The perfect balance. 8337

When the Polestar 1 was revealed to the world last year, the reaction was overwhelming. Complete with its concept car looks, the first car from Polestar left no one in any doubt. This was not a test. This was an exciting new car company with big ambitions. 
Low, sleek and with a captivatingly athletic stance, everyone behind the scenes at Polestar were determined that those beautiful proportions would find their way onto the very first production version in 2019.

But to stay faithful to the original design would mean using some advanced materials. Carbon fibre would not only be needed to maintain the slender proportions and keep the weight down, but also to meet those ambitious performance figures.

But how challenging would the material prove to be? Would designers and engineers be able to find the right balance of materials and would the advantages of carbon fibre really be worth it?

We interviewed Zef van der Putten, Principle Engineer on Polestar 1, to find out more.

Perfecting the use of Carbon fibre

Carbon fibre is still considered exclusive, expensive and lightweight, but that makes it the perfect choice for a car that guarantees so much cutting-edge technology, future thinking and performance.

Having first made an appearance in Formula 1 some thirty years ago, carbon fibre was complex to work with but harness its properties and the advantages were huge. What was obvious was that it was significantly lighter and stronger than other materials. Soon every team was using it and so were high-end performance car manufacturers – its reputation as a serious performance-enhancing material was sealed.

Fast forward to the present day and carbon fibre body structures have become the embodiment of cutting-edge, high-tech performance - reducing weight, increasing performance, lowering the car’s centre of gravity and improving torsional stiffness.

And this is confirmed upon closer inspection of the car. A simple walk around reveals some serious engineering pedigree. The upper body, including the doors, front wings, bonnet and boot-lid are made of Carbon-Fibre Reinforced Polymer (CFRP). And then there’s that low roofline that has mesmerized so many people.

“With a standard steel roof construction, all of these sections would have been bigger - the roof higher and the windows more upright. Making the whole roof construction out of carbon fibre enabled us to realise that low, elegant roofline.” Says Zef.

Your eye automatically follows the line from A-Pillar to C-Pillar. But what you don’t see is what lies beneath: a super stiff pre-fabricated carbon fibre tube that is baked into the two half shelves of the carbon-fibre pillar construction. They are linked laterally by slim, light and ultra-stiff carbon fibre cross-sections.

But that’s not all. The SPA platform is heavily reworked with 320mm removed from the wheelbase and another 200mm in the rear. Then, like all great engineering teams, the group has looked to nature for inspiration and incorporated the ‘Dragonfly’ * – an insect-shaped patch of carbon fibre bonded to the chassis. Its wingspan and abdomen radically improve torsional stiffness at one of the critical points in the body structure between the middle floor and rear construction. The result is dramatic: +45% increase in torsional stiffness in the chassis structure.

* A cleverly shaped patch of CFRP bonded to the steel underbody, stiffens the traditionally weak interface between the middle floor and the rear structure. At Polestar, this component is known as the Dragonfly.

Bonding with the material

When asked what is was like to work with the carbon fibre on the project, Zef had this to say:

”One of the main challenges was to get to know the material. We wanted the perfect solution for Polestar 1 and were prepared to do whatever it took to find it. We’ve learnt a lot and, even if everything didn’t go exactly the way we expected, you often learn more from the surprises. The process has resulted in a very high level of precision and finish.”

Once they’d familiarised themselves with the material, the Polestar engineers set about defining and controlling all the other parameters – these included critical decisions such as which fibre and resin to use, along with how to assemble and paint the various sections.

The team also learnt how to define the material for Computer Aided Engineering (CAE) calculations so that they could test and evaluate the parts. They also knew from experience that carbon fibre behaved differently depending on directional forces. So draping simulations were done to anticipate what the material would do in reality.

And the advantage of all this clever modelling? The directional weaves in the material are now specifically placed in the car to counteract forces and increase strength during different driving conditions.

We were expecting big numbers from the car in terms of performance and small numbers in terms of dimensions and weight. So there's been a lot of research, analysis, testing and also a bit of head scratching along the way. The car is a massive 230kg lighter by integrating the material into the under body which completely neutralises the added weight of the batteries.

Impressive.

The Dragonfly (Odonata: Anisoptera) Nature's answer to strength, speed and agility. Honed through relentless evolution.

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Realising the design

The design concept and execution is very important for any brand. As Polestar 1 was the first car to emerge from the Polestar stable, it was crucial to make a statement and visualise the brand’s design language.

