An innovative production process "captured" in three dimensions

PSI researchers managed to immortalize the ceramic print with 3D tomograms at a speed that allows them to follow the laser point

3D: the tomogram of the 3D printing of the word
A video shows how the sample powder solidified under the influence of the printing laser to form the writing PSI (Video: Malgorzata Makowska/Paul Scherrer Institut)

3D printing can produce very complex shapes. But printing ceramic objects with the help of lasers is generally an even more difficult challenge.
Now researchers from the Paul Scherrer Institute in Villigen and Würenlingen in Swiss canton from Aargau have created tomograms for the first time that reveal what happens at a microscopic level during this manufacturing process.
And the results will help improve this tech very promising.
The study was carried out in collaboration with the technological competence centre Inspire AG, the Zurich Polytechnic and EMPA.
It was funded by Swiss National Fund (SNSF) as a Spark project.
The idea for this research was a follow-up to the Fuorclam project launched in 2017 as part of the Strategic Focus Area (SFA) Advanced Manufacturing program.
“The various projects gave us the opportunity to get to know all the groups in Switzerland involved in research on additive manufacturing and 3D printing“, says the physicist Steven Van Petegem.
“This is an extremely important topic for the future, which Switzerland has recognized.”

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3D: Federica Marone, Malgorzata Makowska and Steven Van Petegem
Federica Marone, Malgorzata Makowska and Steven Van Petegem, from left to right, at the SLS experimental station, where the three-dimensional images were successfully taken
(Photo: Mahir Dzambegovic/Paul Scherrer Institut)

The aerospace, automotive and biomedical industries are ideal for additive printing

3D printing is used to produce many objects.
Additive manufacturing is increasingly used, for example, in the aerospace and automotive industries, as well as medicine.
The method commonly used for metals and plastics is known as Laser-based Powder Bed Fusion.
In LPBF, as it is acronym, the material is applied as a layer of fine powder on a substrate, after which the laser passes over the powder and melts it to give it the desired shape.
The next layer of powder is deposited and melted again by the laser.
The component is built sequentially, layer by layer.

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3D: A high numerical aperture TOMCAT lens from the GigaFRoST camera
A high numerical aperture TOMCAT optic mounted with the GigaFRoST camera, which was developed internally by the Paul Scherrer Institute at the institutional headquarters in Villigen in the Canton of Aargau.

Layer-by-layer laser fusion previously described only with 2D microscopes

The exact conduct of the LPBF process is studied with the help of X-rays at the Swiss Light Source (SLS) of the PSI and others research institutes, but so far these microscopic insights have only provided 2D images.
“We wanted to go a step further and follow the manufacturing process in 3D”, explains Malgorzata Makowska, materials scientist at PSI.
Instead of two-dimensional X-ray images, i researchers they wanted to obtain 3D tomograms with a speed that would allow them to follow the laser spot.
To do this, they had to rotate the sample during the manufacturing process and follow this rapid rotational movement with the laser, which posed a major challenge.
For the first time, the Villigen research team managed to do this, as reported in an article in the journal “Communications Materials”.

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3D: A beamline layout of the Swiss Light Source
A horizontal layout of the beamline of the Swiss Light Source (SLS), the third generation synchrotron installed at the headquarters of the Paul Scherrer Institute in the Aargau town of Villigen.

A magnet and iron oxide to hold the powder in place rotating at 50 Hz

For experiments the scientists they used aluminum oxide.
This ceramic material is typically used, for example, inchemical industry for components exposed to high temperatures, in electrical engineering as an insulator or in medicine for the systems.
However, since this material is extremely hard and brittle, the fabrication of complex shapes with the conventional technology presents enormous difficulties.
“It would be much simpler if you could print such components”, explains the PSI physicist Steven Van Petegem.
“When printing aluminum oxide, however, it is still difficult to achieve a sufficiently dense material and the desired microstructure.”
Experiments conducted at the SLS TOMCAT tomographic beam line provided new insights into the innovative manufacturing process.
The test sample rotated at a speed of 50 Hz (3.000 revolutions per minute) as the laser passed over the powder.
Adapting the printing process to this extremely fast rotation was one of the main difficulties, which researchers they have now surpassed.
Another challenge was to prevent the rotating material from moving away due to centrifugal forces.
I researchers they achieved this by adding a small amount of magnetic iron oxide to aluminum oxide powder particles and then incorporating a magnet to hold the powder in place.
The magnet is mounted under the sample in a small cylinder of 3 millimeters in diameter.

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3D: an infographic from the Swiss Light Source (SLS)
An infographic of the Swiss Light Source (SLS), the futuristic synchrotron located at the Paul Scherrer Institute in Villigen, in the Swiss canton of Aargau, aimed at producing high-brightness electromagnetic radiation

Excellent work by the GigaFRoST camera, capable of 100 3D images per second

“Thanks to the fast GigaFRoST camera, developed in-house at PSI, and a highly efficient microscope, it was possible to acquire 100 3D images per second during the printing process”, explains the beamline scientist Federica Marone.
These images showed what happened to the powder during the laser treatment.
“For the first time we are able to directly visualize the fused volume in 3D”, adds Makowska.
The shape of the so-called "melting basin" surprised researchers.
When they increased the laser power, no depression formed on the surface, as expected.
“On the contrary, the melt spread out like a… pancake and the surface was more or less flat”, comments the materials scientist.

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3D: TOmographic Microscopy and Coherent rAdiology experiments
A beam line for TOMCAT (acronym for TOmographic Microscopy and Coherent rAdiology experimenTs), or "tomographic microscopy and interfering radiology experiments", at the headquarters of the Paul Scherrer Institute in Switzerland

More know-how from an updated SLS and new TOMCAT 2.0 beamlines in 2025

I researchers they were also able to observe the formation of pores and depressions as the material hardened, an important aspect for future applications.
“The ideal would be to have a smooth, attractive material with a well-defined microstructure. But a certain amount of porosity is also very desirable for specific applications”, explains Makowska.
Van Petegem adds: “We hope that our experiments reveal more about the printing process and that we can pass on this knowledge, so that it can be used in practice, although there is still a long way to go.”
The SLS machine upgrade starting soon and the new TOMCAT 2.0 beamlines coming into operation in 2025 will improve current capabilities.
“It will be possible to study denser materials with higher spatial and temporal resolution, fundamental aspects for advancing LPBF technology”, concludes the beamline scientist Christian Schlepütz.

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Operation of the Swiss Light Source synchrotron of the Paul Scherrer Institute

3D: the headquarters of the Paul Scherrer Institute in Aargau
Bird's eye view of the Paul Scherrer Institute in the Canton of Aargau, which also houses the InnovAARE Switzerland Innovation Park between Villigen and Würenlingen