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Binder jetting (BJT) has been extensively explored for additive manufacturing of ceramics due to its ability to create complex structures by processing refractory and hard-to-machine materials. However, achieving a uniform powder bed with high packing density while processing ceramics in BJT remains a challenge. This study systematically examines the role of powder size, powder temperature, flow behavior, and powder size distribution on powder bed formation and resulting part properties. Four different alumina powder sizes (1 μm, 5 μm, 10 μm, and 20 μm) were investigated. Flowability characterizations reveal that 1 μm powder remains poorly flowable at both room and elevated temperatures, while 20 μm powder demonstrates excellent flowability at both temperatures. Smaller powders, especially 1 μm, exhibit around 25% loss in moisture, which results in pronounced agglomeration at room temperature. Discrete element method simulations were used to identify the ideal mixing ratio of the bimodal powder using 5 μm and 20 μm powders. For bimodal powder, both the simulation and the experiments exhibited a preferential deposition of smaller powders in the spreading direction. However, the 5 μm and 20 μm powders did not show any preferential deposition in the simulation, but experiments showed preferential deposition behavior. When using bimodal powder, packing density decreases by 7.65% along the spreading direction, which aligns with an 8.19% drop in part relative density. These findings offer valuable insights into the effects of bimodal powder distribution for controlling powder bed packing density and potentially leveraging spatial density variations for functional applications such as biomedical implants, heat exchangers, and gas filtration. 

Slag defects remain a persisting and prominent problem for steel foundries across the world. Slag defects are surface defects usually caused by oxides transported from the pouring ladle or formed during the initial stages of filling that are transported into the casting cavity during pouring. This study investigates the use of vortex chambers as a component of the gating system and a potential slag trapping mechanism for ferrous metals through computational modeling and experimental validations. Six vortex chamber designs were studied using 3D sand-printing (3DSP) with varying chamber thickness and inlet-outlet height difference. For experimental validation, ASTM A216 WCB steel plates were cast using these vortex chamber designs. The results were compared to a benchmark design consisting of a conventional straight runner section in place of the vortex chamber. Computational results include ingate velocity during filling, entrained air volume fraction, and free surface defect mass. Experimental results include a subsurface pore volume fraction model based on the measured ultrasonic wave speed and attenuation. The experimental results were correlated with the computational results and show strong agreement. The computational results suggest a 31% reduction in melt velocity at the ingate from one of the vortex chamber designs and confirming the reduction in turbulence and reoxidation in the melt stream. However, the experimental results suggest no significant improvement in terms of subsurface porosity for the vortex chamber designs based on previous literature. 

3D sand printing (3DSP) is a comparatively new additive manufacturing (AM) technology which has opened new opportunities for the sand-casting industry. Complex parts with intricate features that were inaccessible through the traditional mold and core making process and would take significant lead time to production can be now easily manufactured using 3DSP technology. Previous studies through numerical modeling have revealed that novel 3D riser geometries offer significant advantages during solidification of the casting by providing higher solidification time, less macro-porosity, and less piping inside the riser. This current study focuses on the experimental validation of the numerical study. Nine different riser geometries were printed as cores using 3DSP which were later installed in a larger sand mold accommodating the rigging (sprue, runners, ingates). Three novel riser shapes (ellipsoid, spherical and fusion) and one traditional cylindrical riser were explored in this study. The spherical risers were studied to understand the effect of the novel riser shape on the neck region. With three repetitions of each design (total of nine designs), a total of 27 castings were manufactured and characterized for statistical analysis. ASTM A216 WCB (wrought carbon steel, grade B) alloy was used to pour all the molds. Results from the ultrasonic tests, flexural test, and X-ray CT inspection show strong agreement with the previous FEA analysis along with 45 % yield improvement, 32 % reduction in riser neck diameter and increased mechanical strength. 

