Sep 7, 2017 | By David

3D printing technology is being adopted as a manufacturing technique by more and more industries, and it continues to improve in terms of reliability, but like any method, it’s still not without its flaws. There’s still much more detail to be discovered about how the 3D printing process can go wrong, and a group of researchers led by the U.S Department of Energy have recently been looking into this. The team, consisting of researchers from Missouri University of Science and Technology, Argonne National Laboratory, and Carnegie Mellon University, led an investigation into structural defects in 3D printed parts.

Metal 3D printing is the most commonly used form of additive manufacturing on a large-scale, and most techniques involve the use of automated lasers, programmed by a digital model to selectively melt areas of a bed of metal powder. The molten metal eventually re-solidifies, and layer-by-layer a specific 3D shape can be built up in this way. How exactly this molding happens remains something of a mystery, however, and the researchers hoped to shed some light on its inner workings in order to figure out what some common causes of structural defects in 3D printed metal parts might be.

The investigation is making use of one of the DoE Office of Science’s most high-tech user facilities, the Advanced Photon Source. A form of recording equipment based on intense synchrotron X-rays enables the whole laser melting process to be studied in real-time. According to Argonne physicist Tao Sun, “The laser-metal interaction happens very quickly. Fortunately, we captured the process at 50,000 frames a second using the high-speed X-ray instrument at the Advanced Photon Source. We can study the resulting movie frame by frame to examine how the material’s microstructure, especially defects and pores, forms.”

The researchers observe and quantify characteristics such as the size or shape of the melt pool, the amount of powder ejection, solidification and porosity formation, and the various transformations between different phases. The details that this X-ray ‘movie’ gives can be used to build elaborate predictive models, using various physical theories and calculations. These models are then used to re-design the 3D printing process, testing out ways that certain structural defects might be avoided. This process, in turn, is studied using the same X-ray technique. In this way the researchers can gain more and more information about metal 3D printing and how to improve its reliability.

Sharing their conclusions and predictive models with laboratories and research institutions all across the country, the team doesn’t just hope to fine-tune the 3D printing techniques currently used, they are also aiming to discover new methods and explore new possibilities.  “Industries are currently limited to a certain set of metal alloys’’, said Aaron Greco, a principal materials scientist at Argonne and project co-leader for Argonne’s additive manufacturing effort. ‘‘But what about new ones? If you understand the physical properties related to how to print new alloys, you can adopt these into the process and speed up the reliability of printing.”

In these high-speed x-ray images, the 3D printer is using a laser to melt metal powder, which causes a 'keyhole' defect within the cooled material. Researchers at Argonne are studying this process and developing guidelines to avoid such errors. (Image by Argonne National Laboratory.)

As well as improving and expanding the range of materials used for industrial 3D printing, the research could also help with the initial design phase of manufacturing more complex parts. Better understanding of how the 3D printing process works would mean that designers wouldn’t have to spend as much time working out how to improve the quality and reliability of their structures. This would allow for digital models to be drastically simplified, with just the key factors being taken into account. According to Greco, “Our work will not only help industries improve efficiency and performance, but increase the likelihood that metal additive manufacturing will be more widely adopted in other applications,”

The results of the research were recently published in the Scientific Reports article, “Real-time monitoring of laser powder bed fusion process using high-speed x-ray imaging and diffraction.” The experiments were performed at the Advanced Photon Source’s 32-ID-B beamline.

 

 

Posted in 3D Printing Technology

 

 

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