Date on Master's Thesis/Doctoral Dissertation

12-2021

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Mechanical Engineering

Degree Program

Mechanical Engineering, PhD

Committee Chair

Hsu, Keng

Committee Member

Popa, Dan

Committee Member

Kate, Kunal

Committee Member

Bhatia, Bikram

Author's Keywords

Fused filament fabrication; reptation; relaxation; laser process; mechanical properties

Abstract

Additive manufacturing (AM), known as three-dimensional (3D) printing, is a fabrication process to build 3D objects layer by layer based on computer aided design (CAD) model or digital 3D model. Fused filament fabrication (FFF) has become a preferred method for additive manufacturing due to its cost-effectiveness and flexibility. However, the parts built using FFF process suffer from lower mechanical strength compared to that fabricated using traditional method and rough surface finish. With this motivation, this dissertation aims to develop and implement a novel in-process laser assisted technique on FFF to heal the microstructure of FFF built objects by enhancing reptation and relaxation to improve mechanical strength and to heal the surface by increasing surface reflow. This technique utilizes laser energy to reduce with residual stress generated by the extrusion-based deposition process, and to heal interfaces between deposited tracks for improvement of interface adhesion, therefore increase mechanical strength. This dissertation demonstrates that the in-process laser assisted technique can fabricate nearly isotropic object with mechanical strength close to solid bulk material. It also demonstrates the capability of reducing the surface roughness significantly. This dissertation investigates in two directions, the first direction is mechanical strength and mechanical behaviors. In-process pre-laser heating was used to enhancing mechanical strength at inter-layer interface (Z-direction), at the interface between adjacent tracks (Y-direction), and along the deposited track(X-direction). The second direction is surface finish of the side surface. In order to quantify the interaction of laser energy on material structure, laser output power, laser melting pool temperature, mechanical strength were measured. SEM were used to characterize the fracture surface to determine the effect of laser on interface healing.

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