Knowing Topology

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Lighter and smarter parts not only impact on part performance, but can also increase safety and reduce manufacturing costs. nTopology’s Todd McDevitt explains how next-generation 3D printing design software is enabling new innovations in lightweighting

Within performance-critical industries such as aerospace and automotive, lightweighting is a key consideration for engineers. Advances in additive manufacturing are helping engineers in these sectors to design lighter and smarter parts that not only enhance performance but also deliver significant lead time and cost-saving benefits. To ensure such parts are designed optimally, sophisticated 3D printing engineering software is vital, particularly as part complexity increases.

One of the key players this field is nTopology. The firm’s engineering software for advanced manufacturing has been created to enable engineers to design complex parts with 3D printing that were previously impossible. “There are two main elements to the platform,” says Todd McDevitt, Director of Product Management. “The first is enabling users to design with complexity, and the other is allowing the engineer to encode the logic of their design through automation.”

Designing With Complexity

“What is unique about nTopology’s platform is how we handle geometry, and to understand that it’s useful to look at standard CAD packages,” McDevitt explains. “They handle geometry through a boundary representation, or b-rep, which is a collection of surfaces that represent a structure. Those surfaces are glued together with topology information, such as lines, edges and vertices.”

This system has been around for a long time, and works well for moderately complex structures that are largely conducive for subtractive engineering. However, with the complexity that additive manufacturing provides this representation can break down. Managing such topology can become extremely complex and fragile, and traditional CAD systems can struggle to cope with this.

“Instead, we represent complex geometry with a single mathematical function that is built up as you interactively create the design of your part,” he continues. “You can then use this information to render the boundary of the structure, meaning that any complex structure can be represented with a mathematical equation that is fully evaluable. There are a couple of benefits to this. The first is that it is extremely fast, and the second is that the file sizes representing these complex geometries are small. This can be described as implicit geometry, a kind of big locker within our platform that enables us to design with complexity.”

This links in with the second aspect of nTopology’s platform: its automation capabilities, made possible via a visual programming paradigm.

McDevitt explains, “You build up your design with a system of blocks that have inputs and outputs, with each block representing your design intent. So, the engineer doesn’t have to physically draw features like ribs or surfaces but instead instructs the block what to do. Then, the block produces a physical representation of the structure.”

This implicit geometry capability allows engineers to work off the basis of intent by leveraging programming language to produce a physical representation of the desired part, without having to draw thousands of features which would be an impractical and extremely slow process.

The platform’s automation also opens up designing for additive manufacturing (DfAM) to engineers who do not possess high levels of coding and programming knowledge.

“The block system is easily shareable with casual users of the software, not everyone is an expert,” McDevitt adds. “It is very easy to package up blocks, define a couple of inputs and outputs, and then give this to an operator who perhaps doesn’t have deep design domain expertise, and they can still take it and modify it in the required way. One example of this is dental brackets or transparent orthodontic aligners which are individual to each patient, but which can be automatically customised off the basis of a pre-designed block logic with the addition of a patient’s anatomical scan. The manufacturing files are then automatically created and made available for printing.”

This feature also allows for the creation of custom blocks that enable the adaptation of a workflow or design process, which can then be packaged up and shared with non-experts.

Lightweighting With DfAM

For high level industrial applications, lightweighting essentially involves doing more with less, such as making a part stronger using less material. However, there is generally a trade-off between cost and the method used to achieve this. With subtractive engineering, the more you take material out of the structure, the more this will cost due to additional machining operations. On the other hand, McDevitt explains, using additive manufacturing to lightweight a part can actually decrease the cost of a part.

“For various industrial sectors we can identify a cost axis based on the appetite for lightweighting,” he says. “Aerospace companies, for example, are prepared to pay more to lightweight their parts than perhaps those in the commercial automotive industry or a manufacturer of pipe pumps that go on a plant floor, where weight is less of a factor. Additive manufacturing is therefore becoming increasingly attractive for those industries that can achieve lightweighting at a reduced cost than is possible with subtractive methods. As certification of additively manufactured parts and technologies continues, this play between cost and lightweighting will open up the economic sense of the technology to different sectors.”

So, how does nTopology fit into this? McDevitt explains that in the past new materials have largely been the focus of lightweighting attempts, followed by the development of different manufacturing methods such as CNC machining and injection moulding. During this time, the design of parts has generally remained the same, but now engineers are looking at how parts can be re-engineered to take full advantage of the manufacturing method and materials in use.

“Redesigning parts for additive manufacturing is the area we are focused on, and there are five key aspects of our software that allows engineers to do this in order to achieve a better product design,” McDevitt says. “One area is topology optimisation, which is a form of generative design where the engineer specifies the functional requirements of a part and the design space, and then the software determines where to put the material to provide that functional performance. The second aspect is using lattice structures – the repetition of a base structure in all directions to produce an overall structure – which provides the desired stiffness and structural integrity but without all the material of a solid component.”

The third feature of the nTopology software is shell and infill, which is the bread and butter approach to design, McDevitt says. “This involves shelling out the inside of a part and filling it with a lattice to give structural integrity but without the weight of the shelled material. The unique difference with our software is enabling engineers to easily vary the shell thickness in different areas of a part in line with its requirements.”

The next area in which the software excels is its conformal ribbing capability, which allows engineers to place ribs on the outside of parts to provide extra stiffness in not just the X- and Y-axis, but that conform wholly to the part’s surface. Lastly, the software enables designers to create perforations in a part to remove unnecessary material, a feature that is particularly useful in the creation of components like aircraft frames.

“All these operations are easily achieved through the software’s capability to automate and encode the design workflow, complemented by field-driven design,” McDevitt adds. “This capability allows engineers to take simulation or experimental results of the stress and strain placed on a part during operation, and use this information to automatically place perforations and varied shell thicknesses throughout the part to ensure optimal performance.”

Advanced Lightweighting Concepts

One additive manufacturing-enabled approach to lightweighting that is gathering pace in several sectors is multifunctionality, McDevitt observes. “What we mean by this is that the lightweighting strategy is deployed to serve more than one performance requirement,” he explains. “For example, a company looking at redesigning a heat exchanger may want the part to do more than just its primary function – to exchange heat – but also to provide support or structural integrity to another part. Maybe the heat exchanger is part of a bracket that holds up an engine, or needs to be able to support another part hanging off of it. This is where additive manufacturing can be used to design and build a highly engineered part that is both lightweight but also strong enough to provide structural integrity to other components.”

Another advanced lightweighting concept made possible with 3D printing is architected materials built on lattice structures. “With additive manufacturing, we have the power to vary a lattice structure in order to tune the physical behaviour of a part or application,” McDevitt says. “Engineers can vary the size of individual lattice pieces, the thickness of the struts in the lattice, and even the lattice’s orientation. One common example of this is sports equipment such as a helmet, which needs to be stiff to absorb impact but also soft for comfort, or crashworthiness in automotive where the lattice structure in a car bumper changes how it absorbs energy under impact.”

Each of these advanced lightweighting concepts is made possible by 3D printing and sophisticated DfAM techniques. “It would be near impossible to design these capabilities using traditional CAD systems,” he adds. “The ability of next-gen software like the nTopology platform to encode and automate this design intent makes it far easier for engineers to design for optimal weight and performance.”

Todd McDevitt is with nTopology