Progress in Additive Manufacturing

Kleszczynski, Stefan; Seidel, Christian

doi: 10.1007/s40964-024-00678-xpmid: N/A

Baldauf, Moritz; Lohrer, Philipp; Hauser, Tobias; Jauer, Lucas; Schleifenbaum, Johannes H.

doi: 10.1007/s40964-024-00655-4pmid: N/A

In wire arc additive manufacturing, the distance between the welding torch and the part has a noticeable influence on part quality. By keeping it constant, consistent shielding gas coverage can be ensured, and welding spatter or process interruptions can be avoided. In this work, images are taken by a welding camera and processed by a deep learning model to extract distance information. Subsequently, a novel control strategy is developed, which skips or repeats layers in order to keep the distance constant during the manufacturing process. The validation shows that the geometric dimensional accuracy of the produced components can be improved by this strategy. Furthermore, process interruptions or collisions between the welding torch and the component due to incorrect slicing settings can be avoided. In addition, the control system determines the actual layer height in the component, which can be used to carry out future slicing processes more precisely and thus reduce the number of control interventions.

Schlicht, Samuel; Drummer, Dietmar

doi: 10.1007/s40964-024-00656-3pmid: N/A

Laser-based powder bed fusion (LPBF) of semi-crystalline polymers enables the support-free layer-wise manufacturing of geometrically diverse, complex components. In contrast to the established quasi-isothermal powder bed fusion of polymers at elevated temperatures, non-isothermal, cold processing strategies allow to significantly extend the range of applicable material systems. Relying on the superposition of discretized, fractal exposure strategies and the implicit mesoscopic compensation of crystallization shrinkage, the support-free LPBF of polypropylene at room temperature is demonstrated. The present paper displays the temporally and spatially discrete exposure of superposed fractal, space-filling curves that enable the support-free LPBF of polypropylene through combining the mesoscopic compensation of crystallization shrinkage and the laser-induced minimization of thermal shrinkage through the implementation of pre-exposure scans. The non-isothermal processing regime was observed to exhibit an intrinsic robustness towards the influence of processing parameters on emerging peak temperatures while showing a significant extent of accumulated heat within manufactured parts. Complementary mechanical characterizations showed an orientation-dependent influence of the applied energy density on emerging mechanical properties, correlated with geometry-dependent temporal process characteristics that implicitly influence the available coalescence time and the timespan available for the thermal homogenization.

Wegner, Jan; Bruckhaus, Lars; Schroer, Martin A.; Rayer, Moritz; Schoenrath, Hanna; Kleszczynski, Stefan

doi: 10.1007/s40964-024-00667-0pmid: N/A

This study investigates the relationship between varying contour scanning parameters and their impact on both surface characteristics and mechanical performance of the glass-forming Zr59.3Cu28.8Al10.4Nb1.5 produced via PBF-LB/M. Near-polished surface states with Ra values below 1 µm were achieved. The study identifies increased laser power as a key factor in reducing the surface roughness, while repetitive scanning exhibits only marginal improvements in surface quality. Partial crystallization on the surface of the amorphous samples is found on the as-built surfaces. However, it appears to be confined to depths below 50 µm. Impressively, the material showcases large mechanical strength in the as-built condition, evidenced by a high flexural strength of 2.2 GPa combined with approximately 1% plastic deformation. These findings offer initial insights into optimizing additive manufacturing processes for BMGs, guiding the enhancement of both surface quality and mechanical robustness in Zr-based metallic glass fabricated via PBF-LB/M techniques.

Bruckhaus, Lars; Wegner, Jan; Schnell, Norman; Schönrath, Hanna; Barreto, Erika Soares; Frey, Maximilian; Ellendt, Nils; Busch, Ralf; Kleszczynski, Stefan

doi: 10.1007/s40964-024-00653-6pmid: N/A

Bulk metallic glasses (BMGs) are materials that, due to their amorphous microstructure, offer a unique combination of high strength, hardness, and elasticity, making them attractive for various applications. Using laser powder bed fusion (PBF-LB/M) enables overcoming the current limitations of BMGs in size and shape imposed by traditional manufacturing methods such as casting. Despite its potential, challenges such as porosity, (nano-) crystallization, and impurities affect the mechanical performance of additively manufactured BMGs. This study focuses on the Cu–Ti-based alloy Vit101, known for its higher strength and improved cost-effectiveness compared to Zr-based BMGs. In-situ high-speed pyrometry and thermal simulations of single tracks are employed to enhance the understanding of processing and controlling the thermal cycling of Vit101. The proposed experimental calibration is performed through an off-axis integration of the pyrometer, allowing for in-situ temperature measurements. The acquired data show sufficient congruence with the simulated cooling profiles. Minimal cooling rates in the range of 104 K/s were measured and simulated above the glass transition temperature, indicating a large leeway for further development of glass-forming alloys. Scan track widths are evaluated for validation, resulting in minor deviations between 0.47% and 3.17%. However, challenges emerge at high scanning speeds, leading to higher deviations attributed to balling phenomena, which are not considered in the numerical model.

