Publication Date

2026

Document Type

Dissertation/Thesis

First Advisor

Cho, Kyu Taek

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Mechanical Engineering

Abstract

Direct Energy Deposition (DED) is a leading metal additive manufacturing method for fabricating complex parts. However, the high thermal gradients during the process, along with their effects on thermal expansion and shrinkage during heating and cooling cycles, result in significant residual stress that imposes substantial limitations on the building process. These stresses can lead to warpage, cracking, and a reduction in overall mechanical performance, challenges that must be addressed in most manufacturing industries. While scanning patterns and clad geometry have often been studied independently, their interaction may provide deeper insights into the causes and effects of these operating conditions on residual stresses. This study investigates strategies to minimize residual stresses in 316L stainless steel components using various building approaches and operating conditions through the investigation of resulting deformations from thermal expansion, internal von Mises stresses, and z-component tensor stresses during the build process.

COMSOL Multiphysics utilizes heat transfer analysis and stress analysis to simulate these effects with respect to various scanning patterns, coolant conditions, and deposition rates as they will dominantly influence geometry and residual stress in the system. The study utilizes four scanning strategies, including raster and zigzag, along with two complex scanning strategies. These strategies are applied to the deposition of round clad structures that overlap to form a smooth upper layer for subsequent deposition. The simulation focuses on a small deposition area, observing its development over the build time for a single layer. The powder feed rate is managed through the powder feed-to-travel speed ratio, a critical parameter that accurately reflects the process by accounting for changes in clad height due to variations in travel speed. The reference system used in this study is an OPTOMEC 850M, with material parameters dependent on 316L steel covering a large range of temperature constraints.

The aim of this research is to identify optimal operating conditions that produce more reliable components with minimized residual stress. Through this it was discovered that laser power had the largest effect on residual stresses in the system throughout its range of usage in industry. It was also confirmed that the residual stresses in zig zag scanning pattern resulted in the highest residual stresses, followed by the regular raster pattern. The two patterns that resulted in the lowest residual stresses in the system were that of alternating raster and the s-shape pattern since they avoid the heat influence zone through their movement on the substrate. Overall trends with laser intensity and PF/TS had consistent rates of increase when changed between different scan patterns. From this research, more research can be done involving the utilization of plasticity material properties currently unavailable to track the true residual stress without estimation, and to further investigate the effect that multiple layers have on the system with a more flexible way to model the build process as fabricated through this research.

Extent

67 pages

Language

en

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type

Text

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