A close-up view of laser melting being used to 3D print in titanium to produce test versions of the ‘optic bench’ at the heart of ESA’s Athena X-ray observatory. A multi-axis robotic arm is being used to produce the complex structure, including deep pockets to place optical mirror modules.

“The essential technological achievement is the fact that 3D printing takes place under local protective gas shielding, without a protective gas chamber,” comments André Seidel, overseeing the project at the Fraunhofer Institute for Material and Beam Technology in Germany.

“This is enabled by a specially-developed process head called COAXShield which uses the noble gas argon to sweep titanium powder into the path of the laser, in the process protecting the newly-printed titanium from contact with the atmosphere.”

This gas protection enables a rapid change between additive manufacturing – laser metal deposition with powder – and subtractive manufacturing – as cryogenically cooled milling tool operated by a second robotic arm removes surplus titanium.

The optic bench itself is placed on a slowly moving 3.4-m diameter turntable between the two robotic arms. The end goal of this ESA Technology Development Element project is to produce a 3-m diameter optical bench, but in principle the procedure can be applied to a wide variety of sizes.

“You can see the metallic bright surface of the titanium, reflecting the honeycomb structure of the protective gas nozzle,” adds André. “Taking account of this for laser melting was a very big challenge, and an absolute milestone in the project.”

Credit: Fraunhofer IWS