Researchers at Lawrence Livermore National Laboratory (LLNL), Livermore, CA, say they have developed a more efficient approach to a challenging problem in additive manufacturing, using selective laser melting (SLM), choosing appropriate process parameters that result in parts having the desired properties.

Direct metal laser melting (DMLM) machine in action: A laser fuses metal powder to form one of many successive layers that will form the final manufactured part.

SLM is a powder-based, additive manufacturing process where a 3D part is produced, layer by layer, using a high-energy laser beam to fuse the metal powder particles. Some SLM applications require parts that are very dense, with less than 1 percent porosity, as the pores or voids are the weakest part of the material and most likely would result in failure.

But building functional parts and components to specific standards and performance specifications can be challenging because a large number of parameters must be set appropriately. Key parameters include laser power, laser speed, distance between laser scan lines, scanning strategy, and powder layer thickness. So, designers need a reliable and cost-effective approach to determine the right parameters to develop parts with properties like high density.

The LLNL researchers identified optimal parameters to print 3D high-density metal parts using simple, computational simulations to explore the process parameter space. These simulations are used to compute the dimensions of the melt pool, which is the pool of liquid formed when the laser melts the metal powder particles.

By using simulations to guide a small number of single-track experiments, they said they 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. At the same time, too high a speed resulted in insufficient melting. The researchers found that the use of different powders affected densities at lower power, but not at higher power.

Although 316L stainless steel was used in this experiment, they said that this can be applied to other metal powders as well.