2.8. Define Manufacturing Constraints

It is important to understand that a optimization solution could create unmanufacturable designs. As a result, any change to the manufacturing process due to an unintended design could undermine the integrity of the original design. Therefore, you (the designer), should apply and specify manufacturing constraints based on your manufacturing process. The Manufacturing Constraint condition, when applied to a optimization system, helps to alleviate design problems by enabling you to specify manufacturing limitations.

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Constraint Types

The application supports manufacturing constraints, per method, as shown here.

Density BasedLevel Set BasedShape OptimizationMixable Density
Member Size (Minimum and Maximum Thickness)
Pull Out Direction (1-sided and 2-sided)
Extrusion
Am Overhang Constraint
Member Size (Minimum and Maximum Thickness and Minimum Gap)
Pull Out Direction (1-sided, 2-sided, Stamping, and No-hole)
Am Overhang Constraint
Housing
Complexity Index
Member Size (Maximum Thickness)
Extrusion
Member Size (Minimum Thickness)
Extrusion
Housing

Requirements and Restrictions

Review the following for the density based and level set methods.

Density Based Method

Note the following requirements and restrictions when you are using the Topology Optimization - Density Based optimization method. The restrictions only apply when one of the manufacturing constraint types is scoped to an Optimization Region or if it has an overlapping region.

  • If you specify an AM Overhang Constraint manufacturing constraint, in combination with:

    • Symmetry, the Build Direction must be in the symmetry plane.

    • Cyclic Repetition, the Build Direction must be parallel to the Axis specified for the Cyclic Repetition.

    • Pattern Repetition, the Build Direction must be perpendicular to the Axis specified for the Pattern Repetition.

  • If you specify an Extrusion and a Cyclic Repetition Design Constraint, the axis of rotation of cyclic constraint must be in the same as the extrusion direction.

  • If you specify an Extrusion and a Symmetry design constraint, the extrusion direction must be in the symmetry plane.

  • If you specify a Pull Out Direction and a Symmetry design constraint, the pull out direction must be in the symmetry plane.

  • If you specify the Pattern Repetition design constraint, in combination with:

    • Extrusion, the pattern direction must be perpendicular to the extrusion direction.

    • Pull Out Direction, the pull-out direction must be perpendicular to the pattern direction.

  • The combination of the following constraint types is not supported:

    • Extrusion and Uniform.

    • Pull Out Direction and Uniform.

    • AM Overhang Constraint and Uniform.

    • AM Overhang Constraint and Member Size, Extrusion, or Pull Out Direction.

Level Set Based Method

Note the following requirements and restrictions when you are using the Topology Optimization - Level Set Based optimization method. The restrictions only apply when one of the manufacturing constraint types is scoped to an Optimization Region or if it has an overlapping region.

  • When you specify a Member Size manufacturing constraint and set the Minimum property to Manual, the application performs two optimizations. The first one does not consider the manufacturing constraint in the solution calculation. However, if the constraint's Minimum value is exceeded at the end of this first run, then a second optimization run is executed using the constraint specifications. This logic makes sure that the optimization does not become trapped in an irrelevant local minimum.

  • If you specify an AM Overhang Constraint manufacturing constraint, in combination with:

    • Symmetry, the Build Direction must be in the symmetry plane.

    • Cyclic Repetition, the Build Direction must be parallel to the Axis specified for the Cyclic Repetition.

    • Pattern Repetition, the Build Direction must be perpendicular to the Axis specified for the Pattern Repetition.

  • If you specify a Pull Out Direction and a Symmetry design constraint, the pull out direction must be in the symmetry plane.

  • If you specify the Pattern Repetition design constraint, in combination with Pull Out Direction, the pull-out direction must be perpendicular to the pattern direction.

Application

The analysis can include only one Manufacturing Constraint object.

  1. To add the object, either look on the Environment Context tab and select Manufacturing Constraint > [manufacturing constraint type] or right-click the Environment object or within the Geometry window and select Insert > [manufacturing constraint type].

  2. Based on the selected constraint type, specify Details properties as required.

Details Properties

The Details pane for this object includes the following properties.

CategoryFields/Options/Description

Scope

Scoping Method: Based upon the type of Manufacturing Constraint you have inserted into the tree, one or more of the following options is available for this property:

  • Geometry Selection: This option indicates that the design region is applied to a geometry or geometries, which are chosen using the graphical selection tools. When you specify Geometry Selection for the Scoping Method, the Geometry property displays.

