Modeling of laser direct deposition processes
Abstract
Laser direct deposition is widely used for rapid freeform fabrication of fully dense components with good metallurgical properties directly from CAD drawings. Because of complex physics involved such as laser powder interaction, laser substrate interaction, track interface evolution and melt-solid interaction, it is important to develop simulation models to better understand the characteristics and mechanisms in the process so that optimization and control of a laser direct deposition process is possible. In this thesis, a new comprehensive three-dimensional self-consistent transient model is presented for laser cladding and direct deposition process, which considers physical behaviors such as powder flow, laser particle interaction, mass addition, heat transfer, fluid flow, melting and solidification. The complex transport phenomena during direct laser deposition of metal matrix composite are also modeled, considering the coupling between particles and matrix material. To track the particle distribution, a species transport equation for particle mass fraction, as well as algebraic expressions considering possible different phase velocities, is combined with the other deposition governing equations. A continuum model is built to deal with different phases (gas, liquid, solid, mushy zone) in the calculation domain. An improved level-set method, which takes the conservative form while being implicitly solved with other governing equations, is proposed to track the evolution of free liquid/gas interface during the deposition process. To make the model more physically complete than those in the literature, a newly-derived mass source term, which considers the rate of the gas phase being replaced by the deposited material due to the moving interface in some control volumes, is incorporated into the continuity equation. Corresponding new source terms of enthalpy and momentum due to the moving interface are also derived and embedded in the energy and momentum equations. The governing equations are discretized using the finite volume approach to better predict the fluid motion mainly driven by capillary and thermocapillary forces. The simulated track heights, widths, molten pool depths, track profiles and particle volume fraction agree with the experimental results. In addition, a novel dual-mesh modeling for laser deposition is also presented for an improved efficiency.
Degree
Ph.D.
Advisors
Shin, Purdue University.
Subject Area
Mechanical engineering|Optics
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