Progress in Additive Manufacturing

Brueckner, Frank; Bremen, Sebastian; Mueller, Bernhard

doi: 10.1007/s40964-020-00125-7pmid: N/A

Bittner, Florian; Thielsch, Juliane; Drossel, Welf-Guntram

doi: 10.1007/s40964-020-00117-7pmid: N/A

In this work, we use laser powder bed fusion (LPBF) to produce Nd–Fe–B magnets. A suitable process window is developed, which allows to fabricate isotropic samples with outstanding magnetic performance. The sample quality is mainly defined by the energy input during LPBF and sintering or delamination occurs, if the process parameter are improperly adjusted. Magnetic and structural properties become better as energy input increases, until the material-specific limit for processability has been reached. Magnets with coercivity of 886 kA/m (µ0Hc = 1.1 T) and maximum energy product of 63 kJ/m3 can be produced from Nd-lean commercial powder without any post treatment. Thereby, our samples represent the new benchmark for permanent magnets produced by additive manufacturing. On the example of coercivity, the impact of laser power, scan velocity and hatch spacing is discussed. It is shown that coercivity can be sufficiently well described by a simple phenomenological model.

Gustmann, Tobias; Gutmann, Florian; Wenz, Franziska; Koch, Peter; Stelzer, Ralph; Drossel, Welf-Guntram; Korn, Hannes

doi: 10.1007/s40964-020-00118-6pmid: N/A

A NiTi shape memory alloy with the nominal composition Ni50.9Ti49.1 (at%) was processed by laser beam melting/laser powder bed fusion and the process parameters as well as the type of scanning strategy (point-like exposure) were optimized in a first step to obtain delicate lattice structures (strut diameters below 200 µm). In the second step, the lattice structures were analyzed by means of optical and electron microscopy as well as computer tomography to obtain the interrelation between the process parameters, strut diameter and the uniformity of the corresponding struts. The processing, especially the laser power and the type of point-like exposure, has a strong influence on the resulting strut diameter and, therefore, on the haptic stiffness of lattice structures and the mechanical properties (deformability, superelasticity). Unlike other approaches, our findings imply that filigree NiTi lattices with high uniformity can be manufactured on a standard industry laser powder bed fusion machine without modifying its hard- or software configuration.

Meyer, Lars; Witt, Gerd

doi: 10.1007/s40964-020-00126-6pmid: N/A

Factors such as not only costs, production time, reproducibility, but also the quality of the components are decisive factors in assessing the economic efficiency of a manufacturing process. With additive manufacturing processes, component production is made possible directly from a 3D CAD model. This means that small series and prototypes can already be produced economically today. In this area, the laser-sintering process, in particular, offers great potential for series production due to its high strength values and ductility. With laser-sintering systems that allow an optical widening of the laser focus, a faster exposure of the component and thus a shortening of the building time is possible. We developed a laser-sintering system whose laser focus diameter is adjustable in its cross-sectional area from 0.47 to 2 mm. The goal for the future is to produce large-area components significantly faster by widening the focus diameter, thus making laser-sintering more productive. In this paper, the focus-dependent melt pool formation is examined in correlation to different hatch distances during the laser-sintering of polyamide 12. For this purpose, a test specimen was developed which can display single tracks as well as a multitude of different track widths for all feasible focus level variations. This knowledge is required to determine and investigate the track width-dependent melt pool formation as a function of the focal diameter of the component cross sections.

Jurisch, Marie; Klöden, Burghardt; Kirchner, Alexander; Walther, Gunnar; Weißgärber, Thomas

doi: 10.1007/s40964-020-00116-8pmid: N/A

Powder bed fusion of difficult-to-weld-steels such as the 42CrMo4 applied in this study is a challenging task. These materials are often susceptible to crack formation. To minimize thermal gradients and residual stresses, laser beam technologies generally require preheating of the substrates. Selective Electron Beam Melting (SEBM), on the other hand, is based on preheating the powder bed and, thus, enables crack-free printing even at greater heights. The present study demonstrates the processing of 42CrMo4 by SEBM. Besides parameter optimization, powder analysis, microstructural characterization as well as mechanical testing were carried out both for the as built and heat-treated conditions. The results indicate that the mechanical properties are comparable to those of conventional manufacturing technologies. Furthermore, a generic demonstrator with complex structures shows the high potential of SEBM for these particularly challenging steels.

Matthes, Sebastian; Kluge, Maximilian; Jahn, Simon; Emmelmann, Claus

doi: 10.1007/s40964-020-00120-ypmid: N/A

In the laser-based powder bed fusion process (L-PBF), the used powder is exposed to a multitude of mechanical and atmospheric parameters along the entire process chain, beginning with the production of the powder, over transportation, storage and processing and ending with the recycling of the material. The chemical composition and shape of individual powder particles, for example, as well as the characteristic properties of the entire powdered material change depending on the duration and intensity of the effects of, among other things, the atmosphere, temperature, humidity and external forces. Once the influencing variables and their effects are known, the changes in the powder can be counteracted in a targeted manner. In this way, it is possible to restore or maintain the powder properties relevant to the L-PBF process, making the overall process more robust and reliable. This paper discusses the results of investigations on significant influencing factors that cause a change in the powder material during L-PBF, representing the cost-intensive titanium alloy Ti-6Al-4V. The results can be used to derive powder handling and management recommendations that can ensure powder quality throughout the service life.

