Dimensional and geometrical precision of parts produced by binder jetting is a crucial issue to be considered aiming at promoting the transition to industrial production. The influence of both the printing and the sintering processes has to be evaluated, and the high shrinkage has to be considered. The task is further complicated by the anisotropy of dimensional change on sintering. The aim of this work is to investigate the dimensional and geometrical precision of cylindrical holes, as affected by the anisotropy of dimensional change on sintering after binder jetting. AISI 316 L powder was used to produce five different geometries, characterized by four holes with different orientation with respect to the printing direction. The geometrical features were measured both in the green and in the sintered state with a coordinate measuring machine, and the dimensional changes, as well as the geometrical variations, were calculated. According to the author’s previous experience, a theoretical model has been defined, which aims at predicting the geometry of the holes as derived by the anisotropic dimensional change on sintering. The expected dimensional change of hole diameters, the variation of cylindricity, and the variation of the axis inclination were calculated by the model and compared to those derived from measurement. Good agreement between predicted and measured results has been observed, providing that the influence of printing process parameters is considered.

Highlights • Performed about 360 plasticity and fracture experiments using a robotic system. • Employed micro-CT and EBSD to characterize microstructural features. • SLM-made AlSi10Mg is stronger, but also more brittle than its cast counterpart. • Property variations are due to porosity in castings and build height effect in the SLM. • Stochastic plasticity and fracture models are determined. Both additively-manufactured and cast metals are known to exhibit stochastic mechanical properties at the macroscopic level. Using a robot-assisted mechanical testing system, more than 360 experiments are performed on flat specimens extracted from AlSi10Mg components that are either cast or made through laser powder bed fusion (LPBF), commonly known as selective laser melting (SLM). Aside from basic EBSD analysis of the respective microstructures, micro-computed tomography is performed revealing a significantly higher porosity and pore size for the cast material. The results from uniaxial tension experiments reveal a 10% higher yield strength (on average) and an about 20% higher ultimate tensile strength for the SLM made AlSi10Mg. The tracking of the specimen origin within the SLM component shows a clear location dependence of the observed hardening response on the build height. The shear and tension fracture experiments revealed a strong stress-state dependence and significantly higher fracture strains for the cast material as compared to its SLM-made counterpart. To facilitate the computer aided engineering of structures with additively-manufactured AlSiMg alloys, a build height dependent hardening model is proposed along with a probabilistic plasticity and fracture modeling framework. Graphical Download : Download high-res image (363KB) Download : Download full-size image

Additive manufacturing has advantages of cutting the time from design to making new parts but it suffers from metallurgical defects such as porosity. For example, wired arc additive manufacturing(WAAM) of new alloys such as Al–Li alloys is very challenging due to the fact that the porosity level is so high as to degrade not only fatigue life but also the static mechanical properties. In this study, we found that large chains of porosity could form at the interdendritic liquid during WAAM of an AA2196 Al–Li alloy. After T6 heat treatment, those chains of porosity actually grow bigger than the as-deposit state, with the microporosity size over 50 µm increasing from 2.8% to 5.8% and the maximum size grow up to 107 µm. Using X-ray Computed Tomography (XCT), we have quantified the spatial distribution of microporosity as a function of hot deformation after WAAM. It was found that the chain of microporosity along the direction of deposition could be effectively eliminated by controlling the strain. Combining the 42% hot deformation and T6 heat treatment, the closure of microporosity together with nano-sized T1 precipitates can be achieved and yield tensile strength (YTS) can be improved by 199%, the ultimate tensile strength (UTS) can be increased by 168%, and the elongation can be extended by 460%, reaching up to 372 MPa, 439 MPa, and 6.9%, respectively. Therefore, the solidification defects during WAAM can be remediated by applying proper hot deformation which is extremely useful for the Al–Li alloys with a long solidification range and high susceptibility to solidification cracking.

The material extrusion (ME) process, which is an additive manufacturing technology applicable to a wide range of polymers, has a drawback in that the inherent bonding between the deposited layers is vulnerable. To this end, we present an efficient strengthening method for the ME process by introducing bidirectional in situ infrared (IR) heating during the polymer melt deposition in the 3D-printing process. The auxiliary IR irradiation was applied to heat as-printed polymers in the deposited area along the printing paths at their glass transition temperature, which expectedly led to molecular diffusion and chain re-entanglement at the deposited interface. Consequently, the heating technique not only helped eliminate the structural defects due to the thermal stress but also helped enhance the mechanical strength, particularly of structures layered in transverse and upright directions. The reinforcement effects were confirmed by conducting tensile tests and thermal imaging analysis on typical polymers such as polylactic acid and polycarbonate. The experimental results demonstrated the feasibility of the proposed heating technique in extending the applicability of a wide range of engineering plastics or composite materials for the ME printing method.

Graphene–polyamide-6 composite (GC) filament was 3D-printed via melt extrusion (ME). The influence of specimen thickness and internal geometric designs on electromagnetic interference shielding effectiveness (EMI SE) and dielectric properties in the X-band frequency range (8.2–12.4 GHz) was investigated. Increasing specimen thickness from 1 to 5 mm did not improve EMI SE due to impedance matching and the associated reductions in electromagnetic (EM) wave reflection. It was demonstrated that the introduction of suitable internal geometric assemblies avoided impedance matching and significantly improved EMI SE. A material model for simulating EM response of 3D-printed GC was developed and experimentally verified. It was found that different internal geometric designs each displayed unique EM responses. However, geometrical inaccuracies in printed specimens resulted in differences between experimental EM response and that predicted by simulations. These inaccuracies stem from the small size of the features relative to the printer resolution and the ME printing methodology. Therefore, the limitations of a printer when replicating complex geometries must be considered to effectively apply internal geometric designs for enhancing EMI SE of 3D-printed components.

