Jan 24, 2018 | By Benedict

The Fraunhofer Institute for Applied Optics and Precision Engineering (IOF) has used SLM 3D printing to reduce the weight of scanner mirrors and space-borne telescope mirrors by 75 per cent. The mirrors will be shown as part of the Photonics West exhibition in San Francisco next week.

At this year’s Photonics West exhibition in California, German research institute Fraunhofer IOF will descend upon the event with a number of quantum and additively manufactured technologies up its sleeve. The Jena-based institute will be demonstrating a number of laser-based innovations, including 3D printed scanner mirrors and space-borne telescope mirrors that are up to 75 per cent lighter than traditionally made alternatives.

According to Fraunhofer IOF, its team of expert engineers has used Selective Laser Melting, a form of metal additive manufacturing, to fabricate these ultra-lightweight metal mirrors. Due to their lightweight design, which includes stochastic and symmetric structures, a mass reduction of up to 75 per cent can be achieved using materials like AlSi12, AlSi40, and Al6061, all of which have now been qualified for the 3D printing process.

This is a big reduction in mass for the metal mirrors, but it’s not the first time that Fraunhofer IOF has made incredibly lightweight metal optics. For many years, the institute has used tools like diamond cutters and chipping technology to turn aluminum into these lightweight structures. But these methods are limited in their scope: substrate geometry is limited, which means only certain simple shapes can be made.

With additive manufacturing, that scope widens considerably. Fraunhofer IOF has used SLM 3D printers generate complex parts out of metal powder, and is constantly attempting to incorporate new materials into the process.

In a recent study, the institute found that hypereutectic aluminum silicon worked well as a 3D printing material, with very high cooling rates used to fuse the powder particles. The resulting mechanical properties were said to be “comparable to or better than” those of conventional alloys of the same chemical composition, while the fine microstructures had a porosity of below 0.05 per cent.

But what’s especially important with the 3D printing of mirrors is reducing weight. The Fraunhofer IOF engineers have been able to do this by generating regular cell structures, regular or irregular lattices, and topologically optimized designs, and by running simulations of structural approaches.

This means that some unnecessary bits of the structure simply get left out. Internal areas of a mirror, areas that do not directly contribute to the stability of the structure, can be reduced in mass by making them less dense.

The printer doesn’t churn out a ready-to-use mirror though. After these lightweight structure are 3D printed using the SLM printer, they are post-processed using other techniques to achieve a high level of optical precision. Fraunhofer IOF says that, after this post-processing step, mirrors of 150 mm in size exhibit “high stability and stiffness” along with surface roughness of <1 nm RMS and form deviation of <150 nm PV.

The Photonics West conference will welcome roughly 20,000 visitors who will get the chance to see around 5,200 presentations and 1,300 exhibitors. Those visitors will also be able to see other exciting innovations from Fraunhofer IOF, including its new AR-plas2 technology that produces organic nanostructures for broadband antireflection coatings (using additive manufacturing in certain areas), laser technology for the preparation and measurement of quantum mechanical properties of photons and atoms, and more.



Posted in 3D Printing Application



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