Binder Jetting Process is an Additive Manufacturing technique (AM) in which a liquid binder is employed for establishing the initial strength and fabricating the geometry of components. In this process, the delivery of the binding agent is accomplished through a drop-on-demand (DOD) printhead by deposition of picoliter-sized droplets of the liquid binder. The velocity of the droplets impinging the powder bed surface might have significant effect on droplet spreading and absorption dynamics, which can be manifested in quality and integrity of the fabricated parts. In the present study, the effect of the printing speed on dimensional accuracy and equilibrium saturation level of printed samples is experimentally investigated and the observed trends are discussed in detail.

Laser polishing (LP) is an emerging technique with the potential to be used for post-build, or in-situ, precision smoothing of rough, fatigue-initiation prone, surfaces of additive manufactured (AM) components. LP uses a laser to re-melt a thin surface layer and smooths the surface by exploiting surface tension effects in the melt pool. However, rapid re-solidification of the melted surface layer and the associated substrate thermal exposure can significantly modify the subsurface material. This study has used an electron beam melted (EBM) Ti6Al4V component, representing the worst case scenario in terms of roughness for a powder bed process, as an example to investigate these issues and evaluate the capability of the LP technique for improving the surface quality of AM parts. Experiments have shown that the surface roughness can be reduced to below Sa = 0.51 μm, which is comparable to a CNC machined surface, and high stress concentrating defects inherited from the AM process were removed by LP. However, the re-melted layer underwent a change in texture, grain structure, and a martensitic transformation, which was subsequently tempered in-situ by repeated beam rastering and resulted in a small increase in sub-surface hardness. In addition, a high level of near-surface tensile residual stresses was generated by the process, although they could be relaxed to near zero by a standard stress relief heat treatment. Graphical abstract Download : Download high-res image (385KB) Download : Download full-size image

Laser sintered aluminum alloys produced by metal 3D printers can replace cast aluminum alloys in aerospace, defense, and marine industries by offering better mechanical properties, less porosity, and competitive fatigue characteristics. One of the major issues currently is the considerable surface roughness of additively manufactured aluminum alloys demanding post-processing procedures such as bead blasting or machining. In the current study, the process parameters such as laser power, scan speed, and hatch spacing were altered such that better surface roughness could be achieved for AlSi10Mg_200C using a Direct Metal Laser Sintering (DMLS) system. The process parameters were chosen such that three samples with the same core properties but different upskin characteristics were produced. The achieved surface roughness of the additively manufactured aluminum samples were almost as low as one fifth of the regular samples manufactured using standard process parameters. The microstructure and the porosity level of the samples printed by different process parameters were studied to reveal the causality of the low surface roughness for the proposed process.

Selective laser melting (SLM) is a promising manufacturing technique for the production of complex metallic components. One of the crucial factors influencing the mechanical properties of the final product is spatter particles formation during the process. In this study, high- speed photography is utilized to record the formation mechanisms and the dynamic behavior of spatter particles. An image processing analysis framework is utilized to assess the distribution of spatter particles under various energy inputs. It is found that changing the laser scan velocity has more influences on spatter formation in comparison with the energy input. The relationship between the numbers of created spatter particles, induced unmelted regions and density variability are interpreted and discussed based on other observations, such as microscopic examination and density analysis of SLM parts. The obtained results could be used to enhance the current manufacturing process parameters optimization methods in SLM process.

We propose a numerical model to simulate the extrusion of a strand of semi-molten material on a moving substrate, within the computation fluid dynamics paradigm. According to the literature, the deposition flow of the strands has an impact on the inter-layer bond formation in extrusion-based additive manufacturing, as well as the surface roughness of the fabricated part. Under the assumptions of an isothermal Newtonian fluid and a creeping laminar flow, the deposition flow is controlled by two parameters: the gap distance between the extrusion nozzle and the substrate, and the velocity ratio of the substrate to the average velocity of the flow inside the nozzle. The numerical simulation fully resolves the deposition flow and provides the cross-section of the printed strand. For the first time, we have quantified the effect of the gap distance and the velocity ratio on the size and the shape of the strand. The cross-section of the strand ranges from being almost cylindrical (for a fast printing and with a large gap) to a flat cuboid with rounded edges (for a slow printing and with a small gap), which substantially differs from the idealized cross-section typically assumed in the literature. Finally, we found that the printing force applied by the extruded material on the substrate has a negative linear relationship with the velocity ratio, for a constant gap.

