Face Blend

Face Blend

Use the Face Blend command to add tangent and curvature continuous blend faces between two or three sets of faces. The cross section of the blend can be circular or conic (symmetric or asymmetric).

The parameters that control the blend’s size can be constant or variable.

A face blend is based on a cross section which is oriented as a rolling ball or a swept disc.

	Rolling Ball The plane of the cross section is defined by the two contact points and the center of the ball. Its orientation may change as the ball rolls between the two faces.
	Swept Disc The plane of the cross section is defined as the normal to the spine curve. Its orientation may change as it sweeps along the spine.

You control how the width of the face blend is defined by choosing a width method.

The blend rails (longitudinal edges) are unconstrained. They vary as defined by the contact points of the rolling ball or swept disc.

The blend rails have a constant distance between them.

The blend rails are constrained to specified curves that act as hold lines.

You specify the shape of the cross section using one of five shape options.

Circular	Tangent Symmetric	Tangent Asymmetric

Curvature Symmetric	Curvature Asymmetric

You can also use Face Blend to:

• Create blends between faces that are in the same body but not adjacent or between faces from different bodies.
• Create blends as separate sheet bodies that are not sewn into the existing bodies.
• Trim the ends of the blend to selected faces or locations.

Where do I find it?

Application	Modeling
Command	Face Blend

Create a constant width face blend

This fender cowling example shows how to create a circular section face blend that is held to a constant width.

Choose Home tab→Base group→Face Blend .

In the Face Blend dialog box, from the Type list, select Two-face .

Select the first face chain.

In this example one face is selected.

(Optional) Click Reverse Direction if necessary.

In this example, the blend is on the outside so the direction vector is pointing outward.

Middle-click to advance.

Select the second face chain.

In this example one face is selected.

(Optional) Click Reverse Direction if necessary.

In this example, the blend is on the outside so the direction vector is pointing outward.

In the Cross Section group, set the following:

• Orientation = Rolling Ball
• Width Method = Constant
• Shape = Circular
• Blend Width = 100

In the Trim group, set the following:

• Trim Blend = To All
• Trim Body to Blend =
• Sew All Faces =

Choose another command or click Apply to create the blend.

Using visualization tools such as reflection lines help in creating quality blends.

Create a swept disc face blend

This example shows how to create a swept disc face blend with a variable radius.

Choose Home tab→Base group→Face Blend .

In the Face Blend dialog box, from the Type list, select Two-face .

Select the first face chain.

In this example one face is selected.

(Optional) Click Reverse Direction if necessary.

Middle-click to advance.

Select the second face chain.

In this example one face is selected.

The face blend is created with the default radius value.

In the Cross Section group, set Orientation to Swept Disc .

Click Select Spine Curve and then select an edge parallel to the blend you want to create.

The spine curve is used for orienting the blend cross section and for defining varying parameters for the law controlled radius.

Where you select the spine curve determines the start end of the blend.

In the Cross Section group, set the following:

• Shape = Circular
• Radius Method = Variable
• Law Type = Linear

Specify values for Radius Start and Radius End.

For this example, the start and end values are 50 and 80, respectively.

In the Settings group, clear the Terminate at Sharp Edge check box.

This allows the blend to cross the crease in the first face chain.

Choose another command or click Apply to create the blend.

Create a face blend tangent to hold lines

This example shows how to create a face blend that is tangent to specified limit curves, or hold lines.

Choose Home tab→Base group→Face Blend .

In the Face Blend dialog box, from the Type list, select Two-face .

Select the first face chain.

In this example one face is selected.

(Optional) Click Reverse Direction if necessary.

Middle-click to advance.

Select the second face chain.

In this example one face is selected.

The face blend is created with the default radius value.

(Optional) Click Reverse Direction if necessary.

In the Cross Section group, set Width Method to Contact Curve .

The Shape option changes to Tangent Asymmetric .

This is the default Shape condition for a width method of Two Constraining Curves.

