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Metal additive manufacturing (AM) is an innovative manufacturing method with numerous metallurgical benefits, including fine and hierarchical microstructures and enhanced mechanical properties, thanks to the utilization of a local heat source and the rapid solidification nature of the process. High levels of productivity, together with the ability to produce complex geometries and large components, have added to the versatile applicability of metal AM with applications already implemented in various sectors such as medicine, transportation, and aerospace. To further enhance the potential benefits of AM in the context of small- to medium-scale bulk production, metallurgical complexities should be determined and investigated. Hence, this review paper focuses on three significant metallurgical aspects of metal AM processes: in situ alloying, functionally graded materials, and surface treatments for AM parts. The current text is expected to offer insights for future research works on metal AM to expand its potential applications in various advanced manufacturing sectors.

A distinctive characteristic of the powder bed fusion with electron beam (PBF-EB) process is the sintering of the powder particles. For certain metallic materials, this is crucial for the success of the subsequent step, the melting, and, generally, the whole process. Despite the sintering mechanisms that occur during the PBF-EB process being similar to well-known powder metallurgy, the neck growth rates are significantly different. Therefore, specific analyses are needed to understand the influence of the PBF-EB process conditions on neck growth and neck growth rate. Additionally, some aspects, such as the rigid body motion of the particles during the sintering process, are still challenging to analyze. This work systematically investigated the effects of different particle diameters and particle diameter ratios. Additionally, the impact of the rigid body motion of the particles in the sintering was analyzed. This work demonstrated that the sintering results significantly depended on the EB-PBF process conditions.

Stereolithography is known as one of the best Additive Manufacturing technologies in terms of geometrical and dimensional precision for polymeric materials. In recent years, a lot of studies have shown that the creation of ceramic resins, through a particular combination of monomeric components and ceramic powders, allows to obtain complex shape geometries thanks to the photopolymerization process. This review highlights the characteristics and properties of ceramic resins, peculiarities of the ceramic stereolithography processes, up to the relationship between the composition of the ceramic resin and the complexity of the post-processing phases. The comparison of different studies allows outlining the most common steps for the production of ceramic resins, as well as the physical and chemical compatibility of the different compounds that must be studied for the good feasibility of the process.

Macroscale modeling plays an essential role in simulating additive manufacturing (AM) processes. However, models at such scales often pay computational time in output accuracy. Therefore, they cannot forecast local quality issues like lack of fusion or surface roughness. For these reasons, this kind of model is never used for process optimization, as it is supposed to work with optimized parameters. In this work, a more accurate but still simple three-dimensional (3D) model is developed to estimate potential faulty process conditions that may cause quality issues or even process failure during the electron beam melting (EBM) process. The model is multilayer, and modeling strategies are developed to have fast and accurate responses. A material state variable allows for the molten material to be represented. That information is used to analyze process quality issues in terms of a lack of fusion and lateral surface roughness. A quiet element approach is implemented to limit the number of elements during the calculation, as well as to simulate the material addition layer by layer. The new material is activated according to a predefined temperature that considers the heat-affected zone. Heat transfer analysis accuracy is comparatively demonstrated with a more accurate literature model. Then, a multilayer simulation validates the model capability in predicting the roughness of a manufactured Ti6Al4V sample. The model capability in predicting a lack of fusion is verified under a critical process condition.

The conventional approach to design and manufacturing often has geometries with an efficient material distribution. For the high-precision machines, that approach involves the design of heavy components that guarantees the stiffness requirements. However, the higher the weight of the part, the higher inertia it has. As a result, when the feed axes are accelerated, the inertial forces deform the machine components and the precision of the machine is reduced. This study investigated the designing for additive manufacturing (DfAM) and designing for assembly (DfA) to increase the material efficiency of components for high-precision applications. A new methodology which considered the design and manufacturing issues and machining as well is given. A comprehensive model for cost evaluation of the part is presented. The case study refers to the rails and the bracket that support and move the flying probe of a testing machine for micro-electromechanical systems (MEMS). The weight of the rails has been decreased by 32% and the components to be assembled have been reduced from 16 to 7. The optimized bracket is more than 50% stiffer than the original one, 10% lighter, and economically competitive.