Additive Manufacturing 3D printing in space - Part 2: Experiments on metal powder

Research in zero gravity: The team of Prof. Dr. Jens Günster, Head of the Division of Ceramic Processing and Biomaterials and Professor of High Performance Ceramics at the Technical University of Clausthal, conducts experiments on additive manufacturing under zero gravity conditions. The aim is to produce components made of stainless steel (e.g. tools) in space.

Prof. Günster is joined by Dr. Andrea Zocca, Jörg Lüchtenborg and Pedro Lima and Gunther Mohr from the Division of Welding Technology. The team is completed by Dr. Thomas Mühler from the Technical University of Clausthal and Marc Sparenberg, a Ph.D. student at the DLR Institute for Composite Structures and Adaptive Systems in Braunschweig. September 2017 marked the first time when the team was able to carry out experiments using the specially designed laser beam smelter in ‘actual’ zero gravity conditions as part of DLR's 30th parabolic flight campaign. More experiments are to follow because the team was able to qualify once again for a place on the parabolic flight. The aim is to manufacture a metal spanner in the week between the 5th and 8th of March.

We expect the first ‘ready to use’ stainless steel components to be manufactured under microgravity.

Prof. Dr. Günster: You participated in last year’s DLR parabolic flight campaign with your ‘Powder-based additive manufacturing in zero gravity’ project. In your view, what is the potential of 3D printing in space?

Additive manufacturing processes are the future of sustainable production: they build up a component from layers of material powder – as opposed to subtractive machining i.e. removing non-needed parts of the material by milling, drilling or spark eroding. As a result, only as much raw material as actually needed is used. These processes are also of interest for space travel, since they enable the manufacturing of building sections, components, spare parts or tools as needed on space stations. Only the powder requires transportation to the space station and not a whole range of components. This saves material and weight and thus also fuel for space transport.

So far, the International Space Station ISS uses a 3D printer that applies a filament of heated plastic layer by layer to produce a three-dimensional object. In this parabolic flight experiment, a consortium of scientists from BAM, the Technical University of Clausthal and the DLR Institute for Composite Structures and Adaptive Systems are testing the industrially highly successful powder-based manufacturing processes for their suitability for use in zero gravity, in order to make their great potential available for future space missions. It is essential that the construction of layers from the powdery starting material, or feedstock, works in the absence of gravity. A gas flow through the build platform and the powder bed results in a flow-based force component that replaces gravity. This process is also patented in the USA.

During the last parabolic flight campaign, you were able to print the first objects in zero gravity. What were the challenges you faced and what are your plans for the second series of experiments?

The first flight campaign in September 2017 used a ceramic powder as feedstock. This was due to the considerable safety requirements imposed by the operator of the flights, the company Novespace. It would already be quite complicated to install a conventional laser beam smelter in an aircraft, but the new process now requires a gas flow through the build platform and the powder bed. Therefore, the first experiment did not use a potentially flammable or even explosive metal powder but a chemically inert ceramic powder.

This was our first campaign and enabled us to test essential functional features of the new coating application process and even sinter the first components using laser radiation. For this purpose, the installation of a protective gas atmosphere in a closed pressure vessel with gas circulation was initially not necessary. This is precisely the goal of the second campaign: a second evolutionary stage of the installation should now enable the processing of metallic powders under a protective gas atmosphere. We expect the first ‘ready to use’ stainless steel components to be manufactured under zero gravity.

Meaning an ‘evolution’ of ceramic to metallic powder...?

While our first campaign focused on ceramic powders, the focus is now on metallic materials. In this context, we rely on the expertise of colleagues from the Division of Testing Devices and Equipment. The process is fundamentally the same for ceramic and metallic materials, but the melting behaviour of metallic materials is significantly different from ceramic ones. It is only the laser-beam process that can enable an ideally complete compression of the metallic powder into a ‘ready to use’ component. Since we stabilise the powder bed with a continuous gas flow, the process set-up also presents a lot of new features.

Will we be able to see a first printed metal tool?

For our second campaign, we launched a completely redesigned layer application technology. This must first prove that it is suitable for applying layers under conditions of zero gravity. Then, this technology will be used for the first time to process metallic materials and, of course, I hope that a useful component can be manufactured. We would like the campaign to produce a tool, a small open-end wrench.