Select the constraint curves on the first face.

In this example a single curve is selected.

Middle-click to advance.

Select the constraint curves on the second face.

In this example a single curve is selected.

Choose another command or click Apply to create the blend.

Create an asymmetrical conic face blend

This example shows how to create an asymmetric conic face blend between the walls and the top of a plastic reservoir on an appliance.

Choose Home tab→Base group→Face Blend .

In the Face Blend dialog box, from the Type list, select Two-face .

Select the first face chain.

In this example the top face of the reservoir is selected.

(Optional) Click Reverse Direction if necessary.

In this example, the blend is on the inside so the direction vector is pointing inward.

Middle-click to advance.

Select the second face chain.

(Optional) Click Reverse Direction if necessary.

In this example, the blend is on the inside so the direction vector is pointing inward.

In the Cross Section group, set the following:

• Orientation = Rolling Ball
• Width Method = Automatic
• Shape = Tangent Asymmetric
• Offset 1 Method = Constant
• Offset 1 Distance = 8
• Offset 2 Method = Constant
• Offset 2 Distance = 6
• Rho Method = Automatic Ellipse

Available handles are displayed.

1. Offset 1 Distance
2. Offset 2 Distance

Handle parameters have corresponding entries in the dialog box.

Click OK.

After you complete blending, you are ready for subsequent detailing such as other blends and shelling of internal volumes.

Create a constrained curvature continuous face blend

This example shows how to create a curvature continuous face blend between a keel pylon and a keel stabilizer while holding the extent of the blend to limit curves. Note: The example is shown with translucency to facilitate interior object selection.

Choose Home tab→Base group→Face Blend .

In the Face Blend dialog box, from the Type list, select Two-face .

Select the first face chain.

In this example one face is selected.

(Optional) Click Reverse Direction if necessary.

In this example, the blend is on the outside so the direction vector is pointing outward.

Middle-click to advance.

Select the second face chain.

(Optional) Click Reverse Direction if necessary.

In this example, the blend is on the outside so the direction vector is pointing outward.

In the Cross Section group, set Width Method to Contact Curve .

Select the constraint curve on the first face chain.

Middle-click to advance.

Select the constraint curve on the second face chain.

In the Cross Section group, set Shape to Curvature Asymmetric .

An information alert displays telling you that you must specify a spine curve if you are constraining curvature.

The Select Spine Curve option also becomes available in the dialog box.

Select the spine as shown.

Click OK.

Visualization tools such as translucency and reflection lines help in creating quality blends.

Create a face blend with three faces

This example shows how to create a three-face blend along a variable-width rib.

Choose Home tab→Base group→Face Blend .

In the Face Blend dialog box, from the Type list, select Three-face .

Select the first face chain.

In this example, a single face is selected.

(Optional) If the normals of a face chain do not point toward the approximate center of the blend, click Reverse Direction .

Middle-click to advance.

Select the second face chain

In this example, a single face is selected.

Middle-click to advance.

Select the middle face chain.

In this example, a single face is selected.

In the Trim group, set the following:

• Trim Blend = To All
• Trim Body to Blend =
• Sew All Faces =

Choose another command or click Apply to create the blend.

Face Blend dialog box

Type
Specifies whether you are blending two face chains, three face chains or using Feature Intersection Edges Note: The available options in the other groups depend on what you select from the Type list.
Two-face
Three-face
Feature Intersection Edge
Faces
Select Face 1 Select Face 2
Select Edge
Select Middle Face
Cross Section
Orientation
Select Spine Curve
Width Method

Creates a face blend that is constrained to selected curves that act as hold lines for the extent of the blend, one on each defining face.

The blend width and radius change to maintain contact with the curves.

Shape

Available when Type is set to Two- face.

Specifies the underlying shape for the cross section of a two face blend. Choose from the following shape options:

The cross section is circular. Its shape is defined by a radius, either constant, or variable.

The cross section is a conic that is symmetric and tangent to the faces.

