About Tightness Restriction for the Resulting Structure

The manufacturing constraints for tightness represent a possibility to prevent the remaining structure from having holes and breakouts in the defined restriction area.

See Also
Defining a Tightness Restriction in Tosca Structure.gui
About Prevention of Undercuts in the Model

The tightness restriction is a variant of the demold manufacturing constraint with the MID_PLANE parameter set to AUTO_TIGHT. The following figure shows an example with the default casting restriction (MID_PLANE=AUTO, left) in comparison to the tightness restriction (MID_PLANE=AUTO_TIGHT, right):



The elements are removed in a similar way to the AUTO option. This means that the elements are removed in the pull direction or in the opposite direction. However, at least one layer of elements will be present in the middle plane. The resulting "middle plane" is not necessarily planar. It might be a curved surface.

The tightness is only checked within the restriction area. It is impossible to ensure a tight connection to elements outside the restriction group in the area of the boundary.

The midplane thickness is controlled by the RADIUS parameter (midplane thickness = 2*RADIUS). The radius should be at least the size of the average element to ensure that a correct midplane can be found.

Important:
  • For 2D models, the definition of a manufacturing constraint leads to a significant reduction of the possible solution space. If this option is used in combination with 2D models, an additional definition for the step width should be added using the OPT_PARAM command (the parameter SPEED=SLOW must be defined).
  • Breakouts might occur if there are thin walls parallel to the pull direction. These areas should be excluded from the restriction group.
  • For some cases (for example, for uniform hexahedral meshes with an aspect ratio higher or lower than 1) the default radius might be too small to determine a valid midplane. The result will contain holes. If this is the case, the radius must be set manually to a high enough value (greater than element edge length in the pull direction).