This instructable will show you how to use topology optimization to make a stiffness optimized structure. This will be demonstrated by making a tea light holder for four tea lights. Topology optimization is a way to optimize the material structure for a load bearing structure. There are a different commercial software that can perform this kind of computing, such as Tosca or Inspire. However, the free software TopOpt 3D is used for this guide. All software used in this instructable can be downloaded for free.
You will need:
Step 1: Get Started in TopOpt 3D
Install TopOpt 3D on your computer. Open the program and select a configuration that you like (graphics quality, screen size, etc.). The first screen will show a default design, we are going to change this one.
The settings need to be correct first. Go to File then Config. Change the Domain size to fine and the Domain aspects to 1x1x1. If you have done that, take a look at the interface. In the bottom bar there are some useful tools (from left to right): the material volume slider, visualisation options, domain space visibility, symmetry, restart optimization and the pauze/play button.
Turn on the Domain space visibility in the bottom bar, it appears as a white outline of a cube. Consequently, click the button underneath the cube (top right of the screen) to change the view from perspective to orthographic. Please note that the model can be rotated using the cube: click and hold the mouse to rotate it.
Step 2: Add the Basic Components
The initial object need to be deleted, thus select the Primitives menu (top left) and select the Delete tool (bottom tool of the list). Click on the current boxes to remove them and ignore the error in red. Now we can make our new design. Make the bottom plate of the tealight holder by in the Primitives menu select Create a cube. Use the Scale tool to change it into an appropriate size (as thin as possible) and use the Move tool to move it to the bottom. Note: make this platform not too large, to prevent the boring creation of just four pillars.
Make four additional platforms in the same way and position them where you want to have your tea lights. Don’t let the platforms exceed the white domain space because the software will only generate support inside this space. Also keep in mind that the platforms should not overlap too much, because we want no plastic above the flames!
Step 3: Define the Loads and Support
To define the loads, use the Set load tool in the Augment menu and click on the four platforms where the candles should be placed (they will turn green). Leave the scale load to 1.0. This tells the software where the tea lights will be. To define the support, use the Set support tool and click on the bottom plate (this will turn red). This tells the software where the support should be. Let all the options be selected to allow support in all directions. Click the play button (in case it was paused) and watch how the software creates a mind-boggling structure!
With the bottom slider the volume of the structure can be change (in the example, it is set to 8%, the lowest volume). It’s how much of the domain space that should be material. As you can see the model looks a bit weird. There are ‘arms’ on top of the plates that prevents a tea light to be placed on top. To avoid this, boundaries must be created to prevent material to be put on top. Let’s go to the next step!
Step 4: Add Constrains
Create four new cubes which covers the whole platform and place them on top of the plates. In the Augment menu select Set passive element void and select the new cubes (they will turn blue). This will tell the software not to place material where the cubes are. Press Simulate and see that the structure changes to not place any material on top of the plates.
If you look at the model from underneath, you can see that there’s no plate on the bottom. This is because the software will only place material where it help support the loads. To make sure there’s a bottom plate (due to possible stability issues), create a new cube, scale it and position it where you want the bottom plate. Select Set passive element material in the Augment menu and click on the new bottom plate. This will tell the software to fill the whole plate with material. Press Simulate to see the new model. Now all the constraints are set: the loads, support and where to put and not to put material.
Step 5: Finalize Your Design
Use the volume slider to change the amount of support until it looks good, lower means slimmer support and higher more bulky. Press the Restart optimization just to see that everything's been accounted for in the structure. When you are happy with the result you can export it by selecting Export in the File menu. Enter your email, filename and make sure to choose obj as filetype. Don't forget to save your work via File --> Save
Step 6: Load the Model in Autodesk Meshmixer
Get the file from your email and be sure to check your junk mail as well!
Start meshmixer and import the obj file. The model might be rotated wrong, in the Edit menu, select Transform and Rotate it correctly (for the model in the image, 'rotate X 90 degrees').
Step 7: Solidify and Smoothen the Model
The model needs to be solid in order to printable (it is now still a mesh file). In the Edit menu select Make solid. Leave all default parameters and select accept. The object browser will appear on your screen. Check that the solid model is selected.
Make sure that the model is solid before trying to smooth it. Select all by pressing Ctrl+a and then select Deform and go to Smooth. Check that the option Shape preserving is set to on. Play with the settings until you’re happy and then accept.
Step 8: Finalise the Model
To check the dimensions go to Analysis menu and select Units/dimensions. Input the dimensions you want it to have (in this case we choose the x-dimension to 135mm), and select done. If the model is offcentered, use the Transform tool to move it back to the center.
To make sure everything's the size you want, go to Analysis and select Measure. Click and hold on the surface you want to measure (first measuring type, X direction, snapping mode: Snap To Vertices). Especially the platforms, so that a tea light can be placed on top of it (in the example, it had to be larger than 40mm). The top value is the maximum value you measured when you were holding down the left mouse button, and the bottom value is the minimum value.
You can also check the stability of the model by selecting Stability in the Analysis menu. The coloured ball should be green, which indicates that the model is stable. Export it as a .stl file (ASCII or Binary are both fine) via the file menu. Now it is ready for 3D printing!
Step 9: 3D Print Your Tealight Holder
The printed model can look like this! Nice to put it on your table during the dark winter days.
Now you know how topology optimization can be used to design an object with optimized shape to save material or just to create unexpected, organic shapes. Have fun and hopefully you can use this in your own projects.