Researchers at Lawrence Livermore National Laboratory (LLNL) have taken a major step toward answering a question plaguing a common metal 3-D printing technique: What interactions can lead to the porosity found in parts produced by laser powder-bed fusion processes?
In a paper published in the recent edition of the journal Acta Materialia online, LLNL researcher LLNL and his team discovered that gas flow, due to evaporation when the laser irradiates the metal powder, is the driving force that clears away powder near the laser’s path during a build. This “denudation” phenomenon reduces the amount of powder available when the laser makes its next pass, causing tiny gaps and defects in the finished part.
Using a custom-built microscope setup, a vacuum chamber and an ultra high-speed camera (provided by the Lab’s High Explosives Applications Facility), Matthews’ team observed the ejection of metal powder away from the laser during the melting process, and, through computer simulation and fluid dynamics principles, built models to help explain the particles’ movement. Wayne King, director of the Accelerated Certification of Additively Manufactured Metals project at LLNL, called the findings a “big step forward” for the process.
“Now having the physics better understood, we can simulate the process more accurately and make enhancements to our manufacturing efforts,” Matthews said. “In the end, we want to be able to use simulation to build the confidence that we’re making parts with little or no defects.”