Creating Adaptive Swept Surfaces

This task shows how to create swept surfaces that use an implicit profile and its constraints along a guiding curve.
These swept surfaces are created based on sections along the guiding curve and constraints that can be specified for each of these sections.

This task also deals with:
 
The implicit profile is a sketch and as such supports the creation of associative sketch elements over multi-cell surfaces. This allows, when creating the swept surface, to impose a constraint over a multi-cell surface that is used as a construction element.
  When designing the profile to be swept, keep in mind that the constraints imposed on the sketched profile affect the resulting swept surface. For instance, with the apparently similar sketch (only its construction differs, but there is a coincidence constraint between the sketch extremity and the point on the guiding curve) you can obtain the following results: 
 

  Sketch based on the point (no coincidence constraint, but a geometric superimposition)
   
 

  Sketch based on the point as the intersection of the sketch and the guiding curve
   
 

  Sketch based on projection of the point in 3D
   
  Similarly, it is best to use angle constraints rather than tangency or perpendicularity constraints, to avoid changes in the sketch orientation as it is swept along the guiding curve. In some cases, with tangency or perpendicularity constraints, the sketch may be inverted and lead to unsatisfactory results.

Open the AdaptiveSweep1.CATPart document.

  1. Click Adaptive Sweep .

    The Adaptive Sweep Definition dialog box appears.

  2. Select the Guiding Curve (Sketch.5 here).

    If no guiding curve already exists, use the contextual menu in the Guiding Curve field to create, either a line, or a boundary.

  3. You can select a Spine if you want it to be different from the guiding curve.

    By default, the spine is the guiding curve.

  4. Selecting a Reference Surface is optional. It is the surface on which the guiding curve lies, and is used to define the axis system in which the swept surface is created. Indeed one of the axes (H or V) is defined as tangent to the reference surface.

    You can now contextually create a reference surface using the commands available when right-clicking the Reference Surface field.
    In our example, may you wish to define a reference surface, select the xy plane. Otherwise the mean plane is used as default.
    If you choose a boundary as the guiding curve, the reference surface automatically is the surface to which the boundary belongs.
    You can de-select a reference surface using the Clear Selection contextual menu on the Reference Surface field.

  5. Select the Sketch to be swept along the guiding curve (Sketch.4 here).

    An axis-system is displayed defining the plane in which the first section is created.

    The axis system is positioned normal to the reference surface.
    We advise you to create the input sketch directly in the Adaptive Sweep command in order to benefit from the automatic positioning of the sketch, and thus improve the robustness of the adaptive sweep.

  6. Select the end point of the guiding curve to create another section.

    The axis-system is displayed at this new section.

  7. Click Sweep sections preview to have a quick wireframe preview of the adaptive sweep surface.

    This option lets you see the evolution of the sketch along the guide curve.

    Three contextual menu items are available on the manipulators:

    • Create a section here: lets you create a section at the manipulator's place. A new point is dropped on the guide curve with the corresponding ratio. If the guide curve is closed, the created point is a 3D coordinates point.

    • Use interpolated manipulator: the interpolation value between the section parameters is computed. You can move the manipulator along the guide curve to visualize the parameters evolution.

    • Show all sections' constraints: lets you visualize all the sections and their constraints at the same time.
    The list in the Sections tab is automatically updated with:
    • the first section being at the intersection of the selected sketch and guiding curve
    • the second section at the selected point on the guiding curve.
    • Click or choose the Remove Section contextual menu, to delete a section from the swept surface. The first section cannot be deleted.
    • Click or choose the Rename Section contextual menu, to give a new - more explicit - name to any user section.
    • Click or choose the Activate Section / Deactivate Section contextual menu, to respectively activate or deactivate adaptive sweep sections.
      When using this option, at least one section must be activated to compute the sweep, otherwise an error is displayed.

  8. Set the Deviation value: it corresponds to a point tolerance.

    Decreasing this value increases the precision but leads to slower performance.
    By default, the value is 0.1mm.

