In-Situ Characterization of Pore Formation Dynamics in Pulsed Wave Laser Powder Bed Fusion

Abstract

Laser powder bed fusion (LPBF) is an additive manufacturing technology with the capability of printing complex metal parts directly from digital models. Between two available emission modes employed in LPBF printing systems, pulsed wave (PW) emission provides more control over the heat input compared to continuous wave (CW) emission, which is highly beneficial for printing parts with intricate features. However, parts printed with pulsed wave LPBF (PW-LPBF) commonly contain pores, which degrade their mechanical properties. In this study, we reveal pore formation mechanisms during PW-LPBF in real time by using an in-situ high-speed synchrotron x-ray imaging technique. We found that vapor depression collapse proceeds when the laser irradiation stops within one pulse, resulting in occasional pore formation during PW-LPBF. We also revealed that the melt ejection and rapid melt pool solidification during pulsed-wave laser melting resulted in cavity formation and subsequent formation of a pore pattern in the melted track. The pore formation dynamics revealed here may provide guidance on developing pore elimination approaches.

Special Issue: The Science and Technology of 3D Printing

“…This Special Issue contains eleven articles, including three reviews [ 3 , 4 , 5 ], one perspective article [ 6 ], and seven research articles [ 7 , 8 , 9 , 10 , 11 , 12 , 13 ] from leading institutes in the United States, China, Australia, Germany, Sweden, the Netherlands, Slovakia, the Czech Republic, Egypt, and United Arab Emirates. These articles cover the 3D printing of diverse materials such as metallic materials [ 5 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ], composites [ 4 , 6 ], and soft materials [ 3 ].…”

“…The articles in this Special Issue cover a wide variety of experimental [ 8 , 9 , 10 , 11 , 13 ], theoretical [ 12 ], and data-science [ 7 ]-based research on the science and technology of 3D printing. For example, experimental investigations were performed to identify the most important factors that affect the microstructure and properties of Ti-6Al-4V parts printed using powder bed fusion [ 9 , 11 ].…”

“…In particular, the effects of powder morphology, preheating temperature, and post-process heat treatment on the size of α-grains, the hardness, and the tensile properties were studied. In addition, formation mechanisms of defects such as pores and cracks, and their harmful effects on the mechanical properties of printed parts were investigated [ 8 , 10 , 12 , 13 ]. A high-speed synchrotron X-ray imaging technique [ 10 ] was used to reveal the mechanisms of the evolution of pores during powder bed fusion.…”

“…In addition, formation mechanisms of defects such as pores and cracks, and their harmful effects on the mechanical properties of printed parts were investigated [ 8 , 10 , 12 , 13 ]. A high-speed synchrotron X-ray imaging technique [ 10 ] was used to reveal the mechanisms of the evolution of pores during powder bed fusion. A new computer-aided quality (CAQ) technology [ 13 ] was proposed and used to determine the amount of porosities in the parts printed using powder bed fusion.…”

Understanding the effects of temporal waveform modulation of the laser emission power in laser powder bed fusion: Part I - Analytical modelling

“…For instance, the complementary use of pulsed and continuous wave emission was explored by Demir et al to avoid the formation of overheated regions [19]. Pore formation dynamics in pulsed wave LPBF have been further investigated via high-speed x-ray transmissive videography by Hojjatzadeh et al [20].…”