Topology Optimization and 3D Printing

While designing a structural member, haven’t you thought to yourself that your design looks like a brick and maybe there’s a way to cut out something to make it lightweight while remaining stiff and strong? It has been a common headache for engineers to find the best way to reduce material on a structural member without making it fail. Let me tell you there’s a method that might blow your mind: Topology Optimization.

So, let’s start with what exactly is Topology Optimization and how it has been applied as a design method before getting into 3D printing as a reliable alternative to traditional manufacturing methods.

What is Topology Optimization

One of many mathematical methods that allow the generation of the most efficient placement of material possible for a given part under required load conditions. The fundamental characteristic that makes topology optimization different from other methods, such as shape optimization and size optimization, is that it won’t change anything on the model outside of the original design volume boundary. So, taking the term “topology” into account it basically means “position”, referring to where material should be removed within a given space.

But for a more illustrative way to put it, haven’t you seen some organically shaped CAD designs for mechanical parts or large-scale structures that give an impression of tree branches or a viscous substance? They look kind of aesthetic, but paradoxically it wasn’t created by a plastic artist but by a programmed algorithm.

Before going into more detail, let’s see some real applications in real life:

Applications

Topology optimization has been mainly used in the following areas:

• Civil Engineering /Architecture: For both structural members and for the whole structure of buildings, bridges, roofs.
• Mechanical Engineering: For machine parts, both static and moving, dealing with a significant strain magnitude. Supports, chassis, suspension parts, brackets are some examples.
• Aerospace industry: One of the main concerns regarding this industry is reducing weight to an optimal proportion, topology optimization is a highly valuable tool for this matter.

It is also employed for:

• Material Science
• Biomechanics
• Prototyping
• Pump and valve systems
• Artistic Sculpturing

The GE Engine Bracket Challenge

One of the most representative cases, if not the most, is a challenge made by General Electric for designers to reduce in the most optimal way a titanium bracket for a jet engine. Engineers took the CAD model of the part and made a finite element method simulation (FEM) to calculate stress distribution for given loads and fixtures, then they applied topology optimization.

The results where astonishing, they managed to reduce the part weight from 4lbs to 1.6lbs (About 60% of its original mass) while maintaining a safety factor of 2 and 31-million-dollar savings through energy efficiency. Finally, they used a selective laser sintering (SLS) 3D printer to manufacture the bracket.

Through CAD software and FEM

Today the most important method to iterate optimized models is through a FEM simulation process found on CAD software. Some of the most known are:

• Autodesk Fusion 360
• Ansys
• Dassault Systemes Abaqus and SolidWorks
• Altair Solidthinking Inspire
• Creo PTC

So regardless of the software, the process tends to be like this:

Preparation for Optimization

Modeling of a basic design concept: Starting from a basic idea and easy to calculate design for a specific requirement. This implies the geometrical volume that will define the boundaries for the topology optimization and the chosen material.

Start the FEM study: Once the basic concept is ready, you start the simulation process. It’s better to start your process with a simple static analysis, but you could apply to more advanced and complex studies such as fatigue, dynamic, vibration, thermal, fluid and many more.

Implement external conditions: Here you must define how loads, fixtures, gravity would interact with the design on its theoretical context.

Create a mesh: For a FEM to work discretely you need to transform your solid into a polygonal mesh body. Commonly being an STL encoding the choice.

Initial results: From here you can run the study calculation to test the initial design and further compare it to the optimized version. Basically, you get distributions for stress, displacement, and factor of safety. If this study fails, the optimized models will certainly fail.

Setup topology optimization: The importance of this step is that you get many options that allow you to get control over how the software calculates optimization. Based on your design intentions and manufacturing choices, you can set specific constraints adapted to your needs. Depending on which software you use, the set of options you get will be different. To put some common examples, you can set the mass fraction you want to reduce, apply symmetries and define areas you want to keep out of the optimization.

After Optimization

Run Optimization: Finally, you get to the part where all the process is done. Given that it’s a complex calculation, it might take some time to complete. Once you get the result, you’ll see those distinctive organic shapes with a reduced mass within your design space. Now you may ask, what do I do with this?

Redesign: Here is where the manufacturing process of choice is the focus of your design aim. Ask yourself, can I really replicate those shapes with the process I chose? So, here is where the thing gets tricky. Thankfully there are many methods to adapt the model for manufacturability, it depends on the limitations of each specific process. You can automatically smoothen your result or you can make manual modifications on your original model using the optimized geometry as guidance, there are many possible methods.

Evaluation: Once you get your new design you can test it with a new FEM study. Normally you’ll see that even with the mass reduced, the model remains stiff. It’s important to consider that the security factor for the new design will drop in relation to the original one, make sure the new factor isn’t below your objective. From here you can decide to further optimize it or leave it as is.

3D Printing as the Manufacturing Choice for TO

Once your design process is done, manufacture is the obvious next step. As seen during the development, topological optimization does not care about manufacturing limitations. So, since topology optimization existence as a mathematical method, it has only served as an ideal reference for designing decisions. That’s where 3D printing, also known as additive manufacturing, has its place as an ideal match for topology optimization. The following are the main reasons:

3D printing has an advantage over other traditional processes on reproducing complex organic shapes. Traditional manufacturing processes like milling, lathing, cast molding and even CNC laser cutters have many more limitations in terms of geometries.

3D printing is a strong choice for fast prototyping. Traditional methods tend to be time-consuming, needing extra steps for tool selection and costly in terms of low volume production.

Luckily CAD software helps to adapt optimization results to manufacturing needs, but it means that you need to sacrifice some optimization in order to achieve manufacturability. For 3D printing neither you must go through extra steps nor lose topological efficiency.

For machining methods, you need to remove material and lose it in the process even if optimized. On the other hand, 3D printing is additive, and you get to really save material.

There are some methods that allow adapting topology optimization to infill density intended for the part. This allows for a higher precision design. We will cover this in a future post.

To learn more about Topology optimisation and how you can utilise it with 3D Printing please contact us on info@solidprint3d.co.uk | 01926 333 777