Lawrence Livermore National Lab researchers say they've developed an efficient way of identifying optimal parameters to print 3D high-density metal parts. Their work, titled "Density of additively-manufactured, 316L SS parts using laser powder-bed fusion at powers up to 400 W," recently published in the International Journal of Advanced Manufacturing Technology. The paper explains a way of selecting parameters for higher-power SLM machines using simple, computational simulations to explore the process parameter space. The simulations are used to compute the dimensions of the melt pool, the pool of liquid formed when the laser melts the metal powder particles. The resulting melt pools are just deep enough to melt through the powder into the substrate below. The researchers say they use simulations to guide a few single-track experiments to quickly arrive at parameter values that result in high-density parts. Kamath and her colleagues, who are part of LLNL's Accelerated Certification of Additively Manufactured Metals (ACAMM) Strategic Initiative (acamm.llnl.gov), are using simulations at various scales to gain insight into the SLM process. "We found that the metal density reduces if the speed is too low, due to voids created as a result of keyhole mode laser melting, where the laser drills into the material," Kamath wrote. "At the same time, too high a speed results in insufficient melting. The key is to find the right parameters where the melting is just enough." The LLNL team found that the use of different powders affected densities at lower power, but not at higher power. "Furthermore, for 316L stainless steel, at higher powers, the density is high over a wider range of scan speeds, unlike at lower powers," the article states. "This would indicate that higher powers could provide greater flexibility in choosing process parameters that optimize various properties of a manufactured part." Although 316L stainless steel was used in this experiment, Kamath said the team's approach can be applied to other metal powders as well. LLNL's findings will eventually be used to help certify properties of metal parts built using SLM. The paper is the first step in understanding how we can exploit computer simulations and a small number of carefully chosen experiments to efficiently determine the process parameters, Kamath said.