Modeling of Heat Transfer and Fluid Flow in the Laser Multilayered Cladding Process
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LASER cladding is used widely to create various surface coatings with a significant thickness that effectively can protect substrates from harsh service conditions,[1–4] However, the correct selection of the process parameters for the building or printing of spatial structures of the required geometry is a difficult task. The processing parameters such as the laser beam power, beam intensity in the processing zone, scanning speed, and powder feed rate have a strong relationship with each other through mutual interaction, and they have a distinct influence on the mechanical properties of the remelted materials and cladding qualities.[4–6] In laser cladding, considering that the severe temperature gradient and mass transportation in the molten pool are caused by the convection of the liquid phase, the geometry of the molten pool absolutely plays a vital role in finally deciding the clad quality. For example, a too-small molten pool resulting from insufficient absorption of laser energy may result in a lack of melting and thus, an insufficient bond of consecutive layers. Conversely, an overlarge penetration will damage the cladding quality because of the diffusion of substrate material into the clad layer,[7] which makes the quality of the surface clad defective. In addition, many FANRONG KONG, Research Engineer, and RADOVAN KOVACEVIC, Herman Brown Chair Professor, are with the Center for Laser-aided Manufacturing, Southern Methodist University, Dallas, TX 75205. Contact e-mail: [email protected] Manuscript submitted July 10, 2009. Article published online July 30, 2010. 1310—VOLUME 41B, DECEMBER 2010
intermediate physical phenomena in the laser cladding process are extremely difficult to observe experimentally because of the presence of intense laser irradiation. Therefore, modeling combined with an experimental validation is an effective way to reveal the complete physical phenomena in the laser cladding process. So far, most efforts of thermal modeling in laser cladding have concentrated on the conduction mode of heat transfer.[8–10] Strong sources of heat convection definitely are in the molten pool as a result of temperature-dependent surface tension variation over the molten pool free surface and a density variation in the bulk of the molten pool, respectively. However, a limited attempt has been accomplished to study the fluid flow combined with solute diffusion in the molten pool of laser cladding. In the early work of the modeling of laser cladding, Kar and Mazumder[11] developed a one-dimensional conduction model to determine the composition of the alloys and cooling process. Hoadley and Rappaz[12] presented a two-dimensional (2D) model to calculate the temperature in the steady-state condition during laser cladding. Later, Han et al.[13] solved 2D fluid flow and energy equations to predict the temperature distribution and geometry of the molten pool in the laser cladding process. Recently, Toyserkani et al.[14] presented a three-dimensional (3D) transient finite-element model for laser cladding with a powder injection.
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