Laser Melting Deposition Additive Manufacturing of Ti6Al4V Biomedical Alloy: Mesoscopic In-Situ Flow Field Mapping via Computational Fluid Dynamics and Analytical Modelling with Empirical Testing.

Muhammad Arif Mahmood,Asif Ur Rehman,Fatih Pitir,Metin Uymaz Salamci,Ion N Mihailescu

doi:10.3390/ma14247749

Muhammad Arif Mahmood, Asif Ur Rehman + Show 3 more

Open Access

https://doi.org/10.3390/ma14247749

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Abstract

Laser melting deposition (LMD) has recently gained attention from the industrial sectors due to producing near-net-shape parts and repairing worn-out components. However, LMD remained unexplored concerning the melt pool dynamics and fluid flow analysis. In this study, computational fluid dynamics (CFD) and analytical models have been developed. The concepts of the volume of fluid and discrete element modeling were used for computational fluid dynamics (CFD) simulations. Furthermore, a simplified mathematical model was devised for single-layer deposition with a laser beam attenuation ratio inherent to the LMD process. Both models were validated with the experimental results of Ti6Al4V alloy single track depositions on Ti6Al4V substrate. A close correlation has been found between experiments and modelling with a few deviations. In addition, a mechanism for tracking the melt flow and involved forces was devised. It was simulated that the LMD involves conduction-mode melt flow only due to the coaxial addition of powder particles. In front of the laser beam, the melt pool showed a clockwise vortex, while at the back of the laser spot location, it adopted an anti-clockwise vortex. During printing, a few partially melted particles tried to enter into the molten pool, causing splashing within the melt material. The melting regime, mushy area (solid + liquid mixture) and solidified region were determined after layer deposition. This research gives an in-depth insight into the melt flow dynamics in the context of LMD printing.

Highlights

Additive manufacturing (AM) provides customized designs, reduces preparation time, and produces complicated shapes
It is important to note that the volume increases dramatically due to a drop in density, resulting in surface tension declination
For computational fluid dynamics (CFD) modelling, the volume of fluid (VOF) and discrete element modelling approaches have been utilized, while simplified mathematical equations have been deduced in the case of an analytical model

Summary

Introduction

Additive manufacturing (AM) provides customized designs, reduces preparation time, and produces complicated shapes. Laser additive manufacturing (LAM) is a subtype of additive manufacturing (AM) that fuses the powder particles with a laser beam to generate high-quality metallic parts [7]. Laser metal deposition (LMD) is a sub-branch of AM with various applications, including surface treatment and coatings [14], the production of functionally graded materials [15] and restoration of broken parts [16]. One additional benefit of employing the LMD methodology is its short production period and reduced waste of materials, opposite to conventional manufacturing techniques [17]. In the LMD method, various input variables exist, including beam power, scan speed, and powder flow rate, which can significantly affect the process, and the integrity of the finished objects [24,25]. Post-characterization techniques such as scanning electron microscopy, electron backscatter diffraction (EBSD) and x-ray computed tomography (XCT) are not capable of providing information about heat and fluid flow [27]

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