Its shape is defined by one of three methods:

• Boundary and Center
• Boundary and Rho
• Center and Rho

Boundary, Center, and Rho can be either constant or variable.

Rho can also be automatically calculated.

In cases where a limit curve is selected and the boundary radius value causes the blend to encounter the limit curve, the blend surface is truncated.

The blend face has a true tangent symmetric shape, but appears non-tangent because it is truncated at the limit curve.

The cross section is conical and is asymmetric and tangent to the faces.

Its shape is defined by specified offsets, either constant or variable, and a specified rho (constant, variable, or automatically calculated).

The cross section is symmetric and curvature continuous to the faces.

Its shape is defined by a boundary radius, either constant or variable, and a specified Depth.

The cross section is asymmetric and curvature continuous to the faces.

Its shape is defined by specified offsets, either constant or variable, a specified Depth (law controlled), and a specified Skew (law controlled).

Radius Method

Available when Shape is set to Circular.

Specifies which method to use to calculate the blend radius.

Keeps the blend radius constant except where you select a tangent constraining curve.

Varies the blend radius based on two or more individual points along a spine curve according to Law Type and Law Value.

For details, see Law Types.

The radius is defined by a limit curve where the blend maintains contact and remains tangent to the curve or edge you select.

The curve must lie within one of the defining face chains.

Conic Method

Available when Shape is set to Tangent Symmetric

The blend is defined by specifying the boundary radius and center radius of the conic section.

The blend is defined by specifying the boundary radius and rho of the conic section.

The blend is defined by specifying the center radius and rho of the conic section.

Boundary Method

Available when Shape is set to Tangent Symmetric or Curvature Symmetric and Conic Method is set to Boundary and Center or Boundary and Rho.

Specifies how to define a symmetrical conic blend using a boundary radius.

Uses a fixed value for the Boundary Radius.

Uses a varying value for the Boundary Radius, defined along a spine curve according to the Law Type and Law Value. For details, see Law Types.

Boundary Radius

Available when Boundary Method is set to Constant.

Specifies a fixed value for the radius of the blend boundary.

Center Method

Available when Shape is set to Tangent Symmetric or Curvature Symmetric and Conic Method is set to Boundary and Center or Center and Rho.

Specifies how to define a symmetrical conic blend using a center radius.

Uses a fixed value for the Center Radius.

Uses a varying value for the Center Radius, defined along a spine curve according to the Law Type and Law Value. For details, see Law Types.

Center Radius

Available when Center Method is set to Constant.

Specifies a fixed value for the radius of the center of the blend section.

Offset 1 Method

Offset 2 Method

Available when Shape is set to Tangent Asymmetric or Curvature Asymmetric.

• Sets the method for the first and second conic offset.
• You can select Constant or Variable for each conic offset.

Offset 1 Distance

Offset 2 Distance

Available when Shape is set to Tangent Asymmetric or Curvature Asymmetric.

Sets the distance of the conic offset from the first face, and from the second face, respectively.

Rho Method

Available when Shape is set to Tangent Symmetric and Conic Method is set to Boundary and Rho or Center and Rho or when Shape is set to Tangent Asymmetric.

Specifies rho for conic cross sections.

Uses a constant value for Rho.

Uses a varying value for Rho, defined along a spine curve according to the Law Type and Law Value.

For details, see Law Types.

Uses a Rho value for a circle, or an ellipse of least eccentricity.

• If the offsets are equal, the blend has a circular cross section.
• If the offsets are not equal, the blend has an elliptical cross section.

Rho

Available when Shape is set to Tangent Symmetric or Tangent Asymmetric and Rho Method is set to Constant

The value of Rho has the following effects on the blend cross section:

0 < Rho < 0.5	Rho less than .5 but greater than zero yields a flatter blend. Cross section is an ellipse. As rho approaches zero, the blend tends towards being flat and resembles a chamfer.
Rho = 0.5	When Rho Type (Settings group) is set to Absolute, the cross section is a parabola. When Rho Type is set to Relative, the cross section is an ellipse of least eccentricity.
0.5 < Rho <1	Rho greater than .5 but less than 1 yields a sharper blend. The cross section is a hyperbola. As rho approaches 1, the blend becomes more L-shaped.

