Design for sustainable AM

Hayley Everett

When it comes to designing for additive manufacturing, what are the key considerations for engineers, and how can these be applied to ensure sustainable product design?

For high-performing industrial applications, lightweighting essentially involves making a part stronger using less material. However, there is usually a trade-off between cost and the method used to achieve this. For instance, with subtractive manufacturing processes, the more you take material out of a structure, the higher the cost due to additional machining operations. However, using additive manufacturing to lightweight a part can decrease its cost, as generally material usage is a big portion of the total manufacturing cost.

In the past, lightweighting attempts have focused largely on replacing materials with other more lightweight alternatives. Now, engineers have entered the next phase of lightweighting by looking at how parts can be re-engineered to take full advantage of new manufacturing methods.

At the core of these efforts is Design for Additive Manufacturing (DfAM), which can be achieved through sophisticated 3D printing engineering software that offers topology optimisation, generative design, and other vital tools to improve part design. nTop (formerly nTopology) is one key player in this field, with its engineering software for advanced manufacturing enabling engineers to design complex parts with 3D printing that were previously impossible. Through the platform, users can design with complexity while encoding the logic of their design for automation.

Considerations for engineers

So, what do engineers need to consider when taking a DfAM approach to lightweighting? Todd McDevitt, Director of Product Management at nTop, explains: “Engineers need to consider how they can design specifically to take advantage of particular additive manufacturing methods. Most design engineers are familiar with conventional manufacturing methods like casting and injection moulding, and there are many similar considerations for designing with these techniques as there are with 3D printing, for example, minimal wall thickness.”

However, there are additional considerations that engineers must take into account when designing a part that will be 3D printed. “When you additively manufacture something, you’re printing layer by layer. So, if you have an arched shape in your structure, you’re going to need to provide some support for that arch during printing,” McDevitt adds. “This is what we call an overhang angle. Assessing and designing for the overhang angle is important, and requires a manufacturing support which becomes part of the printed structure that you need to consider in your design. Manufacturing the support requires additional material and printing time, which you want to try and minimise, so this needs to become part of an engineer’s thought process during the design phase.”

Another important consideration is the print orientation, he continues: “When you’re printing a part layer by layer, the structure is inherently going to be a little bit weaker in the direction in which you are printing, and the structural integrity between the layers might not be as great. So, engineers must think about the orientation of the printing process, which is also important when deciding on the required supports for the print.”

Particularly in regard to cost, being aware of the build volume of the 3D printer to be used is also crucial. “The build volume space is not a commodity, it is expensive. So, you want to pack as many parts into that build volume as possible. This also comes into play with print orientation: by adjusting the print orientation, you have to think about both the strength of the part and how many parts you can get into the build line to print at once.”

More Sustanable design

On a surface level, additive manufacturing can be a more sustainable method of producing lighter parts, as it generally requires less material. However, support materials are still needed to produce many of these parts, and these materials ultimately still end up as waste once they have been removed during post-processing. Therefore, the sustainability of DfAM can be far better assessed by looking at a part’s impact once it is in use, says McDevitt.

“There’s lots of benefits to taking weight out of a product,” he explains. “From an emissions standpoint, taking weight out of a car or airplane can deliver significantly improved fuel efficiency, and this is where the impact on sustainability is huge.”

According to McDevitt, these are the kinds of considerations that engineers must be aware of during the design phase, looking not just at how parts can be produced more sustainably, but also at the impact they will have during their lifecycle once in use. Naturally, there are trade-offs that engineers will face when designing for sustainability, as there is pressure to print parts both economically and quickly, too.

This is usually decided on a case-by-case basis. For instance, in one scenario printing supports could slow down the manufacturing process as removing these supports can be a time-consuming process that requires extra machinery. However, in another scenario, manufacturing supports can actually accelerate the printing process, as the quality of the support material does not matter because it will just be thrown away, meaning the printer can fly through this stage fairly quickly. These considerations all need to be made during the design process, depending on the nature of the part, the ratio of part material to support material, and what each of these materials are made up of.

“Then there are other arguments,” McDevitt continues. “When designing for additive manufacturing, you need to consider where you are putting the printer, environmental control, the printer’s requirements, humidity and other factors, all of which will have an impact on the sustainability of the manufacturing process. Most importantly, though, it is crucial for engineers to take a step back and look at the design of a part not only during the manufacturing process, but also regarding how it will impact the environment throughout its entire life.”