Additive manufacturing is poised to liven the pace and scale of manufacturing. Deploying a range of techniques that use 3-D models to print objects layer by layer, it can generate a variety of intricate designs in less time and with less waste than conventional cutting and milling approaches.

Argonne National Laboratory

Industries in need of high-volume parts, from medicine to aerospace, could hasten production of specialized parts and shorten time to market using additive manufacturing techniques. Yet a number of technical challenges stand in the way.

Mechanisms for building parts layer-by-layer often alter the attributes of finished components in ways that remain poorly understood. These alterations can lead to defects in finished components, undermining their reproducibility and many of the gains of applying additive manufacturing approaches.

Researchers at the U.S. Department of Energy's (DOE) Argonne National Laboratory have developed a new capability for studying defects and other challenges to additive manufacturing. This capability combines high-speed X-ray imaging with infrared imaging at Argonne's Advanced Photon Source (APS), the world-leading source for ultra-bright, high-energy X-ray beams.

Benefits of In-Situ X-Ray Imaging

Tao Sun, an X-ray physicist at the US DOE's Argonne National Laboratory lines up an infrared camera, the first to be installed at an X-ray synchrotron source. This provides 3D images of the printing process in nearly real time to benchmark the printing process. Calibration of the X-ray results to the IR camera will allow for the use of IR cameras to detect defects in processing on manufacturing lines. (Image by Argonne National Laboratory.)

The most accurate analysis of processes and material behaviors comes from in-situ X-imaging and diffraction techniques. At the APS, these techniques are deployed by thousands each year to understand material microstructures and their dynamics in great detail.

High-speed X-ray imaging techniques applied to additive manufacturing enable researchers to visualize and characterize the formation of a material's defects, including cracks and pores within it. They can also be used to quantify structure characteristics such as melt pool size/shape, spattering behaviors, solidification velocity, and phase transformation. These techniques can be operated in high frame rate mode, which is needed to capture the fast series of material events that take place in additive manufacturing. The Advanced Photon Source is the only place in the U.S. capable of performing ultrahigh-speed X-ray studies of additive manufacturing processes.

Coupling X-Ray and Infrared Imaging

While X-ray imaging techniques capture many details related to material microstructures, they miss thermal details that are also key in shaping the way products are built. Additive techniques rely on sources of thermal energy to melt the feed stock and fuse different layers together, so variations in the heating and cooling of a material over various stages in production can affect the structure and attributes of finished parts.

To reduce variation between parts, and optimize additive processes, industry needs a clear understanding of how thermal conditions affect the build process, such as how heating and cooling contribute to residual stresses and distortions. With infrared imaging, researchers can extract some of this knowledge.

High-speed infrared imaging at the APS allows researchers to measure thermal signatures across surfaces in real time. Data from it can help them measure how much and how fast regions within a component heat up and cool down during a build. Coupled with X-ray imaging, researchers have the potential to pinpoint thermal signatures correlated with the formation of a defect, or related phenomena.

Infrared and X-ray imaging each contribute different types of knowledge to our understanding of additive manufacturing. Together they help scientists to analyze the laser-metal interactions that affect component quality and performance, such as the melting and vaporization of the powder, the flow of molten metals, and how they solidify.

How It Works

Infrared and X-ray imaging of the 3D printing of a metal part can help scientists better understand the 3-D printing process so they can benchmark processes and materials to reduce defects. (Image by Argonne National Laboratory.)

To couple X-ray and infrared imaging for additive manufacturing studies, Argonne has affixed a metal 3-D printing simulator and a high-speed infrared camera to 32-ID-B–the APS’ beamline dedicated to additive manufacturing studies. Argonne is the first national laboratory in the United States to integrate each of these tools to a synchrotron beamline.

The 3-D printing apparatus consists of technologies for laser powder bed fusion, which employs lasers to melt and fuse metal, plastic or ceramic powders layer by layer. Beam interactions with metal powders occur at the millisecond or shorter timescales and produce many complex physical processes. Custom parts for airplanes, automobiles, and even metal implants have been made using this technique.

With these components integrated, researchers can peer inside materials as they are built through 3-D laser printing. X-ray imaging captures the microstructures involved while infrared imaging captures thermal details. Researchers can visualize the entire 3-D printing process at 6.5 million frames per second with X-ray imaging, and at 95,000 frames per second with thermal imaging. Spliced together, these images tell the story of what's happening at various stages in the process, from how the laser melts the powder, to the flow of molten metals and their solidification.

Application of Imaging Capabilities

Argonne collaborates with various universities and industry to apply its imaging capabilities to the additive manufacturing studies. With researchers from Carnegie Mellon University and Missouri University of Science and Technology, they've observed and captured for the first time materials formed by 3-D printing in real-time.

Researchers from Argonne and Missouri University of Science and Technology also succeeded in using X-ray imaging to observe the dynamics of powders when they spatter after coming into contact with lasers. This common phenomenon can result in defects in products or quality control issues. X-ray imaging enabled the team to observe and characterize the dynamics of this powder movement, and draw from these experiments possible ways to reduce spattering.

Modeling and Machine Learning

[The Advanced Photon Source generates high-energy X-rays that show 3-D printing in near real time. (Image by Argonne National Laboratory.)

Experimental data gained from X-ray and thermal imaging can also be fed into physics-based computer models to improve their design and accuracy. Experimental data, for example, can help train machine learning models of additive manufacturing processes and materials.

With better process models, researchers and operators of additive manufacturing systems can more reliably predict the outcome of changes to additive manufacturing processing parameters. Similarly, with better material models, researchers can also predict the behavior of new materials being evaluated for use in additive manufacturing.

Additive manufacturing models can also give back to the experimental process by being tested through experiments that are more elaborate. The process creates a virtuous feedback loop where experimental data inform theory and vice versa. The iterative development of numerical modeling and experimental measurements is essential to advancing understanding of the underlying materials physics needed to make 3D-printing truly reliable.

Building understanding of additive manufacturing can also help to streamline and simplify modeling for industry. Today industries use extremely detailed models to define the printing process for complex parts; the complexity of such models undermines their versatility and wide spread adoption.

By identifying the key elements that affect quality and reliability and improving models based on this knowledge, researchers could potentially reduce the number of models needed to solve additive manufacturing problems, and make these models faster and more suitable for industry.

Empowering Industry and Research Communities

As part of Argonne's Manufacturing Initiative, infrared imaging will expand the laboratory's additive manufacturing R&D efforts in support of American industries. Along with providing data to advance the creation of workable algorithms, this tool will help researchers deliver critical insights that industry and developers can use to improve efficiency and product design.

Coupling X-ray and thermal imaging contributes to these ambitions by forming the early connections between applied science and basic science. With thermal imaging tools, which are readily available, operators of additive systems can begin to piece together links between their work and the fundamental research being done at the APS.

This article was written by Tao Sun, physicist and X-ray scientist at Argonne National Laboratory. For more information, contact Tona Kunz at This email address is being protected from spambots. You need JavaScript enabled to view it..


Photonics & Imaging Technology Magazine

This article first appeared in the March, 2019 issue of Photonics & Imaging Technology Magazine.

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