Depth Law Type

Available when Shape is set to Curvature Symmetric or Curvature Asymmetric.

• Specifies the law type to determine depth of blend.
• For details regarding law sub options that may appear, see Law Types.

Shape Skew Law Type

Available when Shape is set to Curvature Asymmetric.

• Specifies the law type to determine the skew of the asymmetric blend.
• For details regarding law sub options that may appear, see Law Types.

Width Limits

Select Sharp Limit Curve

Specifies a curve with which the blend remains coincident, when the blend is large enough to encounter it.

• The radius is maintained where the blend contacts the limit curve.
• The blend is not tangent along the limit curve.

Location list

Specifies whether the Sharp Limit Curve is on the first or second face chain.

Select Tangent Limit Curve

Tangency maintained where the blend contacts the limit curve. Radius varies along the limit curve.

• For circular blends, the ** Tangent Limit Curve** defines the radius of the blend if the specified radius is large enough to encounter it.
• For conic blends, the blend rail opposite the wall containing the ** Tangent Limit Curve** is computed as the smaller of the rail defined by the radius following the Limiting Tangent Curve, or the rail defined by the specified constant or variable offset.

Location list

Specifies whether the ** Tangent Limit Curve** is on the first or second face chain.

Select Middle Tangent Object

Available when Orientation is set to Swept Disc and Shape is set to Circular and Radius Method is set to Variable.

• Makes the blend tangent to three sets of faces.
• Tangency faces constrain the blend so that the geometry dictates the blend radius.

Siemens Digital Industries Software recommends that you use the Three - face type rather than Select Middle Tangent Object to create three-face blends.

Trim

Specifies how NX trims and sews the blend into the part.

Trim Blend list

Lists options to trim blend faces.

• Works in conjunction with the trim and sew check boxes.
• Trim results depend on the combination of the specified Trim Blend option and check box settings.

	To All Trims the blend to the underlying sets of faces.
	To Short Trims the blend as short as possible. The blend end boundaries are constant parameter lines of the wall boundaries.
	To Long Makes the blend as long as possible. The end boundaries are the constant parameter lines determined by the wall boundaries.
	None Generates an untrimmed blend sheet or a sheet trimmed by specified limiting planes.

For sheet bodies, you can trim the participating faces and the blend without sewing the blend.

Trim Body to Blend

Trims all selected input faces to the blend.

	Trim Body to Blend
	Trim Body to Blend

Trim Long Input Faces to Extended Rail

Available when Trim Blend is set to To Short.

Extends the blend rail or hold line to the edges of the face chain on which it resides, and trims the long face chain to the extended rail or hold line.

	Trim Body to Blend Trim Long Input Faces to Extended Rail
	Trim Body to Blend Trim Long Input Faces to Extended Rail

Sew All Faces

Available when the Trim Body to Blend check box is selected.

Sews the blend face to the trimmed input faces.

Length Limit

When checkbox is selected, specifies the objects and locations to use to trim blend faces. The following options are available:

Specifies the type of object to use to limit the blend.

Limits the blend between its start or end using specified planes. You can use this option to trim a face blend and to create end cap faces.

Specify Plane options are available.

Trim to Limit Object trims the blend length to a specified limit object, or to the first intersection point.

Specify Trim Location Point

Specifies a point to define which region to trim whe the plane intersects the blend in multiple locations. The plane normal determines the side to trim.

Trims the blend between its start or end using a face. The selected face or its extension becomes the end cap for the blend.

Specify Face is available.

Trims the blend between its start or end using an edge. The cross section plane through the intersection point of the selected edge or its extension becomes the end cap for the blend.

Select Edge is available.

Reverse Direction is available for all types of limiting objects.

