SUBJECT: Ph.D. Dissertation Defense
BY: Linger Cai
TIME: Tuesday, March 28, 2023, 1:30 p.m.
TITLE: Analytical Modeling of Part Distortion in Additive Manufactuing
COMMITTEE: Dr. Steven Y. Liang, Chair (ME)
Dr. Shannon Yee (ME)
Dr. Shreyes N. Melkote (ME)
Dr. Christopher J. Saldana (ME)
Dr. Hamid Garmestani (MSE)


In recent years, additive manufacturing (AM) technology gained significant attention in industry as a novel manufacturing method for prototyping and complex design. It provided extended flexibility on manufacturing but has deficit on the quality control. With repeated cooling and heating cycles, the parts printed often suffered from severe residual stress and distortion. While Finite Element Method provided a way to rough predict these results, the extensive calculation cost and inaccuracy when dealing with sophisticated geometry made it a less efficient tool for industrial use. In this dissertation, a new analytical model was proposed to fast predict the residual stress and distortion of the printed part. Moving heat source model was used for temperature profile calculations with boundary heat sink added to included the effect of the side surface. Sections on the part with same boundary conditions was grouped together to avoid repeated calculation. Then mechanical model was applied to get the thermal stress and residual stress. Based on the residual stress input, distortion was calculated. The proposed modal also took in the scan strategies which significantly affect the residual stress and distortion. To validated the model, step by step comparison to experimental data, both from literature and experiment, was done, and the proposed model gained reasonable accuracy. Sets of scaled XY crossing part was printed with AlSi10Mg. Both surface residual stress and in-depth residual stress was measured and compared the analytical model prediction. For distortion, the printed XY parts were laser scanned to have the surface data, which was further transferred into deflection data and compared to prediction. Unlike expected, the hatching space was not significantly affective to the residual stress profile in the experiment. During the modeling process, it was found that when calculating temperature, only heat sinks on the boundaries that was 1 mm away from the point of interest was effective to the final temperature profile. Similar threshold values were found in thermal stress calculation and could be used as a foundation to further simplify the calculation process without damaging its validity.