MTC employees are joined by one University of Bristol lecturer to discuss their respective research efforts in electrification, is that the departments represented don’t work together – not yet anyway – and two of the three have never even met virtually before.
TCT speaks to Dan Walton, Senior Research Engineer, MTC; Hoda Amel, Technology Manager, Additive Manufacturing, MTC; and Nick Simpson, Senior Lecturer, Electrical Engineering, University of Bristol as the two organisations are ironing out how exactly they might collaborate. For years, they have been working independently to explore how additive manufacturing (AM) technology could improve the performance of electrical machines and components which, in a time when more efficient sources of power are desired in a range of sectors, is increasingly important. Having generated some promising results around 3D printed motor casings and windings, both sides are now exploring how they can come together: to pool their respective expertise, to generate momentum and, ultimately, take their solutions into industry.
“Nick has got an incredible amount of academic background on [electrification],” Walton begins. “He’s been looking into this since 2015, and I think Nick’s design tools are brilliant, but the UK-based supply chain for this is pretty limited. This is a really nice example of how Nick’s maturing this specific technology around AM for electrification, ultimately wants to get it to industry, and that’s where MTC fits perfectly, in this so-called valley of death that we were set up to address in 2010. If we can get large OEMs who are producing at scale interested in what Nick’s doing, they can start shaping their machines now to look at adopting what Nick’s working on.”
What Nick has been working on is a set of design capabilities that have allowed him to demonstrate how AM can enhance the performance of electrical windings. During the design of electrical windings, the designer will typically pay close attention to the magnetic and electrical loadings, which work together to create the torque, as well as the structure of the component and how that affects the effective efficiency of the motor and its effective thermal performance, all in a bid to mitigate AC loss. Last year, Simpson authored a paper that demonstrated a 20% improvement in continuous output capability when using Direct Metal Laser Sintering to produce an electrical winding component. That there were also ‘significantly greater performance improvements indicated for transient operation over the operation torque-speed envelope’ led the paper to conclude that AM and its topological optimisation capabilities show great promise in improving the specific output of electrical machines.
Simpson elaborates: “If you’ve got a winding slot to a rectangular shape that’s almost entirely filled with copper, it’s effective thermal conductivity is very high. If you’ve got a 50% copper and 50% insulation material, it then drops off a cliff, so you’ve constantly got this battle between the losses that you’re generating and your effective thermal performance in your winding. Now, with additive manufacturing, you’re able to select a particular kind of loss mitigation strategy which dictates the topology of the winding that you’re creating as a function of space, so at the front of the slot closest to the rotor you have more AC loss effect. [Therefore,] you might want to use a different configuration of winding that you would at the back of the slot. The design tools that we’ve developed allow you to do that and it allows you to play around with the topology [and] take advantage of the full geometric freedom of AM, which conventional tools don’t let you do.”
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The significance of the work Simpson and co are doing comes in the context of the likes of the Advanced Propulsion Centre and Aerospace Technologies demanding significant advancements in electrical power systems, whether it be in their weight, reliability, maintainability or efficiency. One of the demands is for greater power density of electrical systems, aiming for up to 25 kilowatts per kilogramme by 2035 compared to between just two and five kilowatts per kilogramme today.
Dr Nick Simpson, University of Bristol
Shaped profile electrical machine winding, CuCrZr.
To improve the power density of an electrical machine, Simpson notes that the losses, which manifest as heat, need to be reduced; the ability to extract the heat needs to be enhanced; and the temperature rating of the electrical insulation materials need to be improved. By printing windings, instead of making them conventionally, Simpson suggests that different electrical insulation coatings can be used to give a ‘much higher temperature survivability’. Meanwhile, the geometric freedom of AM can open up new geometric freedom and cooling features can also be integrated into the parts of a winding that currently only serve a structural purpose, rather than a functional one.
“The end windings of an electric machine are essentially wasted,” Simpson says. “Electrically, they have to be there because you’re continuing the circuit, but in terms of producing useful output torque per amp, it’s pretty much wasted. So can we use that dead space to start to introduce cooling fins by extending surfaces and creating a heat sinking structure or can you directly incorporate liquid cooling into the winding itself so you can directly extract that heat?”
Simpson isn’t alone in exploring AM’s capacity for the integration of cooling capabilities into electrical components. At the MTC, Amel and her team have been working on the additive manufacture of a casing for a power-dense electric motor. Utilising the high-strength A20X aluminium alloy on a powder bed fusion process, the MTC has been able to develop a casing with liquid cooling channels that enabled the motor to produce more power without overheating, while also reducing size and weight by 30% and 10%, respectively.
The A20X alloy material was explored in adherence to the MTC’s 2021/22 roadmap for additive manufacturing, in which high-strength aluminium is listed alongside a ‘maturity assessment of copper in AM’ as key focuses within the organisation’s electric motor development efforts.
“The interest [in both aluminium and copper] would be to see how the high conductivity aluminium in AM would actually compare with the copper in AM because aluminium gives you lower weight and is a more sustainable conductive material compared to copper,” Amel says. “So, our preference would be to see if we can get similar performance from aluminium in terms of conductivity to copper.”
The 3D printing of copper has been one of the big challenges for the likes of Simpson when starting out in this field of research. Back in 2015, when copper wasn’t a market-ready 3D printing material, Simpson would be frustrated that the properties of his alternative metal material were only half as good as copper. Even in more recent times, with a range of 3D printing systems now supporting copper, the capacity within the UK hasn’t been easily accessible for the University of Bristol, who typically outsource their 3D printing requirements to industry partners in the auto and aero fields. Recently however, the MTC has placed an order on an AM platform capable of processing copper. This machine will primarily be used for an ESA project, but with it in the building at MTC’s Coventry facility, it could yet support other research efforts.
It’s convenient timing as two organisations – both with years of research in the additive manufacture of electric systems behind them – look to take the next steps, make the jump across the valley of death, and leave their mark in a range of industries.
“The adoption of AM for electric machines specifically is an enormous opportunity,” summarises Walton. “They are a couple of years away, but I think we should start bringing the good work that Nick’s doing and what other academic institutes are working with to industry. I think we can start seeing a little bit of change in what we’re getting out of products for aerospace or high-end automotive.”
“It’s all trickle-down technology,” Simpson adds. “At the moment, we’re developing technology for very advanced, high-performance applications because, effectively, they can afford it. If you go back to the three things that are needed to improve power density, we can do that through AM – I haven’t come across any other technology that allows us to do those three things simultaneously. And so, there is potential for step changes in performance improvement using these technologies, but there’s a long road to get there. If your measure of importance is an official roadmap that says, as an industry, 'we need this by this time,' then the work that we’re doing is hugely important because we can make significant inroads to meeting those targets by 2035.”
