Electrification in Propulsion Systems: The Opportunity for Additive Manufacturing to take Centre Stage?

Applying advanced engineering to reduce our environmental impact is something we’re passionate about at HiETA, and the electrification revolution that we’re in the middle of seems like a perfect place to apply Additive Manufacturing to realise real, commercially viable benefits.

Electrification in Propulsion Systems: The Opportunity for Additive Manufacturing to take Centre Stage?

In a world driven by power density and cost, there is a place for technologies like Additive Manufacturing, previously reserved for the niche high-value, low volume applications and prototyping stage only, to play a major part in a coming revolution.

The Electric Transformation

The last few years have seen one of the largest shifts in propulsion systems in recent times, with a number of industries moving towards electrification of powertrains and ancillary systems. In automotive the trend has been to move through the various levels of hybridisation towards full battery electric vehicles (BEV), with government legislation (1) promising to stop all production of purely Internal Combustion Engine-powered cars by as soon as 2030. The aerospace market has seen a boom in companies exploring the short range Electric Vertical Take-Off and Landing (EVTOL) market, with larger civil aviation companies all looking at hybrid drive systems.

The Technology Challenge

With the unprecedented level of electrification come the inevitable techno-economic challenges: electric motors and batteries aren’t new technologies; but producing high volumes of them every year at a performance that meets the stringent needs of the motive power markets is a challenge.

Looking specifically at electric motor technology, across all industries the key drivers appear to be the same; make the motors as small and light as possible, using as little active material (e.g magnets) as possible, for as low a cost as possible. This can be summarised by a couple of useful ratios: power density (i.e a ratio of power produced against mass) and cost per kW. The UK Automotive Council has produced a road map outlining how these numbers should track in order to be competitive in the future, with a headline figure of >3x increase in power density alongside >50% reduction in cost/kW required over the next ~15 years (2).


Figure 1 – UK Automotive Council View on Electric Machine Technology Progression

So, at a technology level, what are the key challenges and how do we as an industry address them? There are a host of different machine architectures and designs out there, all competing for commercial traction, but across them all there appears to be a relatively standard thought process, as outlined below.


Figure 2 – The Engineering Path to High Power Density

In essence, if you can run at higher speeds, and keep critical components (such as magnets) cool, then significant power density improvements should be possible.

Enter Additive

So, why Additive Manufacturing? What benefit can it bring to this challenging system? There appear to be four key areas that the technology excels at, that when used in combination give significant system-level benefits.

  • Advanced thermal engineering – the ability to process thin walls, fine features and design highly optimised surfaces mean that heat transfer coefficients can be improved by many multiples vs conventional methods
  • Light-weighting and topology optimisation – much used-buzzwords, but being able to put metal where it is needed and hog it out from where it isn’t, especially in rotating machinery, is step change enabler
  • Integration of components and functionalities – combining cooling features with structural members, active and non-active components and reducing multi-part assemblies to single complex structures is key to increasing efficiency and reducing weight
  • Processing of advanced materials – materials such as magnetics and high strength alloys can be tough to machine and form conventionally, and incorporating fine features and coolant channels within them almost impossible without AM.

Figure 3 – Fine features, multi functionality, difficult materials, low weight – AM offers it all

By way of an example; the image below shows an AM turbine wheel, made from a nickel super-alloy, that has been firstly topology optimised to reduce the mass by ~40%, then had a coolant system added to reduce metal temperatures by up to 200C in operation. This can be directly translated to rotating electric machinery, for example in rotor design where a part will need to be able to withstand high rotational speeds, hold components such as magnets, and also direct cooling to these components.


Figure 4 – Internally Cooled AM Turbine Wheel

Additive for Volume Production?

In order to be truly commercially successful, the Additive industry needs to deliver on two fronts; cost and confidence.

Additive Manufacturing has been around for a while, but is only now starting to break free of its prototyping and super-niche fetters. Machines are getting faster, with more, higher-powered lasers, people are starting to design for the process, and all areas of the value chain are becoming better understood and commercially aligned. No surprise then, part prices are reducing, as shown below.


Figure 5 – Relative total cost of an AM part in 2016 vs present

But will it ever be truly capable of producing parts for ravenous markets such as automotive and aerospace? In all honesty, if you’re looking at like-for-like replacements, almost definitely no, and AM will remain confined to the realm of rapid prototyping for eternity. However, if you can integrate 5 parts, enable an increase in rotational speed of 2x and the associated downsizing of the components that come with it, incorporate cooling features in the active material to mitigate the losses, and do all this at the same time as removing tooling and allowing mass customisation, it starts to look a lot more likely…

Where next for Additive and Electric Machinery?

The opportunity is very real, as the markets are seeking step-change performance gains. The image below shows a comparison of a proven, tested (and outdated?) motor, one of the latest niche high performance motors, and an indication of where the application of Additive Manufacturing could take this system.


Figure 6 – Past, Present, Future?

Conclusions

The world is changing quickly, and conventional design/manufacturing methods are struggling to keep up. If properly used, Additive Manufacturing is a step-change enabling technology that can clearly bring huge advantages to the electric machinery industry – if you know how to use it, and get the most from it. While it may not be widely commercially used today, it’s coming fast and already disrupting markets. Time to get on the bandwagon?

At HiETA we firmly believe this is a great opportunity to exploit our expertise in Additive Manufacturing and thermal expertise, and we will be partnering closely with Equipmake to develop highly power dense next gen Permanent Magnet (PM) machines. Innovate UK also see great potential here, and will be supporting our work with Equipmake and also with Advanced Electric Machines, working on non-PM machines. We couldn’t be more excited about an Additive/Electrified future, and look forward to being under your bonnet soon!

References

1: https://earthbound.report/2018/09/17/countries-that-are-banning-internal-combustion-engines/

2: https://www.apcuk.co.uk/technology-roadmaps/