Modelling and simulation are very important for revealing the relationship between process parameters and internal variables like grain morphology in solidification, precipitate evolution, and solid-state phase transformation in laser additive manufacturing. The impact of the microstructural changes on mechanical behaviors is also a hot topic in laser additive manufacturing. Here we reviewed key developments in thermal modelling, microstructural simulations, and the predictions of mechanical properties in laser additive manufacturing. A volumetric heat source model, including the Gaussian and double ellipsoid heat sources, is introduced. The main methods used in the simulation of microstructures, including Monte Carlo method, cellular automaton, and phase field method, are mainly described. The impacts of the microstructures on mechanical properties are revealed by the physics-based models including a precipitate evolution based model and dislocation evolution based model and by the crystal plasticity model. The key issues in the modelling and simulation of laser additive manufacturing are addressed.

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A Review on Modelling and Simulation of Laser Additive Manufacturing: Heat Transfer, Microstructure Evolutions and Mechanical Properties

Aeration and cohesive effects on flowability in a vibrating powder conveyor

Microstructure, mechanical properties and machinability of 316L stainless steel fabricated by direct energy deposition

Laser Powder Directed Energy Deposition (LP-DED) is a very powerful Additive Manufacturing process for different applications, such as repair operations and the production of functionally graded material. However, the application is still limited, and one of the main reasons is related to the lack of knowledge of the process mechanisms. Since the mechanisms involved in the process, which are mutually related to each other, directly influence the properties of the produced part, their knowledge is crucial. This paper presents a review of the LP-DED mechanisms and the relationship between the input process parameters and related outcomes. The main mechanisms of the LP-DED process, which are identified as (i) laser irradiation and material addition, (ii) melt pool generation, and (iii) subsequent solidification, are discussed in terms of input parameters, with a focus on their effects on the deposition effectiveness, and interrelation among the mechanisms of the deposition process. The results highlight the complexity of the mechanisms involved in the LP-DED process and guide engineers in navigating the challenges of the deposition process, with a specific focus on the critical parameters that should be investigated when new materials are developed, or process optimization is carried out.

https://www.mdpi.com/2076-3417/13/1/117/pdf?version=1671703950

An Overview of the Process Mechanisms in the Laser Powder Directed Energy Deposition

Additive Manufacturing (AM) offers new design and manufacturing opportunities of thin-wall microchannel heat exchangers for aerospace and industrial applications. Laser Powder Directed Energy Deposition (LP-DED) is an AM process providing large scale manufacturing of thin-wall microchannel heat exchangers. Successful industrialization of the LP-DED process requires critical quantification and understanding of the metallurgical, geometric, and process limitations. Specifically, understanding the as-built surface texture, inclusive of roughness and waviness, is significant due to its effects on the friction factor and pressure drop within a heat exchanger. This experimental study completed a design of experiments (DOE) to determine the critical build parameters that impact surface texture for enclosed thin-wall samples. This study summarizes the characterization work of the LP-DED process for 1 mm enclosed walls with an Fe–Ni–Cr (NASA HR-1) alloy. The LP-DED parameters including laser power, powder feedrate, travel speed, layer height, and rotary atomized powder feedstock were modified in the experiment. An evaluation of the DOE samples and resulting surface texture is provided along with conclusions from these experiments. Results indicate that 3D areal and 2D profile (directional) surface texture is estimated by 2x the powder diameter that becomes captured or partially melted on the trailing edge of the melt pool. The fine powder showed a higher sensitivity to parameter changes but resulted in a higher density material and 23% reduction in roughness. Surface texture was also shown to vary between closed channel shapes (internal) due to ricochets, recirculation, and higher volume of powder available to bond compared to external (outer) surfaces. The understanding of the LP-DED process as-built surface texture is essential to fluid flow applications such as heat exchanges and can modify performance for enhanced heat transfer or can be a detriment to pressure drop. 

A.D. Iams

Papers

Influence of particle size on powder rheology and effects on mass flow during directed energy deposition additive manufacturing