Assessment of optical emission analysis for in-process monitoring of powder bed fusion additive manufacturing

ABSTRACT

Developing methods which allow real-time monitoring of powder bed fusion (PBF) additive manufacturing (AM) processes is key to enabling in situ assessments of build quality (e.g. lack of fusion and porosity). Here, we investigate the use of optical emission spectroscopy and high-speed (100 kHz) measurement of select wavelength emissions, based on a line-to-continuum approach, to determine if a correlation between PBF AM process inputs, sensor outputs, and build quality exists. Using an open protocol system interfaced with a 3D Systems ProX 200 machine, sensor data were synchronised with the scanner position and the laser state during the buildup of Inconel-718 components under varying powers, scan speeds, and hatch spacing parameters. Sensor measurements were then compared against post-build computed tomography scans. We show evidence that sensor data, when combined with appropriate analyses, are related to both processing conditions and build quality.

KEYWORDS:

• Process optimisation
• solid freeform fabrication
• in situ monitoring
• powder bed fusion
• Inconel 718

Acknowledgements

The authors gratefully acknowledge the contributions of Griffin Jones and Jared J. Blecher. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the Office of Naval Research. The US Government is authorised to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of Air Force Research Laboratory or the US Government (Case Number: 88ABW-2016-3816).

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes on contributors

Dr Alexander J. Dunbar is a Post-Doctoral Scholar at the Applied Research Laboratory at the Pennsylvania State University. He earned his B.S. in 2011 and his Ph.D. in 2016 in Mechanical Engineering at Bucknell and Penn State, respectively. He has experience in validation and use of finite element analysis for metal powder bed fusion additive manufacturing. In the past, he has developed high-level sensing systems to aid in experimental measurement of the powder bed fusion process. His current work includes process development and improvement of in situ build quality assessment techniques for additive manufacturing.

Dr Abdalla R. Nassar is a Research Associate with the Applied Research Laboratory at Penn State and a Gradate Faculty member of the Engineering Science and Mechanics Department. He is an expert in additive manufacturing (AM) of metals, laser-materials processing, sensing and control systems for laser-based processes, metallurgy of titanium, and cyber-physical systems. As a faculty member, he has developed and taught graduate-level coursework on the foundations of Laser Materials Interactions and Additive Manufacturing. He earned his B.S and Ph.D. in Engineering Science from the Pennsylvania State University in 2008 and 2012, respectively. His work has led to six patent filings along with numerous publications on topics including the digital thread concept for AM, sensing and control of AM processes, thermal sensing, modelling AM processes, laser-plasma nitriding of titanium, characterization of plasma via optical emission spectroscopy, and numerical modelling of laser-sustained plasma.

Additional information

Funding

This work was supported by Air Force Research Laboratory [Grant Number FA8650-12-2-7230] and Office of Naval Research Global [Grant Number N00014-11-1-0668].