Multi-Sensor Investigations of Optical Emissions and their relations to Directed Energy Deposition processes and quality

Open Access
Author:
Stutzman, Christopher B
Area of Honors:
Engineering Science
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Abdalla Ramadan Nassar, Thesis Supervisor
  • Akhlesh Lakhtakia, Honors Advisor
  • Edward William Reutzel, Thesis Supervisor
  • Judith Todd Copley, Faculty Reader
Keywords:
  • Directed Energy Deposition
  • Metal Additive Manufacturing
  • Flaw Detection
  • Optical Emission Spectroscopy
Abstract:
Additive manufacturing (AM) processes are limited in application by systematic and stochastic flaws that are produced during the process. In order to avoid this limitation, sensing strategies for the AM process are being developed. Using optical emissions spectroscopy and plume imaging, flaws generated during directed-energy deposition (DED) AM processes were investigated. Ti- 6Al-4V coupons are built using varying laser power, powder flow rate, and hatching pattern to induce random and systematic flaws. Archimedes density measurements and X-ray computed tomography (CT) scans were completed on each part to determine flaw density and flaw locations. Three quantifiable metrics based on the state of the plume during processing were developed, analyzed and compared to the post-build CT scans: (1) line-to-continuum ratio around 430 nm, (2) line-to-continuum ratio around 520 nm, and (3) total plume area. For coupons built with constant laser power, variations in either powder flow rate or hatch pattern that led to an increase in flaw density were found to be accompanied by an increase in median line-to-continuum ratios around 430 and 520 nm and in total plume area. All three metrics appear to measure the same phenomena, i.e. they were internally consistent with each other. The conclusion is that optical emissions measured during DED processes can be used for flaw detection and presents a path forward for real-time flaw detection and assessment of build quality in DED and powder-bed-fusion processes.