Researchers at University College London (UCL) and the University of Greenwich have demonstrated a new technique that could significantly enhance the quality of 3D-printed components for safety-critical applications, such as aircraft and Formula 1 racing cars.
The study, published in Science, reveals that applying a magnetic field during laser-based 3D printing can reduce the formation of defects in metal alloy components by up to 80 per cent.
According to a news release, the research team used advanced X-ray imaging to investigate the causes of imperfections in complex 3D-printed metal structures.
Conducting high-speed synchrotron X-ray imaging at the Advanced Photon Source (APS) in Chicago, they captured the intricate interaction between the laser and metal powder at time intervals shorter than a thousandth of a second.
Their findings revealed that laser-induced heating generates a keyhole-shaped vapour depression, which, if unstable, leads to the formation of pores that weaken the final product.
Dr Xianqiang Fan, first author of the study from UCL Mechanical Engineering, explained how the application of a magnetic field stabilises this process.
“When the laser heats up the metal, it forms a liquid pool accompanied by a vapour plume, which pushes the molten metal apart, creating a J-shaped depression. Surface tension causes ripples that break off and form pores in the finished component.”
“Applying a magnetic field induces thermoelectric forces that modify the fluid flow, transforming the J-shaped cavity into a more stable ‘I’ shape, thereby preventing pore formation,” he explained.
The laser-based 3D printing process allows for the creation of highly complex alloy components by selectively melting layers of metal powder.
While this enables precision manufacturing for applications ranging from titanium bicycle parts to biomedical implants, the instability of the molten pool remains a challenge.
Professor Peter Lee, senior author from UCL Mechanical Engineering, highlighted the broader implications of the research.
“Though keyhole pores in these types of components have been known about for decades, strategies to prevent their formation have remained largely unknown. One thing that has been shown to occasionally help is applying a magnetic field, but the results have not been repeatable and the mechanism by which it works is disputed,” he stated.
While the findings hold promise, the researchers acknowledge that integrating magnetic fields into large-scale manufacturing processes presents technical challenges.
Professor Andrew Kao, senior author from the University of Greenwich, emphasized the significance of these insights.
“Our research sheds light on the physical forces involved in this type of manufacturing, where there are intricate dynamics between surface tension and viscous forces. Applying the magnetic field disrupts this and further introduces electromagnetic damping and thermoelectric forces and, in this work, the latter acts to beneficially stabilise the process,” he said.
The research is supported by the UK’s Engineering and Physical Sciences Research Council (EPSRC) and the Royal Academy of Engineering.