This paper investigates the porosity distribution and morphology of selective laser melted rotation bending test samples before and after shot peening by means of micro-tomography analysis. The as-built samples show porosity clusters close to the surface, which are attributed to the contour-core scan strategy. In the following steps the effect of shot peening on pore size and morphology in dependency of depth was examined. A strong porosity shrinkage could be achieved in near-surface areas (0–500 μm), but also in depths that did not seem accessible via shot peening, leading to an overall relative porosity reduction between 15–30%. Furthermore, shot peening led to a pore sphericity increase, especially for large pores. The individual orientation of the pores were compared before and after shot peening, where the former mostly had their longest axis in surface normal direction, while the latter showed a more randomly orientation distribution. X-ray diffractography detected residual compressive stresses for the as-built as well as the shot peened samples. Finally fatigue tests were performed, indicating an increase in low- and high-cycle-fatigue resistance after shot peening by 20 MPa.

Slot die coating is growing in popularity because it is a low operational cost and easily scaled processing technique for depositing thin and uniform films rapidly, while minimizing material waste. The complex inner geometry of conventional slot dies require expensive machining that limits accessibility and experimentation. In order to overcome these issues this study follows an open hardware approach, which uses an open source 3-D printer to both fabricate the slot die and then to functionalize a 3-D slot die printing system. Polymer materials are tested and selected for compatibility with common solvents and used to fabricate a custom slot die head. This slot die is then integrated into a 3-D printer augmented with a syringe pump to form an additive manufacturing platform for thin film semiconductor devices. The full design of the slot die system is disclosed here using an open source license including software and operational protocols. This study demonstrates that functional lab-grade slot dies may be 3-D printed using low-cost open source hardware methods A case study using NiO2 found an RMS value 0.486 nm, thickness of 17–49 nm, and a maximum optical transmission of 99.1%, which shows this additive manufacturing approach to slot die depositions as well of fabrication is capable of producing viable layers of advanced electronic materials. Using this method, a cost savings of over 17,000% was obtained when compared to commercial slot die systems for laboratories. Graphical abstract Download : Download high-res image (196KB) Download : Download full-size image

Distortions in Additive Manufacturing (AM) Laser Metal Deposition (LMD) occur in the newly-built component due to rapid heating and solidification and can lead to shape deviations and cracking. This paper presents a novel approach to quantify the distortions experimentally and to use the results in numerical simulation validation. Digital Image Correlation (DIC) is applied together with optical filters to measure in-situ distortions directly on a wall geometry produced with LMD. The wall shows cyclic expansion and shrinking with the edges bending inward and the top of the sample exhibiting a slight u‐shape as residual distortions. Subsequently, a structural Finite Element Analysis (FEA) of the experiment is established, calibrated against experimental temperature profiles and used to predict the in-situ distortions of the sample. A comparison of the experimental and numerical results reveals a good agreement in length direction of the sample and quantitative deviations in height direction, which are attributed to the material model used. The suitability of the novel experimental approach for measurements on an AM sample is shown and the potential for the validated numerical model as a predictive tool to reduce trial-and-error and improve part quality is evaluated.

Design is crucial for additive manufacturing (AM). Not only does it affect manufacturability and cost but more importantly does it determine the functional performance of a part. Design for additive manufacturing (DFAM) methods consider these aspects and aim to leverage the available design freedom in order to generate functionally optimized parts. The following research work presents a method that is based on design principles from the so-called Constructal Theory. Two design principles are selected form this discipline, which considers design a field of science. The first principle outlines how a fluid flow can be distributed efficiently using a tree-shaped structure. The second principle emphasizes to first create the flow structure and then fit the surrounding solid body around it following the flow of mechanical stress. To demonstrate the approach, a case study of a gear wheel design is presented, which integrates cooling lubricant channels and focuses on minimal part mass. Based on analytical relations, a design concept is generated that provides a mass reduction of 25% and a fluid channel structure with minimal required pumping power. The resulting design serves as starting point for a more detailed simulation-based design optimization.