Performing Topology Optimization: A Step-by-Step Guide
Topology optimization has been something of a buzzword in CAD circles for the last few years, and promises to enable designers to produce lightweight organic forms that have never been seen before.
SOLIDWORKS 2018 includes the addition of topology optimization, as we touched on in this article.
Today, we are going to take a look at topology optimization in more detail, and I will guide you through the steps in a tutorial. For this tutorial, we are going to use a generic bracket that I have modeled (see Figure 1). I have uploaded the model onto GrabCAD, so you can download it and try it out too.
So sit back, fire up your copy of SOLIDWORKS 2018, and let’s crack on!
Load up SOLIDWORKS 2018, and then load up the bracket.
Now, go to the SOLIDWORKS Add-ins tab at the ribbon at the top of the screen and load up the Simulation add-in. Then, locate the Simulation tab on the ribbon, click the New Study icon, and select New Study from the drop-down menu.
This will open up the study pane on the left-hand side of the screen. In the study pane, find the Design Insight section, and click Topology Study. You can rename your study here if you would like. I have left it as the default name (Topology Study 1). Then, click the green check mark. This will open a new study pane in the left-hand pane under the design tree.
Before you begin the study, you need to define a material so that SOLIDWORKS will know how to define the material parameters from its material database.
From the top ribbon, in Simulation tab, select Apply Material. From this list, select Alloy Steel (SS), and then click Apply.
Defining the Simulation Parameters
Now that the model is loaded, the type of study has been defined, and a material has been selected for use in the study, you can begin to define the parameters of the study, such as loads, fixtures and design constraints.
Take a look at the Topology Study 1 panel in the left-hand pane. It should look like what is shown in Figure 2.
Next, you will define the fixtures. These will represent the mounting points where bolts will hold the bracket to a wall. Right-click on Fixtures in the Topology Study pane and select Fixed Geometry from the drop-down menu.
Spin the bracket around to the rear side, and then select the inner faces of the eight bolt holes. Seven holes are selected in the example shown in Figure 3. When you have selected all eight bolt holes, you can click the green check mark in the Fixture panel.
Now, you want to apply a load. The plates that make up the bracket are 10mm thick and made from steel. They are also fairly strong (to put it mildly).
For the purposes of this example, let’s assume that you wish to hang something fairly heavy on this bracket. Maybe it’s part of a vehicle inspection ramp, for instance. The application doesn’t really matter, but let’s assume that you want it to be heavy and distributed across the top face of the bracket. Right-click the External Loads option in the Topology Study pane, select Force from the drop-down menu, and enter 1000 kg of force in the Force Value text entry box. Before you close the Force/Torque pane, you must select a face where you wish to apply this mass. I selected the top face of the bracket (the one with four holes on).
Now, you can close the Force/Torque pane by clicking the green check mark.
Goals and Constraints
This is probably the most important part of topology optimization in SOLIDWORKS 2018 because this is where you tell the software your design targets in terms of optimization.
Right-click the Goals and Constrains option in the Topology Study pane, and from here you will see three types of optimization options:
- Best Stiffness to Weight Ratio (default)
- Minimize Maximum Displacement
- Minimize Mass with Displacement Constraint
Choose the first option, Best Stiffness to Weight Ratio. This will open the Goals and Constraints pane (see Figure 4).
Instantly, you can see that the current mass of the non optimized part is 14.05kg. That’s a big old bracket! You could probably build a road bridge with that. I’m thinking that maybe I should have created bigger bolt holes.
Oh well, we won’t worry about it. It’s just an example after all. And, anyway, it will be fun to see how much we can reduce the weight by. That’s what optimization is all about!
Next, go into the Constraint 1 box and type 55 percent into the text box, as shown in Figure 4. This gives a Final Mass of Part equal to 6.3 kg. This value will act as the mass target while the computer runs its iterations.
If you wanted to, you could also activate a second constraint by selecting the Constraint 2 check box. But for now, just use the single constraint, and click the green check mark to exit the Goals and Constraints pane.
Next down the list in the Topology Study pane is the Manufacturing Controls option.
These add constraints that assist with the manufacturability of the part and can be used to keep regions of material that you don’t want removed by the optimization process.
Right-click on the Manufacturing Controls option, and you can see several options, as shown in Figure 5.
For this part, you want to choose Add Preserved Region. Clicking this option will open the Preserved Region pane (see Figure 6).
