An OpeN-AM experimental platform enables to study the microscopic behavior of additive metal welds as they’re being created

Studying the 3D-printed welds microscopically with beams of neutrons allows researchers to better understand factors such as stress caused by heating and cooling. The experiments will help to optimize the fabrication technique for more mainstream use. « VULCAN forges new science for the future of 3D-printed metal | FR: L'étude microscopique des soudures imprimées en 3D à l'aide de faisceaux de neutrons permet aux chercheurs de mieux comprendre des facteurs tels que les contraintes dues au chauffage et au refroidissement. Ces expériences permettront d'optimiser la technique de fabrication en vue d'une utilisation plus courante. " VULCAN forge une nouvelle science pour l'avenir du métal imprimé en 3D . Credit: ORNL / Jill Hemman

The experimental platform system is called OpeN-AM, with OpeN being short for operando neutrons, a term for using neutrons to study something while it’s operating, and AM for additive manufacturing.

Researchers at the Department of Energy’s (DOE’s) Oak Ridge National Laboratory (ORNL) have created a one-of-a-kind automated robotic platform that allows them to study the microscopic behavior of additive metal welds in real time as they’re being created. Insights into how the welds form and behave at such a small scale will help in refining the technology for mainstream use.

A team led by ORNL project lead Alex Plotkowski is designing and deploying the experimental metal manufacturing system used at the VULCAN engineering diffraction instrument at ORNL’s Spallation Neutron Source (SNS). The SNS is a world-leading research facility powered by a linear particle accelerator that uses beams of neutrons to study materials at the atomic scale.

The experimental platform system is called OpeN-AM, with OpeN being short for operando neutrons, a term for using neutrons to study something while it’s operating, and AM for additive manufacturing.

The platform’s main feature is a 6-axis articulating robotic arm that can be equipped with a welding torch or a laser. The former—known as a wire arc system—works by feeding a wire through the end of the torch. As the wire contacts the substrate, an electric current is applied that melts the wire and creates the weld. Alternatively, the laser works by melting the substrate into a pool of liquid metal in which either a wire or powder feedstock is incorporated to create the weld.

Next to the robotic arm is a CNC—or  computer numerical control—machine. CNC machines are used to cut highly complex parts with a level of precision not possible using a manual approach. The combination of the CNC machine and OpeN-AM makes the system a hybrid of additive and subtractive manufacturing techniques: the robotic deposition head adds material, and the CNC machine removes material.

The system is mounted on an adjustable platform that raises, and rotates, offering additional degrees of freedom to collect data along the X, Y, and Z planes. The platform is also outfitted with cooling channels that lower the temperature of the metal to study different conditions and expedite characterization of the welds at room temperature.

There are significant benefits to hybrid additive manufacturing in its ability to fabricate complex components quickly and efficiently; however, the process is highly dynamic and not completely understood. The materials alternate between liquid and solid states as they are exposed to extreme fluctuations in temperatures, creating permanent deformations, or microscopic imperfections, known as residual stress.

Residual stresses can often compromise the material’s performance and lead to unexpected cracks or failures. On the other hand, with a better understanding of how residual stress is created, scientist could  induce stress intentionally to create performance benefits.

There’s only so much you can learn about a material after it’s processed using traditional characterization tools. The goal of the OpeN-AM project is to provide a new, more advanced way of characterizing the process that enables us to see inside the materials as they’re being produced,” said Plotkowski.

“Neutron experiments are a key component that allow us to observe and measure changes in the materials, such as temperature, how phase transformations are happening, and how the distributions of residual stresses are evolving. These insights are critical to optimizing the technology to make materials with improved performance.”

Neutrons are an ideal research tool for these experiments because they can penetrate or pass through almost any material, including dense metals. While other research techniques are better suited for looking closely at the surface of materials, neutrons enable researchers to peer deeply into metals with densely packed atoms for an unprecedented look at a material’s internal dynamics.

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