Cross-Sectional Melt Pool Geometry of Laser Scanned Tracks and Pads on Nickel Alloy 718 for the 2022 Additive Manufacturing Benchmark Challenges.

The Additive Manufacturing Benchmark Series (AM Bench) is a NIST-led organization that provides a continuing series of additive manufacturing benchmark measurements, challenge problems, and conferences with the primary goal of enabling modelers to test their simulations against rigorous, highly controlled additive manufacturing benchmark measurement data. To this end, single-track (1D) and pad (2D) scans on bare plate nickel alloy 718 were completed with thermography, cross-sectional grain orientation and local chemical composition maps, and cross-sectional melt pool size measurements. The laser power, scan speed, and laser spot size were varied for single tracks, and the scan direction was varied for pads.

Measurement Uncertainty of Surface Temperature Distributions for Laser Powder Bed Fusion Processes.

This paper describes advances in measuring the characteristic spatial distribution of surface temperature and emissivity during laser-metal interaction under conditions relevant for laser powder bed fusion (LPBF) additive manufacturing processes. Detailed descriptions of the measurement process, results, and approaches to determining uncertainties are provided. Measurement uncertainties have complex dependencies on multiple process parameters, so the methodology is demonstrated on one set of process parameters and one material.

Transient Laser Energy Absorption, Co-axial Melt Pool Monitoring, and Relationship to Melt Pool Morphology.

Melt pool monitoring (MPM) is a technique used in laser powder bed fusion (LPBF) to extract features from insitu sensor signals that correlate to defect formation or general part fabrication quality. Various melt pool phenomena have been shown to relate to measured transient absorption of the laser energy, which in turn, can be relatable to the melt pool emission measured in MPM systems. This paper describes use of a reflectometer-based instrument to measure the dynamic laser energy absorption during single-line laser scans.

Accurate determination of laser spot position during laser powder bed fusion process thermography.

High-speed thermography is useful tool for researching the laser powder bed fusion process by providing thermal information in heat affected zone. However, it is not directly possible to ascertain the position of the laser spot with respect to the melt pool, which could provide key information regarding how laser energy is distributed and absorbed. In this paper, we demonstrate a procedure for registering the laser spot position with the melt pool using a bright illumination source co-axially aligned with the laser to project a sharp spot on the build plane.

Measurements of melt pool geometry and cooling rates of individual laser traces on IN625 bare plates.

The complex physical nature of the laser powder bed fusion (LPBF) process warrants use of multiphysics computational simulations to predict or design optimal operating parameters or resultant part qualities such as microstructure or defect concentration. Many of these simulations rely on tuning based on characteristics of the laser-induced melt pool, such as the melt pool geometry (length, width, and depth). Additionally, many of numerous interacting variables that make LPBF process so complex can be reduced and controlled by performing simple, single track experiments on bare (no powder) substrates, yet still produce important and applicable physical results.

Optical design and Initial Results from The National Institute of Standards and Technology's AMMT/TEMPS Facility.

The National Institute of Standards and Technology's (NIST) Physical Measurement and Engineering Laboratories are jointly developing the Additive Manufacturing Measurement Testbed (AMMT)/ Temperature and Emittance of Melts, Powders and Solids (TEMPS) facilities. These facilities will be co-located on an open architecture laser-based powder bed fusion system allowing users full access to the system's operation parameters. This will provide users with access to machine-independent monitoring and control of the powder bed fusion process.

Monte Carlo modeling of an integrating sphere reflectometer.

The Monte Carlo method has been applied to numerical modeling of an integrating sphere designed for hemispherical-directional reflectance factor measurements. It is shown that a conventional algorithm of backward ray tracing used for estimation of characteristics of the radiation field at a given point has slow convergence for small source-to-sphere-diameter ratios. A newly developed algorithm that substantially improves the convergence by calculation of direct source-induced irradiation for every point of diffuse reflection of rays traced is described.