Settings

Blend across Tangent Edges

Available when Orientation is set to Rolling Ball.

When selected, blends across neighboring faces along the path of the blend.

Orient Cross Section by Isoparameter Lines

Available when Orientation is set to Swept Disc and Shape is set to Circular.

Cross-section planes are aligned with isoparameter lines on a face.

This option is used primarily for turbine blades, and is not intended for general use. For turbine blade types of surfaces, specifying the isoparameter lines option may produce a blend result, when without it the blend would fail.

Surfaces intersect - blend fails	Surfaces do not intersect - blend succeeds

A blend using isoparameter lines is similar to that of a swept disc blend, but the planes containing the blend cross-section curves are adjusted based on the isoparametric lines of the first set of faces. For this reason, the first set of faces that you select must be the turbine blade surfaces.

If you get errors, some possible solutions include the following:

• Are all defining strings of surfaces smooth and tangent? To check, use Analysis→ Angle and select curve pairs. The angle should be 0 or 180 degrees.
• Is it possible to simplify the hub face/s making them smooth and tangent?
• You could also try using Variable for the Radius Method, and setting the Law Type to Multi-transition. With this approach you may not need to select the Orient Cross Section by Isoparameter Lines option.

Blend Across Sharp Edges

Creates the blend across sharp edge onto neighboring faces along the path of the blend. The angle between faces must be less than or equal to the edge angle.

Use this option when you have slightly sharp edges that a face blend needs to cross, such as parting edges.

Terminate at Sharp Edge

Specifies the behavior of the blend when the height of one of the defining face chains becomes shorter than the specified blend size. An example would be when a blend rail encounters a sharp edge of a defining face.

Use Terminate at Sharp Edge to stop a face blend when it encounters a localized feature, like a notch, that has a sharp edge.

	Terminate at Sharp Edge When the edge is encountered, the blend continues on the extended face as if the edge did not exist, but is trimmed by the lateral face or faces of the encountered edge.
	Terminate at Sharp Edge The blend does not extend beyond the notch. The transverse face of the encountered edge is extended as necessary, and used to limit the blend.

Rho Type

Available when Shape is set to Tangent Asymmetric.

Specifies the type of Rho for conic cross sections.

Sets a rho value that is relative to the angle subtended by the blend. A value of 0.5 yields a circular blend cross section.

Sets a rho value that is independent of the angle subtended by the blend. A value of 0.5 yields a parabolic blend cross section.

Remove Self-intersections

Available when Orientation is set to Rolling Ball and Shape is set to Circular.

• Automatically creates a patch to replace the portions of blend faces that would be self-intersecting if a strict rolling ball definition were applied.
• The patch is not a true representation of a blend produced by a rolling ball, but it is tangent to all of the surfaces to which it connects.

Maximum Edge Angle

Available when Blend Across Sharp Edges is selected.

Specifies the maximum edge angle over which the blend is allowed to be created.

Tolerance

Determines the fit accuracy of the blend to the defining faces.

The fit accuracy determines the degree of smoothness required for transitions from one face to another.

• The edge of the blend created on the adjoining face cannot deviate from the edge of the blend on the current face by more than the tolerance.
• The default value is the distance tolerance modeling preference.

Rho and the shape of conic face blends

	1 Circle 2 Ellipse 3 Parabola 4 Hyperbola

The blend cross section changes with the value of rho as follows:

0 < Rho < 0.5	Rho less than .5 but greater than zero yields a flatter blend. Cross section is an ellipse. As rho approaches zero, the blend tends towards being flat and resembles a chamfer.
Rho = 0.5	When Rho Type (Settings group) is set to Absolute, the cross section is a parabola. When Rho Type is set to Relative, the cross section is an ellipse of least eccentricity.
0.5 < Rho <1	Rho greater than .5 but less than 1 yields a sharper blend. The cross section is a hyperbola. As rho approaches 1, the blend tends towards being sharp, and resembles a corner.