GreenTeam & CERATIZIT – Chasing the world title with titanium 

How fast is fast enough? Last year, the GreenTeam from the University of Stuttgart emphatically answered this question with the team's electrified carbon racing car setting a new world record for 0-100 km/h at 1.461 seconds. But what does fast enough really mean? In 2023, a new version of the e-racer was launched, this time with even more weight-saving titanium components, with the aim of speeding towards the next record and once again defending its title as world champion. CERATIZIT supported the GreenTeam again this season with its tooling and machining expertise.

Speed and acceleration have always had great potential to fascinate. Racing series such as Formula Student set standards that even fans of supercars can only dream of. In 2022, the GreenTeam from the University of Stuttgart raised the bar once again. Not only did the team win the individual international races in impressive style, but the team's racing car also delivered its top performance in a breathtaking world record 1.461 seconds from zero to one hundred kilometres per hour: a level of performance that would make the coils of many a synchronous motor run hot. To put this into perspective, a Bugatti Chiron Super Sport 300+ with 1,825 HP and 1,850 Newton metres of torque (valued at around 4.7 million US dollars) requires a whole 2.17 seconds to reach the same speed.

The GreenTeam Uni Stuttgart e.V. was founded in 2009 and since then has regularly taken part in Formula Student, the international design competition for students. Students independently design and build an electrically powered racing car, which is judged on disciplines such as acceleration and endurance. In 2023, 50 students once again joined forces to defend the top spot in the competition's world rankings. The aim was to deliver unbeatable performance in the four Formula Student events in the Netherlands, Austria, Hungary and Germany.

To achieve this, the carbon racing car needed to slim down. The current model weighs just under 145 kilograms and delivers a maximum output of 180 kilowatts thanks to its all-wheel drive with electric motors developed in-house and a newly designed high-voltage battery. Due to the low vehicle weight, this corresponds to 1750 hp per ton.  "For this year's car, we've once again invested a lot of development time in the unsprung masses, including the wheel package. Together with our partner CERATIZIT, we were able to make significant savings in terms of mass and dimensions," explains Malte Maleika, complete vehicle manager and head of mechanical engineering at GreenTeam. For peak acceleration, this means 2.5 g – roughly comparable to the force exerted on astronauts when a spacecraft re-enters the Earth's atmosphere.

CERATIZIT has been supporting the GreenTeam for several years with tool and process expertise in the production of complex parts. "In 2023, CERATIZIT manufactured the carrier, the stator housing and the brake callipers for us. We are very grateful for this support, as it enables us to make our wheel package very small and very light, meaning that we can package everything in the specially developed carbon rim that we made ourselves," explains Malte Maleika. 

Previously the components were mostly made of aluminium, but in 2023 titanium components were also required. "The aim was to make the electric racing car (referred to internally as E0711-13) even lighter than last year's successful model, which meant turning our attention increasingly towards titanium as a construction material. Aluminium, which had been the team's previous choice, is considered relatively straightforward to machine. But titanium? That's a whole different world and generally more common in the aerospace industry than the automotive sector," explains Stephen Pennington, application engineer at CERATIZIT UK & Ireland Ltd in Sheffield. And why? Because titanium materials have a poor thermal conductivity factor, which results in high temperatures in the shear zone and the heat from machining is not dissipated into the chip as it is with other materials. 

But before we could start machining, there were a number of process parameters to think about. "I travelled back and forth to our CERATIZIT branch in Besigheim several times over a number of weeks. It was there that we (development engineer Sophie Mueller and design engineer Kristian Muehlbeier) did most of the programming and developed the clamping devices," says Stephen Pennington, recalling the productive collaboration between Sheffield and Besigheim. A total of eight wheel carriers and an equal number of motor housings had to be made from aluminium, alongside eight brake callipers and 16 brake pistons from titanium. Partly produced through additive manufacturing in advance, the final machining was then carried out with extremely low tolerances.

However, these were not the only obstacles the team encountered during the project – a number of machining operations had to be performed in awkward-to-reach corners: "Selecting the right tool was crucial to success, along with careful programming. Fortunately, I had unrestricted access to a comprehensive arsenal of tools," chuckles Stephen Pennington. Thanks to his experience with other projects, the solid carbide shank tools from CERATIZIT's SilverLine for titanium machining instantly came to mind. "I knew that these all-rounders would work perfectly, and combined with appropriate cooling, I had found the perfect tool for many of the project tasks." 

When turning the brake pistons in particular, the titanium came off more like a strip than individual chips. The DirectCooling tool holders helped enormously by delivering a targeted jet of coolant directly to the new CTPX710 indexable inserts. "I can't bear to think what would have happened if something had gone wrong with the 3D-printed components during the machining process. That would have thrown the whole schedule off!" admits Stephen Pennington. But thanks to many further tool solutions, everything went like clockwork. 

Particular protection was afforded by process monitoring with ToolScope, which detects even the smallest fluctuations in the machining process, and even stops the machine if necessary before anything worse can happen. "Fortunately, it never came to that. I ran at a slower feed rate and lower speeds with titanium, so as to err on the side of caution. Although I didn't have a great deal of prior experience with titanium, everything went much more smoothly than I could have hoped," says a relieved Stephen Pennington. And the reward for putting in all this hard work? Weight savings of up to 45% on the brake callipers compared to their aluminium predecessors helped the GreenTeam to significantly reduce the overall weight of the racing car.

"When it comes to our partnership with CERATIZIT, we particularly value the good communication with just the right people we need to speak to. This flexibility is extremely important to us, as Formula Student is a very fast-moving project and our partner needs to act quickly too," explains Malte Maleika. Stephen Pennington adds: "Working with the GreenTeam was an amazing experience, in pretty much every regard. Our biggest challenge was the tight schedule in which we had to manufacture the parts and send them back to Stuttgart, so that the car could be launched on time." 

But everything ran seamlessly and the car was ready in time for the first races on the calendar. "The entire project was a real challenge, during which I developed hugely as an engineer, such as machining all these high-tolerance parts within a specific timeframe for a specific application – in this case a Formula E car with a winning make-up." 

Since its inception back in 1979, Formula Student has offered budding engineers a platform for learning and a unique opportunity for students to apply their theoretical knowledge in a practical arena. It is in the spirit of this platform that CERATIZIT supports such projects with young and upcoming talent. Deniz Yilmaz, marketing service manager at CERATIZIT, comments: "What's truly remarkable about our project this year is that every participant, either within our company or in the GreenTeam, was under 30! And just because it's a "student" project it doesn't mean that the tolerances and standards are any less stringent than in automotive construction at corporate level. If you want to send the fastest racing car out on the track, you simply don't have time to compromise!" 

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