    In this case, use selection filters on the Graphics Toolbar to pick your geometric entities (body and element selection only), and then click Apply. Once complete, the property displays the type of geometry (Body, Element, etc.) and the number of selected geometric entities (for example: 1 Body, 12 Elements).

  • Named Selection: This option indicates that the design region is applied to a Named Selection. When you specify Named Selection for the Scoping Method, the Named Selection property displays. This property provides a drop-down list of available user-defined Named Selections (only body-based and element-based Named Selections are supported).

  • Optimization Region: This option indicates that the design region is applied to the specified Optimization Region. When you select Optimization Region for the Scoping Method, the Optimization Region Selection property displays and is automatically set to Optimization Region (the only option).

  • All Optimization Regions: When you have multiple Optimization Regions, this option indicates that the constraint is applied to all defined Optimization Regions.

Definition

Type: This is a read-only property that indicates the object as a Manufacturing Constraint.

Subtype: This is a read-only property that displays the type of Manufacturing Constraint you selected. Options include:

  • Member Size: This subtype provides options to specify the minimum thickness, the maximum thickness, and/or a gap size of the connected parts in the final design.

  • Pull Out Direction: This subtype is used for mold-based manufacturing processes. It enables you to specify the direction to remove the model from the mold in a manner that ensures the integrity of the model.

    When selected, the Pull Out Option property displays. This property has the following options:

    • None (default): The pull out direction is specified using location and orientation only.

    • Stamping: Selecting this option instructs the application to create a design that is more compatible with a stamping or forging process. Like the design of a plate, the final design will not have any perforations along the pull-out direction.

    • No-Hole: Selecting this option makes sure that the design will not have any perforations. It typically aims to ease the filling stage during the casting process.

    Note:

    • For the Density Based method only, if your analysis specifies a Tetrahedrons Mesh Method (SOLID187) and you are also defining a Pull Out Direction, Ansys recommends that you also include the Manufacturing Constraint > Member Size. And, you need to manually specify the Minimum property of the Member Size to at least four times the Tetrahedron element size.

    • You may experience an Exclusion Region specification that is not consistent (the shapes differ) with a Pull Out Direction constraint. For the Topology Optimization – Level Set Based method, the application automatically reshapes the Exclusion Region in order to comply with the pullout direction.

  • Extrusion: Using this manufacturing constraint type, you can make sure that the resulting cross section of your final design is kept constant along the selected plane. For each element of the Optimization Region, the application requires at least two corner nodes to lie on the Axis specified for the Extrusion.

  • The AM Overhang Constraint is used for additive printing. It creates an Overhang Angle constraint that uses the input of Overhang Angle and Build Direction to create self-supporting structures. A structure optimized using AM Overhang Constraint can then be 3D printed without (or with reduced) supports. If the application is not able to build supports for all exclusions, it creates as many as possible and issues a warning.

    Note:  See the LPBF Simulation Guide for details about performing additive manufacturing simulations.

    Important:  For the Density-based Method

    Note the following restrictions and requirements. The AM Overhang Constraint:

    • Can be specified only once in a Structural Optimization analysis.

    • Cannot be used in combination with the Manufacturing Constraints Member Size (with Maximum Member Size defined), Extrusion, or Pull Out Direction.

    • If used with Symmetry Manufacturing Constraint, the Build Direction of the AM Overhang constraint must be in the symmetry plane.

    • If used with the Cyclic Repetition Design Constraint, the Build Direction of the AM Overhang constraint must be parallel to the Axis selection of the Cyclic Repetition constraint.

  • Housing: This manufacturing constraint enables you to create a watertight design that encloses a given set of faces. Topology optimization often generates designs that include holes and perforations. Using this manufacturing constraint, you can create a container to house a given liquid. Ansys recommends that you have at least three layers of elements above the selected faces. The surrounding edges of the selected faces will be automatically set as the Exclusion Region.

  • Complexity Index: Use the Complexity Index manufacturing constraint to control the complexity of optimized designs created during the process. Using the associated Maximum Value property to specify a limit for this qualitative criterion, which is based on a ratio between the volume and the model’s perimeter, you can minimize the creation of overly complex structures. An entry value of 1 in the Maximum Value property forces the application to produce a bulky sphere-like shape. As you increase the value of this entry, you enable the optimization process to reduce materials in many free form ways, therefore making the manufacture of the design more difficult. An entry range of 2-10 is suggested.

Member Size

Density Based Method

When the Member Size constraint type is selected for the Topology Optimization - Density Based method, the following associated properties display in the Member Size category of the Details pane.