With the Selection box active, you can now go into the main design window and select the faces that you wish to preserve. For this example, select the inner face of each and every hole on the part. This will preserve the regions around the holes. If you look down at the bottom of the Preserved Region pane, you can see an option labeled Preserved Area Depth. By default, this is switched off. But for this example, you want to specify the depth of the face that you will preserve, so activate it with the check box, and select 7mm depth. This will preserve a cylindrical region that extends 7mm from the perimeter of the bolt hole.
As you change the depth, you will see the depth displayed in the main graphic area in relation to the selected face(s). You can see this displayed as purple circles in Figure 7.
You have finished with these preserved regions now, so you can click the green check mark to exit.
Next, go back to the Thickness Control option and select a minimum thickness of 8mm. This just means that no section will be reduced below 8mm.
And, finally, go to the Specify Symmetry Planes option, and select half symmetry along the longitudinal plane. This will ensure that the optimization process is mirrored on both sides. Without it, the process will produce somewhat random results. As the forces are acting downward, and there is no torque to worry about, you can select this option.
And that’s all for the manufacturing controls in this case.
Mesh and Run (and Grab a Coffee)
All of the basic constraints are set, and you are ready to mesh.
Go to the Mesh option at the bottom of the Topology Study pane, right-click it, and select Create Mesh. This will open the Mesh pane (see Figure 8). From here, you can control the Mesh Density. A finer mesh will create a more accurate study, but will take longer to mesh. The opposite is true for a coarse mesh (it will take a shorter time to simulate, but may not be as accurate). So, select Fine mesh, because this is a simple model and it won’t take too long.
And that’s all set up. You are ready to run the study and see what happens.
Go to the Simulation tab in the main ribbon at the top of the screen, and click the Run This Study icon. Now, go and make yourself a cup of coffee. This might take a while, depending on your mesh size and the complexity of your model.
4 Coffees Later…
OK—that took longer than expected, but the iterations have converged, and you have something that resembles an optimized part (see Figure 9).
If you double-click the Material Mass1 option in the results inside the Topology Study pane, the pane shown in Figure 10 will appear.
You can see that it didn’t quite reduce down to the target mass 6.3 kg at 55 percent. But you can move the slider left and right to remove more mass, and you can use the color key to identify critical sections that need to remain.
You will notice that the model looks a little lumpy at this point. It’s not very aesthetic, and could benefit from some smoothing. Clicking the Calculate Smoothed Mesh icon will bring up a new pane, where you can fix this. For the smoothest mesh, drag the slider to the right, and it will automatically smooth out the model.
Clicking the green check mark will take you out of the Material Mass pane (see Figure 11).
Notice how the bolt holes in Figure 11 have been preserved with the 7mm depth around the inner face of the holes.
Right, that’s all very nice, but what do you do now with your optimized mesh?
Using the Mesh
Well, you have a few options. You can export it as solid or surface part for further refinement, or you can export it as a graphic for use as an overlay to the original part. In addition, you can export it as a surface and use a third-party plug-in to clean up the optimized mesh and make it all nice.
To export the mesh, right-click the Material Mass1 option in the Topology Study pane, and select Export Smoothed Mesh. This will open up the export pane as shown in Figure 12. You can select to export the mesh as a solid, a surface or a graphic. If you will be exporting the mesh as a solid or a surface, you can convert it to an STL file (or some other file format of your choice) later for use in manufacturing.
Alternatively, you can right-click the Material Mass1 option in the Topology Study pane again, and select the Settings option.
From here, you can superimpose the actual original model onto the optimized shape (see Figure 13), and you can use the optimized plot as a template to carve your model manually.
The final option is to export the mesh as a surface and use a third-party plug-in such as Power Surfacing by nPower.
SOLIDWORKS has been pretty slow in jumping onto the topology optimization boat.
But as this is the first release of the software to feature topology optimization, it’s not a bad effort. You can certainly play around with it and get the basics.
Currently, SOLIDWORKS only supports stiffness-to-weight ratio, and the two deformation optimizations—it doesn’t support strength-to-weight ratio, but this is reportedly in the works.
Also, using the optimized mesh is still a cumbersome process. You have to export the file, or use the overlay and carve the model manually. It would be nice if the software generated a usable and smoothed SLDPRT file automatically. I’m guessing I’m not the only one saying this, so no doubt Dassault Systèmes will listen to users and work on this for a future release.
About the Author
Phillip Keane is currently studying his PhD at the School of Mechanical and Aerospace Engineering at Nanyang Technological University, Singapore. His background is in aerospace engineering, and his current studies are focused on the use of 3D-printed components in spaceflight. He previously worked at Rolls-Royce and Airbus Military and served as an intern for Made In Space and the European Southern Observatory.