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Support structures play a significant role in all additive manufacturing (AM) processes. The type of supports, as well as their size, placement, and other characteristics, greatly determine how effectively and efficiently the AM process works. In order to reduce the amount of material and post-processing requirements, tree-like support structures are revolutionary support structures that have so far been employed in polymer AM and have shown good performance. However, they have not yet been investigated for metal AM processes. Therefore, this study aims to propose and optimize the tree-like support structures for additively manufactured metal (Ti6Al4V) overhangs. The overhang specimens are fabricated using Electron Beam Melting (EBM) with a variety of design and process parameters. The effect of design and process structure parameters on the performance of the support is evaluated and optimized experimentally. MOGA-ll is used to perform multi-objective optimization. The results have shown the feasibility of using tree-like support structures in metal AM. The findings of this study demonstrate how important it is to choose the proper minimum distance between rows in order to reduce support volume and support removal time. Furthermore, the most crucial factors in limiting the overhang deviation are the beam current and beam scanning speed. Additionally, the data demonstrate that lowering the beam current and raising the beam scanning speed significantly reduce deformation. Consequently, it is critical to find the right balance between beam current, beam scanning speed, minimum spacing between rows, and branch top diameters that can produce the lowest support volume, lowest support removal time, and least amount of deformation. [ABSTRACT FROM AUTHOR]

Titanium aluminides qualify adequately for advanced aero-engine applications in place of conventional nickel based superalloys. The combination of high temperature properties and lower density gives an edge to the titanium aluminide alloys. Nevertheless, challenges remain on how to process these essentially intermetallic alloys in to an actual product. Electron Beam Melting (EBM), an Additive Manufacturing Method, can build complex shaped solid parts from a given feedstock powder, thus overcoming the shortcomings of the conventional processing techniques such as machining and forging. The amount of energy supplied by the electron beam has considerable influence on the final build quality in the EBM process. Energy input is decided by the beam voltage, beam scan speed, beam current, and track offset distance. In the current work, beam current and track offset were varied to reflect three levels of energy input. Microstructural and mechanical properties were evaluated for these samples. The microstructure gradually coarsened from top to bottom along the build direction. Whereas higher energy favored lath microstructure, lower energy tended toward equiaxed grains. Computed tomography analysis revealed a greater amount of porosity in low energy samples. In addition, the lack of bonding defects led to premature failure in the tension test of low energy samples. Increase in energy to a medium level largely cancelled out the porosity, thereby increasing the strength. However, this trend did not continue with the high energy samples. Electron microscopy and X-ray diffraction investigations were carried out to understand this non-linear behavior of the strength in the three samples. Overall, the results of this work suggest that the input energy should be considered primarily whenever any new alloy system has to be processed through the EBM route. [ABSTRACT FROM AUTHOR]

Porous metal structures have many benefits over fully dense structures for use in bio-implants. The designs of porous structures can be made more sophisticated by altering their pore volume and strut orientation. Porous structures made from biocompatible materials such as titanium and its alloys can be produced using electron-beam melting, and recent reports have shown the biocompatibility of titanium aluminide (γ-TiAl). In the present work, we produced porous γ-TiAl structures by electron-beam melting, incorporating varying pore volumes. To achieve this, the individual pore dimensions were kept constant, and only the strut thickness was altered. Thus, for the highest pore volume of ~77%, the struts had to be as thin as half a millimeter. To accomplish such fine struts, we used various beam currents and scan strategies. Microscopy showed that selecting a proper scan strategy was most important in producing these fine struts. Microcomputed tomography revealed no major gaps in the struts, and the fine struts displayed compressive stiffness similar to that of natural bone. The characteristics of these highly-porous structures suggest their promise for use in bio-implants. [ABSTRACT FROM AUTHOR]

This study aims to investigate the manufacturability of overhang round holes with and without support. The experiments were conducted by electron beam melting (EBM) using a Ti6Al4V powder. A large number of overhanging holes with and without support were fabricated and evaluated. The geometrical accuracy, mechanical properties, and microstructures were utilized as a measure of the process performance. It was demonstrated that overhanging features can be built successfully without support up to a certain dimension (or threshold value). Beyond that value, a minimal support structure can be employed to achieve the most suitable trade-off between production time, cost, and accuracy. [ABSTRACT FROM AUTHOR]