MATERIALS


and curved three-dimensional shapes. However, instead of fingers and paper, the startup uses industrial robots to precisely control the bending and shaping of stainless steel sheets. The technique was developed with


support from stainless steel producer Outokumpu. It had been researching a related metalforming process in the early 2000s and shared the output of this with the startup after a chance meeting at a technology networking event. Paul Janiak, Outokumpu’s R&D


manager for design and fabrication says: “We’re always keen to promote the use of stainless steel, so we were pleased to share our experience to help Stilride take the concept forward.”


THE LIFE-CYCLE ASSESSMENT The result is an e-scooter design that makes the most of stainless steel, according to Nyvang: “With Stilfold, we are using high-strength stainless steel to create a design statement and a structure in one. The result is a simple, lightweight and corrosion-resistant chassis with fewer components – and a smaller environmental footprint. We commissioned a life-cycle assessment (LCA) so that we can quantify the carbon footprint and compare it with a conventional e-scooter.” The LCA was developed by the


Swedish Environment Institute (IVL). It provides a comparison of the environmental footprint of the materials needed to build and transport the two scooter chassis. It only covers the chassis, so IVL could exclude components that are identical (or almost identical) to both models, such as batteries and motors. It also excludes the energy used during manufacture, as that data was not available to the study. The initial finding of the LCA was


that the materials used in a Stilride Sports Utility Scooter One have a carbon footprint of around 50kg CO2


per chassis for the reference scooter.


STRENGTH FOR LIGHTWEIGHTING One of the reasons for this impressively low carbon footprint is the choice of a high-strength alloy – Outokumpu’s Forta 301 temper-rolled stainless steel


.


That is a significant saving compared with 160kg CO2


sheet. The process of temper rolling creates a work-hardening effect that gives high mechanical strength compared with other steels. As a result, the first prototype


of the Sports Utility Scooter One chassis can carry the same rider using less structural material, making it lightweight, at only 15kg of the bike’s total 80kg weight. In comparison, the reference scooter has a 45kg chassis and weighs 110kg overall. Commenting on this, Nyvang


says: “Lightweighting has multiple advantages; the most noticeable for riders being the better acceleration and ride quality. However, it also improves the range and preserves battery life. The 30kg saving on the weight of the scooter plus its rider will reduce energy consumption by a respectable 5%. “In the longer term, it creates an


opportunity for scooters for city deliveries and logistics fleets that can carry 30kg more payload than other bikes, something we’re looking to develop in the future.” A further benefit is that the


chassis also has fewer components than a conventional scooter (around 20 compared with 150). In turn, manufacturing and logistics chains become simpler, and there is less need for complex sourcing of components and subsystems from different manufacturers.


Riders also benefit, as it’s easier


for them to carry out maintenance on their scooter.


RECYCLING TO THE RESCUE Another important benefit of the use of stainless steel is the circular economy. Stainless steel is the ultimate recyclable material. A study by Yale University found that 85% of stainless steel is recovered as scrap metal at the end of its life, and it can be processed and resmelted over and over again without affecting quality. However, only 44% of new stainless steel is based on recycled scrap. According to Camilla Kaplin,


Outokumpu’s senior manager – environment, recycling makes a huge difference to the carbon footprint. Using one tonne of recycled austenitic scrap material instead of virgin iron ore avoids the emission of 4.3 tonnes of CO2


. She says: “At Outokumpu, we have


the lowest carbon footprint in the stainless steel industry. We base more than 90% of our production on recycled materials and our Tornio mill in Finland is home to Europe’s largest recycling centre. We also purchase low-carbon electricity and use energy efficiency programs to minimise our carbon footprint.


It’s created with a new technique called Stilfold www.engineerlive.com 27


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