Additive manufacturing racecar parts

The aims of the racing series Formula Student Electric (FSE) are educational, but success is measured in lap times and victories.

Electric engines provide extremely high torque and are relatively small, making them a popular racing option. Because of the high power density of these electric motors, selection and design of cooling options has a big influence on the performance and efficiency of the engine. Beyond weight savings, optimal cooling can significantly improve the long-term performance of an electric motor.

In addition to transferable engine power, contemporary vehicle electronics allow each wheel to be configured individually, ensuring the best traction.

Heat, however, is a problem. Motors have little available space to dissipate heat and release that heat in close proximity to the braking system. The temperature build-up and limited cooling solutions – the basic choice is still between air and water – represent a significant challenge. During the 2013/2014 season, the GreenTeam racing team – made up of students at universities near Stuttgart, Germany – opted for water cooling and the concept proved to be promising.

Dominik Schäfer, a powertrain team member says students quickly learned that high temperatures were predominantly caused by heat transfer and convection.

“The reason for this lay in the geometry of the water channels,” Schäfer notes. “Hotspots had formed in areas with low water-flow velocity.”
 

Laser-sintering a cooling system

Additive manufacturing (AM) provided a solution. The GreenTeam was able to build three different prototypes for the cooling unit, from polyamide PA2200, giving students the ability to test options physically instead of relying on simulation. The aim was to achieve sufficient cooling at a minimum water-pump throughput rate.

A larger pump could increase pressure and flow velocity of the water, thereby improving cooling. However, this would require more energy and a corresponding increase in the weight of the battery or the pump. The best way to overcome this trade-off was through perfecting the geometry of cooling channels.

Schäfer tested variations of the water-pump cooling jacket using software for computational fluid dynamics (CFD). The final component looks like a cup with coarse thread-like cooling integrated on the interior wall. This becomes a watertight cooling pipe when the electrical motor is slid into the cup.

To manufacture the complex components in limited quantities – one jacket was needed for each wheel – the students turned to German additive manufacturing equipment provider EOS.

“Production turned out to be fast and simple,” Schäfer explains. “The transfer of the design data also took place without any problems.”

Students used the EOS M 290 to build the component, layer by layer, from a fine metal powder by means of a high-precision laser. The team used EOS aluminum AlSi10Mg because it unites high mechanical and thermal durability with light weight for applications on the race track.
 

Simplified part design

A helix geometry, conceived by Schäfer, provided the racing team with a superior materials option to honeycomb and meander structures.

In addition to built-in cooling channels, the finished component was integrated with the transmission flange and the wheel mounts. By consolidating parts, weight was reduced and final assembly was less complicated. Brackets for water intake and draining were also built into the design. The young engineers were able to reduce weight by 16% compared to the previous year. The final weight was 370g, and cooling performance rose by 37% compared to the 2012/2013 season.

Nikolai Zaepernick, head of strategy and business development at EOS, says the student project shows the potential that AM brings to electric-drive vehicles.

“Experts predict a big future for electromobility,” Zaepernick says. “Wheel-hub electric motors in road vehicles bring similar challenges to those faced in this racing series. Intelligent minds have been successfully working around the issues that arise in this area.”

On the track, the GreenTeam broke the world record in a drag racing competition for Formula Student Germany (FSG), going 75m in just 3.36 seconds.

EOS GmbH
www.eos.info

GreenTeam
www.greenteam-stuttgart.de