Most polymers perform poorly when it’s freezing. In sub-zero temperatures they lose some of their mechanical properties and become brittle. BASF PP Ultrafuse GF30, a polypropylene (PP)-based composite reinforced with 30% addition of glass fiber, is an exception. This, besides its improved surface quality, convinced Clement Jacquelin, the CEO and founder of Athletics 3D, to use it for printing a custom hand stop for a biathlon rifle.
“In most cases, professional athletes come to us because they need sports equipment that is made and tailored specifically for them to further improve their performance,” says Jacquelin. However, in July 2021 Athletics 3D had to deal with an entirely different challenge. During the training camp in Norway with the rest of the French national team, one of the world’s best biathletes had an accident on the road to a cycling session. He crashed and injured his left arm he extended to cushion the fall. The diagnosis in a hospital where he was immediately taken looked bleak. His radius and ulna, two bones in the forearm, were fractured. This meant that the athlete’s forearm supination and ulnar deviation angle were severely limited which rendered aiming with a standard biathlon rifle impossible in the prone position.
The bones had to be surgically secured with a metal stabilizer, and the recovery period was expected to last at least a couple months. To make effective training possible despite the injury, Athletics 3D had to modify the biathlete’s rifle. The goal of the project was to enable the biathlete to shoot with limited ulnar deviation angle. To achieve that, the team at Athletics 3D modified the hand stop, a part where a sling is attached to the bottom of the rifle’s stock.
The design process began with using a Zeiss 3D scanner to make a precise digital model of the original hand stop. Once this was done, the team began to apply changes.
“The first thing we changed was the angle at which the hand stop was held to enable aiming without twisting the wrist, explained Jacquelin. “This way we solved the problem of limited ulnar deviation angle. In the second step, we increased the area of contact between the hand stop and the palm to provide more stability in a position our client had not trained for.”
The team next had to choose the best material for the job that could retain mechanical performance in a wide range of predominately low temperatures.
“World Cup biathlon races are done in temperatures as low as -25°C,” said Jacquelin. “This is the winter sport after all. And such low temperatures tend to degrade the mechanical performance of most polymers. Materials such as PLA [polylactic acid] or even ABS [acrylonitrile butadiene styrene] tend to become brittle when it’s freezing. That’s why the French team coaches insisted on choosing the material that could perform in low-temperature conditions.
“We could not just use popular filaments like standard ABS or PLA. The part had to withstand significant stress, be resistant to impacts and have a great surface quality. This alone limited our options to just a few candidate materials. Finally, what really sealed the deal for BASF Ultrafuse PP GF30 was its thermal stability. The material exhibited the same, excellent performance in both freezing cold and relatively mild temperatures just below 0°C.”
Once the right material was chosen, Athletics 3D pushed the project to their Zortrax M300 Dual 3D printer, which was factory calibrated to work with BASF PP GF30. Zortrax is a manufacturer of 3D printers for both desktop and industrial sectors based in Olsztyn, Poland.
“3D printers often have issues with accurately reproducing irregular, organic shapes,” said Jacquelin. “Performance in tasks like that lets you immediately tell the mediocre 3D printers from the really good ones. Ergonomic shapes we use in our sports gear are always challenging and utmost precision is necessary to achieve the desired effect. That’s why we chose the Zortrax M300 Dual.”
According to the team, the results achieved with the redesigned, 3D printed hand stop were impressive. The first shooting session after the accident took place in September 2021, and the injured biathlete was back to shooting in under two months. Athletics 3D and French team coaches found that shots taken with the new hand stop were even more precise than with the standard one. The metric that went down, however, was the shooting rate.
“Professional sports are very often used as a testbed for new, innovative technologies,” said Mariusz Babula, CEO of Zortrax S.A. “3D printing is no exception. We are proud that Zortrax 3D printers working with materials coming from world-leading manufacturers such as BASF Forward AM can deliver the performance necessary at the very pinnacle of disciplines like biathlon.”
Overall, training sessions with the 3D printed hand stop started in September and lasted till the end of December 2021. When a full movement was restored in the athlete’s wrist, the team decided to go back to the standard hand stop.
“The main reason was that the coaches together with our client decided that increased accuracy did not offset the slower shooting rate” explained Jacquelin. “However, getting back to shooting and competing in World Cup races was made possible at least two months before it normally would have without our 3D printed hand stop.”
BASF Ultrafuse PP GF30 is also used outside of professional sports. Due to its mechanical strength and thermal stability, the PP GF30 is used in automotive industry. The material is also stiff and resistant to various chemicals and UV light. Along with other engineering filaments like BASF Ultrafuse PAHT CF15 or Z-NYLON, BASF Ultrafuse PP GF30 is aimed at users willing to work with the Zortrax M300 Dual 3D printer.