overhanging features so that support structures are not required. Depending on the geometry, this can lead to unreasonable results. You can specify that there is no base plane, in which case boundary features are always printable. Alternatively, you can specify the base plane with a user-defined point in space on the plane perpendicular to the print direction. The point should be above overhanging features that are mandatory and under overhanging features that should be removed.

See Also
Creating a geometric restriction in a topology or sizing optimization
  1. From the main menu bar, select Geometric RestrictionCreate.

    The Create Geometric Restriction dialog box appears.

    Tip: You can initiate the Create procedure in two other ways:

    • Click Create in the Geometric Restriction Manager. (You can display the Geometric Restriction Manager by selecting Geometric RestrictionManager from the main menu bar.)

    • Click the tool in the Optimization module toolbox.

  2. Enter the name of the geometric restriction.
  3. Select Overhang control (Topology) from the list of geometric restrictions, and click Continue.
  4. From the viewport, select the region in which the overhang control restriction is enforced, or click Done to apply the overhang control restriction to the entire model.

    By default, Abaqus/CAE allows you to select all of the model. To select faces or cells, use the Selection toolbar to change the type of object that you can select to Face or Cells. For more information, see Filtering your selection based on the type of object.

    If you would rather select from a list of existing sets, do the following:

    1. Click Sets on the right side of the prompt area.

      Abaqus/CAE displays the Region Selection dialog box containing a list of available sets.

    2. Select the set of interest, and click Continue.

    Note:

    The default selection method is based on the selection method you most recently employed. To revert to the other method, click Select in Viewport or Sets on the right side of the prompt area.

  5. When you have finished selecting the geometric restriction region, click Done in the prompt area. For more information on selecting objects, see Selecting objects within the viewport.

    The Edit Geometric Restriction dialog box appears.

  6. By default, the region in which the Optimization module checks for critical overhanging features is the same as the region in which it enforces the overhang control restriction. If desired, select from the top of the Edit Geometric Restriction dialog box, and select the check region.
  7. Select the base plane to define the printing bed.

    • Select Determine automatically to allow the Optimization module to determine the optimal location of the base plane such that all overhanging features are removed.

    • Select Specify, and click to select a point on the plane perpendicular to the print direction.

    • Select None to indicate that all boundary features should be printed.

  8. By default, the Optimization module assumes the print direction is defined in the global coordinate system. To change the coordinate system, click for the CSYS option and do one of the following:

    • Select an existing datum coordinate system in the viewport.

    • Select an existing datum coordinate system by name.

      1. From the prompt area, click Datum CSYS List to display a list of datum coordinate systems.

      2. Select a name from the list, and click OK.

    • Click Use Global CSYS from the prompt area to revert to the global coordinate system.

    Alternatively, click to define a new datum coordinate system.

  9. Click , and select two points specifying the vector along the print direction.
  10. Enter the Overhang angle. The overhang angle is an angle relative to the print direction that is introduced to the optimized model to ensure the part does not contain unacceptable features. The default value is 45°.
  11. Enter the Radius. The radius defines the size of the cones that are used in the internal check for the overhang criteria. The default value in 1.5 times the average element length.
  12. Click OK to create the overhang control geometric restriction and to exit the editor.