Wang, Xianglong; Muñiz-Lerma, Jose Alberto; Sanchez-Mata, Oscar; Atabay, Sıla Ece; Attarian Shandiz, Mohammad; Brochu, Mathieu

doi: 10.1007/s40964-020-00123-9pmid: N/A

In this study, we explored the feasibility of fabricating single-crystalline or single-crystalline-like stainless steel 316L (SS316L) with different geometries (thin struts, cubes, walls and a simulated pump impeller) using laser powder bed fusion (LPBF). The LPBF-fabricated SS316L thin struts possessed a single-crystalline core featuring a 〈110〉 ∥ building direction (BD) crystallographic texture. The cubes, walls and the pump impeller preserved this 〈110〉 ∥ BD texture and also exhibited a well-defined single-crystalline-like {110}〈001〉 Goss texture. Cellular sub-grain structures with their primary dendrite arm spacing (PDAS) values smaller than 1 μm were discovered in all the samples with their growth directions showing a 45° angular deviation from the BD. Nanoscale precipitates and dislocations were also found in the cellular sub-grain structures of the thin struts. The mechanical properties of different geometries (the thin struts, the walls, and the simulated pump impeller) were studied and compared. The anisotropic mechanical responses of the walls and the simulated pump impeller were correlated with their crystallographic textures.

Ait-Mansour, Ilies; Kretzschmar, Niklas; Chekurov, Sergei; Salmi, Mika; Rech, Joel

doi: 10.1007/s40964-020-00124-8pmid: N/A

Metal-fused filament fabrication is gaining traction due to its low cost and high availability compared to metal powder bed fusion. However, the achievable mechanical properties and effects of shrinkage of this process should be understood thoroughly before it can be implemented as a direct digital manufacturing technology. This study investigates the influence of infill levels and different build orientations on the mechanical properties and shrinkage behavior of 3D-printed, debinded, and sintered components made from BASF Ultrafuse 316LX. The final objective of the work is to define a function for multi-directional shrinkage prediction for any given part geometry to achieve parts with a high degree of dimensional conformity by modifying the original designs accordingly. The Design of Experiment includes tensile and compression testing according to ASTM E8 M-04 and ASTM D695-15, respectively. Tensile testing samples are manufactured in three different build directions and compression testing pins are made with six infill levels. Furthermore, a complex part is printed and its dimensional shrinkage analyzed using 3D scanning. Finally, the multi-directional shrinkage behavior is measured for all samples to establish a shrinkage predictability function by applying linear regression models. Results show that material infill levels have no effect on the shrinkage behavior of printed components. Compressive strength increases with infill level and ultimate tensile strength of parts printed flat indicates the highest tensile testing results, followed by flipped and vertically printed parts. A complex part was manufactured successfully for spare part production, which helped to establish a function with moderate confidence levels for shrinkage predictability.

Camposeco-Negrete, Carmita

doi: 10.1007/s40964-020-00115-9pmid: N/A

Additive manufacturing (AM) has gained attention due to its capacity to produce complex parts. Fused deposition modeling (FDM) is a branch of AM that has great potential. However, it is important to understand how process parameters affect part quality and operation’s productivity. The present paper outlines an experimental study that aimed to optimize three parameters: processing time, the energy consumption of the 3D printer, and dimensional accuracy of parts manufactured by the FDM process, using ASA as the model material. The Taguchi methodology was employed to study the effect of five key parameters (layer thickness, filling pattern, orientation angle, printing plane, and position of the piece on the printing table’s surface) on the variables. The desirability method was considered for defining a set of printing parameters that allowed the optimization of all the variables at the same time. The printing plane was the most significant factor for reducing processing time; the same trend was observed for energy consumption. In the case of dimensional accuracy, the width was mainly influenced by the filling pattern. For length, layer thickness was the dominant factor. Finally, the printing plane was the factor with the greatest influence over the part thickness. A desirability analysis allowed finding out the set of parameters that provided the best trade-off among the variables.

Omidvarkarjan, Daniel; Cipriano, Daniele; Rosenbauer, Ralph; Biedermann, Manuel; Meboldt, Mirko

doi: 10.1007/s40964-020-00119-5pmid: N/A

Feature databases for additively manufactured (AM) designs have been identified as a promising tool to support engineers during the design process. This paper investigates the implementation of such a system by conducting an industrial case study. It provides empirical insights for implementing AM feature databases in industrial practice and a quantitative assessment of its impact on the design process. First, the process of formalizing a firm’s current AM design knowledge is described. By screening existing AM designs, recurring design elements are identified and structured within a feature taxonomy. The technical implementation of the tool is presented with a focus on the database structure and feature parametrization. The twofold repository consists of a web-based cataloguing system for feature look-up and a CAD integration for feature import and modification. The application of the tool in a real development project demonstrated that the feature database supports designers throughout the development process by providing prior validated and scalable design elements. Both development time and cost were reduced by decreasing the number of iterations necessary to achieve a robust design in the detailed design phase. The database also facilitated the conceptual design phase by widening the individual design space of the designer through inspirational input.