The ability to manufacture complex design geometries via Additive Manufacturing (AM) has led to a rapid growth in advancing the design methods, fabrication, and application of Triply Periodic Minimal Surface (TPMS) lattices with minimal surface topologies. Due to its zero-mean curvature, TPMS lattices can be additively manufactured without any sacrificial support structures and offer both design and manufacturing engineers, unprecedented control over the local physical properties (surface area, relative density, etc.) and local mechanical properties (flexural strength, Young’s modulus, etc.). TPMS lattices are of high interest for a wide range of applications such as biomedical implants, energy absorption, and surface fluidic applications such as heat exchangers, and energy storage. Recent advancements in functionally graded TPMS lattice design by varying local lattice geometry has shown to result in different mechanical performance. However, there have been limited studies in understanding the functional grading of AM process conditions (e.g., Laser-Powder Bed Fusion in this study) and lattice sheet thickness to better map the design-processing conditions-properties. The goal of this study is to achieve similar mechanical properties in TPMS sheet lattices with two different TPMS sheet thicknesses by varying laser processing conditions (e.g., contour and hatch conditions in this study). Quasi-static tensile testing of solid samples with corresponding AM conditions and 3-point bending tests of TPMS lattices were performed in accordance with ASTM E8 and ASTM E290, respectively. It was observed that the flexural properties of the 0.75 mm and 0.25 mm TPMS lattices are similar and exhibit different properties with different scan strategies and speed variations under contour-only and hatch-only laser scanning strategies. Also, the 0.75 mm TPMS sheet lattices exhibited 79 % higher flexural stiffness than the 0.25 mm sheet lattices. It was also observed that this observed trend was reversed in the case of tensile properties. Findings from this study can provide new directions towards achieving gradient TPMS lattice designs with varying local mechanical performance by grading the laser scanning strategies to achieve desired mechanical properties and surface topologies. 

Abstract The 3D sand printing (3DSP) process is a binder jetting class of additive manufacturing process that can incorporate complex 3D mold designs and consolidate cores with intricate features that were previously inaccessible. Prior studies in 3DSP mold design have been shown to improve pouring and filling conditions for sand casting. However, the opportunity to improve casting quality by exploring 3D riser designs during the solidification stage has not yet been explored. In this research, three novel 3D riser geometries—ellipsoid, spherical, and a fusion riser (combination of cylindrical and ellipsoid riser) were investigated. The results were compared to the benchmark cylindrical risers to assess casting performance (e.g., reduction in shrinkage porosity, increase in solidification time). Computational solidification simulations have been presented to evaluate the characteristics of the novel risers for three different metal alloys- nickel aluminum bronze (NAB), low-carbon steel A216 (WCB), and aluminum alloy (A319) alloy. From the results of this research, spherical risers were found to provide 45% yield improvement of for the three alloys studied. In addition, the riser neck diameter using a spherical riser experienced up to 77% reduction when compared to the recommended dimensions from previous literature. Finally, one of the spherical riser designs provided 18% improvement in terms of riser-pipe safety height over the benchmark design. Findings from this research will help metalcasting industries to optimize their riser designs for complex casting geometries by implementing 3D riser geometries (via 3DSP) into traditional mold making for yield improvement and defect-free castings. 

The finishing of additive manufactured (AM) components is crucial for endowing them with fatigue resistance. Unfortunately, current AM processes naturally promote anisotropic surface characteristics that make it challenging to optimize finishing processes. In this study, bead-blasting is explored as a process for finishing Electron Beam Melted (EBM) Ti-6Al-4V. The effects of anisotropic roughness characteristics on the mechanics of bead-blasting are delineated using surface texture measurements via optical profilometry and residual stress measurements via X-ray diffraction. As-received surfaces resulting from AM, as well as those that have been Electrical Discharge Machined (EDM), are studied. It is seen that pre-processed roughness textures heavily influence the final textures and residual stresses. These linkages are quantified using a plasticity index as the governing metric—a rougher surface features a larger plastic index, which results in comparatively greater evolution of its texture characteristics than a smoother surface after equivalent bead-blasting treatments. The mechanics of this evolution are delineated using energy-controlled indentation as a model representing a single impact in bead-blasting. It is seen that rougher surfaces featuring complex textures in as-received states also produce complex stress states featuring a greater level of locally tensile stresses during indentation compared with smoother surfaces. Approaches to address these complications are proposed that can potentially transform a printed, non-functional surface into one that is optimized for fatigue resistance. 

Binder Jetting has gained particular interest amongst Additive Manufacturing (AM) techniques because of its wide range of applications, broader feasible material systems, and absence of rapid melting-solidification issues present in other AM processes. Understanding and optimizing printing parameters during the powder spreading process is essential to improve the quality of the final part. In this study, a Discrete Element Method (DEM) simulation is employed to evaluate the powder packing density, flowability, and porosity during powder spreading process utilizing three different powder groups. Two groups are formed with monoidal size distributions (75–84 μm and 100–109 μm), and the third one consisting of a bimodal distribution (50 μm + 100 μm). A thorough investigation into the effects of powder size distribution during the powder spreading step in a binder jetting process is conducted using ceramic foundry sand. It was observed that coarser particles result in higher flowability (62% decrease in repose angle) than finer ones due to the cohesion effect present in the latter. A bimodal size distribution yields the highest packing density (8% increase) and lowest porosity (∼12% reduction) in the powder bed, as the finer particles fill in the voids created between the coarser ones. Findings from this study are directly applicable to binder-jetting AM process, and also offer new insights for AM powder manufacturers.