Powder Bed Surface Quality and Particle Size Distribution for Metal Additive Manufacturing and Comparison with Discrete Element Model

Abstract

Metal additive manufacturing (AM) can produce complex parts that were once considered impossible or too costly to fabricate using conventional machining techniques, making AM machines an exceptional tool for rapid prototyping, one-off parts, and labor-intensive geometries. Due to the growing popularity of this technology, especially in the defense and medical industries, more researchers are looking into the physics and mechanics behind the AM process. Many factors and parameters contribute to the overall quality of a part, one of them being the powder bed itself. So far, little investigation has been dedicated to the behavior of the powder in the powder bed during the lasering process. A powder spreading machine that simulates the powder bed fusion process without the laser was designed by Lawrence Livermore National Laboratory and was built as a platform to observe powder characteristics. The focus for this project was surface roughness and particle size distribution (PSD), and how dose rate and coating speed affect the results. Images of the 316L stainless steel powder on the spreading device at multiple layers were taken and processed and analyzed in MATLAB to access surface quality of each region. Powder from nine regions of the build plate were also sampled and counted to determine regional particle size distribution. As a comparison, a simulation was developed to mimic the adhesive behavior of the powder, and to observe how powder distributes powder when spread. v ACKNOWLEDGMENTS I would first like to thank Dr. Davol for being the calm and collected advisor that I needed for this thesis. Your guidance always put me right back on track while your positivity calmed my nerves. I would like to thank Dr. Mayer for always asking the questions that push me to keep thinking and improving. From you, I have learned to take pride in my work. I would also like to thank Dr. Wang for all of his support throughout this project. I am grateful for the opportunities and encouragement you provided and your willingness to help at a moment's notice.

A Novel Apparatus for the Simulation of Powder Spreading Procedures in Powder-Bed-Based Additive Manufacturing Processes: Design, Calibration, and Case Study

“…Furthermore, a series of advanced and highly automated testers were presented in [17,51,52]. Oropeza et al [17] proposed a testing system containing two motorized platforms for controlled powder supply and spreading, a modular powder spreading mechanism capable of using different spreading tools (e.g., motorized roller, stiff or flexible scraper, hopper), and an imaging system overhanging the powder bed.…”

“…After the recoating operation, the spreading platform can be extracted from the tester and installed on the table of an optical microscope to analyze the degree of surface coverage, the layer roughness, and the flatness of the powder bed. A similar apparatus was developed by Yee et al [52], with the possibility of an in situ evaluation of the surface roughness of the powder bed using a camera attached to the apparatus. Escano et al [53] proposed am apparatus consisting of a motorized scraper and platform adapted to be mounted in an X-ray computed tomography machine to visualize the particle dynamics during spreading, the density, and the surface profile of the formed powder bed.…”

“…To sum up, most of the above proposed solutions are mainly focused on evaluations of powder bed uniformity [17,40,[43][44][45]51,52], while some apparatuses combine an assessment of the powder bed uniformity with that of the powder spreadability [46,47]. Another group of technical solutions consider the powder bed density as the main metric of interest [42] or combine the powder bed density measurements with the powder bed uniformity assessments [41,48].…”