A Numerical Study on the Effects of Processing Parameters and Microstructure for Multi-Track and Multi-Layer Scanning of Directed Energy Deposition Using Inconel 718 Superalloy

  • 黃 昱穎

Student thesis: Doctoral Thesis

Abstract

Because of the increase in manufacturing demands many studies began to focus on additive manufacturing DED is one of the common processing technology However DED has a large number of processing parameters and involves the complicated phenomenon of the solid mechanic and heat flow In order to obtain the temperature field of DED the study uses Ansys Fluent software to establish a three-dimensional numerical model on two-track and two-layer scanning in DED and the dynamic mesh model is used to approximate the situation of metal deposition Through the experimental verification it is proved that the model has certain accuracy in predicting the geometry of metal deposition and the processing temperature field The research results show that as the laser power increases or the laser scanning speed decreases the width and height of metal deposition will increase In the aspect of microstructure the temperature gradient (G) and solidification rate (R) are the two main parameters that affect the deposited microstructure The G/R ratio governs the solidification mode while the cooling rate controls the scale of the deposited microstructure When the laser power decreases the difference of the G/R ratio in a deposition at different locations will decrease so the microstructure will become more consistent Through analysis of optimization it is found that the laser spot radius of 1 5 mm the overlapping ratio of 26 2% the laser power of 1000 W and the scanning speed of 6mm/s have better processing efficiency and higher G/R ratio In the aspect of process improvement substrate preheating can effectively increase the morphology of deposition but the high preheating temperature leads to a low G/R ratio in the deposition and it will produce the equiaxed dendritic easily Moreover reducing idle time and using double-sided scanning have little influence on microstructure but they are beneficial to improve the processing efficiency Layer-by-layer reduction of laser power makes the microstructure more consistent in the multi-layer scanning process
Date of Award2020
Original languageEnglish
SupervisorAlex Chang-Da Wen (Supervisor)

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