Mechanistic models for additive manufacturing of metallic components

Additive manufacturing (AM) methods for rapid prototyping of 3D materials (3D printing) have become increasingly popular with a particular recent emphasis on those methods used for metallic materials. These processes typically involve an accumulation of cyclic phase changes. The widespread interest in these methods is largely stimulated by their unique ability to create components of considerable complexity. However, modeling such processes is exceedingly difficult due to the highly localized and drastic material evolution that often occurs over the course of the manufacture time of each component. Final product characterization and validation are currently driven primarily by experimental means as a result of the lack of robust modeling procedures. In the present work, the authors discuss primary detrimental hurdles that have plagued effective modeling of AM methods for metallic materials while also providing logical speculation into preferable research directions for overcoming these hurdles. The primary focus of this work encompasses the specific areas of high-performance computing, multiscale modeling, materials characterization, process modeling, experimentation, and validation for final product performance of additively manufactured metallic components.

Linking process, structure, property, and performance for metal-based additive manufacturing: computational approaches with experimental support

Wire and arc additive manufacturing : Opportunities and challenges to control the quality and accuracy of manufactured parts

In recently developed Additive Manufacturing (AM) technologies, high-energy sources have been used to fabricate metallic parts, in a layer by layer fashion, by sintering and/or melting metal powders. In particular, Electron Beam Additive Manufacturing (EBAM) utilizes a high-energy electron beam to melt and fuse metal powders to build solid parts. EBAM is one of a few AM technologies capable of making full-density metallic parts and has dramatically extended their applications. Heat transport is the center of the process physics in EBAM, involving a high-intensity, localized moving heat source and rapid self-cooling, and is critically correlated to the part quality and process efficiency. In this study, a finite element model was developed to simulate the transient heat transfer in a part during EBAM subject to a moving heat source with a Gaussian volumetric distribution. The developed model was first examined against literature data. The model was then used to evaluate the powder porosity and the beam size effects on the high temperature penetration volume (melt pool size). The major findings include the following. (1) For the powder layer case, the melt pool size is larger with a higher maximum temperature compared to a solid layer, indicating the importance of considering powders for the model accuracy. (2) With the increase of the porosity, temperatures are higher in the melt pool and the molten pool sizes increase in the depth, but decrease along the beam moving direction. Furthermore, both the heating and cooling rates are higher for a lower porosity level. (3) A larger electron-beam diameter will reduce the maximum temperature in the melt pool and temperature gradients could be much smaller, giving a lower cooling rate. However, for the tested electron beampower level, the beam diameter around 0.4 mm could be an adequate choice.

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Thermal modeling of electron beam additive manufacturing process - powder sintering effects

Hybrid laser arc welding simultaneously utilizes the arc welding and the laser welding, in a common interaction zone. The synergic effects of laser beam and eclectic arc in the same weld pool results in an increase of welding speed and penetration depth along with the enhancement of gap bridging capability and process stability. This paper presents the current status of this hybrid technique in terms of research, developments and applications. Effort is made to present a comprehensive technical know-how about this process through a systematic review of research articles, industrial catalogues, technical notes, etc. In the introductory part of the review, an overview of the hybrid laser arc welding is presented, including operation principle, process requirements, historical developments, benefits and drawbacks of the process. This is followed by a detailed discussion on control parameters those govern the performance of hybrid laser arc welding process. Thereafter, a report of improvements of performance and weld qualities achieved by using hybrid welding process is presented based on review of several research papers. The succeeding sections furnish the examples of industrial applications and the concluding remarks.

Hybrid laser arc welding: State-of-art review

Estimation of the parameters of a Gaussian heat source by the Levenberg–Marquardt method: Application to the electron beam welding

In the hybrid laser-arc welding process, a laser beam and an electric arc are coupled in order to combine the advantages of both processes: high welding speed, low thermal load and high depth penetration thanks to the laser; less demanding on joint preparation/fit-up, typical of arc welding. Thus the hybrid laser-MIG/MAG (Metal Inert or Active Gas) arc welding has very interesting properties: the improvement of productivity results in higher welding speeds, thicker welded materials, joint fit-up allowance, better stability of molten pool and improvement of joint metallurgical quality. The understanding of the main relevant involved physical processes are therefore necessary if one wants for example elaborate adequate simulations of this process. Also, for an efficient use of this process, it is necessary to precisely understand the complex physical phenomena that govern this welding technique. This paper investigates the analysis of the effect of the main operating parameters for the laser alone, MAG alone and hybrid Laser/MAG welding processes. The use of a high speed video camera allows us to precisely characterize the melt pool 3D geometry such as the measurements of its depression and its length and the phenomena occurring inside the melt pool through keyhole-melt pool-droplet interaction. These experimental results will form a database that is used for the validation of a three-dimensional thermal model of the hybrid welding process for a rather wide range of operating parameters where the 3-D geometry of the melt pool is taken into account.

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Analysis of hybrid Nd:Yag laser-MAG arc welding processes.

In this paper, we present a 3D numerical model of Wire Arc Additive Manufacturing to simulate the material deposition and the temperature field from the operating parameters. This predictive model, applied to a Cold Metal Transfer (CMT) process, takes into account electromagnetism, fluid flow and heat transfer in all domains (wire, arc, melt pool, substrate). This model, developed using COMSOL Multiphysics® software, calculates the creation of the molten metal drop at the filler wire tip, the detachment of the drop when the filler material retracts during the short circuiting phase and the growth of the deposit. This innovative work describes for the first time the wire behaviour dynamically and its interaction with the melt pool in 3D in a fully coupled approach. The dynamics of the free surface are treated with the level set method, particularly efficient for strong topological changes. The Lorentz forces, shear stress, arc pressure, and Joule effect are calculated. This model requires only the knowledge of the operating parameters without any assumption on the arc distribution. It aims to simulate the build-up of a 304 stainless steel wall. To validate this model, the melt pool dimensions and shape of the deposit calculated for the first layer are compared to experimental data given by macrographs and high speed videos.

3D heat transfer, fluid flow and electromagnetic model for cold metal transfer wire arc additive manufacturing (Cmt-Waam)

Heat transfer, fluid flow and electromagnetic model of droplets generation and melt pool behaviour for wire arc additive manufacturing

For a better understanding of the physical phenomena associated with the appearance of defects in laser welding, a heat and fluid flow model is developed using Comsol Multiphysics®. This first step of the project is focused on the modeling of a static laser shot on a sample of steel. This 2D axially-symmetric configuration is used to study the main physical phenomena related to the creation of the keyhole. This model takes into account the three phases of the matter: the vaporized metal, the liquid phase and the solid base. To track the evolution of these three phases, coupled equations of energy and momentum are solved. The liquid/vapor interface is tracked using the Level-Set method. The calculated velocity and free surface deformation are analyzed. Melt pool shapes are compared with experimental macrographs and the influence of some parameters such as laser power is discussed.

P. Le Masson

Papers

Estimation of the parameters of a Gaussian heat source by the Levenberg–Marquardt method: Application to the electron beam welding

Analysis of hybrid Nd:Yag laser-MAG arc welding processes.

3D heat transfer, fluid flow and electromagnetic model for cold metal transfer wire arc additive manufacturing (Cmt-Waam)

Heat transfer, fluid flow and electromagnetic model of droplets generation and melt pool behaviour for wire arc additive manufacturing

A two-dimensional axially-symmetric model of keyhole and melt pool dynamics during spot laser welding