  9. Check Angular correction to smooth the sweeping motion along the reference surface. This may be necessary when small discontinuities are detected with regards to the spine tangency or the reference surface's normal. The smoothing is done for any discontinuity which angular deviation is smaller than 0.5 degree, and therefore helps generating better quality for the resulting swept surface.
    By default, the angular correction is set to 0.5 degree.

  10. Click Preview to preview the swept surface:

  11. Click the Parents tab to display the elements making up the sweep.

     
    You can select one of the parents from the list and click , or choose the Replaces Parent contextual item to choose a new parent for the swept surface.
      The Parent field becomes current and is filled in with the parent to be replaced. Contextual commands are available on this field.

  12. Click the Parameters tab to display and redefine the constraints on a given section.

    Use the combo list to define the current section. 

  13. Change the constraint value to 5mm, and click Preview.

    The modified sweep is previewed:
     

  14. Click OK to create the swept surface.

    The surface (identified as Adaptive sweep.xxx) is added to the specification tree.
 

Creating or Selecting a Sketch
Once you have selected the guiding curve, you can select an existing sketch or create one by clicking either or selecting the Create Sketch contextual item on the Sketch field to start the sketcher within the adaptive sweep context.
  • You can select from a wide range of positioned sketches with varying HV axis and origin constraints to create the adaptive swept surfaces. The Adaptive Sweep command handles the sweep transformation internally, without modifying the input sketch.
  • If you want to create a new sketch, the Sketch Creation for Adaptive Sweep dialog box allows you to define the construction elements for a new sketch in relation to existing geometry:

  1. Select a point, used to position the sketch on the guiding curve, as well as the origin of the sketch. Here we created a point on the guiding curve (Point.3).

  2. If needed, select construction elements (another guiding curve, support surfaces, and so forth).

    The selection in the geometry implies a global selection of the 3D elements.
    Two options are available:
    • Positioned Sketch: this option lets you position the created sketch according to the swept surface inputs. Therefore, if you modify the swept surface, the sketch is automatically updated.
      It is available if a point is selected and if the point is on the guiding curve.
    • Aggregated Sketch: this option lets you aggregate the sketch under the swept surface feature in the specification tree.

  3. Click OK.

    The system automatically loads the Sketcher workbench, and provided the correct option is active, sets the sketch plane parallel to the screen. You can then define a new sketch.
    Once you exit the Sketcher by clicking , you return to the adaptive sweep command after the sketch selection, as described above in step 5.
    This local definition of the sketch is particularly interesting as it allows to redefine the swept surface simply by editing the local sketch (add/remove construction elements, or constraints for instance).
     
    In this case, would you want to exit the Adaptive Sweep command, after having created the sketch using the Create Sketch contextual menu, yet retain the sketch itself, simply press the To cancel the command but keep the sketch button in the Adaptive Sweep dialog box.
    You also have the possibility to create your sketch using the Sketcher workbench before entering the Adaptive Sweep command, although it is advised to create it directly in the context of the Adaptive Sweep command. In this case, when you select the 3D construction elements, please be careful to select them directly.
 

Relimitating the Swept Surface

The Relimitation tab enables you to create a multi-sections swept surface using a closed guide. It lets you specify the relimitation type.
You can choose to limit the swept surface only on the start section, only on the end section, on both, or on none.
 

  The swept surface can be closed, if:
  • the guide curve and spine are closed,
  • curves created in the Sketcher are closed.
    • when none of the options are checked: the swept surface is extrapolated up to the spine limits.
    • when both options are checked: the swept surface is limited to corresponding sections
    • when one or both options are unchecked: the swept surface is swept along the spine: it is limited by the spine extremities or by the first guide extremity met along the spine.
      You must deactivate both options to create a closed swept surface.
 

Avoiding Gaps on the Surface
  To avoid unsatisfactory surface quality such as gaps between surfaces for example, you can perform one of the following:

  1. Select a boundary on an adjacent surface as a constraining element when creating the sketch.

    The selection of the boundary allows a better topological splitting, and therefore better quality for the created surface.
    Swept surface (blue) without selected boundary Swept surface (blue) with selected boundary
       

  2. Impose more sections along the guiding curve

  3. Decrease the discretization step value to better define the sweeping along the guiding curve.