“I made my first scooter when I was 19 and have always dreamed of building on that experience. But most of all, I wanted it to be cheap and easy to build with simple tooling, and durable and long-lasting materials. That called for straightforward design with fewer components and less welding.“Most scooters bodies are constructed with a combination of steel and molded plastic. I wanted to create the sort of complex shapes associated with classic scooter design but using the type of folding and cutting that you do in origami.
“I played with the concept and developed a full-sized model in cardboard. When I showed it to my associate Jonas Nyvang, he shared my excitement. We decided to form Stilride to take the idea forward, winning a grant from Sweden’s innovation funding agency Vinnova.”
Chance encounterA chance encounter with an expert from Outokumpu introduced Tue to the possibility of working with high-strength stainless steel. It was not something he had considered as the material usually needs powerful tools to bend and form it into shape.
He said: “The expert told us about a research project that used localized heat treatment to selectively soften sheets of temper-rolled stainless steel to make them easier to form.
“After connecting with Outokumpu's research and development manager Hans Groth, he shared some advice and gave us access to research papers. We used that insight to explore ways to create scooter bodies, for example by folding a section round onto itself and welding it to form enclosed beams that are strong enough to support a rider’s weight at the same time as being lightweight and durable.
“And having worked with stainless steel before, I already knew that it is beautiful, does not need painting and is long-lasting, making it ideal for a low-cost scooter."
Developing the LIGHT.FOLD techniqueWhen researchers at Outokumpu first developed the concept in 2000, they called it blanc forming. However, Stilride has carried out further development covering the whole value chain from digital design tools to production, ultimately developing a new process for designing and manufacturing that they call LIGHT.FOLD
The technique is based on using lasers to apply highly localized heat treatment to temper-rolled stainless steel, focused on de-hardening key areas where the material will need to bend.
The approach is similar using a knife to score card to control the location and extent of folds. By scoring a card multiple times in a fan shape, the card can be formed into a cone. LIGHT.FOLD achieves similar results with stainless steel, using robots to provide control and accuracy to form the sheets into complex 3D shapes.
When working with stainless steel in this way, it’s important to start with temper-rolled sheet as it has been hardened during cold rolling. Temper-rolled sheets are often used by industrial engineers in pressure vessels and chemical storage tanks or to build escape tunnels for oil platforms. However, bending and forming the high-strength sheet is challenging. Therefore, de-hardening selected areas allows large sheets to be bent and formed more readily.
The intense laser heat reverses the process of cold-working, softening the material enough to allow forming with narrow, well defined bending radii. The final forming re-applies the work hardening to some extent so that the structure partially regains the strength of the original flat sheet.
Paul Janiak, Outokumpu’s R&D manager for design and fabrication said: “When you temper-roll a duplex stainless steel like the Forta 301 that Stilride is using, it becomes so hard that it is difficult to bend. In the early 2000s, we developed the method of blanc forming using local heat treatment of 600-800 °C concentrated into narrow lines to selectively change the material’s formability. The interesting thing about using a laser is that you can focus its beam to influence the bending radius. For example, if you want a tightly defined bend, you could have a 1mm wide beam but you can use wider, defocused beams or oscillating patterns to create bends with larger radii.
“We’re always keen to promote the use of stainless steel so we were pleased to share our experience to help Stilride take the blanc-forming concept forward.”
Planning for 2022 launch
According to Stilride’s estimates, their innovative technique and the digital value chain LIGHT.FOLD has potential to save manufacturers and metal fabrication workshops 20 to 50 percent on material and 25 to 45 percent labor costs. This gives it potential for much wider adoption.
However, the current focus is to prove the concept by launching the e-scooter. Having secured its grant in November 2019, Stilride has been making steady progress in spite of the COVID-19 pandemic. The team is planning to carry out type testing and start accepting orders before the end of 2022 and then ramp up production in 2023. Until then, they are continuing to refine the design.
Tue says: “In a typical scooter, you’ll find hundreds of components and design details, as well as a wide variety of materials. All of these need time and attention during design and manufacture, as well as sourcing, procurement, test and qualification of components. And any of them could go wrong and need replacement during the scooter’s lifetime.
“We’re using fewer materials, components and production steps. That makes our scooter less costly to produce. And we’re confident that our scooter will be lighter and more rigid than its competitors thanks to LIGHT.FOLD. We’ll know exactly how much lighter once we have fine-tuned our bending technique and optimized the design to select the ideal sheet thickness to give us the strength we need.”
With an eye to the future, Stilride believes this approach could help to move production closer to the end user, with heat treated sheet being exported for forming and assembly in local machine shops round the world. And Tue and Jonas are also looking at how to apply LIGHT.FOLD to other products.