Although additive manufacturing offers numerous potential advantages for fabricating functional, complex geometry zirconia parts with efficiency, industrial interest in practical applications is currently lacking. This potentially stems from the need for a more comprehensive investigation into the performance of additively manufactured zirconia components, which is essential for promoting and initializing industrial applications. The aim of this study is thus to provide a detailed evaluation of zirconia specimens fabricated by one of the most utilized ceramic additive manufacturing technologies, viz. digital light processing (DLP), with a range of typical zirconia components being printed. Key performance factors captured within include achievable density, surface quality measurements, dimensional accuracy, degree of shrinkage, and mechanical properties. The results of this work demonstrates that the performance of the DLP-prepared zirconia parts is comparable to those of conventionally fabricated zirconia. It is believed that this paper will serve as a good reference for academic and industrial communities interested in this rapidly expanding field.

Assessing the material stiffness of fiber reinforced polymer composites deposited in Large Area Additive Manufacturing (LAAM) is needed to define the process-structure-property mapping for the LAAM technology. While the screw-extrusion-based LAAM systems yield a distribution of fiber aspect ratio (i.e., length to diameter ratio for cylindrical inclusions) within deposited beads, most composite micromechanical models ignore the fiber geometry variation and instead assume a single value of fiber aspect ratio. This paper presents a statistics-based homogenization approach for including the fiber aspect ratio distribution in the prediction of the elastic properties of an extruded polymer composite bead. The fiber length distribution of a 13 wt% Carbon Fiber reinforced Acrylonitrile Butadiene Styrene (CF-ABS) processed through a LAAM deposition system is measured using high resolution optical microscopy. The Weibull probability distribution function is employed to statistically describe the measured values. The fitted probability density function is then incorporated into a fiber orientation homogenization approach to compute the variability of the elastic properties of the extruded composite. Elastic properties predicted by our proposed method are shown to differ from those presented in prior studies that ignored fiber length variability. The fiber aspect ratio reduction from fiber length attrition during the LAAM single screw-extrusion is shown to decrease the predicted flow-direction effective elastic modulus by 7%. Elastic moduli computed using our measured fiber aspect ratio distribution and proposed homogenization approach compare well to reported data from previously associated experimental studies.

The Directed Energy Deposition (DED) process of metals, has a broad range of applications in several industrial sectors. Surface modification, component repairing, production of functionally graded materials and more importantly, manufacturing of complex geometries are major DED’s applications. In this work, a multi-physics numerical model of the DED process of maraging steel is developed to study the influence of the powder stream specifications on the melt pool’s thermal and fluid dynamics conditions. The model is developed based on the Finite Volume Method (FVM) framework using the commercial software package Flow-3D. Different physical phenomena e.g. solidification, evaporation, the Marangoni effect and the recoil pressure are included in the model. As a new feature, the powder particles’ dynamics are modeled using a Lagrangian framework and their impact on the melt pool conditions is taken into account as well. In-situ and ex-situ experiments are carried out using a thermal camera and optical microscopy. The predicted track morphology is in good agreement with the experimental measurements. Besides, the predicted melt pool evolution follows the same trend as observed with the online thermal camera. Furthermore, a parametric study is carried out to investigate the effect of the powder particles incoming velocity on the track morphology. It is shown that the height-to-width ratio of tracks increases while using higher powder velocities. Moreover, it is shown that by tripling the powder particles velocity, the height-to-width ratio increases by 104% and the wettability of the track decreases by 24%.

Highlights • The crystallographic texture stability during LPBF fabrication was investigated. • The texture was stable when “the laser scan direction” matched the <100>. • The orientation along the build direction did not impact the texture stability. In metal additive manufacturing, crystallographic orientation control is a promising method for tailoring the functions of metallic parts. However, despite its importance in the fabrication of texture-controlled functional parts, the stability of the crystallographic texture is not widely discussed. Herein, the crystallographic texture stability under laser powder bed fusion was investigated. Two methodologies were employed. One is that a laser scanning strategy was alternately changed for a specific number of layers. The other is a “seeding” experiment in which single-crystalline substrates with controlled crystallographic orientations in the building (z-) direction and the xy-plane (perpendicular to the building direction) were used as the starting substrate. The transient zone width, where the crystallographic orientation was inherited from the layer beneath, was analyzed to evaluate the texture stability. The crystallographic direction of the seed within the xy-plane, rather than the building direction, determined the transient zone width, i.e., the texture stability. In particular, the texture in the newly deposited portion was stable when the laser scanning direction matched the <100> orientation in the underneath layer, otherwise the crystal orientation switched rapidly, such that the <100> orientation was parallel to the scanning direction. Interestingly, the crystallographic orientation along the building direction in the underneath layer hardly impacted the stability of the texture. Therefore, for the first time, it has been clarified that the <100> orientation in the scanning direction, rather than the building direction, was preferentially stabilized, whereas the orientation in the other directions secondary stabilized. Graphical Download : Download high-res image (636KB) Download : Download full-size image