Creating Blended Surfaces

Several cases are worth surveying:

• blend between curves
• blend between closed contours
• coupling blend
• developable ruled surface

Open the Blend1.CATPart document.

1. Click Blend .

   The Blend Definition dialog box is displayed.

Creating a Blend between Curves

2. Successively select the first curve and its support, then the second curve and its support.
   These can be surface edges, or any curve.

3. Set the continuity type under the Basic tab.

   It defines the continuity connection between the newly created surface and the curves on which it lies.
   The illustration above, shows the Tangency continuity, and the following illustrations show the Point and Curvature continuity types:
   Point continuity on both limits	Curvature

4. Activate the Trim first/second support option, on one or both support surfaces to trim them by the curve and assemble them to the blend surface:

   By default the blend surface borders are tangent to the support surface borders.

   You can also specify whether and where the blend boundaries must be tangent to the supports boundaries: Both extremities: the tangency constraint applies at both ends of the curve None: the tangency constraint is disregarded  Start extremity: the tangency constraint applies at the start endpoint of the curve only End extremity: the tangency constraint applies at the end endpoint of the curve only The Start and End extremities are defined according to the arrows in the blended surface's preview.

5. Set the tension type under the Tension tab.

   It defines the tension of the blend at its limits. It can be constant or linear, and can be set for each limit independently. A third tension type is available: S Type. It enables to set a variable tension.
   	If you choose any of the tension types in the drop-down list, the Default option is deselected.

6. Click OK to create the blended surface.

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

Creating a Blend between Closed Contours

2. Successively select two contours.

3. Click Preview.

   The surface to be generated is twisted.
   To avoid this you need to define a closing point.
   	This capability only applies to closed curves.
   	By default, the system detects and highlights a vertex on each curve that can be used as a closing point, or it creates an extremum point (you can also manually select another one if you wish).

4. Under the Closing Points tab, use the contextual menu and choose Create Projection on the First closing point field.

   The Projection Definition dialog box is displayed.

5. Select the closing point on the second contour, then the first curve onto which the point is to be projected.

6. Click OK in the Projection Definition dialog box.

7. Click OK in the Blend Definition dialog box to create the blended surface.

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

Creating a Coupling Blend

2. Select the elements to be blended and click Preview.

3. Select the Coupling / Spine tab and define the coupling type.

   Ratio: the curves are coupled according to the curvilinear abscissa ratio. Tangency : the curves are coupled according to their tangency discontinuity points. If they do not have the same number of points, they cannot be coupled using this option.  Tangency then curvature: the curves are coupled according to their tangency continuity first then curvature discontinuity points. If they do not have the same number of points, they cannot be coupled using this option.  Vertices: the curves are coupled according to their vertices. If they do not have the same number of vertices, they cannot be coupled using this option.

   When using the above coupling types, the Spine field is disabled.

   Spine: the curve are coupled using a spine curve. This curve can either be a new curve or one of the curves already specified. If no spine is explicitly selected, the first curve is used as the default one. Here is how the blended surface is computed using this coupling mode: at any given point on the spine, a plane normal to the spine is first computed then coupling points corresponding to the intersection of this plane with the limit curves are computed. The blended surface corresponds to the set of lines created with the coupled points. This construction is similar to the one used when creating swept surfaces using a linear profile and two guide curves. In the Spine field, select the spine curve. When using this option, the Display coupling curves option is disabled and any manual coupling is removed.

4. Click in the coupling list or choose Add in the contextual menu and manually select a point on the first section.

   The Coupling dialog box is displayed.

5. Select a corresponding coupling point on each section.

   The Coupling dialog box is updated consequently, and the coupling curve is previewed, provided the Display coupling curves option is active. When a coupling point has been defined on each section, this dialog box automatically disappears.

6. Click OK in the Blend Definition dialog box to create the blended surface.

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

Creating a Ruled Developable Surface

2. Successively select the first curve, then the second curve.

   These cannot form a closed contour.

   
    

3. Select the Create a ruled developable surface option under the Developable tab.

   The Start and End drop-down lists are enabled. The options available under the Start drop-down list are: Connect Both Extremities: to connect the extremities of both curves Free First Curve Origin: to free the first curve origin Free Second Curve Origin: to free the second curve origin The options available under the End drop-down list are: Connect Both Extremities: to connect the extremities of both curves Free First Curve End: to free the first curve end Free Second Curve End: to free the second curve end
   	The icons depicting the chosen options are represented in the geometry area as follows: : indicates that both extremities are connected : indicates that the first curve origin/end is free : indicates that the second curve origin/end is free You can also click on the icons displayed in the geometry area to change the options.

4. Click Preview.
   The maximum value of the Gaussian curve is displayed in the geometry area.

5. Click OK to generate the ruled developed surface.

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

Defining Smooth Parameters

• Angular Correction to smooth the blending motion along the reference guide curves. This may be necessary when small discontinuities are detected with regards to the spine tangency or the reference guide curves' normal. The smoothing is done for any discontinuity which angular deviation is smaller than the input value, and therefore helps generating better quality for the resulting blended surface.
  Over 0.01 degree, the smoothing is cancelled.
  By default, the angular correction is set to 0.5 degree.
• Deviation to smooth the blending motion by deviating from the guide curve(s). A smoothing is performed using correction default parameters in tangency and curvature.
  By default, the deviation is set to 0.001mm, as defined in Tools > Options. Refer to General Settings for more information.
   

Selecting a support is not compulsory. You can create closing points using the contextual menu directly on one of the selected curves, providing no closing point already exists. Use the Replace, Remove, or Reverse buttons, to manage the selected elements (curves, support, closing and coupling points). You can use the contextual menu on the texts displayed on the geometry to set the continuities, trim the supports or manage the curves and support in general.