On the Fast Track

A mechanical engineer uses 3-D printing to rapidly prototype cast components for one-of-a-kind bicycle designs.

Nicholas Leider, Associate Editor

(Click here to see the story as it appears in the April issue of Modern Casting.)

For those involved in metalcasting, it doesn’t take long before you become acutely attune to noticing the industry’s impact in everyday situations. You can be walking down the street and point out a metalcaster’s name embossed on a sewer grate. Or you’ll perk up when you see a commercial for so-and-so’s heavy duty trucks, wondering if there will be a clip from a casting facility.

In short, you start to look for and see metal castings everywhere.

Kim-Niklas Antin is plenty familiar with this phenomenon. Only in his case, connections are drawn between everyday life and bicycling, one of his life’s passions since he first successfully guided a two-wheeler down the street. Once he entered the mechanical engineering program at Aalto University in Helsinki, Antin always wondered what he might be capable of doing.  

“When I first started my studies, I ran into all kinds of different materials and manufacturing technologies. Every time, I thought, ‘Could this be used to make a bicycle frame?’” he said. “At some point, I decided it was now or never and I started actually doing something instead of dreaming about it.”

That “something” started in 2010 and has become the “ideas2cycles” project, a non-profit organization for developing novel bicycle concepts with the latest technology and production methods. Five years in, Antin, along with two collaborators, has produced a number of innovative bicycle designs featuring a variety of materials and manufacturing processes.

Among his most notable designs, the original “The Fixer” prototype was an ultra-light model featuring five investment cast magnesium lugs whose molds were created with 3-D-printed models. Now designing the Fixer’s third iteration, Antin again is using 3-D printing to create sand molds for aluminum castings that will improve performance and appearance.

Antin began working on a design for the first prototype during spare time from his studies. He wanted to produce something different from the conventional bicycle frame, which initially proved more difficult than expected. The area between the chain ring and the back axle was particularly troublesome. There, the chain and back wheel must be free to rotate, while still allowing the cranks (which connect the pedals to the chain ring) to move freely.

After a few months of designs and redesigns, the ideas2cycles team had its first prototype, though it hardly impressed its creator.

“I was scared it was going to break in half. It was a little crooked and went a bit sideways,” Antin said. “The wheels weren’t aligned, but still, it worked to some degree and that was encouraging. I always knew I didn’t just want to do one prototype. I wanted to do several iterations of an idea and develop it.”

Refining that prototype and producing other designs eventually led Antin to explore 3-D printing as a possible method of producing lugs, which connect the bike’s lightweight carbon-fiber tubes. 3-D-printed plastic components were not an option, considering the required mechanical and physical properties. CNC machining to produce molds was entirely too expensive. But Antin then looked into marrying 3-D printing with investment casting after he visited Aalto University’s metalcasting lab, just down the hall in the engineering building.

“I took a basic course on casting but I didn’t really know much,” he said. “Fortunately, at the lab, I was able to talk to people with several decades of experience with metalcasting, including one researcher who had studied magnesium castings.”

Considering the relative simplicity of the components, Antin did thickness analysis in the CAD program instead of using casting-specific software to estimate which parts would cool first and which parts would need a feeder. Thanks to the casting expert’s contacts with a German 3-D printing company, two sets of patterns were printed for free and delivered in a week.

The pattern cluster was built and hand-dipped in the slurry to build the investment shell. De-waxing and casting took place in a single day, producing ready-to-use lugs after minor machining. Unfortunately, two of the first set’s five castings failed due to insufficient wall thickness. Antin added some wax to the second set of patterns, repeated the investment casting process and produced acceptable components.

But that initial failure highlighted an advantage of rapid prototyping through 3-D printing and investment casting, especially for someone looking to produce unconventional designs.

“I want to push the limits of what can be done,” Antin said. “With rapid iterations, I’d rather just test something. If I fail, I can backtrack a little and play it a little safer, instead of playing safe from the beginning and ending up with a heavier structure.”

The acceptable castings weighed just 13.1 oz. (370 g). The frame weighed just 2.2 lbs. (1 kg), before attaching wheels, cranks, handlebars, etc. The prototype, known as the Fixer-Stage 1, led to ideas2cycles winning the “Bits into Atoms” design contest organized by the Finnish Rapid Prototyping Association in April 2012.

In the last three years, the ideas2cycles team has developed two more versions of the Fixer. The second stage featured a metal-free frame, while the third iteration, still in development, will include aluminum-silicon carbide composite lugs cast in 3-D-printed sand molds. The design of the new components took nearly six months to improve stiffness-to-weight ratios, overall performance and appearance.

“We calculated which elements of the meshed volume contributed the most to carrying load and which did not,” he said. “The most unnecessary elements were removed and the calculation was repeated, so only the structurally crucial volume of material remained. This meant even stress distribution.”

The aluminum alloy improved performance compared to the earlier magnesium castings.

“We are using the SiC particles to increase the stiffness of aluminum alloy,” Antin said. “We achieve 96 GPa versus 65 GPa without the carbides. Ductility is also greatly reduced, which means we need defect-free castings so they do not fracture under the load.”

Outside of a small grant from the Aalto Center for Entrepreneurship when ideas2cycles began, the project is largely self-funded, with Antin dedicating both his free time and money to his pet project. But the yearly investment of $1,000-$2,000 a year is well worth it.

“It’s beneficial to my career,” he said. “I’m focusing on nondestructive testing methods in carbon fiber composites for my PhD, so it has benefited me in my working life. It’s also something I love to do.”

Antin is used to hearing if ideas2cycles, currently a non-profit organization, will ever become a business, which doesn’t seem likely. The prototypes, usually one-offs produced in advanced materials via cutting-edge processes, would require astronomical prices. Additionally, any potential customers would demand quality and performance standards that are difficult to achieve in unconventional prototypes.

“One option could be to design bicycles internationally and work with a bicycle company,” Antin said. “I’d also like to land a job with a bicycle company after graduation, rather than start a small company of my own.”

Thanks to streamlined simulation, tooling, casting and machining capabilities, an intricate water passage went from purchase order to prototype in just 17 days.