Date on Master's Thesis/Doctoral Dissertation

5-2020

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Mechanical Engineering

Degree Program

Mechanical Engineering, PhD

Committee Chair

Kate, Kunal

Committee Member

Atre, Sundar

Committee Member

Berfield, Thomas

Committee Member

Satyavolu, Jagannadh

Author's Keywords

metal fused filament fabrication; additive manufacturing of titanium alloy; titanium sintering; mechanical properties; microstructure; effect of oxygen content on mechanical properties

Abstract

Additive manufacturing (AM) is at the mainstream to cater the needs for rapid tooling and small-scale part production. The metal AM of complex geometries is widely accepted and promoted in the industry. While several metal AM technologies exist and are matured to a level where expectation in terms of design and properties are possible to realize. But the metal AM suffers from the heavy expense to acquire equipment, isotropic property challenges, and potential hazards to work with loose reactive metal powder. With this motivation, the dissertation aims to develop the fundamental aspects to print metal parts with bound Ti-6Al-4V powder filaments with the approach of metal fused filament fabrication (MF3). Since fused filament fabrication (FFF) is the most accessible form of AM technology and combining with the conventional sintering process yields the advantage of producing net shape parts to the well-established standards. Ti-6Al-4V is the material of most interest in the aerospace, medical and automotive industry due to its high strength to weight ratio, great corrosion resistance, and bio-inert nature. In order to fabricate three-dimensional components from Ti-6Al-4V using the MF3 process, it is critical to understand and address material, process, and design-related constraints to meet end properties. The goal of this dissertation is to establish a fundamental understanding of the MF3 process with Ti-6Al-4V alloy, to produce parts with comparable properties to the traditional process of metal injection molding (MIM). The effect of Ti-6Al-4V particle size distribution on material printability and the process productivity with MF3 is studied with modeling and experimental observations. It was inferred that bound filament viscosity and strength properties are crucial to its printability and processing rate limits. The Ti-6Al-4V particle size variations were also investigated after printing for the effect of sintering conditions to evaluate the resulting physical, mechanical and microstructural properties. It was found that maintaining a low oxygen concentration in the starting powder and throughout the processing, cycle is crucial to obtain useful mechanical properties with MF3 of Ti-6Al-4V. When designing parts for MF3 (DfMF3), it is important to understand how the filament properties affect processability, part quality, and ensuing properties. But there doesn’t exist any database containing powder-polymer material properties and generating data via experiments can be expensive and time taking. A part of the dissertation investigated models that can predict powder-polymer material properties which are required as input parameters for simulating the MF3 using the Digimat-AM® process design platform for fused filament fabrication. Here, Ti-6Al-4V powder-binder feedstock at powder loading from 56-60 vol.% was used to predict properties such as density, specific heat, thermal conductivity, Young's modulus, viscosity, and specific volume. Thus, estimated material properties served as an input parameter to conduct DfMF3 simulations to understand material-processing-geometry interactions.

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