#### 2.1.14.2. Extrusion Guides

Solid Model generation for curved geometries and thick layups can lead to boundary edges being extruded in undesirable directions. For example, the extrusion of a dome with a hole at the top results in a solid model with a hole that is not cylindrical. The Extrusion Guide feature allows you to control the extrusion direction of the edges in order to rectify this. The edge of the hole can be used as an Extrusion Guide in the vertical direction to create a cylindrical hole.

Figure : Extrusion with and without an Edge Set Guide

Multiple Extrusion Guides can be used for one Solid Model. The extrusion itself is controlled with an edge set and a direction vector or with a geometry. The Extrusion Guide feature also contains a Curvature Control. The Extrusion Guide Properties dialog has the following options:

Figure : Extrusion Guide Properties

- Edge Set: Define the Edge Set along which the Extrusion Guide acts.

- Type: The type of Extrusion Guide.

  - Direction: Defines a direction vector of the extrusion direction of the Edge Set.

    - Orientation Direction: By default, the normal direction of the Edge Set is calculated and defined when an Edge Set is selected. It can also be entered manually.

  - Geometry: CAD file of a boundary surface is used to define the extrusion path.

    - CAD Geometry: Select a previously imported CAD geometry

  - Free: No extrusion path is defined but a curvature correction can be activated independently.

- Radius: Controls the sphere of influence for mesh morphing.

- Depth: controls the bias of the mesh morphing.

- Use Curvature Correction: Apply a curvature correction during the solid model extrusion which results in a smoother extruded surface. Under certain circumstances, deactivating curvature correction can lead to better extrusion results.

You can change the order of Extrusion Guides using the context menu from the tree view. The order in which the Extrusion Guides appear in the tree is their order of execution, which has significant effects when Extrusion Guides intersect.

Figure : Reordering Extrusion Guides

##### 2.1.14.2.1. Mesh Morphing

The generation of a solid model is by extrusion of a shell mesh. By default, extrusion is in the direction of the shell normal direction. The 2-D shell mesh is used as a base for the 3-D solid element mesh, which can have one or more element layers depending on the ply thickness and extrusion method.

The Extrusion Guide only affects the extrusion of the element edges that are part of the guided Edge Set. It is either defined by an Edge Set and direction vector or by an Edge Set and a CAD geometry. While the CAD geometry already is a surface, the Edge Set and direction vector are used to define a surface. In both cases, these surfaces serve as target surfaces in the extrusion.

The guided edge is initially extruded in the normal direction and then the nodes on the resulting free surface are moved to coincide with the target surface of the extrusion guide.

Mesh morphing is a way to control the propagation of the Extrusion Guide effect through the entire mesh.

Mesh morphing is governed by the morphing law, shown in Equation 2–1. It relates the displacement of internal nodes to the displacement of a node of the guided free surface. It can be controlled with the two parameters:

- Radius: All elements within the defined Radius from the Edge Set are extruded with a mesh morphing correction.

- Depth: Defines the bias of the mesh morphing (linear with 1, quadratic with 2,...).

| (2–1)

where:

m0 is the distance a node on the free surface has to move in-plane to coincide with the extrusion guide.
mi is the distance the inward node of the ith shell element moves in-plane as a result of the mesh morphing.
di is the distance between the node in the guided Edge Set and the inward node of the ith shell element.

Figure : Mesh Morphing Diagram

##### 2.1.14.2.2. Extrusion Guide Examples

The following is an example of a direction-type Extrusion Guide with different mesh morphing radii. The location of the edge set is indicated by the circle in the bottom left corner. The mesh morphing is only applied to nodes on the shell surface whose distance to the Edge Set is smaller than the radius.

Figure : Example of a Direction-type Extrusion Guide with Different Mesh Morphing Radii

The following is an example of a geometry-type Extrusion Guide with different mesh morphing depths:

Figure : Example of a Geometry-type Extrusion Guide with Different Mesh Morphing Depths.

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