Researchers Ibo Matthews, Gabe Guss and Phil Depond used cubes like the ones shown here to test how printed metal becomes porous. Image credit: LLNL
3D printing metal structures can be both very useful and very difficult. At Lawrence Livermore National Laboratory, a new study posits that unwanted porosity in printed metal parts – a flaw that also sometimes plagues welded metal – is caused by gas flow interfering with the print’s base powder.
A team led by researcher Ibo Matthews used a microscope, vacuum chamber, fluid dynamics simulations, and an ultra high-speed camera to examine what causes porous flaws in printed metal and create models of what was happening. They found that a gas flow caused by the evaporation when the laser hits the metal powder drives the powder away from the laser. This reduces the amount of powder near the laser and can make it uneven, causing the development of small holes and gaps.
In order to find out how to prevent this, the team needs to keep working on how porosity develops.
“You get to temperatures that are near or at the boiling point of the metal, so you have a strong vapor flux emitted from the melt pool,” Matthews explained. “Prior to this study, there wasn’t an understanding of what effect this flux of metal vapor had on the powder bed.”
This was “a phenomenon that we didn’t know was present in metal powder-bed additive manufacturing,” said Chris Spadaccini, the lab’s director of Additive Manufacturing Initiatives. The simulations will need to be modified in order to account for the newly-discovered behavior.
“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.”
Filed Under: 3D printing • additive • stereolithography, Industrial automation
