Research has opened a new door to the use of recycled metal for 3D printing

In a hall in Lyngby, north of Copenhagen, stands a device that to the untrained eye may resemble an overgrown egg cooker. In reality, however, it is a top-tuned piece of experimental equipment that has the potential to significantly advance 3D printing of metals and the industry behind it.

This has been achieved through a research project that, with support from Independent Research Fund Denmark, was launched in 2019 to develop and study better materials for 3D printing in metal. At the same time, the project also investigated the possibilities of using recycled metal for 3D printing.

A popular technique for 3D printing metallic components relies on laser melting of metal powders.

Of course, this requires that you have metal powder for the printer. The challenge was that the researchers could only buy standard powders with a chemical composition determined by the suppliers. Therefore, there was a need to be able to produce the powder themselves. 

»That is when we saw the opportunity to create an infrastructure that you do not have anywhere else in Denmark. In other words, develop an equipment, so we could have complete freedom to produce exactly the powder we want. That is what we centered the project around,« says Dorte Juul Jensen, professor at the Technical University of Denmark (DTU), who was project leader.

When the project began, the production of metal powders, such as stainless steel, for 3D printing was a closed and non-transparent market.

»There was a frustration that few material suppliers were deciding what is available on the market. We had had a long talk with users of powder about how we can access other materials than those determined by the suppliers. Why should we dig new materials out of the ground when there is so much recycled metal. Can we not reuse it?,« adds Niels Skat Tiedje, associate professor at DTU, who took part in the project with special insight into the production of metal powder.

Equipment was on its way to scrap

Back to the egg cooker, or atomiser, as it is rightly called. It is a device capable of melting metal and turning it into powder that can be used for 3D metal printing.

In reality, the atomiser nearly ended up in the garbage container. It was located at the Risø National Laboratory, which in 2007 was merged with DTU.

Dorte Juul Jensen was head of department there from 2007 to 2011, and she was not ready to let the atomiser retire.

»One of our technicians visited MIT in the United States, where he had seen some similar equipment. We then optimized the design and built a version at Risø, and it was really high quality,« she recalls.

However, the atomizer needed a boost. So, Niels Skat Tiedje worked on it in his spare time along with a few technicians, even before the grant from Independent Research Fund Denmark was received.

Although Niels Skat Tiedje had started, the first year of the research project was mainly spent modernising the atomiser. The task was given to a PhD student, Daniel Cardenas del Rio, who was working full time on the project.

He was also responsible for testing the possibilities of improving different alloys of steel, i.e. the composition of elements that make up steel.

At the same time, Daniel Cardenas del Rio had to investigate some of the problems that can arise when trying to use recycled steel for the metal powder production. For example, figuring out if residues of lubricating oil or other substances from industry would create problems.

Denmark can become a pioneering country

The pump company Grundfos and the Danish Technological Institute were partners in the project. And so were Henrik Wenzel, professor at the Department of Green Technology at the University of Southern Denmark, and his colleagues. They were responsible for carrying out life cycle assessment of the atomisation of recycled steel.

That is, an analysis of how the environmental impact of recycling stainless steel into powder in 3D production would be as compared to conventional recycling. For the total life cycle of stainless steel powder, the calculation had a positive result.

All in all, Denmark has now gained knowledge that can resonate nationally and internationally.

»Denmark now has a completely unique facility that we would not have had if we had not received the grant from Independent Research Fund Denmark. The atomiser was originally located at Risø, but now it is here in Lyngby in its permanent setup. And it stands together with a whole series of metal printers, so the entire production line is now gathered in the same hall,« Dorte Juul Jensen emphasizes.

»Denmark has always been a bit of a frontrunner in recycling everything. And if we can get better in the metal area, which this lays the foundation for, it will be quite significant,« adds Niels Skat Tiedje and continues:

»One thing is that we learn about what happens when you reuse the materials. But right now, there is also a keen interest in the industry to actually do it. It is still in the early stages because it is not easy to do these things. But in the long run, I am sure that Denmark can gain a prominent place in recycling if we play our cards right.«

Dorte Juul Jensen and Niels Skat Tiedje are already working on a number of new projects that build on this original project, which was completed in 2023. 

For example, a project to improve the microstructure of the final 3D-printed product. And another project that is not limited to stainless steel, but instead looks at the possibilities of recycling ordinary scrap iron.

Finally, Independent Research Fund Denmark also supports the TURBMAP project. In the coming years, the research is aimed at developing advanced computational models that can be used to optimize the gas and metal nozzles that compose the heart of the atomiser. They are critical in determining the quality of the powder.

So the atomiser will have plenty to do in the years to come.