Powder-bed fusion is a class of Additive Manufacturing (AM) processes that bond successive layers of powder to facilitate the creation of parts with complex geometries. As AM technology transitions from the fabrication of prototypes to end-use parts, the understanding of the powder properties needed to reliably produce parts of acceptable quality becomes critical. Consequently, this has led to the use of powder characterisation techniques such as scanning electron microscopy, laser light diffraction, X-ray photoelectron spectroscopy, and differential thermal analysis to study the effect of powder characteristics on part properties. Utilisation of these powder characterisation methods to study particle morphology, chemistry, and microstructure has resulted in significant strides being made towards the optimisation of powder properties. This paper reviews methods commonly used in characterising AM powders, and the effects of powder characteristics on the part properties in powder-bed fusion processes.

Multilayer direct laser deposition (DLD) is a fabrication process through which parts are fabricated by creating a molten pool into which metal powder is injected as particles. During fabrication, complex thermal activity occurs in different regions of the build; for example, newly deposited layers will reheat previously deposited layers. The objective of this study was to provide insight into the thermal activity that occurs during the DLD process. This work focused on the effect of the laser parameters of newly deposited layers on the microstructure and mechanical properties of the previously deposited layers in order to characterize these effects to inform proper parameter selection in future DLD fabrication. Varying the parameters showed to produce different effects on the microstructure morphology and property values, leading to some tempering and aging of the steels. The microstructure of the top layer was equiaxed, while the near substrate region was fine dendritic. Typically, both the travel speed and laser power significantly affect the microstructure and hardness. Using the commercial ABAQUS/CAE software, a thermo-mechanical 3D finite element model was developed. This work presents a 3D heat transfer model that considers the continuous addition of powder particles in front of a moving laser beam using ABAQUS/CAE software. The model assumes the deposit geometry appropriate to each experimental condition and calculates the temperature distribution, cooling rates and re-melted layer depth, which can affect the final microstructure. Model simulations were qualitatively compared with experimental results acquired in situ using a K-type thermocouple

Purpose – This paper sets out to summarize the current research, development, and integration of a hybrid process to produce high-temperature metallic materials. It seeks to present the issues and solutions, including the understanding of the direct laser deposition process, and automated process planning. Design/methodology/approach – Research in simulation and modeling, process development, integration, and actual part building for hybrid processing are discussed. Findings – Coupling additive and subtractive processes into a single workstation, the integrated process, or hybrid process, can produce metal parts with machining accuracy and surface finish. Therefore, the hybrid process is potentially a very competitive process to fabricate metallic structures. Originality/value – Rapid prototyping technology has been of interest to various industries that are looking for a process to produce/build a part directly from a CAD model in a short time. Among them, the direct laser deposition process is one of the few processes which directly manufacture a fully dense metal part without intermediate steps. Presented in this paper is the research, development, and system integration to resolve the challenges of the direct metal deposition process including building overhang structures, producing precision surfaces, and making parts with complex structures.