Assembly Optimization Using FEA
In this Skill Builder, you use the parametric variations provided in Stress Analysis to optimize an assembly model. The “design” goal is to minimize the mass of the structure while keeping displacement and stress within allowable values taking into account safety criteria and profile size changes.
Expected completion time: 30 min
Use with: Inventor Simulation Suite 2010 or Inventor Professional 2010
We recommend that you:
- Complete the 3 FEA tutorials that accompany the product before doing this skill builder.
- Familiarize yourself with the ribbon user interface.
Open the Assembly
- Navigate to the assembly location and open Robot Base.iam.
- On the ribbon, click on the Environments tab.
- On the Environments ribbon, click Stress Analysis. The Stress Analysis commands populate the ribbon.
Define the Simulation
- On the ribbon, Manage panel, click Create New Simulation.
- In the Create New Simulation dialog box, enter the following:
- Name: Optimization
- Design Objective: Parametric Dimension
- Simulation Type: Static Analysis
- Click OK. A new simulation is created and the browser is populated with folders.
- On the ribbon bar, Material panel, click Assign Materials.
- For the base_plate:1 component, click the Override Material drop-down list and select Steel. Notice that the Safety Factor column shows that Yield Strength will be used for safety analysis.
- Right click the Override Material cell and click Copy. Right click the other Override Material cells and click Paste. Multiple instances of a component will change with one paste. Click OK to close the dialog box.
Add constraints to denote mechanical and environmental conditions.
- On the ribbon bar, Constraints panel, click Fixed.
- Rotate the model and select the faces that would contact the floor surface.
- Click OK.
Now, we need to define the load where the robot would mount to the base. The mounting plate on the robot is round, and the base plate is square. In order to apply the force in the area where the robot mounts, we must split the base plate face. (This has already been done in the model, so there is no requirement for you to do this.)
- On the ribbon bar, Loads panel, click Force.
- Move the cursor over the center of the base plate component so it highlights the round face. Click to select the face.
- In the Force dialog box, for Magnitude, enter 2000 and click OK. A yellow (default color) glyph denoting the force direction is positioned at the center of the face.
Modify the mesh
We will review the mesh settings and make a minor adjustment.
- On the ribbon bar, Prepare panel, click Mesh Settings.
- In the Mesh Settings dialog box, click Create Curved Mesh Elements. This option creates elements that follow geometry curvature.
- The Use part based measure for Assembly mesh option is checked by default, which is correct for this simulation. This option produces a higher mesh resolution in smaller parts, with a resulting increase in mesh elements overall.
- Click OK to apply the change and close the dialog box.
Previewing the mesh
Previewing the mesh is an optional step. It is good to do when you want to examine the mesh in areas where features are smaller or transition to make sure adequate meshing for your needs will occur.
- On the ribbon bar, Prepare panel, click Mesh View.
Creating Parametric Geometry
Now we will produce a range of geometric configurations involving the width of the model components to facilitate weight optimization. First, we expose model parameters for use as simulation parameters.
- In the Simulation browser, expand the Robot Base.iam node to expose the components in the assembly. Right-click base_plate:1 and click Show Parameters.
- In the Select Parameters dialog box, click the box next to the MemberWidth parameter. This action causes the parameter to populate the parametric table.
Now, we need to define the parameter range.
- On the ribbon bar, Manage panel, click Parametric Table.
- In the Parameters section, base_plate.ipt row, for the MemberWidth parameter, enter 1-2 in the Values cell. When you use the keyboard Enter command the row contents updates.
Once the parameter is defined, we generate the parametric configurations.
- In the Parameters section, right click the MemberWidth row and click Generate All Configurations.
- When the configurations have been generated, you may look at them by using the Current Value slider.
As was mentioned at the outset, the goal is to minimize the mass using the range of geometric configurations and safety factor criteria. The Parametric Table, Design Constraints section, enables access to the results criteria. To add the first design constraint:
- If the Parametric Table is not displaying, in the Manage panel, click Parametric Table.
- In the Design Constraints section, right-click the row and click Add Design Constraint.
- In the Select Design Constraint dialog box, in the Results Component section, click Von Mises Stress. Geometry Selections is set to All Geometry. Click OK. The result component is listed as a design constraint.
- In the Max Von Mises Stress row, click the Constraint Type cell to access the drop-down list. In the drop-down list click Upper limit.
- In the Limit cell, enter 4.5e+004.
- In the Safety Factor cell, enter 1.5.
Add Displacement as a design constraint.
- Repeating step 2 above, add Displacement as a design constraint.
- In the Select Design Constraint dialog box, click Displacement. All Geometry is the default. Click OK.
- In the Constraint Type cell, click Upper limit.
- In the Limit cell, enter 0.01.
Add Mass as a design constraint.
- Right click a row and click Add Design Constraint.
- Select Mass and click OK.
For now, we will leave the constraint type as View the value. The Design Constraints section of the Parametric Table should look like the following:
Run the simulation
- On the ribbon bar, Solve panel, click Simulate.
- In the Simulate dialog box, ensure that the simulation will be run using the Smart set of configurations.
- Click Run.
View and interpret the results
The Simulation browser Results node is populated with the simulation results. However, we will use the Parametric Table and the visualization capabilities to assess the design and optimize for mass.
- On the ribbon bar, Manage panel, click Parametric Table.
- In the Parametric Table, note that result values are posted there, two with green circles preceding them. A green circle indicates that the Result values are within the corresponding safety factors.
- Change the Mass Constraint Type to Minimize.
The parametric values change to show the configuration with the least mass that meets the given constraints. In this case, the original profile width value was 2 inches. The optimized configuration is 1.5 inches, which reduces the mass.
Note: If you move the slider to show a current value of 1.0, the table will update and you will see that maximum displacement exceeds the safety factor criteria. A red square, next to the Result Value, denotes the condition.
Now, let’s look at 3D and XY plots to understand the behavior of the model under the defined boundary conditions.
View and animate 3D plots
After running a simulation you can perform post-processing tasks using the assorted commands in the Display panel. This includes shading options, minimum and maximum labeling, probing, and so on.
The Results node, in the Simulation browser, has been populated with the simulation results based on the criteria we have specified. The Von Mises Stress result (default) is displayed as a 3D color plot.
In this example, because of the connections between profile geometry, stress concentration is expected at the joints. In order to see the stress distribution farther away from the concentration, change the Color Bar settings.
- On the ribbon bar, Display panel, click Color Bar.
- In the dialog box, uncheck Maximum.
- Enter 5 in the edit field above the check box. Click Apply.
- Use the view commands to rotate the model so you can see the underside of the assembly and how the stress is distributed in the members.
To view other results such as Displacement, double-click the browser node and the display updates.
For simulations involving parametric dimensions, moving the slider to the various parameter values will update the display to present the results according to the selected parameter value.
View XY Plots
XY plots show a result component over the range of a parameter. To view an XY plot, right click the parameter row and click XY Plot.
The XY plot displays the Displacement results versus the parametric configurations. Hover the cursor over a plot point to display the displacement value at that point.
There are other post-processing options that can be found in the Display panel, such as probing for values, contour shading, and so on.
In this Skill Builder you learned to:
- Create a simulation.
- Specify materials, constraints, forces, and contact conditions.
- Specify parametric dimensions and generate configurations based on these.
- View the different configurations as 3D color plots and XY plots.
If you have not completed the other FEA tutorials, why not do so now. Or, if you haven’t used Dynamic Simulation, work through those tutorials and learn how to use that simulation output in the Stress Analysis environment.
Consider how this process applies to the products you design and/or manufacture.
This completes this Skill Builder.