Creating a demold control restriction

You can specify a demold geometric restriction for a shape optimization. A demold geometric restriction forces the optimized model to satisfy specified manufacturing requirements; for example, it can prevent undercuts and hollow regions in a part that must be extracted from a mold. You choose the demolding direction by specifying the starting and ending coordinates of a vector representing the axis. You can use the global coordinate system, or you can create a datum coordinate system (see Methods for creating a datum coordinate system, for more information).

See Also
Creating a geometric restriction in a topology or sizing optimization
Creating a geometric restriction in a shape optimization

Context:

The mesh should define a demoldable model before the optimization starts; otherwise, the mesh may become distorted when the optimization creates a demoldable model in the first iteration. The main node can lie anywhere in the region that you select to be governed by the demold control restriction. By default, the main node is the node in the region that the optimization moves out the most (the most growth) or moves in the least (the least shrinkage). The optimization displaces the main node, and the stamp condition applies an equal displacement to the rest of the nodes in the region (the secondary nodes) so that the model remains demoldable. If you are trying to optimize surfaces that are in contact, you can force the Optimization module to select the main node as the node to which the optimization is applying the least growth or the most amount of shrinkage. Alternatively, you can select a single point that will be used as the main node by all other nodes. The optimization determines how much the main node is displaced, and all other nodes are moved the same amount so that the model remains demoldable.

  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. From the Create Geometric Restriction dialog box that appears, enter the name of the geometric restriction.
  3. Select Demold control from the list of geometric restrictions, and click Continue.
  4. From the viewport, select the faces to which the demold control will be applied. For more information, see Using the face curvature method to select multiple faces.

    If you would rather select from a list of existing face 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 faces, click Done in the prompt area.

    The Edit Geometric Restriction dialog box appears.

  6. By default, the region in which the Optimization module checks for collisions is the same as the region in which it enforces the demold restriction. If desired, select from the top of the Edit Geometric Restriction dialog box, and select the collision check region.

    Faces inside the collision check region cannot be penetrated by faces outside the region. If a node attempts to penetrate an element in the collision check region during the shape optimization, the Optimization module scales back the displacement of the node. The collision check region must include the faces to which the demold control will be applied.

  7. Enter the coordinates of the starting point and the ending point of a vector representing the direction along which a mold is withdrawn from the demold region.
  8. Enter the draw angle, which represents the angle of a mold that is being withdrawn from the demold region. The value must be between 0° and 45°.
  9. Enter a positive value for the amount of undercut that can be tolerated in the demold control region.
  10. Select the method that the optimization will use to determine the main point. In most cases you should select Determine from most growth and least shrinkage. You should select Determine from least growth and most shrinkage only if you are trying to optimize faces that are involved in contact.
  11. Enter the tolerance in the X-, Y-, and Z-axes.

    The Optimization module uses the tolerance to identify the nodes on the surface that lie on a plane normal to the axis of symmetry and are equidistant from the axis of symmetry.

  12. If desired, toggle on Ignore in first design cycle (default). When the optimization starts, it assumes a mold could be withdrawn from the demold region. If the mold could not be withdrawn, the Optimization module issues a warning and tries to continue. If you toggle off Ignore in first design cycle, and the mold could not be withdrawn, the Optimization module issues an error message and stops execution.
  13. Click OK to create the demold geometric restriction and to exit the editor.