Schönrath, Hanna; Wegner, Jan; Frey, Maximilian; Schroer, Martin A.; Jin, Xueze; Pérez-Prado, María Teresa; Busch, Ralf; Kleszczynski, Stefan

doi: 10.1007/s40964-024-00668-zpmid: N/A

This paper investigates the additive manufacturing route for a novel glass-forming titanium-based sulfur-containing alloy of the composition Ti60Zr15Cu17S8\documentclass[12pt]{minimal}\usepackage{amsmath}\usepackage{wasysym}\usepackage{amsfonts}\usepackage{amssymb}\usepackage{amsbsy}\usepackage{mathrsfs}\usepackage{upgreek}\setlength{\oddsidemargin}{-69pt}\begin{document}$${\text{Ti}}_{60} {\text{Zr}}_{15} {\text{Cu}}_{17} {\text{S}}_{8}$$\end{document}. This system is a promising candidate for medical devices since the lack of toxic components is combined with a high corrosion resistance and strength. Preliminary experiments and simulations show a general processability of bulk material by powder bed fusion technologies. TEM and XRD reveal an amorphous microstructure of laser-treated surfaces. Ultrasonic atomization is used to fabricate a flowable powder feed stock with spherical morphology and crystalline microstructure, which is suitable for processing in powder bed fusion. Correlations between detected crystalline phase formations and melt pool dynamics are revealed by SEM and EDX. It is shown that bulk samples with a high relative density and partially crystalline microstructure can be manufactured.

Schroeder, Timo; Lehmann, Maja; Horn, Max; Kindermann, Philipp; Uensal, Ismail; Michal, Florian; Lippus, Anja; Schlick, Georg; Seidel, Christian

doi: 10.1007/s40964-024-00663-4pmid: N/A

Power bed fusion of metals using a laser beam (PBF-LB/M) offers unique possibilities to manufacture functionally graded materials (FGM) consisting of different alloys. These so-called multi-material parts enable their material properties to be tailored to local material requirements. In this paper, a new methodical approach for the production of metal FGM with transition zones oriented in different directions and manufacturing sequences of the different materials is investigated. Existing approaches for the manufacturing of these transition zones were enhanced with graded parameter variations, spatial laser movement modulation techniques (wobbling), and geometric approximations using a step structure. For the validation of the approach and the characterization of the transition zones, the manufactured samples were investigated and characterized using optical microscopy and hardness profile measurements. Furthermore, the density of the transition zones was analyzed by image data processing. The feasibility of the presented methods is shown and the production of defect-free transition zones with controlled expansions for functionally graded materials via PBF-LB/M achieved

Forstner, Thomas; Cholewa, Simon; Drummer, Dietmar

doi: 10.1007/s40964-024-00671-4pmid: N/A

The additive manufacturing of metals by material extrusion in a multi-step process (MEX-MSt/M) represents a special process variant of the commonly used material extrusion (MEX) and is based on the processing of highly filled polymer filaments. This technology uses the geometrical freedom and fast processing given by MEX to create individual metal parts after a debinding and sintering process in a cost and time-efficient way. The filaments for MEX-MSt/M are made by incorporating metal powders, such as aluminum, stainless steel, or bronze into a polymer matrix. Due to the challenges that are assigned to the processing of highly filled polymers, like the increased viscosity of the material or clogging of the nozzle, the binder materials have to meet several requirements. Therefore, waxes are often used to enable a better extrusion behavior for MEX; however, the addition of wax also affects other crucial processing properties of the filaments. In this work, the interactions of different types and amounts of waxes on thermal, mechanical, and rheological properties were investigated to create a better understanding of the alternating effects of wax addition into highly filled filaments for processing via MEX. The study demonstrated that an increase in wax contents resulted in both a significant decrease in ductility and an overall improvement in melt flowability. The choice of waxes also affected the particle–matrix interactions, partly leading to an improved wetting of the filler particles.

Angenoorth, Jan; Erhard, Patricia; Wächter, Dennis; Volk, Wolfram; Günther, Daniel

doi: 10.1007/s40964-024-00657-2pmid: N/A

This work investigates a novel method of producing complex-shaped aluminum parts by slurry-based binder jetting and sintering. In this process, a green body is built up by layer-wise deposition of an aqueous aluminum suspension and selective powder bonding by ink-jet printing. The powder bulk generated from the suspension shows an increased density compared to powder-based binder jetting and, thus, a high initial density for the subsequent densification step. This allows for higher final densities and reduced shrinkage. Aluminum is of special interest as it is widely available and of low density but challenging to sinter due to an oxide skin surrounding every particle. The research in this paper investigates the effects of the sintering atmosphere and sintering additives on the microstructure of powder compacts produced by slurry-based binder jetting. The incorporation of magnesium as an additive during the sintering process of aluminum has been found to substantially improve densification during sintering in an argon atmosphere.

Poka, Konstantin; Ali, Sozol; Saeed, Waleed; Merz, Benjamin; Epperlein, Martin; Hilgenberg, Kai

doi: 10.1007/s40964-024-00660-7pmid: N/A

Powder Bed Fusion with Laser Beam of Metals (PBF-LB/M) has gained more industrial relevance and already demonstrated applications at a small series scale. However, its widespread adoption in various use cases faces challenges due to the absence of interfaces to established Manufacturing Execution Systems (MES) that support customers in the predominantly data-driven quality assurance. Current state-of-the-art PBF-LB/M machines utilize communication architectures, such as OPC Unified Architecture (OPC UA), Message Queuing Telemetry Transport (MQTT) and Representational State Transfer Application Programming Interface (REST API). In the context of the Reference Architecture Model Industry 4.0 (RAMI 4.0) and the Internet of Things (IoT), the assets, particularly the physical PBF-LB/M machines, already have an integration layer implemented to communicate data such as process states or sensor values. Missing is an MES component acting as a communication and information layer. To address this gap, the proposed Extract Transform Load (ETL) pipeline aims to extract relevant data from the fabrication of each build cycle down to the level of scan vectors and additionally to register process signals. The suggested data schema for archiving each build cycle adheres to all terms defined by ISO/TC 261—Additive Manufacturing (AM). In relation to the measurement frequency, all data are reorganized into entities, such as the AM machine, build cycle, part, layer, and scan vector. These scan vectors are stored in a runtime-independent format, including all metadata, to be valid and traceable. The resulting machine log represents a comprehensive documentation of each build cycle, enabling data-driven quality assurance at process level.