Illuminating the physics of melting during laser-based manufacturing of IN718 by measuring laser light reflections

Published

July 25, 2026

Author(s)

David Deisenroth, Haoran Shi, Moritz Wittemer, Nismath Valiyakath Vadakkan Habeeb, Kevin Chou, Wenda Tan, Jordan Weaver, Katrin Wudy

Abstract

It has been known since the early years of laser welding that measuring of the energy absorbed into, and reflected away from, metallic materials can provide valuable insights into the physics of the melting process. This work uses a recently developed high-fidelity measurement of the directional distribution of reflected laser light, an integrating hemisphere to measure total reflected laser power, as well as cross sections of the melt tracks perpendicular and parallel to the scan direction. Arrays of five tracks with offset antiparallel scans are melted in bare plate nickel superalloy 718 at processing parameters of relevance to laser-based powder bed fusion of metals (PBF-LB/M). All processing parameters are held constant, except power is varied from 50 W to 545 W. The instantaneous laser coupling (laser absorption) and melt depth along the track increase or decrease nearly in unison within the desirable range of applied power. The strong correlation weakens in the high power, deep keyholing mode when absorption saturates. The directional distributions of reflected laser light show distinct patterns and features that correspond to the stages of the melting process and to the state of the vapor depression. A hazy reflection distribution forms when the incident laser reflects from a ground metal surface, a circular pattern with concentric rings forms in conduction mode, and then radial streaks form in keyhole mode. A high-fidelity melt pool model that includes ray tracing shows favorable agreement between the experimental and simulated reflections at 185 W, 285 W, and 485 W during steady-state melting. The model was used to determine that the physical origin of prominent streaking features of the reflection distributions originate from a single reflection from surface ripples at the cusp of the melt pool. This study establishes reflected laser light measurements as a high-fidelity diagnostic and model validation tool to inform process monitoring approaches in industrial PBF-LB/M systems.

Citation

Additive Manufacturing

Pub Type

Journals

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Keywords

Laser-based metal additive manufacturing, Laser-based powder bed fusion of metals, Laser absorption, Laser coupling, Distribution of reflected laser light, Process monitoring, Model validation

Citation

Deisenroth, D. , Shi, H. , Wittemer, M. , Habeeb, N. , Chou, K. , Tan, W. , Weaver, J. and Wudy, K. (2026), Illuminating the physics of melting during laser-based manufacturing of IN718 by measuring laser light reflections, Additive Manufacturing, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=962100 (Accessed August 20, 2026)

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