As part of the Scarce Element Directive, industry is required to handle the scarce resource of rare earths with care. Against this backdrop, a new development in the field of 3D printing of such metals at the Technical Chemistry Department of the University of Duisburg-Essen (UDE) is becoming increasingly important. The large-scale device, which costs around 950,000 euros, is the only one of its kind in the world and is characterized in particular by the fact that it analyzes the building material during the manufacturing process and thus enables quality monitoring in real time.
In addition to their use in electronic components and in the production of powerful magnets, rare earths are also indispensable components of electric motors. Although there are, in principle, sufficient quantities in the earth's crust, the mining areas are limited and in the hands of a few countries. The global political situation in particular has led to a shortage of these metals in Europe and an associated price increase.
Avoiding defects in 3D parts at an early stage
Manufacturing industrially relevant and complex components from various metals within a few hours is now a reality in the field of additive manufacturing. Using 3D printers, metal powder is applied in thin layers, fused by a laser and the desired object is created layer by layer. However, with some materials, such as permanent magnets, this method reaches its limits. This is because the microstructure of 3D-printed components often differs significantly from conventionally manufactured parts. The key difference here is the extremely high cooling rates. After the laser has passed the area to be melted, the material cools down by more than 1000 °C in less than a second. This means that the elements do not have enough time to arrange themselves in the optimum crystal structure for permanent magnetics. In addition, until now it has only been possible to check the element distribution of the printed magnets using so-called ex-situ methods, i.e. only after the manufacturing process. However, this is not specific to magnetic materials, but applies generally to the field of metallic 3D printing. Defects can only be detected after printing has been completed. "This costs an enormous amount of time and money," explains Dr. Anna Rosa Ziefuß, Group Leader of Surface Chemistry and Laser Processing in Prof. Dr. Stephan Barcikowski's working group. "This is because defective parts are only detected after the process, which can sometimes take several days. In-situ testing, i.e. analysis directly during the printing process, is crucial for effective quality assurance - especially when it comes to sensitive materials for aviation or medicine."
Monitoring the component structure during the printing process
The researchers' idea was therefore to monitor the exact material composition of the components in real time. This is to be achieved using optical emission spectrometry (OES). It is installed in the 3D printer and analyzes each powder layer directly, even at a remarkably high resolution. This is necessary because a layer of powder is only around 42 micrometers thick, which is roughly the diameter of a very fine human hair. The recorded data is then merged into a digital model and analyzed on the computer. While there are already printer systems that can measure the temperature during the process or record irregular melts, pores or cracks, the addition of the factors of composition and distribution is unique worldwide. This was probably also the reason why the German Research Foundation DFG financed this development and thus also the new large-scale device to a large extent.
The researchers at the Technical Chemistry Department of the University of Duisburg-Essen (UDE) now have two years to show that their idea works. The most difficult part is the data analysis. The very high resolution in particular generates an enormous amount of data, which has to be processed accordingly. If you only look at the side surface of a cube with a side length of one centimeter, this already results in around two million measuring points. For three-dimensional components of a relevant size, the amount of data increases exponentially. Subsequent compression of this amount of data without losing relevant data is therefore a particular challenge. However, the printer is already being used, for example in a sub-project of a collaborative research center that deals with the additive manufacturing of permanent magnets.
