A Mill-Turn’s Value for Machining Micro Gears

Amorphology, a NASA spinoff company, is a leader in the application of advanced materials and manufacturing technologies for the improvement of non-lubricated micro-gears for robotics and other industrial applications using “amorphous” metals such as bulk metallic glasses.

These materials have advanced properties compared to steel, titanium and aluminum, as examples, and the company’s patents for several metal alloys are based on developing gears for space and other extreme-cold temperature applications.

Amorphous metals are a non-crystalline class of alloys that cut and chip differently than other materials, the company explains. In its attempt to source a machine tool that could produce its micro-gears, Amorphology conducted tests with several machine suppliers, including Starrag, to assess the precision, cycle times and overall capabilities of the machines as they cut a relatively unknown alloy.

“We were focused on finding the best machine to meet our rapid prototyping, mold insert cutting and post-processing needs,” says Jason Riley, Amorphology’s COO. Ultimately, the company chose Starrag’s Bumotec s191H mill-turn.

After receiving CAD files of the prototype micro-gears and performing machining tests using a Starrag-developed cutting tool at the machine tool builder’s sites in Switzerland and the United States, several sample batches were produced.

“We are targeting high-precision parts with tolerances of often around five microns on certain dimensions,” Riley explains. “Most of our work is focused on rapid prototyping and relatively low batch production quantities in the region of hundreds of parts per month.

“The Bumotec provides the mill-turn capabilities that we currently don’t have, as well as a higher production capacity,” he adds. “The machine supplements our current abilities and it provides capabilities that we don’t have.”

Amorphology points out that the Bumotec s191H can “offer a unique value proposition,” by either machining single pieces or by producing hundreds of components in a lights-out scenario.

In addition to making gears for aerospace uses, Amorphology’s gears are used in cobots, robots and medical devices. For example, most cobots use strainwave gears — the main component being a flexspline, which is a complex, thin-walled part.

The s191H is one of a family of Bumotec mill-turn machining centers targeted at precision machining of often complex parts in a single set up. With 65-mm bar capacity, bar feeder and high-pressure (3 hp) coolant delivery, the s191H can achieve machining capabilities to ±2.5 microns within its X, Y and Z axes range of 410 by 200 by 400 mm courtesy of linear drives and high thermal stability.

In addition, its main spindle is complemented by a sub-spindle that can turn in both horizontal and vertical planes to enable multitasking routines. Tool magazine options extend to up to 90 pockets on a machine that has rapid traverse rates of 50 m/min and a spindle speed of 30,000 rpm (40,000 rpm is an option) that also contribute to its fast cycle times.

Many of Amorphology’s cobot, robot and medical device parts can be cast or injected molded, but at times these micro-parts need to be post-processed to higher tolerances. Starrag Bumotec “cut its teeth” in designing machines for the Swiss watch industry and, as a result, the machines are adept at producing micro-sized, high-value gears. Amorphology projects that the Bumotec s191H will machine micro gearboxes without lubrication.

The company also appreciated the results and in discussions with Starrag about how both organizations could co-operate, it was agreed that Amorphology would feature the Bumotec machine in its Pasadena, California, facility for both companies’ customers to view.

At the demo center, the machine can be seen producing a variety of parts including gears, mold inserts, bulk metallic glasses and traditional metal production parts.

Greg Dunkley, Starrag Bumotec’s vice president of precision engineering, says “Establishing a laboratory environment to showcase the precision, quality and capabilities of the Bumotec s191H will enable aerospace and defense engineers to experience this real-time machining that could be used in their manufacturing operations.”