System developed to study microscopic behaviour of printed metal
Researchers at the US Department of Energy’s (DOE’s) Oak Ridge National Laboratory (ORNL) have created a robotic platform for studying the microscopic behaviour of printed metal in real time.
The new platform, called OpeN-AM, will provide insights into how layers of printed metal fuse together.
Such insights will help researchers further refine additive materials for mainstream use.
The platform’s main feature is a six-axis articulating robotic arm that can be equipped with either a welding torch or a laser.
The former – a wire arc system – uses a metal wire fed through the end of the torch, which is melted via an electric current during printing onto a substrate. Alternatively, the laser works by melting the substrate into a pool of liquid metal, into which either a wire or powder feedstock is fed.
Next to the robotic arm is a CNC machine to deliver subtractive manufacturing techniques: the robotic deposition head adds material while the CNC machine removes material – a combination known as hybrid manufacturing.
Hybrid manufacturing enables complex components to be fabricated 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, it could be induced intentionally to deliver performance benefits.
The OpeN-AM platform has therefore been developed at the Vulcan engineering diffraction instrument at ORNL’s Spallation Neutron Source – a facility powered by a linear particle accelerator that uses beams of neutrons to study materials at the atomic scale.
“The goal of the OpeN-AM project is to provide a new, more advanced way of characterising the process that enables us to see inside the materials as they’re being printed,” said ORNL project lead Alex 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.”
In their experiments, the team printed metal into simple shapes with overlapping layers of welds that were created using different patterns. In some iterations, they varied the temperatures and other process conditions to induce different phase transformations and stress patterns.
The neutron data collected during the experiments will help shed light on the relationships between the processing approach, the material’s behaviour, and how residual stress evolves.