  • Minimum: For the density based optimization method, the options include Program Controlled (default) and Manual. Using the Program Controlled setting, the application automatically sets the minimum size at 2.5 times the mesh element size.

    Min Size property: You display the property by setting the Minimum property to Manual. The application computes the default value using the mesh size of the generated mesh. This value can simplify the Structural Optimization solution run. The Program Controlled setting is applicable even when no Member Size is added to the Structural Optimization analysis.

  • Maximum: The options include Program Controlled (default) and Manual.

    Max Size property: You display the property by setting the Maximum property to Manual. The application does not specify a default value for this property. This is a required entry when you wish to specify a manufacturing process constraint such as casting, extrusion of parts, etc. and when you wish to specify the maximum member size of connected parts in the final design.

Level Set Based & Mixable Density Methods

When the Member Size constraint type is selected for the Topology Optimization - Level Set Based or the Topology Optimization - Mixable Density methods, the following associated properties display in the Member Size category of the Details pane.

  • Minimum: Options include Free (default) and Manual.

    Min Size property: You display this property by setting the Minimum property to Manual. You use this property to manually enter a desired minimum member size length.

  • Maximum (not supported for mixable density method): Options include Free (default) and Manual.

    Max Size property: You display this property by setting the Maximum property to Manual. You use this property to manually enter a desired maximum member size length.

    Note:  For the Topology Optimization - Level Set Based optimization method, the application automatically increases the value four mesh-element sizes if ever the limit is too small.

  • Gap Size (not supported for mixable density method): The purpose of the Gap property is to keep a minimum distance between members. The formulation of this constraint is based on an approximation that aims to limit the amount of material within multiple test regions (one per mesh node). Options include Free (default) and Manual.

    Value property: You display this property by setting the Gap Size property to Manual. You use this property to manually enter a desired member size gap length.

Recommendation:  For the Topology Optimization - Level Set Based optimization method, Ansys recommends that you:

  1. Use the minimum gap constraint in combination with Maximum Member Size constraint and,

  2. Specify a limit that is smaller than two times the limit for the Maximum Member Size (minGap ⪯ 2*MaxThick).

Location and Orientation

When one of the following subtypes is selected, their associated properties display in the Location and Orientation category of the Details view.

Pull Out Direction

When this constraint type is selected, the following associated properties display:

  • Coordinate System: Specify the appropriate Cartesian coordinate system for material removal.

  • Axis: Specify the removal axis. Options include: X-Axis, Y-Axis, Z-Axis.

  • Direction: Specify the removal direction based on the above axis. Options include: Along Axis, Opposite to Axis, or Both Direction.

The Pull Out Direction constraint satisfies the criteria that there is no concave shape inside of the die so that the part cannot be trapped. This makes sure that the die can be successfully separated from a part after forming.
For the options Along Axis and Opposite to Axis only the direction of the coordinate system is relevant.
For Density Based optimization, for the option Both Directions both the origin and axis selection of the coordinate system is important. The Pullout Constraint is applied from the normal plane (normal to the coordinate system axis selection) at the origin and along and opposite to the direction specified by the coordinate system axis. For Level Set Based optimization, also for Both Directions, only the direction is relevant.
Extrusion

When this constraint type is selected, the following associated properties display:

  • Coordinate System: Specify the appropriate Cartesian coordinate system for the extrusion.

  • Axis: Specify the extrusion axis. Options include: X-Axis, Y-Axis, Z-Axis.

AM Overhang Constraint

When this constraint type is selected, the following associated properties display:

  • Coordinate System: You use this property to specify the appropriate Cartesian coordinate system for the overhang angle. By default, this property is set to the Global Coordinate System. You can specify a user-defined Coordinate System as desired.

  • Build Direction: You use this property to specify the direction that you would like the overhang constraint to be applied. Options include +X Axis, +Y Axis, +Z Axis (default), -X Axis, -Y Axis, and -Z Axis.

  • Overhang Angle: You use this property to specify the degree to which the constraint should be applied. The default setting is 45°.

    Note:  For the density based optimization method, the angle should be kept between 27° and 60°.

Housing

When this manufacturing constraint type is selected, the following associated properties display:

  • Scoping Method: Specify how you want to select the region, either using Geometry Selection or using a Named Selection.

  • Geometry: Select your geometry or mesh entities that you want to use to create a watertight cavity. Only node, edge, or face selections are supported.

  • Named Selection: Select a geometry-based or mesh-based Named Selection to be used to create a watertight cavity. Only Named Selections defined by nodes, edges, or faces are supported.

Refer to the Manufacturing Constraint object reference page for additional information.