According to Zef, the material doesn’t really play a big role initially. It’s later, when it comes to surfacing and integration of details, that where the differences become obvious. Carbon fibre takes the design to a whole new level. Restrictions, such as press depth, are suddenly no longer an issue. That means the designers can create much more dramatic surfaces - or more flat ones if they want.

“If we had been working with steel then the bonnet surfacing would be far less dramatic than it is. Now we’ve been able to create the car more like a sculpture and create sharper edges on the feature lines - that makes the car look more technical and refined,” adds Zef.

He continues: ”With carbon fibre in low-volume production, a lot of things can be done by hand. So you can always find solutions, you can talk to the supplier and do things differently to arrive at the right result. Proportions and stance are always really important in any design and we are obviously very pleased with the result.”

Painting carbon fibre is completely different from painting steel. To get the right colour and the finish has meant challenging the team to achieve perfection.

What's on the surface counts

Such an exclusive and expensive material requires expertise and craftsmanship throughout every stage of the process. When it comes to painting the new Polestar 1, there’s been a lot of experimenting and practice.

“Every car designer knows exactly what to do – and what not to do to – when they create a car in steel. But this is something else. Almost everything is possible, says Zef.”

But painting carbon fibre is completely different from painting steel. All the parts arrive from the supplier coated with a primer and to get the right colour and the finish has meant challenging the team to achieve perfection.

And the same goes for the quality control. Where hawk-eyed, highly skilled people once scanned for the smallest imperfections in colour or finish, they found those issues didn’t exist in painted carbon fibre. They’re now looking for completely different quality issues. As with all things at Polestar, the ambition is high, and everyone is continually pushing to find the perfect way to work with the material.

When safety is part of performance

Polestar have performed extensive testing in order to secure the rigorous demands on safety and durability of the Polestar 1. Assembling the carbon fibre parts with the steel platform and the other parts of the Polestar 1 is challenging. Steel is more elastic than carbon fibre and in order to fasten the two materials, Polestar uses specially developed adhesive that can handle the variation in movement from the steel and carbon fibre parts. Zef explains:

“The challenge is that carbon fibre is a linear brittle material and traditional automotive structures normally use materials that get deformed before breaking (like steel for example). Carbon fibre on the other hand, behaves in different ways depending on the direction of the forces.”

The end-result makes the Polestar 1 a car with world leading attributes within crash safety and durability. Merging the carbon fibre body with the steel platform provides the Polestar 1 with the best of both worlds, in terms of driving characteristics and safety.

Reflecting on the details

Every carbon patch is placed by hand to make sure the pattern lines up and every part is also finished off manually.

Looking back on the work so far, carbon fibre makes a strong case for itself. It’s definitely high-tech, still requires a dedicated amount of crafting and there’s a fair amount of patience involved in getting it absolutely right. But when you do, there is a feeling of bespoke, precision engineering and design sophistication that is impossible to ignore. Your perspective changes. You run your hands over the car and know that the surfaces are not pressed in tools by machines, that the carbon patches are each placed by hand and because of that, you know the pattern lines match up. You also know each part is finished off manually and with obsessive detail. Put all this together and it’s a very special feeling.

Will we see more use of carbon fibre in the future? It’s a tough question to answer and there are many parameters that must be decided before a team can make that decision, but one thing is certain: There are lots of places that are ideally suited to carbon fibre in cars and the advantages are worth it. If its use becomes more commonplace, it’s good to know that suppliers are also looking at ways to recycle and re-use the material in the future. Something that is a critical factor in using the material on Polestar 1.

So did the team find the right balance and stay true to the Polestar philosophy: no compromise, no shortcuts?

It would appear that they did… and then some.

Fast facts – Carbon fibre and Polestar 1:

1. Weight. A total saving of -230kg using carbon fibre together with the SPA chassis.
2. Stiffness. Increased Torsional stiffness from 22Nmm-2 to 32Nmm-2. That’s +45%.
3. Centre of Gravity. A steel SPA floor + carbon fibre upper lowers the centre of gravity for superior handling and performance.

Carbon fibre is one of our cutting-edge technologies. There are many more.

Polestar 1 is an Electric Performance Hybrid, an exclusive car that pairs electrification with outstanding performance, gorgeous proportions, exquisite craftsmanship and innovative technology. Every piece is developed and chosen with care. The use of carbon fibre is just one area that demonstrates how serious we are about making Polestar 1 a car without compromise.

Source: Polestar.com