04/26/2023
By Danielle Fretwell

The Francis College of Engineering, Department of Plastics Engineering, invites you to attend a doctoral dissertation defense by Austin Colon on “Rheological and Thermal Modeling of Thermoplastic Material Extrusion Additive Manufacturing.”


Candidate Name: Austin Colon
Degree: Doctoral
Defense Date: Wednesday, May, 10, 2023
Time: 12:30 to 2:30 p.m.
Location: Southwick 240

Committee:

  • Advisor David Kazmer, PE, Ph.D., Professor, Plastics Engineering, University of Massachusetts Lowell
  • Amy Peterson, Ph.D., Associate Professor, Plastics Engineering, University of Massachusetts Lowell
  • Stephen Johnston, Ph.D., Professor, Plastics Engineering, University of Massachusetts Lowell
  • Jay Park, Ph.D., Assistant Professor, Plastics Engineering, University of Massachusetts Lowell
  • Jonathan Seppala, Ph.D., Project Leader, Materials Science and Engineering Division, National Institute of Standards and Technology

Brief Abstract:

In recent years, thermoplastic material extrusion additive manufacturing has grown in popularity by providing users with the ability to manufacture complex geometries from a wide range of materials and by using low-cost equipment. Three areas related to the thermal and rheological behavior of this process are addressed in this dissertation. The first area investigates and models die-swell in material extrusion, since it imparts residual stresses and geometric inconsistencies in the final parts. A study showing the effect of process parameters and nozzle diameter on die-swell and an adaptation of Tanner’s model, which predicts die-swell as a function of shear stress, are presented. Second, isothermal conditions are commonly assumed in the material extrusion hot end, though they are not typically achieved at higher volumetric flow rates due to constraints rooted in hot end design, leading to an upper limit in the print speed. Non-isothermal modeling and experiments for a custom hot end with varying nozzle diameters and process parameters are investigated to study and enhance melting at steady state. To enhance process observability, the third area focuses on studying the pressure dependency chain in the material extrusion printhead, which consists of the extruder motor torque, the infeed pressure required to feed the filament into the hot end, and the direct melt pressure in the hot end. By measuring these three responses via an instrumented printer, the process is better understood, and indirect melt pressure prediction via the upstream sensors is evaluated. This dissertation explores the effects of process parameters and hot end design on die-swell, strategies for improved melting at steady state, and the pressure dependency chain in thermoplastic material extrusion additive manufacturing.

All interested students and faculty members are invited to attend the online defense via remote access.