Mill-turn machining for innovative micro-parts

Examples of the micro-gears produced on the Bumotec
Examples of the micro-gears produced on the Bumotec

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 innovative ‘amorphous’ metals such as bulk metallic glasses.

These materials have advanced features over steel, titanium and aluminium, for example, 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 and, in the company’s quest to source a machine that could produce the micro-gears, it conducted machining 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, mould insert cutting and post-processing needs,” says Amorphology’s chief operating officer, Jason Riley. The Starrag Bumotec s191H mill-turn machining centre outperformed all contenders.”

After receiving CAD files of the prototype gears and undertaking tests using a Starrag-developed cutting tool at the machine tool builder’s sites in Switzerland and the USA, several batches of samples were produced.

Amorphology was impressed with the results and in discussions with Starrag about how both companies could cooperate to grow their respective businesses, it was agreed that Amorphology would showcase the Bumotec in its Pasadena (California) site for both companies’ customers to view.

Amorphology is set to make a wide variety of parts on the machine, from mould inserts to prototype gears, as well as other production bulk metallic glasses and traditional metal parts.

“We are targeting high-precision parts with tolerances of often around 5µm on certain dimensions,” continues Mr Riley. “Most of our work is focused on rapid prototyping and relatively low batch production quantities in the region of 100s of parts per month. The Bumotec provides the mill-turn capabilities that we currently don't have, as well as a higher production capacity.”

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 products are also 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.

Working area of the Starrag Bumotec s191H mill-turn machining centre
Working area of the Starrag Bumotec s191H mill-turn machining centre

The s191H is one of a family of Bumotec mill-turn machining centres targeted at the high-precision machining of often complex parts in a single set-up.

With 65mm bar capacity, bar feed system and high-pressure (3hp) coolant, the s191H can achieve highly accurate (±2.5µm) machining solutions within its X-, Y- and Z-axes range of 410mm, 200mm and 400mm respectively, courtesy of linear drives and high-level thermal stability.

In addition, its main spindle is complemented by a sub-spindle that can turn in both horizontal and vertical planes for multi-process/tasking routines. Tool magazine options extend to up to 90 pockets on a machine that has rapid traverse rates of 50m/minute and a 30,000 (or 40,000)rpm spindle speed that also contributes to its ultra-fast cycle times.

Many of Amorphology’s cobot, robot and medical device parts can be cast or injection moulded, but at times these micro-parts need to be post-processed to extremely high tolerances. Starrag Bumotec cut its teeth in designing machines for the Swiss watch industry and, as a result, the machines are exceptionally adept at producing micro-sized, high-value gears.

Speaking on behalf of Amorphology Mr Riley concludes: “We project that the Bumotec s191H will machine micro gearboxes without lubrication. While we will be machining our patented alloys to very small sizes in instances where production quantities don’t require injection moulding, we will also use the machine to help develop the parameters for amorphous metals. And as we advance, we will be the only company on earth with such knowledge.”




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