A doctoral student at Osnabrück University of Applied Sciences is researching the weldability of additively manufactured and cast steel in order to improve the combination of these two manufacturing processes. Not only plastics, but also metals such as steel can be processed using additive manufacturing technologies such as 3D printing. Additively manufactured steel is already widely used in medical technology and aerospace, as it offers numerous advantages, particularly in the production of complex geometries.
“It is an excellent way to produce individual parts or small batches cost-effectively. In addition, products can be manufactured very individually - for example implants in medical technology. Repairs can also be made easier and cheaper, as only the defective area can be replaced,” says Julianna Posey, a doctoral student at Osnabrück University of Applied Sciences and the University of Maryland Baltimore County (UMBC), USA.
Differences in the microstructure due to different manufacturing processes
The interaction between additively manufactured and traditionally produced steel has hardly been researched to date. In her dissertation, PhD student Posey is therefore specifically investigating welded joints that combine both cast and additively manufactured steel. Different production methods lead to different microstructures in the material, which affect the stability of the joint during welding.
“My focus here is on the fatigue phenomena of the printed steel after welding - in particular the microstructure and how this changes as a result of welding. This is because additively manufactured steel has a different microstructure due to the way it is produced,” explains the US-American, who came to Germany for her doctorate.
Additively manufactured steel is produced in a powder bed, whereby a laser melts the powder in layers to form the desired component. This process causes a very specific heat effect, which can lead to an uneven microstructure. Subsequent heat treatment is therefore required to homogenize this structure and prepare the steel for practical applications.
Support from industry
The doctoral student received support from industry for her research work: the samples she used for her welding tests were specially produced by qualified welding specialists at the Volkswagen plant in Osnabrück. These specially manufactured samples enable Posey to carry out her tests under realistic conditions and thus achieve results that are as close to real-life conditions as possible.
“By obtaining results and information in such an unexplored area, you become something of a specialist. Of course, that was unusual at first. But I was always able to rely on the support of my supervisors, Prof. Dr. Javad Mola from Osnabrück University of Applied Sciences and Dr. Marc Zupan from UMBC, and my colleagues.”
Difficulties in the welded joint of additively manufactured steels
The samples were subjected to a series of tests, including tensile tests and hardness tests, to evaluate the properties and resilience of the welded joints. Posey experimented both with and without filler metals to find the optimum conditions for a stable joint. The results show that the welded joint often breaks on the additively manufactured side, which could be due to the special microstructural properties of this steel.
“My investigations have shown that the welded joint often breaks on the side with the additively manufactured steel. This shows us that we need to adapt the welding process and that we cannot simply process additively manufactured steel in the same way as cast steel. However, tests with filler metals have proven to be promising. The additional material fills the weld gap and absorbs heat, reducing the size of the heat-affected zone.”
