Date on Master's Thesis/Doctoral Dissertation

12-2023

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Mechanical Engineering

Degree Program

Mechanical Engineering, PhD

Committee Chair

Kate, Kunal H.

Committee Co-Chair (if applicable)

Atre, Sundar V.

Committee Member

Atre, Sundar V.

Committee Member

Bhatia, Bikram

Committee Member

Gupta, Gautam

Author's Keywords

Copper additive manufacturing; hot isostatic pressing; mechanical properties; electrical properties; microstructure; density

Abstract

3D printing pure copper with high electrical conductivity and exceptional density has long been challenging. While laser-based additive manufacturing technologies suffered due to copper's highly reflective nature towards laser beams, parts printed via binder-assisted technologies failed to reach over 90% IACS (International Annealed Copper Standard), electrical conductivity. Although promising techniques such as binder jetting, filament, and pellet-based 3D printing that can print copper exist, they however still face difficulties in achieving both high sintered densities and electrical conductivity values. This is due to a lack of comprehensive understanding of property evolution from green to sintered states and the strategies that can be used to enhance the density and electrical properties of Sinter-Based Material Extrusion (MEX) 3D printed copper parts. This dissertation presents an in-depth investigation into the advancements and challenges of 3D printing pure copper, specifically focusing on Material Extrusion (MEX) processes. It emphasizes the viability of bound powder copper feedstocks for Material Extrusion 3D printing. It highlights the importance of achieving 100% density in the green vi stage to ensure over 93% sintered density and 98% Hot Isostatic Pressing (HIP) density. The study delves into the difficulties of 3D printing, sintering, and Hot Isostatic Pressing (HIP) of copper parts, addressing the gap in understanding the scaling of mechanical and electrical properties from the green to the sintered state in the MEX metal 3D printing process. The insights and knowledge gained from this section are then utilized to improve the thermal performance of bound metal MEX 3D printed copper heat sinks. This research explores the uncharted territory of lattice structures for heat sinks, investigating three types of lattice structures through experimental analysis and simulations to explore the potential advantages of lattice structure-based bound metal MEX 3D printing for fabricating high-performance copper heat sinks. Finally, the research focuses on understanding the intricate interplay of material viscosity, mechanical properties, and printing speed in bound-powder-polymer MEX 3D printing. Exploring PLA, TPU, and bronze-filled metal powder-bound filaments, the study investigates their impact on achieving a printed part density of 100±5%. Process maps of density and viscosity were created for each material type, and a full factorial design of experiments was conducted to identify the effects of print conditions on various variables. This section provides crucial insights into the 3D printing process of polymer filaments, offering guidance for new material design and discovery for bound metal filaments. Overall, this dissertation contributes to understanding the challenges and advancements in 3D printing, providing insights into the scaling of mechanical properties, the thermal performance of copper heat sinks, and the complexities of achieving full part density in 3D printed components.

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