Entrapped bubbles are an important problem in conventional glass manufacturing. It is also a significant factor determining the quality of glass products produced using additive manufacturing (AM). This paper reports on the bubble formation and entrapment in filament-fed AM printing of borosilicate glass. This process involves maintaining a local molten region using a CO2 laser. A 2 mm filament is fed continuously into the molten region while CNC stages position the workpiece relative to the laser and filament feed. Two different bubble regimes are identified in experiments with borosilicate glass. These regimes can be related to different physical phenomena, specifically, bubble entrapment at defects in the filaments and bubble formation due to reboil. These can be overcome by selecting defect free filaments and by minimizing the temperature inside the molten region to prevent breaking down the glass. Understanding these mechanisms allows bubble-free glass to be printed. Finally, residual stress in the deposited glass pieces is removed using post-deposition annealing and validated using a polariscope.

Meeting Name

27th Annual International Solid Freeform Fabrication Symposium -- An Additive Manufacturing Conference (2016: Aug. 8-10, Austin, TX)


Mechanical and Aerospace Engineering

Research Center/Lab(s)

Intelligent Systems Center


This work was supported by the National Science Foundation (CMMI-1538464).

Document Type

Article - Conference proceedings

Document Version

Final Version

File Type




Publication Date

10 Aug 2016

Included in

Manufacturing Commons