Shawn Moylan’s research while affiliated with National Institute of Standards and Technology and other places

The Additive Manufacturing Benchmark Test Series (AM Bench) provides rigorous measurement data for validating additive manufacturing (AM) simulations for a broad range of AM technologies and material systems. AM Bench includes extensive in situ and ex situ measurements, simulation challenges for the AM modeling community, and a corresponding conference series. In 2022, the second round of AM Bench measurements, challenge problems, and conference were completed, focusing primarily upon laser powder bed fusion (LPBF) processing of metals, and both material extrusion processing and vat photopolymerization of polymers. In all, more than 100 people from 10 National Institute of Standards and Technology (NIST) divisions and 21 additional organizations were directly involved in the AM Bench 2022 measurements, data management, and conference organization. The international AM community submitted 138 sets of blind modeling simulations for comparison with the in situ and ex situ measurements, up from 46 submissions for the first round of AM Bench in 2018. Analysis of these submissions provides valuable insight into current AM modeling capabilities. The AM Bench data are permanently archived and freely accessible online. The AM Bench conference also hosted an embedded workshop on qualification and certification of AM materials and components.

The spreading of powder is an integral part of powder bed fusion-based additive manufacturing technologies; however, due to the complex nature and the number of interactions between particles, studying the powder spreading process is difficult. In order to gain insight into how the metal powder is spread in powder bed fusion machines using a recoater, a spreading testbed is needed, which provides a method for investigating the powder spreading process and characterizing the powder spread layer. The objective of this testbed is to study and establish fundamental relationships between bulk metal powder characteristics and powder spreading performance. Here, fabrication of a powder spreading testbed (PST) is described. The minimum but necessary functionality of the PST is discussed and potential characterization methods for the powder spread layer are proposed. This document serves as a guideline for future enhancements to the present testbed.

Purpose This paper aims to investigate the influence of nonuniform gas speed across the build area on the melt pool depth during laser powder bed fusion. This study focuses on whether a nonuniform gas speed is a source of process variation within an individual build. Design/methodology/approach Parts with many single-track laser scans were printed and characterized in different locations across the build area coupled with corresponding gas speed profile measurements. Cross-sectional melt pool depth, width and area are compared against build location/gas speed profiles, scan direction and laser scan speed. Findings This study shows that the melt pool depth of single-track laser scans produced on parts are highly variable. Despite this, trends were found showing a reduction in melt pool depth for slow laser scan speeds on the build platform near the inlet nozzle and when the laser scans are parallel to the gas flow direction. Originality/value A unique data set of single-track laser scan cross-sectional melt pool measurements and gas speed measurements was generated to assess process variation associated with nonuniform gas speed. Additionally, a novel sample design was used to increase the number of single-track tests per part, which is widely applicable to studying process variation across the build area.

Additive manufacturing quality assessment often relies on tensile testing as the preferred methodology to qualify builds and materials. The data included in this article provides additional supporting information on our manuscript (Shanbhag et al. [1]) on the effect of specimen geometry and orientation on tensile properties of Ti-6Al-4V manufactured by electron beam powder bed fusion. As such, the data in brief provides in-depth details on the tensile specimen specifications, the tensile specimen build layout and replicate notations, and the tensile testing datasets. The information presented herein complements the manuscript.

While performance testing of additive manufacturing machines is still nascent, standard tests for performance of machine tools used in metal cutting are well established. Our hypothesis is that because directed energy deposition (DED) additive manufacturing machines physically resemble typical vertical machining centers, standard geometric performance tests for machine tools will directly apply to DED machines. Standard tests of positioning error motions and circular motion were successfully conducted on a commercially-available DED system. With all tests providing reasonable and expected results, there is nothing to falsify our hypothesis. One additional consideration is the need for testing of the Z-axis on additive manufacturing machines using target positioning intervals on the order of a typical layer thickness at several positions along the axis.

The particle size distribution (PSD) and particle morphology of metal powders undoubtedly affects the quality of parts produced by additive manufacturing (AM). It is, therefore, crucial to accurately know the PSD and morphology of these powders. There exist several measurement techniques for these quantities, but since each method is based on different physical phenomena, which are sensitive to different aspects of a particle's shape and size, it is unclear how the measured PSDs and morphology compare to one another. In this study, five different techniques are used: sieve analysis, dynamic imaging analysis, laser diffraction analysis, X-ray computed tomography (XCT), and scanning electron microscopy. The first three are commonly used in the powder metallurgy field while the last two are laboratory-based tools capable of providing robust size and shape data. Nominally identical samples of stainless-steel powders were produced via riffling, and each technique was employed to measure effectively the same PSD and in some cases the morphology. In this paper, the differences among these measurement techniques are explored by a comparison of the measured results. Besides the random variations of the various measurement processes, the difference in the results is partly due to the fact that the particles are not perfectly spherical and that there are many multi-particles present. Each of these affect the principle of each method differently. Three-dimensional particle morphology and size data collected via XCT is used to provide insight regarding the discrepancies among other sizing and morphology measurement techniques. (Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States.)

Tensile testing is often proposed as the preferred methodology to qualify builds and materials produced through additive manufacturing. While there is already work demonstrating the difference in measured properties between tensile specimens produced in different build orientations, this does not extend to different specimen geometries. In addition, the body of knowledge in this domain is typically made up of studies that utilize custom combinations of specimen geometries, part finishing, and post-processing, making it challenging to compare results. To study the impact of geometry of tensile specimens on tensile testing results, a selection of standard specimen types provided in ASTM E8/E8M was prepared in Ti-6Al-4V using an electron beam powder-bed fusion additive manufacturing machine. These specimens were characterized to observe any porosity defects, dimensional deviations, and surface topography that could impact performance. It was found that changes in specimen geometry, specimen size, build orientation, and the internal porous defects; have significant effects on the tensile properties of the specimens. The horizontally built specimens had higher yield and tensile strengths, but lower elongation compared to vertically built specimens. With an increase in cross-sectional area, an increase in the yield, tensile strength, and elastic modulus was observed. With an increase in surface area to volume ratio, there was a decrease in the yield and tensile strength. The average solid fraction of the specimens had no influence on any measured tensile properties. Furthermore, with an increase in maximum pore size, the elongation of the specimen decreased.